2,533 research outputs found
Full photon statistics of a light beam transmitted through an optomechanical system
In this paper, we study the full statistics of photons transmitted through an
optical cavity coupled to nanomechanical motion. We analyze the entire temporal
evolution of the photon correlations, the Fano factor, and the effects of
strong laser driving, all of which show pronounced features connected to the
mechanical backaction. In the regime of single-photon strong coupling, this
allows us to predict a transition from sub-Poissonian to super-Poissonian
statistics for larger observation time intervals. Furthermore, we predict
cascades of transmitted photons triggered by multi-photon transitions. In this
regime, we observe Fano factors that are drastically enhanced due to the
mechanical motion.Comment: 8 pages, 7 figure
Reduction of Guided Acoustic Wave Brillouin Scattering in Photonic Crystal Fibers
Guided Acoustic Wave Brillouin Scattering (GAWBS) generates phase and
polarization noise of light propagating in glass fibers. This excess noise
affects the performance of various experiments operating at the quantum noise
limit. We experimentally demonstrate the reduction of GAWBS noise in a photonic
crystal fiber in a broad frequency range using cavity sound dynamics. We
compare the noise spectrum to the one of a standard fiber and observe a 10-fold
noise reduction in the frequency range up to 200 MHz. Based on our measurement
results as well as on numerical simulations we establish a model for the
reduction of GAWBS noise in photonic crystal fibers.Comment: 4 pages, 7 figures; added numerical simulations, added reference
Naturally-phasematched second harmonic generation in a whispering gallery mode resonator
We demonstrate for the first time natural phase matching for optical
frequency doubling in a high-Q whispering gallery mode resonator made of
Lithium Niobate. A conversion efficiency of 9% is achieved at 30 micro Watt
in-coupled continuous wave pump power. The observed saturation pump power of
3.2 mW is almost two orders of magnitude lower than the state-of-the-art. This
suggests an application of our frequency doubler as a source of non-classical
light requiring only a low-power pump, which easily can be quantum noise
limited. Our theoretical analysis of the three-wave mixing in a whispering
gallery mode resonator provides the relative conversion efficiencies for
frequency doubling in various modes
Spin Relaxation in a Quantum Dot due to Nyquist Noise
We calculate electron and nuclear spin relaxation rates in a quantum dot due
to the combined action of Nyquist noise and electron-nuclei hyperfine or
spin-orbit interactions. The relaxation rate is linear in the resistance of the
gate circuit and, in the case of spin-orbit interaction, it depends essentially
on the orientations of both the static magnetic field and the fluctuating
electric field, as well as on the ratio between Rashba and Dresselhaus
interaction constants. We provide numerical estimates of the relaxation rate
for typical system parameters, compare our results with other, previously
discussed mechanisms, and show that the Nyquist mechanism can have an
appreciable effect for experimentally relevant systems.Comment: v2: New discussion of arbitrary gate setups (1 new figure), more
Comments on experiments; 6 pages, 4 figure
Decoherence of a particle in a ring
We consider a particle coupled to a dissipative environment and derive a
perturbative formula for the dephasing rate based on the purity of the reduced
probability matrix. We apply this formula to the problem of a particle on a
ring, that interacts with a dirty metal environment. At low but finite
temperatures we find a dephasing rate , and identify dephasing
lengths for large and for small rings. These findings shed light on recent
Monte Carlo data regarding the effective mass of the particle. At zero
temperature we find that spatial fluctuations suppress the possibility of
having a power law decay of coherence.Comment: 5 pages, 1 figure, proofed version to be published in EP
Electron-nuclei spin relaxation through phonon-assisted hyperfine interaction in a quantum dot
We investigate the inelastic spin-flip rate for electrons in a quantum dot
due to their contact hyperfine interaction with lattice nuclei. In contrast to
other works, we obtain a spin-phonon coupling term from this interaction by
taking directly into account the motion of nuclei in the vibrating lattice. In
the calculation of the transition rate the interference of first and second
orders of perturbation theory turns out to be essential. It leads to a
suppression of relaxation at long phonon wavelengths, when the confining
potential moves together with the nuclei embedded in the lattice. At higher
frequencies (or for a fixed confining potential), the zero-temperature rate is
proportional to the frequency of the emitted phonon. We address both the
transition between Zeeman sublevels of a single electron ground state as well
as the triplet-singlet transition, and we provide numerical estimates for
realistic system parameters. The mechanism turns out to be less efficient than
electron-nuclei spin relaxation involving piezoelectric electron-phonon
coupling in a GaAs quantum dot.Comment: 8 pages, 1 figur
Dephasing of a particle in a dissipative environment
The motion of a particle in a ring of length L is influenced by a dirty metal
environment whose fluctuations are characterized by a short correlation
distance . We analyze the induced decoherence process, and compare
the results with those obtained in the opposing Caldeira-Leggett limit (). A proper definition of the dephasing factor that does not depend on a
vague semiclassical picture is employed. Some recent Monte-Carlo results about
the effect of finite temperatures on "mass renormalization" in this system are
illuminated.Comment: 18 pages, 2 figures, some textual improvements, to be published in
JP
Quantum reconstruction of an intense polarization squeezed optical state
We perform a reconstruction of the polarization sector of the density matrix
of an intense polarization squeezed beam starting from a complete set of Stokes
measurements. By using an appropriate quasidistribution, we map this onto the
Poincare space providing a full quantum mechanical characterization of the
measured polarization state.Comment: 4 pages, 4 eps color figure
Separation quality of a geometric ratchet
We consider an experimentally relevant model of a geometric ratchet in which
particles undergo drift and diffusive motion in a two-dimensional periodic
array of obstacles, and which is used for the continuous separation of
particles subject to different forces. The macroscopic drift velocity and
diffusion tensor are calculated by a Monte-Carlo simulation and by a
master-equation approach, using the correponding microscopic quantities and the
shape of the obstacles as input. We define a measure of separation quality and
investigate its dependence on the applied force and the shape of the obstacles
Continuous variable entanglement distillation of Non-Gaussian Mixed States
Many different quantum information communication protocols such as
teleportation, dense coding and entanglement based quantum key distribution are
based on the faithful transmission of entanglement between distant location in
an optical network. The distribution of entanglement in such a network is
however hampered by loss and noise that is inherent in all practical quantum
channels. Thus, to enable faithful transmission one must resort to the protocol
of entanglement distillation. In this paper we present a detailed theoretical
analysis and an experimental realization of continuous variable entanglement
distillation in a channel that is inflicted by different kinds of non-Gaussian
noise. The continuous variable entangled states are generated by exploiting the
third order non-linearity in optical fibers, and the states are sent through a
free-space laboratory channel in which the losses are altered to simulate a
free-space atmospheric channel with varying losses. We use linear optical
components, homodyne measurements and classical communication to distill the
entanglement, and we find that by using this method the entanglement can be
probabilistically increased for some specific non-Gaussian noise channels
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