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Articles on Quantum physics

Displaying 1 - 20 of 65 articles.

How long before quantum computers can benefit society? That’s Google’s US$5 million question

Adam Lowe , Aston University

Gravity experiments on the kitchen table: why a tiny, tiny measurement may be a big leap forward for physics

Sam Baron , The University of Melbourne

What is quantum advantage? A quantum computing scientist explains an approaching milestone marking the arrival of extremely powerful computers

Daniel Lidar , University of Southern California

New technique uses near-miss particle physics to peer into quantum world − two physicists explain how they are measuring wobbling tau particles

Jesse Liu , University of Cambridge and Dennis V. Perepelitsa , University of Colorado Boulder

Before he developed the atomic bomb, J. Robert Oppenheimer’s early work revolutionized the field of quantum chemistry – and his theory is still used today

Aaron W. Harrison , Austin College

Quantum physics proposes a new way to study biology – and the results could revolutionize our understanding of how life works

Clarice D. Aiello , University of California, Los Angeles

Physicists have used entanglement to ‘stretch’ the uncertainty principle, improving quantum measurements

Lorcan Conlon , Australian National University and Syed Assad , Australian National University

What quantum technology means for Canada’s future

Stephanie Simmons , Simon Fraser University

The magic of touch: how deafblind people taught us to ‘see’ the world differently during COVID

Azadeh Emadi , University of Glasgow

Nobel-winning quantum weirdness undergirds an emerging high-tech industry, promising better ways of encrypting communications and imaging your body

Nicholas Peters , University of Tennessee

This Australian experiment is on the hunt for an elusive particle that could help unlock the mystery of dark matter

Ben McAllister , The University of Western Australia

Quantum physics offers insights about leadership in the 21st century

Randall Carolissen , University of Johannesburg

Quantum entanglement: what it is, and why physicists want to harness it

Nicholas Bornman , University of the Witwatersrand

Is space infinite? We asked 5 experts

Noor Gillani , The Conversation

Can consciousness be explained by quantum physics? My research takes us a step closer to finding out

Cristiane de Morais Smith , Utrecht University

Curious Kids: is light a wave or a particle?

Sam Baron , Australian Catholic University

Can the laws of physics disprove God?

Monica Grady , The Open University

New postage stamp honors Chien-Shiung Wu, trailblazing nuclear physicist

Xuejian Wu , Rutgers University - Newark

Could Schrödinger’s cat exist in real life? Our research may provide the answer

Stefan Forstner , The University of Queensland

Our quantum internet breakthrough could help make hacking a thing of the past

Siddarth Koduru Joshi , University of Bristol

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Science News

Two real-world tests of quantum memories bring a quantum internet closer to reality.

Experiments in cities show how to spread quantum entanglement through a network

In a demonstration of technology needed for a quantum internet, researchers in China generated entanglement between three quantum memories in the city of Hefei (illustrated).

Qianhui Shi

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By Emily Conover

May 23, 2024 at 9:30 am

In the quest to build a quantum internet, scientists are putting their memories to the test. Quantum memories, that is.

Quantum memories are devices that store fragile information in the realm of the very small. They’re an essential component for scientists’ vision of quantum networks that could allow  new types of communication , from ultra-secure messaging to linking up far-flung quantum computers ( SN: 6/28/23 ). Such memories would help scientists  establish quantum connections, or entanglement , throughout a network ( SN: 2/12/20 ).

Now, two teams of scientists have entangled quantum memories in networks nestled into cities, where the hustle and bustle of urban life can pose challenges to quantum communications.

“These two impressive studies are pushing out of the lab and into real-world implementations,” says physicist Benjamin Sussman of the University of Ottawa, who was not involved with the research. “These are not just toy systems, but are really the first steps toward what future networks will look like.”

In a network of two quantum memories connected by a telecommunications fiber link that traversed a 35-kilometer loop through Boston and Cambridge, Mass., scientists  maintained entanglement for about a second , physicist Can Knaut and colleagues report in the May 16  Nature . “That doesn’t sound like a lot for us, but in the domain of quantum, where … everything is more fleeting, one second is actually a really long time,” says Knaut, of Harvard University. 

The researchers used quantum memories built from a tiny hunk of diamond in which two of the diamond’s normal carbon atoms are replaced by one atom of silicon. That substitution creates a defect that serves as a quantum bit, or qubit. In fact, the defect serves as two qubits — one that’s short-lived, and another long-lived qubit that acts as the memory. Scientists prodded the short-lived qubit with a photon, or particle of light. The researchers used that qubit as a go-between in order to entangle the long-lived qubit with the photon. Then the scientists sent the photon through the fiber and repeated the process to entangle the long-lived qubits in each memory.

Meanwhile, in Hefei, China, entanglement was achieved in a network with  three quantum memories  separated by fiber links of about 20 kilometers, researchers report in the same issue of  Nature . 

This team’s quantum memory was based on a large ensemble of rubidium atoms about 1 millimeter in diameter. When hit with a laser, the ensemble of atoms can emit a photon. Rather than shuttling the photon directly to another quantum memory, the photon was sent to a centrally located station, where it was measured along with a photon sent from another memory. That generated entanglement between the two distant parts of the network.

Meeting up in the middle meant the photons didn’t have to travel all the way to the other side of the network, an added bonus. “This scheme is rather efficient, but its experimental realization is rather challenging,” says experimental physicist Xiao-Hui Bao of the University of Science & Technology of China in Hefei. The technique required the team to find methods to correct for changes in the length of the fibers due to temperature shifts and other effects that could cause problems. This painstaking effort is called phase stabilization. “This is the main technology advance we made in this paper,” Bao says.

In contrast, the Boston network had no central station and didn’t require phase stabilization. But both teams achieved what’s called “heralded” entanglement. That means that a signal is sent to confirm that the entanglement was established, which demands that the entanglement persists long enough for information to make its way across the network. That confirmation is important for using such networks for practical applications, says physicist Wolfgang Tittel, who was not involved with either study.

“If you compare … how these two different groups have achieved [heralded entanglement], you see that there are more differences than similarities, and I find that great,” says Tittel, of the University of Geneva. “There are different approaches which are all still very, very promising.”

More Stories from Science News on Quantum Physics

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The neutrino’s quantum fuzziness is beginning to come into focus

A maverick physicist is building a case for scrapping quantum gravity

The development of quantum dots wins the 2023 Nobel prize in chemistry

Clara Sousa-Silva seeks molecular signatures of life in alien atmospheres

Quantum computers could break the internet. Here’s how to save it

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What Is Quantum Physics?

This article was reviewed by a member of Caltech's Faculty .

Quantum physics is the study of matter and energy at the most fundamental level. It aims to uncover the properties and behaviors of the very building blocks of nature.

While many quantum experiments examine very small objects, such as electrons and photons, quantum phenomena are all around us, acting on every scale. However, we may not be able to detect them easily in larger objects. This may give the wrong impression that quantum phenomena are bizarre or otherworldly. In fact, quantum science closes gaps in our knowledge of physics to give us a more complete picture of our everyday lives.

Quantum discoveries have been incorporated into our foundational understanding of materials, chemistry, biology, and astronomy. These discoveries are a valuable resource for innovation, giving rise to devices such as lasers and transistors, and enabling real progress on technologies once considered purely speculative, such as quantum computers . Physicists are exploring the potential of quantum science to transform our view of gravity and its connection to space and time. Quantum science may even reveal how everything in the universe (or in multiple universes) is connected to everything else through higher dimensions that our senses cannot comprehend.

The Origins of Quantum Physics

The field of quantum physics arose in the late 1800s and early 1900s from a series of experimental observations of atoms that didn't make intuitive sense in the context of classical physics. Among the basic discoveries was the realization that matter and energy can be thought of as discrete packets, or quanta, that have a minimum value associated with them. For example, light of a fixed frequency will deliver energy in quanta called "photons." Each photon at this frequency will have the same amount of energy, and this energy can't be broken down into smaller units. In fact, the word "quantum" has Latin roots and means "how much."

Knowledge of quantum principles transformed our conceptualization of the atom, which consists of a nucleus surrounded by electrons. Early models depicted electrons as particles that orbited the nucleus, much like the way satellites orbit Earth. Modern quantum physics instead understands electrons as being distributed within orbitals, mathematical descriptions that represent the probability of the electrons' existence in more than one location within a given range at any given time. Electrons can jump from one orbital to another as they gain or lose energy, but they cannot be found between orbitals.

Other central concepts helped to establish the foundations of quantum physics:

• Wave-particle duality: This principle dates back to the earliest days of quantum science. It describes the outcomes of experiments that showed that light and matter had the properties of particles or waves, depending on how they were measured. Today, we understand that these different forms of energy are actually neither particle nor wave. They are distinct quantum objects that we cannot easily conceptualize.
• Superposition : This is a term used to describe an object as a combination of multiple possible states at the same time. A superposed object is analogous to a ripple on the surface of a pond that is a combination of two waves overlapping. In a mathematical sense, an object in superposition can be represented by an equation that has more than one solution or outcome.
• Uncertainty principle : This is a mathematical concept that represents a trade-off between complementary points of view. In physics, this means that two properties of an object, such as its position and velocity, cannot both be precisely known at the same time. If we precisely measure the position of an electron, for example, we will be limited in how precisely we can know its speed.
• Entanglement : This is a phenomenon that occurs when two or more objects are connected in such a way that they can be thought of as a single system, even if they are very far apart. The state of one object in that system can't be fully described without information on the state of the other object. Likewise, learning information about one object automatically tells you something about the other and vice versa.

Mathematics and the Probabilistic Nature of Quantum Objects

Because many of the concepts of quantum physics are difficult if not impossible for us to visualize, mathematics is essential to the field. Equations are used to describe or help predict quantum objects and phenomena in ways that are more exact than what our imaginations can conjure.

Mathematics is also necessary to represent the probabilistic nature of quantum phenomena. For example, the position of an electron may not be known exactly. Instead, it may be described as being in a range of possible locations (such as within an orbital), with each location associated with a probability of finding the electron there.

Given their probabilistic nature, quantum objects are often described using mathematical "wave functions," which are solutions to what is known as the Schrödinger equation . Waves in water can be characterized by the changing height of the water as the wave moves past a set point. Similarly, sound waves can be characterized by the changing compression or expansion of air molecules as they move past a point. Wave functions don't track with a physical property in this way. The solutions to the wave functions provide the likelihoods of where an observer might find a particular object over a range of potential options. However, just as a ripple in a pond or a note played on a trumpet are spread out and not confined to one location, quantum objects can also be in multiple places—and take on different states, as in the case of superposition—at once.

Observation of Quantum Objects

The act of observation is a topic of considerable discussion in quantum physics. Early in the field, scientists were baffled to find that simply observing an experiment influenced the outcome. For example, an electron acted like a wave when not observed, but the act of observing it caused the wave to collapse (or, more accurately, "decohere") and the electron to behave instead like a particle. Scientists now appreciate that the term "observation" is misleading in this context, suggesting that consciousness is involved. Instead, "measurement" better describes the effect, in which a change in outcome may be caused by the interaction between the quantum phenomenon and the external environment, including the device used to measure the phenomenon. Even this connection has caveats, though, and a full understanding of the relationship between measurement and outcome is still needed.

The Double-Slit Experiment

Perhaps the most definitive experiment in the field of quantum physics is the double-slit experiment . This experiment, which involves shooting particles such as photons or electrons through a barrier with two slits, was originally used in 1801 to show that light is made up of waves. Since then, numerous incarnations of the experiment have been used to demonstrate that matter can also behave like a wave and to demonstrate the principles of superposition, entanglement, and the observer effect.

The field of quantum science may seem mysterious or illogical, but it describes everything around us, whether we realize it or not. Harnessing the power of quantum physics gives rise to new technologies, both for applications we use today and for those that may be available in the future .

Dive Deeper

Why Are Soap Bubbles So Colorful? Iridescence explained by wave theory and quantum electrodynamics

Charlie Marcus Knows That Quantum Facts Aren't Complicated

The Biggest Ideas in the Universe: Sean Carroll

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MIT researchers observe a hallmark quantum behavior in bouncing droplets

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In our everyday classical world, what you see is what you get. A ball is just a ball, and when lobbed through the air, its trajectory is straightforward and clear. But if that ball were shrunk to the size of an atom or smaller, its behavior would shift into a quantum, fuzzy reality. The ball would exist as not just a physical particle but also a wave of possible particle states. And this wave-particle duality can give rise to some weird and sneaky phenomena.

One of the stranger prospects comes from a thought experiment known as the “quantum bomb tester.” The experiment proposes that a quantum particle, such as a photon, could act as a sort of telekinetic bomb detector. Through its properties as both a particle and a wave, the photon could, in theory, sense the presence of a bomb without physically interacting with it.

The concept checks out mathematically and is in line with what the equations governing quantum mechanics allow. But when it comes to spelling out exactly how a particle would accomplish such a bomb-sniffing feat, physicists are stumped. The conundrum lies in a quantum particle’s inherently shifty, in-between, undefinable state. In other words, scientists just have to trust that it works.

But mathematicians at MIT are hoping to dispel some of the mystery and ultimately establish a more concrete picture of quantum mechanics. They have now shown that they can recreate an analog of the quantum bomb tester and generate the behavior that the experiment predicts. They’ve done so not in an exotic, microscopic, quantum setting, but in a seemingly mundane, classical, tabletop setup.

In a paper appearing today in Physical Review A , the team reports recreating the quantum bomb tester in an experiment with a study of bouncing droplets. The team found that the interaction of the droplet with its own waves is similar to a photon’s quantum wave-particle behavior: When dropped into a configuration similar to what is proposed in the quantum bomb test, the droplet behaves in exactly the same statistical manner that is predicted for the photon. If there were actually a bomb in the setup 50 percent of the time, the droplet, like the photon, would detect it, without physically interacting with it, 25 percent of the time.

The fact that the statistics in both experiments match up suggests that something in the droplet’s classical dynamics may be at the heart of a photon’s otherwise mysterious quantum behavior. The researchers see the study as another bridge between two realities: the observable, classical world and the fuzzier quantum realm.

“Here we have a classical system that gives the same statistics as arises in the quantum bomb test, which is considered one of the wonders of the quantum world,” says study author John Bush, professor of applied mathematics at MIT. “In fact, we find that the phenomenon is not so wonderful after all. And this is another example of quantum behavior that can be understood from a local realist perspective.”

Bush’s co-author is former MIT postdoc Valeri Frumkin.

Making waves

To some physicists, quantum mechanics leaves too much to the imagination and doesn’t say enough about the actual dynamics from which such weird phenomena supposedly arise. In 1927, in an attempt to crystallize quantum mechanics, physicist Louis de Broglie presented the pilot wave theory — a still-controversial idea that poses a particle’s quantum behavior is determined not by an intangible, statistical wave of possible states but by a physical “pilot” wave of its own making, that guides the particle through space.

The concept was mostly discounted until 2005, when physicist Yves Couder discovered that de Broglie’s quantum waves could be replicated and studied in a classical, fluid-based experiment. The setup involves a bath of fluid that is made to subtly vibrate up and down, though not quite enough to generate waves on its own. A millimeter-sized droplet of the same fluid is then dispensed over the bath, and as it bounces off the surface, the droplet resonates with the bath’s vibrations, creating what physicists know as a standing wave field that “pilots,” or pushes the droplet along. The effect is of a droplet that appears to walk along a rippled surface in patterns that turn out to be in line with de Broglie’s pilot wave theory.

For the last 13 years, Bush has worked to refine and extend Couder’s hydrodynamic pilot wave experiments and has successfully used the setup to observe droplets exhibiting emergent, quantum-like behavior, including quantum tunneling, single-particle diffraction, and surreal trajectories.

“It turns out that this hydrodynamic pilot-wave experiment exhibits many features of quantum systems which were previously thought to be impossible to understand from a classical perspective,” Bush says.

In their new study, he and Frumkin took on the quantum bomb tester. The thought experiment begins with a conceptual interferometer — essentially, two corridors of the same length that branch out from the same starting point, then turn and converge, forming a rhombus-like configuration as the corridors continue on, each ending in a respective detector.

According to quantum mechanics, if a photon is fired from the interferometer’s starting point, through a beamsplitter, the particle should travel down one of the two corridors with equal probability. Meanwhile, the photon’s mysterious “wave function,” or the sum of all its possible states, travels down both corridors simultaneously. The wave function interferes in such a way to ensure that the particle only appears at one detector (let’s call this D1) and never the other (D2). Hence, the photon should be detected at D1 100 percent of the time, regardless of which corridor it traveled through.

If there is a bomb in one of the two corridors, and a photon heads down this corridor, it predictably triggers the bomb and the setup is blown to bits, and no photon is detected at either detector. But if the photon travels down the corridor without the bomb, something weird happens: Its wave function, in traveling down both corridors, is cut short in one by the bomb. As it’s not quite a particle, the wave does not set off the bomb. But the wave interference is altered in such a way that the particle will be detected with equal probability at D1 and D2. Any signal at D2 therefore would mean that a photon has detected the presence of the bomb, without physically interacting with it. If the bomb is present 50 percent of the time, then this weird quantum bomb detection should occur 25 percent of the time.

In their new study, Bush and Frumkin set up an analogous experiment to see if this quantum behavior could emerge in classical droplets. Into a bath of silicon oil, they submerged a structure similar to the rhombus-like corridors in the thought experiment. They then carefully dispensed tiny oil droplets into the bath and tracked their paths. They added a structure to one side of the rhombus to mimic a bomb-like object and observed how the droplet and its wave patterns changed in response.

In the end, they found that 25 percent of the time a droplet bounced through the corridor without the “bomb,” while its pilot waves interacted with the bomb structure in a way that pushed the droplet away from the bomb. From this perspective, the droplet was able to “sense” the bomb-like object without physically coming into contact with it. While the droplet exhibited quantum-like behavior, the team could plainly see that this behavior emerged from the droplet’s waves, which physically helped to keep the droplet away from the bomb. These dynamics, the team says, may also help to explain the mysterious behavior in quantum particles.

“Not only are the statistics the same, but we also know the dynamics, which was a mystery,” Frumkin says. “And the inference is that an analogous dynamics may underly the quantum behavior.”

"This system is the only example we know which is not quantum but shares some strong wave-particles properties," says theoretical physicist Matthieu Labousse, of ESPCI Paris, who was not involved in the study. "It is very surprising that many examples thought to be peculiar to the quantum world can be reproduced by such a classical system. It enables to understand the barrier between what it is specific to a quantum system and what is not.  The latest results of the group at MIT pushes the barrier very far."

This research is supported, in part, by the National Science Foundation.

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Unlocking the quantum future

At the mit quantum hackathon, a community tackles quantum computing challenges..

Quantum computing is the next frontier for faster and more powerful computing technologies. It has the potential to better optimize routes for shipping and delivery, speed up battery development for electric vehicles, and more accurately predict trends in financial markets. But to unlock the quantum future, scientists and engineers need to solve outstanding technical challenges while continuing to explore new applications.

One place where they’re working towards this future is the MIT Interdisciplinary Quantum Hackathon, or iQuHACK for short (pronounced “i-quack,” like a duck). Each year, a community of quhackers (quantum hackers) gathers at iQuHACK to work on quantum computing projects using real quantum computers and simulators. This year, the hackathon was held both in-person at MIT and online over three days in February.

Quhackers worked in teams to advance the capability of quantum computers and to investigate promising applications. Collectively, they tackled a wide range of projects, such as running a quantum-powered dating service, building an organ donor matching app, and breaking into quantum vaults. While working, quhackers could consult with scientists and engineers in attendance from sponsoring companies. Many sponsors also received feedback and ideas from quhackers to help improve their quantum platforms.

But organizing iQuHACK 2024 was no easy feat. Co-chairs Alessandro Buzzi and Daniela Zaidenberg led a committee of nine members to hold the largest iQuHACK yet. “It wouldn’t have been possible without them,” Buzzi said. The hackathon hosted 260 in-person quhackers and 1,000 remote quhackers, representing 77 countries in total. More than 20 scientists and engineers from sponsoring companies also attended in person as mentors for quhackers.

Each team of quhackers tackled one of 10 challenges posed by the hackathon’s eight major sponsoring companies. Some challenges asked quhackers to improve computing performance, such as by making quantum algorithms faster and more accurate. Other challenges asked quhackers to explore applying quantum computing to other fields, such as finance and machine learning. The sponsors worked with the iQuHACK committee to craft creative challenges with industry relevance and societal impact. “We wanted people to be able to address an interesting challenge [that has] applications in the real world,” says Zaidenberg.

One team of quhackers looked for potential quantum applications and found one close to home: dating. A team member, Liam Kronman, had previously built dating apps but disliked that matching algorithms for normal classical computers “require [an overly] strict setup.” With these classical algorithms, people must be split into two groups — for example, men and women — and matches can only be made between these groups. But with quantum computers, matching algorithms are more flexible and can consider all possible combinations, enabling the inclusion of multiple genders and gender preferences.

Kronman and his team members leveraged these quantum algorithms to build a quantum-powered dating platform called MITqute (pronounced “meet cute”). To date, the platform has matched at least 240 people from the iQuHACK and MIT undergrad communities. In a follow-up survey, 13 out of 41 respondents reported having talked with their match, with at least two pairs setting up dates. “I really lucked out with this one,” one respondent wrote.

Another team of quhackers also based their project on quantum matching algorithms but instead leveraged the algorithms’ power for medical care. The team built a mobile app that matches organ donors to patients, earning them the hackathon’s top social impact award.

But they almost didn’t go through with their project. “At one point, we were considering scrapping the whole thing because we thought we couldn’t implement the algorithm,” says Alma Alex, one of the developers. After talking with their hackathon mentor for advice, though, the team learned that another group was working on a similar type of project — incidentally, the MITqute team. Knowing that others were tackling the same problem inspired them to persevere.

A sense of community also helped to motivate other quhackers. For one of the challenges, quhackers were tasked with hacking into 13 virtual quantum vaults. Teams could see each other’s progress on each vault in real time on a leaderboard, and this knowledge informed their strategies. When the first vault was successfully hacked by a team, progress from many other teams spiked on that vault and slowed down on others, says Daiwei Zhu, a quantum applications scientist at IonQ and one of the challenge’s two architects.

The vault challenge may appear to be just a fun series of puzzles, but the solutions can be used in quantum computers to improve their efficiency and accuracy. To hack into a vault, quhackers had to first figure out its secret key — an unknown quantum state — using a maximum of 20 probing tests. Then, they had to change the key’s state to a target state. These types of characterizations and modifications of quantum states are “fundamental” for quantum computers to work, says Jason Iaconis, a quantum applications engineer at IonQ and the challenge’s other architect.

But the best way to characterize and modify states is not yet clear. “Some of the [vaults] we [didn’t] even know how to solve ourselves,” Zhu says. At the end of the hackathon, six vaults had at least one team mostly hack into them. (In the quantum world where gray areas exist, it’s possible to partly hack into a vault.)

The community of scientists and engineers formed at iQuHACK persists beyond the weekend, and many members continue to grow the community outside the hackathon. Inspired quhackers have gone on to start their own quantum computing clubs at their universities. A few years ago, a group of undergraduate quhackers from different universities formed a Quantum Coalition that now hosts their own quantum hackathons. “It’s crazy to see how the hackathon itself spreads and how many people start their own initiatives,” co-chair Zaidenberg says.

The three-day hackathon opened with a keynote from MIT Professor Will Oliver , which included an overview of basic quantum computing concepts, current challenges, and computing technologies. Following that were industry talks and a panel of six industry and academic quantum experts, including MIT Professor Peter Shor, who is known for developing one of the most famous quantum algorithms. The panelists discussed current challenges, future applications, the importance of collaboration, and the need for ample testing.

Later, sponsors held technical workshops where quhackers could learn the nitty-gritty details of programming on specific quantum platforms. Day one closed out with a talk by research scientist Xinghui Yin on the role of quantum technology at LIGO, the Laser Interferometer Gravitational-Wave Observatory that first detected gravitational waves. The next day, the hackathon’s challenges were announced at 10 a.m., and hacking kicked off at the MIT InnovationHQ. In the afternoon, attendees could also tour MIT quantum computing labs.

Hacking continued overnight at the MIT Museum and ended back at MIT iHQ at 10 a.m. on the final day. iQuhackers then presented their projects to panels of judges. Afterward, industry speakers gave lightning talks about each of their company’s latest quantum technologies and future directions. The hackathon ended with a closing ceremony, where sponsors announced the awards for each of the 10 challenges.

The hackathon was captured in a three-part video by Albert Figurt, a resident artist at MIT. Figurt shot and edited the footage in parallel with the hackathon. Each part represented one day of the hackathon and was released on the subsequent day.

Throughout the weekend, quhackers and sponsors consistently praised the hackathon’s execution and atmosphere. “That was amazing … never felt so much better, one of the best hackathons I did from over 30 hackathons I attended,” Abdullah Kazi, a quhacker, wrote on the iQuHACK Slack.

Ultimately, “[we wanted to] help people to meet each other,” co-chair Buzzi says. “The impact [of iQuHACK] is scientific in some way, but it’s very human at the most important level.”

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The Year in Physics

December 21, 2023

Video : In 2023, physicists found the gravitational wave background that’s made by supermassive black hole collisions, teleported quantum energy in the lab, and puzzled over JWST’s potentially cosmology-breaking discoveries.

Emily Buder/ Quanta Magazine ; Myriam Wares and Ibrahim Rayintakath for Quanta Magazine

Introduction

By one metric, this year’s biggest physics news happened 80 years ago. Yet while the success of a movie about the making of the atomic bomb was a surprise, the discoveries coming out of actual physics laboratories — including the grandest laboratory of them all, the universe itself — were no less impressive than the surge in interest about J. Robert Oppenheimer.

The James Webb Space Telescope , now in year two of science operations, continues to return stunning images of the cosmos, and the trickle of science results from 2022 has now swelled into a torrent. From its perch a million miles away, JWST studies everything from the universe’s most distant galaxies to the planets and moons right next door. The only constant has been surprise: The telescope’s observations continually challenge well-established theories and force scientists to reimagine how familiar cosmic objects came to be — things like stars and planets and black holes.

Black holes are also at the center of one of 2023’s most notable discoveries: evidence for gravitational waves produced by colliding supermassive black holes . To detect those ripples in space-time, several consortia of astronomers scrutinized the cosmos for 15 years — long enough to detect the tiny temporal fluctuations that occur as gravitational waves wash over the Earth.

Closer to home, scientists are busy both manipulating and understanding the quantum world — a realm that often doesn’t play by normal rules. This year saw some remarkable advances in quantum computing’s most basic hardware , the qubits that in their final form could power enormously complex calculations. And, crucially, researchers also made improvements in quantum error correction , which remains one of the trickiest problems to solve.

But these advances don’t mean we’re done understanding the universe from the largest of its scales to the tiniest. Our next orbit around the sun could be full of even more profound revelations.

Courtesy of  Jorryt Matthee . Data from the EIGER  /  FRESCO  surveys

The Cosmos, Unveiled

It has often been said that each time we look at the universe in a new light — or through a new lens — we see things we never imagined. NASA’s James Webb Space Telescope has delivered on that promise. At the turn of the year, astronomers announced that the telescope’s golden, honeycombed eye had stolen glances of the universe’s first stars . JWST has also seen the light from galaxies that glowed some 300 million years after the great big clap that created the universe as we know it. In JWST images, those galaxies are “just so stupidly bright,” said Rohan Naidu of the Massachusetts Institute of Technology. Now, astronomers are struggling to explain how those galaxies grew so big so fast, as their size and precociousness defy expectations.

The same is true for the supermassive black holes that anchor galaxies to the cosmic tapestry. Scientists expected to see a few bulky black holes in the early universe, but JWST is spotting them by the bucketful . And they’re showing up earlier, and with more heft, than expected. Astronomers hope such observations will reveal how those gargantuan black holes formed. “I’ve been waiting for these things for so long,” said Marta Volonteri , an astrophysicist at the Paris Institute of Astrophysics.

Closer to home, in our galaxy’s Orion nebula, JWST recently spotted 42 intriguing pairs of objects that orbit one another. These worlds might be stars, or they might be free-floating planets. It’s hard to tell. But either way, these enigmatic worlds don’t fit neatly into existing theories describing how either stars or free-floating planets form. As with all new ways of seeing, JWST is inspiring far more questions than it answers.

Merrill Sherman/ Quanta Magazine

Stronger Quantum Knots

Earlier this year, quantum researchers announced that they’d taken a step toward developing a more reliable quantum computer . In this system, information is stored topologically; it is woven into almost mythical particles that share memories and remember their pasts. Braiding two of these “non-abelian anyons” together stores information in the twists — thus, you can measure one or the other without losing that information. As my colleague Charlie Wood explained, “By maintaining nearly indestructible records of their journeys through space and time, non-abelian anyons could offer the most promising platform for building error-tolerant quantum computers.”

Then in August, scientists tackling the trickiness of quantum error correction announced that they had developed a powerful new class of codes that could — at least in theory — help with the persnickety problem of flimsy, error-prone quantum bits.

Kristina Armitage/ Quanta Magazine

Quantum Magic

In a feat reminiscent of a magic trick, scientists reported earlier this year that they had pulled energy out of a vacuum. Or had they? Rather than conjuring something from nothing, physicists managed to teleport energy over microscopic distances. The leap worked because the team exploited the strange properties of the quantum vacuum — a peculiar type of nothing that is actually imbued with a sort of sizzling quantum energy.

Earlier this year, scientists discovered a new type of phase transition , akin to the transformation of a solid into a liquid. Except this was a transition in the structure of information. When quantum bits (or qubits) are entangled, measuring one reveals the states of any others. Entanglement can spread, but measurement destroys the web of entanglement — it’s like snipping the wires in a chain-link fence. What happens when entanglement and measurement duke it out in a grid of entangled qubits? The transition between a state in which entanglement survives and one in which it succumbs to the wire cutters of measurement is what physicists identified and observed in the lab. “It’s where the properties in information — how information is shared between things — undergo a very abrupt change,” said Brian Skinner of Ohio State University.

When it comes to these systems, we throw around the term “quantum” almost as if quantum and not-quantum exist in a binary. That isn’t necessarily true. In the effort to quantify quantumness — or the degree to which a quantum system cannot be simulated on a classical computer — researchers recently unveiled a new metric , bringing the total known metrics to three. First there was entanglement. Then there was “magic.” Now, there’s “fermionic magic.”

Olena Shmahalo for Quanta Magazine

Toward Quantum Gravity

It’s an old problem in physics: Quantum mechanics describes the world one way, Einstein’s theory of gravity another, and when the two come together you get nonsense. Some scientists, like Renate Loll , believe that gravity must be quantized; others, like Jonathan Oppenheim , would bet against that idea. While Loll has pioneered a computationally driven approach to quantum gravity that involves deriving the shape of space-time from first principles, Oppenheim is searching for an even deeper fundamental “something” that might connect the two.

And yet quantum gravity keeps showing up in the solutions to seemingly intractable paradoxes.

A group of leading theorists believe they’ve pinpointed the mistake that led to Hawking’s famous black hole information paradox, in which indestructible information inside a black hole is seemingly lost as the black hole evaporates. Hawking’s apparent mistake was that he (and the generations of physicists that followed) didn’t realize that the normally reliable “semiclassical” treatment of gravity can’t handle the complexity of states a black hole can produce, unexpectedly breaking down at the black hole’s outer surface. The group has now developed a more sophisticated theory of gravity that can handle the region just inside the event horizon and doesn’t violate any current experimental data.

A Hum of Gravitational Waves

When galaxies collide, their supermassive central black holes merge — a smashup so violent that it shakes the very fabric of space-time itself. In June, multiple international collaborations announced that they had found the resulting gravitational waves. To do this, the teams used pulsars, rapidly spinning stellar corpses that serve as perfect cosmic clocks. The gravitational waves alter the apparent rhythm of the pulsars, but it took 15 years of study to identify this signature of violent events that continually rock the cosmos.

Editor’s note: Michael Moyer contributed to this article.

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The 12 Most Important and Stunning Quantum Experiments of 2019

Quantum computing seems to inch closer every year.

The smallest scale events have giant consequences. And no field of science demonstrates that better than quantum physics, which explores the strange behaviors of — mostly — very small things. In 2019, quantum experiments went to new and even stranger places and practical quantum computing inched ever closer to reality, despite some controversies. These were the most important and surprising quantum events of 2019.

Google claims "quantum supremacy"

If one quantum news item from 2019 makes the history books, it will probably be a big announcement that came from Google: The tech company announced that it had achieved " quantum supremacy ." That's a fancy way of saying that Google had built a computer that could perform certain tasks faster than any classical computer could. (The category of classical computers includes any machine that relies on regular old 1s and 0s, such as the device you're using to read this article.)

Google's quantum supremacy claim, if borne out, would mark an inflection point in the history of computing. Quantum computers rely on strange small-scale physical effects like entanglement , as well as certain basic uncertainties in the nano-universe, to perform their calculations. In theory, that quality gives these machines certain advantages over classical computers. They can easily break classical encryption schemes, send perfectly encrypted messages, run some simulations faster than classical computers can and generally solve hard problems very easily. The difficulty is that no one's ever made a quantum computer fast enough to take advantage of those theoretical advantages — or at least no one had, until Google's feat this year.

Not everyone buys the tech company's supremacy claim though. Subhash Kak, a quantum skeptic and researcher at Oklahoma State University, laid out several of the reasons in this article for Live Science .

Read more about Google's achievement of quantum supremacy .

The kilogram goes quantum

Another 2019 quantum inflection point came from the world of weights and measures. The standard kilogram, the physical object that defined the unit of mass for all measurements, had long been a 130-year-old, platinum-iridium cylinder weighing 2.2 lbs. and sitting in a room in France. That changed this year.

The old kilo was pretty good, barely changing mass over the decades. But the new kilo is perfect: Based on the fundamental relationship between mass and energy, as well as a quirk in the behavior of energy at quantum scales, physicists were able to arrive at a definition of the kilogram that won't change at all between this year and the end of the universe.

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Read more about the perfect kilogram .

Reality broke a little

A team of physicists designed a quantum experiment that showed that facts actually change depending on your perspective on the situation. Physicists performed a sort of "coin toss" using photons in a tiny quantum computer, finding that the results were different at different detectors, depending on their perspectives.

"We show that, in the micro-world of atoms and particles that is governed by the strange rules of quantum mechanics, two different observers are entitled to their own facts," the experimentalists wrote in an article for Live Science . "In other words, according to our best theory of the building blocks of nature itself, facts can actually be subjective."

Read more about the lack of objective reality .

Entanglement got its glamour shot

For the first time, physicists made a photograph of the phenomenon Albert Einstein described as "spooky action at a distance," in which two particles remain physically linked despite being separated across distances. This feature of the quantum world had long been experimentally verified, but this was the first time anyone got to see it .

Read more about the unforgettable image of entanglement .

Something big went in multiple directions

In some ways the conceptual opposite of entanglement, quantum superposition is enables a single object to be in two (or more) places at once, a consequence of matter existing as both particles and waves. Typically, this is achieved with tiny particles like electrons.

But in a 2019 experiment, physicists managed to pull off superposition at the largest scale ever : using hulking, 2,000-atom molecules from the world of medical science known as "oligo-tetraphenylporphyrins enriched with fluoroalkylsulfanyl chains."

Read about the macro-scale achievement of superposition .

Heat crossed the vacuum

Under normal circumstances, heat can cross a vacuum in only one manner: in the form of radiation. (That's what you're feeling when the sun's rays cross space to beat on your face on a summer day.) Otherwise, in standard physical models, heat moves in two manners: First, energized particles can knock into other particles and transfer their energy. (Wrap your hands around a warm cup of tea to feel this effect.) Second, a warm fluid can displace a colder fluid. (That's what happens when you turn the heater on in your car, flooding the interior with warm air.) So without radiation, heat can't cross a vacuum.

But quantum physics, as usual, breaks the rules. In a 2019 experiment, physicists took advantage of the fact that at the quantum scale, vacuums aren't truly empty. Instead, they're full of tiny, random fluctuations that pop into and out of existence. At a small enough scale, the researchers found, heat can cross a vacuum by jumping from one fluctuation to the next across the apparently empty space.

Read more about heat leaping across the quantum vacuum of space .

Cause and effect might have gone backward

This next finding is far from an experimentally verified discovery, and it's even well outside the realm of traditional quantum physics. But researchers working with quantum gravity — a theoretical construct designed to unify the worlds of quantum mechanics and Einstein's general relativity — showed that under certain circumstances an event might cause an effect that occurred earlier in time.

Certain very heavy objects can influence the flow of time in their immediate vicinity due to general relativity. We know this is true. And quantum superposition dictates that objects can be in multiple places at once. Put a very heavy object (like a big planet) in a state of quantum superposition, the researchers wrote, and you can design oddball scenarios where cause and effect take place in the wrong order .

Read more about cause and effect reversing .

Quantum tunneling cracked

Physicists have long known about a strange effect known as "quantum tunneling," in which particles seem to pass through seemingly impassable barriers . It's not because they're so small that they find holes, though. In 2019, an experiment showed how this really happens.

Quantum physics says that particles are also waves, and you can think of those waves as probability projections for the location of the particle. But they're still waves. Smash a wave against a barrier in the ocean, and it will lose some energy, but a smaller wave will appear on the other side. A similar effect occurs in the quantum world, the researchers found. And as long as there's a bit of probability wave left on the far side of the barrier, the particle has a chance of making it through the obstruction, tunneling through a space where it seems it should not fit.

Read more about the amazing quantum tunneling effect .

Metallic hydrogen may have appeared on Earth

This was a big year for ultra-high-pressure physics. And one of the boldest claims came from a French laboratory, which announced that it had created a holy grail substance for materials science: metallic hydrogen . Under high enough pressures, such as those thought to exist at the core of Jupiter, single-proton hydrogen atoms are thought to act as an alkali metal. But no one had ever managed to generate pressures high enough to demonstrate the effect in a lab before. This year, the team said they'd seen it at 425 gigapascals (4.2 million times Earth's atmospheric pressure at sea level). Not everyone buys that claim , however.

Read more about metallic hydrogen .

We beheld the quantum turtle

Zap a mass of supercooled atoms with a magnetic field , and you'll see "quantum fireworks": jets of atoms firing off in apparently random directions. Researchers suspected there might be a pattern in the fireworks, but it wasn't obvious just from looking. With the aid of a computer, though, researchers discovered a shape to the fireworks effect: a quantum turtle . No one's yet sure why it takes that shape, however.

Read more about the quantum turtle .

A tiny quantum computer turned back time

Time's supposed to move in only one direction: forward. Spill some milk on the ground, and there's no way to perfectly dry out the dirt and return that same clean milk back into the cup. A spreading quantum wave function doesn't unspread.

Except in this case, it did. Using a tiny, two-qubit quantum computer, physicists were able to write an algorithm that could return every ripple of a wave to the particle that created it — unwinding the event and effectively turning back the arrow of time .

Read more about reversing time's arrow .

Another quantum computer saw 16 futures

A nice feature of quantum computers, which rely on superpositions rather than 1s and 0s, is their ability to play out multiple calculations at once. That advantage is on full display in a new quantum prediction engine developed in 2019. Simulating a series of connected events, the researchers behind the engine were able to encode 16 possible futures into a single photon in their engine . Now that's multitasking!

Read more about the 16 possible futures .

• The 10 Weirdest Science Studies of 2019
• 18 Times Quantum Particle Blew Our Minds
• What's That? Your Physics Questions Answered

Originally published on Live Science .

Atoms squished closer together than ever before, revealing seemingly impossible quantum effects

Stunning image shows atoms transforming into quantum waves — just as Schrödinger predicted

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Quantum physics education research over the last two decades: a bibliometric analysis.

1. Introduction

• the relevance of quantum physics education within science education research on the one hand, and
• given the upcoming tasks in teaching modern quantum technologies to a broad audience on the other hand,
• How has the scientific output in terms of research publications and citations of articles on quantum physics education has developed over time from 2000 to 2021 in science education research?
• Who are the most active authors and countries publishing articles on quantum physics education research from 2000 to 2021?
• What are the most relevant publishing venues in science education research through which the results on quantum physics education are disseminated from 2000 to 2021 and which are the most cited articles?
• Can a broad collaboration among researchers and countries in quantum physics education research be observed?
• What are the most relevant keywords, and which co-occurrence patterns exist in articles on quantum physics education research?
• Study design: Definition of research questions and database selection.
• Data collection: Search query and data export.
• Data analysis: Decision on bibliometric methods that can be used to clarify the research questions and selection of software to conduct the data analysis.
• Data visualisation: Selection of visualisation method and appropriate mapping software.
• Interpretation: Interpretation of bibliometric analysis’ results.

2.1. Study Design

2.2. data collection, 2.3. data analysis and visualisation, 2.4. limitations.

• The numbers of published papers (e.g., by author or country) on quantum physics education reported in this article only refer to the bibliographic data documented in Scopus and Web of Science, respectively. Reported values should therefore not be considered as fixed. The latter holds especially true for the exact number of citations, since not necessarily all citations of a given article are recorded in the databases. In this way, orders for the most frequently cited articles or authors could deviate from reality or articles or authors could even be missing unfairly in such orders. However, we argue that the relevance of this limitation is restricted by the well-justified data collection (cf. Section 2 ) based on two of the most relevant databases, Scopus and Web of Science.
• Some authors do not publish many scientific articles but are instead active in important projects or initiatives, for example, or have a strong influence on the research field in other ways. This cannot be taken into account in bibliometric studies.
• In this study, we only focused on articles published in scientific journals so that future studies can also consider other sources, e.g., books or conference proceedings.
• In our analysis, we investigated the number of citations for the articles included in our database. Although the role of self-citations in scientific communication has previously been analyzed across disciplines [ 38 ], there is an ongoing debate “on the principles of the role of author-self citation”, and “there is no real consensus concerning how this type of self-citations should be defined operatively” ([ 39 ], p. 64). We did not specifically analyze self-citations in the field of quantum physics education research in this study but this could be of interest for further research.
• Altmetrics are social web metrics for published articles that are increasingly used as estimates of publications’ impact, cf. [ 40 ]. They are not considered in this study. However, this could be a starting point for further research.

3.1. Development of the Scientific Output on Quantum Physics Education Research

3.2. most active authors and countries publishing articles on quantum physics education research, 3.3. most relevant journals and most cited articels on quantum physics education, 3.4. collaborations among researchers and countries in quantum physics education research, 3.5. keyword co-occurrence patterns in quantum physics education research, 4. discussion and conclusions, 4.1. discussion of performance analysis results (research questions 1–3).

• Main results on research question 1 : The number of published papers on quantum physics education research has increased steadily over the observation period from 31 articles in 2000 to 118 articles in 2020, with an annual growth rate of about 6.9 % .
• Main results on research question 2 : The research on quantum physics education is significantly driven by authors from the USA: more than 1/3 of the documents analysed were published by a corresponding author from the USA. Against this backdrop, it is not surprising that among the top ten most productive authors, seven are from the USA (led by Singh, C.). Furthermore, among the ten leading countries in the research field, five are from Europe (UK, Italy, Germany, Spain and France).
• Main results on research question 3 : The two journals American Journal of Physics and European Journal of Physics published the most papers on quantum physics education research and the number of publications in these journals increased more than in all other journals over the observation period. Among the top ten most cited papers on quantum physics education research, nine articles are published in American Journal of Physics —the latter is true regardless of whether one analyses global or local citations.

4.2. Discussion of Science Mapping Results (Research Questions 4 and 5)

• Main results on research question 4 : The scientific community engaged with quantum physics education research has not formed well-established (international) collaborations yet. Instead, the community is characterised by several smaller and predominantly national collaborations (cf. research question 4).
• Main results on research question 5 : Quantum physics education research comprises two main areas, as a co-word analysis revealed. On the one hand, quantum physics education research is dedicated to reconstructing quantum physics content for teaching; on the other hand, it focuses on empirical research into learning and teaching quantum physics. These two pillars are by no means disconnected, but rather interconnected and are complemented by smaller research areas that primarily focus on quantum physics experiments for laboratory courses. During the observation period, a shift in the research focus from more content-specific work to empirical studies on the teaching and learning of quantum physics can be observed.

Institutional Review Board Statement

Informed consent statement, data availability statement, conflicts of interest.

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10 mind-boggling things you should know about quantum physics

From the multiverse to black holes, here’s your cheat sheet to the spooky side of the universe.

1. The quantum world is lumpy

The quantum world has a lot in common with shoes. You can’t just go to a shop and pick out sneakers that are an exact match for your feet. Instead, you’re forced to choose between pairs that come in predetermined sizes.

The subatomic world is similar. Albert Einstein won a Nobel Prize for proving that energy is quantized. Just as you can only buy shoes in multiples of half a size, so energy only comes in multiples of the same "quanta" — hence the name quantum physics.

The quanta here is the Planck constant , named after Max Planck, the godfather of quantum physics. He was trying to solve a problem with our understanding of hot objects like the sun. Our best theories couldn’t match the observations of the energy they kick out. By proposing that energy is quantized, he was able to bring theory neatly into line with experiment.

2. Something can be both wave and particle

J. J. Thomson won the Nobel Prize in 1906 for his discovery that electrons are particles. Yet his son George won the Nobel Prize in 1937 for showing that electrons are waves. Who was right? The answer is both of them. This so-called wave-particle duality is a cornerstone of quantum physics. It applies to light as well as electrons. Sometimes it pays to think about light as an electromagnetic wave, but at other times it’s more useful to picture it in the form of particles called photons. 

A telescope can focus light waves from distant stars, and also acts as a giant light bucket for collecting photons. It also means that light can exert pressure as photons slam into an object. This is something we already use to propel spacecraft with solar sails, and it may be possible to exploit it in order to maneuver a dangerous asteroid off a collision course with Earth , according to Rusty Schweickart, chairman of the B612 Foundation.

3. Objects can be in two places at once

Wave-particle duality is an example of superposition . That is, a quantum object existing in multiple states at once. An electron, for example, is both ‘here’ and ‘there’ simultaneously. It’s only once we do an experiment to find out where it is that it settles down into one or the other. 

This makes quantum physics all about probabilities. We can only say which state an object is most likely to be in once we look. These odds are encapsulated into a mathematical entity called the wave function. Making an observation is said to ‘collapse’ the wave function, destroying the superposition and forcing the object into just one of its many possible states.

This idea is behind the famous Schrödinger’s cat thought experiment. A cat in a sealed box has its fate linked to a quantum device. As the device exists in both states until a measurement is made, the cat is simultaneously alive and dead until we look.

4. It may lead us towards a multiverse

The idea that observation collapses the wave function and forces a quantum ‘choice’ is known as the Copenhagen interpretation of quantum physics. However, it’s not the only option on the table. Advocates of the ‘many worlds’ interpretation argue that there is no choice involved at all. Instead, at the moment the measurement is made, reality fractures into two copies of itself: one in which we experience outcome A, and another where we see outcome B unfold. It gets around the thorny issue of needing an observer to make stuff happen — does a dog count as an observer, or a robot?

Instead, as far as a quantum particle is concerned, there’s just one very weird reality consisting of many tangled-up layers. As we zoom out towards the larger scales that we experience day to day, those layers untangle into the worlds of the many worlds theory. Physicists call this process decoherence.

5. It helps us characterize stars

Danish physicist Niels Bohr showed us that the orbits of electrons inside atoms are also quantized. They come in predetermined sizes called energy levels. When an electron drops from a higher energy level to a lower energy level, it spits out a photon with an energy equal to the size of the gap. Equally, an electron can absorb a particle of light and use its energy to leap up to a higher energy level.

Astronomers use this effect all the time. We know what stars are made of because when we break up their light into a rainbow-like spectrum, we see colors that are missing. Different chemical elements have different energy level spacings, so we can work out the constituents of the sun and other stars from the precise colors that are absent.

6. Without it the sun wouldn’t shine

The sun makes its energy through a process called nuclear fusion. It involves two protons — the positively charged particles in an atom — sticking together. However, their identical charges make them repel each other, just like two north poles of a magnet. Physicists call this the Coulomb barrier, and it’s like a wall between the two protons. 

Think of protons as particles and they just collide with the wall and move apart: No fusion, no sunlight. Yet think of them as waves, and it’s a different story. When the wave’s crest reaches the wall, the leading edge has already made it through. The wave’s height represents where the proton is most likely to be. So although it is unlikely to be where the leading edge is, it is there sometimes. It’s as if the proton has burrowed through the barrier, and fusion occurs. Physicists call this effect "quantum tunneling".

7. It stops dead stars collapsing

Eventually fusion in the sun will stop and our star will die. Gravity will win and the sun will collapse, but not indefinitely. The smaller it gets, the more material is crammed together. Eventually a rule of quantum physics called the Pauli exclusion principle comes into play. This says that it is forbidden for certain kinds of particles — such as electrons — to exist in the same quantum state. As gravity tries to do just that, it encounters a resistance that astronomers call degeneracy pressure. The collapse stops, and a new Earth-sized object called a white dwarf forms. 

Degeneracy pressure can only put up so much resistance, however. If a white dwarf grows and approaches a mass equal to 1.4 suns, it triggers a wave of fusion that blasts it to bits. Astronomers call this explosion a Type Ia supernova , and it’s bright enough to outshine an entire galaxy.

8. It causes black holes to evaporate

A quantum rule called the Heisenberg uncertainty principle says that it’s impossible to perfectly know two properties of a system simultaneously. The more accurately you know one, the less precisely you know the other. This applies to momentum and position, and separately to energy and time.

It’s a bit like taking out a loan. You can borrow a lot of money for a short amount of time, or a little cash for longer. This leads us to virtual particles. If enough energy is ‘borrowed’ from nature then a pair of particles can fleetingly pop into existence, before rapidly disappearing so as not to default on the loan.

Stephen Hawking imagined this process occurring at the boundary of a black hole, where one particle escapes (as Hawking radiation), but the other is swallowed. Over time the black hole slowly evaporates, as it’s not paying back the full amount it has borrowed. 

9. It explains the universe’s large-scale structure

Our best theory of the universe’s origin is the Big Bang . Yet it was modified in the 1980s to include another theory called inflation . In the first trillionth of a trillionth of a trillionth of a second, the cosmos ballooned from smaller than an atom to about the size of a grapefruit. That’s a whopping 10^78 times bigger. Inflating a red blood cell by the same amount would make it larger than the entire observable universe today.

As it was initially smaller than an atom, the infant universe would have been dominated by quantum fluctuations linked to the Heisenberg uncertainty principle. Inflation caused the universe to grow rapidly before these fluctuations had a chance to fade away. This concentrated energy into some areas rather than others — something astronomers believe acted as seeds around which material could gather to form the clusters of galaxies we observe now.

10. It is more than a little ‘spooky’

As well as helping to prove that light is quantum, Einstein argued in favor of another effect that he dubbed ‘spooky action at distance’. Today we know that this ‘quantum entanglement’ is real, but we still don’t fully understand what’s going on. Let’s say that we bring two particles together in such a way that their quantum states are inexorably bound, or entangled. One is in state A, and the other in state B.

The Pauli exclusion principle says that they can’t both be in the same state. If we change one, the other instantly changes to compensate. This happens even if we separate the two particles from each other on opposite sides of the universe. It’s as if information about the change we’ve made has traveled between them faster than the speed of light, something Einstein said was impossible.

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• Published: 28 April 2023

Fresh perspectives on the foundations of quantum physics

• Eric G. Cavalcanti 1 ,
• Rafael Chaves 2 ,
• Flaminia Giacomini 3 &
• Yeong-Cherng Liang 4  

Nature Reviews Physics volume  5 ,  pages 323–325 ( 2023 ) Cite this article

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• Quantum physics

As we are at the beginning of the second century of quantum physics, we asked four researchers to share their views on new research directions trying to answer old, yet still open, questions in the foundations of quantum theory.

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Acknowledgements

E.G.C. acknowledges L. del Rio, N. Tischler, H. Wiseman, W. Zeng and participants of the Towards Experimental Wigner’s Friends workshop in San Francisco for useful discussions on the LF experimental programme, as well as support from grant no. FQXi-RFP-CPW-2019 from the Foundational Questions Institute and Fetzer Franklin Fund. R.C. acknowledges support from the Serrapilheira Institute (grant no. Serra – 1708-15763) and the Simons Foundation (grant no. 1023171, RC). F.G. would like to thank R. Renner for helpful comments on a first draft of her contribution, and acknowledges support from the Swiss National Science Foundation via the Ambizione Grant PZ00P2-208885. Y.-C.L. is grateful to N. Gisin for the many inspiring discussions on quantum foundations and for introducing to him the exciting topic of entangled measurements, and acknowledges support from the National Science and Technology Council and the National Center for Theoretical Sciences, Taiwan.

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Eric G. Cavalcanti

International Institute of Physics, IIP-UFRN, Natal, Brazil

Rafael Chaves

Institute for Theoretical Physics, ETH Zürich, Zürich, Switzerland

Flaminia Giacomini

Department of Physics and Center for Quantum Frontiers of Research and Technology (QFort), National Cheng Kung University, Tainan, Taiwan

Yeong-Cherng Liang

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Correspondence to Eric G. Cavalcanti , Rafael Chaves , Flaminia Giacomini or Yeong-Cherng Liang .

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The contributors

Eric Cavalcanti is an Associate Professor at Griffith University in Queensland, Australia. He has also worked at the University of Sydney and University of Oxford, after a PhD in Physics from the University of Queensland. His research focus is on quantum foundations and quantum information theory, and he has also made contributions to a wide range of fields including philosophy of science, quantum atom-optics and experimental atomic collisions.

Rafael Chaves is a research leader at the International Institute of Physics in Natal, Brazil. Previously, he worked in ICFO and the Universities of Freiburg and Cologne as a postdoctoral researcher. His contributions include quantum computation, communication and machine learning. The focus of his research is on the interface between quantum information and causal inference, developing new tools and concepts to investigate the emergence of non-classical features in quantum networks.

Flaminia Giacomini is an SNSF Ambizione Fellow at ETH Zurich. She received her PhD from the University of Vienna and then held a postdoctoral fellowship at Perimeter Institute for Theoretical Physics. Her research uses quantum information tools to answer fundamental questions at the interface between quantum theory and general relativity. Her research interests span from conceptual consequences of the lack of a classical spacetime, such as quantum time, quantum reference frames and indefinite causality, to the study of the observational implications of the quantum nature of gravity in table-top experiments.

Yeong-Cherng Liang is a professor of physics and a research group leader based at the National Cheng Kung University (NCKU), Taiwan. He received his PhD from the University of Queensland, Australia, in 2008. He then did postdoctoral research at the University of Sydney, the University of Geneva and ETH Zürich, before taking up a faculty position at NCKU in 2015. His expertise is in quantum foundations, especially quantum nonlocality, quantum entanglement and their applications in quantum information.

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Cavalcanti, E.G., Chaves, R., Giacomini, F. et al. Fresh perspectives on the foundations of quantum physics. Nat Rev Phys 5 , 323–325 (2023). https://doi.org/10.1038/s42254-023-00586-z

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A quantum world on a silicon chip

Researchers develop a platform to probe, control qubits in silicon for quantum networks.

The device uses a simple electric diode to manipulate qubits inside a commercial silicon wafer. (Second Bay Studios/Harvard SEAS)

The quantum internet would be a lot easier to build if we could use existing telecommunications technologies and infrastructure. Over the past few years, researchers have discovered defects in silicon — a ubiquitous semiconductor material —  that could be used to send and store quantum information over widely-used telecommunications wavelengths. Could these defects in silicon be the best choice among all the promising candidates to host qubits for quantum communications?

"It’s still a Wild West out there,” said Evelyn Hu , the Tarr-Coyne Professor of Applied Physics and of Electrical Engineering at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS). “Even though new candidate defects are a promising quantum memory platform, there is often almost nothing known about why certain recipes are used to create them,  and how you can rapidly characterize them and their interactions, even in ensembles.  And ultimately, how can we fine-tune their behavior so they exhibit identical characteristics? If we are ever to make a technology out of this wide world of possibilities, we must have ways to characterize them better, faster and more efficiently.”

Now, Hu and a team of researchers have developed a platform to probe, interact with and control these potentially powerful quantum systems.  The device uses a simple electric diode, one of the most common components in semiconductor chips, to manipulate qubits inside a commercial silicon wafer.  Using this device, the researchers were able to explore how the defect responds to changes in the electric field, tune its wavelength within the telecommunications band and even turn it on and off.

If we are ever to make a technology out of this wide world of possibilities, we must have ways to characterize them better, faster and more efficiently.

“One of the most exciting things about having these defects in silicon is that you can use well-understood devices like diodes in this familiar material to understand a whole new quantum system and do something new with it,” said Aaron Day, a Ph.D. candidate at SEAS. Day co-led the work with Madison Sutula, a research fellow at Harvard. 

While the research team used this approach to characterize defects in silicon, it could be used as a diagnostic and control tool for defects in other material systems. 

The research is published in Nature Communications .

Quantum defects, also known as color centers or quantum emitters, are imperfections in otherwise perfect crystal lattices that can trap single electrons. When those electrons are hit with a laser, they emit photons in specific wavelengths. The defects in silicon that researchers are most interested in for quantum communications are known as G-centers and T-centers. When these defects trap electrons, the electrons emit photons in a wavelength called the O-band, which is widely used in telecommunications.

In this research, the team focused on G-center defects. The first thing they needed to figure out was how to make them. Unlike other types of defects, in which an atom is removed from a crystal lattice, G-center defects are made by adding atoms to the lattice, specifically carbon. But Hu, Day and the rest of the research team found that adding hydrogen atoms is also critical to consistently forming the defect. 

Next, the researchers fabricated electrical diodes using a new approach which optimally sandwiches the defect at the center of every device without degrading the performance of either the defect or the diode.  The fabrication method can create hundreds of devices with embedded defects across a commercial wafer. Hooking the whole device up to apply a voltage, or electric field, the team found that when a negative voltage was applied across the device, the defects turned off and went dark.

“Understanding when a change in environment leads to a loss of signal is important for engineering stable systems in networking applications,” said Day,

The researchers also found that by using a local electric field, they could tune the wavelengths being emitted by the defect, which is important for quantum networking when disparate quantum systems need to be aligned. 

The team also developed a diagnostic tool to image how the millions of defects embedded in the device change in space as the electric field is applied.

“We found that the way we’re modifying the electric environment for the defects has a spatial profile, and we can image it directly by seeing the changes in the intensity of light being emitted by the defects,” said Day. “By using so many emitters and getting statistics on their performance, we now have a good understanding of how defects respond to changes in their environment. We can use that information to inform how to build the best environments for these defects in future devices. We have a better understanding of what makes these defects happy and unhappy.”

Next, the team aims to use the same techniques to understand the T-center defects in silicon.

The research was co-authored by Sutula, Jonathan R. Dietz, Alexander Raun from SEAS, and AWS research scientists Denis D. Sukachev and Mihir K. Bhaskar.

This work was supported by AWS Center for Quantum Networking and the Harvard Quantum Initiative. Harvard’s Office of Technology Development has protected the intellectual property associated with this project and is pursuing commercialization opportunities.

Topics: Applied Physics , Quantum Engineering

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Enabling Nuclear Physics Discoveries with Quantum Computing

A new approach validates quantum algorithms for nuclear physics applications

Quantum simulations may be able to solve nuclear physics problems that are inaccessible by current methods.

(Image by Stephanie King | Pacific Northwest National Laboratory)

With the advent of exascale computing , scientists can perform complex calculations to address difficult challenges in research for energy and national security. However, some problems are still inaccessible for even these powerful computers. For certain types of problems, quantum computers —representing a fundamentally different type of computing—may be able to excel over the world’s fastest exascale supercomputers.

Though quantum computers currently exist, they are generally considered to be too "noisy" to produce accurate calculations. More research and development is needed to increase the error correction and stability of quantum computing devices to produce accurate results. While some scientists are developing the quantum device hardware and circuit designs for these future quantum computers, others like Ang Li, a computer scientist at Pacific Northwest National Laboratory (PNNL) , are preparing and verifying the quantum algorithms that will run on this hardware.

In a new study published in The European Physics Journal A , Li and colleagues from Oak Ridge National Laboratory (ORNL) and Los Alamos National Laboratory created a method to validate quantum algorithms for nuclear physics applications . While Li and his colleagues are not the first to apply quantum computing methods to low-energy physics calculations, their newly developed method makes validating these calculations more efficient—setting the stage for quantum advances over classical calculations in this field.

“Even though we don’t have quantum computers capable of performing certain calculations, we can simulate how they may be able to perform on future quantum platforms through their classical simulation on exascale supercomputers,” said Li. “That way, when the technology does become available, we have algorithms ready to test on the new hardware.”

Li developed the software called Northwest Quantum Simulator (NWQ-Sim) to simulate quantum devices and circuits. Unlike the circuits of classical computers, quantum circuits are not restricted to the use of binary “1” or “0” states. Instead, they use qubits that can exist in both states simultaneously—and every state in between.

In low-energy nuclear physics, scientists perform calculations to understand the structure and stability of atomic nuclei. The particles within the nuclei interact with one another and influence each other’s physical properties. As more particles are taken into consideration, the calculations become more complex. This “curse of dimensionality” is where quantum computing can provide an advantage.

Compared to classical computing, quantum computing is not as affected by the scale of calculations. With each additional quantum bit, or qubit, added to the computer, the quantum system becomes exponentially more powerful. Therefore, larger simulations on quantum computers only require a modest increase in resources—in this case, qubits.

Li’s NWQ-Sim software was modified to validate a quantum projection algorithm that was developed by his co-authors in a previous work. This algorithm progressively amplifies the probability of converging to ground states—the lowest energy state of a system—which provides crucial information about the properties of a system. NWQ-Sim confirms that this projection algorithm could produce sufficiently accurate results for solving challenging low-energy nuclear physics problems, as well as other problems in physics and chemistry, on future quantum computers.

“In concept, quantum calculations have the potential to be more efficient than classical ones for low-energy nuclear physics,” said Li. “Current methods for emulating quantum circuits have too large memory and processing requirements to validate these calculations on classical computers. Our method provides a more efficient way to simulate and verify the proposed quantum projection algorithms, which typically generate extremely deep circuits, for use on a quantum computer.”

To create a more efficient process, Li and his colleagues first mapped the interactions of an atomic nucleus to the qubit space. They then developed projection algorithms for desired low-energy nuclear state preparation and validated the algorithm circuits through numerical simulation on graphics processing units of various high-performance computing systems. They found that their method was highly accurate for verifying simulations involving smaller nuclei, such as helium, oxygen, and calcium.

“Next, we plan to extend this work to larger nuclei, such as iron and nickel,” said Li.

This research was primarily supported by the Quantum Science Center , a Department of Energy, Office of Science, National Quantum Information Science Research Center headquartered at ORNL. This research used resources of the Oak Ridge Leadership Computing Facility and the National Energy Research Scientific Computing Center, both of which are Department of Energy Office of Science user facilities.

Published: June 24, 2024

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DARPA Researchers Highlight Application Areas for Quantum Computing

This post is modified from one originally published by DARPA

Amid efforts to explore quantum computers’ transformative potential, one foundational element remains missing from the discussion about quantum: What are the benchmarks that predict whether tomorrow’s quantum computers will be truly revolutionary? In 2021, DARPA’s  Quantum Benchmarking  program kicked off with the goal of reinventing the metrics critical to  measuring quantum computing progress  and applying scientific rigor to often unsubstantiated claims about quantum computing’s future promise.

Six months into the second phase of the program, five teams have highlighted research findings focused on specific applications where quantum computing might make outsized impact over digital supercomputers. Equally important, researchers estimated what size quantum computer is needed to achieve the desired performance and how valuable the computation would be. Pre-prints of these results are available on  arxiv.org .

Three teams — University of Southern California, HRL Laboratories, and L3Harris — focused on benchmarks and applications while two other teams — Rigetti Computing and Zapata Computing — estimated required quantum computing resources. MIT Lincoln Laboratory, NASA, and Los Alamos National Laboratory provided subject matter expertise, software integration, and test and evaluation capabilities.

The HRL team includes UW–Madison physics professor Matt Otten .

To view the pre-print titles, abstracts, and links to the full text, as well as open-source software code developed by the teams, visit:  Publications highlighting potential impact of quantum computing in specific applications .

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June 24, 2024

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New research uncovers hidden phenomena in ultra-clean quantum materials

by Forschungsverbund Berlin e.V. (FVB)

In a paper published today in Nature Communications , researchers unveiled previously unobserved phenomena in an ultra-clean sample of the correlated metal SrVO 3 . The study offers experimental insights that challenge the prevailing theoretical models of these unusual metals.

The international research team—from the Paul Drude Institute of Solid State Electronics (PDI), Germany; Oak Ridge National Laboratory (ORNL); Pennsylvania State University; University of Pittsburgh; the Pittsburgh Quantum Institute; and University of Minnesota—believes their findings will prompt a re-evaluation of current theories on electron correlation effects, shedding light on the origins of valuable phenomena in these systems, including magnetic properties , high-temperature superconductivity , and the unique characteristics of highly unusual transparent metals.

The perovskite oxide material SrVO 3 is classified as a Fermi liquid—a state describing a system of interacting electrons in a metal at sufficiently low temperatures.

In conventional metals, electrons that conduct electricity move independently, commonly referred to as a Fermi gas. In contrast, Fermi liquids feature significant mutual interactions between electrons, meaning the motion of one electron strongly influences the others. This collective behavior can lead to unique electronic properties with profound technological applications, providing insights into the interactions between electrons in correlated metals.

SrVO 3 serves as an ideal model system for studying electron correlation phenomena due to its crystalline and electronic simplicity. This simplicity is crucial for understanding complex phenomena such as magnetic order or superconductivity, which can complicate theoretical and experimental studies.

Another crucial factor in understanding experimental results that guide theoretical models for electron correlation effects is the presence or absence of defects in the material itself. Dr. Roman Engel-Herbert, study lead and Director of PDI in Berlin, said, "If you want to get to the bottom of one of the best-kept secrets in condensed matter physics, then you must study it in its purest form; in the absence of any extrinsic disturbance. High-quality materials that are virtually defect-free are essential. You need to synthesize ultra-clean materials."

Achieving a defect-free sample of SrVO 3 has been a seemingly insurmountable challenge until now. By employing an innovative thin film growth technique that combines the advantages of molecular beam epitaxy and chemical vapor deposition , the team achieved an unprecedented level of material purity.

Dr. Matt Brahlek, first author of the study, quantifies the improvement: "A simple measure of material purity is the ratio of how easily electricity flows at room temperature compared to low temperature, called the residual resistivity ratio, RRR value. If the metal contains many defects, RRR values are low, typically around 2–5.

"We have been able to synthesize SrVO 3 films with RRR nearly 100 times larger, 200, opening the door to study the true properties of the correlated metal SrVO 3 . In particular, the high material quality allowed accessing special regime at high magnetic fields for the first time, where surprises were found."

The interdisciplinary team of scientists was surprised to discover a series of peculiar transport phenomena that were in sharp contrast to the transport properties measured previously on highly defective samples. Their findings challenge the long-standing scientific consensus regarding SrVO 3 as a simple Fermi liquid.

Engel-Herbert explains, "This situation was very exciting but also puzzling. While we reproduced previously reported transport behavior of SrVO 3 in our highly defective samples, identical measurements in ultraclean samples with high RRR values differed."

Results from defective samples allowed a straight-forward interpretation of the results that matched theoretical expectation. These results were used as experimental evidence that the theoretical understanding correctly captured the electron correlation effects in SrVO 3 . However, the team found that measurements on the ultraclean samples could not be explained so easily.

Brahlek added, "An observation that stands out is the expectation that the number of electrons that carry electricity in a metal is independent of temperature and magnetic field. This is of course true, but the interpretation of the measured quantity is not a direct measure of the carrier concentration.

"Rather, this quantity is mixed up with other aspects of the material properties, such as how defects and temperature impact the flow of electricity. We had to delve deeper into the physics to understand what we saw. That is what makes it so important and exciting."

The researchers believe their discovery can serve as a basis to refine theoretical models and prompt a re-examination of established views and interpretations of materials exhibiting a sizeable electron correlation.

Engel-Herbert says, "Our job as experimental physicists is to push beyond the boundaries of the current understanding of nature. This is where discoveries can be made, where we advance science. As condensed matter physicists, it is key to keep perfecting our object of study by challenging ourselves to push the limits of perfecting materials.

"This can potentially give new insights into the true behavior of this class of materials and enables a comprehensive explanation of the phenomena measured and observed. It takes an interdisciplinary team of experts to do this.

"While the job is not yet completed, our results are an opportunity for the community to recalibrate their theories; re-examining materials we believed were well-understood and re-evaluate their potential for applications."

Journal information: Nature Communications

Provided by Forschungsverbund Berlin e.V. (FVB)

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