1,087 research outputs found
Light-matter interactions in multi-element resonators
We investigate structural resonances in multi-element optical resonators and
provide a roadmap for the description of the interaction of single extended
cavity modes with quantum emitters or mechanical resonators. Using a first
principle approach based on the transfer matrix formalism we analyze, both
numerically and analytically, the static and dynamical properties of three- and
four-mirror cavities. We investigate in particular conditions under which the
confinement of the field in specific subcavities allows for enhanced
light-matter interactions in the context of cavity quantum electrodynamics and
cavity optomechanics
Atomic entanglement generation with reduced decoherence via four-wave mixing
In most proposals for the generation of entanglement in large ensembles of
atoms via projective measurements, the interaction with the vacuum is
responsible for both the generation of the signal that is detected and the spin
depolarization or decoherence. In consequence, one has to usually work in a
regime where the information aquisition via detection is sufficiently slow
(weak measurement regime) such as not to strongly disturb the system. We
propose here a four-wave mixing scheme where, owing to the pumping of the
atomic system into a dark state, the polarization of the ensemble is not
critically affected by spontaneous emission, thus allowing one to work in a
strong measurement regime
Strong coupling and long-range collective interactions in optomechanical arrays
We investigate the collective optomechanics of an ensemble of scatterers
inside a Fabry-Perot resonator and identify an optimized configuration where
the ensemble is transmissive, in contrast with the usual reflective
optomechanics approach. In this configuration, the optomechanical coupling of a
specific collective mechanical mode can be several orders of magnitude larger
than the single-element case, and long-range interactions can be generated
between the different elements since light permeates throughout the array. This
new regime should realistically allow for achieving strong single-photon
optomechanical coupling with massive resonators, realizing hybrid quantum
interfaces, and exploiting collective long-range interactions in arrays of
atoms or mechanical oscillators.Comment: 11 pages, 12 figure
Prospects of reinforcement learning for the simultaneous damping of many mechanical modes
We apply adaptive feedback for the partial refrigeration of a mechanical
resonator, i.e. with the aim to simultaneously cool the classical thermal
motion of more than one vibrational degree of freedom. The feedback is obtained
from a neural network parametrized policy trained via a reinforcement learning
strategy to choose the correct sequence of actions from a finite set in order
to simultaneously reduce the energy of many modes of vibration. The actions are
realized either as optical modulations of the spring constants in the so-called
quadratic optomechanical coupling regime or as radiation pressure induced
momentum kicks in the linear coupling regime. As a proof of principle we
numerically illustrate efficient simultaneous cooling of four independent modes
with an overall strong reduction of the total system temperature.Comment: Machine learning in Optomechanics: coolin
Protected state enhanced quantum metrology with interacting two-level ensembles
Ramsey interferometry is routinely used in quantum metrology for the most
sensitive measurements of optical clock frequencies. Spontaneous decay to the
electromagnetic vacuum ultimately limits the interrogation time and thus sets a
lower bound to the optimal frequency sensitivity. In dense ensembles of
two-level systems the presence of collective effects such as superradiance and
dipole-dipole interaction tends to decrease the sensitivity even further. We
show that by a redesign of the Ramsey-pulse sequence to include different
rotations of individual spins that effectively fold the collective state onto a
state close to the center of the Bloch sphere, partial protection from
collective decoherence and dephasing is possible. This allows a significant
improvement in the sensitivity limit of a clock transition detection scheme
over the conventional Ramsey method for interacting systems and even for
non-interacting decaying atoms
A realization of a quasi-random walk for atoms in time-dependent optical potentials
We consider the time dependent dynamics of an atom in a two-color pumped
cavity, longitudinally through a side mirror and transversally via direct
driving of the atomic dipole. The beating of the two driving frequencies leads
to a time dependent effective optical potential that forces the atom into a
non-trivial motion, strongly resembling a discrete random walk behavior between
lattice sites. We provide both numerical and analytical analysis of such a
quasi-random walk behavior
Cooperative spin decoherence and population transfer
An ensemble of multilevel atoms is a good candidate for a quantum information
storage device. The information is encrypted in the collective ground state
atomic coherence, which, in the absence of external excitation, is decoupled
from the vacuum and therefore decoherence free. However, in the process of
manipulation of atoms with light pulses (writing, reading), one inadvertently
introduces a coupling to the environment, i.e. a source of decoherence. The
dissipation process is often treated as an independent process for each atom in
the ensemble, an approach which fails at large atomic optical depths where
cooperative effects must be taken into account. In this paper, the cooperative
behavior of spin decoherence and population transfer for a system of two,
driven multilevel-atoms is studied. Not surprisingly, an enhancement in the
decoherence rate is found, when the atoms are separated by a distance that is
small compared to an optical wavelength; however, it is found that this rate
increases even further for somewhat larger separations for atoms aligned along
the direction of the driving field's propagation vector. A treatment of the
cooperative modification of optical pumping rates and an effect of polarization
swapping between atoms is also discussed, lending additional insight into the
origin of the collective decay
Transmissive optomechanical platforms with engineered spatial defects
We investigate the optomechanical photon-phonon coupling of a single light
mode propagating through an array of vibrating mechanical elements. As recently
shown for the particular case of a periodic array of membranes embedded in a
high-finesse optical cavity [A. Xuereb, C. Genes and A. Dantan, Phys. Rev.
Lett., \textbf{109}, 223601, (2012)], the intracavity linear optomechanical
coupling can be considerably enhanced over the single element value in the
so-called \textit{transmissive regime}, where for motionless membranes the
whole system is transparent to light. Here, we extend these investigations to
quasi-periodic arrays in the presence of engineered spatial defects in the
membrane positions. In particular we show that the localization of light modes
induced by the defect combined with the access of the transmissive regime
window can lead to additional enhancement of the strength of both linear and
quadratic optomechanical couplings
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