3,692 research outputs found
Optomechanical position detection enhanced by de-amplification using intracavity squeezing
It has been predicted and experimentally demonstrated that by injecting
squeezed light into an optomechanical device it is possible to enhance the
precision of a position measurement. Here, we present a fundamentally different
approach where the squeezing is created directly inside the cavity by a
nonlinear medium. Counterintuitively, the enhancement of the signal to noise
ratio works by de-amplifying precisely the quadrature that is sensitive to the
mechanical motion without losing quantum information. This enhancement works
for systems with a weak optomechanical coupling and/or strong mechanical
damping. This could allow for larger mechanical bandwidth of quantum limited
detectors based on optomechanical devices. Our approach can be
straightforwardly extended to Quantum Non Demolition (QND) qubit detection.Comment: references added, slight change
Correlation induced resonances in transport through coupled quantum dots
We investigate the effect of local electron correlations on transport through
parallel quantum dots. The linear conductance as a function of gate voltage is
strongly affected by the interplay of the interaction U and quantum
interference. We find a pair of novel correlation induced resonances separated
by an energy scale that depends exponentially on U. The effect is robust
against a small detuning of the dot energy levels and occurs for arbitrary
generic tunnel couplings. It should be observable in experiments on the basis
of presently existing double-dot setups.Comment: 4+ pages, 5 figures included, version accepted for publication in PR
AC-Conductance through an Interacting Quantum Dot
We investigate the linear ac-conductance for tunneling through an arbitrary
interacting quantum dot in the presence of a finite dc-bias. In analogy to the
well-known Meir-Wingreen formula for the dc case, we are able to derive a
general formula for the ac-conductance. It can be expressed entirely in terms
of local correlations on the quantum dot, in the form of a Keldysh block
diagram with four external legs. We illustrate the use of this formula as a
starting point for diagrammatic calculations by considering the ac-conductance
of the noninteracting resonant level model and deriving the result for the
lowest order of electron-phonon coupling. We show how known results are
recovered in the appropriate limits.Comment: 4+ pages, 4 figure
Quantum Cloning of Binary Coherent States - Optimal Transformations and Practical Limits
The notions of qubits and coherent states correspond to different physical
systems and are described by specific formalisms. Qubits are associated with a
two-dimensional Hilbert space and can be illustrated on the Bloch sphere. In
contrast, the underlying Hilbert space of coherent states is
infinite-dimensional and the states are typically represented in phase space.
For the particular case of binary coherent state alphabets these otherwise
distinct formalisms can equally be applied. We capitalize this formal
connection to analyse the properties of optimally cloned binary coherent
states. Several practical and near-optimal cloning schemes are discussed and
the associated fidelities are compared to the performance of the optimal
cloner.Comment: 12 pages, 12 figure
Transverse angular momentum of photons
We develop the quantum theory of transverse angular momentum of light beams.
The theory applies to paraxial and quasi-paraxial photon beams in vacuum, and
reproduces the known results for classical beams when applied to coherent
states of the field. Both the Poynting vector, alias the linear momentum, and
the angular momentum quantum operators of a light beam are calculated including
contributions from first-order transverse derivatives. This permits a correct
description of the energy flow in the beam and the natural emergence of both
the spin and the angular momentum of the photons. We show that for collimated
beams of light, orbital angular momentum operators do not satisfy the standard
commutation rules. Finally, we discuss the application of our theory to some
concrete cases.Comment: 10 pages, 2 figure
Fermionic Mach-Zehnder interferometer subject to a quantum bath
We study fermions in a Mach-Zehnder interferometer, subject to a
quantum-mechanical environment leading to inelastic scattering, decoherence,
renormalization effects, and time-dependent conductance fluctuations. Both the
loss of interference contrast as well as the shot noise are calculated, using
equations of motion and leading order perturbation theory. The full dependence
of the shot-noise correction on setup parameters, voltage, temperature and the
bath spectrum is presented. We find an interesting contribution due to
correlations between the fluctuating renormalized phase shift and the output
current, discuss the limiting behaviours at low and high voltages, and compare
with simpler models of dephasing.Comment: 5 pages, 3 figure
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
Nonlinear and Quantum Optics with Whispering Gallery Resonators
Optical Whispering Gallery Modes (WGMs) derive their name from a famous
acoustic phenomenon of guiding a wave by a curved boundary observed nearly a
century ago. This phenomenon has a rather general nature, equally applicable to
sound and all other waves. It enables resonators of unique properties
attractive both in science and engineering. Very high quality factors of
optical WGM resonators persisting in a wide wavelength range spanning from
radio frequencies to ultraviolet light, their small mode volume, and tunable
in- and out- coupling make them exceptionally efficient for nonlinear optical
applications. Nonlinear optics facilitates interaction of photons with each
other and with other physical systems, and is of prime importance in quantum
optics. In this paper we review numerous applications of WGM resonators in
nonlinear and quantum optics. We outline the current areas of interest,
summarize progress, highlight difficulties, and discuss possible future
development trends in these areas.Comment: This is a review paper with 615 references, submitted to J. Op
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
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