Biomedical subjects

Michał Horodecki

Publications and source records attributed to Michał Horodecki.

8 recordsLinked to original sources

PubMed2004

Locking classical correlations in quantum States.

We show that there exist bipartite quantum states which contain a large locked classical correlation that is unlocked by a disproportionately small amount of classical communication. In particular, there are (2n+1)-qubit states for which a one-bit message doubles the optimal classical mutual information between measurement results on the subsystems, from n/2 bits to n bits. This phenomenon is impossible classically. However, states exhibiting this behavior need not be entangled. We study the range of states exhibiting this phenomenon and bound its magnitude.

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PubMed2003

Locally accessible information: how much can the parties gain by cooperating?

We investigate measurements of bipartite ensembles restricted to local operations and classical communication and find a universal Holevo-like upper bound on the locally accessible information. We analyze our bound and exhibit a class of states which saturate it. Finally, we link the bound to the problem of quantification of the nonlocality of the operations necessary to extract locally inaccessible information.

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PubMed2003

Local information as a resource in distributed quantum systems.

A new paradigm for distributed quantum systems where information is a valuable resource is developed. After finding a unique measure for information, we construct a scheme for its manipulation in analogy with entanglement theory. In this scheme, instead of maximally entangled states, two parties distill local states. We show that, surprisingly, the main tools of entanglement theory are general enough to work in this opposite scheme. Up to plausible assumptions, we show that the amount of information that must be lost during the protocol of concentration of local information can be expressed as the relative entropy distance from some special set of states.

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PubMed2003

Local indistinguishability: more nonlocality with less entanglement.

We provide a first operational method for checking local indistinguishability of orthogonal states. It originates from that in Ghosh et al. [Phys. Rev. Lett. 87, 5807 (2001)]], though we deal with pure states. Our method shows that probabilistic local distinguishing is possible for a complete multipartite orthogonal basis if and only if all vectors are product. Also, it leads to local indistinguishability of a set of orthogonal pure states of 3 multiply sign in circle 3, which shows that one can have more nonlocality with less entanglement, where "more nonlocality" is in the sense of "increased local indistinguishability of orthogonal states." This is, to our knowledge, the only known example where d orthogonal states in d multiply sign in circle d are locally indistinguishable.

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PubMed2003

Are there phase transitions in information space?

The interplay between two basic quantities--quantum communication and information--is investigated. Quantum communication is an important resource for quantum states shared by two parties and is directly related to entanglement. Recently, the amount of local information that can be drawn from a state has been shown to be closely related to the nonlocal properties of the state. Here we consider both formation and extraction processes, and analyze informational resources as a function of quantum communication. The resulting diagrams in information space allow us to observe phaselike transitions when correlations become classical.

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PubMed2002

Are the laws of entanglement theory thermodynamical?

We argue that on its face, entanglement theory satisfies laws equivalent to thermodynamics if the theory can be made reversible by adding certain bound entangled states as a free resource during entanglement manipulation. Subject to plausible conjectures, we prove that this is not the case in general, and discuss the implications of this for the thermodynamics of entanglement.

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PubMed2002

Thermodynamical approach to quantifying quantum correlations.

We consider the amount of work which can be extracted from a heat bath using a bipartite state rho shared by two parties. In general it is less then the amount of work extractable when one party is in possession of the entire state. We derive bounds for this "work deficit" and calculate it explicitly for a number of different cases. In particuar, for pure states the work deficit is exactly equal to the distillable entanglement of the state. A form of complementarity exists between physical work which can be extracted and distillable entanglement. The work deficit is a good measure of the quantum correlations in a state and provides a new paradigm for understanding quantum nonlocality.

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PubMed2002

Direct estimations of linear and nonlinear functionals of a quantum state.

We present a simple quantum network, based on the controlled-SWAP gate, that can extract certain properties of quantum states without recourse to quantum tomography. It can be used as a basic building block for direct quantum estimations of both linear and nonlinear functionals of any density operator. The network has many potential applications ranging from purity tests and eigenvalue estimations to direct characterization of some properties of quantum channels. Experimental realizations of the proposed network are within the reach of quantum technology that is currently being developed.

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