148 research outputs found
Transfer of coherence from atoms to mixed field states in a two-photon lossless micromaser
We propose a two-photon micromaser-based scheme for the generation of a
nonclassical state from a mixed state. We conclude that a faster, as well as a
higher degree of field purity is achieved in comparison to one-photon
processes. We investigate the statistical properties of the resulting field
states, for initial thermal and (phase-diffused) coherent states.
Quasiprobabilities are employed to characterize the state of the generated
fields.Comment: 20 pages, 8 figures, to appear in Journal of Modern Optic
Atom-field transfer of coherence in a two-photon micromaser assisted by a classical field
We investigate the transfer of coherence from atoms to a cavity field
initially in a statistical mixture in a two-photon micromaser arrangement. The
field is progressively modified from a maximum entropy state (thermal state)
towards an almost pure state (entropy close to zero) due to its interaction
with atoms sent across the cavity. We trace over the atomic variables, i.e.,
the atomic states are not collapsed by a detector after they leave the cavity.
We find that by applying an external classical driving field it is possible to
substantially increase the field purity without the need of previously
preparing the atoms in a superposition of their energy eigenstates. We also
discuss some of the nonclassical features of the resulting field.Comment: 10 pages, 7 figures, LaTe
Coherence properties of coupled optomechanical cavities
In this work we investigate an optomechanical system consisting of two
cavities coupled to the same mechanical resonator. We consider each cavity
being weakly pumped as well as a small tunneling rate between the cavities. In
such conditions, the system can be studied via quantum Langevin equations and
the steady state solution can be found perturbatively. In order to ensure that
the approximations and methods used to study the system are suitable, the
analytical results were compared to numerical simulations. We study the
statistical properties of the cavity radiation fields and we show that
depending on the values of the parameters of the system, it is possible to
modify the spectrum of the cavities and even enhance the sub-Poissonian
character of the cavity field.Comment: 8 pages, 6 figure
Quantum key distribution using polarized coherent states
We discuss a continuous variables method of quantum key distribution
employing strongly polarized coherent states of light. The key encoding is
performed using the variables known as Stokes parameters, rather than the field
quadratures. Their quantum counterpart, the Stokes operators
(i=1,2,3), constitute a set of non-commuting operators, being the precision of
simultaneous measurements of a pair of them limited by an uncertainty-like
relation. Alice transmits a conveniently modulated two-mode coherent state, and
Bob randomly measures one of the Stokes parameters of the incoming beam. After
performing reconciliation and privacy amplification procedures, it is possible
to distill a secret common key. We also consider a non-ideal situation, in
which coherent states with thermal noise, instead of pure coherent states, are
used for encoding.Comment: Inclusion of a discussion about noise not controlled by Eve;
inclusion of a figure. A simplified version of this paper was submitted to a
Conference in Brazil (XXVII ENFMC) in 16/02/200
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