arXiv subjects

Tao Shi

Publications and source records attributed to Tao Shi.

94 records · Page 6Linked to original sources

arXiv2008

Induced Entanglement Enhanced by Quantum Criticality

Two qubit entanglement can be induced by a quantum data bus interacting with them. In this paper, with the quantum spin chain in the transverse field as an illustration of quantum data bus, we show that such induced entanglement can be enhanced by the quantum phase transition (QPT) of the quantum data bus. We consider two external spins simultaneously coupled to a transverse field Ising chain. By adiabatically eliminating the degrees of the chain, the effective coupling between these two spins are obtained. The matrix elements of the effective Hamiltonian are expressed in terms of dynamical structure factor (DSF) of the chain. The DSF is the Fourier transformation of the Green function of Ising chain and can be calculated numerically by a method introduced in [O. Derzhko, T. Krokhmalskii, Phys. Rev. B \textbf{56}, 11659 (1997)]. Since all characteristics of QPT are embodied in the DSF, the dynamical evolution of the two external spins displays singularity in the vicinity of the critical point.

quant-ph↗

arXiv2007

Coupled cavity QED for coherent control of photon transmission (I): Green function approach for hybrid systems with two-level doping

This is the first one of a series of our papers theoretically studying the coherent control of photon transmission along the coupled resonator optical waveguide (CROW) by doping artificial atoms for various hybrid structures. We will provide the several approaches correspondingly based on Green function, the mean field method and spin wave theory et al. In the present paper we adopt the two-time Green function approach to study the coherent transmission photon in a CROW with homogeneous couplings, each cavity of which is doped by a two-level artificial atom. We calculate the two-time correlation function for photon in the weak-coupling case. Its poles predict the exact dispersion relation, which results in the group velocity coherently controlled by the collective excitation of the doping atoms. We emphasize the role of the population inversion of doping atoms induced by some polarization mechanism.

quant-ph↗

arXiv2006

Decoherence problem in quantum state transfer via an engineered spin chain

A perfect quantum state transfer(QST) has been shown in an engineered spin chain with "always-on interaction". Here, we consider a more realistic problem for such a protocol, the quantum decoherence induced by a spatially distributed environment, which is universally modeled as a bath of harmonic oscillators. By making use of the irreducible tensor method in angular momentum theory, we investigate the effect of decoherence on the efficiency of QST for both cases at zero and finite temperatures. We not only show the generic exponential decay of QST efficiency as the number of sites increase, but also find some counterintuitive effect, the QST can be enhanced as temperature increase.

quant-ph↗

arXiv2005

Characterizing entanglement by momentum-jump in the frustrated Heisenberg ring at quantum phase transition

We study the pairwise concurrences, a measure of entanglement, of the ground states for the frustrated Heisenberg ring to explore the relation between entanglement and quantum phase transition associated with the momentum jump. The groundstate concurrences between any two sites are obtained analytically and numerically. It shows that the summation of all possible pairwise concurrences is an appropriate candidate to depict the phase transition. We also investigate the role that the momentum takes in the jump of concurrence at the critical points. We find that an abrupt momentum change rusults in the maximal concurrence difference of two degenerate ground states.

quant-ph↗