336 research outputs found
Super-bunched bright squeezed vacuum state
In this paper we experimentally study the statistical properties of a bright
squeezed vacuum state containing up to 10^13 photons per mode (10 uJ per
pulse), produced via high gain parametric down conversion (PDC). The effects of
bunching and superbunching of photons were observed for a single mode PDC
radiation by second-order intensity correlation function measurements with
analog detectors.Comment: 4 pages, 3 figures, submitted to Optics Letter
Quantum uniqueness
In the classical world one can construct two identical systems which have
identical behavior and give identical measurement results. We show this to be
impossible in the quantum domain. We prove that after the same quantum
measurement two different quantum systems cannot yield always identical
results, provided the possible measurement results belong to a non orthogonal
set. This is interpreted as quantum uniqueness - a quantum feature which has no
classical analog. Its tight relation with objective randomness of quantum
measurements is discussed.Comment: Presented at 4th Feynman festival, June 22-26, 2009, in Olomouc,
Czech Republic
Universal optical amplification without nonlinearity
We propose and experimentally realize a new scheme for universal
phase-insensitive optical amplification. The presented scheme relies only on
linear optics and homodyne detection, thus circumventing the need for nonlinear
interaction between a pump field and the signal field. The amplifier
demonstrates near optimal quantum noise limited performance for a wide range of
amplification factors.Comment: 5 pages, 4 figure
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
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
Feasibility of free space quantum key distribution with coherent polarization states
We demonstrate for the first time the feasibility of free space quantum key
distribution with continuous variables under real atmospheric conditions. More
specifically, we transmit coherent polarization states over a 100m free space
channel on the roof of our institute's building. In our scheme, signal and
local oscillator are combined in a single spatial mode which auto-compensates
atmospheric fluctuations and results in an excellent interference. Furthermore,
the local oscillator acts as spatial and spectral filter thus allowing
unrestrained daylight operation.Comment: 12 pages, 8 figures, extensions in sections 2, 3.1, 3.2 and 4. This
is an author-created, un-copyedited version of an article accepted for
publication in New Journal of Physics (Special Issue on Quantum Cryptography:
Theory and Practice). IOP Publishing Ltd is not responsible for any errors or
omissions in this version of the manuscript or any version derived from i
Nonlocal restoration of two-mode squeezing in the presence of strong optical loss
We present the experimental realization of a theoretical effect discovered by
Olivares and Paris, in which a pair of entangled optical beams undergoing
independent losses can see nonlocal correlations restored by the use of a
nonlocal resource correlating the losses. Twin optical beams created in an
entangled Einstein-Podolsky-Rosen (EPR) state by an optical parametric
oscillator above threshold were subjected to 50% loss from beamsplitters in
their paths. The resulting severe degradation of the signature quantum
correlations observed between the two beams was then suppressed when another,
independent EPR state impinged upon the other input ports of the beamsplitters,
effectively entangling the losses inflicted to the initial EPR state. The
additional EPR beam pair was classically coherent with the primary one but had
no quantum correlations with it. This result may find applications as a quantum
tap for entanglement.Comment: 14 pages, 6 figures, submitted for publicatio
Generation of Continuous Variable Einstein-Podolsky-Rosen Entanglement via the Kerr Nonlinearity in an Optical Fibre
We report on the generation of a continuous variable Einstein-Podolsky-Rosen
(EPR) entanglement using an optical fibre interferometer. The Kerr nonlinearity
in the fibre is exploited for the generation of two independent squeezed beams.
These interfere at a beam splitter and EPR entanglement is obtained between the
output beams. The correlation of the amplitude (phase) quadratures are measured
to be 4.0+-0.2 (4.0+-0.4) dB below the quantum noise limit. The sum criterion
for these squeezing variances 0.80+-0.03 < 2 verifies the nonseparability of
the state. The product of the inferred uncertainties for one beam 0.64+-0.08 is
well below the EPR limit of unity.Comment: RevTeX, 4 pages, 3 figures, to be published in Phys. Rev. Let
Witnessing effective entanglement in a continuous variable prepare&measure setup and application to a QKD scheme using postselection
We report an experimental demonstration of effective entanglement in a
prepare&measure type of quantum key distribution protocol. Coherent
polarization states and heterodyne measurement to characterize the transmitted
quantum states are used, thus enabling us to reconstruct directly their
Q-function. By evaluating the excess noise of the states, we experimentally
demonstrate that they fulfill a non-separability criterion previously presented
by Rigas et al. [J. Rigas, O. G\"uhne, N. L\"utkenhaus, Phys. Rev. A 73, 012341
(2006)]. For a restricted eavesdropping scenario we predict key rates using
postselection of the heterodyne measurement results.Comment: 12 pages, 12 figures, 2 table
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