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arXiv:2006.03408 · Physical Review Letters

Strongly Correlated States of Light and Repulsive Photons in Chiral Chains of Three-Level Quantum Emitters

Ole A. Iversen, Thomas Pohl

Published Feb 26, 2021• 48 citations
arXivHTMLPDF

Abstract

We study the correlated transport of photons through a chain of three-level emitters that are coupled chirally to a photonic mode of a waveguide. It is found that this system can transfer a weak classical input into a strongly correlated state of light in a unitary manner. Our analysis reveals two-photon scattering eigenstates, that are akin to Fano resonances or shape resonances in particle collisions and facilitate the emergence of antibunched light with long-range correlations upon crossing a critical length of the chain. By operating close to conditions of electromagnetically induced transparency of the three-level medium, a high degree of antibunching and photon transmission can be maintained in the presence of moderate losses. These features suggest a promising mechanism for single-photon generation and may open the door to exploring correlated quantum many-body states of light with repulsively interacting photons.

DOI
10.1103/physrevlett.126.083605

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We study the correlated transport of photons through a chain of three-level emitters that are coupled chirally to a photonic mode of a waveguide. It is found that this system can transfer a weak classical input into a strongly correlated state of light in a unitary manner. Our analysis reveals two-photon scattering eigenstates, that are akin to Fano resonances or shape resonances in particle collisions and facilitate the emergence of antibunched light with long-range correlations upon crossing a critical length of the chain. By operating close to conditions of electromagnetically induced transparency of the three-level medium, a high degree of antibunching and photon transmission can be maintained in the presence of moderate losses. These features suggest a promising mechanism for single-photon generation and may open the door to exploring correlated quantum many-body states of light with repulsively interacting photons.
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.
We study correlated two-photon transport in a (quasi-)one-dimensional photonic waveguide coupled to a three-level Λ-type emitter driven by a classical light field. Two-photon correlation is much stronger in the waveguide for a driven three-level emitter (3LE) than a two-level emitter. The driven 3LE waveguide shows electromagnetically induced transparency (EIT), and we investigate the scaling of EIT for one and two photons. We show that the two transmitted photons are bunched together at any distance separation when energy of the incident photons meets "two-photon resonance" criterion for EIT.
We study the generation of strongly correlated photons by coupling an atom to photonic quantum fields in a one-dimensional waveguide. Specifically, we consider a three-level or four-level system for the atom. Photon-photon bound states emerge as a manifestation of the strong photon-photon correlation mediated by the atom. Effective repulsive or attractive interaction between photons can be produced, causing either suppressed multiphoton transmission (photon blockade) or enhanced multiphoton transmission (photon-induced tunneling). As a result, nonclassical light sources can be generated on demand by sending coherent states into the proposed system. We calculate the second-order correlation function of the transmitted field and observe bunching and antibunching caused by the bound states. Furthermore, we demonstrate that the proposed system can produce photon pairs with a high degree of spectral entanglement, which have a large capacity for carrying information and are important for large-alphabet quantum communication.
The scattering between light and individual saturable quantum emitters can induce strong optical nonlinearities and correlations between individual light quanta. Typically, this leads to an effective attraction that can generate exotic bound states of photons, which form quantum mechanical precursors of optical solitons, as found in many optical media. Here, we study the propagation of light through an optical waveguide that is chirally coupled to three-level quantum emitters. We show that the additional laser coupling to a third emitter state not only enables control of the properties of the bound state but can even eliminate it entirely. This makes it possible to turn an otherwise focusing nonlinearity into a repulsive photon-photon interaction. We demonstrate this emerging photon-photon repulsion by analyzing the quantum dynamics of multiple photons in large emitter arrays and reveal a dynamical fragmentation of incident uncorrelated light fields and self-ordering into regular trains of single photons. These striking effects expand the rich physics of waveguide quantum electrodynamics into the domain of repulsive photons and establish a conceptually simple platform to explore optical self-organization phenomena at the quantum level. We discuss implementations of this setting in cold-atom experiments and propose an approach based on arrays of mesoscopic Rydberg-atom ensembles.
Abstract Correlated two‐photon scattering in a waveguide quantum electrodynamics system consisting of a four‐level ‐type emitter (4LE) sidely coupled to a one‐dimensional (1D) waveguide is studied. In the two‐photon regime, scattering eigenstates of the system are constructed by imposing an open boundary condition and defining the incident state as a free plane wave, which includes a photon–photon bound state that passes through the 4LE as a composite single particle. In the multilevel system, the bound state can be tuned by the interference to generate controllable types of interactions (attractive or repulsive) and interaction strengths. Photon‐induced tunneling (bunching) in transmission and photon blockade (antibunching) in reflection are found in the system. In addition, the scattering photon pair off the system is strongly entangled in momentum space.
We theoretically study the few-and many-body dynamics of photons in chiral waveguides.In particular, we examine pulse propagation through an ensemble of N two-level systems chirally coupled to a waveguide.We show that the system supports correlated multiphoton bound states, which have a welldefined photon number n and propagate through the system with a group delay scaling as 1=n 2 .This has the interesting consequence that, during propagation, an incident coherent-state pulse breaks up into different bound-state components that can become spatially separated at the output in a sufficiently long system.For sufficiently many photons and sufficiently short systems, we show that linear combinations of n-body bound states recover the well-known phenomenon of mean-field solitons in self-induced transparency.Our work thus covers the entire spectrum from few-photon quantum propagation, to genuine quantum many-body (atom and photon) phenomena, and ultimately the quantum-to-classical transition.Finally, we demonstrate that the bound states can undergo elastic scattering with additional photons.Together, our results demonstrate that photon bound states are truly distinct physical objects emerging from the most elementary light-matter interaction between photons and two-level emitters.Our work opens the door to studying quantum many-body physics and soliton physics with photons in chiral waveguide QED.