3,441 research outputs found
Two-mode squeezed vacuum and squeezed light in correlated interferometry
We study in detail a system of two interferometers aimed to the detection of
extremely faint phase-fluctuations. This system can represent a breakthrough
for detecting a faint correlated signal that would remain otherwise
undetectable even using the most sensitive individual interferometric devices,
that are limited by the shot noise. If the two interferometers experience
identical phase-fluctuations, like the ones introduced by the so called
"holographic noise", this signal should emerge if their output signals are
correlated, while the fluctuations due to shot noise and other independent
contributions will vanish. We show how the injecting quantum light in the free
ports of the interferometers can reduce the photon noise of the system beyond
the shot-noise, enhancing the resolution in the phase-correlation estimation.
We analyze both the use of two-mode squeezed vacuum or twin-beam state (TWB)
and of two independent squeezing states. Our results basically confirms the
benefit of using squeezed beams together with strong coherent beams in
interferometry, even in this correlated case. However, mainly we concentrate on
the possible use of TWB, discovering interesting and probably unexplored areas
of application of bipartite entanglement and in particular the possibility of
reaching in principle surprising uncertainty reduction
Toward third order ghost imaging with thermal light
Recently it has been suggested that an enhancement in the visibility of ghost
images obtained with thermal light can be achieved exploiting higher order
correlations [3]. This paper reports on the status of an higher order ghost
imaging experiment carried on at INRIM labs exploiting a pseudo-thermal source
and a CCD camera.Comment: To be published in Proceedings of Recent advances in Foundations of
Quantum Mechanics and Quantum Informatio
Experimental estimation of quantum discord for polarization qubit and the use of fidelity to assess quantum correlations
We address the experimental determination of entropic quantum discord for
systems made of a pair of polarization qubits. We compare results from full and
partial tomography and found that the two determinations are statistically
compatible, with partial tomography leading to a smaller value of discord for
depolarized states. Despite the fact that our states are well described, in
terms of fidelity, by families of depolarized or phase-damped states, their
entropic discord may be largely different from that predicted for these classes
of states, such that no reliable estimation procedure beyond tomography may be
effectively implemented. Our results, together with the lack of an analytic
formula for the entropic discord of a generic two-qubit state, demonstrate that
the estimation of quantum discord is an intrinsically noisy procedure. Besides,
we question the use of fidelity as a figure of merit to assess quantum
correlations
Direct experimental observation of nonclassicality in ensembles of single photon emitters
In this work we experimentally demonstrate for the first time a recently
proposed criterion adressed to detect nonclassical behavior in the fluorescence
emission of ensembles of single-photon emitters. In particular, we apply the
method to study clusters of NV centres in diamond observed via
single-photon-sensitive confocal microscopy. Theoretical considerations on the
behavior of the parameter at any arbitrary order in presence of poissonian
noise are presented and, finally, the opportunity of detecting manifold
coincidences is discussed
Statistical Estimation of Quantum Tomography Protocols Quality
A novel operational method for estimating the efficiency of quantum state
tomography protocols is suggested. It is based on a-priori estimation of the
quality of an arbitrary protocol by means of universal asymptotic fidelity
distribution and condition number, which takes minimal value for better
protocol. We prove the adequacy of the method both with numerical modeling and
through the experimental realization of several practically important protocols
of quantum state tomography
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