34,012 research outputs found
Full counting statistics of Majorana interferometers
We study the full counting statistics of interferometers for chiral Majorana
fermions with two incoming and two outgoing Dirac fermion channels. In the
absence of interactions, the FCS can be obtained from the scattering
matrix that relates the outgoing Dirac fermions to the incoming Dirac
fermions. After presenting explicit expressions for the higher-order current
correlations for a modified Hanbury Brown-Twiss interferometer, we note that
the cumulant-generating function can be interpreted such that unit-charge
transfer processes correspond to two independent half-charge transfer
processes, or alternatively, to two independent electron-hole conversion
processes. By a combination of analytical and numerical approaches, we verify
that this factorization property holds for a general scattering matrix,
i.e. for a general interferometer geometry.Comment: 22 pages, 3 figures, contributed to the special issue of Physica E
"Frontiers in Quantum Electronic Transport - In Memory of Markus Buttiker
Distilling common randomness from bipartite quantum states
The problem of converting noisy quantum correlations between two parties into
noiseless classical ones using a limited amount of one-way classical
communication is addressed. A single-letter formula for the optimal trade-off
between the extracted common randomness and classical communication rate is
obtained for the special case of classical-quantum correlations. The resulting
curve is intimately related to the quantum compression with classical side
information trade-off curve of Hayden, Jozsa and Winter. For a general
initial state we obtain a similar result, with a single-letter formula, when we
impose a tensor product restriction on the measurements performed by the
sender; without this restriction the trade-off is given by the regularization
of this function. Of particular interest is a quantity we call ``distillable
common randomness'' of a state: the maximum overhead of the common randomness
over the one-way classical communication if the latter is unbounded. It is an
operational measure of (total) correlation in a quantum state. For
classical-quantum correlations it is given by the Holevo mutual information of
its associated ensemble, for pure states it is the entropy of entanglement. In
general, it is given by an optimization problem over measurements and
regularization; for the case of separable states we show that this can be
single-letterized.Comment: 22 pages, LaTe
Wigner representation for polarization-momentum hyperentanglement generated in parametric down conversion, and its application to complete Bell-state measurement
We apply the Wigner function formalism to the study of two-photon
polarization-momentum hyperentanglement generated in parametric down
conversion. It is shown that the consideration of a higher number of degrees of
freedom is directly related to the extraction of additional uncorrelated sets
of zeropoint modes at the source. We present a general expression for the
description of the quantum correlations corresponding to the sixteen Bell base
states, in terms of four beams whose amplitudes are correlated through the
stochastic properties of the zeropoint field. A detailed analysis of the two
experiments on complete Bell-state measurement included in [Walborn et al.,
Phys. Rev. A 68, 042313 (2003)] is made, emphasizing the role of the zeropoint
field. Finally, we investigate the relationship between the zeropoint inputs at
the source and the analysers, and the limits on optimal Bell-state measurement.Comment: 28 pages, 4 figure
Local model of entangled photon experiments compatible with quantum predictions based on the reality of the vacuum fields
Arguments are provided for the reality of the quantum vacuum fields. A
polarization correlation experiment with two maximally entangled photons
created by spontaneous parametric down-conversion is studied in the Weyl-Wigner
formalism, that reproduces the quantum predictions. An interpretation is
proposed in terms of stochastic processes assuming that the quantum vacuum
fields are real. This proves that local realism is compatible with a violation
of Bell inequalities, thus rebutting the claim that it has been refuted by
experiments. Entanglement appears as a correlation between fluctuations of a
signal field and vacuum fields.
Key words; local realism, Bell inequalities, entangled photons, Weyl-Wigner,
loopholes,vacuum fieldsComment: 20 pages. This is the final form of the article. The last section has
been substantially modifie
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