Demonstration of the Interaction between Two Stopped Light Pulses

TL;DR

This paper experimentally demonstrates that two stopped light pulses can interact via a medium, enabling long interaction times and high efficiency at very low photon levels, advancing low light physics.

Contribution

First experimental demonstration of interaction between two stopped light pulses using electromagnetically induced transparency, achieving low photon-level switching.

Findings

Interaction time can be as long as possible with stopped light pulses.

Switching activated at 0.56 photons per atomic absorption cross section.

Potential for further reduction of light level by increasing medium density.

Abstract

We report the first experimental demonstration that two light pulses were made motionless and interacted with each other via a medium. The interaction time is, in principle, as long as possible and a considerable efficiency can be achieved even below single-photon level. We utilized the optical process of one photon pulse switched by another based on the effect of electromagnetically induced transparency to demonstrate the enhancement of optical nonlinear efficiency. With moving light pulses, the switching is activated at energy per area of 2 photons per atomic absorption cross section in the best situation as discussed in [Phys. Rev. Lett. 82, 4611 (1999)]. With motionless light pulses, we demonstrated that the switching is activated at 0.56 photons per atomic absorption cross section and that the light level can be further reduced by increasing the optical density of the medium. Our work enters a new regime of low light physics.