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Incorporating nature of science elements in A-level physics lessons in Singapore.

2020, Subramaniam, R. (Ramanathan), Wong, Choun Pei, Wee, Andrew, Kwek, Leong Chuan, Sow, Chorng Haur, Chew, Charles, Wong, Darren

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Luttinger liquid of photons and spin-charge separation in hollow-core fibers

2011, Angelakis, Dimitris G., Huo, Ming-Xia, Kyoseva, Elica, Kwek, Leong Chuan

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.

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Quantum zeno effect of general quantum operations

2013, Li, Ying, Herrera-Marti, David A., Kwek, Leong Chuan

In this paper, we show that the quantum Zeno effect can occur for generalized quantum measurements or operations. As a consequence of frequently performing nonselective measurements (or trace-preserving completely positive maps), the evolution of a certain measurement-invariant state is governed by an effective Hamiltonian defined by the measurement (or map) and the free-evolution Hamiltonian. For selective measurements, the state may change randomly with time according to measurement outcomes, but some physical quantities (operators) still evolve according to the effective Hamiltonian.

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Quantum tomographic cryptography with a semiconductor single photon source

2005, Kaszlikowski, Dagomir, Kwek, Leong Chuan, Lim, Jenn Yang, Willeboordse, Frederick H., Looi, Shiang Yong

We analyze the security of so-called quantum-tomographic cryptography with the source producing entangled photons via an experimental scheme proposed by Fattal et al. [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.

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Information theoretic approach to single-particle and two-particle interference in multi-path interferometers

2003, Kaszlikowski, Dagomir, Kwek, Leong Chuan, Zukowski, Marek, Englert, Berthold-Georg

We propose entropic measures for the strength of single-particle and two- particle interference in interferometric experiments where each particle of a pair traverses a multi-path interferometer. Optimal single-particle interference excludes any two-particle interference, and vice versa. We report an inequality that states the compromises allowed by quantum mechanics in intermediate situations, and identify a class of two-particle states for which the upper bound is reached. Our approach is applicable to symmetric two-partite systems of any finite dimension.

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Stochastic resonance of quantum discord

2011, Lee, Chee Kong, Kwek, Leong Chuan, Cao, Jianshu

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.

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Digital quantum simulation of the spin-boson model under Markovian open-system dynamics

2022, Burger, Andreas, Kwek, Leong Chuan, Poletti, Dario

Digital quantum computers have the potential to simulate complex quantum systems. The spin-boson model is one of such systems, used in disparate physical domains. Importantly, in a number of setups, the spin-boson model is open, i.e., the system is in contact with an external environment which can, for instance, cause the decay of the spin state. Here, we study how to simulate such open quantum dynamics in a digital quantum computer, for which we use an IBM hardware. We consider in particular how accurate different implementations of the evolution result as a function of the level of noise in the hardware and of the parameters of the open dynamics. For the regimes studied, we show that the key aspect is to simulate the unitary portion of the dynamics, while the dissipative part can lead to a more noise resistant simulation. We consider both a single spin coupled to a harmonic oscillator, and also two spins coupled to the oscillator. In the latter case, we show that it is possible to simulate the emergence of correlations between the spins via the oscillator.

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Long-distance entanglement generation with scalable and robust two-dimensional quantum network

2012, Li, Ying, Cavalcanti, Daniel, Kwek, Leong Chuan

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.

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Effective Hamiltonian approach to adiabatic approximation in open systems

2013, Yi, X. X., Tong, Dianmin, Kwek, Leong Chuan, Oh, Choo Hiap

The adiabatic approximation in open systems is formulated through the effective Hamiltonian approach. By introducing an ancilla, we embed the open system dynamics into a non-Hermitian quantum dynamics of a composite system, the adiabatic evolution of the open system is then defined as the adiabatic dynamics of the composite system. Validity and invalidity conditions for this approximation are established and discussed. A High-order adiabatic approximation for open systems is introduced. As an example, the adiabatic condition for an open spin- 1 2 particle in time-dependent magnetic fields is analyzed.

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Multicomponent Bell inequality and its violation for continuous-variable systems

2005, Chen, Jing-Ling, Wu, Chunfeng, Kwek, Leong Chuan, Kaszlikowski, Dagomir, Zukowski, Marek, Oh, Choo Hiap

Multicomponent correlation functions are developed by utilizing d -outcome measurements. Based on multicomponent correlation functions, we propose a Bell inequality for bipartite d -dimensional systems. Violation of the Bell inequality for continuous-variable (CV) systems is investigated. The violation of maximally entangled states can exceed the Cirel’son bound; the maximal violation is 2.969 81. For finite values of the squeezing parameter, the violation strength of CV states increases with dimension d . Numerical results show that the violation strength of CV states with finite squeezing parameters is stronger than that of maximally entangled states.