Universal Measurement-Based Quantum Computation in a One-Dimensional Architecture Enabled by Dual-Unitary Circuits.

A powerful tool emerging from the study of many-body quantum dynamics is that of dual-unitary circuits, which are unitary even when read "sideways," i.e., along the spatial direction. Here, we show that this provides the ideal framework to understand and expand on the notion of measurement-based quantum computation (MBQC). In particular, applying a dual-unitary circuit to a many-body state followed by appropriate measurements effectively implements quantum computation in the spatial direction. We show how the dual-unitary dynamics generated by the dynamics of the paradigmatic one-dimensional kicked Ising chain with certain parameter choices generate resource states for universal deterministic MBQC. Specifically, after k time steps, equivalent to a depth-k quantum circuit, we obtain a resource state for universal MBQC on ∼3k/4 encoded qubits. Our protocol allows generic quantum circuits to be "rotated" in space-time and gives new ways to exchange between resources like qubit number and coherence time in quantum computers. Beyond the practical advantages, we also interpret the dual-unitary evolution as generating an infinite sequence of new symmetry-protected topological phases with spatially modulated symmetries, which gives a vast generalization of the well-studied one-dimensional cluster state and shows that our protocol is robust to symmetry-respecting deformations.

Landau-Forbidden Quantum Criticality in Rydberg Quantum Simulators.

The Landau-Ginzburg-Wilson theory of phase transitions precludes a continuous transition between two phases that spontaneously break distinct symmetries. However, quantum mechanical effects can intertwine the symmetries, giving rise to an exotic phenomenon called deconfined quantum criticality (DQC). In this Letter, we study the ground state phase diagram of a one-dimensional array of individually trapped neutral atoms interacting strongly via Rydberg states, and demonstrate through extensive numerical simulations that it hosts a variety of symmetry-breaking phases and their transitions including DQC. We show how an enlarged, emergent continuous symmetry arises at the DQCs, which can be experimentally observed in the joint distribution of two distinct order parameters, obtained within measurement snapshots in the standard computational basis. Our findings highlight quantum simulators of Rydberg atoms not only as promising platforms to experimentally realize such exotic phenomena, but also as unique ones allowing access to physical properties not obtainable in traditional experiments.

Complete Hilbert-Space Ergodicity in Quantum Dynamics of Generalized Fibonacci Drives.

Ergodicity of quantum dynamics is often defined through statistical properties of energy eigenstates, as exemplified by Berry's conjecture in single-particle quantum chaos and the eigenstate thermalization hypothesis in many-body settings. In this work, we investigate whether quantum systems can exhibit a stronger form of ergodicity, wherein any time-evolved state uniformly visits the entire Hilbert space over time. We call such a phenomenon complete Hilbert-space ergodicity (CHSE), which is more akin to the intuitive notion of ergodicity as an inherently dynamical concept. CHSE cannot hold for time-independent or even time-periodic Hamiltonian dynamics, owing to the existence of (quasi)energy eigenstates which precludes exploration of the full Hilbert space. However, we find that there exists a family of aperiodic, yet deterministic drives with minimal symbolic complexity-generated by the Fibonacci word and its generalizations-for which CHSE can be proven to occur. Our results provide a basis for understanding thermalization in general time-dependent quantum systems.

Exact Emergent Quantum State Designs from Quantum Chaotic Dynamics.

We present exact results on a novel kind of emergent random matrix universality that quantum many-body systems at infinite temperature can exhibit. Specifically, we consider an ensemble of pure states supported on a small subsystem, generated from projective measurements of the remainder of the system in a local basis. We rigorously show that the ensemble, derived for a class of quantum chaotic systems undergoing quench dynamics, approaches a universal form completely independent of system details: it becomes uniformly distributed in Hilbert space. This goes beyond the standard paradigm of quantum thermalization, which dictates that the subsystem relaxes to an ensemble of quantum states that reproduces the expectation values of local observables in a thermal mixed state. Our results imply more generally that the distribution of quantum states themselves becomes indistinguishable from those of uniformly random ones, i.e., the ensemble forms a quantum state design in the parlance of quantum information theory. Our work establishes bridges between quantum many-body physics, quantum information and random matrix theory, by showing that pseudorandom states can arise from isolated quantum dynamics, opening up new ways to design applications for quantum state tomography and benchmarking.

Quantum phases of matter on a 256-atom programmable quantum simulator.

Motivated by far-reaching applications ranging from quantum simulations of complex processes in physics and chemistry to quantum information processing1, a broad effort is currently underway to build large-scale programmable quantum systems. Such systems provide insights into strongly correlated quantum matter2-6, while at the same time enabling new methods for computation7-10 and metrology11. Here we demonstrate a programmable quantum simulator based on deterministically prepared two-dimensional arrays of neutral atoms, featuring strong interactions controlled by coherent atomic excitation into Rydberg states12. Using this approach, we realize a quantum spin model with tunable interactions for system sizes ranging from 64 to 256 qubits. We benchmark the system by characterizing high-fidelity antiferromagnetically ordered states and demonstrating quantum critical dynamics consistent with an Ising quantum phase transition in (2 + 1) dimensions13. We then create and study several new quantum phases that arise from the interplay between interactions and coherent laser excitation14, experimentally map the phase diagram and investigate the role of quantum fluctuations. Offering a new lens into the study of complex quantum matter, these observations pave the way for investigations of exotic quantum phases, non-equilibrium entanglement dynamics and hardware-efficient realization of quantum algorithms.

Quantum phases of Rydberg atoms on a kagome lattice.

We analyze the zero-temperature phases of an array of neutral atoms on the kagome lattice, interacting via laser excitation to atomic Rydberg states. Density-matrix renormalization group calculations reveal the presence of a wide variety of complex solid phases with broken lattice symmetries. In addition, we identify a regime with dense Rydberg excitations that has a large entanglement entropy and no local order parameter associated with lattice symmetries. From a mapping to the triangular lattice quantum dimer model, and theories of quantum phase transitions out of the proximate solid phases, we argue that this regime could contain one or more phases with topological order. Our results provide the foundation for theoretical and experimental explorations of crystalline and liquid states using programmable quantum simulators based on Rydberg atom arrays.

Spin transport in a tunable Heisenberg model realized with ultracold atoms.

Simple models of interacting spins have an important role in physics. They capture the properties of many magnetic materials, but also extend to other systems, such as bosons and fermions in a lattice, gauge theories, high-temperature superconductors, quantum spin liquids, and systems with exotic particles such as anyons and Majorana fermions1,2. To study and compare these models, a versatile platform is needed. Realizing such systems has been a long-standing goal in the field of ultracold atoms. So far, spin transport has only been studied in systems with isotropic spin-spin interactions3-12. Here we realize the Heisenberg model describing spins on a lattice, with fully adjustable anisotropy of the nearest-neighbour spin-spin couplings (called the XXZ model). In this model we study spin transport far from equilibrium after quantum quenches from imprinted spin-helix patterns. When spins are coupled only along two of three possible orientations (the XX model), we find ballistic behaviour of spin dynamics, whereas for isotropic interactions (the XXX model), we find diffusive behaviour. More generally, for positive anisotropies, the dynamics ranges from anomalous superdiffusion to subdiffusion, whereas for negative anisotropies, we observe a crossover in the time domain from ballistic to diffusive transport. This behaviour is in contrast with expectations from the linear-response regime and raises new questions in understanding quantum many-body dynamics far away from equilibrium.

Complex Density Wave Orders and Quantum Phase Transitions in a Model of Square-Lattice Rydberg Atom Arrays.

We describe the zero-temperature phase diagram of a model of a two-dimensional square-lattice array of neutral atoms, excited into Rydberg states and interacting via strong van der Waals interactions. Using the density-matrix renormalization group algorithm, we map out the phase diagram and obtain a rich variety of phases featuring complex density wave orderings, upon varying lattice spacing and laser detuning. While some of these phases result from the classical optimization of the van der Waals energy, we also find intrinsically quantum-ordered phases stabilized by quantum fluctuations. These phases are surrounded by novel quantum phase transitions, which we analyze by finite-size scaling numerics and Landau theories. Our work highlights Rydberg quantum simulators in higher dimensions as promising platforms to realize exotic many-body phenomena.

Emergent SU(2) Dynamics and Perfect Quantum Many-Body Scars.

Motivated by recent experimental observations of coherent many-body revivals in a constrained Rydberg atom chain, we construct a weak quasilocal deformation of the Rydberg-blockaded Hamiltonian, which makes the revivals virtually perfect. Our analysis suggests the existence of an underlying nonintegrable Hamiltonian which supports an emergent SU(2)-spin dynamics within a small subspace of the many-body Hilbert space. We show that such perfect dynamics necessitates the existence of atypical, nonergodic energy eigenstates-quantum many-body scars. Furthermore, using these insights, we construct a toy model that hosts exact quantum many-body scars, providing an intuitive explanation of their origin. Our results offer specific routes to enhancing coherent many-body revivals and provide a step toward establishing the stability of quantum many-body scars in the thermodynamic limit.

Periodic Orbits, Entanglement, and Quantum Many-Body Scars in Constrained Models: Matrix Product State Approach.

We analyze quantum dynamics of strongly interacting, kinetically constrained many-body systems. Motivated by recent experiments demonstrating surprising long-lived, periodic revivals after quantum quenches in Rydberg atom arrays, we introduce a manifold of locally entangled spin states, representable by low-bond dimension matrix product states, and derive equations of motion for them using the time-dependent variational principle. We find that they feature isolated, unstable periodic orbits, which capture the recurrences and represent nonergodic dynamical trajectories. Our results provide a theoretical framework for understanding quantum dynamics in a class of constrained spin models, which allow us to examine the recently suggested explanation of "quantum many-body scarring" [Nat. Phys. 14, 745 (2018)NPAHAX1745-247310.1038/s41567-018-0137-5], and establish a possible connection to the corresponding phenomenon in chaotic single-particle systems.

Probing Quantum Thermalization of a Disordered Dipolar Spin Ensemble with Discrete Time-Crystalline Order.

We investigate thermalization dynamics of a driven dipolar many-body quantum system through the stability of discrete time crystalline order. Using periodic driving of electronic spin impurities in diamond, we realize different types of interactions between spins and demonstrate experimentally that the interplay of disorder, driving, and interactions leads to several qualitatively distinct regimes of thermalization. For short driving periods, the observed dynamics are well described by an effective Hamiltonian which sensitively depends on interaction details. For long driving periods, the system becomes susceptible to energy exchange with the driving field and eventually enters a universal thermalizing regime, where the dynamics can be described by interaction-induced dephasing of individual spins. Our analysis reveals important differences between thermalization of long-range Ising and other dipolar spin models.

Floquet Mechanism for Non-Abelian Fractional Quantum Hall States.

Three-body correlations, which arise between spin-polarized electrons in the first excited Landau level, are believed to play a key role in the emergence of enigmatic non-Abelian fractional quantum Hall (FQH) effects. Inspired by recent advances in Floquet engineering, we investigate periodic driving of anisotropic two-body interactions as a route for controllably creating and tuning effective three-body interactions in the FQH regime. We develop an analytic formalism to describe this Floquet-FQH protocol, which is distinct from previous approaches that instead focus on band structure engineering via modulation of single-particle hopping terms. By systematically analyzing the resulting interactions using generalized pseudopotentials, we show that our Floquet-FQH approach leads to repulsive as well as attractive three-body interactions that are highly tunable and support a variety of non-Abelian multicomponent FQH states. Finally, we propose an implementation of the protocol in optically dressed ultracold polar molecules with modulated Rabi frequencies.

Bounds on Energy Absorption and Prethermalization in Quantum Systems with Long-Range Interactions.

Long-range interacting systems such as nitrogen vacancy centers in diamond and trapped ions serve as experimental setups to probe a range of nonequilibrium many-body phenomena. In particular, via driving, various effective Hamiltonians with physics potentially quite distinct from short-range systems can be realized. In this Letter, we derive general rigorous bounds on the linear response energy absorption rates of periodically driven systems of spins or fermions with long-range interactions that are sign changing and fall off as 1/r^{α} with α>d/2. We show that the disorder averaged energy absorption rate at high temperatures decays exponentially with the driving frequency. This strongly suggests the presence of a prethermal plateau in which dynamics is governed by an effective, static Hamiltonian for long times, and we provide numerical evidence to support such a statement. Our results are relevant for understanding timescales of heating and new dynamical regimes described by effective Hamiltonians in such long-range systems.

Critical Time Crystals in Dipolar Systems.

We analyze the quantum dynamics of periodically driven, disordered systems in the presence of long-range interactions. Focusing on the stability of discrete time crystalline (DTC) order in such systems, we use a perturbative procedure to evaluate its lifetime. For 3D systems with dipolar interactions, we show that the corresponding decay is parametrically slow, implying that robust, long-lived DTC order can be obtained. We further predict a sharp crossover from the stable DTC regime into a regime where DTC order is lost, reminiscent of a phase transition. These results are in good agreement with the recent experiments utilizing a dense, dipolar spin ensemble in diamond [Nature (London) 543, 221 (2017)NATUAS0028-083610.1038/nature21426]. They demonstrate the existence of a novel, critical DTC regime that is stabilized not by many-body localization but rather by slow, critical dynamics. Our analysis shows that the DTC response can be used as a sensitive probe of nonequilibrium quantum matter.

Evaluation of the suicide prevention program in Kaohsiung City, Taiwan, using the CIPP evaluation model.

The purpose of this study is to evaluate the effectiveness of the Kaohsiung Suicide Prevention Center (KSPC) of Kaohsiung City, Taiwan, during the period from June 2005 to June 2008. We used a modified CIPP evaluation model to evaluate the suicide prevention program in Kaohsiung. Four evaluation models were applied to evaluate the KSPC: a context evaluation of the background and origin of the center, an input evaluation of the resources of the center, a process evaluation of the activities of the suicide prevention project, and a product evaluation of the ascertainment of project objectives. The context evaluation revealed that the task of the KSPC is to lower mortality. The input evaluation assessed the efficiency of manpower and the grants supported by Taiwan's Department of Health and Kaohsiung City government's Bureau of Health. In the process evaluation, we inspected the suicide prevention strategies of the KSPC, which are a modified version of the National Suicide Prevention Strategy of Australia. In the product evaluation, four major objectives were evaluated: (1) the suicide rate in Kaohsiung, (2) the reported suicidal cases, (3) crisis line calls, and (4) telephone counseling. From 2005 to 2008, the number of telephone counseling sessions (1,432, 2,010, 7,051, 12,517) and crisis line calls (0, 4,320, 10,339, 14,502) increased. Because of the increase in reported suicidal cases (1,328, 2,625, 2,795, and 2,989, respectively), cases which were underreported in the past, we have increasingly been able to contact the people who need help. During this same time period, the half-year suicide re-attempt rate decreased significantly for those who received services, and the committed suicide rate (21.4, 20.1, 18.2, and 17.8 per 100,000 populations, respectively) also decreased. The suicide prevention program in Kaohsiung is worth implementing on a continual basis if financial constraints are addressed.

A three-year follow-up study of the psychosocial predictors of delayed and unresolved post-traumatic stress disorder in Taiwan Chi-Chi earthquake survivors.

AIMS: To predict the longitudinal course of post-traumatic stress disorder (PTSD) in survivors three years following a catastrophic earthquake using multivariate data presented six months after the earthquake. METHODS: Trained assistants and psychiatrists used the Disaster-related Psychological Screening Test (DRPST) to interview earthquake survivors 16 years and older and to assess current and incidental psychopathology. A total of 1756 respondents were surveyed over the three-year follow-up period. RESULTS: A total of 38 (9.1%) of the original 418 PTSD subjects and 40 of the original 1338 (3.0%) non-PTSD subjects were identified as having PTSD at the 3-year post-earthquake follow up. Younger age, significant financial loss, and memory/attention impairment were predictive factors of unresolved PTSD and delayed PTSD. CONCLUSIONS: The longitudinal course of PTSD three years after the earthquake could be predicted as early as six months after the earthquake on the basis of demographic data, PTSD-related factors, and putative factors for PTSD.

The characteristics of and risk factors associated with incarcerated sex offenders in Taiwan.

This article presents the demographic characteristics of a sample of Taiwanese sex offenders, examines the rate of sexual recidivism in Taiwan, and describes which factors distinguish recidivists from non-recidivists. This article assesses the recidivism rate of a sample of 503 male sex offenders incarcerated from 1999 to 2004. The sample is divided into two groups: non-recidivists (88.7%) and recidivists (11.3%). The variables are categorized into demographic characteristics, criminal history, interpersonal relationships, and offending behaviors. Multivariate logistic regression analysis suggests that recidivism is significantly related to male victims, poor interactions with employers, verbal control (i.e., threats to or verbal control of victims), weapon control (threatening or controlling victims with weapons), and familiarity with victims. Furthermore, this article will establish a database for demographic characteristics and associated risk factors related to recidivism in incarcerated sex offenders in Taiwan. These data will be useful for preventing future sex crimes.

A comparison of quality of life and depression between female married immigrants and native married women in Taiwan.

BACKGROUNDS: Immigration to Taiwan is often connected with marriage, resulting in the presence of so-called married immigrants or foreign brides. AIMS: To compare the quality of life (QOL) and prevalence of depression between female married immigrants and native married women. METHODS: Trained assistants used the Medical Outcomes Study Short Form-36 (MOS SF-36) and the disaster-related psychological screening test (DRPST) to interview 1,602 married women who were 16-50 years of age. Half (801) of the participants were female immigrants, whilst the remainder comprised the age-matched control group that consisted of 801 native married women. Participants who scored C2 (probable major depressive episode) on the DRPST were assessed according to DSM-IV criteria by a senior psychiatrist. The MOS SF-36 measures QOL and has two dimensions: the physical component summary (PCS) and the mental component summary (MCS). RESULTS: Married immigrants had a lower prevalence (3.5%) of major depressive episodes than native women (8.9%) in Taiwan. Variables such as an increased severity of psychosocial impact were the best predictors of a lower PCS and MCS. CONCLUSION: Compared to Taiwanese native married women, fewer married immigrants had stressful life events or depression, and they reported higher QOL. After controlling for putative confounding factors, the married immigrants still had better mental QOL and a lower prevalence rate of depression