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 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 Ergodic and localized regions in quantum spin glasses on the Bethe lattice

2017 ◽  
Vol 375 (2108) ◽  
pp. 20160424 ◽  
Author(s):  
G. Mossi ◽  
A. Scardicchio
Keyword(s):  
Spin Glass ◽  
Spin Glasses ◽  
Quantum Dynamics ◽  
Bethe Lattice ◽  
Transverse Field ◽  
Quantum Systems ◽  
Quantum Spin ◽  
Many Body ◽  
Spin Glass Phase ◽  
Ising Spin

By considering the quantum dynamics of a transverse-field Ising spin glass on the Bethe lattice, we find the existence of a many-body localized (MBL) region at small transverse field and low temperature. The region is located within the thermodynamic spin glass phase. Accordingly, we conjecture that quantum dynamics inside the glassy region is split into a small MBL region and a large delocalized (but not necessarily ergodic) region. This has implications for the analysis of the performance of quantum adiabatic algorithms. This article is part of the themed issue ‘Breakdown of ergodicity in quantum systems: from solids to synthetic matter’.

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 Testing a Quantum Annealer as a Quantum Thermal Sampler

2021 ◽  
Vol 2 (2) ◽  
pp. 1-20
Author(s):  
Zoe Gonzalez Izquierdo ◽  
Itay Hen ◽  
Tameem Albash
Keyword(s):  
Thermal Properties ◽  
Quantum Monte Carlo ◽  
Thermal State ◽  
Transverse Field ◽  
Quantum Annealing ◽  
Many Body ◽  
Expectation Values ◽  
Many Body Systems ◽  
Transverse Field Ising Model ◽  
Open Question

Motivated by recent experiments in which specific thermal properties of complex many-body systems were successfully reproduced on a commercially available quantum annealer, we examine the extent to which quantum annealing hardware can reliably sample from the thermal state in a specific basis associated with a target quantum Hamiltonian. We address this question by studying the diagonal thermal properties of the canonical one-dimensional transverse-field Ising model on a D-Wave 2000Q quantum annealing processor. We find that the quantum processor fails to produce the correct expectation values predicted by Quantum Monte Carlo. Comparing to master equation simulations, we find that this discrepancy is best explained by how the measurements at finite transverse fields are enacted on the device. Specifically, measurements at finite transverse field require the system to be quenched from the target Hamiltonian to a Hamiltonian with negligible transverse field, and this quench is too slow. The limitations imposed by such hardware make it an unlikely candidate for thermal sampling, and it remains an open question what thermal expectation values can be robustly estimated in general for arbitrary quantum many-body systems.

scholarly journals Closed hierarchy of Heisenberg equations in integrable models with Onsager algebra

2021 ◽  
Vol 10 (6) ◽  
Author(s):  
Oleg Lychkovskiy
Keyword(s):  
Transverse Field ◽  
Integrable Models ◽  
Small Subset ◽  
Many Body ◽  
Analytical Treatment ◽  
System A ◽  
Onsager Algebra ◽  
Heisenberg Equations ◽  
Transverse Field Ising Model ◽  
Large Hierarchy

Dynamics of a quantum system can be described by coupled Heisenberg equations. In a generic many-body system these equations form an exponentially large hierarchy that is intractable without approximations. In contrast, in an integrable system a small subset of operators can be closed with respect to commutation with the Hamiltonian. As a result, the Heisenberg equations for these operators can form a smaller closed system amenable to an analytical treatment. We demonstrate that this indeed happens in a class of integrable models where the Hamiltonian is an element of the Onsager algebra. We explicitly solve the system of Heisenberg equations for operators from this algebra. Two specific models are considered as examples: the transverse field Ising model and the superintegrable chiral 3-state Potts model.

scholarly journals Quantum Computing in the NISQ era and beyond

Quantum ◽  
2018 ◽  
Vol 2 ◽  
pp. 79 ◽  
Author(s):  
John Preskill
Keyword(s):  
Quantum Computing ◽  
Quantum Physics ◽  
Quantum Computer ◽  
Fault Tolerant ◽  
Quantum Circuits ◽  
Quantum Gates ◽  
Quantum Computers ◽  
Many Body ◽  
Significant Step ◽  
Near Future

Noisy Intermediate-Scale Quantum (NISQ) technology will be available in the near future. Quantum computers with 50-100 qubits may be able to perform tasks which surpass the capabilities of today's classical digital computers, but noise in quantum gates will limit the size of quantum circuits that can be executed reliably. NISQ devices will be useful tools for exploring many-body quantum physics, and may have other useful applications, but the 100-qubit quantum computer will not change the world right away - we should regard it as a significant step toward the more powerful quantum technologies of the future. Quantum technologists should continue to strive for more accurate quantum gates and, eventually, fully fault-tolerant quantum computing.

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