37 research outputs found
Quantum homodyne tomography of a two-photon Fock state
We present a continuous-variable experimental analysis of a two-photon Fock
state of free-propagating light. This state is obtained from a pulsed
non-degenerate parametric amplifier, which produces two intensity-correlated
twin beams. Counting two photons in one beam projects the other beam in the
desired two-photon Fock state, which is analyzed by using a pulsed homodyne
detection. The Wigner function of the measured state is clearly negative. We
developed a detailed analytic model which allows a fast and efficient analysis
of the experimental results.Comment: 4 pages, 6 figures Revised version : corrected typo and reference
Photonique quantique / Quantum photonics
Recherche Page web : https://www.college-de-france.fr/site/young-team-incubator/Presentation__3.htm
Increasing entanglement between Gaussian states by coherent photon subtraction
We experimentally demonstrate that the entanglement between Gaussian
entangled states can be increased by non-Gaussian operations. Coherent
subtraction of single photons from Gaussian quadrature-entangled light pulses,
created by a non-degenerate parametric amplifier, produces delocalized states
with negative Wigner functions and complex structures, more entangled than the
initial states in terms of negativity. The experimental results are in very
good agreement with the theoretical predictions
Dispersive optical nonlinearities in an EIT-Rydberg medium
We investigate dispersive optical nonlinearities that arise from Rydberg
excitation blockade in cold Rydberg gases. We consider a two-photon transition
scheme and study the non-linear response to a weak optical probe in presence of
a strong control beam. For very low probe fields, the dominant nonlinearities
are of the third order and they can be exactly evaluated in a steady state
regime. In a more general case, the change in average atomic populations and
coherences due to Rydberg interactions can be characterized by properly defined
scaling parameters, which are generally complex numbers but in certain
situations take the usual meaning of the number of atoms in a blockade sphere.
They can be used in a simple "universal scaling" formula to determine the
dispersive optical nonlinearity of the medium. We also develop a novel
technique to account for the Rydberg interaction effects, by simplifying the
treatment of nonlocal interaction terms, the so-called collisional integrals.
We find algebraic relations that only involve two-body correlations, which can
be solved numerically. All average populations and coherences are then obtained
straightforwardly.Comment: 9 pages, 4 figure
Generating non-Gaussian states using collisions between Rydberg polaritons
We investigate theoretically the deterministic generation of quantum states
with negative Wigner functions, by using giant non-linearities due to
collisional interactions between Rydberg polaritons. The state resulting from
the polariton interactions may be transferred with high fidelity into a
photonic state, which can be analyzed using homodyne detection followed by
quantum tomography. Besides generating highly non-classical states of the
light, this method can also provide a very sensitive probe for the physics of
the collisions involving Rydberg states.Comment: 5 pages, 3 figure
Controlling the quantum state of a single photon emitted from a single polariton
We investigate in detail the optimal conditions for a high fidelity transfer
from a single-polariton state to a single-photon state and subsequent homodyne
detection of the single photon. We assume that, using various possible
techniques, the single polariton has initially been stored as a spin-wave
grating in a cloud of cold atoms inside a low-finesse cavity. This state is
then transferred to a single-photon optical pulse using an auxiliary beam. We
optimize the retrieval efficiency and determine the mode of the local
oscillator that maximizes the homodyne efficiency of such a photon. We find
that both efficiencies can have values close to one in a large region of
experimental parameters.Comment: 10 pages, 8 figure