200 research outputs found
Discrete Wigner functions and the phase space representation of quantum teleportation
We present a phase space description of the process of quantum teleportation
for a system with an dimensional space of states. For this purpose we
define a discrete Wigner function which is a minor variation of previously
existing ones. This function is useful to represent composite quantum system in
phase space and to analyze situations where entanglement between subsystems is
relevant (dimensionality of the space of states of each subsystem is
arbitrary). We also describe how a direct tomographic measurement of this
Wigner function can be performed.Comment: 8 pages, 1 figure, to appear in Phys Rev
Test of quantum nonlocality for cavity fields
There have been studies on formation of quantum-nonlocal states in spatially
separate two cavities. We suggest a nonlocal test for the field prepared in the
two cavities. We couple classical driving fields with the cavities where a
nonlocal state is prepared. Two independent two-level atoms are then sent
through respective cavities to interact off-resonantly with the cavity fields.
The atomic states are measured after the interaction. Bell's inequality can be
tested by the joint probabilities of two-level atoms being in their excited or
ground states. We find that quantum nonlocality can also be tested using a
single atom sequentially interacting with the two cavities. Potential
experimental errors are also considered. We show that with the present
experimental condition of 5% error in the atomic velocity distribution, the
violation of Bell's inequality can be measured.Comment: 14pages, 2figures. accepted to Phys. Rev.
Recovering coherence from decoherence: a method of quantum state reconstruction
We present a feasible scheme for reconstructing the quantum state of a field
prepared inside a lossy cavity. Quantum coherences are normally destroyed by
dissipation, but we show that at zero temperature we are able to retrieve
enough information about the initial state, making possible to recover its
Wigner function as well as other quasiprobabilities. We provide a numerical
simulation of a Schroedinger cat state reconstruction.Comment: 8 pages, in RevTeX, 4 figures, accepted for publication in Phys. Rev.
A (november 1999
Conditional large Fock state preparation and field state reconstruction in Cavity QED
We propose a scheme for producing large Fock states in Cavity QED via the
implementation of a highly selective atom-field interaction. It is based on
Raman excitation of a three-level atom by a classical field and a quantized
field mode. Selectivity appears when one tunes to resonance a specific
transition inside a chosen atom-field subspace, while other transitions remain
dispersive, as a consequence of the field dependent electronic energy shifts.
We show that this scheme can be also employed for reconstructing, in a new and
efficient way, the Wigner function of the cavity field state.Comment: 4 Revtex pages with 3 postscript figures. Submitted for publicatio
Sampling functions for multimode homodyne tomography with a single local oscillator
We derive various sampling functions for multimode homodyne tomography with a
single local oscillator. These functions allow us to sample multimode
s-parametrized quasidistributions, density matrix elements in Fock basis, and
s-ordered moments of arbitrary order directly from the measured quadrature
statistics. The inevitable experimental losses can be compensated by proper
modification of the sampling functions. Results of Monte Carlo simulations for
squeezed three-mode state are reported and the feasibility of reconstruction of
the three-mode Q-function and s-ordered moments from 10^7 sampled data is
demonstrated.Comment: 12 pages, 8 figures, REVTeX, submitted Phys. Rev.
Quantum jumps of light recording the birth and death of a photon in a cavity
A microscopic system under continuous observation exhibits at random times
sudden jumps between its states. The detection of this essential quantum
feature requires a quantum non-demolition (QND) measurement repeated many times
during the system evolution. Quantum jumps of trapped massive particles
(electrons, ions or molecules) have been observed, which is not the case of the
jumps of light quanta. Usual photodetectors absorb light and are thus unable to
detect the same photon twice. They must be replaced by a transparent counter
'seeing' photons without destroying them3. Moreover, the light has to be stored
over a duration much longer than the QND detection time. We have fulfilled
these challenging conditions and observed photon number quantum jumps.
Microwave photons are stored in a superconducting cavity for times in the
second range. They are repeatedly probed by a stream of non-absorbing atoms. An
atom interferometer measures the atomic dipole phase shift induced by the
non-resonant cavity field, so that the final atom state reveals directly the
presence of a single photon in the cavity. Sequences of hundreds of atoms
highly correlated in the same state, are interrupted by sudden
state-switchings. These telegraphic signals record, for the first time, the
birth, life and death of individual photons. Applying a similar QND procedure
to mesoscopic fields with tens of photons opens new perspectives for the
exploration of the quantum to classical boundary
Bebida contendo abacaxi (Ananas comosus) e beterraba (Beta vulgaris) para crianças: tratar termicamente ou não?
Edição dos Resumos do VI Congresso Latinoamericano e XII Congresso Brasileiro de Higienistas de Alimentos, II Encontro Nacional de Vigilùncia das Zoonoses, IV Encontro do Sistema Brasileiro de Inspeção de Produtos de Origem Animal, Gramado, abr. 2013
Self-homodyne tomography of a twin-beam state
A self-homodyne detection scheme is proposed to perform two-mode tomography
on a twin-beam state at the output of a nondegenerate optical parametric
amplifier. This scheme has been devised to improve the matching between the
local oscillator and the signal modes, which is the main limitation to the
overall quantum efficiency in conventional homodyning. The feasibility of the
measurement is analyzed on the basis of Monte-Carlo simulations, studying the
effect of non-unit quantum efficiency on detection of the correlation and the
total photon-number oscillations of the twin-beam state.Comment: 13 pages (two-column ReVTeX) including 21 postscript figures; to
appear on Phys. Rev.
Squeezing arbitrary cavity-field states through their interaction with a single driven atom
We propose an implementation of the parametric amplification of an arbitrary
radiation-field state previously prepared in a high-Q cavity. This nonlinear
process is accomplished through the dispersive interactions of a single
three-level atom (fundamental |g>, intermediate |i>, and excited |e> levels)
simultaneously with i) a classical driving field and ii) a previously prepared
cavity mode whose state we wish to squeeze. We show that, in the adiabatic
approximantion, the preparation of the initial atomic state in the intermediate
level |i> becomes crucial for obtaing the degenerated parametric amplification
process.Comment: Final published versio
Synthesis and tomographic characterization of the displaced Fock state of light
Displaced Fock states of the electromagnetic field have been synthesized by
overlapping the pulsed optical single-photon Fock state |1> with coherent
states on a high-reflection beamsplitter and completely characterized by means
of quantum homodyne tomography. The reconstruction reveals highly non-classical
properties of displaced Fock states, such as negativity of the Wigner function
and photon number oscillations. This is the first time complete tomographic
reconstruction has been performed on a highly non-classical optical state
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