7 research outputs found
Absence of Thermalization in Finite Isolated Interacting Floquet Systems
Conventional wisdom suggests that the long time behavior of isolated
interacting periodically driven (Floquet) systems is a featureless maximal
entropy state characterized by an infinite temperature. Efforts to thwart this
uninteresting fixed point include adding sufficient disorder to realize a
Floquet many-body localized phase or working in a narrow region of drive
frequencies to achieve glassy non-thermal behavior at long time. Here we show
that in clean systems the Floquet eigenstates can exhibit non-thermal behavior
due to finite system size. We consider a one-dimensional system of spinless
fermions with nearest-neighbor interactions where the interaction term is
driven. Interestingly, even with no static component of the interaction, the
quasienergy spectrum contains gaps and a significant fraction of the Floquet
eigenstates, at all quasienergies, have non-thermal average doublon densities.
We show that this non-thermal behavior arises due to emergent integrability at
large interaction strength and discuss how the integrability breaks down with
power-law dependence on system size.Comment: 10+8 pages, 13 figure
Controlled Population of Floquet-Bloch States via Coupling to Bose and Fermi Baths
External driving is emerging as a promising tool for exploring new phases in
quantum systems. The intrinsically non-equilibrium states that result, however,
are challenging to describe and control. We study the steady states of a
periodically driven one-dimensional electronic system, including the effects of
radiative recombination, electron-phonon interactions, and the coupling to an
external fermionic reservoir. Using a kinetic equation for the populations of
the Floquet eigenstates, we show that the steady-state distribution can be
controlled using the momentum and energy relaxation pathways provided by the
coupling to phonon and Fermi reservoirs. In order to utilize the latter, we
propose to couple the system and reservoir via an energy filter which
suppresses photon-assisted tunneling. Importantly, coupling to these reservoirs
yields a steady state resembling a band insulator in the Floquet basis. The
system exhibits incompressible behavior, while hosting a small density of
excitations. We discuss transport signatures, and describe the regimes where
insulating behavior is obtained. Our results give promise for realizing Floquet
topological insulators.Comment: 24 pages, 7 figures; with appendice
Fault-tolerant Post-Selection for Low Overhead Magic State Preparation
We introduce a framework for fault-tolerant post-selection (FTPS) of
fault-tolerant codes and channels -- such as those based on surface-codes --
using soft-information metrics based on visible syndrome and erasure
information. We introduce several metrics for ranking configurations of
syndromes and erasures. In particular, we introduce the \emph{logical gap} (and
variants thereof) as a powerful soft-information metric for predicting logical
error rates of fault-tolerant channels based on topological error-correcting
codes. The logical gap is roughly the unsigned weight difference between
inequivalent logical corrections and is adaptable to any tailored noise model
or decoder. We deploy this framework to prepare high-quality surface code magic
states with low overhead under a model of independent and identically
distributed (\emph{i.i.d.}) Pauli and erasure errors. Post-selection strategies
based on the logical gap can suppress the encoding error rate of a magic state
preparation channel to the level of the physical error rate with low overhead.
For example, when operating at the bulk threshold of the corresponding
surface code, an overall reduction of the encoding error rate by a factor of
is achievable with a relative overhead factor of (approximately
times less than that of simple syndrome-counting rules). We analyze a
schematic buffer architecture for implementing post-selection rules on magic
state factories in the context of magic state distillation. The FTPS framework
can be utilized for mitigating errors in more general fault-tolerant logical
channels.Comment: 10+7 pages, 13 figures, comments welcom
Steady state of interacting Floquet insulators
Floquet engineering offers tantalizing opportunities for controlling the dynamics of quantum many-body systems and realizing new nonequilibrium phases of matter. However, this approach faces a major challenge: generic interacting Floquet systems absorb energy from the drive, leading to uncontrolled heating which washes away the sought-after behavior. How to achieve and control a nontrivial nonequilibrium steady state is therefore of crucial importance. In this work, we study the dynamics of an interacting one-dimensional periodically driven electronic system coupled to a phonon heat bath. Using the Floquet-Boltzmann equation (FBE) we show that the electronic populations of the Floquet eigenstates can be controlled by the dissipation. We find the regime in which the steady state features an insulator-like filling of the Floquet bands, with a low density of additional excitations. Furthermore, we develop a simple rate equation model for the steady state excitation density that captures the behavior obtained from the numerical solution of the FBE over a wide range of parameters
Steady states of interacting Floquet insulators
Floquet engineering offers tantalizing opportunities for controlling the dynamics of quantum many-body systems and realizing new nonequilibrium phases of matter. However, this approach faces a major challenge: generic interacting Floquet systems absorb energy from the drive, leading to uncontrolled heating which washes away the sought-after behavior. How to achieve and control a nontrivial nonequilibrium steady state is therefore of crucial importance. In this work, we study the dynamics of an interacting one-dimensional periodically driven electronic system coupled to a phonon heat bath. Using the Floquet-Boltzmann equation (FBE) we show that the electronic populations of the Floquet eigenstates can be controlled by the dissipation. We find the regime in which the steady state features an insulator-like filling of the Floquet bands, with a low density of additional excitations. Furthermore, we develop a simple rate equation model for the steady state excitation density that captures the behavior obtained from the numerical solution of the FBE over a wide range of parameters