arXiv subjects

Lan Zhou

Publications and source records attributed to Lan Zhou.

At least 127 records · Page 7Linked to original sources

arXiv2012

Efficient entanglement concentration for arbitrary less-entangled N-atom state

A recent paper (Phys. Rev. A 86, 034305 (2012)) proposed an entanglement concentration protocol (ECP) for less-entangled $N$-atom GHZ state with the help of the photonic Faraday rotation. It is shown that the maximally entangled atom state can be distilled from two pairs of less-entangled atom states. In this paper, we put forward an improved ECP for arbitrary less-entangled N-atom GHZ state with only one pair of less-entangled atom state, one auxiliary atom and one auxiliary photon. Moreover, our ECP can be used repeatedly to obtain a higher success probability. If consider the practical operation and imperfect detection, our protocol is more efficient. This ECP may be useful in current quantum information processing.

quant-ph↗

arXiv2012

Efficient single-photon entanglement concentration for quantum communications

We present two protocols for the single-photon entanglement concentration. With the help of the 50:50 beam splitter, variable beam splitter and an auxiliary photon, we can concentrate a less-entangled single-photon state into a maximally single-photon entangled state with some probability. The first protocol is implemented with linear optics and the second protocol is implemented with the cross-Kerr nonlinearity. Our two protocols do not need two pairs of entangled states shared by the two parties, which makes our protocols more economic. Especially, in the second protocol, with the help of the cross-Kerr nonlinearity, the sophisticated single photon detector is not required. Moreover, the second protocol can be reused to get higher success probability. All these advantages may make our protocols useful in the long-distance quantum communication.

quant-ph↗

arXiv2012

Efficient multipartite entanglement concentration of electron-spin state with charge detection

We present two entanglement concentration protocols (ECPs) for arbitrary three-electron W state based on their charges and spins. Different from other ECPs, in both two ECPs, with the help of the electronic polarization beam splitter (PBS) and charge detection, the less-entangled W state can be concentrated into a maximally entangled state only with some single charge qubits. The second ECP is more optimal than the first one, for by constructing the complete parity check gate, the second ECP can be used repeatedly to further concentrate the less-entangled state and obtain a higher success probability. Therefore, both the ECPs, especially the second one may be useful in current quantum information processing.

quant-ph↗

arXiv2012

Efficient entanglement concentration for arbitrary less-entangled NOON state assisted with single photon

We put forward two efficient entanglement concentration protocols (ECPs) for distilling the maximally entangled NOON state from arbitrary less-entangled NOON state with only an auxiliary single photon. With the help of the weak cross-Kerr nonlinearities, both the two ECPs can be used repeatedly to get a high success probability. In the first ECP, the auxiliary single photon should be shared by the two parties say Alice and Bob. In the second ECP, the auxiliary single photon is only possessed by Bob, which can greatly increase the practical success probability by avoiding the transmission loss. Moreover, Bob can operate the whole protocol alone, which makes the protocol more simple. Therefore, our two ECPs, especially the second ECP may be more useful and convenient in the current quantum information processing.

quant-ph↗

arXiv2012

Optimal entanglement concentration for quantum dot and optical microcavities systems

A recent paper [Chuan Wang, Phys. Rev. A \textbf{86}, 012323 (2012)] discussed an entanglement concentration protocol (ECP) for partially entangled electrons using a quantum dot and microcavity coupled system. In his paper, each two-electron spin system in a partially entangled state can be concentrated with the assistance of an ancillary quantum dot and a single photon. In this paper, we will present an optimal ECP for such entangled electrons with the help of only one single photon. Compared with the protocol of Wang, the most significant advantage is that during the whole ECP, the single photon only needs to pass through one microcavity which will increase the total success probability if the cavity is imperfect. The whole protocol can be repeated to get a higher success probability. With the feasible technology, this protocol may be useful in current long-distance quantum communications.

quant-ph↗

arXiv2012

Non-Abelian geometrical control of a qubit in an NV center in diamond

We propose an approach for an optical qubit rotation in the negatively charged nitrogen-vacancy (NV) center in diamond. The qubit is encoded in the ground degenerate states at the relatively low temperature limit. The basic idea of the rotation procedure is the non-Abelian geometric phase in an adiabatic passage, which is produced by the nonadiabatic transition between the two degenerate dark states. The feasibility is based on the success of modeling the NV center as an excited-doublet four-level atom.

quant-ph↗

arXiv2012

Efficient W state entanglement concentration using quantum-dot and optical microcavities

We present an entanglement concentration protocols (ECPs) for less-entangled W state with quantum-dot and microcavity coupled system. The present protocol uses the quantum nondemolition measurement on the spin parity to construct the parity check gate. Different from other ECPs, this less-entangled W state with quantum-dot and microcavity coupled system can be concentrated with the help of some single photons. The whole protocol can be repeated to get a higher success probability. It may be useful in current quantum information processing.

quant-ph↗

arXiv2012

Bloch oscillations of quasispin polaritons in a magneto-optically controlled atomic ensemble

We consider the propagation of a quantized polarized light in a magneto-optically manipulated atomic ensemble with a tripod configuration. Polariton formalism is applied when the medium is subjected to a washboard magnetic field under electromagnetically induced transparency. The dark-state polariton with multiple components is achieved. We analyze quantum dynamics of the dark-state polariton by some experiment data from rubidium D1-line. It is found that one component propagates freely, however the wavepacket trajectory of the other component performs Bloch oscillations.

quant-ph↗

arXiv2012

Efficient $N$-particle $W$ state concentration with different parity check gates

We present an universal way to concentrate an arbitrary $N$-particle less-entangled $W$ state into a maximally entangled $W$ state with different parity check gates. It comprises two protocols. The first protocol is based on the linear optical elements say the partial parity check gate and the second one uses the quantum nondemolition (QND) to construct the complete parity check gate. Both of which can achieve the concentration task. These protocols have several advantages. First, it can obtain a maximally entangled W state only with the help of some single photons, which greatly reduces the number of entanglement resources. Second, in the first protocol, only linear optical elements are required which is feasible with current techniques. Third, in the second protocol, it can be repeated to perform the concentration step and get a higher success probability. All these advantages make it be useful in current quantum communication and computation applications.

quant-ph↗

arXiv2012

Efficient two-step entanglement concentration for arbitrary W states

We present two two-step practical entanglement concentration protocols (ECPs) for concentrating an arbitrary three-particle less-entangled W state into a maximally entangled W state assisted with single photons. The first protocol uses the linear optics and the second protocol adopts the cross-Kerr nonlinearity to perform the protocol. In the first protocol, based on the post-selection principle, three parties say Alice, Bob and Charlie in different distant locations can obtain the maximally entangled W state from the arbitrary less-entangled W state with a certain success probability. In the second protocol, it dose not require the parties to posses the sophisticated single-photon detectors and the concentrated photon pair can be retained after performing this protocol successfully. Moreover, the second protocol can be repeated to get a higher success probability. Both protocols may be useful in practical quantum information applications.

quant-ph↗

arXiv2012

Efficient entanglement concentration for three-photon W states with parity check measurement

We present an optimal entanglement concentration ECP for an arbitrary less-entangled W state. By two of the parties say Alice and Charlie performing one parity check measurements, they can obtain the maximally entangled W state with a certain probability. Otherwise, they can obtain another lesser-entangled W state with another probability, which can be used to reconcentrated into a maximally entangled W state. By iterating this ECP several times, it has the maximal success probability. This ECP maybe an optimal one and is useful in current quantum information processing.

quant-ph↗

arXiv2012

Efficient electronic entanglement concentration assisted with single mobile electron

We present an efficient entanglement concentration protocol (ECP) for mobile electrons with charge detection. This protocol is quite different from other ECPs for one can obtain a maximally entangled pair from a pair of less-entangled state and a single mobile electron with a certain probability. With the help of charge detection, it can be repeated to reach a higher success probability. It also does not need to know the coefficient of the original less-entangled states. All these advantages may make this protocol useful in current distributed quantum information processing.

quant-ph↗

arXiv2012

Efficient single-photon-assisted entanglement concentration for partially entangled photon pairs

We present two realistic entanglement concentration protocols (ECPs) for pure partially entangled photons. A partially entangled photon pair can be concentrated to a maximally entangled pair with only an ancillary single photon in a certain probability, while the conventional ones require two copies of partially entangled pairs at least. Our first protocol is implemented with linear optics and the second one is implemented with cross-Kerr nonlinearities. Compared with other ECPs, they do not need to know the accurate coefficients of the initial state. With linear optics, it is feasible with current experiment. With cross-Kerr nonlinearities, it does not require the sophisticated single-photon detectors and can be repeated to get a higher success probability. Moreover, the second protocol can get the higher entanglement transformation efficiency and it maybe the most economical one by far. Meanwhile, both of protocols are more suitable for multi-photon system concentration, because they need less operations and classical communications. All these advantages make two protocols be useful in current long-distance quantum communications.

quant-ph↗

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.

quant-ph↗

arXiv2011

Lattice relaxation of dimer islands on Ge(001) during homoepitaxy by pulsed laser deposition

In low-temperature pulsed growth two-dimensional islands form and coarsen into ~10 nm features. The islands produce well-defined displaced x-ray diffraction peaks due to relaxation of anisotropic surface stress of the (2x1) reconstruction with expansion and contraction present in orthogonal directions. The relaxation carries over into multilevel islands, suggesting that domains in subsequent layers form metastable stress domains. We infer that the island distribution differs from continuous deposition, enhancing the population of monodisperded islands exhibiting anisotropic relaxation.

cond-mat.mtrl-sci↗

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.

quant-ph↗

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.

quant-ph↗

arXiv2010

Pressure-dependent transition from atoms to nanoparticles in magnetron sputtering: Effect on WSi2 film roughness and stress

We report on the transition between two regimes from several-atom clusters to much larger nanoparticles in Ar magnetron sputter deposition of WSi2, and the effect of nanoparticles on the properties of amorphous thin films and multilayers. Sputter deposition of thin films is monitored by in situ x-ray scattering, including x-ray reflectivity and grazing incidence small angle x-ray scattering. The results show an abrupt transition at an Ar background pressure Pc; the transition is associated with the threshold for energetic particle thermalization, which is known to scale as the product of the Ar pressure and the working distance between the magnetron source and the substrate surface. Below Pc smooth films are produced, while above Pc roughness increases abruptly, consistent with a model in which particles aggregate in the deposition flux before reaching the growth surface. The results from WSi2 films are correlated with in situ measurement of stress in WSi2/Si multilayers, which exhibits a corresponding transition from compressive to tensile stress at Pc. The tensile stress is attributed to coalescence of nanoparticles and the elimination of nano-voids.

cond-mat.mtrl-sci↗