The interplay between non-Hermiticity and disorder plays an important role in condensed matter physics. Here, we report the universal critical behaviors of the Anderson transitions driven by non-Hermitian disorders for a three-dimensional (3D) Anderson model and 3D U(1) model, which belong to 3D cla...

[Phys. Rev. Lett. 126, 090402] Published Fri Mar 05, 2021

]]>Nonlocal games with advantageous quantum strategies give arguably the most fundamental demonstration of the power of quantum resources over their classical counterparts. Recently, certain multiplayer generalizations of nonlocal games have been used to prove unconditional separations between limited ...

[Phys. Rev. Lett. 126, 090505] Published Fri Mar 05, 2021

]]>We present a unified exact tensor network approach to compute the ground state energy, identify the optimal configuration, and count the number of solutions for spin glasses. The method is based on tensor networks with the tropical algebra defined on the semiring of $(\mathbb{R}\cup \{-\infty \},\oplus ,\odot )$. Contracting the tro...

[Phys. Rev. Lett. 126, 090506] Published Fri Mar 05, 2021

]]>In an effort to address integrability breaking in cold gas experiments, we extend the integrable hydrodynamics of the Lieb-Liniger model with two additional components representing the population of atoms in the first and second transverse excited states, thus enabling a description of quasi-1D cond...

[Phys. Rev. Lett. 126, 090602] Published Fri Mar 05, 2021

]]>The efficient and reliable characterization of quantum states plays a vital role in most, if not all, quantum information processing tasks. In this work, we present a universally optimal protocol for verifying entangled states by employing the so-called quantum nondemolition measurements, such that ...

[Phys. Rev. Lett. 126, 090504] Published Thu Mar 04, 2021

]]>A multiqubit topological quantum protocol is implemented using a superconducting quantum simulator to braid non-Abelian anyons.

[Phys. Rev. Lett. 126, 090502] Published Wed Mar 03, 2021

]]>Superconducting qubits are a leading platform for scalable quantum computing and quantum error correction. One feature of this platform is the ability to perform projective measurements orders of magnitude more quickly than qubit decoherence times. Such measurements are enabled by the use of quantum...

[Phys. Rev. Lett. 126, 090503] Published Wed Mar 03, 2021

]]>A cold atomic ensemble suits well for optical quantum memories, and its entanglement with a single photon forms the building block for quantum networks that give promise for many revolutionary applications. Efficiency and lifetime are among the most important figures of merit for a memory. In this L...

[Phys. Rev. Lett. 126, 090501] Published Tue Mar 02, 2021

]]>In recent experiments, the light-matter interaction has reached the ultrastrong coupling limit, which can give rise to dynamical generalizations of spatial symmetries in periodically driven systems. Here, we present a unified framework of dynamical-symmetry-protected selection rules based on Floquet...

[Phys. Rev. Lett. 126, 090601] Published Tue Mar 02, 2021

]]>There exist real quantum states which can be perfectly distinguished via local operations and classical communication, but which cannot be distinguished with any nonzero probability if one of the parties has no access to imaginarity.

[Phys. Rev. Lett. 126, 090401] Published Mon Mar 01, 2021

]]>In a new version of Maxwell’s demon, the tiny being plays the role of a gambler who knows when to quit.

[Phys. Rev. Lett. 126, 080603] Published Fri Feb 26, 2021

]]>We characterize metrologically useful multipartite entanglement by representing partitions with Young diagrams. We derive entanglement witnesses that are sensitive to the shape of Young diagrams and show that Dyson’s rank acts as a resource for quantum metrology. Common quantifiers, such as the enta...

[Phys. Rev. Lett. 126, 080502] Published Thu Feb 25, 2021

]]>The energy dissipation rate in a nonequilibrium reaction system can be determined by the reaction rates in the underlying reaction network. By developing a coarse-graining process in state space and a corresponding renormalization procedure for reaction rates, we find that energy dissipation rate ha...

[Phys. Rev. Lett. 126, 080601] Published Tue Feb 23, 2021

]]>The transition between ergodic and many-body localization (MBL) phases lies at the heart of understanding quantum thermalization of many-body systems. Here, we predict a many-body critical (MBC) phase with finite-size scaling analysis in the one-dimensional extended Aubry-André-Harper-Hubbard model,...

[Phys. Rev. Lett. 126, 080602] Published Tue Feb 23, 2021

]]>A major challenge in developing quantum computing technologies is to accomplish high precision tasks by utilizing multiplex optimization approaches, on both the physical system and algorithm levels. Loss functions assessing the overall performance of quantum circuits can provide the foundation for m...

[Phys. Rev. Lett. 126, 080501] Published Mon Feb 22, 2021

]]>Quantum annealing (QA) and the quantum approximate optimization algorithm (QAOA) are two special cases of the following control problem: apply a combination of two Hamiltonians to minimize the energy of a quantum state. Which is more effective has remained unclear. Here we analytically apply the fra...

[Phys. Rev. Lett. 126, 070505] Published Fri Feb 19, 2021

]]>Weakly interacting Fermi gases simulate spin lattices in energy space, offering a rich platform for investigating information spreading and spin coherence in a large many-body quantum system. We show that the collective spin vector can be determined as a function of energy from the measured spin den...

[Phys. Rev. Lett. 126, 070601] Published Fri Feb 19, 2021

]]>A spin system crossing a quantum phase transition nonadiabatically may undergo exponential suppression of excitations in the presence of asymmetries.

[Phys. Rev. Lett. 126, 070602] Published Fri Feb 19, 2021

]]>We have recently shown how a polarized beam in Talbot-Lau interferometric imaging can be used to analyze strong magnetic fields through the spin dependent differential phase effect at field gradients. While in that case an adiabatic spin coupling with the sample field is required, here we investigat...

[Phys. Rev. Lett. 126, 070401] Published Thu Feb 18, 2021

]]>Detector backaction can be completely evaded when the state of a one-electron quantum cyclotron is detected, but it nonetheless significantly broadens the quantum-jump resonance line shapes from which the cyclotron frequency can be deduced. This limits the accuracy with which the electron magnetic m...

[Phys. Rev. Lett. 126, 070402] Published Thu Feb 18, 2021

]]>The Heisenberg scaling, which scales as ${N}^{-1}$ in terms of the number of particles or ${T}^{-1}$ in terms of the evolution time, serves as a fundamental limit in quantum metrology. Better scalings, dubbed as “super-Heisenberg scaling,” however, can also arise when the generator of the parameter involves many-...

[Phys. Rev. Lett. 126, 070503] Published Thu Feb 18, 2021

]]>The accurate computation of ground and excited states of many-fermion quantum systems is one of the most consequential, contemporary challenges in the physical and computational sciences whose solution stands to benefit significantly from the advent of quantum computing devices. Existing methodologi...

[Phys. Rev. Lett. 126, 070504] Published Thu Feb 18, 2021

]]>We develop a coherent beam splitter for single electrons driven through two tunnel-coupled quantum wires by surface acoustic waves (SAWs). The output current through each wire oscillates with gate voltages to tune the tunnel coupling and potential difference between the wires. This oscillation is as...

[Phys. Rev. Lett. 126, 070501] Published Tue Feb 16, 2021

]]>The ability to efficiently simulate random quantum circuits using a classical computer is increasingly important for developing noisy intermediate-scale quantum devices. Here, we present a tensor network states based algorithm specifically designed to compute amplitudes for random quantum circuits w...

[Phys. Rev. Lett. 126, 070502] Published Tue Feb 16, 2021

]]>We study the decay mechanism of the gapped lowest-lying axial excitation of a quasipure atomic Bose-Einstein condensate confined in a cylindrical box trap. Owing to the absence of accessible lower-energy modes, or direct coupling to an external bath, this excitation is protected against one-body (li...

[Phys. Rev. Lett. 126, 060402] Published Fri Feb 12, 2021

]]>The exact critical Casimir amplitude is derived for anisotropic systems within the $d=2$ Ising universality class by combining conformal field theory with anisotropic ${\phi}^{4}$ theory. Explicit results are presented for the general anisotropic scalar ${\phi}^{4}$ model and for the fully anisotropic triangular-lattice ...

[Phys. Rev. Lett. 126, 060601] Published Fri Feb 12, 2021

]]>A phase reference has been a standard requirement in continuous-variable quantum sensing and communication protocols. However, maintaining a phase reference is challenging due to environmental fluctuations, preventing quantum phenomena such as entanglement and coherence from being utilized in many s...

[Phys. Rev. Lett. 126, 060502] Published Wed Feb 10, 2021

]]>The laws of quantum mechanics forbid the perfect copying of an unknown quantum state, known as the no-cloning theorem. In spite of this, approximate cloning with imperfect fidelity is possible, which opens up the field of quantum cloning. In general, quantum cloning can be divided into discrete vari...

[Phys. Rev. Lett. 126, 060503] Published Wed Feb 10, 2021

]]>An energy gap develops near quantum critical point of quantum phase transition in a finite many-body (MB) system, facilitating the ground state transformation by adiabatic parameter change. In real application scenarios, however, the efficacy for such a protocol is compromised by the need to balance...

[Phys. Rev. Lett. 126, 060401] Published Tue Feb 09, 2021

]]>A protocol based on space-time duality is used to find the purity of a quantum state for simulations of a class of nonunitary circuits, without any postselection.

[Phys. Rev. Lett. 126, 060501] Published Tue Feb 09, 2021

]]>Gain-dissipative platforms consisting of lasers, optical parametric oscillators and nonequilibrium condensates operating at the condensation or coherence threshold have been recently proposed as efficient analog simulators of the two-local spin Hamiltonians with continuous or discrete degrees of fre...

[Phys. Rev. Lett. 126, 050504] Published Fri Feb 05, 2021

]]>Randomness expansion where one generates a longer sequence of random numbers from a short one is viable in quantum mechanics but not allowed classically. Device-independent quantum randomness expansion provides a randomness resource of the highest security level. Here, we report the first experiment...

[Phys. Rev. Lett. 126, 050503] Published Thu Feb 04, 2021

]]>We simulate a zero-temperature pure ${Z}_{3}$ lattice gauge theory in $2+1$ dimensions by using an iPEPS (infinite projected entangled-pair state) *Ansatz* for the ground state. Our results are therefore directly valid in the thermodynamic limit. They clearly show two distinct phases separated by a phase trans...

[Phys. Rev. Lett. 126, 050401] Published Tue Feb 02, 2021

]]>One of the main topological invariants that characterizes several topologically ordered phases is the many-body Chern number (MBCN). Paradigmatic examples include several fractional quantum Hall phases, which are expected to be realized in different atomic and photonic quantum platforms in the near ...

[Phys. Rev. Lett. 126, 050501] Published Mon Feb 01, 2021

]]>The analogy between an equilibrium partition function and the return probability in many-body unitary dynamics has led to the concept of dynamical quantum phase transition (DQPT). DQPTs are defined by nonanalyticities in the return amplitude and are present in many models. In some cases, DQPTs can b...

[Phys. Rev. Lett. 126, 040602] Published Fri Jan 29, 2021

]]>A system that hosts an analytical mobility edge has been realized in a Bose-Einstein condensate through the use of laser-coupled momentum modes.

[Phys. Rev. Lett. 126, 040603] Published Fri Jan 29, 2021

]]>Although the spectral properties of random graphs have been a long-standing focus of network theory, the properties of right eigenvectors of directed graphs have so far eluded an exact analytic treatment. We present a general theory for the statistics of the right eigenvector components in directed ...

[Phys. Rev. Lett. 126, 040604] Published Fri Jan 29, 2021

]]>Driven quantum systems may realize novel phenomena absent in static systems, but driving-induced heating can limit the timescale on which these persist. We study heating in interacting quantum many-body systems driven by *random* sequences with $n$-multipolar correlations, corresponding to a polynomiall...

[Phys. Rev. Lett. 126, 040601] Published Thu Jan 28, 2021

]]>Quantum entanglement and nonlocality are inextricably linked. However, while entanglement is necessary for nonlocality, it is not always sufficient in the standard Bell scenario. We derive sufficient conditions for entanglement to give rise to genuine multipartite nonlocality in networks. We find th...

[Phys. Rev. Lett. 126, 040501] Published Wed Jan 27, 2021

]]>In this study, we investigate out-of-time-order correlators (OTOCs) in systems with power-law decaying interactions such as ${R}^{-\alpha}$, where $R$ is the distance. In such systems, the fast scrambling of quantum information or the exponential growth of information propagation can potentially occur according t...

[Phys. Rev. Lett. 126, 030604] Published Fri Jan 22, 2021

]]>We consider a disordered Hubbard model and show that, at sufficiently weak disorder, a single spin-down mobile impurity can thermalize an extensive initially localized system of spin-up particles. Thermalization is enabled by resonant processes that involve correlated hops of the impurity and locali...

[Phys. Rev. Lett. 126, 030603] Published Thu Jan 21, 2021

]]>In recent years, the out-of-time-order correlator (OTOC) has emerged as a diagnostic tool for information scrambling in quantum many-body systems. Here, we present exact analytical results for the OTOC for a typical pair of random local operators supported over two regions of a bipartition. Quite re...

[Phys. Rev. Lett. 126, 030601] Published Wed Jan 20, 2021

]]>A numerical technique allows the verification of analytical bounds for the SYK model and the investigation of chaotic behavior in generic quantum many-body systems of high dimensions.

[Phys. Rev. Lett. 126, 030602] Published Wed Jan 20, 2021

]]>In the context of experimental advances in the realization of artificial magnetic fields in quantum gases, we discuss feasible schemes to extend measurements of the Hall polarization to a study of the Hall voltage, allowing for direct comparison with solid state systems. Specifically, for the paradi...

[Phys. Rev. Lett. 126, 030501] Published Tue Jan 19, 2021

]]>A small prototype of a drone-based quantum network has successfully relayed a quantum signal over a kilometer of free space.

[Phys. Rev. Lett. 126, 020503] Published Fri Jan 15, 2021

]]>Discrete time crystals are periodically driven systems that display spontaneous symmetry breaking of time translation invariance in the form of indefinite subharmonic oscillations. We introduce a thermodynamically consistent model for a discrete time crystal and analyze it using the framework of sto...

[Phys. Rev. Lett. 126, 020603] Published Fri Jan 15, 2021

]]>We study the dissipative preparation of many-body entangled Gaussian states in bosonic lattice models which could be relevant for quantum technology applications. We assume minimal resources, represented by systems described by particle-conserving quadratic Hamiltonians, with a single localized sque...

[Phys. Rev. Lett. 126, 020402] Published Thu Jan 14, 2021

]]>A novel, high-resolution fluorescence imaging technique reveals a pattern, known as a Pauli crystal, that can emerge in a cloud of trapped, noninteracting fermions.

[Phys. Rev. Lett. 126, 020401] Published Wed Jan 13, 2021

]]>The act of observing a quantum object fundamentally perturbs its state, resulting in a random walk toward an eigenstate of the measurement operator. Ideally, the measurement is responsible for all dephasing of the quantum state. In practice, imperfections in the measurement apparatus limit or corrup...

[Phys. Rev. Lett. 126, 020502] Published Wed Jan 13, 2021

]]>We use a reinforcement learning approach to reduce entropy production in a closed quantum system brought out of equilibrium. Our strategy makes use of an external control Hamiltonian and a policy gradient technique. Our approach bears no dependence on the quantitative tool chosen to characterize the...

[Phys. Rev. Lett. 126, 020601] Published Wed Jan 13, 2021

]]>In equilibrium physics, spontaneous symmetry breaking and elementary excitation are two concepts closely related with each other: the symmetry and its spontaneous breaking not only control the dynamics and spectrum of elementary excitations, but also determine their underlying structures. In this Le...

[Phys. Rev. Lett. 126, 020602] Published Tue Jan 12, 2021

]]>The problem of simulating complex quantum processes on classical computers gave rise to the field of quantum simulations. Quantum simulators solve problems, such as boson sampling, where classical counterparts fail. In another field of physics, the unification of general relativity and quantum theor...

[Phys. Rev. Lett. 126, 020501] Published Mon Jan 11, 2021

]]>High-quality long-distance entanglement is essential for both quantum communication and scalable quantum networks. Entanglement purification is to distill high-quality entanglement from low-quality entanglement in a noisy environment and it plays a key role in quantum repeaters. The previous signifi...

[Phys. Rev. Lett. 126, 010503] Published Fri Jan 08, 2021

]]>Knots have a twisted history in quantum physics. They were abandoned as failed models of atoms. Only much later was the connection between knot invariants and Wilson loops in topological quantum field theory discovered. Here we show that knots tied by the eigenenergy strings provide a complete topol...

[Phys. Rev. Lett. 126, 010401] Published Thu Jan 07, 2021

]]>We report high-fidelity state readout of a trapped ion qubit using a trap-integrated photon detector. We determine the hyperfine qubit state of a single ${}^{9}{\mathrm{Be}}^{+}$ ion held in a surface-electrode rf ion trap by counting state-dependent ion fluorescence photons with a superconducting nanowire single-photon...

[Phys. Rev. Lett. 126, 010501] Published Wed Jan 06, 2021

]]>Quantum criticality, as a fascinating quantum phenomenon, may provide significant advantages for quantum sensing. Here we propose a dynamic framework for quantum sensing with a family of Hamiltonians that undergo quantum phase transitions (QPTs). By giving the formalism of the quantum Fisher informa...

[Phys. Rev. Lett. 126, 010502] Published Wed Jan 06, 2021

]]>We derive a thermodynamic uncertainty relation for general open quantum dynamics, described by a joint unitary evolution on a composite system comprising a system and an environment. By measuring the environmental state after the system-environment interaction, we bound the counting observables in t...

[Phys. Rev. Lett. 126, 010602] Published Tue Jan 05, 2021

]]>We derive geometrical bounds on the irreversibility in both quantum and classical Markovian open systems that satisfy the detailed balance condition. Using information geometry, we prove that irreversible entropy production is bounded from below by a modified Wasserstein distance between the initial...

[Phys. Rev. Lett. 126, 010601] Published Mon Jan 04, 2021

]]>Spin-orbital-angular-momentum (SOAM) coupling has been realized in recent experiments of Bose-Einstein condensates [Chen *et al.*, Phys. Rev. Lett. **121**, 113204 (2018) and Zhang *et al.*, Phys. Rev. Lett. **122**, 110402 (2019)], where the orbital angular momentum imprinted upon bosons leads to quantized vor...

[Phys. Rev. Lett. 125, 260407] Published Thu Dec 31, 2020

]]>Optical approaches to quantum computation require the creation of multimode photonic quantum states in a controlled fashion. Here we experimentally demonstrate phase locking of two all-optical quantum memories, based on a concatenated cavity system with phase reference beams, for the time-controlled...

[Phys. Rev. Lett. 125, 260508] Published Thu Dec 31, 2020

]]>We introduce a new approach to Gottesman-Kitaev-Preskill (GKP) states that treats their finite-energy version in an exact manner. Based on this analysis, we develop new qubit-oscillator circuits that autonomously stabilize a GKP manifold, correcting errors without relying on qubit measurements. Fina...

[Phys. Rev. Lett. 125, 260509] Published Thu Dec 31, 2020

]]>The performance of quantum key distribution (QKD) is severely limited by multiphoton pulses emitted by laser sources due to the photon-number splitting attack. Coherent-one-way (COW) QKD has been introduced as a promising solution to overcome this limitation, and thus extend the achievable distance ...

[Phys. Rev. Lett. 125, 260510] Published Thu Dec 31, 2020

]]>The theoretical investigation of nonadiabatic processes is hampered by the complexity of the coupled electron-nuclear dynamics beyond the Born-Oppenheimer approximation. Classically, the simulation of such reactions is limited by the unfavorable scaling of the computational resources as a function o...

[Phys. Rev. Lett. 125, 260511] Published Thu Dec 31, 2020

]]>As two valuable quantum resources, Einstein-Podolsky-Rosen entanglement and steering play important roles in quantum-enhanced communication protocols. Distributing such quantum resources among multiple remote users in a network is a crucial precondition underlying various quantum tasks. We experimen...

[Phys. Rev. Lett. 125, 260506] Published Wed Dec 30, 2020

]]>Self-testing is a procedure for characterizing quantum resources with the minimal level of trust. Up to now it has been used as a device-independent certification tool for particular quantum measurements, channels, and pure entangled states. In this work we introduce the concept of self-testing more...

[Phys. Rev. Lett. 125, 260507] Published Wed Dec 30, 2020

]]>Thermodynamic uncertainty relations yield a lower bound on entropy production in terms of the mean and fluctuations of a current. We derive their general form for systems under arbitrary time-dependent driving from arbitrary initial states and extend these relations beyond currents to state variable...

[Phys. Rev. Lett. 125, 260604] Published Wed Dec 30, 2020

]]>Spin glasses and many-body localization (MBL) are prime examples of ergodicity breaking, yet their physical origin is quite different: the former phase arises due to rugged classical energy landscape, while the latter is a quantum-interference effect. Here, we study quantum dynamics of an isolated 1...

[Phys. Rev. Lett. 125, 260405] Published Mon Dec 28, 2020

]]>Photonic quantum memory is the core element in quantum information processing (QIP). For the scalable and convenient practical applications, great efforts have been devoted to the integrated quantum memory based on various waveguides fabricated in solids. However, on-demand storage of qubits, which ...

[Phys. Rev. Lett. 125, 260504] Published Mon Dec 28, 2020

]]>The famous Kibble-Zurek mechanism offers us a significant clue to study quantum phase transitions out of equilibrium. Here, we investigate an intriguing phenomenon of a spin-orbit coupled Bose-Einstein condensate by quenching the Raman coupling strength from a high-symmetry phase (nonmagnetic phase)...

[Phys. Rev. Lett. 125, 260603] Published Mon Dec 28, 2020

]]>The quantum approximate optimization algorithm (QAOA) employs variational states generated by a parameterized quantum circuit to maximize the expected value of a Hamiltonian encoding a classical cost function. Whether or not the QAOA can outperform classical algorithms in some tasks is an actively d...

[Phys. Rev. Lett. 125, 260505] Published Thu Dec 24, 2020

]]>The Nambu-Goldstone (NG) modes in a nonrelativistic system can be classified into two types from their characteristic features: being of either an odd (type I) or an even (type II) power energy-momentum dispersion. Conventionally, the type-II NG modes may universally arise from spontaneous breaking ...

[Phys. Rev. Lett. 125, 260402] Published Wed Dec 23, 2020

]]>Contrary to expectations, negativity in a quasiprobability function is not required for universal quantum computation.

[Phys. Rev. Lett. 125, 260404] Published Wed Dec 23, 2020

]]>Researchers shared tamper-proof quantum information across nearly 20 km of open air in an urban environment.

[Phys. Rev. Lett. 125, 260503] Published Wed Dec 23, 2020

]]>Effective and efficient forecasting relies on identification of the relevant information contained in past observations—the predictive features—and isolating it from the rest. When the future of a process bears a strong dependence on its behavior far into the past, there are many such features to st...

[Phys. Rev. Lett. 125, 260501] Published Tue Dec 22, 2020

]]>When engineering microscopic machines, increasing efficiency can often come at a price of reduced reliability due to the impact of stochastic fluctuations. Here we develop a general method for performing multiobjective optimization of efficiency and work fluctuations in thermal machines operating cl...

[Phys. Rev. Lett. 125, 260602] Published Tue Dec 22, 2020

]]>We revisit the “counterfactual quantum communication” of Salih *et al.* [1], who claim that an observer “Bob” can send one bit of information to a second observer “Alice” without any physical particle traveling between them. We show that a locally conserved, massless current—specifically, a current of...

[Phys. Rev. Lett. 125, 260401] Published Mon Dec 21, 2020

]]>The dynamics of the next quantum jump for a qubit [two level system] coupled to a readout resonator [damped driven harmonic oscillator] is calculated. A quantum mechanical treatment of readout resonator reveals nonexponential short time behavior which could facilitate detection of the state of the q...

[Phys. Rev. Lett. 125, 260403] Published Mon Dec 21, 2020

]]>A cold waveguide provides a reliable conduit for transferring states between remote qubits, making it potentially useful for building networks connecting superconducting circuits.

[Phys. Rev. Lett. 125, 260502] Published Mon Dec 21, 2020

]]>Contrary to the conventional wisdom in Hermitian systems, a continuous quantum phase transition between gapped phases is shown to occur without closing the energy gap $\mathrm{\Delta}$ in non-Hermitian quantum many-body systems. Here, the relevant length scale $\xi \simeq {v}_{\mathrm{LR}}/\mathrm{\Delta}$ diverges because of the breakdown of the Lieb-R...

[Phys. Rev. Lett. 125, 260601] Published Mon Dec 21, 2020

]]>We consider a noninteracting many-fermion system populating levels of a unitary random matrix ensemble (equivalent to the $q=2$ complex Sachdev-Ye-Kitaev model)—a generic model of single-particle quantum chaos. We study the corresponding many-particle level statistics by calculating the spectral form ...

[Phys. Rev. Lett. 125, 250601] Published Fri Dec 18, 2020

]]>A long period of linear growth in the spectral form factor provides a universal diagnostic of quantum chaos at intermediate times. By contrast, the behavior of the spectral form factor in disordered integrable many-body models is not well understood. Here we study the two-body Sachdev-Ye-Kitaev mode...

[Phys. Rev. Lett. 125, 250602] Published Fri Dec 18, 2020

]]>Demonstrating a quantum computational speed-up is a crucial milestone for near-term quantum technology. Recently, sampling protocols for quantum simulators have been proposed that have the potential to show such a quantum advantage, based on commonly made assumptions. The key challenge in the theore...

[Phys. Rev. Lett. 125, 250501] Published Thu Dec 17, 2020

]]>We develop an inverse geometric optimization technique that allows the derivation of optimal and robust exact solutions of low-dimension quantum control problems driven by external fields. We determine in the dynamical variable space optimal trajectories constrained to robust solutions by Euler-Lagr...

[Phys. Rev. Lett. 125, 250403] Published Wed Dec 16, 2020

]]>We experimentally study universal nonequilibrium dynamics of two-dimensional atomic Bose gases quenched from repulsive to attractive interactions. We observe the manifestation of modulational instability that, instead of causing collapse, fragments a large two-dimensional superfluid into multiple wa...

[Phys. Rev. Lett. 125, 250401] Published Tue Dec 15, 2020

]]>Many-body localization in interacting quantum systems can be cast as a disordered hopping problem on the underlying Fock-space graph. A crucial feature of the effective Fock-space disorder is that the Fock-space site energies are strongly correlated—maximally so for sites separated by a finite dista...

[Phys. Rev. Lett. 125, 250402] Published Tue Dec 15, 2020

]]>Besides mobility and diffusivity, anomalous transport is described by a third term controlling the symmetry breaking and can be caused not only by spatial Levy flights of the walker, but also by long trapping in time.

[Phys. Rev. Lett. 125, 240606] Published Fri Dec 11, 2020

]]>We discuss general features of charge transport in nonrelativistic classical field theories invariant under non-Abelian unitary Lie groups by examining the full structure of two-point dynamical correlation functions in grand-canonical ensembles at finite charge densities (polarized ensembles). Upon ...

[Phys. Rev. Lett. 125, 240607] Published Fri Dec 11, 2020

]]>Classical mechanics obeys the intuitive logic that a physical event happens at a definite spatial point. Entanglement, however, breaks this logic by enabling interactions without a specific location. In this work we study these delocalized interactions. These are quantum interactions that create les...

[Phys. Rev. Lett. 125, 240406] Published Thu Dec 10, 2020

]]>$\mathcal{P}\mathcal{T}$-symmetric theory is developed to extend quantum mechanics to a complex region, but it wins its great success first in classical systems, for example, optical waveguides and electric circuits, etc., because there are so many counterintuitive phenomena and striking applications, including unidirect...

[Phys. Rev. Lett. 125, 240506] Published Thu Dec 10, 2020

]]>For a decade the fate of a one-dimensional gas of interacting bosons in an external trapping potential remained mysterious. We here show that whenever the underlying integrability of the gas is broken by the presence of the external potential, the inevitable diffusive rearrangements between the quas...

[Phys. Rev. Lett. 125, 240604] Published Thu Dec 10, 2020

]]>We propose a new dynamical method to connect equilibrium quantum phase transitions and quantum coherence using out-of-time-order correlations (OTOCs). Adopting the iconic Lipkin-Meshkov-Glick and transverse-field Ising models as illustrative examples, we show that an abrupt change in coherence and e...

[Phys. Rev. Lett. 125, 240605] Published Thu Dec 10, 2020

]]>Quantum nonlocality can be observed in networks even in the case where every party can only perform a single measurement, i.e., does not receive any input. So far, this effect has been demonstrated under the assumption that all sources in the network are fully independent from each other. Here we in...

[Phys. Rev. Lett. 125, 240403] Published Wed Dec 09, 2020

]]>We show that a simple experimental setting of a locally pumped and lossy array of two-level quantum systems can stabilize states with strong long-range coherence. Indeed, by explicit analytic construction, we show there is an extensive set of steady-state density operators, from minimally to maximal...

[Phys. Rev. Lett. 125, 240404] Published Wed Dec 09, 2020

]]>High fidelity two-qubit gates exhibiting low cross talk are essential building blocks for gate-based quantum information processing. In superconducting circuits, two-qubit gates are typically based either on rf-controlled interactions or on the *in situ* tunability of qubit frequencies. Here, we prese...

[Phys. Rev. Lett. 125, 240502] Published Wed Dec 09, 2020

]]>High-quality two-qubit gate operations are crucial for scalable quantum information processing. Often, the gate fidelity is compromised when the system becomes more integrated. Therefore, a low-error-rate, easy-to-scale two-qubit gate scheme is highly desirable. Here, we experimentally demonstrate a...

[Phys. Rev. Lett. 125, 240503] Published Wed Dec 09, 2020

]]>The standard definition of genuine multipartite entanglement stems from the need to assess the quantum control over an ever-growing number of quantum systems. We argue that this notion is easy to hack: in fact, a source capable of distributing bipartite entanglement can, by itself, generate genuine $\mathrm{...}$

[Phys. Rev. Lett. 125, 240505] Published Wed Dec 09, 2020

]]>Quantum many-body systems out of equilibrium can host intriguing phenomena such as transitions to exotic dynamical states. Although this emergent behaviour can be observed in experiments, its potential for technological applications is largely unexplored. Here, we investigate the impact of collectiv...

[Phys. Rev. Lett. 125, 240602] Published Wed Dec 09, 2020

]]>In this Letter we set up a suggestive number theory interpretation of a quantum ladder system made of $\mathcal{N}$ coupled chains of spin $1/2$. Using the hard-core boson representation and a leg-Hamiltonian made of a magnetic field and a hopping term, we can associate to the spins ${\sigma}_{a}$ the prime numbers ${p}_{a}$ so tha...

[Phys. Rev. Lett. 125, 240603] Published Wed Dec 09, 2020

]]>Many-body localization (MBL) provides a mechanism to avoid thermalization in many-body quantum systems. Here, we show that an *emergent* symmetry can protect a state from MBL. Specifically, we propose a ${\mathbb{Z}}_{2}$ symmetric model with nonlocal interactions, which has an analytically known, SU(2) invariant, cr...

[Phys. Rev. Lett. 125, 240401] Published Tue Dec 08, 2020

]]>Symmetry-breaking transitions are a well-understood phenomenon of closed quantum systems in quantum optics, condensed matter, and high energy physics. However, symmetry breaking in open systems is less thoroughly understood, in part due to the richer steady-state and symmetry structure that such sys...

[Phys. Rev. Lett. 125, 240405] Published Tue Dec 08, 2020

]]>