Revealing inherent quantum interference and entanglement of a Dirac particle

TL;DR

This paper uncovers a fundamental quantum interference pattern in phase space underlying Dirac particles, linking Zitterbewegung to nonclassicality and entanglement, confirmed through simulation and superconducting qubit experiments.

Contribution

It reveals a universal interference behavior in Dirac particles beyond classical analogs, demonstrated via phase space analysis and experimental emulation.

Findings

Identification of a nonclassical interference pattern in phase space

Negativity in phase space quasiprobability distribution

Experimental confirmation using superconducting qubits

Abstract

Although originally predicted in relativistic quantum mechanics, Zitterbewegung can also appear in some classical systems, which leads to the important question of whether Zitterbewegung of Dirac particles is underlain by a more fundamental and universal interference behavior without classical analogs. We here reveal such an interference pattern in phase space, which underlies but goes beyond Zitterbewegung, and whose nonclassicality is manifested by the negativity of the phase space quasiprobability distribution, and the associated pseudospin-momentum entanglement. We confirm this discovery by numerical simulation and an on-chip experiment, where a superconducting qubit and a quantized microwave field respectively emulate the internal and external degrees of freedom of a Dirac particle. The measured quasiprobability negativities agree well with the numerical simulation. Besides being of fundamental importance, the demonstrated nonclassical effects are useful in quantum technology.