17 research outputs found
Exponential Lifetime Improvement in Topological Quantum Memories
We propose a simple yet efficient mechanism for passive error correction in
topological quantum memories. Our scheme relies on driven-dissipative ancilla
systems which couple to local excitations (anyons) and make them "sink" in
energy, with no required interaction among ancillae or anyons. Through this
process, anyons created by some thermal environment end up trapped in potential
"trenches" that they themselves generate, which can be interpreted as a "memory
foam" for anyons. This self-trapping mechanism provides an energy barrier for
anyon propagation, and removes entropy from the memory by favoring anyon
recombination over anyon separation (responsible for memory errors). We
demonstrate that our scheme leads to an exponential increase of the
memory-coherence time with system size , up to an upper bound
which can increase exponentially with , where is
the temperature and is some energy scale defined by potential
trenches. This results in a double exponential increase of the memory time with
, which greatly improves over the Arrhenius (single-exponential)
scaling found in typical quantum memories.Comment: 18 pages including appendices; 8 figure
Controlled parity switch of persistent currents in quantum ladders
We investigate the behavior of persistent currents for a fixed number of
noninteracting fermions in a periodic quantum ladder threaded by Aharonov-Bohm
and transverse magnetic fluxes and . We show that the coupling
between ladder legs provides a way to effectively change the ground-state
fermion-number parity, by varying . Specifically, we demonstrate that
varying by (one flux quantum) leads to an apparent fermion-number
parity switch. We find that persistent currents exhibit a robust
periodicity as a function of , despite the fact that leads to modifications of order of the energy spectrum, where
is the number of sites in each ladder leg. We show that these parity-switch and
periodicity effects are robust with respect to temperature and disorder,
and outline potential physical realizations using cold atomic gases and, for
bosonic analogs of the effects, photonic lattices.Comment: 5 pages, 4 figures + Supplemental Materia
Topological Polaritons
The interaction between light and matter can give rise to novel topological
states. This principle was recently exemplified in Floquet topological
insulators, where \emph{classical} light was used to induce a topological
electronic band structure. Here, in contrast, we show that mixing \emph{single}
photons with excitons can result in new topological polaritonic states --- or
"topolaritons". Taken separately, the underlying photons and excitons are
topologically trivial. Combined appropriately, however, they give rise to
non-trivial polaritonic bands with chiral edge modes allowing for
unidirectional polariton propagation. The main ingredient in our construction
is an exciton-photon coupling with a phase that winds in momentum space. We
demonstrate how this winding emerges from spin-orbit coupling in the electronic
system and an applied Zeeman field. We discuss the requirements for obtaining a
sizable topological gap in the polariton spectrum, and propose practical ways
to realize topolaritons in semiconductor quantum wells and monolayer transition
metal dichalcogenides.Comment: For Supplementary Information and Video see source files; v3: updated
to published versio
Topological Polaritons and Excitons in Garden Variety Systems
Topological polaritons (aka topolaritons) present a new frontier for
topological behavior in solid-state systems. They combine light and matter,
which allows to probe and manipulate them in a variety of ways. They can also
be made strongly interacting, due to their excitonic component. So far,
however, their realization was deemed rather challenging. Here we present a
scheme which allows to realize topolaritons in garden variety zinc-blende
quantum wells. Our proposal requires a moderate magnetic field and a potential
landscape which can be implemented, e.g., via surface acoustic waves or
patterning. We identify indirect excitons in double quantum wells as a
particularly appealing alternative for topological states in exciton-based
systems. Indirect excitons are robust and long lived (with lifetimes up to
milliseconds), and, therefore, provide a flexible platform for the realization,
probing, and utilization of topological coupled light-matter states.Comment: 6 pages, 4 figures; v2: improved figures and text, with added details
regarding achievable topological gap
Chiral Bogoliubons in Nonlinear Bosonic Systems
We present a versatile scheme for creating topological Bogoliubov excitations
in weakly interacting bosonic systems. Our proposal relies on a background
stationary field that consists of a Kagome vortex lattice, which breaks
time-reversal symmetry and induces a periodic potential for Bogoliubov
excitations. In analogy to the Haldane model, no external magnetic field or net
flux is required. We construct a generic model based on the two-dimensional
(2D) nonlinear Schr\"odinger equation and demonstrate the emergence of
topological gaps crossed by chiral Bogoliubov edge modes. Our scheme can be
realized in a wide variety of physical systems ranging from nonlinear optical
systems to exciton-polariton condensates.Comment: 6 pages, 3 figures; with Supplemental Material (5 pages; in source
Exponential Lifetime Improvement in Topological Quantum Memories
We propose a simple yet efficient mechanism for passive error correction in topological quantum memories. Our scheme relies on driven-dissipative ancilla systems which couple to local excitations (anyons) and make them “sink” in energy, with no required interaction among ancillae or anyons. Through this process, anyons created by some thermal environment end up trapped in potential “trenches” that they themselves generate, which can be interpreted as a “memory foam” for anyons. This self-trapping mechanism provides an energy barrier for anyon propagation and removes entropy from the memory by favoring anyon recombination over anyon separation (responsible for memory errors). We demonstrate that our scheme leads to an exponential increase of the memory-coherence time with system size L, up to an upper bound L_(max), which can increase exponentially with Δ/T, where T is the temperature and Δ is some energy scale defined by potential trenches. This results in a double exponential increase of the memory time with Δ/T, which greatly improves over the Arrhenius (single-exponential) scaling found in typical quantum memories
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
Chiral Bogoliubov excitations in nonlinear bosonic systems
We present a versatile scheme for creating topological Bogoliubov excitations in weakly interacting bosonic systems. Our proposal relies on a background stationary field that consists of a Kagome vortex lattice, which breaks time-reversal symmetry and induces a periodic potential for Bogoliubov excitations. In analogy to the Haldane model, no external magnetic field or net flux is required. We construct a generic model based on the two-dimensional (2D) nonlinear Schrödinger equation and demonstrate the emergence of topological gaps crossed by chiral Bogoliubov edge modes. Our scheme can be realized in a wide variety of physical systems ranging from nonlinear optical systems to exciton-polariton condensates
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