314 research outputs found
Angle-resolved photoemission spectroscopy with quantum gas microscopes
Quantum gas microscopes are a promising tool to study interacting quantum
many-body systems and bridge the gap between theoretical models and real
materials. So far they were limited to measurements of instantaneous
correlation functions of the form , even though
extensions to frequency-resolved response functions would provide important information about the elementary
excitations in a many-body system. For example, single particle spectral
functions, which are usually measured using photoemission experiments in
electron systems, contain direct information about fractionalization and the
quasiparticle excitation spectrum. Here, we propose a measurement scheme to
experimentally access the momentum and energy resolved spectral function in a
quantum gas microscope with currently available techniques. As an example for
possible applications, we numerically calculate the spectrum of a single hole
excitation in one-dimensional models with isotropic and anisotropic
antiferromagnetic couplings. A sharp asymmetry in the distribution of spectral
weight appears when a hole is created in an isotropic Heisenberg spin chain.
This effect slowly vanishes for anisotropic spin interactions and disappears
completely in the case of pure Ising interactions. The asymmetry strongly
depends on the total magnetization of the spin chain, which can be tuned in
experiments with quantum gas microscopes. An intuitive picture for the observed
behavior is provided by a slave-fermion mean field theory. The key properties
of the spectra are visible at currently accessible temperatures.Comment: 16+7 pages, 10+2 figure
Decay of super-currents in condensates in optical lattices
In this paper we discuss decay of superfluid currents in boson lattice
systems due to quantum tunneling and thermal activation mechanisms. We derive
asymptotic expressions for the decay rate near the critical current in two
regimes, deep in the superfluid phase and close to the superfluid-Mott
insulator transition. The broadening of the transition at the critical current
due to these decay mechanisms is more pronounced at lower dimensions. We also
find that the crossover temperature below which quantum decay dominates is
experimentally accessible in most cases. Finally, we discuss the dynamics of
the current decay and point out the difference between low and high currents.Comment: Contribution to the special issue of Journal of Superconductivity in
honor of Michael Tinkham's 75th birthda
Quantum Electrodynamic Control of Matter: Cavity-Enhanced Ferroelectric Phase Transition
The light-matter interaction can be utilized to qualitatively alter physical properties of materials. Recent theoretical and experimental studies have explored this possibility of controlling matter by light based on driving many-body systems via strong classical electromagnetic radiation, leading to a time-dependent Hamiltonian for electronic or lattice degrees of freedom. To avoid inevitable heating, pump-probe setups with ultrashort laser pulses have so far been used to study transient light-induced modifications in materials. Here, we pursue yet another direction of controlling quantum matter by modifying quantum fluctuations of its electromagnetic environment. In contrast to earlier proposals on light-enhanced electron-electron interactions, we consider a dipolar quantum many-body system embedded in a cavity composed of metal mirrors and formulate a theoretical framework to manipulate its equilibrium properties on the basis of quantum light-matter interaction. We analyze hybridization of different types of the fundamental excitations, including dipolar phonons, cavity photons, and plasmons in metal mirrors, arising from the cavity confinement in the regime of strong light-matter interaction. This hybridization qualitatively alters the nature of the collective excitations and can be used to selectively control energy-level structures in a wide range of platforms. Most notably, in quantum paraelectrics, we show that the cavity-induced softening of infrared optical phonons enhances the ferroelectric phase in comparison with the bulk materials. Our findings suggest an intriguing possibility of inducing a superradiant-type transition via the light-matter coupling without external pumping. We also discuss possible applications of the cavity-induced modifications in collective excitations to molecular materials and excitonic devices
Photonic quantum transport in a nonlinear optical fiber
We theoretically study the transmission of few-photon quantum fields through a strongly nonlinear optical medium. We develop a general approach to investigate nonequilibrium quantum transport of bosonic fields through a finite-size nonlinear medium and apply it to a recently demonstrated experimental system where cold atoms are loaded in a hollow-core optical fiber. We show that when the interaction between photons is effectively repulsive, the system acts as a single-photon switch. In the case of attractive interaction, the system can exhibit either antibunching or bunching, associated with the resonant excitation of bound states of photons by the input field. These effects can be observed by probing statistics of photons transmitted through the nonlinear fiber
Interferometric probe of paired states
We propose a new method for detecting paired states in either bosonic or
fermionic systems using interference experiments with independent or weakly
coupled low dimensional systems. We demonstrate that our method can be used to
detect both the FFLO and the d-wave paired states of fermions, as well as
quasicondensates of singlet pairs for polar F=1 atoms in two dimensional
systems. We discuss how this method can be used to perform phase-sensitive
determination of the symmetry of the pairing amplitude.Comment: 17 pages, 5 figure
Non-Abelian symmetries and disorder: a broad non-ergodic regime and anomalous thermalization
Symmetries play a central role in single-particle localization. Recent
research focused on many-body localized (MBL) systems, characterized by new
kind of integrability, and by the area-law entanglement of eigenstates. We
investigate the effect of a non-Abelian symmetry on the dynamical
properties of a disordered Heisenberg chain. While symmetry is
inconsistent with the conventional MBL, a new non-ergodic regime is possible.
In this regime, the eigenstates exhibit faster than area-law, but still a
strongly sub-thermal scaling of entanglement entropy. Using exact
diagonalization, we establish that this non-ergodic regime is indeed realized
in the strongly disordered Heisenberg chains. We use real-space renormalization
group (RSRG) to construct approximate excited eigenstates, and show their
accuracy for systems of size up to . As disorder strength is decreased, a
crossover to the thermalizing phase occurs. To establish the ultimate fate of
the non-ergodic regime in the thermodynamic limit, we develop a novel approach
for describing many-body processes that are usually neglected by RSRG,
accessing systems of size . We characterize the resonances that arise
due to such processes, finding that they involve an ever growing number of
spins as the system size is increased. The probability of finding resonances
grows with the system size. Even at strong disorder, we can identify a large
lengthscale beyond which resonances proliferate. Presumably, this eventually
would drive the system to a thermalizing phase. However, the extremely long
thermalization time scales indicate that a broad non-ergodic regime will be
observable experimentally. Our study demonstrates that symmetries control
dynamical properties of disordered, many-body systems. The approach introduced
here provides a versatile tool for describing a broad range of disordered
many-body systems.Comment: 25 pages, 21 figure
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