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Nguyen Ba An

Publications and source records attributed to Nguyen Ba An.

At least 19 recordsLinked to original sources
arXiv2024

Controlled-Joint Remote Implementation of Operators and its Possible Generalization

The existing notion of the shared entangled state-assisted remote preparation of unitary operator (equivalently the existing notion of quantum remote control) using local operation and classical communication is generalized to a scenario where under the control of a supervisor two users can jointly implement arbitrary unitaries (one unknown unitary operation by each or equivalently a single unitary decomposed into two unitaries of the same dimension and given to two users) on an unknown quantum state available with a geographically separated user. It is explicitly shown that the task can be performed using a four-qubit hyperentangled state, which is entangled simultaneously in both spatial and polarization degrees of freedom of photons. The proposed protocol which can be viewed as primitive for distributed photonic quantum computing is further generalized to the case that drops the restrictions on the number of controllers and the number of parties performing unitaries and allows both the numbers to be arbitrary. It is also shown that all the existing variants of quantum remote control schemes can be obtained as special cases of the present scheme.

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arXiv2021

Heralded preparation of polarization entanglement via quantum scissors

Quantum entanglement is at the heart of quantum information sciences and quantum technologies. In the optical domain, the most common type of quantum entanglement is polarization entanglement, which is usually created in a postselection manner involving destructive photon detection and thus hindering further applications which require readily available entanglement resources. In this work, we propose a scheme to prepare multipartite entangled states of polarized photons in a heralded manner, i.e., without postselection. We exploit the quantum scissors technique to truncate a given continuous-variable entanglement into the target entangled states which are of hybrid discrete-continuous or solely discrete types. We consider two implementations of the quantum scissors: one modified from the original quantum scissors [Pegg et al., Phys. Rev. Lett. 81, 1604 (1998)] using single photons and linear optics and the other designed here using a type-II two-mode squeezer. We clarify the pros and cons of these two implementations as well as discussing practical aspects of the entanglement preparation. Our work illustrates an interface between various types of optical entanglement and the proposed quantum scissors techniques could serve as alternative methods for heralded generation of polarization entanglement.

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arXiv2021

Heralded hybrid CV-DV entanglement generation by quantum interference between CV state and DV delocalized photon

Hybrid entangled states prove to be necessary for quantum information processing within heterogeneous quantum networks. A method with irreducible number of consumed resources that firmly provides hybrid CV-DV entanglement for any input conditions of the experimental setup is proposed. Namely, a family of CV states is introduced. Each of such CV states is first superimposed on a beam-splitter with a delocalized photon and then detected by a photo-detector behind the beam-splitter. Detection of any photon number heralds generation of a hybrid CV-DV entangled state in the outputs, independent of transmission/reflection coefficients of the beam-splitter and size of the input CV state. Nonclassical properties of the generated state are studied and their entanglement degree in terms of negativity is calculated. There are wide domains of values of input parameters of the experimental setup that can be chosen to make the generated state maximally entangled. The proposed method is also applicable to truncated versions of the input CV states. We also propose a simple method to produce even/odd CV states.

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arXiv2019

Expanding possibilities of quantum state engineering and amplifying optical Schrodinger kitten state

We demonstrate an optical method to engineer optical Schrödinger cat states (SCSs) of large size beta ranging from beta=2 to beta=3 with high fidelity close to 0.99. Our approach uses the alpha-representation of the SCSs in infinite Hilbert space with base in terms of displaced number states characterized by the displacement amplitude alpha. An arbitrary alpha-representation of SCSs enables manipulation of the amplitudes in wider ranges of parameters, greatly expanding the possibilities for generation of desired nonclassical states. The optical scheme we consider is quite universal for implementation of the conditioned states close to SCSs with use of linear-optics elements and detectors projecting unitarily transformed input states onto the target one. Different states (e.g., number state or coherent state or superposed state) are selected as the input to the optical scheme. In particular, an input small-size Schroodinger kitten state can give rise to an output large-size SCS.

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arXiv2017

Entanglement of photons in their dual wave-particle nature

Wave-particle duality is the most fundamental description of the nature of a quantum object which behaves like a classical particle or wave depending on the measurement apparatus. On the other hand, entanglement represents nonclassical correlations of composite quantum systems, being also a key resource in quantum information. Despite the very recent observations of wave-particle superposition and entanglement, whether these two fundamental traits of quantum mechanics can emerge simultaneously remains an open issue. Here we introduce and experimentally realize a scheme that deterministically generates wave-particle entanglement of two photons. The elementary tool allowing this achievement is a scalable single-photon setup which can be in principle extended to generate multiphoton wave-particle entanglement. Our study reveals that photons can be entangled in their dual wave-particle nature and opens the way to potential applications in quantum information protocols exploiting the wave-particle degrees of freedom to encode qubits.

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arXiv2014

Shortcuts to adiabatic passage for population transfer and maximum entanglement creation between two atoms in a cavity

We use the approach of "transitionless quantum driving" proposed by Berry to construct shortcuts to the population transfer and the creation of maximal entanglement between two $Λ$-type atoms based on the cavity quantum electronic dynamics (CQED) system. An effective Hamiltonian is designed by resorting to an auxiliary excited level, a classical driving field and an extra cavity field mode to supplement or substitute the original reference Hamiltonian, and steer the system evolution along its instantaneous eigenstates in an arbitrarily short time, speeding up the rate of population transfer and creation of maximal entanglement between the two atoms inside a cavity. Numerical simulation demonstrates that our shortcuts' performance is robust against the decoherences caused by atomic spontaneous emission and cavity photon leakage.

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arXiv2013

Generation of N-atom W-class states in spatially separated cavities

We propose a feasible and efficient scheme to generate $N$-atom $W$-class states in spatially separated cavities without using any classical driving pulses. We adopt the model in which the couplings between different atoms are mediated only by virtual excitations of the cavity and fiber fields, so the scheme is insensitive to the cavity decay and fiber photon leakage. We carry out both theoretical investigation in a decoherence-free subspace and numerical calculation accounting for decoherence due to the atomic spontaneous emission as well as the decay of cavity and fiber modes. The theoretical and numerical results agree in the large atom-cavity detuning regime. Our scheme proves to be useful in scalable distributed quantum networks.

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arXiv2013

One-step generation of multi-atom Greenberger-Horne-Zeilinger states in separate cavities via adiabatic passage

We propose a scheme to deterministically generate Greenberger-Horne-Zeilinger states of $N\geq 3$ atoms trapped in spatially separated cavities connected by optical fibers. The scheme is based on the technique of fractional stimulated Raman adiabatic passage which is one-step in the sense that one needs just wait for the desired entangled state to be generated in the stationary regime. The parametrized shapes of the Rabi frequencies of the classical fields that drive the two end atoms are chosen appropriately to realize the scheme. We also show numerically that the proposed scheme is insensitive to the fluctuations of the pulses' parameters and, at the same time, robust against decoherence caused by the dissipation due to fiber decay. Moreover, a relatively high fidelity can be obtained even in the presence of cavity decay and atomic spontaneous emission.

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arXiv2009

Entanglement dynamics for the double Tavis-Cummings model

A double Tavis-Cummings model (DTCM) is developed to simulate the entanglement dynamics of realistic quantum information processing where two entangled atom-pairs $AB$ and $CD$ are distributed in such a way that atoms $AC$ are embedded in a cavity $a$ while $BD$ are located in another remote cavity $b$. The evolutions of different types of initially shared entanglement of atoms are studied under various initial states of cavity fields. The results obtained in the DTCM are compared with that obtained in the double Jaynes-Cummings model (DJCM) [J. Phys. B \textbf{40}, S45 (2007)] and an interaction strength theory is proposed to explain the parameter domain in which the so-called entanglement sudden death occurs for both the DTCM and DJCM.

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arXiv2006

Reply to Yang et al.'s comment

This is to reply to a recent comment by Yang, Yuan and Zhang on ``Teleportation of two-quNit entanglement: Exploiting local resorces''.

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arXiv2006

GHZ-type and W-type entangled coherent states: generation and Bell-type inequality tests without photon counting

We study GHZ-type and W-type three-mode entangled coherent states. Both the types of entangled coherent states violate Mermin's version of the Bell inequality with threshold photon detection (i.e., without photon counting). Such an experiment can be performed using linear optics elements and threshold detectors with significant Bell violations for GHZ-type entangled coherent states. However, to demonstrate Bell-type inequality violations for W-type entangled coherent states, additional nonlinear interactions are needed. We also propose an optical scheme to generate W-type entangled coherent states in free-traveling optical fields. The required resources for the generation are a single-photon source, a coherent state source, beam splitters, phase shifters, photodetectors, and Kerr nonlinearities. Our scheme does not necessarily require strong Kerr nonlinear interactions, i.e., weak nonlinearities can be used for the generation of the W-type entangled coherent states. Furthermore, it is also robust against inefficiencies of the single-photon source and the photon detectors.

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arXiv2006

Quantum exam

Absolutely and asymptotically secure protocols for organizing an exam in a quantum way are proposed basing judiciously on multipartite entanglement. The protocols are shown to stand against common types of eavesdropping attack.

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arXiv2004

Quantum dialogue

We propose an entanglement-based protocol for two people to simultaneously exchange their messages. We show that the protocol is asymptotically secure against the disturbance attack, the intercept-and-resend attack and the entangle-and-measure attack. Our protocol is experimentally feasible within current technologies.

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arXiv2001

Generation of fan-states of radiation field in a cavity

A scheme of generating recently introduced fan-states | α, 2k>_F (αis complex, k=1,2,3,...) is proposed basing on a Λ-type atom-cavity field interaction. We show that with suitable atomic preparations and measurements a passage of a sequence of N atoms through a cavity may transform an initial field coherent state | α> to a fan-state | α, 2k>_F with k=2^{N-2}.

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arXiv2001

Flower-like squeezing in the motion of a laser-driven trapped ion

We investigate the Nth order amplitude squeezing in the fan-state |ξ;2k,f>_F which is a linear superposition of the 2k-quantum nonlinear coherent states. Unlike in usual states where an ellipse is the symbol of squeezing, a 4k-winged flower results in the fan state. We first derive the analytical expression of squeezing for arbitrary k, N, f and then study in detail the case of a laser-driven trapped ion characterized by a specific form of the nonlinear function f. We show that the lowest order in which squeezing may appear and the number of directions along which the amplitude may be squeezed depend only on k whereas the precise directions of squeezing are determined also by the other physical parameters involved. Finally, we present a scheme to produce such fan-states.

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