Curved spacetime in a quantum simulator

   In the background: the gravitational lens effect, an example of an effect explained by relativity. With quantum particles, analogous effects can be studied.
Image Credit: NASA / TU Wien

New techniques can answer questions that were previously inaccessible experimentally - including questions about the relationship between quantum mechanics and relativity.

The theory of relativity works well when you want to explain cosmic-scale phenomena - such as the gravitational waves created when black holes collide. Quantum theory works well when describing particle-scale phenomena - such as the behavior of individual electrons in an atom. But combining the two in a completely satisfactory way has yet to be achieved. The search for a "quantum theory of gravity" is considered one of the significant unsolved tasks of science.

This is partly because the mathematics in this field is highly complicated. At the same time, it is tough to perform suitable experiments:  One would have to create situations in which phenomena of both the relativity theory play an important role, for example, a spacetime curved by heavy masses, and at the same time, quantum effects become visible, for example the dual particle and wave nature of light.

Ultralow temperature terahertz microscope capabilities enable better quantum technology

Terahertz microscope with cryogenic insert.
Image Credit: Courtesy of Ames National Laboratory

A team of scientists from the Department of Energy’s Ames National Laboratory have developed a way to collect terahertz imaging data on materials under extreme magnetic and cryogenic conditions. They accomplished their work with a new scanning probe microscope. 

This microscope was recently developed at Ames Lab. The team used the ultralow temperature terahertz microscope to take measurements on superconductors and topological semimetals. These materials were exposed to high magnetic fields and temperatures below liquid helium (below 4.2 Kelvins or -452 degrees Fahrenheit).

According to Jigang Wang, a scientist at Ames Lab, professor of Physics and Astronomy at Iowa State University, and the team leader, the team has been improving their terahertz microscope since it was first completed in 2019. “We have improved the resolution in terms of the space, time and energy,” said Wang. “We have also simultaneously improved operation to very low temperatures and high magnetic fields.”

Study reveals new ways for exotic quasiparticles to “relax”

By sandwiching bits of perovskite between two mirrors and stimulating them with laser beams, researchers were able to directly control the spin state of quasiparticles known as exciton-polariton pairs, which are hybrids of light and matter.
Illustration Credit: Courtesy of the researchers
(CC BY-NC-ND 3.0)

New findings from a team of researchers at MIT and elsewhere could help pave the way for new kinds of devices that efficiently bridge the gap between matter and light. These might include computer chips that eliminate inefficiencies inherent in today’s versions, and qubits, the basic building blocks for quantum computers, that could operate at room temperature instead of the ultracold conditions needed by most such devices.

The new work, based on sandwiching tiny flakes of a material called perovskite in between two precisely spaced reflective surfaces, is detailed in the journal Nature Communications, in a paper by MIT recent graduate Madeleine Laitz PhD ’22, postdoc Dane deQuilettes, MIT professors Vladimir Bulovic, Moungi Bawendi and Keith Nelson, and seven others.

By creating these perovskite sandwiches and stimulating them with laser beams, the researchers were able to directly control the momentum of certain “quasiparticles” within the system. Known as exciton-polariton pairs, these quasiparticles are hybrids of light and matter. Being able to control this property could ultimately make it possible to read and write data to devices based on this phenomenon.

With new experimental method, researchers probe spin structure in 2D materials for first time

In the study, researchers describe what they believe to be the first measurement showing direct interaction between electrons spinning in a 2D material and photons coming from microwave radiation.
 Graphic Credit: Jia Li, an assistant professor of physics at Brown.

For two decades, physicists have tried to directly manipulate the spin of electrons in 2D materials like graphene. Doing so could spark key advances in the burgeoning world of 2D electronics, a field where super-fast, small and flexible electronic devices carry out computations based on quantum mechanics.

Standing in the way is that the typical way in which scientists measure the spin of electrons — an essential behavior that gives everything in the physical universe its structure — usually doesn’t work in 2D materials. This makes it incredibly difficult to fully understand the materials and propel forward technological advances based on them. But a team of scientists led by Brown University researchers believe they now have a way around this longstanding challenge. They describe their solution in a new study published in Nature Physics.

In the study, the team — which also include scientists from the Center for Integrated Nanotechnologies at Sandia National Laboratories, and the University of Innsbruck — describe what they believe to be the first measurement showing direct interaction between electrons spinning in a 2D material and photons coming from microwave radiation. Called a coupling, the absorption of microwave photons by electrons establishes a novel experimental technique for directly studying the properties of how electrons spin in these 2D quantum materials — one that could serve as a foundation for developing computational and communicational technologies based on those materials, according to the researchers.

Jellybeans – a sweet solution for overcrowded circuitry in quantum computer chips

Engineers show that a jellybean-shaped quantum dot creates more breathing space in a microchip packed with qubits.

The silicon microchips of future quantum computers will be packed with millions, if not billions of qubits – the basic units of quantum information – to solve the greatest problems facing humanity. And with millions of qubits needing millions of wires in the microchip circuitry, it was always going to get cramped in there.

But now engineers at UNSW Sydney have made an important step towards solving a long-standing problem about giving their qubits more breathing space -- and it all revolves around jellybeans.

Not the kind we rely on for a sugar hit to get us past the 3pm slump. But jellybean quantum dots –elongated areas between qubit pairs that create more space for wiring without interrupting the way the paired qubits interact with each other.

As lead author Associate Professor Arne Laucht explains, the jellybean quantum dot is not a new concept in quantum computing, and has been discussed as a solution to some of the many pathways towards building the world’s first working quantum computer.

Entangled quantum circuits

Par­tial sec­tion of the 30-​meter-long quantum con­nec­tion between two su­per­con­duct­ing cir­cuits. The va­cuum tube (center) con­tains a mi­crowave wave­guide that is cooled to around –273°C and con­nects the two quantum cir­cuits.
Pho­to Credit: ETH Zurich / Daniel Wink­ler

A group of researchers led by Andreas Wallraff, Professor of Solid State Physics at ETH Zurich, has performed a loophole-free Bell test to disprove the concept of “local causality” formulated by Albert Einstein in response to quantum mechanics. By showing that quantum mechanical objects that are far apart can be much more strongly correlated with each other than is possible in conventional systems, the researchers have provided further confirmation for quantum mechanics. What’s special about this experiment is that the researchers were able for the first time to perform it using superconducting circuits, which are considered to be promising candidates for building powerful quantum computers.

Quantum Entanglement of Photons Doubles Microscope Resolution

Using a "spooky" phenomenon of quantum physics, Caltech researchers have discovered a way to double the resolution of light microscopes.
Photo Credit: Lance Hayashida/Caltech

In a paper appearing in the journal Nature Communications, a team led by Lihong Wang, Bren Professor of Medical Engineering and Electrical Engineering, shows the achievement of a leap forward in microscopy through what is known as quantum entanglement. Quantum entanglement is a phenomenon in which two particles are linked such that the state of one particle is tied to the state of the other particle regardless of whether the particles are anywhere near each other. Albert Einstein famously referred to quantum entanglement as "spooky action at a distance" because it could not be explained by his relativity theory.

According to quantum theory, any type of particle can be entangled. In the case of Wang's new microscopy technique, dubbed quantum microscopy by coincidence (QMC), the entangled particles are photons. Collectively, two entangled photons are known as a biphoton, and, importantly for Wang's microscopy, they behave in some ways as a single particle that has double the momentum of a single photon.

Since quantum mechanics says that all particles are also waves, and that the wavelength of a wave is inversely related to the momentum of the particle, particles with larger momenta have smaller wavelengths. So, because a biphoton has double the momentum of a photon, its wavelength is half that of the individual photons.

Beyond Moore’s Law: Innovations in solid-state physics include ultra-thin ‘two-dimensional’ materials and more

From left to right: Kaustav Banerjee and Arnab Pal
Photo Credit: Lilli McKinney

In the ceaseless pursuit of energy-efficient computing, new devices designed at UC Santa Barbara show promise for enhancements in information processing and data storage.

Researchers in the lab of Kaustav Banerjee, a professor of electrical and computer engineering, have published a new paper describing several of these devices, “Quantum-engineered devices based on 2D materials for next-generation information processing and storage,” in the journal Advanced Materials. Arnab Pal, who recently received his doctorate, is the lead author.

Each device is intended to address challenges associated with conventional computing in a new way. All four operate at very low voltages and are characterized as being low leakage, as opposed to the conventional metal-oxide semiconductor field-effect transistors (MOSFETs) found in smartphones that drain power even when turned off. But because they are based on processing steps similar to those used to make MOSFETs, the new devices could be produced at scale using existing industry-standard manufacturing processes for semiconductors.

The most promising of the two information-processing devices, according to Banerjee, is the spin-based field-effect transistor, or spin-FET, which takes advantage of the magnetic moment — or spin — of the electrons that power the device. In this case, the materials belong to the transition metal dichalcogenide group of compounds, which are based on transition metals. 

Paradoxical quantum phenomenon measured for the first time

Photo Credit: © Thomas Schweigler, TU Wien

How do quantum particles share information? A peculiar conjecture about quantum information has been experimentally confirmed at the TU Wien.

Some things are related, others are not. Suppose you randomly select a person from a crowd who is significantly taller than the average. In that case, there is a good chance that they will also weigh more than the average. Statistically, one quantity also contains some information about the other.

Quantum physics allows for even stronger links between different quantities: different particles or parts of an extensive quantum system can "share" a certain amount of information. There are curious theoretical predictions about this: surprisingly, the measure of this "mutual information" does not depend on the size of the system but only on its surface. This surprising result has been confirmed experimentally at the TU Wien and published in "Nature Physics". Theoretical input to the experiment and its interpretation came from the Max-Planck-Institut für Quantenoptik in Garching, FU Berlin, ETH Zürich and New York University.

Scientists Create a Longer-Lasting Exciton that May Open New Possibilities in Quantum Information Science

Alessandra Lanzara at Berkeley Lab.
Photo Credit: Mark Joseph Hanson

In a new study, scientists have observed long-lived excitons in a topological material, opening intriguing new research directions for optoelectronics and quantum computing. 

Excitons are charge-neutral quasiparticles created when light is absorbed by a semiconductor. Consisting of an excited electron coupled to a lower-energy electron vacancy or hole, an exciton is typically short-lived, surviving only until the electron and hole recombine, which limits its usefulness in applications. 

“If we want to make progress in quantum computing and create more sustainable electronics, we need longer exciton lifetimes and new ways of transferring information that don’t rely on the charge of electrons,” said Alessandra Lanzara, who led the study. Lanzara is a senior faculty scientist at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and a UC Berkeley physics professor. “Here we’re leveraging topological material properties to make an exciton that is long lived and very robust to disorder.” 

In a topological insulator, electrons can only move on the surface. By creating an exciton in such a material, the researchers hoped to achieve a state in which an electron trapped on the surface was coupled to a hole that remained confined in the bulk. Such a state would be spatially indirect – extending from the surface into the bulk – and could retain the special spin properties inherent to topological surface states. 

The quantum spin liquid that isn't one

Prof. Andrej Pustogow
Photo Credit: Courtesy of TU Wien

The simplest explanation is often the best - this also applies to fundamental science. Researchers from TU Wien and Toho University recently showed that a supposed quantum spin liquid can be described by more conventional physics.

For two decades, it was believed that a possible quantum spin liquid was discovered in a synthetically produced material. In this case, it would not follow the laws of classical physics even on a macroscopic level, but rather those of the quantum world. There is great hope in these materials: they would be suitable for applications in quantum entangled information transmission (quantum cryptography) or even quantum computation.

Now, however, researchers from TU Wien and Toho University in Japan have shown that the promising material, κ-(BEDT-TTF)2Cu2(CN)3, is not the predicted quantum spin liquid, but a material that can be described using known concepts.

In their recent publication in the journal "Nature Communications", the researchers report how they investigated the mysterious quantum state by measuring the electrical resistance in κ-(BEDT-TTF)2Cu2(CN)3 as a function of temperature and pressure. In 2021, Andrej Pustogow from the Institute of Solid-State Physics at TU Wien has already investigated the magnetic properties of this material, opens an external URL in a new window.

UC Irvine physicists discover first transformable nano-scale electronic devices

The golden parts of the device depicted in the above graphic are transformable, an ability that is “not realizable with the current materials used in industry,” says Ian Sequeira, a Ph.D. student who worked to develop the technology in the laboratory of Javiar Sanchez-Yamahgishi, UCI assistant professor of physics & astronomy.
Image Credit: Yuhui Yang / UCI

The nano-scale electronic parts in devices like smartphones are solid, static objects that once designed and built cannot transform into anything else. But University of California, Irvine physicists have reported the discovery of nano-scale devices that can transform into many different shapes and sizes even though they exist in solid states.

It’s a finding that could fundamentally change the nature of electronic devices, as well as the way scientists research atomic-scale quantum materials. The study is published this week in Science Advances.

“What we discovered is that for a particular set of materials, you can make nano-scale electronic devices that aren’t stuck together,” said Javier Sanchez-Yamagishi, an assistant professor of physics & astronomy whose lab performed the new research. “The parts can move, and so that allows us to modify the size and shape of a device after it’s been made.”

Surprise from the quantum world

The ferromagnetism of the topological isolator manganese-bismuth-telluride only arises when the atomic structure fails. To do this, some manganese atoms (green) must be moved out of their original position (second green atomic plane from above). Only when there are manganese atoms in all levels with bismuth atoms (gray) is the magnetic orientation of the manganese atoms so contagious that ferromagnetism arises.
Illustration Credit: Jörg Bandmann / ct.qmat

The Würzburg-Dresden Cluster of Excellence ct.qmat has designed a ferromagnetic topological isolator - a milestone on the way to energy-efficient quantum technologies.

As early as 2019, an international research team around the material chemist Anna Isaeva - then junior professor at the Würzburg-Dresden Cluster of Excellence ct.qmat - complexity and topology in quantum materials - succeeded in producing the first antiferromagnetic topological isolator manganese-bismuth-tilluride. (Mn2Te4) a little sensation.

This miracle material no longer needs a strong external magnetic field - it brings its own inner magnetic field with it. This offers the opportunity for new types of electronic components that magnetically encode information and transport it on the surface without resistance. This could make information technology more sustainable and energy-saving in the future, for example. Since then, researchers worldwide have been analyzing different facets of this promising quantum material.

Researchers create exotic quantum light states

The graphic symbolizes how photons are coupled after they have been scattered on an artificial atom - a so-called quantum dot - in a cavity resonator.
Illustration Credit: © University of Basel

Coupled light particles could advance both medical imaging and quantum computing.

Light particles, also called photons, do not normally interact with each other. An international research team has now been able to show for the first time that a few photons can be manipulated in a controlled manner and brought into interaction. This opens up new opportunities in the development of quantum technologies. The results are described by a team from the University of Basel, the University of Sydney and the Ruhr University Bochum in the journal Nature Physics, published online on the 20th. March 2023.

Measure distances and transmit information using light

Photons do not interact with each other in a vacuum; they can fly through each other undisturbed. This makes them valuable for data transfer because information can be transported almost trouble-free at the speed of light. Light is helpful not only for data transmission, but also in certain measuring instruments, because it can be used to determine tiny distances, for example in medical imaging. The sensitivity of such measuring instruments depends on the average number of photons in the system.

Sculpting quantum materials for the electronics of the future

Artistic view. Curvature of the space fabric due to the superposition of spin and orbital states at the interface between lanthanum aluminate (LaAlO3) and strontium titanate (SrTiO3).
Illustration Credit: © Xavier Ravinet – UNIGE

An international team led by the UNIGE has developed a quantum material in which the fabric of space inhabited by electrons can be curved on-demand.

The development of new information and communication technologies poses new challenges to scientists and industry. Designing new quantum materials - whose exceptional properties stem from quantum physics - is the most promising way to meet these challenges. An international team led by the University of Geneva (UNIGE) and including researchers from the universities of Salerno, Utrecht and Delft, has designed a material in which the dynamics of electrons can be controlled by curving the fabric of space in which they evolve. These properties are of interest for next-generation electronic devices, including the optoelectronics of the future. These results can be found in the journal Nature Materials.

The telecommunications of the future will require new, extremely powerful electronic devices. These must be capable of processing electromagnetic signals at unprecedented speeds, in the picosecond range, i.e. one thousandth of a billionth of a second. This is unthinkable with current semiconductor materials, such as silicon, which is widely used in the electronic components of our telephones, computers and game consoles. To achieve this, scientists and industry are focusing on the design of new quantum materials.

High-performance detectors to combat spies

Using these sensors, scientists were able to generate a secret key at a rate of 64 megabits per second over 10 km of fibre optic cable.
Photo Credit: © M. Perrenoud - G. Resta / UNIGE

A team from UNIGE and ID Quantique has developed single-photon detectors with unprecedented performance. These results open new perspectives for quantum cryptography.

How can we combat data theft, which is a real issue for society? Quantum physics has the solution. Its theories make it possible to encode information (a qubit) in single particles of light (a photon) and to circulate them in an optical fiber in a highly secure way. However, the widespread use of this telecommunications technology is hampered in particular by the performance of the single-photon detectors. A team from the University of Geneva (UNIGE), together with the company ID Quantique, has succeeded in increasing their speed by a factor of twenty. This innovation, to be discovered in the journal Nature Photonics, makes it possible to achieve unprecedented performances in quantum key distribution.

Buying a train ticket, booking a taxi, getting a meal delivered: these are all transactions carried out daily via mobile applications. These are based on payment systems involving an exchange of secret information between the user and the bank. To do this, the bank generates a public key, which is transmitted to their customer, and a private key, which it keeps secret. With the public key, the user can modify the information, make it unreadable and send it to the bank. With the private key, the bank can decipher it.

Researchers take a step towards turning interactions that normally ruin quantum information into a way of protecting it

Illustration of non-Hermitian topology and open quantum systems.
Illustration Credit: Jose Lado/Aalto University.

A new method for predicting the behavior of quantum devices provides a crucial tool for real-world applications of quantum technology

Researchers have found a way to predict the behavior of many-body quantum systems coupled to their environment. The work represents a way to protect quantum information in quantum devices, which is crucial for real-world applications of quantum technology.

In a study published in Physical Review Letters, researchers at Aalto University in Finland and IAS Tsinghua University in China report a new way to predict how quantum systems, such as groups of particles, behave when they are connected to the external environment. Usually, connecting a system such as a quantum computer to its environment creates decoherence and leaks, which ruin any information about what’s happening inside the system. Now, the researchers have developed a technique which turns that problem into its solution.

The research was carried out by Aalto doctoral researcher Guangze Chen under the supervision of Professor Jose Lado and in collaboration with Fei Song from IAS Tsinghua. Their approach combines techniques from two domains, quantum many-body physics and non-Hermitian quantum physics.

Tubular nanomaterial of carbon makes ideal home for spinning quantum bits

Artistic rendering of chemically modified carbon nanotube hosting a spinning electron as qubit.
Illustration Credit: Argonne National Laboratory

Scientists find that a tubular nanomaterial of carbon makes for ideal host to keep quantum bits spinning in place for use in quantum information technologies.

Scientists are vigorously competing to transform the counterintuitive discoveries about the quantum realm from a century past into technologies of the future. The building block in these technologies is the quantum bit, or qubit. Several different kinds are under development, including ones that use defects within the symmetrical structures of diamond and silicon. They may one day transform computing, accelerate drug discovery, generate unhackable networks and more.

Working with researchers from several universities, scientists at the U.S. Department of Energy’s (DOE) Argonne National Laboratory have discovered a method for introducing spinning electrons as qubits in a host nanomaterial. Their test results revealed record long coherence times — the key property for any practical qubit because it defines the number of quantum operations that can be performed in the lifetime of the qubit.

Breakthrough in Tin-Vacancy Centers for Quantum Network Applications

Tin-vacancy (Sn-V) centers in diamond have the potential to function as quantum nodes in quantum networks to transmit information. However, they pose limitations while showing optical properties to generate quantum entanglement. Tokyo Tech researchers have now overcome this challenge by generating stable Sn-V centers that can produce photons with nearly identical frequencies and linewidths, paving the way for the advancement of Sn-V centers as a quantum-light matter interface.

Quantum entanglement refers to a phenomenon in quantum mechanics in which two or more particles become linked such that the state of each particle cannot be described independently of the others, even when they are separated by a large distance. The principle, referred to by Albert Einstein as "spooky action at a distance", is now utilized in quantum networks to transfer information. The building blocks of these networks—quantum nodes—can generate and measure quantum states.

Among the candidates that can function as quantum nodes, the Sn-V center in diamond (a defect where a tin (Sn) atom replaces a carbon atom, resulting in an interstitial Sn atom between two carbon vacancies) has been shown to have suitable properties for quantum network applications. The Sn-V center is expected to exhibit a long spin coherence time in the millisecond range at Kelvin temperatures, allowing it to maintain its quantum state for a relatively long period of time. However, these centers have yet to produce photons with similar characteristics, which is a necessary criterion for creating remote entangled quantum states between quantum network nodes.

SLAC, Stanford researchers make a new type of quantum material with a dramatic distortion pattern

This illustration shows how an electronic tug-of-war between the layers of a new quantum material has warped its atomic lattice into a dramatic herringbone-like pattern. Scientists at SLAC and Stanford who created the material are just starting to explore how this 'huge' distortion affects the material's properties.   
Illustration Credit: Greg Stewart/SLAC National Accelerator Laboratory

Created by an electronic tug-of-war between the material's atomic layers, this ‘beautiful’ herringbone-like pattern could give rise to unique features that scientists are just starting to explore.

Researchers at the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University have created a new type of quantum material whose atomic scaffolding, or lattice, has been dramatically warped into a herringbone pattern.

The resulting distortions are “huge” compared to those achieved in other materials, said Woo Jin Kim, a postdoctoral researcher at the Stanford Institute for Materials and Energy Sciences (SIMES) at SLAC who led the study. 

“This is a very fundamental result, so it’s hard to make predictions about what may or may not come out of it, but the possibilities are exciting,” said SLAC/Stanford Professor and SIMES Director Harold Hwang. 

“Based on theoretical modeling from members of our team, it looks like the new material has intriguing magnetic, orbital and charge order properties that we plan to investigate further,” he said. Those are some of the very properties that scientists think give quantum materials their surprising characteristics. 

The research team described their work in a paper published in Nature today.