32 research outputs found
Four-photon scattering in birefringent fibers
Four-photon scattering in nonlinear waveguides is an important physical
process that allows photon-pair generation in well defined guided modes, with
high rate and reasonably low noise. Most of the experiments to date used the
scalar four-photon scattering process in which the pump photons and the
scattered photons have the same polarization. In birefringent waveguides,
vectorial four-photon scattering is also allowed: these vectorial scattering
processes involve photons with different polarizations. In this article, the
theory of four-photon scattering in nonlinear, birefringent, and dispersive
fibers is developed in the framework of the quantum theory of light. The work
focusses on the spectral properties and quantum correlations (including
entanglement) of photon-pairs generated in high-birefringence and
low-birefringence fibers.Comment: 12 pages, 5 figures, submitted to Phys. Rev.
Vector modulation instability induced by vacuum fluctuations in highly birefringent fibers in the anomalous dispersion regime
We report a detailed experimental study of vector modulation instability in
highly birefringent optical fibers in the anomalous dispersion regime. We prove
that the observed instability is mainly induced by vacuum fluctuations. The
detuning of the spectral peaks agrees with linear perturbation analysis. The
exact shape of the spectrum is well reproduced by numerical integration of
stochastic nonlinear Schrodinger equations describing quantum propagation.Comment: 11 pages, 4 figures, to be published in Optics Letter
Experimental quantum key distribution over highly noisy channels
Error filtration is a method for encoding the quantum state of a single
particle into a higher dimensional Hilbert space in such a way that it becomes
less sensitive to phase noise. We experimentally demonstrate this method by
distributing a secret key over an optical fiber whose noise level otherwise
precludes secure quantum key distribution. By filtering out the phase noise, a
bit error rate of 15.3% +/- 0.1%, which is beyond the security limit, can be
reduced to 10.6% +/- 0.1%, thereby guaranteeing the cryptographic security.Comment: 4 pages, 2 figure
Provably Secure Experimental Quantum Bit-String Generation
Coin tossing is a cryptographic task in which two parties who do not trust
each other aim to generate a common random bit. Using classical communication
this is impossible, but non trivial coin tossing is possible using quantum
communication. Here we consider the case when the parties do not want to toss a
single coin, but many. This is called bit string generation. We report the
experimental generation of strings of coins which are provably more random than
achievable using classical communication. The experiment is based on the ``plug
and play'' scheme developed for quantum cryptography, and therefore well suited
for long distance quantum communication.Comment: 4 pages, 3 figures. Submitted to Phys. Rev. Lett. A complete security
analysis for the experiment is given in quant-ph/040812
Coherent imaging of extended objects
When used with coherent light, optical imaging systems, even
diffraction-limited, are inherently unable to reproduce both the amplitude and
the phase of a two-dimensional field distribution because their impulse
response function varies slowly from point to point (a property known as
non-isoplanatism). For sufficiently small objects, this usually results in a
phase distortion and has no impact on the measured intensity. Here, we show
that the intensity distribution can also be dramatically distorted when objects
of large extension or of special shapes are imaged. We illustrate the problem
using two simple examples: the pinhole camera and the aberration-free thin
lens. The effects predicted by our theorical analysis are also confirmed by
experimental observations.Comment: 10 pages, 9 figures, submitted to Optics Communication
Scalar and vector modulation instabilities induced by vacuum fluctuations in fibers: numerical study
We study scalar and vector modulation instabilities induced by the vacuum
fluctuations in birefringent optical fibers. To this end, stochastic coupled
nonlinear Schrodinger equations are derived. The stochastic model is equivalent
to the quantum field operators equations and allow for dispersion,
nonlinearity, and arbitrary level of birefringence. Numerical integration of
the stochastic equations is compared to analytical formulas in the case of
scalar modulation instability and non depleted pump approximation. The effect
of classical noise and its competition with vacuum fluctuations for inducing
modulation instability is also addressed.Comment: 33 pages, 5 figure
Spatial Light Modulators for the Manipulation of Individual Atoms
We propose a novel dipole trapping scheme using spatial light modulators
(SLM) for the manipulation of individual atoms. The scheme uses a high
numerical aperture microscope to map the intensity distribution of a SLM onto a
cloud of cold atoms. The regions of high intensity act as optical dipole force
traps. With a SLM fast enough to modify the trapping potential in real time,
this technique is well suited for the controlled addressing and manipulation of
arbitrarily selected atoms.Comment: 9 pages, 5 figure
Cross-polarized photon-pair generation and bi-chromatically pumped optical parametric oscillation on a chip
Nonlinear optical processes are one of the most important tools in modern optics with a broad spectrum of applications in, for example, frequency conversion, spectroscopy, signal processing and quantum optics. For practical and ultimately widespread implementation, on-chip devices compatible with electronic integrated circuit technology offer great advantages in terms of low cost, small footprint, high performance and low energy consumption. While many on-chip key components have been realized, to date polarization has not been fully exploited as a degree of freedom for integrated nonlinear devices. In particular, frequency conversion based on orthogonally polarized beams has not yet been demonstrated on chip. Here we show frequency mixing between orthogonal polarization modes in a compact integrated microring resonator and demonstrate a bi-chromatically pumped optical parametric oscillator. Operating the device above and below threshold, we directly generate orthogonally polarized beams, as well as photon pairs, respectively, that can find applications, for example, in optical communication and quantum optics