Now showing 1 - 10 of 158
  • Publication
    Open Access
    Entanglement witness for spin glass
    (2015)
    Koh, Chee Yeong
    ;
    We derived the entanglement witness (EW) in Ising model for both the magnetic susceptibility and specifi c heat capacity of a spin glass. The magnetic susceptibility EW curve for LiHoxY1-xF4 is formulated and compared with the existing data of LiHo0:167Y0:833F4 to identify the entangled and unentangled regions. The EW for the magnetic susceptibility was found to cut the cusp of the experimental result at a critical temperature of about 0.2669 K. The speci fic heat capacity EW curve for CuxMn is formulated and compared with the existing data of Cu0:279Mn to identify the entangled and unentangled region for the various applied magnetic field B. With increasing B, the critical temperature where the EW curve intersects the experimental data, increases as well.
    WOS© Citations 4Scopus© Citations 4  88  160
  • Publication
    Open Access
    Bures fidelity of displaced squeezed thermal states
    (American Physical Society, 1998) ;
    Wang, Xiang-Bin
    ;
    Oh, Choo Hiap
    Fidelity has always been an important concept in quantum optics. Recently, it was found that fidelity can also play a key role in quantum information and communication theory. Fidelity can be interpreted as the probability that a decoded message possesses the same information content as the message prior to coding and transmission. In this paper, we give a formula of Bures fidelity for displaced squeezed thermal states directly by the displacement and squeezing parameters and briefly discuss how the results can apply to quantum information theory.
    WOS© Citations 14Scopus© Citations 18  158  201
  • Publication
    Open Access
    Dynamical quantum phase transitions and non-Markovian dynamics
    (American Physical Society, 2020)
    Kyaw, Thi Ha
    ;
    Bastidas, Victor M.
    ;
    Tangpanitanon, Jirawat
    ;
    Guillermo, Romero
    ;
    In the context of closed quantum systems, when a system prepared in its ground state undergoes a sudden quench, the resulting Loschmidt echo can exhibit zeros, resembling the Fisher zeros in the theory of classical equilibrium phase transitions. These zeros lead to nonanalytical behavior of the corresponding rate function, which is referred to as dynamical quantum phase transitions (DQPTs). In this work, we investigate DQPTs in the context of open quantum systems that are coupled to both Markovian and non-Markovian dephasing baths via a conserved quantity. The general framework is corroborated by studying the nonequilibrium dynamics of a transverse-field Ising ring. We show the robustness of DQPT signatures under the action of both engineered dephasing baths, independently on how strongly they couple to the quantum system. Our theory provides insight on the effect of non-Markovian environments on DQPTs.
    WOS© Citations 22Scopus© Citations 26  106  139
  • Publication
    Open Access
    Entanglement of a 2-qubit system coupled to a bath of quantum spin glass
    (2014)
    Koh, Chee Yeong
    ;
    We study the quantum entanglement (concurrence) of a 2-qubit system coupled to a small spin glass bath of 2 to n ≥ 4 qubits. The bath is described by the quantum XX Heisenberg model with random J coupling and varying magnetic field h. We look at the dynamics of the steady state average concurrence for the system and obtain a general formula to describe the concurrence with J = 0 and h = 0 for n bath sites. The physics of 2-qubit system coupled with n bath sites for J = 0 is analytically described for small n. The result for large n was numerically found to be qualitatively similar. For small fluctuation in J, a mean steady state average concurrence of about 0.5 is obtained.
    WOS© Citations 5Scopus© Citations 5  93  275
  • Publication
    Open Access
    Hardy’s paradox for high-dimensional systems
    (American Physical Society, 2013)
    Chen, Jing-Ling
    ;
    Cabello, Adan
    ;
    Xu, Zhen-Peng
    ;
    Su, Hong-Yi
    ;
    Wu, Chunfeng
    ;
    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.
    WOS© Citations 31Scopus© Citations 36  157  183
  • Publication
    Open Access
    Kinematic approach to off-diagonal geometric phases of nondegenerate and degenerate mixed states
    (American Physical Society, 2005)
    Tong, Dianmin
    ;
    Sjöqvist, Erik
    ;
    Filipp, Stefan
    ;
    ;
    Oh, Choo Hiap
    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.
    WOS© Citations 13Scopus© Citations 14  326  160
  • Publication
    Open Access
    Luttinger liquid of photons and spin-charge separation in hollow-core fibers
    (American Physical Society, 2011)
    Angelakis, Dimitris G.
    ;
    Huo, Ming-Xia
    ;
    Kyoseva, Elica
    ;
    In this work we show that light-matter excitations (polaritons) generated inside a hollow-core onedimensional 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.
    WOS© Citations 40Scopus© Citations 41  310  180
  • Publication
    Open Access
    Robust-fidelity atom-photon entangling gates in the weak-coupling regime
    (American Physical Society, 2012)
    Li, Ying
    ;
    Aolita, Leandro
    ;
    Chang, Darrick E.
    ;
    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.
    WOS© Citations 45Scopus© Citations 50  253  133
  • Publication
    Metadata only
    Simulating energy transfer in molecular systems with digital quantum computers
    (2022)
    Lee, Chee Kong
    ;
    Lau, Jonathan Wei Zhong
    ;
    Shi, Liang
    ;
    Quantum computers have the potential to simulate chemical systems beyond the capability of classical computers. Recent developments in hybrid quantum-classical approaches enable the determinations of the ground or low energy states of molecular systems. Here, we extend near-term quantum simulations of chemistry to time-dependent processes by simulating energy transfer in organic semiconducting molecules. We developed a multiscale modeling workflow that combines conventional molecular dynamics and quantum chemistry simulations with hybrid variational quantum algorithm to compute the exciton dynamics in both the single excitation subspace (i.e., Frenkel Hamiltonian) and the full-Hilbert space (i.e., multiexciton) regimes. Our numerical examples demonstrate the feasibility of our approach, and simulations on IBM Q devices capture the qualitative behaviors of exciton dynamics, but with considerable errors. We present an error mitigation technique that combines experimental results from the variational and Trotter algorithms, and obtain significantly improved quantum dynamics. Our approach opens up new opportunities for modeling quantum dynamics in chemical, biological, and material systems with quantum computers.
    WOS© Citations 5Scopus© Citations 5  77
  • Publication
    Open Access
    Phase diffusion and the small-noise approximation in linear amplifiers: Limitations and beyond
    (2019)
    Chia, Andy
    ;
    Hajdušek, Michal
    ;
    Fazio, Rosario
    ;
    ;
    Vedral, Vlatko
    The phase of an optical field inside a linear amplifier is widely known to diffuse with a diffusion coefficient that is inversely proportional to the photon number. The same process occurs in lasers which limits its intrinsic linewidth and makes the phase uncertainty difficult to calculate. The most commonly used simplification is to assume a narrow photon-number distribution for the optical field (which we call the small-noise approximation). For coherent light, this condition is determined by the average photon number. The small-noise approximation relies on (i) the input to have a good signal-to-noise ratio, and (ii) that such a signal-to-noise ratio can be maintained throughout the amplification process. Here we ask: For a coherent input, how many photons must be present in the input to a quantum linear amplifier for the phase noise at the output to be amenable to a small-noise analysis? We address these questions by showing how the phase uncertainty can be obtained without recourse to the small-noise approximation. It is shown that for an ideal linear amplifier (i.e. an amplifier most favourable to the small-noise approximation), the small-noise approximation breaks down with only a few photons on average. Interestingly, when the input strength is increased to tens of photons, the small-noise approximation can be seen to perform much better and the process of phase diffusion permits a small-noise analysis. This demarcates the limit of the small-noise assumption in linear amplifiers as such an assumption is less true for a nonideal amplifier.
    WOS© Citations 5Scopus© Citations 4  274  86