86 research outputs found
Reversible Quantum Interface for Tunable Single-sideband Modulation
Using Electromagnetically Induced Transparency (EIT) in a Cesium vapor, we
demonstrate experimentally that the quantum state of a light beam can be mapped
into the long lived Zeeman coherences of an atomic ground state. Two
non-commuting variables carried by light are simultaneously stored and
subsequentely read-out, with no noise added. We compare the case where a
tunable single sideband is stored independently of the other one to the case
where the two symmetrical sidebands are stored using the same EIT transparency
window.Comment: 4 pages, 6 figure
Direct measurement of decoherence for entanglement between a photon and stored atomic excitation
Violations of a Bell inequality are reported for an experiment where one of
two entangled qubits is stored in a collective atomic memory for a user-defined
time delay. The atomic qubit is found to preserve the violation of a Bell
inequality for storage times up to 21 microseconds, 700 times longer than the
duration of the excitation pulse that creates the entanglement. To address the
question of the security of entanglement-based cryptography implemented with
this system, an investigation of the Bell violation as a function of the
cross-correlation between the generated nonclassical fields is reported, with
saturation of the violation close to the maximum value allowed by quantum
mechanics.Comment: 4 pages, 3 figures. Minor changes. Published versio
Demonstration of Einstein-Podolsky-Rosen Steering Using Hybrid Continuous- and Discrete-Variable Entanglement of Light
Einstein-Podolsky-Rosen steering is known to be a key resource for one-sided
device-independent quantum information protocols. Here we demonstrate steering
using hybrid entanglement between continuous- and discrete-variable optical
qubits. To this end, we report on suitable steering inequalities and detail the
implementation and requirements for this demonstration. Steering is
experimentally certified by observing a violation by more than 5 standard
deviations. Our results illustrate the potential of optical hybrid entanglement
for applications in heterogeneous quantum networks that would interconnect
disparate physical platforms and encodings
Quantum memory for light via stimulated off-resonant Raman process: beyond the three-level Lambda-scheme approximation
We consider a quantum memory scheme based on the conversion of a signal pulse
into a long-lived spin coherence via stimulated off-resonant Raman process. For
a storing medium consisting of alkali atoms, we have calculated the
Autler-Townes resonance structure created by a strong control field. By taking
into account the upper hyperfine states of the D1 optical transition, we show
important deviations from the predictions of the usual three-level
Lambda-scheme approximation and we demonstrate an enhancement of the process
for particular detunings of the control. We estimate the memory efficiency one
can obtain using this configuration.Comment: 8 pages, 6 figure
Electromagnetically induced transparency in inhomogeneously broadened Lambda-transition with multiple excited levels
Electromagnetically induced transparency (EIT) has mainly been modelled for
three-level systems. In particular, a considerable interest has been dedicated
to the Lambda-configuration, with two ground states and one excited state.
However, in the alkali-metal atoms, which are commonly used, hyperfine
interaction in the excited state introduces several levels which simultaneously
participate in the scattering process. When the Doppler broadening is
comparable with the hyperfine splitting in the upper state, the three-level
Lambda model does not reproduce the experimental results. Here we theoretically
investigate the EIT in a hot vapor of alkali-metal atoms and demonstrate that
it can be strongly reduced due to the presence of multiple excited levels.
Given this model, we also show that a well-designed optical pumping enables to
significantly recover the transparency
Strong relative intensity squeezing by 4-wave mixing in Rb vapor
We have measured -3.5 dB (-8.1 dB corrected for losses) relative intensity
squeezing between the probe and conjugate beams generated by stimulated,
nondegenerate four-wave mixing in hot rubidium vapor. Unlike early observations
of squeezing in atomic vapors based on saturation of a two-level system, our
scheme uses a resonant nonlinearity based on ground-state coherences in a
three-level system. Since this scheme produces narrowband, squeezed light near
an atomic resonance it is of interest for experiments involving cold atoms or
atomic ensembles.Comment: Submitted to Optics Letter
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
- …