Large Cross-Phase Modulations at the Few-Photon Level

TL;DR

This paper demonstrates a phase-dependent cross-phase modulation scheme in a double-{ extLambda} system that achieves large phase shifts at very low photon numbers, enabling strong photon interactions without cavities.

Contribution

It introduces a novel phase-controlled XPM method in a double-{ extLambda} system that produces significant phase shifts at the few-photon level without cavities.

Findings

Achieved { extpi}-level phase shift with only 8 photons per pulse.

Controlled the medium's properties by adjusting optical field phases.

Potential for strong photon interactions in quantum information processing.

Abstract

We demonstrate an efficient cross-phase modulation (XPM) based on a closed-loop double-{\Lambda} system. The property of the double-{\Lambda} medium can be controlled by changing the phases of the applied optical fields. This phase-dependent XPM scheme can achieve large phase modulations at low-light intensities without requiring cavities or tightly focusing of laser beams. With this scheme, we observe a {\pi}-level phase shift with two pulses both consisting of 8 photons in cold rubidium atoms. Such novel scheme provides a simple route to generate strong interactions between photons and may have potential applications in all-optical quantum signal processing.