307 research outputs found
Probing magnetic order in ultracold lattice gases
A forthcoming challenge in ultracold lattice gases is the simulation of
quantum magnetism. That involves both the preparation of the lattice atomic gas
in the desired spin state and the probing of the state. Here we demonstrate how
a probing scheme based on atom-light interfaces gives access to the order
parameters of nontrivial quantum magnetic phases, allowing us to characterize
univocally strongly correlated magnetic systems produced in ultracold gases.
This method, which is also nondemolishing, yields spatially resolved spin
correlations and can be applied to bosons or fermions. As a proof of principle,
we apply this method to detect the complete phase diagram displayed by a chain
of (rotationally invariant) spin-1 bosons.Comment: published versio
Heating in Nanophotonic Traps for Cold Atoms
Laser-cooled atoms that are trapped and optically interfaced with light in
nanophotonic waveguides are a powerful platform for fundamental research in
quantum optics as well as for applications in quantum communication and quantum
information processing. Ever since the first realization of such a hybrid
quantum nanophotonic, heating rates of the atomic motion observed in various
experimental settings have typically been exceeding those in comparable
free-space optical microtraps by about three orders of magnitude. This
excessive heating is a roadblock for the implementation of certain protocols
and devices. Its origin has so far remained elusive and, at the typical
atom-surface separations of less than an optical wavelength encountered in
nanophotonic traps, numerous effects may potentially contribute to atom
heating. Here, we theoretically describe the effect of mechanical vibrations of
waveguides on guided light fields and provide a general theory of
particle-phonon interaction in nanophotonic traps. We test our theory by
applying it to the case of laser-cooled cesium atoms in nanofiber-based
two-color optical traps. We find excellent quantitative agreement between the
predicted heating rates and experimentally measured values. Our theory predicts
that, in this setting, the dominant heating process stems from the
optomechanical coupling of the optically trapped atoms to the continuum of
thermally occupied flexural mechanical modes of the waveguide structure. Beyond
unraveling the long-standing riddle of excessive heating in nanofiber-based
atom traps, we also study the dependence of the heating rates on the relevant
system parameters. Our findings allow us to propose several strategies for
minimizing the heating. Finally, our findings are also highly relevant for
optomechanics experiments with dielectric nanoparticles that are optically
trapped close to nanophotonic waveguides.Comment: Published version. 35 pages (including appendices), 7 figures, 18
tables, and 3 pages of supplemental materia
Optomechanics assisted with a qubit: From dissipative state preparation to many-body physics
We propose and analyze nonlinear optomechanical protocols that can be
implemented by adding a single atom to an optomechanical cavity. In particular,
we show how to engineer the environment in order to dissipatively prepare the
mechanical oscillator in a superposition of Fock states with fidelity close to
one. Furthermore, we discuss how a single atom in a cavity with several
mechanical oscillators can be exploited to realize nonlinear many-body physics
by stroboscopically driving the mechanical oscillators. We show how to prepare
non-classical many-body states by either applying coherent protocols or
engineering dissipation. The analysis of the protocols is carried out using a
perturbation theory for degenerate Liouvillians and numerical tools. Our
results apply to other systems where a qubit is coupled to a mechanical
oscillator via a bosonic mode, e.g., in cavity quantum electromechanics
Quantum Ratchets for Quantum Communication with Optical Superlattices
We propose to use a quantum ratchet to transport quantum information in a
chain of atoms trapped in an optical superlattice. The quantum ratchet is
created by a continuous modulation of the optical superlattice which is
periodic in time and in space. Though there is zero average force acting on the
atoms, we show that indeed the ratchet effect permits atoms on even and odd
sites to move along opposite directions. By loading the optical lattice with
two-level bosonic atoms, this scheme permits to perfectly transport a qubit or
entangled state imprinted in one or more atoms to any desired position in the
lattice. From the quantum computation point of view, the transport is achieved
by a smooth concatenation of perfect swap gates. We analyze setups with
noninteracting and interacting particles and in the latter case we use the
tools of optimal control to design optimal modulations. We also discuss the
feasibility of this method in current experiments.Comment: Published version, 9 pages, 5 figure
Master equation approach to optomechanics with arbitrary dielectrics
We present a master equation describing the interaction of light with
dielectric objects of arbitrary sizes and shapes. The quantum motion of the
object, the quantum nature of light, as well as scattering processes to all
orders in perturbation theory are taken into account. This formalism extends
the standard master equation approach to the case where interactions among
different modes of the environment are considered. It yields a genuine quantum
description, including a renormalization of the couplings and decoherence
terms. We apply this approach to analyze cavity cooling of the center-of-mass
mode of large spheres. Furthermore, we derive an expression for the
steady-state phonon numbers without relying on resolved-sideband or bad-cavity
approximations.Comment: 17 pages, 5 figure
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