scholarly journals Probing Rényi entanglement entropy via randomized measurements

Science ◽  
2019 ◽  
Vol 364 (6437) ◽  
pp. 260-263 ◽  
Author(s):  
Tiff Brydges ◽  
Andreas Elben ◽  
Petar Jurcevic ◽  
Benoît Vermersch ◽  
Christine Maier ◽  
...  
Keyword(s):  
Quantum System ◽  
Entanglement Entropy ◽  
Quantum Systems ◽  
Quantum States ◽  
Many Body ◽  
Trapped Ion ◽  
Statistical Correlations ◽  
Quantum Simulator ◽  
Entanglement Structure ◽  
Arbitrary Quantum

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.

scholarly journals Observation of a prethermal discrete time crystal

Science ◽  
2021 ◽  
Vol 372 (6547) ◽  
pp. 1192-1196
Author(s):  
A. Kyprianidis ◽  
F. Machado ◽  
W. Morong ◽  
P. Becker ◽  
K. S. Collins ◽  
...  
Keyword(s):  
Quantum System ◽  
Discrete Time ◽  
High Frequency ◽  
Statistical Physics ◽  
Time Window ◽  
General Strategy ◽  
Many Body ◽  
Trapped Ion ◽  
Quantum Simulator ◽  
Equilibrium Phases

Extending the framework of statistical physics to the nonequilibrium setting has led to the discovery of previously unidentified phases of matter, often catalyzed by periodic driving. However, preventing the runaway heating that is associated with driving a strongly interacting quantum system remains a challenge in the investigation of these newly discovered phases. In this work, we utilize a trapped-ion quantum simulator to observe the signatures of a nonequilibrium driven phase without disorder—the prethermal discrete time crystal. Here, the heating problem is circumvented not by disorder-induced many-body localization, but rather by high-frequency driving, which leads to an expansive time window where nonequilibrium phases can emerge. Floquet prethermalization is thus presented as a general strategy for creating, stabilizing, and studying intrinsically out-of-equilibrium phases of matter.

THE TRAPPED-ION QUBIT: COHERENT CONTROL IN INFINITE-DIMENSIONAL QUANTUM SYSTEMS

2009 ◽  
Vol 24 (32) ◽  
pp. 2565-2578
Author(s):  
C. RANGAN
Keyword(s):  
Quantum Computing ◽  
Quantum System ◽  
Quantum Control ◽  
Coherent Control ◽  
Quantum Information Processing ◽  
Quantum Systems ◽  
Infinite Dimensional ◽  
Trapped Ion ◽  
Rich Variety ◽  
Control Research

Theories of quantum control have, until recently, made the assumption that the Hilbert space of a quantum system can be truncated to finite dimensions. Such truncations, which can be achieved for most quantum systems via bandwidth restrictions, have enabled the development of a rich variety of quantum control and optimal control schemes. Recent studies in quantum information processing have addressed the control of infinite-dimensional quantum systems such as the quantum states of a trapped-ion. Controllability in an infinite-dimensional quantum system is hard to prove with conventional methods, and infinite-dimensional systems provide unique challenges in designing control fields. In this paper, we will discuss the control of a popular system for quantum computing the trapped-ion qubit. This system, modeled by a spin-half particle coupled to a quantized harmonic oscillator, is an example for a surprisingly rich variety of control problems. We will show how this infinite-dimensional quantum system can be examined via the lens of the Finite Controllability Theorem, two-color STIRAP, the generalized Heisenberg system, etc. These results are important from the viewpoint of developing more efficient quantum control protocols, particularly in quantum computing systems. This work shows how one can expand the scope of quantum control research to beyond that of finite-dimensional quantum systems.

scholarly journals Initialization of quantum simulators by sympathetic cooling

2020 ◽  
Vol 6 (10) ◽  
pp. eaaw9268 ◽  
Author(s):  
Meghana Raghunandan ◽  
Fabian Wolf ◽  
Christian Ospelkaus ◽  
Piet O. Schmidt ◽  
Hendrik Weimer
Keyword(s):  
Energy State ◽  
Hamiltonian Dynamics ◽  
Many Body ◽  
Sympathetic Cooling ◽  
Trapped Ion ◽  
Physical Chemical ◽  
Quantum Simulators ◽  
Auxiliary Particle ◽  
Quantum Simulator ◽  
Chemical And Biological Systems

Simulating computationally intractable many-body problems on a quantum simulator holds great potential to deliver insights into physical, chemical, and biological systems. While the implementation of Hamiltonian dynamics within a quantum simulator has already been demonstrated in many experiments, the problem of initialization of quantum simulators to a suitable quantum state has hitherto remained mostly unsolved. Here, we show that already a single dissipatively driven auxiliary particle can efficiently prepare the quantum simulator in a low-energy state of largely arbitrary Hamiltonians. We demonstrate the scalability of our approach and show that it is robust against unwanted sources of decoherence. While our initialization protocol is largely independent of the physical realization of the simulation device, we provide an implementation example for a trapped ion quantum simulator.

scholarly journals Detecting Entanglement Structure in Continuous Many-Body Quantum Systems

2022 ◽  
Vol 128 (2) ◽  
Author(s):  
Philipp Kunkel ◽  
Maximilian Prüfer ◽  
Stefan Lannig ◽  
Robin Strohmaier ◽  
Martin Gärttner ◽  
...  
Keyword(s):  
Quantum Systems ◽  
Many Body ◽  
Entanglement Structure

scholarly journals Many-Body Localization and the Emergence of Quantum Darwinism

Entropy ◽  
2021 ◽  
Vol 23 (11) ◽  
pp. 1377
Author(s):  
Nicolás Mirkin ◽  
Diego A. Wisniacki
Keyword(s):  
Quantum System ◽  
Entanglement Entropy ◽  
Redundant Information ◽  
Many Body ◽  
Initial State ◽  
Mobility Edge ◽  
Critical Degree ◽  
Quantum Darwinism ◽  
Effect Of Disorder ◽  
The Many

Quantum Darwinism (QD) is the process responsible for the proliferation of redundant information in the environment of a quantum system that is being decohered. This enables independent observers to access separate environmental fragments and reach consensus about the system’s state. In this work, we study the effect of disorder in the emergence of QD and find that a highly disordered environment is greatly beneficial for it. By introducing the notion of lack of redundancy to quantify objectivity, we show that it behaves analogously to the entanglement entropy (EE) of the environmental eigenstate taken as an initial state. This allows us to estimate the many-body mobility edge by means of our Darwinistic measure, implicating the existence of a critical degree of disorder beyond which the degree of objectivity rises the larger the environment is. The latter hints the key role that disorder may play when the environment is of a thermodynamic size. At last, we show that a highly disordered evolution may reduce the spoiling of redundancy in the presence of intra-environment interactions.

scholarly journals Many-Body Dephasing in a Trapped-Ion Quantum Simulator

2020 ◽  
Vol 125 (12) ◽  
Author(s):  
Harvey B. Kaplan ◽  
Lingzhen Guo ◽  
Wen Lin Tan ◽  
Arinjoy De ◽  
Florian Marquardt ◽  
...  
Keyword(s):  
Many Body ◽  
Trapped Ion ◽  
Quantum Simulator

scholarly journals Generation of thermofield double states and critical ground states with a quantum computer

2020 ◽  
Vol 117 (41) ◽  
pp. 25402-25406
Author(s):  
D. Zhu ◽  
S. Johri ◽  
N. M. Linke ◽  
K. A. Landsman ◽  
C. Huerta Alderete ◽  
...  
Keyword(s):  
Ion Trap ◽  
Quantum Computer ◽  
Condensed Matter ◽  
Transverse Field ◽  
Quantum Systems ◽  
Quantum Circuits ◽  
Zero Temperature ◽  
Many Body ◽  
Transverse Field Ising Model ◽  
Entanglement Structure

Finite-temperature phases of many-body quantum systems are fundamental to phenomena ranging from condensed-matter physics to cosmology, yet they are generally difficult to simulate. Using an ion trap quantum computer and protocols motivated by the quantum approximate optimization algorithm (QAOA), we generate nontrivial thermal quantum states of the transverse-field Ising model (TFIM) by preparing thermofield double states at a variety of temperatures. We also prepare the critical state of the TFIM at zero temperature using quantum–classical hybrid optimization. The entanglement structure of thermofield double and critical states plays a key role in the study of black holes, and our work simulates such nontrivial structures on a quantum computer. Moreover, we find that the variational quantum circuits exhibit noise thresholds above which the lowest-depth QAOA circuits provide the best results.

scholarly journals Dynamical manifestations of quantum chaos: correlation hole and bulge

2017 ◽  
Vol 375 (2108) ◽  
pp. 20160434 ◽  
Author(s):  
E. J. Torres-Herrera ◽  
Lea F. Santos
Keyword(s):  
Quantum Chaos ◽  
Entanglement Entropy ◽  
Quantum Systems ◽  
Direct Access ◽  
Many Body ◽  
Initial State ◽  
Von Neumann ◽  
Interacting Systems ◽  
Correlation Hole ◽  
The Many

A main feature of a chaotic quantum system is a rigid spectrum where the levels do not cross. We discuss how the presence of level repulsion in lattice many-body quantum systems can be detected from the analysis of their time evolution instead of their energy spectra. This approach is advantageous to experiments that deal with dynamics, but have limited or no direct access to spectroscopy. Dynamical manifestations of avoided crossings occur at long times. They correspond to a drop, referred to as correlation hole, below the asymptotic value of the survival probability and to a bulge above the saturation point of the von Neumann entanglement entropy and the Shannon information entropy. By contrast, the evolution of these quantities at shorter times reflects the level of delocalization of the initial state, but not necessarily a rigid spectrum. The correlation hole is a general indicator of the integrable–chaos transition in disordered and clean models and as such can be used to detect the transition to the many-body localized phase in disordered interacting systems. This article is part of the themed issue ‘Breakdown of ergodicity in quantum systems: from solids to synthetic matter’.

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