22,245 research outputs found
True photo-counting statistics of multiple on-off detectors
We derive a closed photo-counting formula, including noise counts and a
finite quantum efficiency, for photon number resolving detectors based on
on-off detectors. It applies to detection schemes such as array detectors and
multiplexing setups. The result renders it possible to compare the
corresponding measured counting statistics with the true photon number
statistics of arbitrary quantum states. The photo-counting formula is applied
to the discrimination of photon numbers of Fock states, squeezed states, and
odd coherent states. It is illustrated for coherent states that our formula is
indispensable for the correct interpretation of quantum effects observed with
such devices.Comment: 7 pages, 4 figure
Necessary and sufficient conditions for bipartite entanglement
Necessary and sufficient conditions for bipartite entanglement are derived,
which apply to arbitrary Hilbert spaces. Motivated by the concept of witnesses,
optimized entanglement inequalities are formulated solely in terms of arbitrary
Hermitian operators, which makes them useful for applications in experiments.
The needed optimization procedure is based on a separability eigenvalue
problem, whose analytical solutions are derived for a special class of
projection operators. For general Hermitian operators, a numerical
implementation of entanglement tests is proposed. It is also shown how to
identify bound entangled states with positive partial transposition.Comment: 7 pages, 2 figur
Nonclassicality filters and quasiprobabilities
Necessary and sufficient conditions for the nonclassicality of bosonic
quantum states are formulated by introducing nonclassicality filters and
nonclassicality quasiprobability distributions. Regular quasiprobabilities are
constructed from characteristic functions which can be directly sampled by
balanced homodyne detection. Their negativities uncover the nonclassical
effects of general quantum states. The method is illustrated by visualizing the
nonclassical nature of a squeezed state.Comment: Significantly revised version, more emphasis on practical applicatio
Experimental determination of a nonclassical Glauber-Sudarshan P function
A quantum state is nonclassical if its Glauber-Sudarshan P function fails to
be interpreted as a probability density. This quantity is often highly
singular, so that its reconstruction is a demanding task. Here we present the
experimental determination of a well-behaved P function showing negativities
for a single-photon-added thermal state. This is a direct visualization of the
original definition of nonclassicality. The method can be useful under
conditions for which many other signatures of nonclassicality would not
persist.Comment: 4 pages, 4 figure
Representation of entanglement by negative quasi-probabilities
Any bipartite quantum state has quasi-probability representations in terms of
separable states. For entangled states these quasi-probabilities necessarily
exhibit negativities. Based on the general structure of composite quantum
states, one may reconstruct such quasi-propabilities from experimental data.
Because of ambiguity, the quasi-probabilities obtained by the bare
reconstruction are insufficient to identify entanglement. An optimization
procedure is introduced to derive quasi-probabilities with a minimal amount of
negativity. Negativities of optimized quasi-probabilities unambiguously prove
entanglement, their positivity proves separability.Comment: 9 pages, 2 figures; An optimization procedure for the
quasi-probabilities has been adde
Electromagnetic field quantization in a linear polarizable and magnetizable medium
By modeling a linear polarizable and magnetizable medium (magneto-dielectric)
with two quantum fields, namely E and M, electromagnetic field is quantized in
such a medium consistently and systematically. A Hamiltonian is proposed from
which, using the Heisenberg equations, Maxwell and constitutive equations of
the medium are obtained. For a homogeneous medium, the equation of motion of
the quantum vector potential, , is derived and solved analytically.
Two coupling functions which describe the electromagnetic properties of the
medium are introduced. Four examples are considered showing the features and
the applicability of the model to both absorptive and nonabsorptive
magneto-dielectrics.Comment: 23 pages, Accepted for publication in Phy.Rev
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