147 research outputs found
Non-monotonic dependence of projection probabilities as a function of distinguishability
Typically, quantum superpositions, and thus measurement projections of
quantum states involving interference, decrease (or increase) monotonically as
a function of increased distinguishability. Distinguishability, in turn, can be
a consequence of decoherence, for example caused by the (simultaneous) loss of
excitation or due to inadequate mode matching (either deliberate or
indeliberate). It is known that for some cases of multi-photon interference,
non-monotonic decay of projection probabilities occurs, which has so far been
attributed to interference between four or more two photons. We show that such
a non-monotonic behaviour of projection probabilities is not unnatural, and can
also occur for single-photon and even semiclassical states. Thus, while the
effect traces its roots from indistinguishability and thus interference, the
states for which this can be observed do not need to have particular quantum
features.Comment: This is an author-created, un-copyedited version of an article
accepted for publication in New Journal of Physics. IOP Publishing Ltd is not
responsible for any errors or omissions in this version of the manuscript or
any version derived from i
Local uncertainty relations serving as measures of entanglement in a bipartite two-level system
We comment on the recent suggestion to use a family of local uncertainty
relations as a standard way of quantifying entanglement in two-qubit systems.
Some statements made on the applicability of the proposed "measures" are overly
optimistic. We exemplify how these specific "measures" fall short, and present
a minor modification of the general theory which uses the same experimentally
gathered information, but in a slightly different, better way.Comment: 5 pages, 1 figur
A size criterion for macroscopic superposition states
An operational measure to quantify the sizes of some ``macroscopic quantum
superpositions'', realized in recent experiments, is proposed. The measure is
based on the fact that a superposition presents greater sensitivity in
interferometric applications than its superposed constituent states. This
enhanced sensitivity, or ``interference utility'', may then be used as a size
criterion among superpositions.Comment: LaTeX2e-REVTeX4, 9 pages, 3 figures. V2: introduction and discussion
slightly altere
Arbitrarily High Super-Resolving Phase Measurements at Telecommunication Wavelengths
We present two experiments that achieve phase super-resolution at
telecommunication wavelengths. One of the experiments is realized in the space
domain and the other in the time domain. Both experiments show high
visibilities and are performed with standard lasers and single-photon
detectors. The first experiment uses six-photon coincidences, whereas the
latter needs no coincidence measurements, is easy to perform, and achieves, in
principle, arbitrarily high phase super-resolution. Here, we demonstrate a
30-fold increase of the resolution. We stress that neither entanglement nor
joint detection is needed in these experiments, demonstrating that neither is
necessary to achieve phase super-resolution.Comment: 5 pages, 7 figure
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