Abstract
Exploring non-Hermitian phenomenology is an exciting frontier of modern physics. However, the demonstration of a non-Hermitian phenomenon that is quantum in nature has remained elusive. Here, we predict quantum non-Hermitian phenomena: the fractional quantum Zeno (FQZ) effect and FQZ-induced photon antibunching. We consider a quantum optics platform with reservoir engineering, where nonlinear emitters are coupled to a bath of decaying bosonic modes whose own decay rates form band structures. By engineering the dissipation band, the spontaneous emission of emitters can be suppressed by strong dissipation through an algebraic scaling with fractional exponents—the FQZ effect. This fractional scaling originates uniquely from the divergent dissipative density of states near the dissipation band edge, different from the traditional closed-bath context. We find FQZ-induced strong photon antibunching in the steady state of a driven emitter even for weak nonlinearities. Remarkably, we identify that the sub-Poissonian quantum statistics of photons, which has no classical analogs, stems here from the key role of non-Hermiticity. Our setup is experimentally feasible with the techniques used to design lattice models with dissipative couplings.
- Received 26 July 2022
- Accepted 13 June 2023
DOI:https://doi.org/10.1103/PhysRevX.13.031009
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Isolated quantum systems are idealized, useful for studying quantum phenomena in a simplified manner. But real quantum systems interact with their environment (known as a bath) and undergo dissipation. (In this case, the evolution of the system is partly described mathematically by what is called a non-Hermitian Hamiltonian.) By engineering the interaction with the bath and the bath itself, one can control the evolution and resulting properties of the system, accessing interesting phenomena that are impossible to realize in isolated systems. Here, we show how engineered non-Hermiticity gives rise to novel phenomena with a genuine quantum nature. We also systematically develop a theoretical framework to deal with this situation.
We investigate a system of atoms (or artificial atoms) embedded in a particular type of bath, which in turn interacts with an outer bath. By engineering such hierarchical baths, the atomic properties, such as the spontaneous emission of excited atoms, can be influenced in an unprecedented manner. In particular, when the inner bath dissipates strongly by itself, we find the atomic emission is suppressed—a manifestation of the quantum Zeno effect—in an unusual way; the algebraic scaling with the relevant parameters acquires fractional power. This behavior cannot occur if the inner bath is isolated. We show this phenomenon also induces photon antibunching, where photons try to avoid each other, as opposed to their usual preference of staying together. Usually, antibunching occurs when there are strong nonlinearities, but we find it can be strong even for weak nonlinearities, which are driven by dissipation.
Our work opens the door to exploring non-Hermitian quantum optics and represents a significant step toward understanding non-Hermitian quantum many-body effects.
