ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sun, 29 Mar 2020 00:46:25 GMT2020-03-29T00:46:25Z501571- Hardy's paradox for high-dimensional systemshttps://scholarbank.nus.edu.sg/handle/10635/116380Title: Hardy's paradox for high-dimensional systems
Authors: Chen, J.-L.; Cabello, A.; Xu, Z.-P.; Su, H.-Y.; Wu, C.; Kwek, L.C.
Abstract: Hardy's proof is considered the simplest proof of nonlocality. Here we introduce an equally simple proof that (i) has Hardy's as a particular case, (ii) shows that the probability of nonlocal events grows with the dimension of the local systems, and (iii) is always equivalent to the violation of a tight Bell inequality. Our proof has all the features of Hardy's and adds the only ingredient of the Einstein-Podolsky-Rosen scenario missing in Hardy's proof: It applies to measurements with an arbitrarily large number of outcomes. © 2013 American Physical Society.
Mon, 30 Dec 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1163802013-12-30T00:00:00Z
- Superstrings, gauge fields and black holeshttps://scholarbank.nus.edu.sg/handle/10635/99026Title: Superstrings, gauge fields and black holes
Authors: Baaquie, B.E.; Kwek, L.C.
Abstract: There has been spectacular progress in the development of string and superstring theories since its inception thirty years ago. Development in this area has never been impeded by the lack of experimental confirmation. Indeed, numerous bold and imaginative strides have been taken and the sheer elegance and logical consistency of the arguments have served as a primary motivation for string theorists to push their formulations ahead. In fact the development in this area has been so rapid that new ideas quickly become obsolete. On the other hand, this rapid development has proved to be the greatest hindrance for novices interested in this area. These notes serve as a gentle introduction to this topic. In these elementary notes, we briefly review the RNS formulation of superstring theory, GSO projection, D-branes, bosonic strings, dualities, dynamics of D-branes and the microscopic description of Bekenstein entropy of a black hole.
Wed, 20 Jun 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/990262001-06-20T00:00:00Z
- Quantum nonlocality of massive qubits in a moving framehttps://scholarbank.nus.edu.sg/handle/10635/112501Title: Quantum nonlocality of massive qubits in a moving frame
Authors: Su, H.-Y.; Wu, Y.-C.; Chen, J.-L.; Wu, C.; Kwek, L.C.
Abstract: We perform numerical tests on the quantum nonlocality of two-level quantum systems (qubits) observed by a uniformly moving observer. Under a suitable momentum setting, the quantum nonlocality of two-qubit nonmaximally entangled states could be weakened drastically by the Lorentz transformation, allowing for the existence of local-hidden-variable models, whereas three-qubit genuinely entangled states are robust. In particular, the generalized Greenberger-Horne- Zeilinger state remains nonlocal under arbitrary Wigner rotation and the generalized W state could admit local-hidden-variable models within a rather narrow range of parameters. © 2013 American Physical Society.
Wed, 28 Aug 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1125012013-08-28T00:00:00Z
- Security of quantum key distributions with entangled quditshttps://scholarbank.nus.edu.sg/handle/10635/97875Title: Security of quantum key distributions with entangled qudits
Authors: Durt, T.; Kaszlikowski, D.; Chen, J.-L.; Kwek, L.C.
Abstract: The generality of Ekert's entanglement-based cryptographic protocol where qubits were relaced by N or d-dimensional system was presented. The information gained by a potential eavesdropper was derived, to study its robustness against optimal incoherent attacks, during a cloning -based individual attack. It was shown that the accepatable error rate of the N-DEB protocol increases with the dimension N. It was found that the maximal error rate provides a good qualitative measure of the security of the protocol.
Mon, 01 Mar 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/978752004-03-01T00:00:00Z
- Operator quantum zeno effect: Protecting quantum information with noisy two-qubit interactionshttps://scholarbank.nus.edu.sg/handle/10635/112479Title: Operator quantum zeno effect: Protecting quantum information with noisy two-qubit interactions
Authors: Wang, S.-C.; Li, Y.; Wang, X.-B.; Kwek, L.C.
Abstract: The time evolution of some quantum states can be slowed down or even stopped under frequent measurements. This is the usual quantum Zeno effect. Here, we report an operator quantum Zeno effect, in which the evolution of some physical observables is slowed down through measurements even though the quantum state changes randomly with time. Based on the operator quantum Zeno effect, we show how we can protect quantum information from decoherence with two-qubit measurements, realizable with noisy two-qubit interactions. © 2013 American Physical Society.
Fri, 08 Mar 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124792013-03-08T00:00:00Z
- Fractional spin Hall effect in atomic Bose gaseshttps://scholarbank.nus.edu.sg/handle/10635/52946Title: Fractional spin Hall effect in atomic Bose gases
Authors: Liu, X.-J.; Liu, X.; Kwek, L.C.; Oh, C.H.
Abstract: We propose fractional spin Hall effect (FSHE) by coupling pseudospin states of cold bosonic atoms to optical fields. The present scheme is an extension to interacting bosonic system of the recent work on optically induced spin Hall effect in noninteracting atomic system. The system has two different types of ground states. The first type of ground state is a 1/3-factor Laughlin function and has the property of chiral-antichiral interchange antisymmetry, while the second type is shown to be a 1/4-factor wave function with chiral-antichiral symmetry. The fractional statistics corresponding to the fractional spin Hall states are studied in detail and are discovered to be different from that corresponding to the fractional quantum Hall (FQH) states. Therefore the present FSHE can be distinguished from FQH regime in the measurement. © 2009 The American Physical Society.
Wed, 01 Apr 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/529462009-04-01T00:00:00Z
- Protecting two-qubit quantum states by π-phase pulseshttps://scholarbank.nus.edu.sg/handle/10635/112489Title: Protecting two-qubit quantum states by π-phase pulses
Authors: Hu, J.-Z.; Wang, X.-B.; Kwek, L.C.
Abstract: We study the state decay of two qubits interacting with a common harmonic oscillator reservoir. We find both a decoherence error and the error caused by the amplitude change of the superradiant state. We show that frequent π-phase pulses can eliminate both types of errors and therefore protect a two-qubit odd-parity state more effectively than the frequent measurement method. This shows that the methods using dynamical decoupling and the quantum Zeno effects actually can give rather different results when the operation frequency is finite. © 2010 The American Physical Society.
Thu, 16 Dec 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124892010-12-16T00:00:00Z
- Coherent cavity networks with complete connectivityhttps://scholarbank.nus.edu.sg/handle/10635/116266Title: Coherent cavity networks with complete connectivity
Authors: Kyoseva, E.; Beige, A.; Kwek, L.C.
Abstract: When cavity photons couple to an optical fiber with a continuum of modes, they usually leak out within a finite amount of time. However, if the fiber is about 1 m long and linked to a mirror, photons bounce back and forth within the fiber on a much faster time scale. As a result, dynamical decoupling prevents the cavity photons from entering the fiber. In this paper, we use the simultaneous dynamical decoupling of a large number of distant cavities from the fiber modes of linear optics networks to mediate effective cavity-cavity interactions in a large variety of configurations. Coherent cavity networks with complete connectivity can be created with potential applications in quantum computing and in the simulation of the complex interaction Hamiltonians of biological systems. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Sun, 01 Jan 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1162662012-01-01T00:00:00Z
- Examination of the adiabatic approximation in open systemshttps://scholarbank.nus.edu.sg/handle/10635/115715Title: Examination of the adiabatic approximation in open systems
Authors: Tong, D.M.; Yi, X.X.; Fan, X.J.; Kwek, L.C.; Oh, C.H.
Abstract: We examine the notion of the adiabatic approximation in open systems by applying it to closed systems. Our results shows that the notion is equivalent to the standard adiabatic approximation if the systems are initially in eigenstates, and it leads to a more general expression if the systems are in mixed states. © 2007 Elsevier B.V. All rights reserved.
Mon, 31 Mar 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1157152008-03-31T00:00:00Z
- Berry phase in magnetoelectric materialshttps://scholarbank.nus.edu.sg/handle/10635/116050Title: Berry phase in magnetoelectric materials
Authors: Kwek, L.C.; Kwan, M.K.
Abstract: Weak magnetism of antiferromagnetic crystals, such as MnCO3, CoCO3, and spin arrangement in antiferromagnets of low symmetry can be studied using the Dzyaloshinskii-Moriya (DM) interaction. Such interactions may also be present sometimes in some spin-chain systems like magnetoelectric multiferroics. These materials could in principle be prime candidates for solid state NMR quantum computing based on manipulation of geometric phases. However, recent preliminary studies appear to show that a small presence of DM interaction could dampen magnitudes of the geometric phases. © 2009 World Scientific Publishing Company.
Thu, 01 Jan 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1160502009-01-01T00:00:00Z
- Asymmetric multipartite greenberger-horne-zeilinger states and bell inequalitieshttps://scholarbank.nus.edu.sg/handle/10635/95825Title: Asymmetric multipartite greenberger-horne-zeilinger states and bell inequalities
Authors: Gosal, D.; Kaszlikowski, D.; Kwek, L.C.; Zukowski, M.; Oh, C.H.
Abstract: The multiparticle generalized Greenberger-Horne-Zeilinger (GHZ) states are discussed. It is found that for a specific range of parameters and for an odd number of qubits they do not violate any Bell inequality for correlation functions. The results show that multiparticle Clauser-Horne-type (CH) inequalities involving probabilities are stronger tools for analyzing violations of local realism in multiparticle systems as compared to inequalities involving correlation functions. The Pitovsky-Svozil CH-type inequalities form a more stringent constraint on local realism as compared to WWWZB correlation-function.
Fri, 01 Oct 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/958252004-10-01T00:00:00Z
- Coherent control of long-distance steady-state entanglement in lossy resonator arrayshttps://scholarbank.nus.edu.sg/handle/10635/116267Title: Coherent control of long-distance steady-state entanglement in lossy resonator arrays
Authors: Angelakis, D.G.; Dai, L.; Kwek, L.C.
Abstract: We show that coherent control of the steady-state long-distance entanglement between pairs of cavity-atom systems in an array of lossy and driven coupled resonators is possible. The cavities are doped with atoms and are connected through waveguides, other cavities or fibers depending on the implementation. We find that the steady-state entanglement can be coherently controlled through the tuning of the phase difference between the driving fields. It can also be surprisingly high in spite of the pumps being classical fields. For some implementations where the connecting element can be a fiber, long-distance steady-state quantum correlations can be established. Furthermore, the maximal of entanglement for any pair is achieved when their corresponding direct coupling is much smaller than their individual couplings to the third party. This effect is reminiscent of the establishment of coherence between otherwise uncoupled atomic levels using classical coherent fields. We suggest a method to measure this entanglement by analyzing the correlations of the emitted photons from the array and also analyze the above results for a range of values of the system parameters, different network geometries and possible implementation technologies. © EPLA, 2010.
Thu, 01 Jul 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1162672010-07-01T00:00:00Z
- Correlations and thermalization in driven cavity arrayshttps://scholarbank.nus.edu.sg/handle/10635/116707Title: Correlations and thermalization in driven cavity arrays
Authors: Dai, L.; Angelakis, D.G.; Kwek, L.C.; Mancini, S.
Abstract: We show that long-distance steady-state quantum correlations (entanglement) between pairs of cavity-atom systems in an array of lossy and driven coupled resonators can be established and controlled. The maximal of entanglement for any pair is achieved when their corresponding direct coupling is much smaller than their individual couplings to the third party. This effect is reminiscent of the coherent trapping of the - type three-level atoms using two classical coherent fields. Different geometries for coherent control are considered. For finite temperature, the steady state of the coupled lossy atomcavity arrays with driving fields is in general not a thermal state. Using an appropriate distance measure for quantum states, we find that the change rate of the degree of thermalization with respect to the driving strength is consistent with the entanglement of the system. © 2011 American Institute of Physics.
Sat, 01 Jan 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1167072011-01-01T00:00:00Z
- Photonic multiqubit states from a single atomhttps://scholarbank.nus.edu.sg/handle/10635/116523Title: Photonic multiqubit states from a single atom
Authors: Li, Y.; Aolita, L.; Kwek, L.C.
Abstract: We propose a protocol for the creation of photonic Greenberger-Horne- Zeilinger and linear cluster states emitted from a single atom-or ion-coupled to an optical cavity field. The method is based on laser pulses with different polarizations and exploits the atomic transition amplitudes to state-selectively achieve the desired transitions. The scheme lies within reach of current technology. © 2011 American Physical Society.
Tue, 22 Mar 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1165232011-03-22T00:00:00Z
- Wave-particle duality in multi-path interferometers: General concepts and three-path interferometershttps://scholarbank.nus.edu.sg/handle/10635/112544Title: Wave-particle duality in multi-path interferometers: General concepts and three-path interferometers
Authors: Englert, B.-G.; Kaszlikowski, D.; Kwek, L.C.; Chee, W.H.
Abstract: For two-path interferometers, the which-path predictability P and the fringe visibility ν are familiar quantities that are much used to talk about wave-particle duality in a quantitative way. We discuss several candidates that suggest themselves as generalizations P of P for multi-path interferometers, and treat the case of three paths in considerable detail. To each choice for the path knowledge P , the interference strength V - the corresponding generalization of ν - is found by a natural, operational procedure. In experimental terms, it amounts to finding those equal-weight superpositions of the path amplitudes which maximize P for the emerging intensities. Mathematically speaking, one needs to identify a certain optimum one among the Fourier transforms of the state of the interfering quantum object. Wave-particle duality is manifest, inasmuch as P = 1 implies V = 0 and V = 1 implies P = 0, whatever definition is chosen. The possible values of the pair (P,V) are restricted to an area with corners at (P,V) = (0,0) , (P,V) = (1,0), and (P,V) = (0,1) , with the shape of the border line from (1,0) to (0,1), depending on the particular choice for P and the induced definition of V. © 2008 World Scientific Publishing Company.
Fri, 01 Feb 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1125442008-02-01T00:00:00Z
- Transmission of classical information via quantum entanglementhttps://scholarbank.nus.edu.sg/handle/10635/98993Title: Transmission of classical information via quantum entanglement
Authors: Kwek, L.C.; Liu, Y.; Oh, C.H.; Wang, X.-B.
Abstract: It has been shown that entanglement can improve transmission of classical information in a two-Pauli channel but not in a depolarizing channel. In this letter, we propose a modified channel that can straddle between the two-Pauli channel and the depolarizing channel and analyse the efficiency of transmission of classical states using mutual information. Our modified channel provides a natural mechanism for accounting for the difference in behaviour through these different channels.
Mon, 15 Oct 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/989932001-10-15T00:00:00Z
- Long-distance entanglement generation with scalable and robust two-dimensional quantum networkhttps://scholarbank.nus.edu.sg/handle/10635/112459Title: Long-distance entanglement generation with scalable and robust two-dimensional quantum network
Authors: Li, Y.; Cavalcanti, D.; Kwek, L.C.
Abstract: We present a protocol for generating entanglement over long distances in a two-dimensional quantum network based on the surface-error-correction code. This protocol requires a fixed number of quantum memories at each node of the network and tolerates error rates of up to 1.67% in the quantum channels. If local operations are of an error rate of 10 -3, error rates of about 1.27% in the quantum channels are tolerable. © 2012 American Physical Society.
Fri, 29 Jun 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124592012-06-29T00:00:00Z
- Robust-fidelity atom-photon entangling gates in the weak-coupling regimehttps://scholarbank.nus.edu.sg/handle/10635/116576Title: Robust-fidelity atom-photon entangling gates in the weak-coupling regime
Authors: Li, Y.; Aolita, L.; Chang, D.E.; Kwek, L.C.
Abstract: We describe a simple entangling principle based on the scattering of photons off single emitters in one-dimensional waveguides (or extremely lossy cavities). The scheme can be applied to polarization- or time bin-encoded photonic qubits, and features a filtering mechanism that works effectively as a built-in error-correction directive. This automatically maps imperfections from the dominant sources of errors into heralded losses instead of infidelities, something highly advantageous, for instance, in quantum information applications. The scheme is thus adequate for high-fidelity maximally entangling gates even in the weak-coupling regime. These, in turn, can be directly used to store and retrieve photonic-qubit states, thereby completing an atom-photon interface toolbox, or applied to sequential measurement-based quantum computations with atomic memories. © 2012 American Physical Society.
Fri, 19 Oct 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1165762012-10-19T00:00:00Z
- A novel coproduct of suq (2) and its relation to XXZ spin chain modelhttps://scholarbank.nus.edu.sg/handle/10635/95659Title: A novel coproduct of suq (2) and its relation to XXZ spin chain model
Authors: Kwek, L.C.; Oh, C.H.; Singh, K.
Abstract: While it is normal to restrict the deformation parameter q in the coproduct of the quantum group suq (2) to the positive reals, the naive replacement of q by -q results in a coproduct that does not respect algebra homomorphism. However, it is possible to define a twisted coproduct in this case that respects the algebra homomorphism. Application to XXZ spin chain model is discussed. © 2001 Elsevier Science B.V.
Mon, 05 Feb 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/956592001-02-05T00:00:00Z
- Quantum cryptography: Security criteria reexaminedhttps://scholarbank.nus.edu.sg/handle/10635/97670Title: Quantum cryptography: Security criteria reexamined
Authors: Kaszlikowski, D.; Gopinathan, A.; Liang, Y.C.; Kwek, L.C.; Englert, B.-G.
Abstract: The generally accepted security criteria for a whole class of protocols for quantum cryptography was analyzed. It was shown that the security criteria are flawed. The reason of the flaw was a standard assumption of the security analysis, namely that the so-called square-root measurement is optimal for eavesdropping purposes, is not true in general. The results show that there are rather large parameter regimes in which the optimal measurement extracts substantially more information that the square-root measurement.
Wed, 01 Sep 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/976702004-09-01T00:00:00Z
- Operator-sum representation of time-dependent density operators and its applicationshttps://scholarbank.nus.edu.sg/handle/10635/97435Title: Operator-sum representation of time-dependent density operators and its applications
Authors: Tong, D.M.; Kwek, L.C.; Oh, C.H.; Chen, J.-L.; Ma, L.
Abstract: An arbitrary time-dependent density operator of an open system was described in terms of an operator-sum representation. Its initial condition and the path of its evolution in the state space were ignored. A general expression of Kraus operators for arbitrary time-dependent density operator was obtained. The significance of the results was proved through several examples.
Sat, 01 May 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/974352004-05-01T00:00:00Z
- Multipartite entanglement detection via structure factorshttps://scholarbank.nus.edu.sg/handle/10635/115819Title: Multipartite entanglement detection via structure factors
Authors: Krammer, P.; Kampermann, H.; Bruß, D.; Bertlmann, R.A.; Kwek, L.C.; MacChiavello, C.
Abstract: We establish a relation between entanglement of a many-body system and its diffractive properties, where the link is given by structure factors. Based on these, we provide a general analytical construction of multiqubit entanglement witnesses. The proposed witnesses contain two-point correlations. They could be either measured in a scattering experiment or via local measurements, depending on the underlying physical system. For some explicit examples of witnesses we analyze the properties of the states that are detected by them. We further study the robustness of these witnesses with respect to noise. © 2009 The American Physical Society.
Thu, 03 Sep 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1158192009-09-03T00:00:00Z
- Quantum computational universality of the Cai-Miyake-Dür-Briegel two-dimensional quantum state from Affleck-Kennedy-Lieb-Tasaki quasichainshttps://scholarbank.nus.edu.sg/handle/10635/112492Title: Quantum computational universality of the Cai-Miyake-Dür-Briegel two-dimensional quantum state from Affleck-Kennedy-Lieb-Tasaki quasichains
Authors: Wei, T.-C.; Raussendorf, R.; Kwek, L.C.
Abstract: Universal quantum computation can be achieved by simply performing single-qubit measurements on a highly entangled resource state, such as cluster states. Cai, Miyake, Dür, and Briegel recently constructed a ground state of a two-dimensional quantum magnet by combining multiple Affleck-Kennedy-Lieb- Tasaki quasichains of mixed spin-3/2 and spin-1/2 entities and by mapping pairs of neighboring spin-1/2 particles to individual spin-3/2 particles. They showed that this state enables universal quantum computation by single-spin measurements. Here, we give an alternative understanding of how this state gives rise to universal measurement-based quantum computation: by local operations, each quasichain can be converted to a one-dimensional cluster state and entangling gates between two neighboring logical qubits can be implemented by single-spin measurements. We further argue that a two-dimensional cluster state can be distilled from the Cai-Miyake-Dür-Briegel state. © 2011 American Physical Society.
Wed, 19 Oct 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124922011-10-19T00:00:00Z
- Quantum nonlocality of Heisenberg XX model with site-dependent coupling strengthhttps://scholarbank.nus.edu.sg/handle/10635/97697Title: Quantum nonlocality of Heisenberg XX model with site-dependent coupling strength
Authors: Wu, C.; Chen, J.-L.; Tong, D.M.; Kwek, L.C.; Oh, C.H.
Abstract: We show that the generalized Bell inequality is violated in the extended Heisenberg model when the temperature is below a threshold value. The threshold temperature values are obtained by constructing exact solutions of the model using the temperature-dependent correlation functions. The effect due to the presence of an external magnetic field is also illustrated.
Fri, 26 Nov 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/976972004-11-26T00:00:00Z
- Bell inequalities for three particleshttps://scholarbank.nus.edu.sg/handle/10635/115609Title: Bell inequalities for three particles
Authors: Chen, J.-L.; Wu, C.; Kwek, L.C.; Oh, C.H.
Abstract: We present tight Bell inequalities expressed by probabilities for three four- and five-dimensional systems. A tight structure of Bell inequalities for three d -dimensional systems (qudits) is proposed. Some interesting Bell inequalities of three qubits reduced from those of three qudits are also studied. © 2008 The American Physical Society.
Mon, 08 Sep 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1156092008-09-08T00:00:00Z
- Spin chain under next nearest neighbor interactionhttps://scholarbank.nus.edu.sg/handle/10635/115942Title: Spin chain under next nearest neighbor interaction
Authors: Kwek, L.C.; Takahashi, Y.; Choo, K.W.
Abstract: We perform a numerical study on the concurrence of the ground state Heisenberg XXX with next-nearest-neighbor interaction with open and periodic boundary condition. © 2009 IOP Publishing Ltd.
Thu, 01 Jan 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1159422009-01-01T00:00:00Z
- Quantum tunneling timehttps://scholarbank.nus.edu.sg/handle/10635/97713Title: Quantum tunneling time
Authors: Wang, Z.S.; Kwek, L.C.; Lai, C.H.; Oh, C.H.
Abstract: The calculation of quantum tunneling time, which was based on the transition duration of wave peak from one side of the barrier to the other, was described. The imaginary part of the tunneling time was associated with the energy derivatives of the probability amplitudes, while the real part was an extension of the phase tunneling time with quantum corrections. It was assumed that the wave packets between the two sides of the barrier was used to distribute sharply at a given energy without loss of generality. The calculation of the imaginary time was found to be same as the calculation of the flux-flux correlation function.
Sat, 01 May 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/977132004-05-01T00:00:00Z
- Entanglement witness for spin glasshttps://scholarbank.nus.edu.sg/handle/10635/127974Title: Entanglement witness for spin glass
Authors: Koh C.Y.; Kwek L.C.
Thu, 01 Jan 2015 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1279742015-01-01T00:00:00Z
- Coherent quantum transport in photonic latticeshttps://scholarbank.nus.edu.sg/handle/10635/112397Title: Coherent quantum transport in photonic lattices
Authors: Perez-Leija, A.; Keil, R.; Kay, A.; Moya-Cessa, H.; Nolte, S.; Kwek, L.-C.; Rodríguez-Lara, B.M.; Szameit, A.; Christodoulides, D.N.
Abstract: Transferring quantum states efficiently between distant nodes of an information processing circuit is of paramount importance for scalable quantum computing. We report on an observation of a perfect state transfer protocol on a lattice, thereby demonstrating the general concept of transporting arbitrary quantum information with high fidelity. Coherent transfer over 19 sites is realized by utilizing judiciously designed optical structures consisting of evanescently coupled waveguide elements. We provide unequivocal evidence that such an approach is applicable in the quantum regime, for both bosons and fermions, as well as in the classical limit. Our results illustrate the potential of the perfect state transfer protocol as a promising route towards integrated quantum computing on a chip. © 2013 American Physical Society.
Mon, 14 Jan 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1123972013-01-14T00:00:00Z
- Quantum-tomographic cryptography with a semiconductor single-photon sourcehttps://scholarbank.nus.edu.sg/handle/10635/97720Title: Quantum-tomographic cryptography with a semiconductor single-photon source
Authors: Kaszlikowski, D.; Kwek, L.C.; Yang, L.J.; Yong, L.S.; Willeboordse, F.H.
Abstract: We analyze the security of so-called quantum-tomographic cryptography with the source producing entangled photons via an experimental scheme proposed by Fattal [Phys. Rev. Lett. 92, 37903 (2004)]. We determine the range of the experimental parameters for which the protocol is secure against the most general incoherent attacks. © 2005 The American Physical Society.
Thu, 01 Sep 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/977202005-09-01T00:00:00Z
- Luttinger liquid of photons and spin-charge separation in hollow-core fibershttps://scholarbank.nus.edu.sg/handle/10635/115175Title: Luttinger liquid of photons and spin-charge separation in hollow-core fibers
Authors: Angelakis, D.G.; Huo, M.; Kyoseva, E.; Kwek, L.C.
Abstract: In this work we show that light-matter excitations (polaritons) generated inside a hollow-core one-dimensional fiber filled with two types of atoms, can exhibit Luttinger liquid behavior. We first explain how to prepare and drive this quantum-optical system to a strongly interacting regime, described by a bosonic two-component Lieb-Liniger model. Utilizing the connection between strongly interacting bosonic and fermionic systems, we then show how spin-charge separation could be observed by probing the correlations in the polaritons. This is performed by first mapping the polaritons to propagating photon pulses and then measuring the effective photonic spin and charge densities and velocities by analyzing the correlations in the emitted photon spectrum. The necessary regime of interactions is achievable with current quantum-optical technology. © 2011 American Physical Society.
Mon, 11 Apr 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1151752011-04-11T00:00:00Z
- Geometric phase and entanglement for massive spin-1 particleshttps://scholarbank.nus.edu.sg/handle/10635/52961Title: Geometric phase and entanglement for massive spin-1 particles
Authors: Wang, Z.S.; Kwek, L.C.; Lai, C.H.; Oh, C.H.
Abstract: The cyclic evolution of a spin-1 system is studied under the spin-spin interaction between the transverse and the longitudinal states. The eigenstates of the systems are obtained by generalized and extended Jordan-Wigner transformation with an angle φ described the path of particle propagation. According to the wave functions of time evaluation for many-particle systems, the entanglement effects and geometric phase are observed. The systems with more than two particles, in contrast to the two particle system, evolve in time with two parameters. © EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2005.
Sun, 01 May 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/529612005-05-01T00:00:00Z
- Gisin's theorem for three qubitshttps://scholarbank.nus.edu.sg/handle/10635/96729Title: Gisin's theorem for three qubits
Authors: Chen, J.-L.; Wu, C.; Kwek, L.C.; Oh, C.H.
Abstract: The gisin's theorem for three quibits are discussed. A theorem was presented initially that all generalized GHZ states of a three quibit system violates a bell inequality in terms of probabilities. The theorem shows that it was possible for a bell inequality in terms of probability to be violated by all pure entangled generalized GHZ state. The results show that bell inequality can be used to measure the degree of entanglement of the state by knowing that a pure state is a 2-entangled state of three quibit system or not.
Fri, 01 Oct 2004 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/967292004-10-01T00:00:00Z
- Diagonalization of diffusion matrix in Grover's algorithmhttps://scholarbank.nus.edu.sg/handle/10635/52873Title: Diagonalization of diffusion matrix in Grover's algorithm
Authors: Kwek, L.C.; Oh, C.H.; Singh, K.; Wang, X.-B.
Abstract: An important process in Grover's quantum search algorithm is the iterative application of the inversion and diffusion matrix. This process can be represented by a unitary matrix, S. In this letter, we diagonalize this matrix and show how the matrix can be interpreted geometrically. (C) 2000 Elsevier Science B.V.
Mon, 06 Mar 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/528732000-03-06T00:00:00Z
- Noncyclic phase for neutrino oscillationhttps://scholarbank.nus.edu.sg/handle/10635/53059Title: Noncyclic phase for neutrino oscillation
Authors: Wang, X.-B.; Kwek, L.C.; Liu, Y.; Oh, C.H.
Abstract: We provide explicit formulas for the noncyclic phases or Pancharatnam phases of neutrino oscillations. Since the Pancharatnam phase is a generalization of the Berry phase, our results generalize the previous findings for the Berry phase in a recent paper [M. Blasone, P. A. Henning, and G. Vitiello, Phys. Lett. B 466 262 (1999)]. Unlike the Berry phase, the noncyclic phase offers a distinctive advantage in terms of measurement and prediction. In particular, for three-flavor mixing, our explicit formula offers an alternative means of determining the CP-violating phase. Our results can also be extended easily to explore the noncyclic phase associated with neutron-antineutron oscillations. © 2001 The American Physical Society.
Mon, 01 Jan 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/530592001-01-01T00:00:00Z
- Manipulating atomic states via optical orbital angular-momentumhttps://scholarbank.nus.edu.sg/handle/10635/53022Title: Manipulating atomic states via optical orbital angular-momentum
Authors: Liu, X.-J.; Liu, X.; Kwek, L.-C.; Oh, C.H.
Abstract: Optical orbital angular-momentum (OAM) has more complex mechanics than the spin degree of photons, and may have a broad range of application. Manipulating atomic states via OAM has become an interesting topic. In this paper, we first review the general theory of generating adiabatic gauge field in ultracold atomic systems by coupling atoms to external optical fields with OAM, and point out the applications of the generated adiabatic gauge field. Then, we review our work in this field, including the generation of macroscopic superposition of vortex-antivortex states and spin Hall effect (SHE) in cold atoms. © 2008 Higher Education Press and Springer-Verlag GmbH.
Sun, 01 Jun 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/530222008-06-01T00:00:00Z
- Uncertainty relation of mixed states by means of Wigner-Yanase-Dyson informationhttps://scholarbank.nus.edu.sg/handle/10635/116019Title: Uncertainty relation of mixed states by means of Wigner-Yanase-Dyson information
Authors: Li, D.; Li, X.; Wang, F.; Huang, H.; Li, X.; Kwek, L.C.
Abstract: The variance of an observable in a quantum state is usually used to describe Heisenberg uncertainty relation. For mixed states, the variance includes quantum and classical uncertainties. By means of the skew information and the decomposition of the variance, a stronger uncertainty relation was presented by Luo. In this paper, by using Wigner-Yanase-Dyson information which is a generalization of the skew information, we propose a general uncertainty relation of mixed states. © 2009 The American Physical Society.
Fri, 01 May 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1160192009-05-01T00:00:00Z
- Probing multipartite entanglement in spin chain via structure factorshttps://scholarbank.nus.edu.sg/handle/10635/115245Title: Probing multipartite entanglement in spin chain via structure factors
Authors: Kwek, L.C.
Abstract: Multi-qubit entanglement could act as a useful resource for many quantum information communication and processing tasks like quantum networking processes. Genuine non-trivial multi-qubit entanglement could delineates quantum physics from classical physics. Detection of multipartite entanglement however is a theoretical and experimental challenge. A useful tool for this purpose are entanglement witnesses. Recently, we provide an analytical construction of multi-qubit entanglement witnesses using static structure factors (SSF) and study the robustness of the witnesses with respect to noise. In this article, we consider the effectiveness of the entanglement witness based on SSF for probing spin chain. © 2011 Pleiades Publishing, Ltd.
Mon, 01 Aug 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1152452011-08-01T00:00:00Z
- Kinematic approach to off-diagonal geometric phases of nondegenerate and degenerate mixed stateshttps://scholarbank.nus.edu.sg/handle/10635/97019Title: Kinematic approach to off-diagonal geometric phases of nondegenerate and degenerate mixed states
Authors: Tong, D.M.; Sjöqvist, E.; Filipp, S.; Kwek, L.C.; Oh, C.H.
Abstract: Off-diagonal geometric phases have been developed in order to provide information of the geometry of paths that connect noninterfering quantal states. We propose a kinematic approach to off-diagonal geometric phases for pure and mixed states. We further extend the mixed-state concept proposed in [Phys. Rev. Lett. 90, 050403 (2003)] to degenerate density operators. The first- and second-order off-diagonal geometric phases are analyzed for unitarily evolving pairs of pseudopure states. ©2005 The American Physical Society.
Tue, 01 Mar 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/970192005-03-01T00:00:00Z
- Quantum mechanical photoncount formula derived by entangled state representationhttps://scholarbank.nus.edu.sg/handle/10635/116553Title: Quantum mechanical photoncount formula derived by entangled state representation
Authors: Hu, L.-Y.; Wang, Z.-S.; Kwek, L.C.; Fan, H.-Y.
Abstract: By introducing the thermo entangled state representation, we derive four new photocount distribution formulas for a given light field density operator. It is shown that these new formulas, which are convenient to calculate the photocount, can be expressed as integrations over a Laguerre - Gaussian function with a characteristic function, Wigner function, Q-function and P-function, respectively. © 2011 Chinese Physical Society and IOP Publishing Ltd.
Mon, 01 Aug 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1165532011-08-01T00:00:00Z
- Geometric phase in open two-level systemhttps://scholarbank.nus.edu.sg/handle/10635/52962Title: Geometric phase in open two-level system
Authors: Wang, Z.S.; Kwek, L.C.; Lai, C.H.; On, C.H.
Abstract: A mapping is established in connecting density matrices, associated with an evolution of a quantum open system, with vector ray in a complex projective Hilbert space. By using the corresponding vector ray to represent the open two-level system, we may observe the geometric phase for the open two-level system. The geometric phase of the open two-level system depends only on the smooth (open or closed) curve in the complex projective Hilbert space of ray, which is formulated entirely in terms of geometric structures on this space. © EDP Sciences.
Thu, 15 Jun 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/529622006-06-15T00:00:00Z
- Superfluid qubit systems with ring shaped optical latticeshttps://scholarbank.nus.edu.sg/handle/10635/116611Title: Superfluid qubit systems with ring shaped optical lattices
Authors: Amico, L.; Aghamalyan, D.; Auksztol, F.; Crepaz, H.; Dumke, R.; Kwek, L.C.
Abstract: We study an experimentally feasible qubit system employing neutral atomic currents. Our system is based on bosonic cold atoms trapped in ring-shaped optical lattice potentials. The lattice makes the system strictly one dimensional and it provides the infrastructure to realize a tunable ring-ring interaction. Our implementation combines the low decoherence rates of neutral cold atoms systems, overcoming single site addressing, with the robustness of topologically protected solid state Josephson flux qubits. Characteristic fluctuations in the magnetic fields affecting Josephson junction based flux qubits are expected to be minimized employing neutral atoms as flux carriers. By breaking the Galilean invariance we demonstrate how atomic currents through the lattice provide an implementation of a qubit. This is realized either by artificially creating a phase slip in a single ring, or by tunnel coupling of two homogeneous ring lattices. The single qubit infrastructure is experimentally investigated with tailored optical potentials. Indeed, we have experimentally realized scaled ring-lattice potentials that could host, in principle, n ∼ 10 of such ring-qubits, arranged in a stack configuration, along the laser beam propagation axis. An experimentally viable scheme of the two-ring-qubit is discussed, as well. Based on our analysis, we provide protocols to initialize, address, and read-out the qubit.
Thu, 06 Mar 2014 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1166112014-03-06T00:00:00Z
- Quantum nonlocality of N -qubit W stateshttps://scholarbank.nus.edu.sg/handle/10635/97698Title: Quantum nonlocality of N -qubit W states
Authors: Wu, C.; Chen, J.-L.; Kwek, L.C.; Oh, C.H.
Abstract: An experimental setup for testing quantum nonlocality of N qubits is proposed. This method is a generalization of the optical setup proposed by Banaszek and Wódkiewicz [Phys. Rev. Lett. 82, 2009 (1999)]. The quantum nonlocality of N qubits can be obtained through its violation of N -qubit Bell inequalities. The correlation function measured in the experiment is described by the Wigner function. The effect of inefficient detector is also considered. © 2006 The American Physical Society.
Sun, 01 Jan 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/976982006-01-01T00:00:00Z
- 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
- General approach to functional forms for the exponential quadratic operators in coordinate-momentum spacehttps://scholarbank.nus.edu.sg/handle/10635/96699Title: General approach to functional forms for the exponential quadratic operators in coordinate-momentum space
Authors: Wang, X.-B.; Oh, C.H.; Kwek, L.C.
Abstract: In a recent paper (Nieto M M 1996 Quantum Semiclass. Opt. 8 1061, quant-ph/9605032), the one-dimensional squeezed and harmonic oscillator time-displacement operators were reordered in coordinate-momentum space. In this paper, we give a general approach for reordering the multidimensional exponential quadratic operator (EQO) in coordinate-momentum space. An explicit computational formula is provided and applied to the single-mode and double-mode EQO through the squeezed operator and the time-displacement operator of the harmonic oscillator.
Fri, 08 May 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/966991998-05-08T00:00:00Z
- Stochastic resonance of quantum discordhttps://scholarbank.nus.edu.sg/handle/10635/112522Title: Stochastic resonance of quantum discord
Authors: Lee, C.K.; Kwek, L.C.; Cao, J.
Abstract: We study the stochastic resonance of quantum discord ("discord resonance") in coupled quantum systems and make a comparison with the stochastic resonance of entanglement ("entanglement resonance"). It is found that the discord resonance is much more robust against dephasing noise and thermal effects than the entanglement resonance. We also show that, unlike the entanglement resonance, the level of dissipation at which the discord resonance occurs is not sensitive to dephasing noise. These results suggest that it is easier to detect the discord resonance in actual experiments, where the dephasing noise and temperature are difficult to control. © 2011 American Physical Society.
Mon, 19 Dec 2011 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1125222011-12-19T00:00:00Z
- Scheme for unconventional geometric quantum computation in cavity QEDhttps://scholarbank.nus.edu.sg/handle/10635/97867Title: Scheme for unconventional geometric quantum computation in cavity QED
Authors: Feng, X.-L.; Wang, Z.; Wu, C.; Kwek, L.C.; Lai, C.H.; Oh, C.H.
Abstract: In this paper, we present a scheme for implementing the unconventional geometric two-qubit phase gate with nonzero dynamical phase based on two-channel Raman interaction of two atoms in a cavity. We show that the dynamical phase and the total phase for a cyclic evolution are proportional to the geometric phase in the same cyclic evolution; hence they possess the same geometric features as does the geometric phase. In our scheme, the atomic excited state is adiabatically eliminated, and the operation of the proposed logic gate involves only the metastable states of the atoms; thus the effect of the atomic spontaneous emission can be neglected. The influence of the cavity decay on our scheme is examined. It is found that the relations regarding the dynamical phase, the total phase, and the geometric phase in the ideal situation are still valid in the case of weak cavity decay. Feasibility and the effect of the phase fluctuations of the driving laser fields are also discussed. © 2007 The American Physical Society.
Wed, 09 May 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/978672007-05-09T00:00:00Z
- Tightly localized stationary pulses in a multilevel atomic systemhttps://scholarbank.nus.edu.sg/handle/10635/98409Title: Tightly localized stationary pulses in a multilevel atomic system
Authors: Liu, X.-J.; Liu, X.; Liu, Z.-X.; Kwek, L.C.; Oh, C.H.
Abstract: We show that the pulse matching phenomenon can be obtained in the general multilevel system with electromagnetically induced transparency. For this we find a different way to create tightly localized stationary pulses by using counterpropagating pump fields. The present process is a spatial compression of excitation so that it allows us to shape and further intensify the localized stationary pulses, without using standing waves of pump fields or spatially modulated pump fields. © 2007 The American Physical Society.
Wed, 07 Feb 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/984092007-02-07T00:00:00Z
- Electronic entanglement purification scheme enhanced by charge detectionshttps://scholarbank.nus.edu.sg/handle/10635/96424Title: Electronic entanglement purification scheme enhanced by charge detections
Authors: Feng, X.-L.; Kwek, L.C.; Oh, C.H.
Abstract: We present an entanglement purification scheme for the mixed entangled states of electrons with the aid of charge detections. Our scheme adopts the electronic polarizing beam splitters rather than the controlled-NOT (CNOT) operations, but the total successful probability of our scheme can reach the quantity as large as that of the the CNOT-operation-based protocol and twice as large as that of linear-optics-based protocol for the purification of photonic entangled states. Thus our scheme can achieve a high successful prabability without the usage of CNOT operations. © 2005 The American Physical Society.
Wed, 01 Jun 2005 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/964242005-06-01T00:00:00Z
- Effective dynamics of cold atoms flowing in two ring-shaped optical potentials with tunable tunnelinghttps://scholarbank.nus.edu.sg/handle/10635/112424Title: Effective dynamics of cold atoms flowing in two ring-shaped optical potentials with tunable tunneling
Authors: Aghamalyan, D.; Amico, L.; Kwek, L.C.
Abstract: We study the current dynamics of coupled atomic condensates flowing in two ring-shaped optical potentials. We provide a specific setup where the ring-ring coupling can be tuned in an experimentally feasible way. It is demonstrated that the imaginary time effective action of the system in a weak coupling regime provides a two-level-system dynamics for the phase slip across the two rings. Through two-mode Gross- Pitaevskii mean-field equations, the real-time dynamics of the population imbalance and the phase difference between the two condensates is thoroughly analyzed analytically, as a function of the relevant physical parameters of the system. In particular, we find that the macroscopic quantum self-trapping phenomenon is induced in the system if the flowing currents assume a nonvanishing difference. © 2013 American Physical Society.
Fri, 13 Dec 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1124242013-12-13T00:00:00Z