Now showing 1 - 10 of 157
  • Publication
    Open Access
    Protecting two-qubit quantum states by π-phase pulses
    (2010)
    Hu, Jia-Zhong
    ;
    Wang, Xiang-Bin
    ;
    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.
    WOS© Citations 7Scopus© Citations 7  118  146
  • Publication
    Open Access
    Incorporating nature of science elements in A-level physics lessons in Singapore.
    (National Institute of Education (Singapore), 2020)
    Subramaniam, R. (Ramanathan)
    ;
    Wong, Choun Pei
    ;
    Wee, Andrew
    ;
    ;
    Sow, Chorng Haur
    ;
    Chew, Charles
    ;
    Wong, Darren
      188  126
  • Publication
    Open Access
    Coherent eavesdropping attacks in quantum cryptography: Nonequivalence of quantum and classical key distillation
    (American Physical Society, 2005)
    Kaszlikowski, Dagomir
    ;
    Lim, Jenn Yang
    ;
    ;
    Englert, Berthold-Georg
    The security of a cryptographic key that is generated by communication through a noisy quantum channel relies on the ability to distill a shorter secure key sequence from a longer insecure one. We show that—for protocols that use quantum channels of any dimension and completely characterize them by state tomography—the noise threshold for classical advantage distillation of a specific kind is substantially lower than the threshold for quantum entanglement distillation if the eavesdropper can perform powerful coherent attacks. In marked contrast, earlier investigations had shown that the thresholds are identical for incoherent attacks on the same classical distillation scheme. It remains an open question whether other schemes for classical advantage distillation have higher thresholds for coherent eavesdropping attacks.
    WOS© Citations 2Scopus© Citations 3  124  115
  • Publication
    Open Access
    General formalism of Hamiltonians for realizing a prescribed evolution of a qubit
    (2003)
    Tong, Dianmin
    ;
    Chen, Jing-Ling
    ;
    ;
    Lai, C. H.
    ;
    Oh, Choo Hiap
    We investigate the inverse problem concerning the evolution of a qubit system, specifically we consider how one can establish the Hamiltonians that account for the evolution of a qubit along a prescribed path in the projected Hilbert space. For a given path, there are infinite Hamiltonians which can realize the same evolution. A general form of the Hamiltonians is constructed in which one may select the desired one for implementing a prescribed evolution. This scheme can be generalized to higher dimensional systems.
    WOS© Citations 3  116  68
  • Publication
    Metadata only
    Quantum computers: Theory and algorithms
    (Springer, 2023)
    Baaquie, Belal Ehsan
    ;
    Highlights the advantages of a quantum over a classical computer. Reviews the concepts of the classical and quantum computers along with circuits and gates. Uses the Deutsch, Grover, and Shor algorithms for highlighting key features of quantum computing
    Scopus© Citations 3  21
  • Publication
    Open Access
    Quantum Fredkin and Toffoli gates on a versatile programmable silicon photonic chip
    (2022)
    Li, Yuan
    ;
    Wan, Lingxiao
    ;
    Zhang, Hui
    ;
    Zhu, Huihui
    ;
    Shi, Yuzhi
    ;
    Chin, Lip Ket
    ;
    Zhou, Xiaoqi
    ;
    ;
    Liu, Ai Qun
    Quantum logic gates are backbones of quantum information processing (QIP), wherein the typical three-qubit Fredkin and Toffoli gates are essential in quantum computation and communication. So far, the quantum Fredkin gate has only been demonstrated with pre-entangled input states in free-space optics, which limits its usage for independent input photons. Here, we put forward an exquisite scheme and experimentally perform a proof-of-principle demonstration of three-qubit Fredkin and Toffoli gates on a programmable quantum photonic chip. Our scheme can also be used to realize a series of other two-qubit quantum gates. Our work sheds light on the merits of quantum photonic chip in implementing quantum logic gates, and paves the way for advanced quantum chip processors.
    WOS© Citations 6Scopus© Citations 9  255  79
  • Publication
    Open Access
    Continuous multipartite entangled state in Wigner representation and violation of the Zukowski-Brukner inequality
    (American Physical Society, 2005)
    Wu, Chunfeng
    ;
    Chen, Jing-Ling
    ;
    ;
    Oh, Choo Hiap
    ;
    Xue, Kang
    We construct an explicit Wigner function for the N-mode squeezed state. Based on a previous observation that the Wigner function describes correlations in the joint measurement of the phase-space displaced parity operator, we investigate the nonlocality of the multipartite entangled state by the violation of the Żukowski-Brukner N-qubit Bell inequality. We find that quantum predictions for such a squeezed state violate these inequalities by an amount that grows with the number N.
    WOS© Citations 9Scopus© Citations 9  327  186
  • Publication
    Open Access
    Encoding error correction in an integrated photonic chip
    (American Physical Society, 2023)
    Zhang, Hui
    ;
    Wan, Lingxiao
    ;
    Paesani, Stefano
    ;
    Laing, Anthony
    ;
    Shi, Yuzhi
    ;
    Cai, Hong
    ;
    Luo, Xianshu
    ;
    Lo, Guo Qiang
    ;
    ;
    Liu, Ai Qun
    Integrated photonics provides a versatile platform for encoding and processing quantum information. However, the encoded quantum states are sensitive to noise, which limits their capability to perform complicated quantum computations. Here, we use a five-qubit linear cluster state on a silicon photonic chip to implement a quantum error-correction code and demonstrate its capability of identifying and correcting a single-qubit error. The encoded quantum information is reconstructed from a single-qubit error and an average state fidelity of 0.863 ± 0.032 is achieved for different input states. We further extend the scheme to demonstrate a fault-tolerant measurement-based quantum computation (MBQC) on stabilizer formalism that allows us to redo the qubit operation against the failure of the teleportation process. Our work provides a proof-of-concept working prototype of error correction and MBQC in an integrated photonic chip.
    WOS© Citations 2  16  34
  • Publication
    Open Access
    Effective dynamics of cold atoms flowing in two ring-shaped optical potentials with tunable tunneling
    (American Physical Society, 2013)
    Aghamalyan, Davit
    ;
    Amico, Luigi
    ;
    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.
    WOS© Citations 37Scopus© Citations 40  156  194
  • Publication
    Open Access
    Repeat-until-success distributed quantum computation by using single-photon interference at a beam splitter
    (2008)
    Feng, Xun-Li
    ;
    Qian, Jun
    ;
    ;
    Oh, Choo Hiap
    A repeat-until-success (RUS) measurement-based scheme for the implementation of the distributed quantum computation by using single-photon interference at a 50:50 beam splitter is proposed. It is shown that the 50:50 beam splitter can naturally project a suitably encoded matter-photon state to either a desired entangling gate-operated state of the matter qubits or to their initial state when the photon is detected. The recurrence of the initial state permits us to implement the desired entangling gate in a RUS way. To implement a distributed quantum computation we suggest an encoding method by means of the effect of dipole-induced transparency proposed recently [E. Waks and J. Vuckovic, Phys. Rev. Lett. 96, 153601 (2006)]. The effects of the unfavorable factors on our scheme are also discussed.
    WOS© Citations 4Scopus© Citations 4  139  142