126 research outputs found
Electronic noise-free measurements of squeezed light
We study the implementation of a correlation measurement technique for the
characterization of squeezed light. We show that the sign of the covariance
coefficient revealed from the time resolved correlation data allow us to
distinguish between squeezed, coherent and thermal states. In contrast to the
traditional method of characterizing squeezed light, involving measurement of
the variation of the difference photocurrent, the correlation measurement
method allows to eliminate the contribution of the electronic noise, which
becomes a crucial issue in experiments with dim sources of squeezed light.Comment: submitted for publicatio
Generation of picosecond pulsed coherent state superpositions
We present the generation of approximated coherent state superpositions -
referred to as Schr\"odinger cat states - by the process of subtracting single
photons from picosecond pulsed squeezed states of light at 830 nm. The squeezed
vacuum states are produced by spontaneous parametric down-conversion (SPDC) in
a periodically poled KTiOPO4 crystal while the single photons are
probabilistically subtracted using a beamsplitter and a single photon detector.
The resulting states are fully characterized with time-resolved homodyne
quantum state tomography. Varying the pump power of the SPDC, we generated
different states which exhibit non-Gaussian behavior.Comment: 17 pages, 8 figures, 3 table
Raman-induced limits to efficient squeezing in optical fibers
We report new experiments on polarization squeezing using ultrashort photonic
pulses in a single pass of a birefringent fiber. We measure what is to our
knowledge a record squeezing of -6.8 +/- 0.3 dB in optical fibers which when
corrected for linear losses is -10.4 +/- 0.8 dB. The measured polarization
squeezing as a function of optical pulse energy, which spans a wide range from
3.5-178.8 pJ, shows a very good agreement with the quantum simulations and for
the first time we see the experimental proof that Raman effects limit and
reduce squeezing at high pulse energy.Comment: 3 pages, 3 figure
Experimental demonstration of a Hadamard gate for coherent state qubits
We discuss and experimentally demonstrate a probabilistic Hadamard gate for
coherent state qubits. The scheme is based on linear optical components,
non-classical resources and the joint projective action of a photon counter and
a homodyne detector. We experimentally characterize the gate for the coherent
states of the computational basis by full tomographic reconstruction of the
transformed output states. Based on the parameters of the experiment we
simulate the fidelity for all coherent state qubits on the Bloch sphere
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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