ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sat, 04 Feb 2023 16:18:00 GMT2023-02-04T16:18:00Z50121- Optimal asymmetric quantum cloning for quantum information and computationhttps://scholarbank.nus.edu.sg/handle/10635/112480Title: Optimal asymmetric quantum cloning for quantum information and computation
Authors: Kay, A.; Ramanathan, R.; Kaszlikowshi, D.
Abstract: While the no-cloning theorem, which forbids the perfect copying of quantum states, is well-known as one of the defining features of quantum mechanics, the question of how well the theory allows a state to be cloned is yet to be completely solved. In this paper, rigorous solutions to the problem of M → N asymmetric cloning of qudits are obtained in a number of interesting cases. The central result is the solution to the 1 → N universal asymmetric qudit cloning problem for which the exact trade-off in the fidelities of the clones for every N and d is derived. Analogous results are proven for qubits when M = N - 1. We also consider state-dependent 1 → N qubit cloning, providing a general parametrization in terms of a Heisenberg star Hamiltonian. In all instances, we determine the feasibility of implementing the cloning economically, i.e., without an ancilla, and determine the dimension of the ancilla when an economic implementation is not possible. © Rinton Press.
Tue, 01 Jan 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124802013-01-01T00:00:00Z
- Geometric phase for mixed stateshttps://scholarbank.nus.edu.sg/handle/10635/114336Title: Geometric phase for mixed states
Authors: Kwek, L.C.; Tong, D.M.; Chen, J.L.; Du, J.F.; Choo, K.W.; Ravishankar, R.; Kaszlikowski, D.; Oh, C.H.
Abstract: We present a kinematic approach for obtaining the geometric phase of a mixed state under nonunitary evolution. This phase is gauge-invariant and measurable and leads to well-known results for unitary evolution. © Nauka/Interperiodica 2006.
Wed, 01 Feb 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1143362006-02-01T00:00:00Z
- 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
- 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
- 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
- Optimal Cloning and Singlet Monogamyhttps://scholarbank.nus.edu.sg/handle/10635/112481Title: Optimal Cloning and Singlet Monogamy
Authors: Kay, A.; Kaszlikowski, D.; Ramanathan, R.
Abstract: The inability to produce two perfect copies of an unknown state is inherently linked with the inability to produce maximal entanglement between multiple spins. Despite this, there is no quantitative link between how much entanglement can be generated between spins, and how well an unknown state can be cloned. This situation is remedied by giving a set of sufficient conditions such that a Completely Positive map can be optimally implemented as a teleportation operation into a standard, reference, state. The case of arbitrary 1→N asymmetric cloning of d-dimensional spins can then be solved exactly, yielding the concept of "singlet monogamy." The utility of this relation is demonstrated by calculating properties of Heisenberg systems, and contrasting them with the results from standard monogamy arguments. © 2009 The American Physical Society.
Thu, 06 Aug 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124812009-08-06T00:00:00Z
- 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
- 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
- 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
- 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
- Entanglement in doped resonating valence bond stateshttps://scholarbank.nus.edu.sg/handle/10635/112428Title: Entanglement in doped resonating valence bond states
Authors: Ramanathan, R.; Kaszlikowski, D.; Wiesniak, M.; Vedral, V.
Abstract: We investigate the entanglement properties of resonating valence bond (RVB) states on a two-dimensional lattice in the presence of dopants that remove electrons from the lattice creating holes. The movement of the holes generated by the Hubbard Hamiltonian in the regime of strong Coulomb repulsion in this setting could be responsible for the phenomenon of high-temperature superconductivity as hypothesized by. We argue that there is a particular density of dopants (holes) where the entanglement contained in the lattice attains its maximal value for the nearest-neighbor RVB liquid state. This result implies that many-body entanglement may be related to quantum phase transitions that are modeled by RVB theory. © 2008 The American Physical Society.
Mon, 01 Dec 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124282008-12-01T00:00:00Z
- 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