1,059 research outputs found
Evolution of the N ion Jaynes-Cummings model beyond the standard rotating wave approximation
A unitary transformation of the N-ion Jaynes-Cummings hamiltonian is
proposed. It is shown that any approximate expression of the evolution operator
associated with the transformed hamiltonian retains its validity independently
from the intensity of the external driving field. In particular, using the
rotating wave approximation, one obtains a solution for the N-ion
Jaynes-Cummings model which improves the standard rotating wave approximation
solution.Comment: Presented at the Wigner Centennial Conference (Pecs, Hungary, July
2002) (to appear on Journal of Optics B, provisionally scheduled for June
2003 issue
Experimental pre-assessing entanglement in Gaussian states mixing
We suggest and demonstrate a method to assess entanglement generation schemes
based on mixing of Gaussian states at a beam splitter (BS). Our method is based
on the fidelity criterion and represents a tool to analyze the effect of losses
and noise before the BS in both symmetric and asymmetric channels with and
without thermal effects. More generally, our scheme allows one to pre-assess
entanglement resources and to optimize the design of BS-based schemes for the
generation of continuous variable entanglement.Comment: 10 pages, 15 figure
Transmittivity measurements by means of squeezed vacuum light
A method for measuring the transmittivity of optical samples by using
squeezed--vacuum radiation is illustrated. A squeezed vacuum field generated by
a below--threshold optical parametric oscillator is propagated through a
nondispersive medium and detected by a homodyne apparatus. The variance of the
detected quadrature is used for measuring the transmittivity. With this method
it is drastically reduced the number of photons passing through the sample
during the measurement interval. The results of some tests are reported.Comment: 14 pages, 8 figure
Tunable non-Gaussian resources for continuous-variable quantum technologies
We introduce and discuss a set of tunable two-mode states of
continuous-variable systems, as well as an efficient scheme for their
experimental generation. This novel class of tunable entangled resources is
defined by a general ansatz depending on two experimentally adjustable
parameters. It is very ample and flexible as it encompasses Gaussian as well as
non-Gaussian states. The latter include, among others, known states such as
squeezed number states and de-Gaussified photon-added and photon-subtracted
squeezed states, the latter being the most efficient non-Gaussian resources
currently available in the laboratory. Moreover, it contains the classes of
squeezed Bell states and even more general non-Gaussian resources that can be
optimized according to the specific quantum technological task that needs to be
realized. The proposed experimental scheme exploits linear optical operations
and photon detections performed on a pair of uncorrelated two--mode Gaussian
squeezed states. The desired non-Gaussian state is then realized via ancillary
squeezing and conditioning. Two independent, freely tunable experimental
parameters can be exploited to generate different states and to optimize the
performance in implementing a given quantum protocol. As a concrete instance,
we analyze in detail the performance of different states considered as
resources for the realization of quantum teleportation in realistic conditions.
For the fidelity of teleportation of an unknown coherent state, we show that
the resources associated to the optimized parameters outperform, in a
significant range of experimental values, both Gaussian twin beams and
photon-subtracted squeezed states.Comment: 13 pages, 7 figure
Continuous-Variable Entangled States of Light carrying Orbital Angular Momentum
The orbital angular momentum of light, unlike spin, is an
infinite-dimensional discrete variable and may hence offer enhanced
performances for encoding, transmitting, and processing information in the
quantum regime. Hitherto, this degree of freedom of light has been studied
mainly in the context of quantum states with definite number of photons. On the
other hand, field-quadrature continuous-variable quantum states of light allow
implementing many important quantum protocols not accessible with photon-number
states. Here, we present the first generation and complete experimental
characterization of a bipartite continuous-variable Gaussian entangled state
endowed with non-zero orbital angular momentum. A q-plate is used to transfer
the continuous-variable entanglement initially generated in polarization into
orbital angular momentum. We then apply a reconfigurable homodyne detector to
various combinations of orbital angular momentum modes in order to reconstruct
the entire quantum-state covariance matrix, by directly measuring the
fluctuations of quadrature operators. Our work is a step towards generating
multipartite continuous-variable entanglement in a single optical beam.Comment: To appear in Phys. Rev.
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