arXiv subjects

Xi-Jun Ren

Publications and source records attributed to Xi-Jun Ren.

5 recordsLinked to original sources

arXiv2025

Entanglement entropy of particles in a perturbative scattering

The entanglement among scattering particles in an exemplary quantum electrodynamics (QED) process is studied perturbatively. To increase the computational accuracy, we need to consider virtual photon loop diagrams, which lead to infrared divergence. Therefore, when including higher-order corrections in perturbative theory, we use the dressed state formalism proposed by Chuang and Faddeev-Kulish, which provides a finite S-matrix element. The entanglement entropy calculation shows that the entanglement is distributed linearly over the scattering cross section under the perturbation approximation

hep-th↗

arXiv2021

Entanglement entropy and monotones in scattering process

In this paper, we study the entanglement property of a 4-particle system. In this system, two initially entangled electrons A and C are scattered by two uncorrelated positrons B and D, respectively. We calculate the entanglements among the particles both before and after the double QED scattering ($AB\rightarrow AB, CD\rightarrow CD$). We find that the change of entanglement entropy between subsystems A and B during the scattering processs is proportional to the total cross section, $σ_{tot}=σ_{AB}\timesσ_{CD}$. Even though there is no direct interaction between subsystems A and C (or B and D), the scattering process induces entanglement change among them which is also proportional to $σ_{tot}$. This result shows some kind of entanglement sharing property in multipartite system. In order to further investigate the entanglement sharing, we calculate the entanglement monotones which quantify the genuine multipartite entanglement in a multipartite system. For our chosen scattering process, $e^+e^-\rightarrowμ^+μ^-$, however, we find that the outgoing state is a W-type 4-partite entangled state which has no genuine 4-partite entanglement.

hep-th↗

arXiv2013

Non-monogamy of quantum discord and upper bounds for quantum correlation

We consider a monogamy inequality of quantum discord in a pure tripartite state and show that it is equivalent to an inequality between quantum mutual information and entanglement of formation of two parties. Since this inequality does not hold for arbitrary bipartite states, quantum discord can generally be both monogamous and polygamous. We also carry out numerical calculations for some special states. The upper bounds of quantum discord and classical correlation are also discussed and we give physical analysis on the invalidness of a previous conjectured upper bound of quantum correlation. Our results provide new insights for further understanding of distributions of quantum correlations.

quant-ph↗

arXiv2011

Unified Universal Quantum Cloning Machine and Fidelities

We present a unified universal quantum cloning machine, which combines several different existing universal cloning machines together including the asymmetric case. In this unified framework, the identical pure states are projected equally into each copy initially constituted by input and one half of the maximally entangled states. We show explicitly that the output states of those universal cloning machines are the same. One importance of this unified cloning machine is that the cloning procession is always the symmetric projection which reduces dramatically the difficulties for implementation. Also it is found that this unified cloning machine can be directly modified to the general asymmetric case. Besides the global fidelity and the single-copy fidelity, we also present all possible arbitrary-copy fidelities.

quant-ph↗

arXiv2008

Permutation-invariant monotones for multipartite entanglement characterization

In this work we consider the permutational properties of multipartite entanglement monotones. Based on the fact that genuine multipartite entanglement is a property of the entire multi-qubit system, we argue that ideal definitions for its characterizing quantities must be permutation-invariant. Using this criterion, we examine the three 4-qubit entanglement monotones introduced by Osterloh and Siewert [Phys. Rev. A. 72, 012337]. By expressing them in terms of quantities whose permutational properties can be easily derived, we find that one of these monotones is not permutation-invariant. We propose a permutation-invariant entanglement monotone to replace it, and show that our new monotone properly measures the genuine 4-qubit entanglement in 4-qubit cluster-class states. Our results provide some useful insights in understanding multipartite entanglement.

quant-ph↗