latest research topics in quantum physics

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Quantum physics articles from across Nature Portfolio

Quantum physics is the study of matter and energy at its most fundamental level. A central tenet of quantum physics is that energy comes in indivisible packets called quanta. Quanta behave very differently to macroscopic matter: particles can behave like waves, and waves behave as though they are particles.

A quantum solid made of electrons: observing the elusive Wigner crystal

In ordinary materials, electrons move too quickly for their negative electric charges to affect their interactions. But at low temperatures and densities, they can be made to crystallize into an exotic type of electron solid — a phenomenon predicted by Eugene Wigner 90 years ago and only now directly observed.

A voltage-balanced device for quantum resistance metrology

The quantum anomalous Hall effect holds promise for quantum resistance metrology, but has been limited to low operating currents. A measurement scheme that increases the effect’s operational current is now demonstrated — a scheme that could also be used more generally to improve the performance of existing primary quantum standards of resistance based on the conventional quantum Hall effect.

Intel brings quantum-computing microchips a step closer

By adapting methods for fabricating and testing conventional computer chips, researchers have brought silicon-based quantum computers closer to reality — and to accessing the immense benefits of a mature chipmaking industry.

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• Matter waves and particle beams
• Quantum information
• Quantum mechanics
• Quantum metrology
• Quantum simulation
• Single photons and quantum effects
• Theoretical physics

Latest Research and Reviews

Microwave quantum memcapacitor effect

Nonlinear memory devices such as memristors, memcapacitors, and meminductors, are the building blocks of energy-efficient neuromorphic computing. Here, the authors propose a superconducting circuit design acting as a microwave quantum memcapacitor, which could be implemented in neuromorphic quantum computing architectures.

• Shubham Kumar
• Francisco Albarrán-Arriagada

Quantum control of a cat qubit with bit-flip times exceeding ten seconds

A type of qubit that has inherent resistance to bit-flip errors has been manipulated with a bit-flip time of more than 10 s without losing that error protection.

Strong tunable coupling between two distant superconducting spin qubits

The hybrid architecture of Andreev spin qubits made using semiconductor–superconductor nanowires means that supercurrents can be used to inductively couple qubits over long distances.

• Marta Pita-Vidal
• Jaap J. Wesdorp
• Christian Kraglund Andersen

Anisotropic exchange interaction of two hole-spin qubits

A successful silicon spin qubit design should be rapidly scalable by benefiting from industrial transistor technology. This investigation of exchange interactions between two FinFET qubits provides a guide to implementing two-qubit gates for hole spins.

• Simon Geyer
• Bence Hetényi
• Andreas V. Kuhlmann

Synthetic dimensions for topological and quantum phases

Quantum simulators study important models of condensed matter and high-energy physics. Research on synthetic dimensions has paved the way for studying exotic phenomena, such as curved space-times, topological phases of matter, lattice gauge theories, twistronics without a twist, and more

• Javier Argüello-Luengo
• Utso Bhattacharya
• Maciej Lewenstein

Analysis of quantum key distribution based on unified model of sequential state discrimination strategy

• Min Namkung
• Younghun Kwon

News and Comment

A compact neutral-atom fault-tolerant quantum computer based on new quantum codes

A practical and hardware-efficient blueprint for fault-tolerant quantum computing has been developed, using quantum low-density-parity-check codes and reconfigurable neutral-atom arrays. The scheme requires ten times fewer qubits and paves the way towards large-scale quantum computing using existing experimental technologies.

Harnessing quantum information to advance computing

We highlight the vibrant discussions on quantum computing and quantum algorithms that took place at the 2024 American Physical Society March Meeting and invite submissions that notably drive the field of quantum information science forward.

Measuring qubits with thermometers

A new approach to measuring qubits offers an alternative path to scaling quantum computers.

• William D. Oliver

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Quantum Physics news

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The quantum theory of gravitation, effective field theories and strings: Past and present

Gravity is one of four fundamental interactions. The most precise description of this force is still provided by Einstein's General Theory of Relativity, published in 1915, an entirely classical theory. This description sets ...

General Physics

8 hours ago

New super-pure silicon chip opens path to powerful quantum computers

Researchers at the Universities of Melbourne and Manchester have invented a breakthrough technique for manufacturing highly purified silicon that brings powerful quantum computers a big step closer.

Condensed Matter

19 hours ago

Attosecond core-level spectroscopy reveals real-time molecular dynamics

Chemical reactions are complex mechanisms. Many different dynamic processes are involved, affecting both the electrons and the nucleus of the present atoms. Very often, the strongly coupled electron and nuclear dynamics induce ...

Optics & Photonics

May 6, 2024

Experiment opens door for millions of qubits on one chip

Researchers from the University of Basel and the NCCR SPIN have achieved the first controllable interaction between two hole spin qubits in a conventional silicon transistor. The breakthrough opens up the possibility of integrating ...

Quantum Physics

New quantum sensing scheme could lead to enhanced high-precision nanoscopic techniques

Researchers from the University of Portsmouth have unveiled a quantum sensing scheme that achieves the pinnacle of quantum sensitivity in measuring the transverse displacement between two interfering photons.

May 4, 2024

Physicists create an optical tweezer array of individual polyatomic molecules for the first time

A team of physicists at Harvard University has succeeded in trapping individual polyatomic molecules in optical tweezer arrays for the first time. In their paper published in the journal Nature, the group describes how they ...

May 3, 2024

Physicists pioneer new quantum sensing platform

Quantum sensors detect the smallest of environmental changes—for example, an atom reacting to a magnetic field. As these sensors "read" the unique behaviors of subatomic particles, they also dramatically improve scientists' ...

The BREAD Collaboration is searching for dark photons using a coaxial dish antenna

Approximately 80% of the matter in the universe is predicted to be so-called "dark matter," which does not emit, reflect, or absorb light and thus cannot be directly detected using conventional experimental techniques.

Physicists arrange atoms in close proximity, paving way for exploring exotic states of matter

Proximity is key for many quantum phenomena, as interactions between atoms are stronger when the particles are close. In many quantum simulators, scientists arrange atoms as close together as possible to explore exotic states ...

May 2, 2024

Twisting and binding matter waves with photons in a cavity

Precisely measuring the energy states of individual atoms has been a historical challenge for physicists due to atomic recoil. When an atom interacts with a photon, the atom "recoils" in the opposite direction, making it ...

Researcher creates optical magnetometer prototype that detects errors in MRI scans

Hvidovre Hospital has the world's first prototype of a sensor capable of detecting errors in MRI scans using laser light and gas. The new sensor, developed by a young researcher at the University of Copenhagen and Hvidovre ...

Significant new discovery in teleportation research: Noise can improve the quality of quantum teleportation

Researchers have succeeded in conducting an almost perfect quantum teleportation despite the presence of noise that usually disrupts the transfer of quantum state. The results have been published in the journal Science Advances.

Research demonstrates high qubit control fidelity and uniformity in single-electron control

The journal Nature has published a research paper, "Probing single electrons across 300-mm spin qubit wafers," demonstrating state-of-the-art uniformity, fidelity and measurement statistics of spin qubits. The industry-leading ...

Researchers find unexpected roadblock to conductivity in Mott insulators

In the realm of condensed matter physics, few phenomena captivate physicists' curiosity as much as Mott insulators. According to traditional theory, this odd class of materials should be capable of conducting electricity, ...

Researchers build new device that is a foundation for quantum computing

Scientists led by the University of Massachusetts Amherst have adapted a device called a microwave circulator for use in quantum computers, allowing them for the first time to precisely tune the exact degree of nonreciprocity ...

May 1, 2024

New work reveals the 'quantumness' of gravity

Gravity is part of our everyday life. Still, the gravitational force remains mysterious: to this day we do not understand whether its ultimate nature is geometrical, as Einstein envisaged, or governed by the laws of quantum ...

Generating graph states of atomic ensembles via photon-mediated entanglement

Graph states, a class of entangled quantum states that can be represented by graphs, have been the topic of numerous recent physics studies, due to their intriguing properties. These unique properties could make them particularly ...

Physicists discover new way to make strange metal

By tinkering with a quantum material characterized by atoms arranged in the shape of a sheriff's star, MIT physicists and colleagues have unexpectedly discovered a new way to make a state of matter known as a strange metal. ...

Scientists show that there is indeed an 'entropy' of quantum entanglement

Bartosz Regula from the RIKEN Center for Quantum Computing and Ludovico Lami from the University of Amsterdam have shown, through probabilistic calculations, that there is indeed, as had been hypothesized, a rule of entropy ...

New system boosts efficiency of quantum error correction

The fragile qubits that make up quantum computers offer a powerful computational tool, yet also present a conundrum: How can engineers create practical, workable quantum systems out of bits that are so easily disturbed—and ...

Apr 29, 2024

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Laser excitation of Th-229 nucleus: New findings suggest classical quantum physics and nuclear physics can be combined

Researchers discover 'topological Kerr effect' in two-dimensional quantum magnets

Quantum challenge to be solved one mile underground

Unveiling a new quantum frontier: Frequency-domain entanglement

Research demonstrates a new mechanism of order formation in quantum systems

The end of the quantum tunnel: Exact instanton transseries for quantum mechanics

Demonstration of heralded three-photon entanglement on a photonic chip

Scientists at the MAJORANA Collaboration look for rule-violating electrons

Light stands still in a deformed crystal

Scientists tune the entanglement structure in an array of qubits

Lead-vacancy centers in diamond as building blocks for large-scale quantum networks

The big quantum chill: Scientists modify common lab refrigerator to cool faster with less energy

Manipulating the geometry of the 'electron universe' in magnets

Tailoring electron vortex beams with customizable intensity patterns by electron diffraction holography

Tunable quantum anomalous Hall effects in van der Waals heterostructures

Announcing the birth of QUIONE, a unique analog quantum processor

Steering toward quantum simulation at scale

Springing simulations forward with quantum computing

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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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Researchers discover new ‘unexpected’ phenomenon in quantum physics of materials

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Researchers at Northeastern have discovered a new quantum phenomenon in a specific class of materials, called antiferromagnetic insulators, that could yield new ways of powering “spintronic” and other technological devices of the future. 

The discovery illuminates “how heat flows in a magnetic insulator, [and] how [researchers] can detect that heat flow,” says Gregory Fiete , a physics professor

Gregory Fiete, a professor of physics at Northeastern. Photo by Matthew Modoono/Northeastern University

at Northeastern and co-author of the research. The novel effects, published in Nature Physics this week and demonstrated experimentally, were observed by combining lanthanum ferrite (LaFeO3) with a layer of platinum or tungsten.

“That layered coupling is what is responsible for the phenomenon,” says Arun Bansil , university distinguished professor in the Department of Physics at Northeastern, who also took part in the study. 

The discovery may have numerous potential applications, such as improving heat sensors, waste-heat recycling, and other thermoelectric technologies, Bansil says. This phenomenon could even lead to development of a new power source for these—and other—budding technologies. Northeastern graduate  student Matt Matzelle and Bernardo Barbiellini, a computational and theoretical physicist at the Lappeenranta University of Technology, who is currently visiting Northeastern, participated in the research.  

Illustrating the teams’ findings requires considerable magnification (literally) to observe the world of atomic-scale particles—specifically, at the nano-lives of electrons. It also requires an understanding of several properties of electrons—that they possess something called “spin,” have a charge, and can, when moving through a material, generate heat flow. 

Electron spin, or angular momentum, describes a fundamental property of electrons defined in one of two potential states: Up or down. There are many different ways these “up or down” spins of the electrons (also thought of as north-south poles) orient themselves in space, which in turn gives rise to different types of magnetisms. It all depends, Bansil says, on the ways atoms are patterned in a given material.

In a magnetic system, typically the spins in that material have aligned themselves in the same direction. That electron arrangement in magnetic (or “ferromagnetic”) crystals is what produces that force that attracts or repels other crystals. Lots of magnetic materials also conduct electricity when electrons are able to flow through them. Those materials are called conductors, since they are able to conduct electricity.

Arun Bansil, University Distinguished Professor of physics. Photo by Matthew Modoono/Northeastern University

In addition to generating an electric current, the movement of electrons through a material also carries a heat current. When an external electromagnetic field is applied to materials that conduct electricity, a heat current results. 

“Heat is just when these electrons are jiggling around faster or slower, so, as a result, they can carry more or less thermal energy,” Bansil says. 

Usually the spin current flows in the same direction of the heat current, Bansil says. But, in the specific materials used in this study, “it flows perpendicular to the direction of the heat current.”

“That is what is new here,” Bansil says. 

It’s this “unexpected” interaction that opens the door to new ways of thinking about power generation. 

“What we want to do is create a current of magnetism that generates electrical power, and the way you do that is by generating a voltage,” Fiete says.

To do that, researchers combined the antiferromagnetic insulating material (here LaFeO3) with another heavier element, such as platinum or tungsten, which are conductors. The coupling throws the electrons slightly off-kilter. 

“This particular material has the spins that are, on closest neighboring atoms, nearly perfectly anti-oriented,” Fiete says, “meaning they’re a little bit canted . They’re not perfectly anti-oriented—they are mostly, but there’s a little bit of a twist. And that little offset is actually very important, because it’s part of what gives rise to the interesting effects that we see in the project.”

That’s what gives this particular class of materials its name: Canted antiferromagnet.  

An emerging class of electronic devices, so-called “spintronics,” rely on the manipulation of electron spin with the aim of improving information processing capabilities in future technologies. Another related field, called spin caloritronics, focuses on “how you convert heat flow into the flow of magnetism, or spin flow, and ultimately into a voltage,” Fiete says. 

“The quantum physics of materials is of particular interest because it directly connects with a lot of technologies: Technologies in quantum computing, quantum sensing, and quantum communications,” Fiete says. “And the idea that is really gaining traction … right now is: How do we transition research from the university, like the kind my team is involved in, into technologies that will impact the way that we live our lives?”

For media inquiries , please contact [email protected].

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Physicists arrange atoms in extremely close proximity

The technique opens possibilities for exploring exotic states of matter and building new quantum materials..

Proximity is key for many quantum phenomena, as interactions between atoms are stronger when the particles are close. In many quantum simulators, scientists arrange atoms as close together as possible to explore exotic states of matter and build new quantum materials.

They typically do this by cooling the atoms to a stand-still, then using laser light to position the particles as close as 500 nanometers apart — a limit that is set by the wavelength of light. Now, MIT physicists have developed a technique that allows them to arrange atoms in much closer proximity, down to a mere 50 nanometers. For context, a red blood cell is about 1,000 nanometers wide.

The physicists demonstrated the new approach in experiments with dysprosium, which is the most magnetic atom in nature. They used the new approach to manipulate two layers of dysprosium atoms, and positioned the layers precisely 50 nanometers apart. At this extreme proximity, the magnetic interactions were 1,000 times stronger than if the layers were separated by 500 nanometers.

What’s more, the scientists were able to measure two new effects caused by the atoms’ proximity. Their enhanced magnetic forces caused “thermalization,” or the transfer of heat from one layer to another, as well as synchronized oscillations between layers. These effects petered out as the layers were spaced farther apart.

“We have gone from positioning atoms from 500 nanometers to 50 nanometers apart, and there is a lot you can do with this,” says Wolfgang Ketterle , the John D. MacArthur Professor of Physics at MIT. “At 50 nanometers, the behavior of atoms is so much different that we’re really entering a new regime here.”

Ketterle and his colleagues say the new approach can be applied to many other atoms to study quantum phenomena. For their part, the group plans to use the technique to manipulate atoms into configurations that could generate the first purely magnetic quantum gate — a key building block for a new type of quantum computer.

The team has published their results today in the journal Science . The study’s co-authors include lead author and physics graduate student Li Du, along with Pierre Barral, Michael Cantara, Julius de Hond, and Yu-Kun Lu — all members of the MIT-Harvard Center for Ultracold Atoms , the Department of Physics, and the Research Laboratory of Electronics at MIT.

Peaks and valleys

To manipulate and arrange atoms, physicists typically first cool a cloud of atoms to temperatures approaching absolute zero, then use a system of laser beams to corral the atoms into an optical trap.

Laser light is an electromagnetic wave with a specific wavelength (the distance between maxima of the electric field) and frequency. The wavelength limits the smallest pattern into which light can be shaped to typically 500 nanometers, the so-called optical resolution limit. Since atoms are attracted by laser light of certain frequencies, atoms will be positioned at the points of peak laser intensity. For this reason, existing techniques have been limited in how close they can position atomic particles, and could not be used to explore phenomena that happen at much shorter distances.

“Conventional techniques stop at 500 nanometers, limited not by the atoms but by the wavelength of light,” Ketterle explains. “We have found now a new trick with light where we can break through that limit.”

The team’s new approach, like current techniques, starts by cooling a cloud of atoms — in this case, to about 1 microkelvin, just a hair above absolute zero — at which point, the atoms come to a near-standstill. Physicists can then use lasers to move the frozen particles into desired configurations.

Then, Du and his collaborators worked with two laser beams, each with a different frequency, or color, and circular polarization, or direction of the laser’s electric field. When the two beams travel through a super-cooled cloud of atoms, the atoms can orient their spin in opposite directions, following either of the two lasers’ polarization. The result is that the beams produce two groups of the same atoms, only with opposite spins.

Each laser beam formed a standing wave, a periodic pattern of electric field intensity with a spatial period of 500 nanometers. Due to their different polarizations, each standing wave attracted and corralled one of two groups of atoms, depending on their spin. The lasers could be overlaid and tuned such that the distance between their respective peaks is as small as 50 nanometers, meaning that the atoms gravitating to each respective laser’s peaks would be separated by the same 50 nanometers.

But in order for this to happen, the lasers would have to be extremely stable and immune to all external noise, such as from shaking or even breathing on the experiment. The team realized they could stabilize both lasers by directing them through an optical fiber, which served to lock the light beams in place in relation to each other.

“The idea of sending both beams through the optical fiber meant the whole machine could shake violently, but the two laser beams stayed absolutely stable with respect to each others,” Du says.

Magnetic forces at close range

As a first test of their new technique, the team used atoms of dysprosium — a rare-earth metal that is one of the strongest magnetic elements in the periodic table, particularly at ultracold temperatures. However, at the scale of atoms, the element’s magnetic interactions are relatively weak at distances of even 500 nanometers. As with common refrigerator magnets, the magnetic attraction between atoms increases with proximity, and the scientists suspected that if their new technique could space dysprosium atoms as close as 50 nanometers apart, they might observe the emergence of otherwise weak interactions between the magnetic atoms.

“We could suddenly have magnetic interactions, which used to be almost neglible but now are really strong,” Ketterle says.

The team applied their technique to dysprosium, first super-cooling the atoms, then passing two lasers through to split the atoms into two spin groups, or layers. They then directed the lasers through an optical fiber to stabilize them, and found that indeed, the two layers of dysprosium atoms gravitated to their respective laser peaks, which in effect separated the layers of atoms by 50 nanometers — the closest distance that any ultracold atom experiment has been able to achieve.

At this extremely close proximity, the atoms’ natural magnetic interactions were significantly enhanced, and were 1,000 times stronger than if they were positioned 500 nanometers apart. The team observed that these interactions resulted in two novel quantum phenomena: collective oscillation, in which one layer’s vibrations caused the other layer to vibrate in sync; and thermalization, in which one layer transferred heat to the other, purely through magnetic fluctuations in the atoms.

“Until now, heat between atoms could only by exchanged when they were in the same physical space and could collide,” Du notes. “Now we have seen atomic layers, separated by vacuum, and they exchange heat via fluctuating magnetic fields.”

The team’s results introduce a new technique that can be used to position many types of atom in close proximity. They also show that atoms, placed close enough together, can exhibit interesting quantum phenomena, that could be harnessed to build new quantum materials, and potentially, magnetically-driven atomic systems for quantum computers.

“We are really bringing super-resolution methods to the field, and it will become a general tool for doing quantum simulations,” Ketterle says. “There are many variants possible, which we are working on.”

This research was funded, in part, by the National Science Foundation and the Department of Defense.

• Paper: “Atomic physics on a 50-nm scale: Realization of a bilayer system of dipolar atoms”

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Physicists arrange atoms in extremely close proximity

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Proximity is key for many quantum phenomena, as interactions between atoms are stronger when the particles are close. In many quantum simulators, scientists arrange atoms as close together as possible to explore exotic states of matter and build new quantum materials.

They typically do this by cooling the atoms to a stand-still, then using laser light to position the particles as close as 500 nanometers apart — a limit that is set by the wavelength of light. Now, MIT physicists have developed a technique that allows them to arrange atoms in much closer proximity, down to a mere 50 nanometers. For context, a red blood cell is about 1,000 nanometers wide.

The physicists demonstrated the new approach in experiments with dysprosium, which is the most magnetic atom in nature. They used the new approach to manipulate two layers of dysprosium atoms, and positioned the layers precisely 50 nanometers apart. At this extreme proximity, the magnetic interactions were 1,000 times stronger than if the layers were separated by 500 nanometers.

What’s more, the scientists were able to measure two new effects caused by the atoms’ proximity. Their enhanced magnetic forces caused “thermalization,” or the transfer of heat from one layer to another, as well as synchronized oscillations between layers. These effects petered out as the layers were spaced farther apart.

“We have gone from positioning atoms from 500 nanometers to 50 nanometers apart, and there is a lot you can do with this,” says Wolfgang Ketterle, the John D. MacArthur Professor of Physics at MIT. “At 50 nanometers, the behavior of atoms is so much different that we’re really entering a new regime here.”

Ketterle and his colleagues say the new approach can be applied to many other atoms to study quantum phenomena. For their part, the group plans to use the technique to manipulate atoms into configurations that could generate the first purely magnetic quantum gate — a key building block for a new type of quantum computer.

The team has published their results today in the journal Science . The study’s co-authors include lead author and physics graduate student Li Du, along with Pierre Barral, Michael Cantara, Julius de Hond, and Yu-Kun Lu — all members of the MIT-Harvard Center for Ultracold Atoms, the Department of Physics, and the Research Laboratory of Electronics at MIT.

Peaks and valleys

To manipulate and arrange atoms, physicists typically first cool a cloud of atoms to temperatures approaching absolute zero, then use a system of laser beams to corral the atoms into an optical trap.

Laser light is an electromagnetic wave with a specific wavelength (the distance between maxima of the electric field) and frequency. The wavelength limits the smallest pattern into which light can be shaped to typically 500 nanometers, the so-called optical resolution limit. Since atoms are attracted by laser light of certain frequencies, atoms will be positioned at the points of peak laser intensity. For this reason, existing techniques have been limited in how close they can position atomic particles, and could not be used to explore phenomena that happen at much shorter distances.

“Conventional techniques stop at 500 nanometers, limited not by the atoms but by the wavelength of light,” Ketterle explains. “We have found now a new trick with light where we can break through that limit.”

The team’s new approach, like current techniques, starts by cooling a cloud of atoms — in this case, to about 1 microkelvin, just a hair above absolute zero — at which point, the atoms come to a near-standstill. Physicists can then use lasers to move the frozen particles into desired configurations.

Then, Du and his collaborators worked with two laser beams, each with a different frequency, or color, and circular polarization, or direction of the laser’s electric field. When the two beams travel through a super-cooled cloud of atoms, the atoms can orient their spin in opposite directions, following either of the two lasers’ polarization. The result is that the beams produce two groups of the same atoms, only with opposite spins.

Each laser beam formed a standing wave, a periodic pattern of electric field intensity with a spatial period of 500 nanometers. Due to their different polarizations, each standing wave attracted and corralled one of two groups of atoms, depending on their spin. The lasers could be overlaid and tuned such that the distance between their respective peaks is as small as 50 nanometers, meaning that the atoms gravitating to each respective laser’s peaks would be separated by the same 50 nanometers.

But in order for this to happen, the lasers would have to be extremely stable and immune to all external noise, such as from shaking or even breathing on the experiment. The team realized they could stabilize both lasers by directing them through an optical fiber, which served to lock the light beams in place in relation to each other.

“The idea of sending both beams through the optical fiber meant the whole machine could shake violently, but the two laser beams stayed absolutely stable with respect to each others,” Du says.

Magnetic forces at close range

As a first test of their new technique, the team used atoms of dysprosium — a rare-earth metal that is one of the strongest magnetic elements in the periodic table, particularly at ultracold temperatures. However, at the scale of atoms, the element’s magnetic interactions are relatively weak at distances of even 500 nanometers. As with common refrigerator magnets, the magnetic attraction between atoms increases with proximity, and the scientists suspected that if their new technique could space dysprosium atoms as close as 50 nanometers apart, they might observe the emergence of otherwise weak interactions between the magnetic atoms.

“We could suddenly have magnetic interactions, which used to be almost neglible but now are really strong,” Ketterle says.

The team applied their technique to dysprosium, first super-cooling the atoms, then passing two lasers through to split the atoms into two spin groups, or layers. They then directed the lasers through an optical fiber to stabilize them, and found that indeed, the two layers of dysprosium atoms gravitated to their respective laser peaks, which in effect separated the layers of atoms by 50 nanometers — the closest distance that any ultracold atom experiment has been able to achieve.

At this extremely close proximity, the atoms’ natural magnetic interactions were significantly enhanced, and were 1,000 times stronger than if they were positioned 500 nanometers apart. The team observed that these interactions resulted in two novel quantum phenomena: collective oscillation, in which one layer’s vibrations caused the other layer to vibrate in sync; and thermalization, in which one layer transferred heat to the other, purely through magnetic fluctuations in the atoms.

“Until now, heat between atoms could only by exchanged when they were in the same physical space and could collide,” Du notes. “Now we have seen atomic layers, separated by vacuum, and they exchange heat via fluctuating magnetic fields.”

The team’s results introduce a new technique that can be used to position many types of atom in close proximity. They also show that atoms, placed close enough together, can exhibit interesting quantum phenomena, that could be harnessed to build new quantum materials, and potentially, magnetically-driven atomic systems for quantum computers.

“We are really bringing super-resolution methods to the field, and it will become a general tool for doing quantum simulations,” Ketterle says. “There are many variants possible, which we are working on.”

This research was funded, in part, by the National Science Foundation and the Department of Defense.

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Solar panels reflect sparkling light from the sun. Credit: bombermoon / iStock

Lehigh Physicists Pioneer Quantum Material for Solar Efficiency Breakthrough

Physics Professor Chinedu Ekuma and doctoral student Srihari Kastuar published their research in the journal Science Advances .

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• Chinedu Ekuma

Physicists at Lehigh have developed a quantum material, atomically thin CuxGeSe/SnS, which is positioned as a leading candidate in a new class of materials aimed at significantly enhancing solar panel efficiency.

The development holds promise for advancing solar technology to meet the increasing global demand for clean energy.

A simulated prototype employing this material in the active layer of a solar cell exhibited an average photovoltaic absorption rate of 80%, a high generation rate of photoexcited carriers, and an external quantum efficiency (EQE) reaching an unprecedented 190%—a measure that far exceeds the theoretical Shockley-Queisser efficiency limit for silicon-based materials and pushes the field of quantum materials for photovoltaics to new heights.

“This work represents a significant advancement in sustainable energy solutions, showcasing innovative approaches that could revolutionize solar energy efficiency and accessibility in the near future,” said Chinedu Ekuma, professor of physics.

Ekuma, along with doctoral student Srihari Kastuar, published their research in the journal Science Advances .

Since publication, the potential breakthrough development has received glowing coverage from science-focused news outlets across the globe . Ekuma also recently presented the findings at a gathering of scientists convened by the U.S. Department of Energy, where the research was met with enthusiasm.

A Quantum Leap in Solar Efficiency

The remarkable efficiency of the material is largely due to its unique "intermediate band states," which are specific energy levels within the material's electronic structure that optimally convert solar energy. These states feature energy levels positioned within subband gaps—ranging from approximately 0.78 to 1.26 electron volts—ideal for efficient sunlight absorption and charge carrier production. In addition, the material performs especially well with high levels of absorption in the infrared and visible regions of the electromagnetic spectrum.

Typically, traditional solar cells achieve a maximum EQE of 100%, correlating to the generation and collection of one electron for each photon absorbed. However, the Lehigh-developed material utilizes intermediate band states to capture photon energy typically lost in conventional cells, including energy lost through reflection and heat production.

Srihari Kastuar

“Our engineered material excels beyond other intermediate band semiconductors as it hosts IB states without significant alterations to the crystal structure or the introduction of defects," explained Kastuar. "The intercalated copper atoms induce effects typically achieved through heavy-doping."

The novel material was developed using "van der Waals gaps," minuscule spaces between layered two-dimensional materials that can host atoms, molecules or ions. By intercalating zerovalent copper atoms between layers of germanium selenide (GeSe) and tin sulfide (SnS), the researchers tuned the material properties to enhance its photovoltaic performance.

But is it practical?

Ekuma, an expert in computational condensed matter physics, developed the simulated prototype as a proof of concept after extensive computer modeling of the system demonstrated theoretical promise.

Although integrating the newly designed quantum material into current solar energy systems will require further research and development, Ekuma pointed out that the experimental technique used to create these materials is already highly advanced.

Scientists have, over time, mastered a method that precisely inserts atoms, ions and molecules into materials, and encouraging results from a fabricated sample of the material were reported shortly after Ekuma’s initial publication.

A team of experimentalists, including scientists from Worcester Polytechnic Institute and the University of California-Davis, fabricated a sample of the material and conducted a variety of advanced analyses to characterize its properties.

Those results, published in the journal Applied Materials and Interfaces , concluded that intercalating zero-valent copper into layers of GeS was indeed a promising strategy offering “profound effects” for the enhanced functioning of photoelectric devices and solar energy conversion systems.

“Its rapid response and enhanced efficiency strongly indicate the potential of Cu-intercalated GeSe/SnS as a quantum material for use in advanced photovoltaic applications, offering an avenue for efficiency improvements in solar energy conversion,” Ekuma said.

Beyond enhanced performance in solar applications, the material offers additional advantages in terms of environmental sustainability. Copper and germanium are well-established materials that are less toxic than lead-based materials used in some solar panels. In addition, GeSe is an accessible resource, six times more abundant than antimony (Sb), an element currently used in many thin-film solar cells.

“Our material is a promising candidate for the development of next-generation, high-efficient solar cells, which will play a crucial role in addressing global energy needs,” Ekuma said.

The research was funded in part by a grant from the U.S. Department of Energy.

Story by Dan Armstrong

Read more stories on the Lehigh News Center.

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A safe approach to quantum gravity

After 25 years of steady progress, recent advances in theory and computing are enabling researchers to connect an approach to quantum gravity called asymptotic safety to the Standard Model. Frank Saueressig and Maximilian Becker explain the power and potential of this approach.

The LHC experiments at CERN have been extremely successful in verifying the Standard Model (SM) of particle physics to very high precision. From the theoretical perspective, however, this model has two conceptual shortcomings. One is that the SM appears to be an “effective field theory” that is valid up to a certain energy scale only; the other is that gravity is not part of the model. This raises the question of what a theory comprising particle physics and gravity that is valid for all energy scales might look like. This directly leads to the domain of quantum gravity.

The typical scale associated with quantum-gravity effects is the Planck scale: 10 15  TeV, or 10 –35  m. This exceeds the scales accessible at the LHC by approximately 14 orders of magnitude, forcing us to ask: what can theorists possibly gain from investigating physics at energies beyond the Planck scale? The answer is simple: the SM includes many free parameters that must be fixed by experimental data. Since the number of these parameters proliferates when higher order interactions are included, one would like to constrain this high-dimensional parameter space.

At low energies, this can be done by implementing bounds derived from demanding unitarity and causality of physical processes. Ideally, one would like to derive similar constraints from consistency at trans-Planckian scales where quantum-gravity effects may play a major role. At first sight, this may seem counterintuitive. It is certainly true that gravity treated as an effective field theory itself does not yield any effect measurable at LHC scales due to its weakness; the additional constraints then arise from requiring that the effective field theories underlying the SM and gravity can be combined and extended into a framework that is valid at all energy scales. Presumably, this will not work for all effective field theories. Taking a “bottom-up” approach (identifying the set of theories for which this extension is possible) may constrain the set of free parameters. Conversely, to be phenomenologically viable, any theory describing trans-Planckian physics must be compatible with existing knowledge at the scales probed by collider experiments. This “top-down” approach may then constrain the potential physics scenarios happening at the quantum-gravity scale – a trajectory that has been followed, for example, by the swampland programme initiated from string theory at all scales.

From the theoretical viewpoint, the SM is formulated in the language of relativistic quantum field theories. On this basis, it is possible that the top-down route becomes more realistic the closer the formulation of trans-Planckian physics sticks to this language. For example, string theory is a promising candidate for a consistent description of trans-Planckian physics. However, connecting the theory to the SM has proven to be very difficult, mainly due to the strong symmetry requirements underlying the formulation. In this regard, the “asymptotic safety” approach towards quantum gravity may offer a more tractable option for implementing the top-down idea since it uses the language of relativistic quantum field theory.

Asymptotic safety

What is the asymptotic-safety scenario, and how does it link quantum gravity to particle physics? Starting from the gravity side, we have a successful classical theory: Einstein’s general relativity. If one tries to upgrade this to a quantum theory, things go wrong very quickly. In the early 1970s, it was shown by Gerard ’t Hooft and Martinus Veltman that applying the perturbative quantisation techniques that have proved highly successful for particle-physics theories fail for general relativity. In short, it introduces an infinite number of parameters (one for each allowed local interaction) and thus requires an infinite number of independent measurements to determine what the values of those parameters are. Although this path leads us to a quantum theory of gravity valid at all scales, the construction lacks predictive power. Still, it results in a perfectly predictive effective field theory describing gravity up to the Planck scale.

This may seem discouraging when attempting to formulate a quantum field theory of gravity without introducing new symmetry principles, for example supersymmetry, to remove additional free parameters. A loophole is provided by Kenneth Wilson’s modern understanding of renormalisation. Here, the basic idea is to organise quantum fluctuations according to their momentum and integrate-out these fluctuations, starting from the most energetic ones and proceeding towards lower energy modes. This creates what is called the Wilsonian renormalisation-group “flow” of a theory. Healthy high-energy completions are provided by renormalisation-group fixed points. At these special points the theory becomes scale-invariant, which ensures the absence of divergences. The fixed point also provides predictive power via the condition that the renormalisation-group flow hits the fixed point at high energies (see “Safety belt” figure). For asymptotically-free theories, where all interactions switch off at high energies, the underlying renormalisation-group fixed point is the free theory. This can be seen in the example of quantum chromodynamics (QCD): if the QCD gauge coupling diminishes when going to higher and higher energies, it approaches a fixed point at arbitrary high energies that is non-interacting. One can also envision high-energy completions based on a renormalisation-group fixed point with non-vanishing interactions, which is commonly referred to as asymptotic safety.

Forces of nature

In the context of gravity, the asymptotic-safety scenario was first proposed by Steven Weinberg in the late 1970s. Starting with the seminal work by Martin Reuter (University of Mainz) in 1998, the existence of a renormalisation-group fixed point suitable for rendering gravity asymptotically safe – the so-called Reuter fixed point – is supported by a wealth of first-principle computations. While similar constructions are well known in condensed-matter physics, the Reuter fixed point is distinguished by the fact that it may provide a unified description of all forces of nature. As such, it may have profound consequences for our understanding of the physics inside a black hole, give predictions for parameters of the SM such as the Higgs-boson mass, or disfavour certain types of physics beyond the SM.

The asymptotic-safety approach towards quantum gravity may offer a more tractable option for implementing the top-down idea

The predictive power of the fixed point arises as follows. Only a finite set of parameters exist that describe consistent quantum field theories emanating from the fixed point. One then starts to systematically integrate-out quantum fluctuations (from high to low energy), resulting in a family of effective descriptions in which the quantum fluctuations are taken into account. In practice, this process is implemented by the running of the theory’s couplings, generating what are known as renormalisation-group trajectories. To be phenomenologically viable, the endpoint of the renormalisation group trajectory must be compatible with observations. In the end, only one (or potentially none) of the trajectories emanating from the fixed point will provide a description of nature (see “Going with the flow” image). According to the asymptotic-safety principle, this trajectory must be identified by fixing the free parameters left by the fixed point based on experiments. Once this process is completed, the construction fixes all couplings in the effective field theory in terms of a few free parameters. Since this entails an infinite number of relations that can be probed experimentally, the construction is falsifiable.

Particle physics link

The link to particle physics follows from the observation that the asymptotic-safety construction remains operative once gravity is supplemented by the matter fields of the SM. Non-abelian gauge groups – such as those underlying the electroweak and strong forces, Yukawa interactions and fermion masses – are readily accommodated. A wide range of proof-of-concepts show that this is feasible, gradually bringing the ultimate computation involving the full SM into reach. The fact that gravity remains interacting at the smallest length scales too implies that the construction will feature non-minimal couplings between matter and the gravitational field as well as matter self-interactions of a very specific type. The asymptotic-safety mechanism may then provide the foundation for a realistic quantum field theory unifying all fundamental forces of nature.

Can particle physics tell us whether this specific idea about quantum gravity is on the right track? After all there still exists the vast hierarchy between the energy scales probed by collider experiments and the Planck scale. Surprisingly, the answer is positive! Conceptually, the interacting renormalisation-group fixed point for the gravity–matter theory again gives a set of viable quantum field theories in terms of a fixed number of free parameters. First estimates conducted by Jan Pawlowski and coworkers at Heidelberg University suggest that this number is comparable to the number of free parameters in the SM.

In practice, one may then be tempted to make the following connection. Currently, observables probed by collider physics are derived from the SM effective field theory. Hence, they depend on the couplings of the effective field theory. The asymptotic-safety mechanism expresses these couplings in terms of the free parameters associated with the interacting fixed point. Once the SM effective field theory is extended to include operators of sufficiently high mass dimension, the asymptotic-safety dictum predicts highly non-trivial relations between the couplings parameterising the effective field theory. These relations can be confronted with observations that test whether the observables measured experimentally are subject to these constraints. This can either be provided by matching to existing particle-physics data obtained at the LHC, or by astrophysical observations probing the strong-gravity regime. The theoretical programme of deriving such relations is currently under development. A feasible benchmark, showing that the underlying physics postulates are on the right track, would then be to “post-dict” the experimental results already available. Showing that a theory formulated at the Planck scale is compatible with the SM effective field theory would be a highly non-trivial achievement in itself.

Showing that a theory formulated at the Planck scale is compatible with the SM effective field theory would be a highly non-trivial achievement in itself

This line of testing quantum gravity experimentally may be seen as orthogonal to more gravity-focused tests that attempt to decipher the quantum nature of gravity. Recent ideas in these directions have evolved around developing tabletop experiments that probe the quantum superposition of macroscopic objects at sub-millimetre scales, which could ultimately be developed into a quantum-Cavendish experiment that probes the gravitational field of source masses in spatial quantum superposition states. The emission of a graviton could then lead to decoherence effects which give hints that gravity indeed has a force carrier similar to the other fundamental forces. Of course, one could also hope that experiments probing gravity in the strong-gravity regime find deviations from general relativity. So far, this has not been the case. This is why particle physics may be a prominent and fruitful arena in which to also test quantum-gravity theories such as asymptotic safety in the future.

For decades, quantum-gravity research has been disconnected from directly relevant experimental data. As a result, the field has developed a vast variety of approaches that aim to understand the laws of physics at the Planck scale. These include canonical quantisation, string theory, the AdS/CFT correspondence, loop quantum gravity and spin foams, causal dynamical triangulations, causal set theory, group field theory and asymptotic safety. The latter has recently brought a new perspective on the field: supplementing the quantum-gravity sector of the theory by the matter degrees of freedom of the SM opens an exciting window through which to confront the construction with existing particle-physics data. As a result, this leads to new avenues of research at the intersection between particle physics and gravity, marking the onset of a new era in quantum-gravity research in which the field travels from a purely theoretical to an observationally guided endeavour.

Further reading

M Reuter and F Saueressig 2019 Quantum Gravity and the Functional Renormalization Group: The Road towards Asymptotic Safety (Cambridge University Press). F Saueressig 2023 In Handbook of Quantum Gravity (eds C Bambi, L Modesto and I L Shapiro; Springer) arXiv:232.14152. A Eichhorn and M Schiffer 2023 In Handbook of Quantum Gravity (eds C Bambi, L Modesto and I L Shapiro; Springer) arXiv:2212.07456. Á Pastor-Gutiérrez et al. 2023 SciPost Phys. 15 105; arXiv:2207.09817.

Frank Saueressig and Maximilian Becker Radboud University Nijmegen.

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Powering the quantum revolution: Quantum engines on the horizon

Quantum mechanics is a branch of physics that explores the properties and interactions of iparticles at very small scale, such as atoms and molecules. This has led to the development of new technologies that are more powerful and efficient compared to their conventional counterparts, causing breakthroughs in areas such as computing, communication, and energy.

At the Okinawa Institute of Science and Technology (OIST), researchers at the Quantum Systems Unit have collaborated with scientists from the University of Kaiserslautern-Landau and the University of Stuttgart to design and build an engine that is based on the special rules that particles obey at very small scales.

They have developed an engine that uses the principles of quantum mechanics to create power, instead of the usual way of burning fuel. The paper describing these results is co-authored by OIST researchers Keerthy Menon, Dr. Eloisa Cuestas, Dr. Thomas Fogarty and Prof. Thomas Busch and has been published in the journal Nature.

In a classical car engine, usually a mixture of fuel and air is ignited inside a chamber. The resulting explosion heats the gas in the chamber, which in turn pushes a piston in and out, producing work that turns the wheels of the car.

In their quantum engine the scientists have replaced the use of heat with a change in the quantum nature of the particles in the gas. To understand how this change can power the engine, we need to know that all particles in nature can be classified as either bosons or fermions, based on their special quantum characteristics.

At very low temperatures, where quantum effects become important, bosons have a lower energy state than fermions, and this energy difference can be used to power an engine. Instead of heating and cooling a gas cyclically like a classical engine does, the quantum engine works by changing bosons into fermions and back again.

"To turn fermions into bosons, you can take two fermions and combine them into a molecule. This new molecule is a boson. Breaking it up allows us to retrieve the fermions again. By doing this cyclically, we can power the engine without using heat," Prof. Thomas Busch, leader of the Quantum Systems Unit explained.

While this type of engine only works in the quantum regime, the team found that its efficiency is quite high and can reach up to 25% with the present experimental set up built by the collaborators in Germany.

This new engine is an exciting development in the field of quantum mechanics and has the potential to lead to further advances in the burgeoning area of quantum technologies. But does this mean we will soon see quantum mechanics powering the engines of our cars? "While these systems can be highly efficient, we have only done a proof-of-concept together with our experimental collaborators," explained Keerthy Menon. "There are still many challenges in building a useful quantum engine."

Heat can destroy the quantum effects if the temperature gets too high, so researchers must keep their system as cold as possible. However, this requires a substantial amount of energy to run the experiment at these low temperatures in order to protect the sensitive quantum state.

The next steps in the research will involve addressing fundamental theoretical questions about the system's operation, optimizing its performance, and investigating its potential applicability to other commonly used devices, such as batteries and sensors.

• Quantum Physics
• Quantum Computing
• Spintronics
• Quantum Computers
• Computers and Internet
• Spintronics Research
• Quantum number
• Quantum entanglement
• Introduction to quantum mechanics
• Quantum tunnelling
• Quantum dot
• Linus Pauling
• Bose-Einstein condensate

Story Source:

Materials provided by Okinawa Institute of Science and Technology (OIST) Graduate University . Note: Content may be edited for style and length.

Journal Reference :

• Jennifer Koch, Keerthy Menon, Eloisa Cuestas, Sian Barbosa, Eric Lutz, Thomás Fogarty, Thomas Busch, Artur Widera. A quantum engine in the BEC–BCS crossover . Nature , 2023; 621 (7980): 723 DOI: 10.1038/s41586-023-06469-8

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