arXiv subjects

Shu-Shen Li

Publications and source records attributed to Shu-Shen Li.

78 records · Page 5Linked to original sources

arXiv2007

Disentanglement of two qubits coupled to an XY spin chain: Role of quantum phase transition

We study the disentanglement of two spin qubits which interact with a general XY spin-chain environment. The dynamical process of the disentanglement is numerically and analytically investigated in the vicinity of quantum phase transition (QPT) of the spin chain in both weak and strong coupling cases. We find that the disentanglement of the two qubits is in general enhanced greatly when the environmental spin chain is exposed to QPT. We give a detailed analysis to facilitate the understanding of the QPT-enhanced decaying behavior of the disentanglement factor. Furthermore, the scaling behavior in the disentanglement dynamics is also revealed and analyzed.

quant-ph↗

arXiv2006

Loschmidt Echo and Berry phase of the quantum system coupled to the XY spin chain: Proximity to quantum phase transition

We study the Loschmidt echo (LE) of a coupled system consisting of a central spin and its surrounding environment described by a general XY spin-chain model. The quantum dynamics of the LE is shown to be remarkably influenced by the quantum criticality of the spin chain. In particular, the decaying behavior of the LE is found to be controlled by the anisotropy parameter of the spin chain. Furthermore, we show that due to the coupling to the spin chain, the ground-state Berry phase for the central spin becomes nonanalytical and its derivative with respect to the magnetic parameter $λ$ in spin chain diverges along the critical line $λ=1$, which suggests an alternative measurement of the quantum criticality of the spin chain.

quant-ph↗

arXiv2006

Detecting a set of entanglement measures in an unknown tripartite quantum state by local operations and classical communication

We propose a more general method for detecting a set of entanglement measures, i.e. negativities, in an \emph{arbitrary} tripartite quantum state by local operations and classical communication. To accomplish the detection task using this method, three observers, Alice, Bob and Charlie, do not need to perform the partial transposition maps by the structural physical approximation; instead, they are only required to collectively measure some functions via three local networks supplemented by a classical communication. With these functions, they are able to determine the set of negativities related to the tripartite quantum state.

quant-ph↗

arXiv2005

Thermal entanglement in a two-spin-qutrit system under a nonuniform external magnetic field

The thermal entanglement in a two-spin-qutrit system with two spins coupled by exchange interaction under a magnetic field in an arbitrary direction is investigated. Negativity, the measurement of entanglement, is calculated. We find that for any temperature the evolvement of negativity is symmetric with respect to magnetic field. The behavior of negativity is presented for four different cases. The results show that for different temperature, different magnetic field give maximum entanglement. Both the parallel and antiparallel magnetic field cases are investigated qualitatively (not quantitatively) in detail, we find that the entanglement may be enhanced under an antiparallel magnetic field.

quant-ph↗

arXiv2005

Noiseless method for checking the Peres separability criterion by local operations and classical communication

We present a method for checking Peres separability criterion in an arbitrary bipartite quantum state $ρ_{AB}$ within local operations and classical communication scenario. The method does not require the prior state reconstruction and the structural physical approximation. The main task for the two observers, Alice and Bob, is to estimate some specific functions. After getting these functions, they can determine the minimal eigenvalue of $ρ^{T_{B}}_{AB}$, which serves as an entanglement indicator in lower dimensions.

quant-ph↗

arXiv2004

Photoluminescence pressure coefficients of InAs/GaAs quantum dots

We have investigated the band-gap pressure coefficients of self-assembled InAs/GaAs quantum dots by calculating 17 systems with different quantum dot shape, size, and alloying profile using atomistic empirical pseudopotential method within the ``strained linear combination of bulk bands'' approach. Our results confirm the experimentally observed significant reductions of the band gap pressure coefficients from the bulk values. We show that the nonlinear pressure coefficients of the bulk InAs and GaAs are responsible for these reductions. We also find a rough universal pressure coefficient versus band gap relationship which agrees quantitatively with the experimental results. We find linear relationships between the percentage of electron wavefunction on the GaAs and the quantum dot band gaps and pressure coefficients. These linear relationships can be used to get the information of the electron wavefunctions.

cond-mat.mtrl-sci↗