191 research outputs found
Generation Engineering of Heralded Narrowband Colour Entangled States
Efficient heralded generation of entanglement together with its manipulation
is of great importance for quantum communications. In addition, states
generated with bandwidths naturally compatible with atomic transitions allow a
more efficient mapping of light into matter which is an essential requirement
for long distance quantum communications. Here we propose a scheme where the
indistinguishability between two spontaneous four-wave mixing processes is
engineered to herald generation of single-photon frequency-bin entangled
states, i.e., single-photons shared by two distinct frequency modes. We show
that entanglement can be optimised together with the generation probability,
while maintaining absorption negligible. Besides, the scheme illustrated for
cold rubidium atoms is versatile and can be implemented in several other
physical systems
Large Phase-by-Phase Modulations in Atomic Interfaces
Phase-resonant closed-loop optical transitions can be engineered to achieve broadly tunable light phase shifts. Such a novel phase-by-phase control mechanism does not require a cavity and is illustrated here for an atomic interface where a classical light pulse undergoes radian level phase modulations all-optically controllable over a few micron scale. It works even at low intensities and hence may be relevant to new applications of all-optical weak-light signal processing
Heralded noiseless amplification and attenuation of non-gaussian states of light
We examine the behavior of non-Gaussian states of light under the action of
probabilistic noiseless amplification and attenuation. Surprisingly, we find
that the mean field amplitude may decrease in the process of noiseless
amplification -- or increase in the process of noiseless attenuation, a
counterintuitive effect that Gaussian states cannot exhibit. This striking
phenomenon could be tested with experimentally accessible non-Gaussian states,
such as single-photon added coherent states. We propose an experimental scheme,
which is robust with respect to the major experimental imperfections such as
inefficient single-photon detection and imperfect photon addition. In
particular, we argue that the observation of mean field amplification by
noiseless attenuation should be feasible with current technology
A high-fidelity noiseless amplifier for quantum light states
Noise is the price to pay when trying to clone or amplify arbitrary quantum
states. The quantum noise associated to linear phase-insensitive amplifiers can
only be avoided by relaxing the requirement of a deterministic operation. Here
we present the experimental realization of a probabilistic noiseless linear
amplifier that is able to amplify coherent states at the highest level of
effective gain and final state fidelity ever reached. Based on a sequence of
photon addition and subtraction, and characterized by a significant
amplification and low distortions, this high-fidelity amplification scheme may
become an essential tool for quantum communications and metrology, by enhancing
the discrimination between partially overlapping quantum states or by
recovering the information transmitted over lossy channels.Comment: 5 pages, 4 figure
Nonclassicality Quasiprobability of Single-Photon Added Thermal States
We report the experimental reconstruction of a nonclassicality
quasiprobability for a single-photon added thermal state. This quantity has
significant negativities, which is necessary and sufficient for the
nonclassicality of the quantum state. Our method presents several advantages
compared to the reconstruction of the P function, since the nonclassicality
filters used in this case can regularize the quasiprobabilities as well as
their statistical uncertainties. A-priori assumptions about the quantum state
are therefore not necessary. We also demonstrate that, in principle, our method
is not limited by small quantum efficiencies.Comment: 6 pages, 4 figure
Tomographic test of Bell's inequality for a time-delocalized single photon
Time-domain balanced homodyne detection is performed on two well-separated
temporal modes sharing a single photon. The reconstructed density matrix of the
two-mode system is used to prove and quantify its entangled nature, while the
Wigner function is employed for an innovative tomographic test of Bell's
inequality based on the theoretical proposal by Banaszek and Wodkiewicz [Phys.
Rev. Lett. 82, 2009 (1999)]. Provided some auxiliary assumptions are made, a
clear violation of Banaszek-Bell's inequality is found.Comment: 7 pages, 3 figures: revised version with additional material;
accepetd for publication in Phys. Rev.
Experimental determination of a nonclassical Glauber-Sudarshan P function
A quantum state is nonclassical if its Glauber-Sudarshan P function fails to
be interpreted as a probability density. This quantity is often highly
singular, so that its reconstruction is a demanding task. Here we present the
experimental determination of a well-behaved P function showing negativities
for a single-photon-added thermal state. This is a direct visualization of the
original definition of nonclassicality. The method can be useful under
conditions for which many other signatures of nonclassicality would not
persist.Comment: 4 pages, 4 figure
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