151 research outputs found
Quantum state engineering using conditional measurement on a beam splitter
State preparation via conditional output measurement on a beam splitter is
studied, assuming the signal mode is mixed with a mode prepared in a Fock state
and photon numbers are measured in one of the output channels. It is shown that
the mode in the other output channel is prepared in either a photon-subtracted
or a photon-added Jacobi polynomial state, depending upon the difference
between the number of photons in the input Fock state and the number of photons
in the output Fock state onto which it is projected. The properties of the
conditional output states are studied for coherent and squeezed input states,
and the probabilities of generating the states are calculated. Relations to
other states, such as near-photon-number states and squeezed-state-excitations,
are given and proposals are made for generating them by combining the scheme
with others. Finally, effects of realistic photocounting and Fock-state
preparation are discussed.Comment: 8 figures using a4.st
Continuous-variable teleportation improvement by photon subtraction via conditional measurement
We show that the recently proposed scheme of teleportation of continuous
variables [S.L. Braunstein and H.J. Kimble, Phys. Rev. Lett. 80, 869 (1998)]
can be improved by a conditional measurement in the preparation of the
entangled state shared by the sender and the recipient. The conditional
measurement subtracts photons from the original entangled two-mode squeezed
vacuum, by transmitting each mode through a low-reflectivity beam splitter and
performing a joint photon-number measurement on the reflected beams. In this
way the degree of entanglement of the shared state is increased and so is the
fidelity of the teleported state.Comment: 7 pages REVTeX, 7 figure
Double jumps and transition rates for two dipole-interacting atoms
Cooperative effects in the fluorescence of two dipole-interacting atoms, with
macroscopic quantum jumps (light and dark periods), are investigated. The
transition rates between different intensity periods are calculated in closed
form and are used to determine the rates of double jumps between periods of
double intensity and dark periods, the mean duration of the three intensity
periods and the mean rate of their occurrence. We predict, to our knowledge for
the first time, cooperative effects for double jumps, for atomic distances from
one and to ten wave lengths of the strong transition. The double jump rate, as
a function of the atomic distance, can show oscillations of up to 30% at
distances of about a wave length, and oscillations are still noticeable at a
distance of ten wave lengths. The cooperative effects of the quantities and
their characteristic behavior turn out to be strongly dependent on the laser
detuning.Comment: Substantially revised versio
Conditional teleportation using optical squeezers and photon counting
We suggest a scheme of using two-mode squeezed vacuum for conditional
teleportation of quantum states of optical field. Alice mixes the input state
with one of the squeezed modes on another squeezing device and detects the
output photon numbers. The result is then communicated to Bob who shifts the
photon number of his part accordingly. This is a principally realizable
modification of the recent scheme [G.J. Milburn and S.L. Braunstein, Phys. Rev.
A 60, 937 (1999)] where measurements of photon number difference and phase sum
are considered. We show that for some classes of states this method can yield
very high fidelity of teleportation, nevertheless, the success probability may
be limited.Comment: 5 pages, 4 figures; notations simplified, more explicit explanatio
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