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Topological excitons

Nature Physics - Thu, 23/12/2021 - 00:00

Nature Physics, Published online: 23 December 2021; doi:10.1038/s41567-021-01466-y

A condensate of excitons was theoretically conjectured in the 1960s but has been challenging to pinpoint experimentally. Evidence has now emerged that it could be the ground state of tungsten ditelluride, a rich topological material.

Degree-preserving network growth

Nature Physics - Thu, 23/12/2021 - 00:00

Nature Physics, Published online: 23 December 2021; doi:10.1038/s41567-021-01417-7

Network models rarely fix the number of connections of each node during evolution, despite this being needed in real-world applications. Addressing this need, a new approach can grow scale-free networks without preferential attachment.

Evidence for a monolayer excitonic insulator

Nature Physics - Thu, 23/12/2021 - 00:00

Nature Physics, Published online: 23 December 2021; doi:10.1038/s41567-021-01422-w

Insulating states that are formed because of pairing between electrons and holes are known to exist in engineered bilayer structures in high magnetic fields. Now evidence suggests they can occur in a monolayer crystal at zero field.

Evidence for equilibrium exciton condensation in monolayer WTe<sub>2</sub>

Nature Physics - Thu, 23/12/2021 - 00:00

Nature Physics, Published online: 23 December 2021; doi:10.1038/s41567-021-01427-5

Exciton condensation has been observed in various three-dimensional (3D) materials. Now, monolayer WTe2—a 2D topological insulator—also shows the phenomenon. Strong electronic interactions allow the excitons to form and condense at high temperature.

Riemannian geometry of resonant optical responses

Nature Physics - Thu, 23/12/2021 - 00:00

Nature Physics, Published online: 23 December 2021; doi:10.1038/s41567-021-01465-z

The modern understanding of quantum transport relies on geometric concepts such as the Berry phase. The geometric approach has now been extended to the theory of optical transitions.

Probing quantum information propagation with out-of-time-ordered correlators

Nature Physics - Thu, 23/12/2021 - 00:00

Nature Physics, Published online: 23 December 2021; doi:10.1038/s41567-021-01430-w

The complexity of many-body quantum states makes their evolution difficult to simulate with classical computers. Experiments on a 2D nine-qubit device demonstrate that the key properties of quantum lattices can be accessed by measuring out-of-time-ordered correlators.

Polar state reversal in active fluids

Nature Physics - Thu, 23/12/2021 - 00:00

Nature Physics, Published online: 23 December 2021; doi:10.1038/s41567-021-01442-6

Active matter exhibits a plethora of collective phenomena in both biological and artificial systems. In a model system of colloidal rollers, polar states in active liquids can be controlled.

OK Computer

Nature Physics - Mon, 20/12/2021 - 00:00

Nature Physics, Published online: 20 December 2021; doi:10.1038/s41567-021-01436-4

Promising machine learning techniques can deduce the properties of merging black holes from gravitational wave signals a million times faster than current state-of-the-art methods.

A secret source

Nature Physics - Mon, 20/12/2021 - 00:00

Nature Physics, Published online: 20 December 2021; doi:10.1038/s41567-021-01459-x

Superconducting devices ubiquitously have an excess of broken Cooper pairs, which can hamper their performance. It is widely believed that external radiation is responsible but a study now suggests there must be an additional, unknown source.

Bulk and edge properties of twisted double bilayer graphene

Nature Physics - Mon, 20/12/2021 - 00:00

Nature Physics, Published online: 20 December 2021; doi:10.1038/s41567-021-01419-5

Twisted double bilayer graphene is predicted to be a topological insulator under certain conditions. Simultaneous bulk and edge measurements now show metallic transport with a bulk bandgap, suggestive of this prediction.

Enhancement of superexchange due to synergetic breathing and hopping in corner-sharing cuprates

Nature Physics - Mon, 20/12/2021 - 00:00

Nature Physics, Published online: 20 December 2021; doi:10.1038/s41567-021-01439-1

Cuprates exhibit exotic states because of the interplay between spin, charge and orbital degrees of freedom. Ab initio calculations now show that a mechanism called orbital expansion plays a key role in the magnetic properties of cuprates.

Nonlinear interferometry beyond classical limit enabled by cyclic dynamics

Nature Physics - Mon, 20/12/2021 - 00:00

Nature Physics, Published online: 20 December 2021; doi:10.1038/s41567-021-01441-7

Nonlinear interferometry based on time reversal enables entanglement-enhanced measurements without the need for low-noise detection. An alternative approach now exploits cyclic dynamics and shows performance beyond the standard quantum limit.

Bayesian parameter estimation using conditional variational autoencoders for gravitational-wave astronomy

Nature Physics - Mon, 20/12/2021 - 00:00

Nature Physics, Published online: 20 December 2021; doi:10.1038/s41567-021-01425-7

A method for estimating the source properties of gravitational-wave events shows a speed-up of six orders of magnitude over established approaches. This is a promising tool for follow-up observations of electromagnetic counterparts.

Measuring the capabilities of quantum computers

Nature Physics - Mon, 20/12/2021 - 00:00

Nature Physics, Published online: 20 December 2021; doi:10.1038/s41567-021-01409-7

Evaluations of quantum computers across architectures need reliable benchmarks. A class of benchmarks that can directly reflect the structure of any algorithm shows that different quantum computers have considerable variations in performance.

A superconductor free of quasiparticles for seconds

Nature Physics - Mon, 20/12/2021 - 00:00

Nature Physics, Published online: 20 December 2021; doi:10.1038/s41567-021-01433-7

The performance of superconducting devices can be degraded by quasiparticle generation mechanisms that are difficult to identify and eliminate. Now, a small superconducting island can be kept quasiparticle free for seconds at a time.

Making weaves

Nature Physics - Fri, 17/12/2021 - 00:00

Nature Physics, Published online: 17 December 2021; doi:10.1038/s41567-021-01477-9

Acoustic waveguides have been used to implement the long-theorized phenomenon of non-Abelian braiding, in which abstract geometric constructions are used to generate transformations between different modes.

A fast push to photon pairs

Nature Physics - Thu, 16/12/2021 - 00:00

Nature Physics, Published online: 16 December 2021; doi:10.1038/s41567-021-01410-0

Solid-state sources of entangled photons with tailored properties are key elements for integrated quantum computing. Refractive-index perturbations propagating faster than the speed of light may offer a practical approach for generating entangled photon pairs.

An improved recipe for error detection

Nature Physics - Thu, 16/12/2021 - 00:00

Nature Physics, Published online: 16 December 2021; doi:10.1038/s41567-021-01450-6

The reliability of quantum computers depends on the correction of noise-induced errors, which requires additional resources. Experiments on superconducting qubits have now demonstrated the capabilities of a less-demanding scheme for error detection.

Crystals break up with a twist

Nature Physics - Thu, 16/12/2021 - 00:00

Nature Physics, Published online: 16 December 2021; doi:10.1038/s41567-021-01437-3

When crystal defects are present in an ensemble of spinning colloids that induce transverse forces on each other, the defects assemble into grain boundaries that can break the system apart into a set of crystal whorls.

Nonlinear effects get into shape

Nature Physics - Thu, 16/12/2021 - 00:00

Nature Physics, Published online: 16 December 2021; doi:10.1038/s41567-021-01426-6

Nonlinear optical effects are by default weak but they can be enhanced by sculpting the resulting spectrally periodic pulses from a fibre laser into an optimal shape.

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University of Crete - Department of Physics  - Voutes University Campus - GR-71003 Heraklion, Greece
phone: +30 2810 394300 - email: chair@physics.uoc.gr