Showing papers in "Physical Review X in 2019"
TL;DR: In this paper, the authors presented the results from three gravitational-wave searches for coalescing compact binaries with component masses above 1 Ma during the first and second observing runs of the advanced GW detector network.
Abstract: We present the results from three gravitational-wave searches for coalescing compact binaries with component masses above 1 Ma™ during the first and second observing runs of the advanced gravitational-wave detector network. During the first observing run (O1), from September 12, 2015 to January 19, 2016, gravitational waves from three binary black hole mergers were detected. The second observing run (O2), which ran from November 30, 2016 to August 25, 2017, saw the first detection of gravitational waves from a binary neutron star inspiral, in addition to the observation of gravitational waves from a total of seven binary black hole mergers, four of which we report here for the first time: GW170729, GW170809, GW170818, and GW170823. For all significant gravitational-wave events, we provide estimates of the source properties. The detected binary black holes have total masses between 18.6-0.7+3.2 Mâ™ and 84.4-11.1+15.8 Mâ™ and range in distance between 320-110+120 and 2840-1360+1400 Mpc. No neutron star-black hole mergers were detected. In addition to highly significant gravitational-wave events, we also provide a list of marginal event candidates with an estimated false-alarm rate less than 1 per 30 days. From these results over the first two observing runs, which include approximately one gravitational-wave detection per 15 days of data searched, we infer merger rates at the 90% confidence intervals of 110-3840 Gpc-3 y-1 for binary neutron stars and 9.7-101 Gpc-3 y-1 for binary black holes assuming fixed population distributions and determine a neutron star-black hole merger rate 90% upper limit of 610 Gpc-3 y-1.
2,336 citations
TL;DR: In this paper, the authors improved initial estimates of the binary's properties, including component masses, spins, and tidal parameters, using the known source location, improved modeling, and recalibrated Virgo data.
Abstract: On August 17, 2017, the Advanced LIGO and Advanced Virgo gravitational-wave detectors observed a low-mass compact binary inspiral. The initial sky localization of the source of the gravitational-wave signal, GW170817, allowed electromagnetic observatories to identify NGC 4993 as the host galaxy. In this work, we improve initial estimates of the binary's properties, including component masses, spins, and tidal parameters, using the known source location, improved modeling, and recalibrated Virgo data. We extend the range of gravitational-wave frequencies considered down to 23 Hz, compared to 30 Hz in the initial analysis. We also compare results inferred using several signal models, which are more accurate and incorporate additional physical effects as compared to the initial analysis. We improve the localization of the gravitational-wave source to a 90% credible region of 16 deg2. We find tighter constraints on the masses, spins, and tidal parameters, and continue to find no evidence for nonzero component spins. The component masses are inferred to lie between 1.00 and 1.89 M when allowing for large component spins, and to lie between 1.16 and 1.60 M (with a total mass 2.73-0.01+0.04 M) when the spins are restricted to be within the range observed in Galactic binary neutron stars. Using a precessing model and allowing for large component spins, we constrain the dimensionless spins of the components to be less than 0.50 for the primary and 0.61 for the secondary. Under minimal assumptions about the nature of the compact objects, our constraints for the tidal deformability parameter Λ are (0,630) when we allow for large component spins, and 300-230+420 (using a 90% highest posterior density interval) when restricting the magnitude of the component spins, ruling out several equation-of-state models at the 90% credible level. Finally, with LIGO and GEO600 data, we use a Bayesian analysis to place upper limits on the amplitude and spectral energy density of a possible postmerger signal.
715 citations
TL;DR: In this paper, a complete theory of symmetry and topology in non-Hermitian physics is developed, and a classification of topological phases in arbitrary dimensions and symmetry classes is presented.
Abstract: Non-Hermiticity enriches topological phases beyond the existing Hermitian framework. Whereas their unusual features with no Hermitian counterparts were extensively explored, a full understanding about the role of symmetry in non-Hermitian physics has still been elusive, and there remains an urgent need to establish their topological classification in view of rapid theoretical and experimental progress. Here, we develop a complete theory of symmetry and topology in non-Hermitian physics. We demonstrate that non-Hermiticity ramifies the celebrated Altland-Zirnbauer symmetry classification for insulators and superconductors. In particular, charge conjugation is defined in terms of transposition rather than complex conjugation due to the lack of Hermiticity, and hence chiral symmetry becomes distinct from sublattice symmetry. It is also shown that non-Hermiticity enables a Hermitian-conjugate counterpart of the Altland-Zirnbauer symmetry. Taking into account sublattice symmetry or pseudo-Hermiticity as an additional symmetry, the total number of symmetry classes is 38 instead of 10, which describe intrinsic non-Hermitian topological phases as well as non-Hermitian random matrices. Furthermore, due to the complex nature of energy spectra, non-Hermitian systems feature two different types of complex-energy gaps, pointlike and linelike vacant regions. On the basis of these concepts and K-theory, we complete classification of non-Hermitian topological phases in arbitrary dimensions and symmetry classes. Remarkably, non-Hermitian topology depends on the type of complex-energy gaps, and multiple topological structures appear for each symmetry class and each spatial dimension, which are also illustrated in detail with concrete examples. Moreover, the bulk-boundary correspondence in non-Hermitian systems is elucidated within our framework, and symmetries preventing the non-Hermitian skin effect are identified. Our classification not only categorizes recently observed lasing and transport topological phenomena, but also predicts a new type of symmetry-protected topological lasers with lasing helical edge states and dissipative topological superconductors with nonorthogonal Majorana edge states. Furthermore, our theory provides topological classification of Hermitian and non-Hermitian free bosons. Our work establishes a theoretical framework for the fundamental and comprehensive understanding of non-Hermitian topological phases and paves the way toward uncovering unique phenomena and functionalities that emerge from the interplay of non-Hermiticity and topology.
402 citations
TL;DR: The growth of entanglement in a quantum system changes qualitatively when it is observed more frequently than a certain critical rate as discussed by the authors, an important insight for describing quantum systems computationally.
Abstract: The growth of entanglement in a quantum system changes qualitatively when it is observed more frequently than a certain critical rate, an important insight for describing quantum systems computationally.
328 citations
TL;DR: A topological insulator with magnetic elements shows surprising conductive behavior on its surface, presenting either a hurdle to realizing exotic quantum phenomena or a boon to devices with new charge transport mechanisms as mentioned in this paper.
Abstract: A topological insulator with magnetic elements shows surprising conductive behavior on its surface, presenting either a hurdle to realizing exotic quantum phenomena or a boon to devices with new charge transport mechanisms.
285 citations
TL;DR: In this paper, a ten-qubit system based on spins in impure diamond achieves coherence times of over a minute, which is the fastest known coherence time for a ten qubit system.
Abstract: A ten-qubit system based on spins in impure diamond achieves coherence times of over a minute.
272 citations
TL;DR: Simulations of the network using models for digit- and image-classification reveal a "standard quantum limit" for optical neural networks, set by photodetector shot noise, which suggests performance below the thermodynamic limit for digital irreversible computation is theoretically possible in this device.
Abstract: A scheme for implementing optical neural networks offers the energy benefits of optical components while being scalable to large systems, promising low-energy processing with order-of-magnitude improvements in network performance.
242 citations
TL;DR: In this article, the authors combine first-principles calculations and angle-resolved photoemission spectroscopy (ARPES) experiments to reveal that EuSn2As2 is an antiferromagnetic TI with the observation of Dirac SSs consistent with their prediction.
Abstract: In magnetic topological insulators (TIs), the interplay between magnetic order and nontrivial topology can induce fascinating topological quantum phenomena, such as the quantum anomalous Hall effect, chiral Majorana fermions, and axion electrodynamics. Recently, a great deal of attention has been focused on the intrinsic magnetic TIs, where disorder effects can be eliminated to a large extent, which is expected to facilitate the emergence of topological quantum phenomena. Despite intensive efforts, experimental evidence of the topological surface states (SSs) remains elusive. Here, by combining first-principles calculations and angle-resolved photoemission spectroscopy (ARPES) experiments, we reveal that EuSn2As2 is an antiferromagnetic TI with the observation of Dirac SSs consistent with our prediction. We also observe nearly gapless Dirac SSs in antiferromagnetic TIs MnBi2nTe3n+1 (n=1 and 2), which are absent in previous ARPES results. These results provide clear evidence for nontrivial topology of these intrinsic magnetic TIs. Furthermore, we find that the topological SSs show no observable changes across the magnetic transition within the experimental resolution, indicating that the magnetic order has a quite small effect on the topological SSs, which can be attributed to weak hybridization between the localized magnetic moments, from either 4f or 3d orbitals, and the topological electronic states. This finding provides insights for further research that the correlations between magnetism and topological states need to be strengthened to induce larger gaps in the topological SSs, which will facilitate the realization of topological quantum phenomena at higher temperatures.
215 citations
TL;DR: In this paper, a new theory reveals the topological origin of the mismatch between the number of left and right-handed Dirac quasiparticles in twisted bilayer graphene, which is a step toward identifying new topological phases of matter.
Abstract: A new theory reveals the topological origin of the mismatch between the number of left- and right-handed Dirac quasiparticles in twisted bilayer graphene, which is a step toward identifying new topological phases of matter.
201 citations
TL;DR: In this article, the onset of self-organized supersolid behavior in droplets of a quantum dipolar gas, a phase of matter where the gas simultaneously forms a superfluid and a spatially ordered state, was studied.
Abstract: Experiments show the onset of self-organized supersolid behavior in droplets of a quantum dipolar gas, a phase of matter where the gas simultaneously forms a superfluid and a spatially ordered state.
198 citations
TL;DR: In this paper, a high-resolution angle-resolved photoemission spectroscopy study was carried out on the intrinsic magnetic topological insulator MnBi2Te4 and the results showed that the topological surface states are mediated by multidomains of different magnetization orientations.
Abstract: The intrinsic magnetic topological insulator MnBi2Te4 exhibits rich topological effects such as quantum anomalous Hall effect and axion electrodynamics. Here, by combining the use of synchrotron and laser light sources, we carry out comprehensive and high-resolution angle-resolved photoemission spectroscopy studies on MnBi2Te4 and clearly identify its topological electronic structure. In contrast to theoretical predictions and previous studies, we observe topological surface states with diminished gap forming a characteristic Dirac cone. We argue that the topological surface states are mediated by multidomains of different magnetization orientations. In addition, the temperature evolution of the energy bands clearly reveals their interplay with the magnetic phase transition by showing interesting differences between the bulk and surface states, respectively. The investigation of the detailed electronic structure of MnBi2Te4 and its temperature evolution provides important insight into not only the exotic properties of MnBi2Te4, but also the generic understanding of the interplay between magnetism and topological electronic structure in magnetic topological quantum materials.
TL;DR: In this article, a universal recovery channel is proposed to recover information from a damaged code by restricting access to only a portion of the boundary, which can be interpreted as a non-commutative version of Bayes's rule.
Abstract: In the context of quantum theories of spacetime, one overarching question is how quantum information in the bulk spacetime is encoded holographically in boundary degrees of freedom. It is particularly interesting to understand the correspondence between bulk subregions and boundary subregions in order to address the emergence of locality in the bulk quantum spacetime. For the AdS/CFT correspondence, it is known that this bulk information is encoded redundantly on the boundary in the form of an error-correcting code. Having access only to a subregion of the boundary is as if part of the holographic code has been damaged by noise and rendered inaccessible. In quantum-information science, the problem of recovering information from a damaged code is addressed by the theory of universal recovery channels. We apply and extend this theory to address the problem of relating bulk and boundary subregions in AdS/CFT, focusing on a conjecture known as entanglement wedge reconstruction. Existing work relies on the exact equivalence between bulk and boundary relative entropies, but these are only approximately equal in bulk effective field theory, and in similar situations it is known that predictions from exact entropic equalities can be qualitatively incorrect. We show that the framework of universal recovery channels provides a robust demonstration of the entanglement wedge reconstruction conjecture as well as new physical insights. Most notably, we find that a bulk operator acting in a given boundary region’s entanglement wedge can be expressed as the response of the boundary region’s modular Hamiltonian to a perturbation of the bulk state in the direction of the bulk operator. This formula can be interpreted as a noncommutative version of Bayes’s rule that attempts to undo the noise induced by restricting to only a portion of the boundary. To reach these conclusions, we extend the theory of universal recovery channels to finite-dimensional operator algebras and demonstrate that recovery channels approximately preserve the multiplicative structure of the operator algebra.
TL;DR: In this article, a new protocol for distributing keys in a quantum network overcomes theoretical bounds for key transmission rates, potentially enabling the implementation of secure communication in large networks in large quantum networks.
Abstract: A new protocol for distributing keys in a quantum network overcomes theoretical bounds for key transmission rates, potentially enabling implementation of secure communication in large networks.
TL;DR: The supersolidity phase of matter achieved long-lived hallmarks of supersolidities via two different techniques, setting the stage for future investigations into the phase's behavior.
Abstract: Experiments achieve long-lived hallmarks of supersolidity---an exotic phase of matter where superfluidity and crystalline order coexist---via two different techniques, setting the stage for future investigations into the phase's behavior.
TL;DR: In this paper, a complete classification of the bulk-boundary correspondence for topological crystalline phases relates the bulk material properties to the dimensionality and conductance of topologically protected boundary states.
Abstract: A new complete classification of the bulk-boundary correspondence for topological crystalline phases relates the bulk material properties to the dimensionality and conductance of topologically protected boundary states.
TL;DR: In this article, the nitrogen-vacancy (NV) center in diamond exhibits spin-dependent fluorescence and long spin coherence times under ambient conditions, enabling applications in quantum information processing and sensing.
Abstract: The nitrogen-vacancy (NV) center in diamond exhibits spin-dependent fluorescence and long spin coherence times under ambient conditions, enabling applications in quantum information processing and sensing. NV centers near the surface can have strong interactions with external materials and spins, enabling new forms of nanoscale spectroscopy. However, NV spin coherence degrades within 100 nm of the surface, suggesting that diamond surfaces are plagued with ubiquitous defects. Prior work on characterizing near-surface noise has primarily relied on using NV centers themselves as probes; while this has the advantage of exquisite sensitivity, it provides only indirect information about the origin of the noise. Here we demonstrate that surface spectroscopy methods and single-spin measurements can be used as complementary diagnostics to understand sources of noise. We find that surface morphology is crucial for realizing reproducible chemical termination, and use this insight to achieve a highly ordered, oxygen-terminated surface with suppressed noise. We observe NV centers within 10 nm of the surface with coherence times extended by an order of magnitude.
TL;DR: In this article, a mathematical analysis fully quantifies a leading hypothesis for how quantum systems achieve thermal equilibrium despite being fully reversible, and a mathematical model is proposed to show that quantum systems do not reach thermal equilibrium.
Abstract: A mathematical analysis fully quantifies a leading hypothesis for how quantum systems achieve thermal equilibrium despite being fully reversible.
TL;DR: Gromov et al. as mentioned in this paper presented an effective field theory approach to the fracton phases based on the notion of a multipole algebra, which is an extension of space-time symmetries of a charge-conserving matter.
Abstract: Author(s): Gromov, A | Abstract: We present an effective field theory approach to the fracton phases. The approach is based on the notion of a multipole algebra. It is an extension of space(time) symmetries of a charge-conserving matter that includes global symmetries responsible for the conservation of various components of the multipole moments of the charge density. We explain how to construct field theories invariant under the action of the algebra. These field theories generally break rotational invariance and exhibit anisotropic scaling. We further explain how to partially gauge the multipole algebra. Such gauging makes the symmetries responsible for the conservation of multipole moments local, while keeping rotation and translations symmetries global. It is shown that upon such gauging one finds the symmetric tensor gauge theories, as well as the generalized gauge theories discussed recently in the literature. We refer to all such theories as multipole gauge theories. The outcome of the gauging procedure depends on the choice of the multipole algebra. In particular, we show how to construct an effective theory for the U(1) version of the Haah code based on the principles of symmetry and provide a two-dimensional example with operators supported on a Sierpinski triangle. We show that upon condensation of charged excitations, fracton phases of both types as well as various Symmetry-protected topological phases emerge. Finally, the relation between the present approach and the formalism based on polynomials over finite fields is discussed.
TL;DR: In this paper, the authors considered the self-dual, periodically driven, quantum spin chains and derived the time evolution of entropies of finite blocks of spins in the thermodynamic limit.
Abstract: The spreading of entanglement in out-of-equilibrium quantum systems is currently at the center of intense interdisciplinary research efforts involving communities with interests ranging from holography to quantum information. Here we provide a constructive and mathematically rigorous method to compute the entanglement dynamics in a class of “maximally chaotic,” periodically driven, quantum spin chains. Specifically, we consider the so-called “self-dual” kicked Ising chains initialized in a class of separable states and devise a method to compute exactly the time evolution of the entanglement entropies of finite blocks of spins in the thermodynamic limit. Remarkably, these exact results are obtained despite the maximally chaotic models considered: Their spectral correlations are described by the circular orthogonal ensemble of random matrices on all scales. Our results saturate the so-called “minimal cut” bound and are in agreement with those found in the contexts of random unitary circuits with infinite-dimensional local Hilbert space and conformal field theory. In particular, they agree with the expectations from both the quasiparticle picture, which accounts for the entanglement spreading in integrable models, and the minimal membrane picture, recently proposed to describe the entanglement growth in generic systems. Based on a novel “duality-based” numerical method, we argue that our results describe the entanglement spreading from any product state at the leading order in time when the model is nonintegrable.
TL;DR: This work demonstrates an increased resistance to noise by identifying two pathways to exploit high-dimensional entangled states and certifies entanglement in the photonic orbital-angular-momentum and energy-time degrees of freedom up to noise conditions corresponding to a noise fraction of 72 % and 92 % respectively.
Abstract: Photons entangled in high dimensions are more resilient to noise, making them ideal for quantum communication applications.
TL;DR: In this article, the experimental work has been supported by the European Research Council (ERC), the Scottish Funding Council, the UK EPSRC and the Swiss National Science Foundation (SNSF).
Abstract: Funding: The experimental work has been supported by the European Research Council (ERC), the Scottish Funding Council, the UK EPSRC and the Swiss National Science Foundation (SNSF). Theoretical work was supported by the ERC grant ERC-319286-QMAC and by the SNSF (NCCR MARVEL).
TL;DR: In this article, the authors consider a Brownian particle which, in addition to being in contact with a thermal bath, is driven by fluctuating forces which stem from active processes in the system, such as self-propulsion o...
Abstract: We consider a Brownian particle which, in addition to being in contact with a thermal bath, is driven by fluctuating forces which stem from active processes in the system, such as self-propulsion o ...
TL;DR: In this paper, the authors demonstrate that 2D van der Waals magnets could provide a platform for information and computing applications based on magnonics and demonstrate the long-distance magnon transport.
Abstract: Observations of long-distance magnon transport---the propagation of quantized spin waves---demonstrate that 2D van der Waals magnets could provide a platform for information and computing applications based on magnonics.
TL;DR: This work finds that discrimination tasks provide a unified operational description for quantification and manipulation of resources by showing that the family of robustness measures can be understood as the maximum advantage provided by any physical resource in several different discrimination tasks, as well as establishing that such discrimination problems can fully characterize the allowed transformations within the given resource theory.
Abstract: A unifying framework for quantum resources shows that the utility of many physical phenomena in quantum information processing tasks can be described in a common formalism based on state and channel discrimination.
TL;DR: In this article, random quantum circuits with fractonic charges, which exhibit restricted mobility, fail to thermalize after a long time, thus showing a new mechanism for achieving many-body localization.
Abstract: Random quantum circuits with fractonic charges, which exhibit restricted mobility, fail to thermalize after a long time, thus showing a new mechanism for achieving many-body localization.
TL;DR: In this paper, a mathematical analysis showed that multilayer graphene hosts topological flat bands and orbital ferromagnetism, both of which contribute to exotic electrical transport and optical properties.
Abstract: A new mathematical analysis shows that multilayer graphene hosts topological flat bands and orbital ferromagnetism, both of which contribute to exotic electrical transport and optical properties.
TL;DR: In this article, a new theoretical framework was proposed for understanding prethermalization, a common but poorly understood two-step process through which some quantum gases reach thermal equilibrium, and a simple yet general mechanism was provided.
Abstract: A new theoretical framework provides a simple yet general mechanism for understanding prethermalization, a common but poorly understood two-step process through which some quantum gases reach thermal equilibrium.
TL;DR: This work proves that the error threshold of the modified surface code for pure dephasing noise is $50\%$, i.e., that all qubits are fully dephased, and that this threshold can be achieved by a polynomial time decoding algorithm.
Abstract: Quantum error correcting ``surface codes'' can be tailored to the specific noise characteristics of the system, promising substantial gains in future quantum computing implementations.
TL;DR: In this paper, a model for the ringdown of accurate numerical relativity simulations was proposed to estimate the mass and spin of the remnant black hole from binary black hole mergers by comparing the ring down gravitational wave signal to results from studies of perturbed Kerr spacetimes.
Abstract: It is possible to infer the mass and spin of the remnant black hole from binary black hole mergers by comparing the ringdown gravitational wave signal to results from studies of perturbed Kerr spacetimes. Typically, these studies are based on the fundamental quasinormal mode of the dominant l=m=2 harmonic. By modeling the ringdown of accurate numerical relativity simulations, we find, in agreement with previous findings, that the fundamental mode alone is insufficient to recover the true underlying mass and spin, unless the analysis is started very late in the ringdown. Including higher overtones associated with this l=m=2 harmonic resolves this issue and provides an unbiased estimate of the true remnant parameters. Further, including overtones allows for the modeling of the ringdown signal for all times beyond the peak strain amplitude, indicating that the linear quasinormal regime starts much sooner than previously expected. This result implies that the spacetime is well described as a linearly perturbed black hole with a fixed mass and spin as early as the peak. A model for the ringdown beginning at the peak strain amplitude can exploit the higher signal-to-noise ratio in detectors, reducing uncertainties in the extracted remnant quantities. These results should be taken into consideration when testing the no-hair theorem.
TL;DR: A quantum teleportation protocol provides a means of differentiating between quantum scrambling and decoherence, a crucial diagnostic for quantum information systems as mentioned in this paper, which can be used to distinguish between quantum information and quantum information.
Abstract: A quantum teleportation protocol provides a means of differentiating between quantum scrambling and decoherence, a crucial diagnostic for quantum information systems.