Quantum Zeno effects across a parity-time symmetry breaking transition in atomic momentum space

Tao Chen,Teng Xiao,Wei Gou,Bo Yan,Wei Yi,Dizhou Xie,Jun Jing

doi:10.1038/s41534-021-00417-y

Abstract

We experimentally study quantum Zeno effects in a parity-time (PT) symmetric cold atom gas periodically coupled to a reservoir. Based on the state-of-the-art control of inter-site couplings of atoms in a momentum lattice, we implement a synthetic two-level system with passive PT symmetry over two lattice sites, where an effective dissipation is introduced through repeated couplings to the rest of the lattice. Quantum Zeno (anti-Zeno) effects manifest in our experiment as the overall dissipation of the two-level system becoming suppressed (enhanced) with increasing coupling intensity or frequency. We demonstrate that quantum Zeno regimes exist in the broken PT symmetry phase, and are bounded by exceptional points separating the PT symmetric and PT broken phases, as well as by a discrete set of critical coupling frequencies. Our experiment establishes the connection between PT-symmetry-breaking transitions and quantum Zeno effects, and is extendable to higher dimensions or to interacting regimes, thanks to the flexible control with atoms in a momentum lattice.

Highlights

Coherent evolution of a quantum system can be frozen when frequently interrupted by measurements or perturbations
While quantum Zeno effects naturally emerge in the deep parity-time broken (PTB) regime that can be mapped to an open system possessing continuous and strong coupling with a dissipative reservoir[29], the fate of quantum Zeno effects is less well known in the parity-time symmetric (PTS)
We study both the PT symmetry breaking transition and the quantum Zeno effects through the dissipative dynamics

Summary

INTRODUCTION

Coherent evolution of a quantum system can be frozen when frequently interrupted by measurements or perturbations. With an appropriate repetition rate of measurements, the evolution of the system can be accelerated under what is known as the antiZeno effect[22] Both quantum Zeno and anti-Zeno effects are alternatively accessible through continuous strong couplings or fast unitary kicks[3,17,23] that couple a system to an auxiliary Hilbert space. While quantum Zeno effects naturally emerge in the deep PTB regime that can be mapped to an open system possessing continuous and strong coupling with a dissipative reservoir[29], the fate of quantum Zeno (anti-Zeno) effects is less well known in the PTS regime or near exceptional points, both of which typically occur at much smaller dissipation strengths[29,30,31]. We experimentally confirm such a connection in a PT symmetric, synthetic two-level system, embedded in a momentum lattice of cold atoms

RESULTS

DISCUSSION

METHODS