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Low dissipation, tunable coupling to other quantum systems, and unique features of phonons in the aspects of propagation, detection and others suggest the applications of quantized mechanical resonators in phonon-based quantum information processing (QIP) in a way different from their photonic counterpart. In this paper, we propose the first protocol of entanglement concentration for nonlocal phonons from quantized mechanical vibration. We combine the optomechanical cross-Kerr interaction with the Mach-Zehnder interferometer and, by means of twice optomechanical interactions and the photon analysis with respect to the output of the interferometer, achieve ideal entanglement concentration about less-entangled nonlocal phonon Bell and Greenberger-Horne-Zeilinger states. Our protocol is useful for preserving the entangled phonons for the use of high quality phonon-based QIP in future., 7 pages, 5 figures

We investigate the entanglement dynamics of two local two-state quantum systems coupling to a bosonic mode and a common structured bath. Here the bosonic mode is damped by a broadband reservoir and acts as a probe mode for the use of continuous quantum measurement feedback, and the bath has a structure characterized by the Ohmic spectral density. We first present the non-Markovian master equation for the two-state quantum systems and then the corresponding hierarchical equations of motion (HEOM). We illustrate the equivalence between the HEOM approach and the perturbation theory. HEOM-calculations show that the quantum measurement feedback plays a positive role in the entanglement generation, and the non-Markovian effect of the Ohmic bath could greatly enhance this action. We reveal in detail the dependence of the scheme on the spectral density parameters, the temperature of the bath, and the measurement feedback strength. The numerical results are obtained with the HEOM truncated at the third order, which are equal to those obtained with sixth-order perturbation theory.

We propose a scheme for transferring entanglement from one photonic degree of freedom to another through Raman interactions between a photon pair in cavity modes and atomic ensemble. The condition for deterministically generating the entanglement encoded in frequency or both frequency and polarization is obtained. The scheme could be immune to the photon loss originating from cavity-mode damping, spontaneous emission, and the dephasing due to atomic thermal motion. For current techniques, there are no major difficulties for this scheme to be realized experimentally.

An additional weak harmonic forcing is added to the Duffing equation, and its ability of suppressing chaos is analyzed in the global parameter space. It is found that the phase difference between the two sinusoidal forces plays a very important role in suppressing chaos. A new type of intermittency characterized by periodic appearance of regular and chaotic motions, called the breathing effect in this Letter, is observed when the two harmonic forces deviate slightly from resonance.

We study the ancilla-free $1\ensuremath{\rightarrow}2$ phase-covariant telecloning for qudits. We show that the fidelity of the two clones can probabilistically reach that of the clones in the optimal $1\ensuremath{\rightarrow}2$ phase-covariant cloning (involving an ancilla). More interestingly, that can realize the above nonlocal cloning tasks are suitable nonmaximally entangled states rather than the maximally entangled states.

Recently, a genuine four-qubit entangled state ${\ensuremath{\mid}{\ensuremath{\chi}}^{00}⟩}_{3214}$ has been proposed [Y. Yeo and W. K. Chua, Phys. Rev. Lett. 96, 060502 (2006)]. This state has many interesting entanglement properties and possible applications in quantum information processing and fundamental tests of quantum physics. Here we present a simple scheme for generating such a state in an ion-trap system. We also demonstrate how to discriminate between the 16 basis states ${{\ensuremath{\mid}{\ensuremath{\chi}}^{ij}⟩}_{3214}={\ensuremath{\sigma}}_{3}^{i}{\ensuremath{\sigma}}_{1}^{j}{\ensuremath{\mid}{\ensuremath{\chi}}^{00}⟩}_{3214},i,j=0,1,2,3}$.

Light amplification in a collective atomic recoil laser with an active medium confined in an external harmonic trap is investigated. Our study confirms the possibility of a great promotion of the lasing efficiency due to the collective atomic recoil motion being modified by the trapping potential. The physical explanation of this laser behavior is given.