%0 Journal Article %D 2021 %T Observation of a prethermal discrete time crystal %A Antonis Kyprianidis %A Francisco Machado %A William Morong %A Patrick Becker %A Kate S. Collins %A Dominic V. Else %A Lei Feng %A Paul W. Hess %A Chetan Nayak %A Guido Pagano %A Norman Y. Yao %A Christopher Monroe %X

The conventional framework for defining and understanding phases of matter requires thermodynamic equilibrium. Extensions to non-equilibrium systems have led to surprising insights into the nature of many-body thermalization and the discovery of novel phases of matter, often catalyzed by driving the system periodically. The inherent heating from such Floquet drives can be tempered by including strong disorder in the system, but this can also mask the generality of non-equilibrium phases. In this work, we utilize a trapped-ion quantum simulator to observe signatures of a non-equilibrium driven phase without disorder: the prethermal discrete time crystal (PDTC). Here, many-body heating is suppressed not by disorder-induced many-body localization, but instead via high-frequency driving, leading to an expansive time window where non-equilibrium phases can emerge. We observe a number of key features that distinguish the PDTC from its many-body-localized disordered counterpart, such as the drive-frequency control of its lifetime and the dependence of time-crystalline order on the energy density of the initial state. Floquet prethermalization is thus presented as a general strategy for creating, stabilizing and studying intrinsically out-of-equilibrium phases of matter.

%8 2/2/2021 %G eng %U https://arxiv.org/abs/2102.01695 %0 Journal Article %J Phys. Rev. Lett. %D 2020 %T Many-Body Dephasing in a Trapped-Ion Quantum Simulator %A Harvey B. Kaplan %A Lingzhen Guo %A Wen Lin Tan %A Arinjoy De %A Florian Marquardt %A Guido Pagano %A Christopher Monroe %X

How a closed interacting quantum many-body system relaxes and dephases as a function of time is a fundamental question in thermodynamic and statistical physics. In this work, we observe and analyse the persistent temporal fluctuations after a quantum quench of a tunable long-range interacting transverse-field Ising Hamiltonian realized with a trapped-ion quantum simulator. We measure the temporal fluctuations in the average magnetization of a finite-size system of spin-1/2 particles and observe the experimental evidence for the theoretically predicted regime of many-body dephasing. We experiment in a regime where the properties of the system are closely related to the integrable Hamiltonian with global spin-spin coupling, which enables analytical predictions even for the long-time non-integrable dynamics. We find that the measured fluctuations are exponentially suppressed with increasing system size, consistent with theoretical predictions. 

%B Phys. Rev. Lett. %V 125 %8 8/24/2020 %G eng %U https://arxiv.org/abs/2001.02477 %N 120605 %R https://doi.org/10.1103/PhysRevLett.125.120605 %0 Journal Article %J Physical Review Research %D 2020 %T Towards analog quantum simulations of lattice gauge theories with trapped ions %A Zohreh Davoudi %A Mohammad Hafezi %A Christopher Monroe %A Guido Pagano %A Alireza Seif %A Andrew Shaw %X

Gauge field theories play a central role in modern physics and are at the heart of the Standard Model of elementary particles and interactions. Despite significant progress in applying classical computational techniques to simulate gauge theories, it has remained a challenging task to compute the real-time dynamics of systems described by gauge theories. An exciting possibility that has been explored in recent years is the use of highly-controlled quantum systems to simulate, in an analog fashion, properties of a target system whose dynamics are difficult to compute. Engineered atom-laser interactions in a linear crystal of trapped ions offer a wide range of possibilities for quantum simulations of complex physical systems. Here, we devise practical proposals for analog simulation of simple lattice gauge theories whose dynamics can be mapped onto spin-spin interactions in any dimension. These include 1+1D quantum electrodynamics, 2+1D Abelian Chern-Simons theory coupled to fermions, and 2+1D pure Z2 gauge theory. The scheme proposed, along with the optimization protocol applied, will have applications beyond the examples presented in this work, and will enable scalable analog quantum simulation of Heisenberg spin models in any number of dimensions and with arbitrary interaction strengths.

%B Physical Review Research %V 2 %8 4/8/2020 %G eng %U https://arxiv.org/abs/1908.03210 %N 023015 %R https://doi.org/10.1103/PhysRevResearch.2.023015 %0 Journal Article %J Phys. Rev. Lett. %D 2019 %T Confined Dynamics in Long-Range Interacting Quantum Spin Chains %A Fangli Liu %A Rex Lundgren %A Paraj Titum %A Guido Pagano %A Jiehang Zhang %A Christopher Monroe %A Alexey V. Gorshkov %X

We study the quasiparticle excitation and quench dynamics of the one-dimensional transverse-field Ising model with power-law (1/rα) interactions. We find that long-range interactions give rise to a confining potential, which couples pairs of domain walls (kinks) into bound quasiparticles, analogous to mesonic bound states in high-energy physics. We show that these bound states have dramatic consequences for the non-equilibrium dynamics following a global quantum quench, such as suppressed spreading of quantum information and oscillations of order parameters. The masses of these bound states can be read out from the Fourier spectrum of these oscillating order parameters. We then use a two-kink model to qualitatively explain the phenomenon of long-range-interaction-induced confinement. The masses of the bound states predicted by this model are in good quantitative agreement with exact diagonalization results. Moreover, we illustrate that these bound states lead to weak thermalization of local observables for initial states with energy near the bottom of the many-body energy spectrum. Our work is readily applicable to current trapped-ion experiments.

%B Phys. Rev. Lett. %V 122 %8 04/17/2019 %G eng %U https://arxiv.org/abs/1810.02365 %N 150601 %R https://doi.org/10.1103/PhysRevLett.122.150601 %0 Journal Article %J Phys. Rev. A %D 2019 %T Heisenberg-Scaling Measurement Protocol for Analytic Functions with Quantum Sensor Networks %A Kevin Qian %A Zachary Eldredge %A Wenchao Ge %A Guido Pagano %A Christopher Monroe %A James V. Porto %A Alexey V. Gorshkov %X

We generalize past work on quantum sensor networks to show that, for d input parameters, entanglement can yield a factor O(d) improvement in mean squared error when estimating an analytic function of these parameters. We show that the protocol is optimal for qubit sensors, and conjecture an optimal protocol for photons passing through interferometers. Our protocol is also applicable to continuous variable measurements, such as one quadrature of a field operator. We outline a few potential applications, including calibration of laser operations in trapped ion quantum computing.

%B Phys. Rev. A %V 100 %8 10/7/2019 %G eng %U https://arxiv.org/abs/1901.09042 %N 042304 %R https://doi.org/10.1103/PhysRevA.100.042304