ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Mon, 18 Nov 2019 11:35:48 GMT2019-11-18T11:35:48Z50991- Regional versus global entanglement in resonating-valence-bond stateshttps://scholarbank.nus.edu.sg/handle/10635/97789Title: Regional versus global entanglement in resonating-valence-bond states
Authors: Chandran, A.; Kaszlikowski, D.; Sen, A.; Sen, U.; Vedral, V.
Abstract: We investigate the entanglement properties of resonating-valence-bond states on two and higher dimensional lattices, which play a significant role in our understanding of various many-body systems. We show that these states are genuinely multipartite entangled, while there is only a negligible amount of two-site entanglement. We comment on possible physical implications of our findings. © 2007 The American Physical Society.
Thu, 25 Oct 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/977892007-10-25T00:00:00Z
- Quantum physics meets biologyhttps://scholarbank.nus.edu.sg/handle/10635/97702Title: Quantum physics meets biology
Authors: Arndt, M.; Juffmann, T.; Vedral, V.
Abstract: Quantum physics and biology have long been regarded as unrelated disciplines, describing nature at the inanimate microlevel on the one hand and living species on the other hand. Over the past decades the life sciences have succeeded in providing ever more and refined explanations of macroscopic phenomena that were based on an improved understanding of molecular structures and mechanisms. Simultaneously, quantum physics, originally rooted in a world-view of quantum coherences, entanglement, and other nonclassical effects, has been heading toward systems of increasing complexity. The present perspective article shall serve as a "pedestrian guide" to the growing interconnections between the two fields. We recapitulate the generic and sometimes unintuitive characteristics of quantum physics and point to a number of applications in the life sciences. We discuss our criteria for a future "quantum biology," its current status, recent experimental progress, and also the restrictions that nature imposes on bold extrapolations of quantum theory to macroscopic phenomena. © HFSP Publishing.
Tue, 01 Dec 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/977022009-12-01T00:00:00Z
- How much of one-way computation is just thermodynamics?https://scholarbank.nus.edu.sg/handle/10635/96836Title: How much of one-way computation is just thermodynamics?
Authors: Anders, J.; Hajdušek, M.; Markham, D.; Vedral, V.
Abstract: In this paper we argue that one-way quantum computation can be seen as a form of phase transition with the available information about the solution of the computation being the order parameter. We draw a number of striking analogies between standard thermodynamical quantities such as energy, temperature, work, and corresponding computational quantities such as the amount of entanglement, time, potential capacity for computation, respectively. Aside from being intuitively pleasing, this picture allows us to make novel conjectures, such as an estimate of the necessary critical time to finish a computation and a proposal of suitable architectures for universal one-way computation in 1D. © 2008 Springer Science+Business Media, LLC.
Sun, 01 Jun 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/968362008-06-01T00:00:00Z
- Information and physicshttps://scholarbank.nus.edu.sg/handle/10635/96929Title: Information and physics
Authors: Vedral, V.
Abstract: In this paper I discuss the question: what comes first, physics or information? The two have had a long-standing, symbiotic relationship for almost a hundred years out of which we have learnt a great deal. Information theory has enriched our interpretations of quantum physics, and, at the same time, offered us deep insights into general relativity through the study of black hole thermodynamics. Whatever the outcome of this debate, I argue that physicists will be able to benefit from continuing to explore connections between the two. © 2012 by the authors; licensee MDPI, Basel, Switzerland.
Sun, 01 Jan 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/969292012-01-01T00:00:00Z
- Entanglement in many-body systemshttps://scholarbank.nus.edu.sg/handle/10635/96487Title: Entanglement in many-body systems
Authors: Amico, L.; Fazio, R.; Osterloh, A.; Vedral, V.
Abstract: Recent interest in aspects common to quantum information and condensed matter has prompted a flurry of activity at the border of these disciplines that were far distant until a few years ago. Numerous interesting questions have been addressed so far. Here an important part of this field, the properties of the entanglement in many-body systems, are reviewed. The zero and finite temperature properties of entanglement in interacting spin, fermion, and boson model systems are discussed. Both bipartite and multipartite entanglement will be considered. In equilibrium entanglement is shown tightly connected to the characteristics of the phase diagram. The behavior of entanglement can be related, via certain witnesses, to thermodynamic quantities thus offering interesting possibilities for an experimental test. Out of equilibrium entangled states are generated and manipulated by means of many-body Hamiltonians. © 2008 The American Physical Society.
Tue, 06 May 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/964872008-05-06T00:00:00Z
- Nonadiabatic geometric quantum computationhttps://scholarbank.nus.edu.sg/handle/10635/97328Title: Nonadiabatic geometric quantum computation
Authors: Wang, Z.S.; Wu, C.; Feng, X.-L.; Kwek, L.C.; Lai, C.H.; Oh, C.H.; Vedral, V.
Abstract: A different way to realize nonadiabatic geometric quantum computation is proposed by varying parameters in the Hamiltonian for nuclear-magnetic resonance, where the dynamical and geometric phases are implemented separately without the usual operational process. Therefore the phase accumulated in the geometric gate is a pure geometric phase for any input state. In comparison with the conventional geometric gates by rotating operations, our approach simplifies experimental implementations making them robust to certain experimental errors. In contrast to the unconventional geometric gates, our approach distinguishes the total and geometric phases and offers a wide choice of the relations between the dynamical and geometric phases. © 2007 The American Physical Society.
Fri, 05 Oct 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/973282007-10-05T00:00:00Z
- Local characterization of one-dimensional topologically ordered stateshttps://scholarbank.nus.edu.sg/handle/10635/97081Title: Local characterization of one-dimensional topologically ordered states
Authors: Cui, J.; Amico, L.; Fan, H.; Gu, M.; Hamma, A.; Vedral, V.
Abstract: We consider one-dimensional Hamiltonian systems whose ground states display symmetry-protected topological order. We show that ground states within the topological phase cannot be connected with each other through local operations and classical communication between a bipartition of the system. Our claim is demonstrated by analyzing the entanglement spectrum and Rényi entropies of different physical systems that provide examples for symmetry-protected topological phases. Specifically, we consider the spin-1/2 cluster-Ising model and a class of spin-1 models undergoing quantum phase transitions to the Haldane phase. Our results provide a probe for symmetry-protected topological order. Since the picture holds even at the system's local scale, our analysis can serve as a local experimental test for topological order. © 2013 American Physical Society.
Wed, 11 Sep 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/970812013-09-11T00:00:00Z
- Quantum entanglementhttps://scholarbank.nus.edu.sg/handle/10635/98986Title: Quantum entanglement
Authors: Vedral, V.
Wed, 01 Jan 2014 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/989862014-01-01T00:00:00Z
- Nonlocality of a single particlehttps://scholarbank.nus.edu.sg/handle/10635/97354Title: Nonlocality of a single particle
Authors: Dunningham, J.; Vedral, V.
Abstract: There has been a great deal of debate surrounding the issue of whether it is possible for a single photon to exhibit nonlocality. A number of schemes have been proposed that claim to demonstrate this effect, but each has been met with significant opposition. The objections hinge largely on the fact that these schemes use unobservable initial states and so, it is claimed, they do not represent experiments that could actually be performed. Here we show how it is possible to overcome these objections by presenting an experimentally feasible scheme that uses realistic initial states. Furthermore, all the techniques required for photons are equally applicable to atoms. It should, therefore, also be possible to use this scheme to verify the nonlocality of a single massive particle. © 2007 The American Physical Society.
Fri, 02 Nov 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/973542007-11-02T00:00:00Z
- Requirement of dissonance in assisted optimal state discriminationhttps://scholarbank.nus.edu.sg/handle/10635/115913Title: Requirement of dissonance in assisted optimal state discrimination
Authors: Zhang, F.-L.; Chen, J.-L.; Kwek, L.C.; Vedral, V.
Abstract: A fundamental problem in quantum information is to explore what kind of quantum correlations is responsible for successful completion of a quantum information procedure. Here we study the roles of entanglement, discord, and dissonance needed for optimal quantum state discrimination when the latter is assisted with an auxiliary system. In such process, we present a more general joint unitary transformation than the existing results. The quantum entanglement between a principal qubit and an ancilla is found to be completely unnecessary, as it can be set to zero in the arbitrary case by adjusting the parameters in the general unitary without affecting the success probability. This result also shows that it is quantum dissonance that plays as a key role in assisted optimal state discrimination and not quantum entanglement. A necessary criterion for the necessity of quantum dissonance based on the linear entropy is also presented. PACS numbers: 03.65.Ta, 03.67.Mn, 42.50.Dv.
Tue, 01 Jan 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1159132013-01-01T00:00:00Z
- Natural mode entanglement as a resource for quantum communicationhttps://scholarbank.nus.edu.sg/handle/10635/112468Title: Natural mode entanglement as a resource for quantum communication
Authors: Heaney, L.; Vedral, V.
Abstract: Natural particle-number entanglement resides between spatial modes in coherent ultracold atomic gases. However, operations on the modes are restricted by a superselection rule that forbids coherent superpositions of different particle numbers. This seemingly prevents mode entanglement being used as a resource for quantum communication. In this Letter, we demonstrate that mode entanglement of a single massive particle can be used for dense coding and quantum teleportation despite the superselection rule. In particular, we provide schemes where the dense coding linear photonic channel capacity is reached without a shared reservoir and where the full quantum channel capacity is achieved if both parties share a coherent particle reservoir. © 2009 The American Physical Society.
Wed, 11 Nov 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124682009-11-11T00:00:00Z
- Necessary and sufficient condition for nonzero quantum discordhttps://scholarbank.nus.edu.sg/handle/10635/97304Title: Necessary and sufficient condition for nonzero quantum discord
Authors: Dakić, B.; Vedral, V.; Brukner, C.
Abstract: Quantum discord characterizes "nonclassicality" of correlations in quantum mechanics. It has been proposed as the key resource present in certain quantum communication tasks and quantum computational models without containing much entanglement. We obtain a necessary and sufficient condition for the existence of nonzero quantum discord for any dimensional bipartite states. This condition is easily experimentally implementable. Based on this, we propose a geometrical way of quantifying quantum discord. For two qubits this results in a closed form of expression for discord. We apply our results to the model of deterministic quantum computation with one qubit, showing that quantum discord is unlikely to be the reason behind its speedup. © 2010 The American Physical Society.
Tue, 02 Nov 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/973042010-11-02T00:00:00Z
- Classical and quantum correlations under decoherencehttps://scholarbank.nus.edu.sg/handle/10635/95991Title: Classical and quantum correlations under decoherence
Authors: Maziero, J.; Céleri, L.C.; Serra, R.M.; Vedral, V.
Abstract: Recently some authors have pointed out that there exist nonclassical correlations which are more general, and possibly more fundamental, than entanglement. For these general quantum correlations and their classical counterparts, under the action of decoherence, we identify three general types of dynamics that include a peculiar sudden change in their decay rates. We show that, under suitable conditions, the classical correlation is unaffected by decoherence. Such dynamic behavior suggests an operational measure of both classical and quantum correlations that can be computed without any extremization procedure. © 2009 The American Physical Society.
Wed, 07 Oct 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/959912009-10-07T00:00:00Z
- The Elusive Source of Quantum Speeduphttps://scholarbank.nus.edu.sg/handle/10635/98267Title: The Elusive Source of Quantum Speedup
Authors: Vedral, V.
Abstract: We discuss two qualities of quantum systems: various correlations existing between their subsystems and the distinguishability of different quantum states. This is then applied to analysing quantum information processing. While quantum correlations, or entanglement, are clearly of paramount importance for efficient pure state manipulations, mixed states present a much richer arena and reveal a more subtle interplay between correlations and distinguishability. The current work explores a number of issues related with identifying the important ingredients needed for quantum information processing. We discuss the Deutsch-Jozsa algorithm, the Shor algorithm, the Grover algorithm and the power of a single qubit class of algorithms. In the latter, a quantity called discord is seen to be more important than entanglement. One section is dedicated to cluster states where entanglement is crucial, but its precise role is highly counter-intuitive. Here we see that the notion of distinguishability becomes a more useful concept. © 2010 Springer Science+Business Media, LLC.
Fri, 01 Jan 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/982672010-01-01T00:00:00Z
- Kaszlikowski et al. Reply:https://scholarbank.nus.edu.sg/handle/10635/98981Title: Kaszlikowski et al. Reply:
Authors: Kaszlikowski, D.; Sen, A.; Sen, U.; Vedral, V.
Mon, 08 Dec 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/989812008-12-08T00:00:00Z
- Sustained quantum coherence and entanglement in the avian compasshttps://scholarbank.nus.edu.sg/handle/10635/112524Title: Sustained quantum coherence and entanglement in the avian compass
Authors: Gauger, E.M.; Rieper, E.; Morton, J.J.L.; Benjamin, S.C.; Vedral, V.
Abstract: In artificial systems, quantum superposition and entanglement typically decay rapidly unless cryogenic temperatures are used. Could life have evolved to exploit such delicate phenomena? Certain migratory birds have the ability to sense very subtle variations in Earth's magnetic field. Here we apply quantum information theory and the widely accepted "radical pair" model to analyze recent experimental observations of the avian compass. We find that superposition and entanglement are sustained in this living system for at least tens of microseconds, exceeding the durations achieved in the best comparable man-made molecular systems. This conclusion is starkly at variance with the view that life is too "warm and wet" for such quantum phenomena to endure. © 2011 American Physical Society.
Tue, 25 Jan 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1125242011-01-25T00:00:00Z
- Spatial entanglement from off-diagonal long-range order in a Bose-Einstein condensatehttps://scholarbank.nus.edu.sg/handle/10635/97975Title: Spatial entanglement from off-diagonal long-range order in a Bose-Einstein condensate
Authors: Heaney, L.; Anders, J.; Kaszlikowski, D.; Vedral, V.
Abstract: We investigate spatial entanglement-particle-number entanglement between regions of space-in an ideal bosonic gas. We quantify the amount of spatial entanglement around the transition temperature for condensation (TC) by probing the gas with two localized two-level systems. We show that spatial entanglement in the gas is directly related to filling of the ground-state energy level and therefore to the off-diagonal long-range order of the system and the onset of condensation. © 2007 The American Physical Society.
Wed, 07 Nov 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/979752007-11-07T00:00:00Z
- Wigner rotations and an apparent paradox in relativistic quantum informationhttps://scholarbank.nus.edu.sg/handle/10635/98587Title: Wigner rotations and an apparent paradox in relativistic quantum information
Authors: Saldanha, P.L.; Vedral, V.
Abstract: It is shown that a general model for particle detection in combination with a linear application of the Wigner rotations, which correspond to momentum-dependent changes of the particle spin under Lorentz transformations, to the state of a massive relativistic particle in a superposition of two counterpropagating momentum states leads to a paradox. The paradox entails the instantaneous transmission of information between two spatially separated parties. A solution to the paradox is given when the physical construction of the corresponding state is taken into account, suggesting that we cannot in general linearly apply the Wigner rotations to a quantum state without considering the appropriate physical interpretation. © 2013 American Physical Society.
Wed, 03 Apr 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/985872013-04-03T00:00:00Z
- Classical to quantum in large-number limithttps://scholarbank.nus.edu.sg/handle/10635/116260Title: Classical to quantum in large-number limit
Authors: Modi, K.; Fazio, R.; Pascazio, S.; Vedral, V.; Yuasa, K.
Abstract: We construct a quantumness witness following the work of Alicki & van Ryn (AvR). We reformulate the AvR test by defining it for quantum states rather than for observables. This allows us to identify the necessary quantities and resources to detect quantumness for any given system. The first quantity turns out to be the purity of the system. When applying the witness to a system with even moderate mixedness, the protocol is unable to reveal any quantumness. We then show that having many copies of the system leads the witness to reveal quantumness. This seems contrary to the Bohr correspondence, which asserts that, in the large-number limit, quantum systems become classical, whereas the witness shows quantumness when several non-quantum systems, as determined by the witness, are considered together. However, the resources required to detect the quantumness increase dramatically with the number of systems. We apply the quantumness witness for systems that are highly mixed but in the large-number limit that resembles nuclear magnetic resonance (NMR) systems. We make several conclusions about detecting quantumness in NMR-like systems. © 2012 The Royal Society.
Sat, 13 Oct 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1162602012-10-13T00:00:00Z
- Unification of quantum and classical correlations and quantumness measureshttps://scholarbank.nus.edu.sg/handle/10635/116800Title: Unification of quantum and classical correlations and quantumness measures
Authors: Modi, K.; Vedral, V.
Abstract: We give a pedagogical introduction to quantum discord and discuss the problem of separation of total correlations in a given quantum state into entanglement, dissonance, and classical correlations using the concept of relative entropy. This allows us to put all correlations on an equal footing. Entanglement and dissonance jointly belong to what is known as quantum discord. Our methods are completely applicable for multipartite systems of arbitrary dimensions. We finally show, using relative entropy, how different notions of quantum correlations are related to each other. This gives a single theory that incorporates all correlations, quantum and classical, and different methods of quantifying them. © 2011 American Institute of Physics.
Sat, 01 Jan 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1168002011-01-01T00:00:00Z
- Qantum correlations in biomoleculeshttps://scholarbank.nus.edu.sg/handle/10635/98860Title: Qantum correlations in biomolecules
Authors: Vedral, V.
Abstract: In this paper we identify quantum entanglement, quantum discord and classical correlations as the main classes of correlations present in many body systems, such as biomolecules. We show how to witness the presene of entanglement and quantum discord. All witnesses can be accessed with simple measurements and implemented with current technology. We discuss the relationship between the speed of processing and presence of correlations and illustrate it in the case of photosynthesis and magnetoreception. © 2011 Published by Elsevier Ltd.
Sat, 01 Jan 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/988602011-01-01T00:00:00Z
- Statistical mechanics of the cluster Ising modelhttps://scholarbank.nus.edu.sg/handle/10635/98019Title: Statistical mechanics of the cluster Ising model
Authors: Smacchia, P.; Amico, L.; Facchi, P.; Fazio, R.; Florio, G.; Pascazio, S.; Vedral, V.
Abstract: We study a Hamiltonian system describing a three-spin-1/2 clusterlike interaction competing with an Ising-like antiferromagnetic interaction. We compute free energy, spin-correlation functions, and entanglement both in the ground and in thermal states. The model undergoes a quantum phase transition between an Ising phase with a nonvanishing magnetization and a cluster phase characterized by a string order. Any two-spin entanglement is found to vanish in both quantum phases because of a nontrivial correlation pattern. Nevertheless, the residual multipartite entanglement is maximal in the cluster phase and dependent on the magnetization in the Ising phase. We study the block entropy at the critical point and calculate the central charge of the system, showing that the criticality of the system is beyond the Ising universality class. © 2011 American Physical Society.
Tue, 02 Aug 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/980192011-08-02T00:00:00Z
- Quantum nonlocality test by spectral joint measurements of qubits in driven cavityhttps://scholarbank.nus.edu.sg/handle/10635/97699Title: Quantum nonlocality test by spectral joint measurements of qubits in driven cavity
Authors: Yuan, H.; Wei, L.F.; Huang, J.S.; Vedral, V.
Abstract: We propose a feasible approach to test quantum nonlocality with two qubits dispersively coupled to a driven cavity. Our proposal is based on spectral joint measurements of two qubits, i.e., their quantum states in the computational basis states {|kl,k,l=0,1} can be measured nondestructively by detecting the steady-state transmission spectra of the driven cavity. With this kind of measurements, the existence of Bell state can be robustly confirmed instead of conventional quantum state tomography. Then this kind of measurements is further utilized to test CHSH-Bell inequality. The advantage and feasibility of our proposal are also discussed. © Copyright EPLA, 2012.
Mon, 01 Oct 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/976992012-10-01T00:00:00Z
- Entanglement at the quantum phase transition in a harmonic latticehttps://scholarbank.nus.edu.sg/handle/10635/96483Title: Entanglement at the quantum phase transition in a harmonic lattice
Authors: Rieper, E.; Anders, J.; Vedral, V.
Abstract: The entanglement properties of phase transition in a twodimensional harmonic lattice, similar to the one observed in recent ion trap experiments, are discussed for both finite number of particles and thermodynamical limit. We show that for the ground state at the critical value of the trapping potential, two entanglement measures, the negativity between two neighbouring sites and the block entropy for blocks of size 1, 2 and 3, change abruptly. Entanglement thus indicates quantum phase transitions in general, not only in the finite-dimensional case considered inWu et al (2004 Phys. Rev. Lett. 93 250404). Finally, we consider the thermal state and compare its exact entanglement with a temperature entanglement witness introduced in Anders (2008 Phys. Rev. A 77 062102). © IOP Publishing Ltd. and Deutsche Physikalische Gesellschaft.
Fri, 26 Feb 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/964832010-02-26T00:00:00Z
- Entanglement in disordered and non-equilibrium systemshttps://scholarbank.nus.edu.sg/handle/10635/96486Title: Entanglement in disordered and non-equilibrium systems
Authors: Hide, J.; Vedral, V.
Abstract: We calculate an entanglement witness for a disordered spin system using the method of functional many-body perturbation theory, comparing the effect of taking a quenched and an annealed average over the disorder. We find, on considering the example of an XX Heisenberg spin chain with a Dzyaloshinskii-Moriya interaction, that disorder in the Dzyaloshinskii-Moriya interaction increases the region of entanglement detected by the witness. We also discuss a method of detecting entanglement in far from equilibrium systems. © 2009 Elsevier B.V. All rights reserved.
Fri, 01 Jan 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/964862010-01-01T00:00:00Z
- Global asymmetry of many-qubit correlations: A lattice-gauge-theory approachhttps://scholarbank.nus.edu.sg/handle/10635/112446Title: Global asymmetry of many-qubit correlations: A lattice-gauge-theory approach
Authors: Williamson, M.S.; Ericsson, M.; Johansson, M.; Sjöqvist, E.; Sudbery, A.; Vedral, V.
Abstract: We introduce a bridge between the familiar gauge field theory approaches used in many areas of modern physics such as quantum field theory and the stochastic local operations and classical communication protocols familiar in quantum information. Although the mathematical methods are the same, the meaning of the gauge group is different. The measure we introduce, "twist," is constructed as a Wilson loop from a correlation-induced holonomy. The measure can be understood as the global asymmetry of the bipartite correlations in a loop of three or more qubits; if the holonomy is trivial (the identity matrix), the bipartite correlations can be globally untwisted using general local qubit operations, the gauge group of our theory, which turns out to be the group of Lorentz transformations familiar from special relativity. If it is not possible to globally untwist the bipartite correlations in a state using local operations, the twistedness is given by a nontrivial element of the Lorentz group, the correlation-induced holonomy. We provide several analytical examples of twisted and untwisted states for three qubits, the most elementary nontrivial loop one can imagine. © 2011 American Physical Society.
Fri, 02 Sep 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124462011-09-02T00:00:00Z
- Quantum correlation without classical correlationshttps://scholarbank.nus.edu.sg/handle/10635/112493Title: Quantum correlation without classical correlations
Authors: Kaszlikowski, D.; Sen, A.; Sen, U.; Vedral, V.; Winter, A.
Abstract: We show that genuine multiparty quantum correlations can exist on its own, without a supporting background of genuine multiparty classical correlations, even in macroscopic systems. Such possibilities can have important implications in the physics of quantum information and phase transitions. © 2008 The American Physical Society.
Wed, 13 Aug 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124932008-08-13T00:00:00Z
- Entanglement production in non-equilibrium thermodynamicshttps://scholarbank.nus.edu.sg/handle/10635/96493Title: Entanglement production in non-equilibrium thermodynamics
Authors: Vedral, V.
Abstract: We define and analyse the concept of entanglement production during the evolution of a general quantum mechanical dissipative system. While it is important to minimise entropy production in order to achieve thermodynamical efficiency, maximising the rate of change of entanglement is important in quantum information processing. Quantitative relations are obtained between entropy and entanglement productions, under specific assumptions detailed in the text. We apply these to the processes of dephasing and decay of correlations between two initially entangled qubits. Both the Master equation treatment as well as the higher Hilbert space analysis are presented. Our formalism is very general and contains as special cases many reported individual instance of entanglement dynamics, such as, for example, the recently discovered notion of the sudden death of entanglement. © 2009 IOP Publishing Ltd.
Thu, 01 Jan 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/964932009-01-01T00:00:00Z
- Detection and engineering of spatial mode entanglement with ultracold bosonshttps://scholarbank.nus.edu.sg/handle/10635/115062Title: Detection and engineering of spatial mode entanglement with ultracold bosons
Authors: Goold, J.; Heaney, L.; Busch, T.; Vedral, V.
Abstract: We outline an interferometric scheme for the detection of bimode and multimode spatial entanglement of finite-temperature interacting Bose gases. Whether entanglement is present in the gas depends on the existence of the single-particle reduced density matrix between different regions of space. We apply the scheme to the problem of a harmonically trapped repulsive boson pair and show that while entanglement is rapidly decreasing with temperature, a significant amount remains for all interaction strengths at zero temperature. Thus, by tuning the interaction parameter, the distribution of entanglement between many spatial modes can be modified. © 2009 The American Physical Society.
Fri, 28 Aug 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1150622009-08-28T00:00:00Z
- Heat capacity as an indicator of entanglementhttps://scholarbank.nus.edu.sg/handle/10635/117034Title: Heat capacity as an indicator of entanglement
Authors: Wieśniak, M.; Vedral, V.; Brukner, C.
Abstract: We demonstrate that the presence of entanglement in macroscopic bodies (e.g., solids) in thermodynamical equilibrium could be revealed by measuring heat capacity. The idea is that if the system was in a separable state, then for certain Hamiltonians heat capacity would not tend asymptotically to zero as the temperature approaches absolute zero. Since this would contradict the third law of thermodynamics, one concludes that the system must contain entanglement. The separable bounds are obtained by minimalization of the heat capacity over separable states and using its universal low-temperature behavior. Our results open up a possibility to use standard experimental techniques of solid-state physics-namely, heat-capacity measurements-to detect entanglement in macroscopic samples. © 2008 The American Physical Society.
Tue, 12 Aug 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1170342008-08-12T00:00:00Z
- Quantum phases with differing computational powerhttps://scholarbank.nus.edu.sg/handle/10635/112504Title: Quantum phases with differing computational power
Authors: Cui, J.; Gu, M.; Kwek, L.C.; Santos, M.F.; Fan, H.; Vedral, V.
Abstract: The observation that concepts from quantum information has generated many alternative indicators of quantum phase transitions hints that quantum phase transitions possess operational significance with respect to the processing of quantum information. Yet, studies on whether such transitions lead to quantum phases that differ in their capacity to process information remain limited. Here we show that there exist quantum phase transitions that cause a distinct qualitative change in our ability to simulate certain quantum systems under perturbation of an external field by local operations and classical communication. In particular, we show that in certain quantum phases of the XY model, adiabatic perturbations of the external magnetic field can be simulated by local spin operations, whereas the resulting effect within other phases results in coherent non-local interactions. We discuss the potential implications to adiabatic quantum computation, where a computational advantage exists only when adiabatic perturbation results in coherent multi-body interactions. © 2012 Macmillan Publishers Limited. All rights reserved.
Sun, 01 Jan 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1125042012-01-01T00:00:00Z
- Behavior of entanglement and Cooper pairs under relativistic boostshttps://scholarbank.nus.edu.sg/handle/10635/95861Title: Behavior of entanglement and Cooper pairs under relativistic boosts
Authors: Palge, V.; Vedral, V.; Dunningham, J.A.
Abstract: Recent work has shown how single-particle entangled states are transformed when boosted in relativistic frames for certain restricted geometries. Here we extend that work to consider completely general inertial boosts. We then apply our single-particle results to multiparticle entanglements by focusing on Cooper pairs of electrons. We show that a standard Cooper pair state consisting of a spin-singlet acquires spin-triplet components in a relativistically boosted inertial frame, regardless of the geometry. We also show that, if we start with a spin-triplet pair, two out of the three triplet states acquire a singlet component, the size of which depends on the geometry. This transformation between the different singlet and triplet superconducting pairs may lead to a better understanding of unconventional superconductivity. © 2011 American Physical Society.
Fri, 14 Oct 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/958612011-10-14T00:00:00Z
- Effects of quantum coherence in metalloprotein electron transferhttps://scholarbank.nus.edu.sg/handle/10635/115081Title: Effects of quantum coherence in metalloprotein electron transfer
Authors: Dorner, R.; Goold, J.; Heaney, L.; Farrow, T.; Vedral, V.
Abstract: Many intramolecular electron transfer (ET) reactions in biology are mediated by metal centers in proteins. This process is commonly described by a model of diffusive hopping according to the semiclassical theories of Marcus and Hopfield. However, recent studies have raised the possibility that nontrivial quantum mechanical effects play a functioning role in certain biomolecular processes. Here, we investigate the potential effects of quantum coherence in biological ET by extending the semiclassical model to allow for the possibility of quantum coherent phenomena using a quantum master equation based on the Holstein Hamiltonian. We test the model on the structurally defined chain of seven iron-sulfur clusters in nicotinamide adenine dinucleotide plus hydrogen:ubiquinone oxidoreductase (complex I), a crucial respiratory enzyme and one of the longest chains of metal centers in biology. Using experimental parameters where possible, we find that, in limited circumstances, a small quantum mechanical contribution can provide a marked increase in the ET rate above the semiclassical diffusive-hopping rate. Under typical biological conditions, our model reduces to well-known diffusive behavior. © 2012 American Physical Society.
Wed, 26 Sep 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1150812012-09-26T00:00:00Z
- Experimental demonstration of a unified framework for mixed-state geometric phaseshttps://scholarbank.nus.edu.sg/handle/10635/96552Title: Experimental demonstration of a unified framework for mixed-state geometric phases
Authors: Zhu, J.; Shi, M.; Vedral, V.; Peng, X.; Suter, D.; Du, J.
Abstract: Geometric phases have been found in every major branch of physics and play an important role in mathematics and quantum computation. Here, we unify two proposed definitions of the geometric phase in mixed states - Uhlmann's phase and Sjöqvist's phase - in a new formalism based on interferometry and further provide an experimental demonstration in NMR. This is also the first experimental measurement of Uhlmann's geometric phase. © 2011 Europhysics Letters Association.
Fri, 01 Apr 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/965522011-04-01T00:00:00Z
- Entanglement spectrum: Identification of the transition from vortex-liquid to vortex-lattice state in a weakly interacting rotating Bose-Einstein condensatehttps://scholarbank.nus.edu.sg/handle/10635/96495Title: Entanglement spectrum: Identification of the transition from vortex-liquid to vortex-lattice state in a weakly interacting rotating Bose-Einstein condensate
Authors: Liu, Z.; Guo, H.-L.; Vedral, V.; Fan, H.
Abstract: We use entanglement to investigate the transition from vortex-liquid phase to vortex-lattice phase in a weakly interacting rotating Bose-Einstein condensate. For the torus geometry, the ground-state entanglement spectrum is analyzed to distinguish these two phases. The low-lying part of the ground-state entanglement spectrum, as well as the behavior of its lowest level, changes clearly when the transition occurs. For the sphere geometry, the entanglement gap in the conformal limit is also studied. We also show that the decrease in entanglement between particles can be regarded as a signal of the transition. © 2011 American Physical Society.
Mon, 24 Jan 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/964952011-01-24T00:00:00Z
- Classification of macroscopic quantum effectshttps://scholarbank.nus.edu.sg/handle/10635/127811Title: Classification of macroscopic quantum effects
Authors: Farrow T; Vedral V
Thu, 01 Jan 2015 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1278112015-01-01T00:00:00Z
- Emergent Thermodynamics in a Quenched Quantum Many-Body Systemhttps://scholarbank.nus.edu.sg/handle/10635/96445Title: Emergent Thermodynamics in a Quenched Quantum Many-Body System
Authors: Dorner, R.; Goold, J.; Cormick, C.; Paternostro, M.; Vedral, V.
Abstract: We study the statistics of the work done, fluctuation relations, and irreversible entropy production in a quantum many-body system subject to the sudden quench of a control parameter. By treating the quench as a thermodynamic transformation we show that the emergence of irreversibility in the nonequilibrium dynamics of closed many-body quantum systems can be accurately characterized. We demonstrate our ideas by considering a transverse quantum Ising model that is taken out of equilibrium by an instantaneous change of the transverse field. © 2012 American Physical Society.
Thu, 18 Oct 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/964452012-10-18T00:00:00Z
- Quantumness without quantumness: Entanglement as classical correlations in higher dimensionshttps://scholarbank.nus.edu.sg/handle/10635/97718Title: Quantumness without quantumness: Entanglement as classical correlations in higher dimensions
Authors: Vedral, V.
Abstract: I exploit the formal equivalence between the ground state of a d-dimensional quantum system and a d + 1-dimensional classical Ising chain to represent quantum entanglement in terms of classical correlations only. This offers a general "local hidden variable model" for all quantum phenomena existing in one dimension lower than the (hidden variable) classical model itself. The local hidden variable model is not contradicted by the implications of Bell's theorem. Formal theory is presented first and then exemplified by the quantum Ising spin chain in a transverse magnetic field. Here I explicitly show how to derive any two site entanglement in the transverse model from the partition function of the classical Ising spin chain existing in two dimensions. Some speculations are then presented regarding possible fundamental implications of these results.
Sat, 01 Sep 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/977182007-09-01T00:00:00Z
- Quantum instability and edge entanglement in the quasi-long-range orderhttps://scholarbank.nus.edu.sg/handle/10635/53122Title: Quantum instability and edge entanglement in the quasi-long-range order
Authors: Son, W.; Amico, L.; Plastina, F.; Vedral, V.
Abstract: We investigate the buildup of quasi-long-range order in the XX chain with a transverse magnetic field at finite size. As the field is varied, the ground state of the system displays multiple level crossings producing a sequence of entanglement jumps. Using the partial fidelity and susceptibility, we study the transition to the thermodynamic limit and argue that the topological order can be described in terms of kink-antikink pairs and marked by edge spin entanglement. © 2009 The American Physical Society.
Mon, 02 Feb 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/531222009-02-02T00:00:00Z
- 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
- Witnessing the quantumness of a single system: From anticommutators to interference and discordhttps://scholarbank.nus.edu.sg/handle/10635/116674Title: Witnessing the quantumness of a single system: From anticommutators to interference and discord
Authors: Fazio, R.; Modi, K.; Pascazio, S.; Vedral, V.; Yuasa, K.
Abstract: We introduce a method to witness the quantumness of a system. The method relies on the fact that the anticommutator of two classical states is always positive. By contrast, we show that there is always a nonpositive anticommutator due to any two quantum states. We notice that interference depends on the trace of the anticommutator of two states, and it is therefore operationally more suitable to detect quantumness by looking at anticommutators of states rather than their commutators. © 2013 American Physical Society.
Thu, 23 May 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1166742013-05-23T00:00:00Z
- Quantum physics: Hot entanglementhttps://scholarbank.nus.edu.sg/handle/10635/98988Title: Quantum physics: Hot entanglement
Authors: Vedral, V.
Thu, 09 Dec 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/989882010-12-09T00:00:00Z
- Geometric-phase backaction in a mesoscopic qubit-oscillator systemhttps://scholarbank.nus.edu.sg/handle/10635/96723Title: Geometric-phase backaction in a mesoscopic qubit-oscillator system
Authors: Vacanti, G.; Fazio, R.; Kim, M.S.; Palma, G.M.; Paternostro, M.; Vedral, V.
Abstract: We illustrate a reverse Von Neumann measurement scheme in which a geometric phase induced on a quantum harmonic oscillator is measured using a microscopic qubit as a probe. We show how such a phase, generated by a cyclic evolution in the phase space of the harmonic oscillator, can be kicked back on the qubit, which plays the role of a quantum interferometer. We also extend our study to finite-temperature dissipative Markovian dynamics and discuss potential implementations in micro- and nanomechanical devices coupled to an effective two-level system. © 2012 American Physical Society.
Wed, 29 Feb 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/967232012-02-29T00:00:00Z
- Quantumness and entanglement witnesseshttps://scholarbank.nus.edu.sg/handle/10635/97717Title: Quantumness and entanglement witnesses
Authors: Facchi, P.; Pascazio, S.; Vedral, V.; Yuasa, K.
Abstract: We analyze the recently introduced notion of quantumness witnesses and compare it to that of entanglement witnesses. We show that any entanglement witness is also a quantumness witness. We then consider some physically relevant examples and explicitly construct some witnesses. © 2012 IOP Publishing Ltd.
Fri, 16 Mar 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/977172012-03-16T00:00:00Z
- Experimental generation of quantum discord via noisy processeshttps://scholarbank.nus.edu.sg/handle/10635/96557Title: Experimental generation of quantum discord via noisy processes
Authors: Lanyon, B.P.; Jurcevic, P.; Hempel, C.; Gessner, M.; Vedral, V.; Blatt, R.; Roos, C.F.
Abstract: Quantum systems in mixed states can be unentangled and yet still nonclassically correlated. These correlations can be quantified by the quantum discord and might provide a resource for quantum information processing tasks. By precisely controlling the interaction of two ionic qubits with their environment, we investigate the capability of noise to generate discord. Firstly, we show that noise acting on only one quantum system can generate discord between two. States generated in this way are restricted in terms of the rank of their correlation matrix. Secondly, we show that classically correlated noise processes are capable of generating a much broader range of discordant states with correlation matrices of any rank. Our results show that noise processes prevalent in many physical systems can automatically generate nonclassical correlations and highlight fundamental differences between discord and entanglement. © 2013 American Physical Society.
Thu, 05 Sep 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/965572013-09-05T00:00:00Z
- Entanglement and nonlocality of a single relativistic particlehttps://scholarbank.nus.edu.sg/handle/10635/96481Title: Entanglement and nonlocality of a single relativistic particle
Authors: Dunningham, J.; Palge, V.; Vedral, V.
Abstract: Recent work has argued that the concepts of entanglement and nonlocality must be taken seriously even in systems consisting of only a single particle. These treatments, however, are nonrelativistic, and, if single-particle entanglement is fundamental, it should also persist in a relativistic description. Here, we consider a spin-1/2 particle in a superposition of two different velocities as viewed by an observer in a relativistically boosted inertial frame and show that the entanglement between the two velocity modes survives right up to the speed of light. We also discuss how quantum gates could be implemented in this way and apply our results to the case of a superconductor. In particular, we show that an s -wave superconductor would have p -wave components for a boosted observer. © 2009 The American Physical Society.
Thu, 15 Oct 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/964812009-10-15T00:00:00Z
- Topological features of good resources for measurement-based quantum computationhttps://scholarbank.nus.edu.sg/handle/10635/98941Title: Topological features of good resources for measurement-based quantum computation
Authors: Markham, D.; Anders, J.; Hajdušek, M.; Vedral, V.
Abstract: We study how graph states on fractal lattices can be used to perform measurement-based quantum computation, and investigate which topological features allow this application. We find fractal lattices of arbitrary dimension greater than one that all act as good resources for measurement-based quantum computation, and sets of fractal lattices with dimension greater than one that do not. The difference is put down to other topological factors such as ramification and connectivity. This is in direct analogy to the tendency of lattices to observe criticality in spin systems. We also discuss the analogy between thermodynamics and one-way computation in this context. This work adds confidence to the analogy and highlights new features of what we require for universal resources for measurement-based quantum computation. This paper is an extended version of Markham et al. (2010), which appeared in the proceedings of DCM 2010. © 2013 Cambridge University Press.
Fri, 01 Feb 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/989412013-02-01T00:00:00Z
- Entanglement in pure and thermal cluster stateshttps://scholarbank.nus.edu.sg/handle/10635/96488Title: Entanglement in pure and thermal cluster states
Authors: Hajdušek, M.; Vedral, V.
Abstract: We present a closest separable state to cluster states, which in turn allows us to calculate the entanglement scaling using relative entropy of entanglement. We reproduce known results for pure cluster states and show how our method can be used in quantifying entanglement in noisy cluster states. Operational meaning is given to our method, which clearly demonstrates how these closest separable states can be constructed from two-qubit clusters in the case of pure states. We also discuss the issue of finding the critical temperature at which the cluster state becomes only classically correlated and the importance of this temperature to our method. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Tue, 11 May 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/964882010-05-11T00:00:00Z
- Optomechanical to mechanical entanglement transformationhttps://scholarbank.nus.edu.sg/handle/10635/97467Title: Optomechanical to mechanical entanglement transformation
Authors: Vacanti, G.; Paternostro, M.; Palma, G.M.; Vedral, V.
Abstract: We present a scheme for generating entanglement between two mechanical oscillators that have never interacted with each other by using an entanglement-swapping protocol. The system under study consists of a Michelson-Morley interferometer comprising mechanical systems embodied by two cantilevers. Each of them is coupled to a field mode via the radiation pressure mechanism. Entanglement between the two mechanical systems is set by measuring the output modes of the interferometer. We also propose a control mechanism for the amount of entanglement based on path-length difference between the two arms. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Tue, 30 Sep 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/974672008-09-30T00:00:00Z
- Enhancing the detection of natural thermal entanglement with disorderhttps://scholarbank.nus.edu.sg/handle/10635/52915Title: Enhancing the detection of natural thermal entanglement with disorder
Authors: Hide, J.; Son, W.; Vedral, V.
Abstract: Physical systems have some degree of disorder present in them. We discuss how to treat natural, thermal entanglement in any random macroscopic system from which a thermodynamic witness bounded by a constant can be found. We propose that functional many-body perturbation theory be applied to allow either a quenched or an annealed average over the disorder to be taken. We find, when considering the example of an XX Heisenberg spin chain with a random coupling strength, that the region of natural entanglement detected by both witnesses can be enhanced by the disorder. © 2009 The American Physical Society.
Mon, 09 Mar 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/529152009-03-09T00:00:00Z