48 research outputs found
A pulsed source of continuous variable polarization entanglement
We have experimentally demonstrated polarization entanglement using
continuous variables in an ultra-short pulsed laser system at telecommunication
wavelengths. Exploiting the Kerr-nonlinearity of a glass fibre we generated a
polarization squeezed pulse with S2 the only non-zero Stokes parameter thus S1
and S3 being the conjugate pair. Polarization entanglement was generated by
interference of the polarization squeezed field with a vacuum on a 50:50 beam
splitter. The two resultant beams exhibit strong quantum noise correlations in
S1 and S3. The sum noise signal of S3 was at the respective shot noise level
and the difference noise signal of S1 fell 2.9dB below this value
Assessing the Polarization of a Quantum Field from Stokes Fluctuation
We propose an operational degree of polarization in terms of the variance of
the projected Stokes vector minimized over all the directions of the Poincar\'e
sphere. We examine the properties of this degree and show that some problems
associated with the standard definition are avoided. The new degree of
polarization is experimentally determined using two examples: a bright squeezed
state and a quadrature squeezed vacuum.Comment: 4 pages, 2 figures. Comments welcome
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
Entanglement and squeezing in a two-mode system: theory and experiment
We report on the generation of non separable beams produced via the
interaction of a linearly polarized beam with a cloud of cold cesium atoms
placed in an optical cavity. We convert the squeezing of the two linear
polarization modes into quadrature entanglement and show how to find out the
best entanglement generated in a two-mode system using the inseparability
criterion for continuous variable [Duan et al., Phys. Rev. Lett. 84, 2722
(2000)]. We verify this method experimentally with a direct measurement of the
inseparability using two homodyne detections. We then map this entanglement
into a polarization basis and achieve polarization entanglement.Comment: submitted to J. Opt. B for a Special Issue on Foundations of Quantum
Optic
Simulations and Experiments on Polarisation Squeezing in Optical Fibre
We investigate polarisation squeezing of ultrashort pulses in optical fibre,
over a wide range of input energies and fibre lengths. Comparisons are made
between experimental data and quantum dynamical simulations, to find good
quantitative agreement. The numerical calculations, performed using both
truncated Wigner and exact phase-space methods, include nonlinear and
stochastic Raman effects, through coupling to phonons variables. The
simulations reveal that excess phase noise, such as from depolarising GAWBS,
affects squeezing at low input energies, while Raman effects cause a marked
deterioration of squeezing at higher energies and longer fibre lengths. The
optimum fibre length for maximum squeezing is also calculated.Comment: 19 pages, lots of figure
Polarization squeezing of intense pulses with a fiber Sagnac interferometer
We report on the generation of polarization squeezing of intense, short light
pulses using an asymmetric fiber Sagnac interferometer. The Kerr nonlinearity
of the fiber is exploited to produce independent amplitude squeezed pulses. The
polarization squeezing properties of spatially overlapped amplitude squeezed
and coherent states are discussed. The experimental results for a single
amplitude squeezed beam are compared to the case of two phase-matched,
spatially overlapped amplitude squeezed pulses. For the latter, noise variances
of -3.4dB below shot noise in the S0 and the S1 and of -2.8dB in the S2 Stokes
parameters were observed, which is comparable to the input squeezing magnitude.
Polarization squeezing, that is squeezing relative to a corresponding
polarization minimum uncertainty state, was generated in S1.Comment: v4: 2 small typos corrected v3: misc problems with Tex surmounted -
mysteriously missing text returned to results - vol# for Korolkova et al. PRA
v2: was a spelling change in author lis
Experimental entanglement distillation of mesoscopic quantum states
The distribution of entangled states between distant parties in an optical
network is crucial for the successful implementation of various quantum
communication protocols such as quantum cryptography, teleportation and dense
coding [1-3]. However, owing to the unavoidable loss in any real optical
channel, the distribution of loss-intolerant entangled states is inevitably
inflicted by decoherence, which causes a degradation of the transmitted
entanglement. To combat the decoherence, entanglement distillation, which is
the process of extracting a small set of highly entangled states from a large
set of less entangled states, can be used [4-14]. Here we report on the
mesoscopic distillation of deterministically prepared entangled light pulses
that have undergone non-Gaussian noise. The entangled light pulses [15-17] are
sent through a lossy channel, where the transmission is varying in time
similarly to light propagation in the atmosphere. By employing linear optical
components and global classical communication, the entanglement is
probabilistically increased.Comment: 13 pages, 4 figures. It's the first submitted version to the Nature
Physics. The final version is already published on Nature Physics vol.4,
No.12, 919 - 923 (2008
All-fibre source of amplitude-squeezed light pulses
An all-fibre source of amplitude squeezed solitons utilizing the self-phase
modulation in an asymmetric Sagnac interferometer is experimentally
demonstrated. The asymmetry of the interferometer is passively controlled by an
integrated fibre coupler, allowing for the optimisation of the noise reduction.
We have carefully studied the dependence of the amplitude noise on the
asymmetry and the power launched into the Sagnac interferometer. Qualitatively,
we find good agreement between the experimental results, a semi-classical
theory and earlier numerical calculations [Schmitt etl.al., PRL Vol. 81,
p.2446, (1998)]. The stability and flexibility of this all-fibre source makes
it particularly well suited to applications in quantum information science
Atmospheric Channel Characteristics for Quantum Communication with Continuous Polarization Variables
We investigate the properties of an atmospheric channel for free space
quantum communication with continuous polarization variables. In our
prepare-and-measure setup, coherent polarization states are transmitted through
an atmospheric quantum channel of 100m length on the roof of our institute's
building. The signal states are measured by homodyne detection with the help of
a local oscillator (LO) which propagates in the same spatial mode as the
signal, orthogonally polarized to it. Thus the interference of signal and LO is
excellent and atmospheric fluctuations are autocompensated. The LO also acts as
spatial and spectral filter, which allows for unrestrained daylight operation.
Important characteristics for our system are atmospheric channel influences
that could cause polarization, intensity and position excess noise. Therefore
we study these influences in detail. Our results indicate that the channel is
suitable for our quantum communication system in most weather conditions.Comment: 6 pages, 4 figures, submitted to Applied Physics B following an
invitation for the special issue "Selected Papers Presented at the 2009
Spring Meeting of the Quantum Optics and Photonics Section of the German
Physical Society
Quantum many-body simulations using Gaussian phase-space representations
Phase-space representations are of increasing importance as a viable and
successful means to study exponentially complex quantum many-body systems from
first principles. This review traces the background of these methods, starting
from the early work of Wigner, Glauber and Sudarshan. We focus on modern
phase-space approaches using non-classical phase-space representations. These
lead to the Gaussian representation, which unifies bosonic and fermionic
phase-space. Examples treated include quantum solitons in optical fibers,
colliding Bose-Einstein condensates, and strongly correlated fermions on
lattices.Comment: Short Review (10 pages); Corrected typo in eq (14); Added a few more
reference