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Pawel Kurzynski

Publications and source records attributed to Pawel Kurzynski.

At least 55 records · Page 3Linked to original sources
arXiv2015

Macroscopic limit of nonclassical correlations

We consider macroscopic correlations in a bipartite system consisting of 2N particles described by a generalised probabilistic theory. In particular, we discuss a case of N PR-boxes shared between two parties. We characterise macroscopic measurements as collective measurements of the same property on all the boxes in the same region. Such measurements are assumed to reveal only the average value of the measured collective property. We show that for two measurements per observer and N greater or equal 2 there always exist a joint probability distribution explaining all observable data and therefore the system admits local hidden variables. Next, we generalise this result to include measurement of fluctuations and additional measurement settings. Finally, we discuss our result in the context of previous works in which contradictory results were presented.

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arXiv2015

Delayed Choice Contextuality: A way to rule out Contextual Hidden Variables

A PhD student is locked inside a box, imitating a quantum system by mimicking the measurement statistics of any viable observable nominated by external observers. Inside a second box lies a genuine quantum system. Either box can be used to pass a test for contextuality - and from the perspective of an external observer, be operationally indistinguishable. There is no way to discriminate between the two boxes based on the output statistics of any contextuality test. This poses a serious problem for contextuality tests to be used as viable tests for device independent quantumness, and severely limits realistic use of contextuality as an operational resource. Here we rectify this problem by building experimental techniques for distinguishing a contextual system that is genuinely quantum, and one that mimics it through clever use of hidden variables.

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arXiv2015

State-recycling method for testing contextuality

Quantum nonlocality and contextuality are two phenomena stemming from nonclassical correlations. Whereas the former requires entanglement that is consumed in the measurement process the latter can occur for any state if one chooses a proper set of measurements. Despite this stark differences experimental tests of both phenomena were similar so far. For each run of the experiment one had to use a different copy of a physical system prepared according to the same procedure, or the system had to be brought to its initial state. Here we show that this is not necessary and that the state-independent contextuality can be manifested in a scenario in which each measurement round is done on an output state from the previous round.

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arXiv2015

Entropic tests of multipartite nonlocality and state-independent contextuality

We introduce a multipartite extension of an information-theoretic distance first introduced in [Nature 341, 119 (1989)]. We use this new distance to derive entropic tests of multipartite nonlocality for three and for an arbitrary even number of qubits as well as a test of state-independent contextuality. In addition, we re-derive the tripartite Mermin inequality and a state-independent non-contextuality inequality by Cabello [Phys. Rev. Lett. 101, 210401 (2008)]. This suggests that the information-theoretic distance approach to multipartite nonlocality and state-independent contextuality can provide a more general treatment of nonclassical correlations than the orthodox approach based on correlation functions.

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arXiv2014

Information-theoretic Bell inequalities based on Tsallis entropy

We numerically investigate entropic Bell inequalities for a pair of entangled qutrits using information-theoretic distances. We show that for this class of inequalities Tsallis entropy is more suitable than Shannon as it reveals non-classicality for a larger set of quantum states. Finally, we find that like probability based inequalities, entropic ones are maximally violated by the non-maximally entangled qutrit state.

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arXiv2014

Entropic Version of the Greenberger-Horne-Zeilinger Paradox

Consider four binary +-1 variables A, B, C and D for which classical reasoning implies ABCD = 1. In this case the knowledge of A, B, C automatically provides knowledge of D because D = ABC. However, the Greenberger-Horne-Zeilinger paradox shows that despite classical prediction one can find quantum states and observables with well defined outcomes for which D = -ABC. In this work we formulate an information-theoretic version of this paradox. We show that for a tripartite quantum system one can find a set of four properties for which classical reasoning implies that D = ABC, yet quantum theory predicts that one can know everything about A, B, C and nothing about D.

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arXiv2014

Fundamental monogamy relation between contextuality and nonlocality

We show that the no-disturbance principle imposes a tradeoff between locally contextual correlations violating the Klyachko-Can-Binicioglu-Shumovski inequality and spatially separated correlations violating the Clauser-Horne-Shimony-Holt inequality. The violation of one inequality forbids the violation of the other. We also obtain the corresponding monogamy relation imposed by quantum theory for a qutrit-qubit system. Our results show the existence of fundamental monogamy relations between contextuality and nonlocality that suggest that entanglement might be a particular form of a more fundamental resource.

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arXiv2014

On compression of non-classically correlated bit strings

In this short note we present a new approach to non-classical correlations that is based on the compression rates for bit strings generated by Alice and Bob. We use normalised compression distance introduced by Cilibrasi and Vitanyi to derive information-theoretic inequalities that must be obeyed by classically correlated bit strings and that are violated by PR-boxes. We speculate about a violation of our inequalities by quantum mechanical correlations.

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arXiv2013

Coherent states of composite bosons

We present a systematic analysis on coherent states of composite bosons consisting of two distinguishable particles. By defining an effective composite boson (coboson) annihilation operator, we derive its eigenstate and commutator. Depending on the elementary particles comprising the composite particles, we gauge the resemblance between this eigenstate and traditional coherent states through typical measures of nonclassicality, such as quadrature variances and Mandel's Q parameter. Furthermore, we show that the eigenstate of the coboson annihilation operator is useful in estimating the maximum eigenvalue of the coboson number operator.

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arXiv2013

The triangle principle: a new approach to non-contextuality and local realism

In this paper we study an application of an information distance between two measurements to the problem of non-contextuality and local realism. We postulate the triangle principle which states that any information distance is well defined on any pair of measurements, even if the two measurements cannot be jointly performed. As a consequence, the triangle inequality for this distance is obeyed for any three measurements. This simple principle is valid in any classical realistic theory, however it does not hold in quantum theory. It allows us to re-derive in an astonishingly simple way a large class of non-contextuality and local realistic inequalities via multiple applications of the triangle inequality. We also show that this principle can be applied to derive monogamy relations. The triangle principle is different than the assumption of non-contextuality and local realism, which is defined as a lack of existence of a joined probability distribution giving rise to all measurable data. Therefore, we show that one can design Bell-Kochen-Specker tests using a different principle.

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arXiv2013

An experimental proposal for revealing contextuality in almost all qutrit states

Contextuality is a foundational phenomenon underlying key differences between quantum theory and classical realistic descriptions of the world. Here we propose an experimental test which is capable of revealing contextuality in all qutrit systems, except the completely mixed state, provided we choose the measurement basis appropriately. The 3-level system is furnished by the polarization and spatial degrees of freedom of a single photon, which encompass three orthogonal modes. Projective measurements along rays in the 3-dimensional Hilbert space are made by linear optical elements and detectors which are sensitive to a single mode. We also discuss the impact of detector inefficiency and losses and review the theoretical foundations of this test.

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arXiv2013

Contextuality in bosonic bunching

We show that under certain assumptions one can derive a variant of Specker's non-contextual inequality for a system of three indistinguishable bosonic particles. The inequality states that the sum of probabilities of three pairwise exclusive events is bounded by one. This inequality cannot be violated using standard quantum mechanical projectors. On the other hand, due to bosonic properties this bound is violated up to 3/2. We also argue that the violation of this inequality can be considered as a test of bosonic nature.

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arXiv2013

Recent advances in contextuality tests

Our everyday experiences support the hypothesis that physical systems exist independently of the act of observation. Concordant theories are characterized by the objective realism assumption whereby the act of measurement simply reveals preexisting well defined elements of reality. In stark contrast quantum mechanics portrays a world in which reality loses its objectivity and is in fact created by observation. Quantum contextuality as first discovered by Bell [Rev. Mod. Phys. 38, 447 (1966)] and Kochen-Specker [J. Math. Mech. 17, 59 (1967)] captures aspects of this philosophical clash between classical and quantum descriptions of the world. Here we briefly summarize some of the more recent advances in the field of quantum contextuality. We approach quantum contextuality through its close relation to Bell type nonlocal scenarios and highlight some of the rapidly developing tests and experimental implementations.

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arXiv2013

The relation between nonlocality and contextuality for a biphoton

We investigate the set of qutrit states in terms of symmetric states of two qubits that violate the minimal contextual inequality, namely the Klyachko-Can-Binicoglu-Shumovsky (KCBS) inequality. The physical system that provides a natural framework for this problem is a biphoton which consists of two photons in the same spatio-temporal mode and whose effective polarization behaves as a three-level quantum system. The relationship between the KCBS contextual inequality and the Clauser-Horne-Shimony-Holt (CHSH) inequality is investigated. We find that every biphotonic state that is contextual with respect to KCBS is nonlocal as per the CHSH test when the two photons are apart, but the converse is not true.

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arXiv2012

Bosonic bunching reveals strong contextual behaviour

We show that violation of Klyachko-Can-Binicioglu-Shumovsky [Phys. Rev. Lett. {\bf 101}, 020403 (2008)] pentagram-like inequality can exceed $\sqrt{5}$ provided that exclusive events do not have to be comeasurable and that one uses bosonic systems which exhibit bunching effects. We also show that in this case one can find three pairwise exclusive events whose sum of probabilities is 3/2.

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