Aurelia Butler

While the number of qubits and the stability of quantum states are still limiting current quantum computing devices, there are questions where these processors are already able to leverage their enormous computing power. In collaboration with the Google Quantum AI team scientists from the Technical University of Munich (TUM) and the University of Nottingham used a quantum processor to simulate the ground state of a so-called toric code Hamiltonian — an archetypical model system in modern condensed matter physics, which was originally proposed in the context of quantum error correction.
What would it be like if we lived in a flat two-dimensional world? Physicists predict that quantum mechanics would be even stranger in that case resulting in exotic particles — so-called “anyons” — that cannot exist in the three-dimensional world we live in. This unfamiliar world is not just a curiosity but may be key to unlocking quantum materials and technologies of the future.
In collaboration with the Google Quantum AI team scientists from the Technical University of Munich and the University of Nottingham used a highly controllable quantum processor to simulate such states of quantum matter. Their results appear in the current issue of the scientific journal Science.
Emergent quantum particles in two-dimensional systems
All particles in our universe come in two flavors, bosons or fermions. In the three-dimensional world we live in, this observation stands firm. However, it was theoretically predicted almost 50 years ago that other types of particles, dubbed anyons, could exist when matter is confined to two dimensions.
While these anyons do not appear as elementary particles in our universe, it turns out that anyonic particles can emerge as collective excitations in so-called topological phases of matter, for which the Nobel prize was awarded in 2016.
“Twisting pairs of these anyons by moving them around one another in the simulation unveils their exotic properties — physicists call it braiding statistics,” says Dr. Adam Smith from the University of Nottingham.
A simple picture for these collective excitations is “the wave” in a stadium crowd — it has a well-defined position, but it cannot exist without the thousands of people that make up the crowd. However, realizing and simulating such topologically ordered states experimentally has proven to be extremely challenging.
Quantum processors as a platform for controlled quantum simulations
In landmark experiments, the teams from TUM, Google Quantum AI, and the University of Nottingham programmed Google’s quantum processor to simulate these two-dimensional states of quantum matter. “Google’s quantum processor named ‘Sycamore’ can be precisely controlled and is a well-isolated quantum system, which are key requirements for performing quantum computations,” says Kevin Satzinger, a scientist from the Google team.
The researchers came up with a quantum algorithm to realize a state with topological order, which was confirmed by simulating the creation of anyon excitations and twisting them around one another. Fingerprints from long-range quantum entanglement could be confirmed in their study. As a possible application, such topologically ordered states can be used to improve quantum computers by realizing new ways of error correction. First steps toward this goal have already been achieved in their work.
“Near term quantum processors will represent an ideal platform to explore the physics of exotic quantum phases matter,” says Prof. Frank Pollmann from TUM. “In the near future, quantum processors promise to solve problems that are beyond the reach of current classical supercomputers.”
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Quantum computing is taking a new leap forward due to research done in collaboration between University of Helsinki, Aalto University, University of Turku, and IBM Research Europe-Zurich. The team of researchers have proposed a scheme to reduce the number of calculations needed to read out data stored in the state of a quantum processor. This, in turn, will make quantum computers more efficient, faster, and ultimately more sustainable.
Quantum computers have the potential to solve important problems that are beyond reach even for the most powerful supercomputers, but they require an entirely new way of programming and creating algorithms.
Universities and major tech companies are spearheading research on how to develop these new algorithms. In a recent collaboration between University of Helsinki, Aalto University, University of Turku, and IBM Research Europe-Zurich, a team of researchers have developed a new method to speed up calculations on quantum computers. The results are published in the journal PRX Quantum of the American Physical Society.
– Unlike classical computers, which use bits to store ones and zeros, information is stored in the qubits of a quantum processor in the form of a quantum state, or a wavefunction, says postdoctoral researcher Guillermo García-Pérez from the Department of Physics at the University of Helsinki, first author of the paper.
Special procedures are thus required to read out data from quantum computers. Quantum algorithms also require a set of inputs, provided for example as real numbers, and a list of operations to be performed on some reference initial state.
– The quantum state used is, in fact, generally impossible to reconstruct on conventional computers, so useful insights must be extracted by performing specific observations (which quantum physicists refer to as measurements) says García-Pérez.
The problem with this is the large number of measurements required for many popular applications of quantum computers (like the so-called Variational Quantum Eigensolver, which can be used to overcome important limitations in the study of chemistry, for instance in drug discovery). The number of calculations required is known to grow very quickly with the size of the system one wants to simulate, even if only partial information is needed. This makes the process hard to scale up, slowing down the computation and consuming a lot of computational resources.
The method proposed by García-Pérez and co-authors uses a generalized class of quantum measurements that are adapted throughout the calculation in order to extract the information stored in the quantum state efficiently. This drastically reduces the number of iterations, and therefore the time and computational cost, needed to obtain high-precision simulations.
The method can reuse previous measurement outcomes and adjust its own settings. Subsequent runs are increasingly accurate, and the collected data can be reused again and again to calculate other properties of the system without additional costs.
– We make the most out of every sample by combining all data produced. At the same time, we fine-tune the measurement to produce highly accurate estimates of the quantity under study, such as the energy of a molecule of interest. Putting these ingredients together, we can decrease the expected runtime by several orders of magnitude, says García-Pérez.
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Light not only plays a key role as an information carrier for optical computer chips, but also in particular for the next generation of quantum computers. Its lossless guidance around sharp corners on tiny chips and the precise control of its interaction with other light are the focus of research worldwide. Scientists at Paderborn University have now demonstrated, for the very first time, the spatial confinement of a light wave to a point smaller than the wavelength in a ‘topological photonic crystal’. These are artificial electromagnetic materials that facilitate robust manipulation of light. The state is protected by special properties and is important for use in quantum chips, for example. The findings have now been published in renowned journal “Science Advances.”
Topological crystals function on the basis of specific structures, the properties of which remain largely unaffected by disturbances and deviations. While in normal photonic crystals the effects needed for light manipulation are fragile and can be affected by defects in the material structure, for example, in topological photonic crystals, they are protected from this. The topological structures allow properties such as unidirectional light propagation and increased robustness for guiding photons, small particles of light — features that are crucial for future light-based technologies.
Photonic crystals influence the propagation of electromagnetic waves with the help of an optical band gap for photons, which blocks the movement of light in certain directions. Scattering usually occurs — some photons are reflected back, while others are reflected away. “With topological light states that span an extended range of photonic crystals, you can prevent this. In normal optical waveguides and fibers, back reflection poses a major problem because it leads to unwanted feedback. Loss during propagation hinders large-scale integration in optical chips, in which photons are responsible for transmitting information. With the help of topological photonic crystals, novel unidirectional waveguides can be achieved that transmit light without any back reflection, even in the presence of arbitrarily large disorder,” explains Professor Thomas Zentgraf, head of the Ultrafast Nanophotonics research group at Paderborn University. The concept, which has its origins in solid-state physics, has already led to numerous applications, including robust light transmission, topological delay lines, topological lasers and quantum interference.
“It was also recently proven that topological photonic crystals based on a weak topology with a crystal dislocation in the periodic structure also exhibit these special properties and also support what are known as topologically-protected strongly spatially localised light states. When something is topologically protected, any changes in the parameters do not affect the protected properties. Localised light states are extremely useful for non-linear amplification, miniaturisation of photonic components and integration of photonic quantum chips,” adds Zentgraf. In this context, weak topological states are special states for the light that result not only from the topological band structure, but also from the formation of the crystal structure.
In a joint experiment, researchers from Paderborn University and RWTH Aachen University used a special near-field optical microscope to demonstrate the existence of such strongly localised light states in topological structures. “We showed that the versatility of weak topology can produce a strongly spatially localised optical field in an intentionally induced structural dislocation,” explains Jinlong Lu, a PhD student in Zentgraf’s group and lead author of the paper. “Our study demonstrates a viable strategy for achieving a topologically-protected, localised zero-dimensional state for light,” adds Zentgraf. With their work, the researchers have proven that near-field microscopy is a valuable tool for characterising topological structures with nanoscale resolution at optical frequencies.
The findings provide a basis for the use of strongly localised optical light states based on weak topology. Phase-change materials with a tunable refractive index could therefore also be used for the nanostructures used in the experiment to produce robust and active topological photonic elements. “We’re now working on concepts to equip the dislocation centres in the crystal structure with special quantum emitters for single photon generation,” says Zentgraf, adding: “These could then be used in future optical quantum computers, for which single photon generation plays an important role.”
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Physicists from Exeter and Trondheim have developed a theory describing how space reflection and time reversal symmetries can be exploited, allowing for greater control of transport and correlations within quantum materials.
Two theoretical physicists, from the University of Exeter (United Kingdom) and the Norwegian University of Science and Technology (in Trondheim, Norway), have built a quantum theory describing a chain of quantum resonators satisfying space reflection and time reversal symmetries. They have shown how the different quantum phases of such chains are associated with remarkable phenomena, which may be useful in the design of future quantum devices relying on strong correlations.
A common distinction in physics is between open and closed systems. Closed systems are isolated from any external environment, such that energy is conserved because there is nowhere for it to escape to. Open systems are connected to the outer world, and via exchanges with the environment they are subject to energy gains and energy losses. There is an important third case. When the energy flowing in and flowing out of the system is finely balanced, an intermediate situation between being open and closed arises. This equilibrium can occur when the system obeys a combined symmetry of space and time, that is when (1) switching left and right and (2) flipping the arrow of time leave the system essentially unchanged.
In their latest research, Downing and Saroka discuss the phases of a quantum chain of resonators satisfying space reflection and time reversal symmetries. There are principally two phases of interest, a trivial phase (accompanied by intuitive physics) and a nontrivial phase (marked with surprising physics). The border between these two phases is marked by an exceptional point. The researchers have found the locations of these exceptional points for a chain with an arbitrary number of resonators, providing insight into the scaling up of quantum systems obeying these symmetries. Importantly, the nontrivial phase allows for unconventional transport effects and strong quantum correlations, which may be used to control the behaviour and propagation of light at nanoscopic length scales.
This theoretical study may be useful for the generation, manipulation and control of light in low-dimensional quantum materials, with a view to building light-based devices exploiting photons, the particles of light, as workhorses down at sizes around one billionth of a meter.
Charles Downing, from the University of Exeter, commented: “Our work on parity-time symmetry in open quantum systems further emphasises how symmetry underpins our understanding of the physical world, and how we may benefit from it.”
Vasil Saroka, from the Norwegian University of Science and Technology, added: “We hope that our theoretical work on parity-time symmetry can inspire further experimental research in this exciting area of physics.”
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A floating, robotic film designed at UC Riverside could be trained to hoover oil spills at sea or remove contaminants from drinking water.
Powered by light and fueled by water, the film could be deployed indefinitely to clean remote areas where recharging by other means would prove difficult.
“Our motivation was to make soft robots sustainable and able to adapt on their own to changes in the environment. If sunlight is used for power, this machine is sustainable, and won’t require additional energy sources,” said UCR chemist Zhiwei Li. “The film is also re-usable.”
Researchers dubbed the film Neusbot after neustons, a category of animals that includes water striders. These insects traverse the surface of lakes and slow-moving streams with a pulsing motion, much like scientists have been able to achieve with the Neusbot, which can move on any body of water.
While other scientists have created films that bend in response to light, they have not been able to generate the adjustable, mechanical oscillation of which Neusbot is capable. This type of motion is key to controlling the robot and getting it to function where and when you want.
Technical details of this achievement are described in a new Science Robotics paper. More

In research published in the journal Cell Systems, Professor Lenore Cowen of the Tufts Department of Computer Science and colleagues from Massachusetts Institute of Technology (MIT) collaborated to design a structurally-motivated deep learning method built from recent advances in neural language modeling. The team’s deep-learning model, called D-SCRIPT, was able to predict protein-protein interactions (PPIs) from primary amino acid sequences.
Those predictions allow researchers to model PPI networks with a clustering method and enable the detection of functional subnetworks, or modules. Scientists study organisms’ PPI networks as a means of understanding their signaling circuitry, which could lead to better prediction of cell behavior and gene functions, while finding functional modules in PPI networks could help researchers reach stronger understandings of cellular functional organization.
Cowen along with researchers Sam Sledzieski, Rohit Singh, and renowned computational biologist Bonnie Berger from MIT’s Computer Science and Artificial Intelligence Lab found that the D-SCRIPT model, trained on more than 38,000 human PPIs, was better able to generalize when compared to the current state-of-the-art approach (the deep-learning method PIPR), and therefore could characterize fly proteins. They also applied D-SCRIPT to screen for PPIs related to cow digestion and identified functional gene modules that related to immune response and metabolism.
The researchers concluded that the D-SCRIPT model trained on human PPI data could be applied to many species of interest — critically, even those that have been rarely studied or that lack PPI data.
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In 1973, physicist Philip W. Anderson theorized the existence of a new state of matter that has been a major focus of the field, especially in the race for quantum computers.
This bizarre state of matter is called a quantum spin liquid and, contrary to the name, has nothing to do with everyday liquids like water. Instead, it’s all about magnets that never freeze and the way electrons in them spin. In regular magnets, when the temperature drops below a certain temperature, the electrons stabilize and form a solid piece of matter with magnetic properties. In quantum spin liquid, the electrons don’t stabilize when cooled, don’t form into a solid, and are constantly changing and fluctuating (like a liquid) in one of the most entangled quantum states ever conceived.
The different properties of quantum spin liquids have promising applications that can be used to advance quantum technologies such as high-temperature superconductors and quantum computers. But the problem about this state of matter has been its very existence. No one had ever seen it — at least, that had been the case for almost 50 years.
Today, a team of Harvard-led physicists said they have finally experimentally documented this long sought-after exotic state of matter. The work is described in a new study in the journal Science and marks a big step toward being able to produce this elusive state on demand and to gain a novel understanding of its mysterious nature.
“It is a very special moment in the field ,” said Mikhail Lukin, the George Vasmer Leverett Professor of Physics, co-director of the Harvard Quantum Initiative (HQI), and one of the senior authors of the study. “You can really touch, poke, and prod at this exotic state and manipulate it to understand its properties. …It’s a new state of matter that people have never been able to observe.”
The learnings from this science research could one day provide advancements for designing better quantum materials and technology. More specifically, the exotic properties from quantum spin liquids could hold the key to creating more robust quantum bits — known as topological qubits — that are expected to be resistant to noise and external interference. More

Detecting light beyond the visible red range of our eyes is hard to do, because infrared light carries so little energy compared to ambient heat at room temperature. This obscures infrared light unless specialised detectors are chilled to very low temperatures, which is both expensive and energy-intensive.
Now researchers led by the University of Cambridge have demonstrated a new concept in detecting infrared light, showing how to convert it into visible light, which is easily detected.
In collaboration with colleagues from the UK, Spain and Belgium, the team used a single layer of molecules to absorb the mid-infrared light inside their vibrating chemical bonds. These shaking molecules can donate their energy to visible light that they encounter, ‘upconverting’ it to emissions closer to the blue end of the spectrum, which can then be detected by modern visible-light cameras.
The results, reported in the journal Science, open up new low-cost ways to sense contaminants, track cancers, check gas mixtures, and remotely sense the outer universe.
The challenge faced by the researchers was to make sure the quaking molecules met the visible light quickly enough. “This meant we had to trap light really tightly around the molecules, by squeezing it into crevices surrounded by gold,” said first author Angelos Xomalis from Cambridge’s Cavendish Laboratory.
The researchers devised a way to sandwich single molecular layers between a mirror and tiny chunks of gold, only possible with ‘meta-materials’ that can twist and squeeze light into volumes a billion times smaller than a human hair.
“Trapping these different colours of light at the same time was hard, but we wanted to find a way that wouldn’t be expensive and could easily produce practical devices,” said co-author Dr Rohit Chikkaraddy from the Cavendish Laboratory, who devised the experiments based on his simulations of light in these building blocks.
“It’s like listening to slow-rippling earthquake waves by colliding them with a violin string to get a high whistle that’s easy to hear, and without breaking the violin,” said Professor Jeremy Baumberg of the NanoPhotonics Centre at Cambridge’s Cavendish Laboratory, who led the research.
The researchers emphasise that while it is early days, there are many ways to optimise the performance of these inexpensive molecular detectors, which then can access rich information in this window of the spectrum.
From astronomical observations of galactic structures to sensing human hormones or early signs of invasive cancers, many technologies can benefit from this new detector advance.
The research was conducted by a team from the University of Cambridge, KU Leuven, University College London (UCL), the Faraday Institution, and Universitat Politècnica de València.
The research is funded as part of a UK Engineering and Physical Sciences Research Council (EPSRC) investment in the Cambridge NanoPhotonics Centre, as well as the European Research Council (ERC), Trinity College Cambridge and KU Leuven.
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