Now showing 1 - 10 of 163
  • Publication
    Open Access
    Uncertainty relation of mixed states by means of Wigner-Yanase-Dyson information
    (American Physical Society, 2009)
    Li, D.
    ;
    Li, X.
    ;
    Wang, F.
    ;
    Huang, H.
    ;
    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 [Phys. Rev. A 72, 042110 (2005)]. 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.
    WOS© Citations 18Scopus© Citations 19  157  264
  • Publication
    Metadata only
    Geometry-corrected quadratic optimization algorithm for NDDO-Descendant Semiempirical Models
    (American Chemical Society, 2024)
    Ong, Adrian Wee Wen
    ;
    Cao, Steve Yeuran
    ;
    Chan, Leemen Chee Yong
    ;
    Lim, Javier
    ;
    The long-held assumption that the optimization of parameters for NDDO-descendant semiempirical methods may be performed without precise geometry optimization is assessed in detail; the relevant equations for the analytical evaluation of the geometry-corrected derivatives of molecular properties that account for changes in the optimum geometry are then presented. The first and second derivatives calculated from our implementation of MNDO are used for a limited reparameterization of 1,113 CHNO molecules taken from the PM7 training set, demonstrating an improvement over the PARAM program used in the optimization of parameters for the PMx methods.
      31
  • Publication
    Open Access
    Sufficiency criterion for the validity of the adiabatic approximation
    (American Physical Society, 2007)
    Tong, Dianmin
    ;
    Singh, K.
    ;
    ;
    Oh, Choo Hiap
    We examine the quantitative condition which has been widely used as a criterion for the adiabatic approximation but was recently found insufficient. Our results indicate that the usual quantitative condition is sufficient for a special class of quantum mechanical systems. For general systems, it may not be sufficient, but it along with additional conditions is sufficient. The usual quantitative condition and the additional conditions constitute a general criterion for the validity of the adiabatic approximation, which is applicable to all N−dimensional quantum systems. Moreover, we illustrate the use of the general quantitative criterion in some physical models.
    WOS© Citations 93Scopus© Citations 99  350  382
  • Publication
    Open Access
    Coincidence Bell inequality for three three-dimensional systems
    (American Physical Society, 2004)
    Acin, A.
    ;
    Chen, Jing-Ling
    ;
    Gisin, N.
    ;
    Kaszlikowski, Dagomir
    ;
    ;
    Oh, Choo Hiap
    ;
    Zukowski, Marek
    We construct a Bell inequality for coincidence probabilities on a three three-dimensional (qutrit) system. We show that this inequality is violated when each observer measures two noncommuting observables, defined by the so-called unbiased six-port beam splitter, on a maximally entangled state of two qutrits. The strength of the violation agrees with the numerical results presented by Kaszlikowski et al. , quant-ph/0202019. It is proven that the inequality defines facets of the polytope of local variable models.
    WOS© Citations 37Scopus© Citations 38  363  257
  • Publication
    Open Access
    Direct estimation of functionals of density operators by local operations and classical communication
    (American Physical Society, 2003)
    Alves, Carolina Moura
    ;
    Horodecki, Pawel
    ;
    Oi, Daniel K. L.
    ;
    ;
    Ekert, Artur K.
    We present a method of direct estimation of important properties of a shared bipartite quantum state, within the “distant laboratories” paradigm, using only local operations and classical communication. We apply this procedure to spectrum estimation of shared states, and locally implementable structural physical approximations to incompletely positive maps. This procedure can also be applied to the estimation of channel capacity and measures of entanglement.
    Scopus© Citations 5WOS© Citations 40  185  209
  • Publication
    Open Access
    Tunable quantum switch realized with a single Λ-level atom coupled to the microtoroidal cavity
    (American Physical Society, 2019)
    Aghamalyan, Davit
    ;
    You, Jia Bin
    ;
    Chu, Hong-Son
    ;
    Png, Ching Eng
    ;
    Krivitsky, Leonid
    ;
    We propose a realization of the quantum switch for coherent light fields for the fiber-coupled microdisk cavities. We demonstrate by combining numerical and analytical methods that both in strong coupling and bad cavity limits it is possible to change a system's behavior from being fully transparent to being fully reflective by varying the amplitude of the external control field. We remark that tuning the amplitude of the control field instead of cavity-atom coupling strength, which was suggested by S. Parkins et al., [Phys. Rev. A 90, 053822 (2014)] for two-level atoms and works only in the strong coupling limit, brings more control and tunability over the transmitted and reflected intensities. We also demonstrate the possibility of controlling the statistics of the input coherent field with the control field which opens the venue for obtaining quantum states of light.
    WOS© Citations 6Scopus© Citations 7  149  181
  • Publication
    Open Access
    Scheme for unconventional geometric quantum computation in cavity QED
    (American Physical Society, 2007)
    Feng, Xun-Li
    ;
    Wang, Zisheng
    ;
    Wu, Chunfeng
    ;
    ;
    Lai, C. H.
    ;
    Oh, Choo Hiap
    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.
    WOS© Citations 51Scopus© Citations 54  192  168
  • Publication
    Open Access
    Beating the Clauser-Horne-Shimony-Holt and the Svetlichny games with optimal states
    (American Physical Society, 2016)
    Su, Hong-Yi
    ;
    Ren, Changliang
    ;
    Chen, Jing-Ling
    ;
    Zhang, Fu-Ling
    ;
    Wu, Chunfeng
    ;
    Xu, Zhen-Peng
    ;
    Gu, Mile
    ;
    Sai Vinjanampathy
    ;
    We study the relation between the maximal violation of Svetlichny’s inequality and the mixedness of quantum states and obtain the optimal state (i.e., maximally nonlocal mixed states, or MNMS, for each value of linear entropy) to beat the Clauser-Horne-Shimony-Holt and the Svetlichny games. For the two-qubit and three-qubit MNMS, we showed that these states are also the most tolerant state against white noise, and thus serve as valuable quantum resources for such games. In particular, the quantum prediction of the MNMS decreases as the linear entropy increases, and then ceases to be nonlocal when the linear entropy reaches the critical points 2/3 and 9/14 for the two- and three-qubit cases, respectively. The MNMS are related to classical errors in experimental preparation of maximally entangled states.
    WOS© Citations 3Scopus© Citations 3  335  204
  • Publication
    Open Access
    Recent progress in quantum photonic chips for quantum communication and internet
    (Springer, 2023)
    Luo, Wei
    ;
    Cao, Lin
    ;
    Shi, Yuzhi
    ;
    Wan, Lingxiao
    ;
    Zhang, Hui
    ;
    Li, Shuyi
    ;
    Chen, Guanyu
    ;
    Li, Yuan
    ;
    Li, Sijin
    ;
    Wang, Yunxiang
    ;
    Sun, Shihai
    ;
    Muhammad Faeyz Karim
    ;
    Cai, Hong
    ;
    ;
    Liu, Ai Qun
    Recent years have witnessed significant progress in quantum communication and quantum internet with the emerging quantum photonic chips, whose characteristics of scalability, stability, and low cost, flourish and open up new possibilities in miniaturized footprints. Here, we provide an overview of the advances in quantum photonic chips for quantum communication, beginning with a summary of the prevalent photonic integrated fabrication platforms and key components for integrated quantum communication systems. We then discuss a range of quantum communication applications, such as quantum key distribution and quantum teleportation. Finally, the review culminates with a perspective on challenges towards high-performance chip-based quantum communication, as well as a glimpse into future opportunities for integrated quantum networks.
    WOS© Citations 11Scopus© Citations 70  96  192
  • Publication
    Metadata only
    Big science in ASEAN in the twenty-first century?
    (IOP Publishing, 2023)
    Tsesmelis, Emmanuel
    ;

    Beyond Japan and China, chapter 50 by E Tsesmelis and Leong-Chuan Kwek offers an overview of how Big Science and the scientific community have been developing in Southeast Asia in the recent past and an outlook for science in the region for the twenty-first century. An active and dynamic scientific research landscape has been realized in academia, government, and industry, which can lead to exciting opportunities for the future. After a brief introduction to the historical development of science in southeast Asia, prospects for growth in the area of Big Science are depicted.

      70