Quantum nonlinear optics with counter-propagating photons

TL;DR

This paper demonstrates strong, tunable interactions between counter-propagating photons mediated by Rydberg polaritons, enabling photon blockade and multi-photon interactions, advancing quantum nonlinear optics and quantum computing.

Contribution

It introduces the first experimental realization of strong photon interactions with counter-propagating Rydberg polaritons, including photon blockade and multi-photon effects.

Findings

Achieved record-long anti-correlation range exceeding 1 microsecond.

Observed complete photon blockade of entire pulses.

Demonstrated enhanced multi-photon interactions.

Abstract

Realizing strong interactions between individual photons is a cornerstone for advancing photonic quantum computing and quantum nonlinear optics. Here, we experimentally demonstrate strong interactions between counter-propagating photons mediated by Rydberg polaritons, achieving a record-long anti-correlation range exceeding $1~\mu s$. This extended range enables the use of photon pulses that are long enough to fit within the polariton bandwidth, yet short enough to remain within the interaction range. Under these conditions, we observe complete photon blockade of entire pulses, tunable by the pulse timing, thus demonstrating the potential for controlled, deterministic operations. Extending to the three-photon regime, we observe enhanced interactions when a photon encounters two counter-propagating photons. Our results, supported by analytical theory and rigorous numerical simulations, establish counter-propagating Rydberg polaritons as a powerful platform for engineering interactions in quantum light fields.