Estimation of Electrostatic Interaction Energies on a Trapped-Ion Quantum Computer.

We present the first hardware implementation of electrostatic interaction energies by using a trapped-ion quantum computer. As test system for our computation, we focus on the reduction of NO to N2O catalyzed by a nitric oxide reductase (NOR). The quantum computer is used to generate an approximate ground state within the NOR active space. To efficiently measure the necessary one-particle density matrices, we incorporate fermionic basis rotations into the quantum circuit without extending the circuit length, laying the groundwork for further efficient measurement routines using factorizations. Measurements in the computational basis are then used as inputs for computing the electrostatic interaction energies on a classical computer. Our experimental results strongly agree with classical noise-less simulations of the same circuits, finding electrostatic interaction energies within chemical accuracy despite hardware noise. This work shows that algorithms tailored to specific observables of interest, such as interaction energies, may require significantly fewer quantum resources than individual ground state energies would require in the straightforward supermolecular approach.

Quantum Information Scrambling in a Trapped-Ion Quantum Simulator with Tunable Range Interactions.

In ergodic many-body quantum systems, locally encoded quantum information becomes, in the course of time evolution, inaccessible to local measurements. This concept of "scrambling" is currently of intense research interest, entailing a deep understanding of many-body dynamics such as the processes of chaos and thermalization. Here, we present first experimental demonstrations of quantum information scrambling on a 10-qubit trapped-ion quantum simulator representing a tunable long-range interacting spin system, by estimating out-of-time ordered correlators (OTOCs) through randomized measurements. We also analyze the role of decoherence in our system by comparing our measurements to numerical simulations and by measuring Rényi entanglement entropies.

Cross-Platform Verification of Intermediate Scale Quantum Devices.

We describe a protocol for cross-platform verification of quantum simulators and quantum computers. We show how to measure directly the overlap Tr[ρ_{1}ρ_{2}] and the purities Tr[ρ_{1,2}^{2}], and thus a fidelity of two, possibly mixed, quantum states ρ_{1} and ρ_{2} prepared in separate experimental platforms. We require only local measurements in randomized product bases, which are communicated classically. As a proof of principle, we present the measurement of experiment-theory fidelities for entangled 10-qubit quantum states in a trapped ion quantum simulator.

Probing Rényi entanglement entropy via randomized measurements.

Entanglement is a key feature of many-body quantum systems. Measuring the entropy of different partitions of a quantum system provides a way to probe its entanglement structure. Here, we present and experimentally demonstrate a protocol for measuring the second-order Rényi entropy based on statistical correlations between randomized measurements. Our experiments, carried out with a trapped-ion quantum simulator with partition sizes of up to 10 qubits, prove the overall coherent character of the system dynamics and reveal the growth of entanglement between its parts, in both the absence and presence of disorder. Our protocol represents a universal tool for probing and characterizing engineered quantum systems in the laboratory, which is applicable to arbitrary quantum states of up to several tens of qubits.

Environment-Assisted Quantum Transport in a 10-qubit Network.

The way in which energy is transported through an interacting system governs fundamental properties in nature such as thermal and electric conductivity or phase changes. Remarkably, environmental noise can enhance the transport, an effect known as environment-assisted quantum transport (ENAQT). In this Letter, we study ENAQT in a network of coupled spins subject to engineered static disorder and temporally varying dephasing noise. The interacting spin network is realized in a chain of trapped atomic ions, and energy transport is represented by the transfer of electronic excitation between ions. With increasing noise strength, we observe a crossover from coherent dynamics and Anderson localization to ENAQT and finally a suppression of transport due to the quantum Zeno effect. We find that in the regime where ENAQT is most effective, the transport is mainly diffusive, displaying coherences only at very short times. Further, we show that dephasing characterized by non-Markovian noise can maintain coherences longer than white noise dephasing, with a strong influence of the spectral structure on the transport efficiency. Our approach represents a controlled and scalable way to investigate quantum transport in many-body networks under static disorder and dynamic noise.

Adjustment disorders, posttraumatic stress disorder, and depressive disorders in old age: findings from a community survey.

Based on a new psychopathological model of adjustment disorders (AJD), we propose that AJDs are particular forms of stress response syndromes, in which intrusions, avoidance of reminders, and failure to adapt are core symptoms. We aim to demonstrate that these AJD symptom groups constitute a disorder that is distinct from posttraumatic stress disorder (PTSD), complicated grief disorder, major depressive disorder, and subsyndromal depression, by estimating their prevalence and comorbidities. A representative sample of elderly persons from Zurich, aged 65 to 96 years, was assessed by standardized interviews or self-report questionnaires. Index events for AJD were indicated by 52% of the sample set, with a 2.3% current prevalence of AJD. Prevalence rates for other disorders were 0.7% PTSD, 4.2% subsyndromal PTSD, 4.2% complicated grief disorder, 2.3% major depressive disorder, and 9.3% subsyndromal depression. The comorbidity rate for AJD and other Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition disorders is 46%, and that between AJD and subsyndromal disorders is 38%. Use of mental health care for AJD is low. This article concludes that the new concept of AJD constitutes a meaningful psychopathological model and thus warrants a place in standardized psychiatric taxonomies. Although this study was restricted to a sample of the elderly, it provides evidence regarding AJD prevalence, comorbidity, and associated health care use, all of which indicate its utility.