16 research outputs found
Quantum reading of digital memory with non-Gaussian entangled light
It has been shown recently (Phys. Rev. Lett. 106, 090504 (2011)) that
entangled light with Einstein-Podolsky-Rosen (EPR) correlations retrieves
information from digital memory better than any classical light. In identifying
this, a model of digital memory with each cell consisting of reflecting medium
with two reflectivities (each memory cell encoding the binary numbers 0 or 1)
is employed. The readout of binary memory essentially corresponds to
discrimination of two Bosonic attenuator channels characterized by different
reflectivities. The model requires an entire mathematical paraphernalia of
continuous variable Gaussian setting for its analysis, when arbitrary values of
reflectivities are considered. Here we restrict to a basic quantum read-out
mechanism with non-Gaussian entangled states of light, with the binary channels
to be discriminated being ideal memory characterized by reflectivity one i.e.,
an identity channel and thermal noise channel, where the signal light
illuminating the memory location gets completely lost (zero reflectivity) and
only a white thermal noise hitting the upper side of the memory reaches the
decoder. We compare the quantum reading efficiency of entangled light with any
classical source of light in this model. We show that entangled transmitters
offer better reading performance than any classical transmitters of light in
the regime of low signal intensity.Comment: 7 pages, 6 figures, To appear in Phys. Rev.
Joint Measurability and Temporal Steering
Quintino et. al. (Phys. Rev. Lett. 113, 160402 (2014)) and Uola et. al.
(Phys. Rev. Lett. 113, 160403 (2014)) have recently established an intrinsic
relation between non-joint measurability and Einstein-Podolsky- Rosen steering.
They showed that a set of measurements is incompatible (i.e., not jointly
measurable) if and only if it can be used for the demonstration of steering. In
this paper, we prove the temporal analog of this result viz., a set of
measurements are incompatible if and only if it exhibits temporal steering.Comment: 6 pages,no figures, typos corrected, improved presentation; To appear
in JOSA B feature issue "80 years of Steering and the Einstein-Podolsky-Rosen
Paradox
Advances in photonic quantum sensing
Quantum sensing has become a mature and broad field. It is generally related
with the idea of using quantum resources to boost the performance of a number
of practical tasks, including the radar-like detection of faint objects, the
readout of information from optical memories or fragile physical systems, and
the optical resolution of extremely close point-like sources. Here we first
focus on the basic tools behind quantum sensing, discussing the most recent and
general formulations for the problems of quantum parameter estimation and
hypothesis testing. With this basic background in our hands, we then review
emerging applications of quantum sensing in the photonic regime both from a
theoretical and experimental point of view. Besides the state-of-the-art, we
also discuss open problems and potential next steps.Comment: Review in press on Nature Photonics. This is a preliminary version to
be updated after publication. Both manuscript and reference list will be
expande
Conditional entropic uncertainty and quantum correlations
Uncertainty relations reflect the inevitability inbuilt within the quantum framework, preventing prediction of precise outcomes for non-commuting observables. Maassen–Uffinkentropic uncertainty relation (Maassen and Uffink, 1988) captures the trade-off in the spread of the outcomes of a pair of non-commuting observables. Entropic uncertainty relation in the presence of quantum memory (Berta et al., 2010) brought about a fascinating twist by showing that quantum side information, enabled via entanglement, helps in beating the uncertainty of non-commuting observables. In this paper we investigate conditional entropic uncertainty relation and bring out an interplay between non-classical correlations – arising from sequential measurements in a single quantum system – and the entropic uncertainty bound. Our main result is formulated as a theorem, which establishes that if correlations between outcomes of sequential measurements are classical, the uncertainty bound on the sum of conditional entropies of non-commuting observables does not get reduced below the Maassen–Uffink bound
Equivalence of classicality and separability based on P phase-space representation of symmetric multiqubit states
Classical and quantum world views differ in peculiar ways. Understanding decisive quantum features - for which no classical explanation exist - and their interrelations is of foundational interest. Moreover, recognizing non-classical features carries practical significance in information processing tasks as it offers insights as to why quantum protocols work better than their classical counterparts. We focus here on two celebrated notions of non-classicality viz.; negativity of P phase-space representation and entanglement in symmetric multiqubit systems. We prove that they imply each other. © 2013 Springer Science+Business Media New York
Quantum which-way information and fringe visibility when the detector is entangled with an ancilla
Quantum-mechanical wave-particle duality is quantified in terms of a trade-off relation between the fringe visibility and the which-way distinguishability in an interference experiment. This relation was recently generalized by Banaszek et al. Nat. Commun. 4, 2594 (2013)2041-172310.1038/ ncomms3594 when the particle is equipped with an internal degree of freedom such as spin. Here, we extend the visibility-distinguishability trade-off relation to quantum interference of a particle possessing an internal degree of freedom, when the which-way detector state is entangled with an ancillary system. We introduce an extended which-way distinguishability DE and the associated extended fringe visibility VE, satisfying the inequality DE2+VE2 in this scenario. We illustrate, with the help of three specific examples, that while the which-way information inferred solely from the detector state (without ancilla) vanishes, the extended distinguishability retrievable via measurements on the detector-ancilla entangled state is nonzero. Furthermore, in all the three examples, the extended visibility and the generalized visibility (which was introduced by Banaszek et al.) match identically with each other. © 2014 American Physical Society