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arXiv:2003.01050 · Physical Review A

Asymmetric coupling between two quantum emitters

Charles Andrew Downing, Juan Camilo López Carreño, Antonio I. Fernández‐Domínguez, Elena del Valle

Published Jul 23, 2020• 26 citations
arXivHTMLPDF

Abstract

We study a prototypical model of two coupled two-level systems, where the competition between coherent and dissipative coupling gives rise to a rich phenomenology. In particular, we analyze the case of asymmetric coupling, as well as the limiting case of chiral (or one-way) coupling. We investigate various quantum optical properties of the system, including its steady-state populations, power spectrum, and second-order correlation functions, and outline the characteristic features which emerge in each quantity as one sweeps through the nontrivial landscape of effective complex couplings. Most importantly, we reveal instances of population trapping, unexpected spectral features, and strong emission correlations.

DOI
10.1103/physreva.102.013723

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We study a prototypical model of two coupled two-level systems, where the competition between coherent and dissipative coupling gives rise to a rich phenomenology. In particular, we analyze the case of asymmetric coupling, as well as the limiting case of chiral (or one-way) coupling. We investigate various quantum optical properties of the system, including its steady-state populations, power spectrum, and second-order correlation functions, and outline the characteristic features which emerge in each quantity as one sweeps through the nontrivial landscape of effective complex couplings. Most importantly, we reveal instances of population trapping, unexpected spectral features, and strong emission correlations.
We study a driven-dissipative duo of two-level systems in an open quantum systems approach, modeling a pair of atoms or (more generally) meta-atoms. Allowing for complex-valued couplings in the setup, which are of both a coherent and incoherent character, gives rise to a diverse coupling landscape. We consider several points on this landscape, for example where the coupling between the two coupled two-level systems is dominated by coherent, incoherent, unsymmetrical, and even unidirectional interactions. Traversing the coupling terrain leads to remarkable features in the populations of the pair, correlations, and optical spectra. Most notably, the famous Mollow triplet spectrum for a single atom may be superseded for a pair by a Mollow quintuplet (or even by a spectral singlet) and the setup allows for population trapping to arise, all depending upon the precise nature of the coupling between the two-level systems.
We present a combined classical and quantum electrodynamics description of the coupling between two circularly polarized quantum emitters held above a metal surface supporting surface plasmons. Depending on their position and their natural frequency, the emitter-emitter interactions evolve from being reciprocal to nonreciprocal, which makes the system a highly tunable platform for chiral coupling at the nanoscale. By relaxing the stringent material and geometrical constraints for chirality, we explore the interplay between coherent and dissipative coupling mechanisms in the system. Thus, we reveal a quasichiral regime in which its quantum optical properties are governed by its subradiant state, giving rise to extremely sharp spectral features and strong photon correlations.
Abstract. We apply our recently developed theory of frequency-filtered and time-resolved N-photon correlations [1] to study the two-photon spectra of a variety of systems of increasing complexity: single mode emitters with two limiting statistics (one harmonic oscillator or a two-level system) and the various combinations that arise from their coupling. We consider both the linear and nonlinear regimes under incoherent excitation. We find that even the simplest systems display a rich dynamics of emission, not accessible by simple single photon spectroscopy. In the strong coupling regime, novel two-photon emission processes involving virtual states are revealed. Furthermore, two general results are unraveled by two-photon correlations with narrow linewidth detectors: i) filtering induced bunching and ii) breakdown of the semi-classical theory. We show how to overcome this shortcoming in a fully-quantized picture. PACS numbers: 42.50.Ar,42.50.Lc,05.10.Gg,42.25.Kb,42.79.Pw ar X iv
A criterion for strong coupling between two quantum emitters and a single resonant light mode in a cavity is presented. The criterion takes into account the escape of cavity photons and the spontaneous emission of the emitters, which are modeled as two-level systems. By using such a criterion, the dissipative Tavis-Cummings ladder of states is constructed, and it is shown that the inclusion of one more emitter with respect to the Jaynes-Cummings (single emitter) case increases the effective parameter region in which nthn\text{th}nth-order Rabi splitting is observed.
We apply our recently developed theory of frequency-filtered and time-resolved N -photon correlations (del Valle et al 2012 Phys. Rev. Lett. 109 183601) to study the two-photon spectra of a variety of systems of increasing complexity: single-mode emitters with two limiting statistics (one harmonic oscillator or a two-level system) and the various combinations that arise from their coupling. We consider both the linear and nonlinear regimes under incoherent excitation. We find that even the simplest systems display a rich dynamics of emission, not accessible by simple single-photon spectroscopy. In the strong coupling regime, two-photon emission processes involving virtual states are revealed. Furthermore, two general results are unravelled by two-photon correlations with narrow linewidth detectors: (i) filtering-induced bunching and (ii) breakdown of the semi-classical theory. We show how to overcome the latter in a fully quantized picture.
We show that strongly correlated photon transport can be observed in waveguides containing optically dense ensembles of emitters. Remarkably, this occurs even for weak coupling efficiencies. Specifically, we compute the photon transport properties through a chirally coupled system of N two-level systems driven by a weak coherent field, where each emitter can also scatter photons out of the waveguide. The photon correlations arise due to an interplay of nonlinearity and coupling to a loss reservoir, which creates a strong effective interaction between transmitted photons. The highly correlated photon states are less susceptible to losses than uncorrelated photons and have a power-law decay with N. This is described using a simple universal asymptotic solution governed by a single scaling parameter which describes photon bunching and power transmission. We show numerically that, for randomly placed emitters, these results hold even in systems without chirality. The effect can be observed in existing tapered fiber setups with trapped atoms.