109 research outputs found
Quantum optical non-linearities induced by Rydberg-Rydberg interactions: a perturbative approach
In this article, we theoretically study the quantum statistical properties of
the light transmitted through or reflected from an optical cavity, filled by an
atomic medium with strong optical non-linearity induced by Rydberg-Rydberg van
der Waals interactions. Atoms are driven on a two-photon transition from their
ground state to a Rydberg level via an intermediate state by the combination of
a weak signal field and a strong control beam. By using a perturbative
approach, we get analytic results which remain valid in the regime of weak
feeding fields, even when the intermediate state becomes resonant. Therefore
they allow us to investigate quantitatively new features associated with the
resonant behaviour of the system. We also propose an effective non-linear
three-boson model of the system which, in addition to leading to the same
analytic results as the original problem, sheds light on the physical processes
at work in the system
Teleportation of Nonclassical Wave Packets of light
We report on the experimental quantum teleportation of strongly nonclassical
wave packets of light. To perform this full quantum operation while preserving
and retrieving the fragile non-classicality of the input state, we have
developed a broadband, zero-dispersion teleportation apparatus that works in
conjunction with time-resolved state preparation equipment. Our approach brings
within experimental reach a whole new set of hybrid protocols involving
discrete- and continuous-variable techniques in quantum information processing
for optical sciences
On the distillation and purification of phase-diffused squeezed states
Recently it was discovered that non-Gaussian decoherence processes, such as
phase-diffusion, can be counteracted by purification and distillation protocols
that are solely built on Gaussian operations. Here, we make use of this
experimentally highly accessible regime, and provide a detailed experimental
and theoretical analysis of several strategies for purification/distillation
protocols on phase-diffused squeezed states. Our results provide valuable
information for the optimization of such protocols with respect to the choice
of the trigger quadrature, the trigger threshold value and the probability of
generating a distilled state
Experimental Demonstration of Macroscopic Quantum Coherence in Gaussian States
We witness experimentally the presence of macroscopic coherence in Gaussian
quantum states using a recently proposed criterion (E.G. Cavalcanti and M.
Reid, Phys. Rev. Lett. 97, 170405 (2006)). The macroscopic coherence stems from
interference between macroscopically distinct states in phase space and we
prove experimentally that even the vacuum state contains these features with a
distance in phase space of shot noise units (SNU). For squeezed
states we found macroscopic superpositions with a distance of up to
SNU. The proof of macroscopic quantum coherence was investigated
with respect to squeezing and purity of the states.Comment: 5 pages, 6 figure
A bridge between the single-photon and squeezed-vacuum state
The two modes of the Einstein-Podolsky-Rosen quadrature entangled state
generated by parametric down-conversion interfere on a beam splitter of
variable splitting ratio. Detection of a photon in one of the beam splitter
output channels heralds preparation of a signal state in the other, which is
characterized using homodyne tomography. By controlling the beam splitting
ratio, the signal state can be chosen anywhere between the single-photon and
squeezed state
Demonstrating various quantum effects with two entangled laser beams
We report on the preparation of entangled two mode squeezed states of yet
unseen quality. Based on a measurement of the covariance matrix we found a
violation of the Reid and Drummond EPR-criterion at a value of only 0.36\pm0.03
compared to the threshold of 1. Furthermore, quantum state tomography was used
to extract a single photon Fock state solely based on homodyne detection,
demonstrating the strong quantum features of this pair of laser-beams. The
probability for a single photon in this ensemble measurement exceeded 2/3
- …