ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Mon, 03 Oct 2022 02:04:06 GMT2022-10-03T02:04:06Z50261- Multi-bloch vector representation of the qutrithttps://scholarbank.nus.edu.sg/handle/10635/116467Title: Multi-bloch vector representation of the qutrit
Authors: Kurzyński, P.
Abstract: An ability to describe quantum states directly by average values of measurement outcomes is provided by the Bloch vector. For an informationally complete set of measurements one can construct unique Bloch vector for any quantum state. However, not every Bloch vector corresponds to a quantum state. It seems that only for two-dimensional quantum systems it is easy to distinguish proper Bloch vectors from improper ones, i.e. the ones corresponding to quantum states from the other ones. I propose an alternative approach to the problem in which more than one vector is used. In particular, I show that a state of the qutrit can be described by the three qubit-like Bloch vectors. © Rinton Press.
Sun, 01 May 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1164672011-05-01T00:00:00Z
- Experimental realization of generalized qubit measurements based on quantum walkshttps://scholarbank.nus.edu.sg/handle/10635/119900Title: Experimental realization of generalized qubit measurements based on quantum walks
Authors: Zhao, Yuan-yuan; Yu, Neng-kun; Kurzynski, Pawel Krzysztof; Xiang, Guo-yong; Li, Chuan-Feng; Guo, Guang-Can
Mon, 06 Apr 2015 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1199002015-04-06T00:00:00Z
- Probing the quantum-classical boundary with compression softwarehttps://scholarbank.nus.edu.sg/handle/10635/175258Title: Probing the quantum-classical boundary with compression software
Authors: Poh H.S.; Markiewicz M.; Kurzy?ski P.; Cerè A.; Kaszlikowski D.; Kurtsiefer C.
Abstract: We adapt an algorithmic approach to the problem of local realism in a bipartite scenario. We assume that local outcomes are simulated by spatially separated universal Turing machines. The outcomes are calculated from inputs encoding information about a local measurement setting and a description of the bipartite system sent to both parties. In general, such a description can encode some additional information not available in quantum theory, i.e., local hidden variables. Using the Kolmogorov complexity of local outcomes we derive an inequality that must be obeyed by any local realistic theory. Since the Kolmogorov complexity is in general uncomputable, we show that this inequality can be expressed in terms of lossless compression of the data generated in such experiments and that quantum mechanics violates it. Finally, we confirm experimentally our findings using pairs of polarisation-entangled photons and readily available compression software. We argue that our approach relaxes the independent and identically distributed (i.i.d.) assumption, namely that individual bits in the outcome bit-strings do not have to be i.i.d. © 2016 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Fri, 01 Jan 2016 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1752582016-01-01T00:00:00Z
- Quantum information approach to Bose-Einstein condensation of composite bosonshttps://scholarbank.nus.edu.sg/handle/10635/175277Title: Quantum information approach to Bose-Einstein condensation of composite bosons
Authors: Lee, S.-Y; Thompson, J; Raeisi, S; Kurzy?ski, P; Kaszlikowski, D
Abstract: We consider composite bosons (cobosons) comprised two elementary particles, fermions or bosons, in an entangled state. First, we show that the effective number of cobosons implies the level of correlation between the two constituent particles. For the maximum level of correlation, the effective number of cobosons is the same as the total number of cobosons, which can exhibit the original Bose-Einstein condensation (BEC). In this context, we study a model of BEC for indistinguishable cobosons with a controllable parameter, i.e., entanglement between the two constituent particles. We find that bi-fermions behave in a predictable way, i.e., the effective number of the ground state coboson is an increasing function of entanglement between a pair of constituent fermions. Interestingly, bi-bosons exhibit the opposite behavior - the effective number of the ground state coboson is a decreasing function of entanglement between a pair of constituent bosons. © 2015 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Thu, 01 Jan 2015 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1752772015-01-01T00:00:00Z
- From contextuality of a single photon to realism of an electromagnetic wavehttps://scholarbank.nus.edu.sg/handle/10635/213239Title: From contextuality of a single photon to realism of an electromagnetic wave
Authors: Markiewicz, M.; Kaszlikowski, D.; Kurzynski, P.; Wójcik, A.
Abstract: Violations of Bell inequalities have been an incontestable indicator of non-classicality since the seminal paper by John Bell. However, recent claims of Bell inequalities violations with classical light have cast some doubts on their significance as hallmarks of non-classicality. Here, we challenge those claims. The crux of the problem is that such classical experiments simulate quantum probabilities with intensities of classical fields. However, fields intensities measurements are radically different from single-photon detections, which are primitives of any genuine Bell experiment. We show that this fundamental difference between field intensities measurements and single photon detections shifts the classical bound of relevant Bell inequalities to its non-signaling limit, leaving no place for their violations. © 2019, The Author(s).
Tue, 01 Jan 2019 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/2132392019-01-01T00:00:00Z
- On the problem of contextuality in macroscopic magnetization measurementshttps://scholarbank.nus.edu.sg/handle/10635/112476Title: On the problem of contextuality in macroscopic magnetization measurements
Authors: Soeda, A.; Kurzyński, P.; Ramanathan, R.; Grudka, A.; Thompson, J.; Kaszlikowski, D.
Abstract: We show that sharp measurements of total magnetization cannot be used to reveal contextuality in macroscopic many-body systems of spins of arbitrary dimension. We decompose each such measurement into set of projectors corresponding to well-defined value of total magnetization. We then show that such sets of projectors are too restricted to construct Kochen-Specker sets. © 2013 Elsevier B.V. All rights reserved.
Fri, 29 Nov 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124762013-11-29T00:00:00Z
- Generalized monogamy of contextual inequalities from the no-disturbance principlehttps://scholarbank.nus.edu.sg/handle/10635/52952Title: Generalized monogamy of contextual inequalities from the no-disturbance principle
Authors: Ramanathan, R.; Soeda, A.; Kurzyński, P.; Kaszlikowski, D.
Abstract: In this Letter, we demonstrate that the property of monogamy of Bell violations seen for no-signaling correlations in composite systems can be generalized to the monogamy of contextuality in single systems obeying the Gleason property of no disturbance. We show how one can construct monogamies for contextual inequalities by using the graph-theoretic technique of vertex decomposition of a graph representing a set of measurements into subgraphs of suitable independence numbers that themselves admit a joint probability distribution. After establishing that all the subgraphs that are chordal graphs admit a joint probability distribution, we formulate a precise graph-theoretic condition that gives rise to the monogamy of contextuality. We also show how such monogamies arise within quantum theory for a single four-dimensional system and interpret violation of these relations in terms of a violation of causality. These monogamies can be tested with current experimental techniques. © 2012 American Physical Society.
Wed, 01 Aug 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/529522012-08-01T00:00:00Z
- Trapping a particle of a quantum walk on the linehttps://scholarbank.nus.edu.sg/handle/10635/116659Title: Trapping a particle of a quantum walk on the line
Authors: Wójcik, A.; Łuczak, T.; Kurzyński, P.; Grudka, A.; Gdala, T.; Bednarska-Bzdȩga, M.
Abstract: We observe that changing a phase at a single point in a discrete quantum walk results in a rather surprising localization effect. For certain values of this phase change the possibility of localization strongly depends on the internal coin state of the walker. © 2012 American Physical Society.
Fri, 27 Jan 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1166592012-01-27T00:00:00Z
- Criteria for two distinguishable fermions to form a bosonhttps://scholarbank.nus.edu.sg/handle/10635/52851Title: Criteria for two distinguishable fermions to form a boson
Authors: Ramanathan, R.; Kurzynski, P.; Chuan, T.K.; Santos, M.F.; Kaszlikowski, D.
Abstract: We study the necessary conditions for systems composed of two distinguishable fermions to exhibit bosonic behavior. We base our analysis on tools of quantum information theory such as entanglement, local operations and classical communication and the majorization criterion for probability distributions. Introduction of these tools yields new insights into the old and important problem of identifying the conditions for existence of composite bosons. We precisely identify the role entanglement plays in the formation and behavior of such composite particles. © 2011 American Physical Society.
Fri, 16 Sep 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/528512011-09-16T00:00:00Z
- Contextuality in bosonic bunchinghttps://scholarbank.nus.edu.sg/handle/10635/112401Title: Contextuality in bosonic bunching
Authors: Kurzyński, P.; Soeda, A.; Thompson, J.; Kaszlikowski, D.
Abstract: In the classical probability theory a sum of probabilities of three pairwise exclusive events is always bounded by one. This is also true in quantum mechanics if these events are represented by pairwise orthogonal projectors. However, this might not be true if the three events refer to a system of indistinguishable particles. We show that one can find three pairwise exclusive events for a system of three bosonic particles whose corresponding probabilities sum to 3/2. This can be done under assumptions of realism and noncontextuality, i.e., that it is possible to assign outcomes to events before measurements are performed and in a way that does not depend on a particular measurement setup. The root of this phenomenon comes from the fact that for indistinguishable particles there are events that can be deduced to be exclusive under the aforementioned assumptions, but at the same time are complementary because the corresponding projectors are not orthogonal. © 2014 American Physical Society.
Tue, 14 Jan 2014 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124012014-01-14T00:00:00Z
- Hidden-variable problem for a continuous family of spin-1 measurementshttps://scholarbank.nus.edu.sg/handle/10635/52973Title: Hidden-variable problem for a continuous family of spin-1 measurements
Authors: Kurzyński, P.; Soeda, A.; Bzdȩga, B.; Kaszlikowski, D.
Abstract: We study a continuous set of spin-1 measurements and show that for a special family of measurements parametrized by a single variable θ the possibility of hidden-variable description depends on the rationality of θ/π. © 2013 American Physical Society.
Thu, 28 Feb 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/529732013-02-28T00:00:00Z
- Reference frames for Bell inequality violation in the presence of superselection ruleshttps://scholarbank.nus.edu.sg/handle/10635/53131Title: Reference frames for Bell inequality violation in the presence of superselection rules
Authors: Paterek, T.; Kurzyński, P.; Oi, D.K.L.; Kaszlikowski, D.
Abstract: Superselection rules (SSRs) constrain the allowed states and operations in quantum theory. They limit preparations and measurements and hence impact our ability to observe non-locality, in particular the violation of Bell inequalities. We show that a reference frame compatible with a particle number SSR does not allow observers to violate a Bell inequality if and only if it is prepared using only local operations and classical communication. In particular, jointly prepared separable reference frames are sufficient for obtaining violations of a Bell inequality. We study the size and non-local properties of such reference frames using superselection-induced variance. These results suggest the need for experimental Bell tests in the presence of superselection. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Fri, 01 Apr 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/531312011-04-01T00:00:00Z
- Local realism of macroscopic correlationshttps://scholarbank.nus.edu.sg/handle/10635/53014Title: Local realism of macroscopic correlations
Authors: Ramanathan, R.; Paterek, T.; Kay, A.; Kurzyński, P.; Kaszlikowski, D.
Abstract: We identify conditions under which correlations resulting from quantum measurements performed on macroscopic systems (systems composed of a number of particles of the order of the Avogadro number) can be described by local realism. We argue that the emergence of local realism at the macroscopic level is caused by an interplay between the monogamous nature of quantum correlations and the fact that macroscopic measurements do not reveal properties of individual particles. © 2011 American Physical Society.
Wed, 03 Aug 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/530142011-08-03T00:00:00Z
- Particle addition and subtraction channels and the behavior of composite particleshttps://scholarbank.nus.edu.sg/handle/10635/53082Title: Particle addition and subtraction channels and the behavior of composite particles
Authors: Kurzyński, P.; Ramanathan, R.; Soeda, A.; Chuan, T.K.; Kaszlikowski, D.
Abstract: Composite particles made of elementary fermions can exhibit a wide range of behavior ranging from fermionic to bosonic depending on the quantum state of the fermions and the experimental situation considered. This behavior is captured by the fundamental operations of single-particle addition and subtraction and two-particle interference. We analyze the quantum channels that implement the physical operations of addition and subtraction of indistinguishable particles. In particular, we construct optimal Kraus operators to implement these probabilistic operations for systems of a finite number of particles. We then use these to measure the quality of bosonic and fermionic behavior in terms of single-particle addition and subtraction and two-particle interference. For the specific case of composite particles made of two distinguishable fermions, we find a transition from fermionic to bosonic behavior as a function of the entanglement between the two constituents.We also apply these considerations to composite particles of two distinguishable bosons and identify the relation between entanglement and bosonic behavior for these systems. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Sat, 01 Sep 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/530822012-09-01T00:00:00Z
- Discrete-time quantum walk approach to state transferhttps://scholarbank.nus.edu.sg/handle/10635/115067Title: Discrete-time quantum walk approach to state transfer
Authors: Kurzyński, P.; Wójcik, A.
Abstract: We show that a quantum-state transfer, previously studied as a continuous-time process in networks of interacting spins, can be achieved within the model of discrete-time quantum walks with a position-dependent coin. We argue that, due to additional degrees of freedom, discrete-time quantum walks allow one to observe effects which cannot be observed in the corresponding continuous-time case. First, we study a discrete-time version of the engineered coupling protocol due to Christandl and then we discuss the general idea of conversion between continuous-time quantum walks and discrete-time quantum walks. © 2011 American Physical Society.
Mon, 13 Jun 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1150672011-06-13T00:00:00Z
- Coherent states of composite bosonshttps://scholarbank.nus.edu.sg/handle/10635/112398Title: Coherent states of composite bosons
Authors: Lee, S.-Y.; Thompson, J.; Kurzyński, P.; Soeda, A.; Kaszlikowski, D.
Abstract: We present a systematic analysis of 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. © 2013 American Physical Society.
Tue, 03 Dec 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1123982013-12-03T00:00:00Z
- Correlation complementarity yields bell monogamy relationshttps://scholarbank.nus.edu.sg/handle/10635/52847Title: Correlation complementarity yields bell monogamy relations
Authors: Kurzyński, P.; Paterek, T.; Ramanathan, R.; Laskowski, W.; Kaszlikowski, D.
Abstract: We present a method to derive Bell monogamy relations by connecting the complementarity principle with quantum nonlocality. The resulting monogamy relations are stronger than those obtained from the no-signaling principle alone. In many cases, they yield tight quantum bounds on the amount of violation of single and multiple qubit correlation Bell inequalities. In contrast with the two-qubit case, a rich structure of possible violation patterns is shown to exist in the multipartite scenario. © 2011 American Physical Society.
Tue, 03 May 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/528472011-05-03T00:00:00Z
- Entropic test of quantum contextualityhttps://scholarbank.nus.edu.sg/handle/10635/52917Title: Entropic test of quantum contextuality
Authors: Kurzyński, P.; Ramanathan, R.; Kaszlikowski, D.
Abstract: We study the contextuality of a three-level quantum system using classical conditional entropy of measurement outcomes. First, we analytically construct the minimal configuration of measurements required to reveal contextuality. Next, an entropic contextual inequality is formulated, analogous to the entropic Bell inequalities derived by Braunstein and Caves, that must be satisfied by all noncontextual theories. We find optimal measurements for violation of this inequality. The approach is easily extendable to higher dimensional quantum systems and more measurements. Our theoretical findings can be verified in the laboratory with current technology. © 2012 American Physical Society.
Wed, 11 Jul 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/529172012-07-11T00:00:00Z
- Experimental realization of generalized qubit measurements based on quantum walkshttps://scholarbank.nus.edu.sg/handle/10635/127983Title: Experimental realization of generalized qubit measurements based on quantum walks
Authors: Zhao Y.-Y.; Yu N.-K.; Kurzynski P.; Xiang G.-Y.; Li C.-F.; Guo G.-C.
Thu, 01 Jan 2015 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1279832015-01-01T00:00:00Z
- Information-theoretic Bell inequalities based on Tsallis entropyhttps://scholarbank.nus.edu.sg/handle/10635/127987Title: Information-theoretic Bell inequalities based on Tsallis entropy
Authors: Wajs M.; Kurzynski P.; Kaszlikowski D.
Thu, 01 Jan 2015 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1279872015-01-01T00:00:00Z
- Contextuality of almost all qutrit states can be revealed with nine observableshttps://scholarbank.nus.edu.sg/handle/10635/52844Title: Contextuality of almost all qutrit states can be revealed with nine observables
Authors: Kurzyński, P.; Kaszlikowski, D.
Abstract: We propose a test of quantum contextuality for a single three-level system that uses nine projective measurements. It has the form of an inequality that has to be satisfied by any noncontextual theory. We show that for any qutrit state, except for the maximally mixed state, one can always find a set of nine observables for which the corresponding inequality is violated. This inequality is a test of contextuality that may offer insight into the relation between state-dependent and state-independent contextuality tests present in the literature. © 2012 American Physical Society.
Wed, 31 Oct 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/528442012-10-31T00:00:00Z
- Fundamental monogamy relation between contextuality and nonlocalityhttps://scholarbank.nus.edu.sg/handle/10635/112443Title: Fundamental monogamy relation between contextuality and nonlocality
Authors: Kurzyński, P.; Cabello, A.; Kaszlikowski, D.
Abstract: We show that the no-disturbance principle imposes a tradeoff between locally contextual correlations violating the Klyachko-Can-Binicioǧlu- 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. © 2014 American Physical Society.
Mon, 10 Mar 2014 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124432014-03-10T00:00:00Z
- Information-theoretic metric as a tool to investigate nonclassical correlationshttps://scholarbank.nus.edu.sg/handle/10635/112454Title: Information-theoretic metric as a tool to investigate nonclassical correlations
Authors: Kurzyński, P.; Kaszlikowski, D.
Abstract: In this paper we study an application of an information-theoretic distance between two measurements to investigate nonclassical correlations. We postulate the triangle principle, which states that any information-theoretic distance is valid for any sets of measurements, regardless if they can be jointly measured or not. 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 may not hold in quantum theory. It leads to the derivation of certain inequalities whose violations are an indicator of nonclassicality. Some of these inequalities formally look the same as those found in the literature on local realism and noncontextuality, but we also derive completely different inequalities. We also show that our geometrical approach naturally implies monogamy of nonclassical correlations. © 2014 American Physical Society.
Sun, 01 Jun 2014 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124542014-06-01T00:00:00Z
- An experimental proposal for revealing contextuality in almost all qutrit stateshttps://scholarbank.nus.edu.sg/handle/10635/112381Title: An experimental proposal for revealing contextuality in almost all qutrit states
Authors: Thompson, J.; Pisarczyk, R.; Kurzyński, P.; Kaszlikowski, D.
Abstract: 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 single mode. We also discuss the impact of detector inefficiency and losses and review the theoretical foundations of this test.
Tue, 01 Jan 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1123812013-01-01T00:00:00Z
- Relation between nonlocality and contextuality for a biphotonhttps://scholarbank.nus.edu.sg/handle/10635/53134Title: Relation between nonlocality and contextuality for a biphoton
Authors: Soeda, A.; Kurzyński, P.; Ramanathan, R.; Modi, K.; Kaszlikowski, D.
Abstract: 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 spatiotemporal 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. © 2013 American Physical Society.
Mon, 25 Feb 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/531342013-02-25T00:00:00Z
- Quantum walk as a generalized measuring devicehttps://scholarbank.nus.edu.sg/handle/10635/112507Title: Quantum walk as a generalized measuring device
Authors: Kurzyński, P.; Wójcik, A.
Abstract: We show that a one-dimensional discrete time quantum walk can be used to implement a generalized measurement in terms of a positive operator value measure (POVM) on a single qubit. More precisely, we show that for a single qubit any set of rank 1 and rank 2 POVM elements can be generated by a properly engineered quantum walk. In such a scenario the measurement of a particle at a position x=i corresponds to a measurement of a POVM element Ei on a qubit. Since the idea of quantum walks originates from the von Neumann model of measurement, in which the change of the position of the pointer depends on the state of the system that is being measured, we argue that von Neumann measurements can be naturally extended to POVMs if one includes the internal evolution of the system in the model. © 2013 American Physical Society.
Tue, 14 May 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1125072013-05-14T00:00:00Z