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arXiv:2608.14807

Multicolor nonlinear chiral quantum optics: beyond phase

Cedric Dufresne, Annabelle Makowski, Nir Rotenberg

quant-phSubmitted Aug 14, 2026• Announced Aug 18, 2026• 0 citations
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Abstract

Chiral quantum nonlinearities that arise when light interacts with quantum emitters are known to modulate only the phase but not the amplitude of scattered photons, enabling the creation of non-reciprocal photonic elements, quantum logic gates, and quantum network protocols. In this work, we show that the addition of a second photon beam drastically changes this picture, enabling both phase and amplitude modulation. Surprisingly, coherent photon transfer between the different beams enables a stronger amplitude modulation than standard symmetric interactions. This is most obvious in the coherent, three-photon amplification, which we predict peaks with a 30% efficiency in a chiral geometry, 3x the efficiency of the symmetric configuration. Our results uncover a new regime of chiral quantum optics and provide a route towards more efficient all-optical control at few-photon energies.

Comments
5 pages, 4 figures

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Chiral quantum nonlinearities that arise when light interacts with quantum emitters are known to modulate only the phase but not the amplitude of scattered photons, enabling the creation of non-reciprocal photonic elements, quantum logic gates, and quantum network protocols. In this work, we show that the addition of a second photon beam drastically changes this picture, enabling both phase and amplitude modulation. Surprisingly, coherent photon transfer between the different beams enables a stronger amplitude modulation than standard symmetric interactions. This is most obvious in the coherent, three-photon amplification, which we predict peaks with a 30% efficiency in a chiral geometry, 3x the efficiency of the symmetric configuration. Our results uncover a new regime of chiral quantum optics and provide a route towards more efficient all-optical control at few-photon energies.
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Controlling light photon-by-photon is central to quantum optics. At a fundamental level, photon interactions are mediated by their coupling to atoms, and ultimate control requires deterministic light-matter interfacing of single photons to single atoms. Extending this paradigm to radiatively couple multiple individual atoms in a deterministic and scalable manner opens the arena of many-body quantum optics. Here, we realize such a setting by coherently coupling solid-state artificial atoms to a nanophotonic waveguide and demonstrate higher-order photon correlations that are controlled by the number of quantum emitters. We study the scaling of nonlinear photonic transport induced by emitter-photon scattering and demonstrate that adding a quantum emitter generates higher-order photon correlations. Specifically, we experimentally observe genuine three-photon correlations from a pair of collectively coupled emitters, while contributions from lower photon numbers are suppressed. In addition, we scale to three resonant quantum emitters coupled to the waveguide. These advancements demonstrate the onset of many-body quantum optics in waveguide quantum electrodynamics, enabling new photonic quantum simulators, the creation of many-body entangled states, and the exploration of novel quantum phase transitions.
Chiral quantum optics is central to developing scalable quantum networks, yet existing approaches rely predominantly on linear single-photon regimes. It remains unclear how to generate directional multiphotons. Here we show that giant emitters coupled to nonlinear quantum optical baths enable tunable directional correlated photons, revealing a mechanism for multiphoton directional emission. We demonstrate that the propagation phases of correlated photons, together with the coupling phases of giant emitters, can generate destructive interference in one direction while enhancing emission in the opposite direction, making directionality fully tunable. Building on this mechanism, we introduce a nonlinear cascaded quantum network paradigm mediated by “correlated flying qubits”, providing a configurable building block enabling distinct many-body applications beyond linear unidirectional setups. These results reveal a rich landscape for engineering multiphoton propagation and correlations through interference in giant emitter-nonlinear bath architectures, offering pathways for quantum networks and strongly correlated light-matter platforms. Chiral quantum optics is a prerequisite for communication protocols in quantum networks, but current methods are limited to the single-photon regime. The authors demonstrate that multiple giant emitters coupled to a nonlinear waveguide enable tunable multiphoton directional emission via interference, establishing a configurable building block for multiphoton cascaded quantum networks.
The achievement of sufficiently fast interactions between two optical fields at the few-photon level would provide a key enabler for a broad range of quantum technologies. One critical hurdle in this endeavor is the lack of a comprehensive quantum theory of the generation of nonlinearities by ensembles of emitters. Distinct approaches applicable to different regimes have yielded important insights: i) a semiclassical approach reveals that, for many-photon coherent fields, the contributions of independent emitters add independently allowing ensembles to produce strong optical nonlinearities via EIT; ii) a quantum analysis has shown that in the few-photon regime collective coupling effects prevent ensembles from inducing these strong nonlinearities. Rather surprisingly, experimental results with around twenty photons are in line with the semi-classical predictions. Theoretical analysis has been fragmented due to the difficulty of treating nonlinear many-body quantum systems. Here we are able to solve this problem by constructing a powerful theory of the generation of optical nonlinearities by single emitters and ensembles. The key to this construction is the application of perturbation theory to perturbations generated by subsystems. This theory reveals critical properties of ensembles that have long been obscure. The most remarkable of these is the discovery that quantum effects prevent ensembles generating single-photon nonlinearities only within the rotating-wave regime; outside this regime single-photon nonlinearities scale as the number of emitters. The theory we present here also provides an efficient way to calculate nonlinearities for arbitrary multi-level driving schemes, and we expect that it will prove a powerful foundation for further advances in this area.