News
Tue January 1, 2013
Attractive Photons in a Quantum Nonlinear Medium
In this paper, we demonstrate for the first time a bound state of two photons. We illuminate a dense and cold atomic ensemble with weak laser light underconditions of electromagnetically induced transparency to an atomic Rydberg state. When we detune the control laser coupling the unstable intermediate state to the Rydberg level, the probe photons that are traveling slowly through the medium acquire mass due to dispersion, and acquire an effective interaction mediated by the long-range interaction between two Rydberg atoms. The situation can be approximately described by a one-dimensional Schroedinger equation with an attractive potential well, and we observe a bound state of two photons, as evidenced by bunching of the outgoing light.
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