1,721,348 research outputs found
A dynamical model for quantum memory channels
No full textA dynamical model for quantum channels is introduced which allows one to pass continuously from the memoryless case to the case in which memory effects are present. The quantum and classical communication rates of the model are defined and explicit expression is provided in some limiting case. In this context, we introduce noise attenuation strategies where part of the signals are sacrificed to modify the channel environment. The case of qubit channel with phase damping noise is analysed in detail
Entaglement and statistics in Hong-Ou-Mandel interferometry
No full textHong-Ou-Mandel interferometry allows one to detect the presence of entanglement in two-photon input states. The same result holds for two-particle input states which obey fermionic statistics. In the latter case, however, antibouncing introduces qualitative differences in the interferometer response. This effect is analyzed in a gedanken experiment where the particles entering the interferometer are assumed to belong to a one-parameter family of quons which continuously interpolate between the bosonic and fermionic statistics
Inequalities for quantum channels assisted by limited resources
No full textThe information capacities and "distillability" of a quantum channel are studied in the presence of auxiliary resources. These include prior entanglement shared between the sender and receiver and free classical bits of forward and backward communication. Inequalities and trade-off curves are derived. In particular an alternative proof is given that in the absence of feedback and shared entanglement, forward classical communication does not increase the quantum capacity of a channel
Separability conditions from entropic uncertainty relations
No full textWe derive a collection of separability conditions for bipartite systems of dimension dxd which is based on the entropic version of the uncertainty relations. A detailed analysis of the two-qubit case is given by comparing the new separability conditions with existing criteria
Improved transfer of quantum information using a local memory
No full textWe demonstrate that the quantum communication between two parties can be significantly improved if the receiver is allowed to store the received signals in a quantum memory before decoding them. In the limit of an infinite memory, the transfer is perfect. We prove that this scheme allows the transfer of arbitrary multipartite states along Heisenberg chains of spin-1/2 particles with random coupling strengths
Zero-Fluctuation Quantum Work Extraction
Full text linkWe study the possibility of deterministic protocols for extracting work from quantum systems. Focusing on the two-point measurement work extraction scenario, we prove that, with enough copies of the system, such zero-fluctuation protocols always exist if the Hamiltonian has a rational spectrum. Leveraging this result, we show that for any Hamiltonian, it is possible to construct an unitary driving protocol on sufficiently many copies of the system with work fluctuations strictly bounded within an arbitrary interval , albeit requiring exponentially many copies in .19 pages, 5 figures. Comments welcome
Qubit quantum channels: a characteristic function approach
No full textA characterization of qubit quantum channels is introduced. In analogy to what happens in the context of bosonic channels we exploit the possibility of representing the states of the system in terms of characteristic function. The latter are functions of noncommuting variables (Grassmann variables) and are defined in terms of generalized displacement operators. In this context we introduce the set of Gaussian channels and show that they share similar properties with the corresponding bosonic counterpart
A new approach to characterize qubit channels
No full textWe analyze qubit channels by exploiting the possibility of representing two-level quantum systems in terms of characteristic functions. To do so, we use functions of non-commuting variables (Grassmann variables), defined in terms of generalized displacement operators, following an approach which resemble the one adopted for continuous–variable (Bosonic) systems. It allows us to introduce the notion of qubit Gaussian channels and to show that they share similar properties with the corresponding continuous–variable counterpart. Some examples of qubit channels are investigated using this approach
Incompatibility in quantum parameter estimation
Full text linkIn this paper we introduce a measure of genuine quantum incompatibility in the estimation task of multiple parameters, that has a geometric character and is backed by a clear operational interpretation. This measure is then applied to some simple systems in order to track the effect of a local depolarizing noise on the incompatibility of the estimation task. A semidefinite program is described and used to numerically compute the figure of merit when the analytical tools are not sufficient, among these we include an upper bound computable from the symmetric logarithmic derivatives only. Finally we discuss how to obtain compatible models for a general unitary encoding on a finite-dimensional probe
Extracting work from correlated many-body quantum systems
Full text linkThe presence of correlations in the input state of a non-interacting
many-body quantum system can lead to an increase in the amount of work we can
extract from it under global unitary processes (ergotropy). The present work
explore such effect on translationally invariant systems relaying on the Matrix
Product Operator formalism to define a measure of how much they are correlated.
We observe that in the thermodynamic limit of large number of sites, complete
work extraction can be attained for relatively small correlation strength (a
reduction of a 2 factor in dB unit). Most importantly such an effect appears
not to be associated with the presence of quantum correlations (e.g.
entanglement) in the input state (classical correlation sources), and to be
attainable by only using incoherent ergotropy. As a byproduct of our analysis
we also present a rigorous formulation of the heuristic typicality argument
first formulated in [Alicki and Fannes, 2013], which gives the maximum work
extractable for a set of many identical quantum systems in the asymptotic
limit.Comment: 21 pages, 5 figure
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