arXiv subjects

Le-Man Kuang

Publications and source records attributed to Le-Man Kuang.

At least 73 records · Page 4Linked to original sources

arXiv2013

Nonmaximally entangled states can be better for quantum correlation distribution and storage

For carrying out many quantum information protocols entanglement must be established in advance between two distant parties. Practically, inevitable interaction of entangled subsystems with their environments during distribution and storage will result in degradation of entanglement. Here we investigate the decoherence of two-qubit entangled states in the local amplitude noise. We show that there exists a set of partially entangled states that are more robust than maximally entangled states in terms of the residual quantum correlation measured by concurrence, fully entangled fraction, and quantum discord. This result indicates that nonmaximally entangled states can outperform maximally entangled states for quantum correlation distribution and storage under the amplitude damping. It also educes a notable consequence that the ordering of states under quantum correlation monotones can be reversed even by local trace-preserving and completely positive maps.

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arXiv2013

Many-to-one remote information concentration for qudits and multipartite entanglement

Telecloning and its reverse process, referred to as remote information concentration(RIC), have attracted considerable interest because of their potential applications in quantum-information processing. We here present a general scheme for RIC in d-level systems (qudits), in which the quantum information initially distributed in many spatially separated qudits can be remotely and deterministically concentrated to a single qudit via an entangled channel without performing any global operations. We show that the entangled channel of RIC can be different types of entangled states, including mixed states as well as pure ones. More interestingly, these mixed states include a bound entangled state which has a similar form to the generalized Smolin state but has different characteristics from it. We also show that there exists a multipartite entangled state which can be used to implement both telecloning and RIC in the two-level system. Our many-to-one RIC protocol could be slightly modified to perform some types of many-to-many RIC tasks.

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arXiv2013

Dephasing-assisted parameter estimation in the presence of dynamical decoupling

We study the dephasing-assisted precision of parameter estimation (PPE) enhancement in atom interferometer under dynamical decoupling (DD) pulses. Through calculating spin squeezing (SS) and quantum Fisher information (QFI), we find that dephasing noise can improve PPE by inducing SS, and the DD pulses can maximize the improvement. It is indicated that in the presence of DD pulses, the dephasing-induced SS can reach the limit of \textquotedblleft one-axis twisting\textquotedblright\ model, $ξ^2\simeq N^{-2/3}$ with $ξ^2$ being the SS parameter and N the number of atoms. In particular, we find that the DD pulses can amplify the dephasing-induced QFI by a factor of $\simeq N/2$ compared with the noise-free case, which means that under the control of DD pulses, the dephasing noise can enhance the PPE to the scale of $\sqrt{2}/N$, the same order of magnitude of Heisenberg limit (1/N).

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arXiv2012

Atomic and photonic entanglement concentration via photonic Faraday rotation

We propose two alternative entanglement concentration protocols (ECPs) using the Faraday rotation of photonic polarization. Through the single-photon input-output process in cavity QED, it is shown that the maximally entangled atomic (photonic) state can be extracted from two partially entangled states. The distinct feature of our protocols is that we can concentrate both atomic and photonic entangled states via photonic Faraday rotation, and thus they may be universal and useful for entanglement concentration in the experiment. Furthermore, as photonic Faraday rotation works in low-$Q$ cavities and only involves virtual excitation of atoms, our ECPs are insensitive to both cavity decay and atomic spontaneous emission.

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arXiv2012

Quantum discord amplification induced by quantum phase transition via a cavity-Bose-Einstein-condensate system

We propose a theoretical scheme to realize a sensitive amplification of quantum discord (QD) between two atomic qubits via a cavity-Bose-Einstein condensate (BEC) system which was used to firstly realize the Dicke quantum phase transition (QPT) [Nature 464, 1301 (2010)]. It is shown that the influence of the cavity-BEC system upon the two qubits is equivalent to a phase decoherence environment. It is found that QPT in the cavity-BEC system is the physical mechanism of the sensitive QD amplification.

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arXiv2012

Photonic two-qubit parity gate with tiny cross-Kerr nonlinearity

The cross-Kerr nonlinearity (XKNL) effect can induce efficient photon interactions in principle with which photonic multiqubit gates can be performed using far fewer physical resources than linear optical schemes. Unfortunately, it is extremely challenging to generate giant cross-Kerr nonlinearities. In recent years, much effort has been made to perform multiqubit gates via weak XKNLs. However, the required nonlinearity strengths are still difficult to achieve in the experiment. We here propose an XKNL-based scheme for realizing a two-photon polarization-parity gate, a universal two-qubit gate, in which the required strength of the nonlinearity could be orders of magnitude weaker than those required for previous schemes. The scheme utilizes a ring cavity fed by a coherent state as a quantum information bus which interacts with a path mode of the two polarized photons (qubits). The XKNL effect makes the bus pick up a phase shift dependent on the photon number of the path mode. Even when the potential phase shifts are very small they can be effectively measured using photon-number resolving detectors, which accounts for the fact that our scheme can work in the regime of tiny XKNL. The measurement outcome reveals the parity (even parity or odd parity) of the two polarization qubits.

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arXiv2011

Inherent Mach-Zehnder interference with "which-way" detection for single particle scattering in one dimension

We study the coherent transport of single photon in a one-dimensional coupled-resonator-array, "non-locally" coupled to a two-level system. Since its inherent structure is a Mach-Zehnder interferometer, we explain the destructive interference phenomenon of the transmission spectrums according to the effect of which-way detection. The quantum realization of the present model is a nano-electromechanical resonator arrays with two nearest resonators coupled to a single spin via their attached magnetic tips. Its classical simulation is a waveguide of coupled defected cavity array with double couplings to a side defected cavity.

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arXiv2011

Quantum thermalization of two coupled two-level systems in eigenstate and bare-state representations

We study analytically the quantum thermalization of two coupled two-level systems (TLSs), which are connected with either two independent heat baths (IHBs) or a common heat bath (CHB). We understand the quantum thermalization in eigenstate and bare-state representations when the coupling between the two TLSs is stronger and weaker than the TLS-bath couplings, respectively. In the IHB case, we find that when the two IHBs have the same temperatures, the two coupled TLSs in eigenstate representation can be thermalized with the same temperature as those of the IHBs. However, in the case of two IHBs at different temperatures, just when the energy detuning between the two TLSs satisfies a special condition, the two coupled TLSs in eigenstate representation can be thermalized with an immediate temperature between those of the two IHBs. In bare-state representation, we find a counterintuitive phenomenon that, under some conditions, the temperature of the TLS connected with the high-temperature bath is lower than that of the other TLS, which is connected with the low-temperature bath. In the CHB case, the coupled TLSs in eigenstate representation can be thermalized with the same temperature as that of the CHB in nonresonant cases. In bare-state representation, the TLS with a larger energy separation can be thermalized to a thermal equilibrium with a lower temperature. In the resonant case, we find a phenomenon of anti-thermalization. We also study the steady-state entanglement between the two TLSs in both the IHB and CHB cases.

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arXiv2011

Decoherence-free dynamics of quantum discord for two correlated qubits in finite-temperature reservoirs

We investigate decoherence-free evolution (DFE) of quantum discord (QD) for two initially-correlated qubits in two finite-temperature reservoirs using an exactly solvable model. We study QD dynamics of the two qubits coupled to two independent Ohmic reservoirs when the two qubits are initially prepared in X-type quantum states. It is found that reservoir temperature significantly affects the DFE dynamics. We show that it is possible to control the DFE and to prolong the DFE time by choosing suitable parameters of the two-qubit system and reservoirs.

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arXiv2010

Coherent excitation-energy transfer and quantum entanglement in a dimer

We study coherent energy transfer of a single excitation and quantum entanglement in a dimer, which consists of a donor and an acceptor modeled by two two-level systems. Between the donor and the acceptor, there exists a dipole-dipole interaction, which provides the physical mechanism for coherent energy transfer and entanglement generation. The donor and the acceptor couple to two independent heat baths with diagonal couplings that do not dissipate the energy of the non-coupling dimer. Special attention is paid to the effect on single-excitation energy transfer and entanglement generation of the energy detuning between the donor and the acceptor and the temperatures of the two heat baths. It is found that, the probability for single-excitation energy transfer largely depends on the energy detuning in the low temperature limit. Concretely, the positive and negative energy detunings can increase and decrease the probability at the steady state, respectively. In the high temperature limit, however, the effect of the energy detuning on the probability is neglectably small. We also find that the probability is neglectably dependent on the bath temperature difference of the two heat baths. In addition, it is found that quantum entanglement can be generated in the process of coherent energy transfer. As the bath temperature increases, the generated steady state entanglement decreases. For a given bath temperature, the steady-state entanglement decreases with the increasing of the absolute value of the energy detuning.

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arXiv2010

Controllable coupling and quantum correlation dynamics of two double quantum dots coupled via a transmission line resonator

We propose a theoretical scheme to generate a controllable and switchable coupling between two double-quantum-dot (DQD) spin qubits by using a transmission line resonator (TLR) as a bus system. We study dynamical behaviors of quantum correlations described by entanglement correlation (EC) and discord correlation (DC) between two DQD spin qubits when the two spin qubits and the TLR are initially prepared in $X$-type quantum states and a coherent state, respectively. We demonstrate that in the EC death regions there exist DC stationary states in which the stable DC amplification or degradation can be generated during the dynamical evolution. It is shown that these DC stationary states can be controlled by initial-state parameters, the coupling, and detuning between qubits and the TLR. We reveal the full synchronization and anti-synchronization phenomena in the EC and DC time evolution, and show that the EC and DC synchronization and anti-synchronization depends on the initial-state parameters of the two DQD spin qubits. These results shed new light on dynamics of quantum correlations.

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arXiv2010

Zeno-anti-Zeno crossover via external fields in a one-dimensional coupled-cavity waveguide

We have studied a hybrid system of a one-dimensional coupled-cavity waveguide with a two-level system inside, which subject to a external periodical field. Using the extended Hilbert space formalism, the time-dependent Hamiltonian is reduced into an equivalent time-independent one. Via computing the Floquet-Green's function, the Zeno-anti-Zeno crossover is controlled by the driven intensity and frequency, and the detuning between the cavity and the two-level system.

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arXiv2010

Tailorable couplings of a cantilever with a superconducting charge qubit: Quantum state engineering

We propose a theoretical scheme to realize tailorable couplings between a cantilever and a superconducting charge qubit. By tuning the controllable parameters of the qubit, both linear and nonlinear couplings between the cantilever and the qubit can be achieved. Based on these couplings, we show the preparation of the cantilever into some interesting quantum states, such as superposed coherent states and squeezed states, via manipulating and detecting the qubit. We also study the influence of the environment on quantum states of the cantilever. It is indicated that decoherence induced by the environment can drive the cantilever from superposed coherent states into the steady coherent state. It is also found that the environment can induce the steady-state position squeezing of the cantilever under a critical temperature. These results will shed new light on production of nonclassical effects of the cantilever.

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arXiv2010

Quantum decoherence in a hybrid atom-optical system of a one-dimensional coupled-resonator waveguide and an atom

Decoherence for a one-dimensional coupled-resonator waveguide with a two-level system inside one of resonators, induced by their interaction with corresponding environments, is investigated. Each environment is modeled as a continuum of harmonic oscillators. By finding the eigenstates of the hybrid system, which is the dressed state of the hybrid system, we calculate the lifetime of one excitation, which characterizes the existence of quantum coherence in such hybrid system and the basic quantum nature.

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arXiv2010

Amplification of quantum discord between two uncoupled qubits in a common environment by phase decoherence

We study analytically the dynamic behaviors of quantum correlation measured by quantum discord between two uncoupled qubits, which are immersed in a common Ohmic environment. We show that the quantum discord of the two noninteracting qubits can be greatly amplified or protected for certain initially prepared $X$-type states in the time evolution. Especially, it is found that there does exist the stable amplification of the quantum discord for the case of two identical qubits, and the quantum discord can be protected for the case of two different qubits with a large detuning. It is also indicated that in general there does exist a sudden change of the quantum discord in the time evolution at a critic time point $t_c$, and the discord amplification and protection may occur only in the time interval $0<t\leq t_c$ for certain $X$-type states. This sheds new light on the creation and protection of quantum correlation.

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arXiv2010

Dynamic sensitivity of phton-dressed atomic ensenmble with quantum criticality

We study the dynamic sensitivity of an atomic ensemble dressed by a single-mode cavity field (called a photon-dressed atomic ensemble), which is described by the Dicke model near the quantum critical point. It is shown that when an extra atom in a pure initial state passes through the cavity, the photon-dressed atomic ensemble will experience a quantum phase transition, showing an explicit sudden change in its dynamics characterized by the Loschmidt echo of this quantum critical system. With such dynamic sensitivity, the Dicke model can resemble to the cloud chamber for detecting a flying particle by the enhanced trajectory due to the classical phase transition.

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arXiv2009

Quantum switch for single-photon transport in a coupled superconducting transmission line resonator array

We propose and study an approach to realize quantum switch for single-photon transport in a coupled superconducting transmission line resonator (TLR) array with one controllable hopping interaction. We find that the single-photon with arbitrary wavevector can transport in a controllable way in this system. We also study how to realize controllable hopping interaction between two TLRs via a superconducting quantum interference device (SQUID). When the frequency of the SQUID is largely detuned from those of the two TLRs, the variables of the SQUID can be adiabatically eliminated and thus a controllable interaction between two TLRs can be obtained.

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arXiv2009

Two-mode excited entangled coherent states and their entanglement properties

We introduce two types of two-mode excited entangled coherent states (TMEECSs) $|Ψ_{\pm}(α,m,n)>$, study their entanglement characteristics, and investigate the influence of photon excitations on quantum entanglement. It is shown that for the state $|Ψ_{+}(α,m,n)>$ the two-mode photon excitations affect seriously entanglement character while the the state $|Ψ_{-}(α,m,n)>$ is always a maximally entangled state. We show how such states can be produced by using cavity QED and quantum measurements. It is found that the entanglement amount of the TMEECSs is larger than that of the single-mode excited entangled coherent states with the same photon excitation number.

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