Abstract

Photonic information processing requires giant optical non-linearities to implement logic gates between photons and optical switches at the single photon level. A very promising non-linear medium is a "one dimensional atom", that is a directional high-finesse cavity containing a resonant two-level system in the Purcell regime as pointed out by Hofmann et al [1]. We aim at experimentally demonstrating this effect using a single quantum dot in a symmetric micropillar, the directionality of the micropillar ensuring the one-dimensionality of the problem. Taking into account the leaks, we have theoretically computed the transmission function of this medium in two regimes : the linear regime where the pump is weak, and the regime where the pump is strong enough to saturate the two-level system [2]. We have represented in figure la the transmission function of the medium as a function of the detuning between the quantum dot and the incoming field. The broad envelope corresponds to the empty leaky cavity. The on-resonance transmission is T=(Q/Q₀)², Q₀ being the finite quality factor of the cavity due to the coupling to the one-dimensional continuum of radiative modes, Q the total quality factor including the coupling to undesired leaky modes. If the cavity contains a resonant quantum dot, the transmission at resonance is reduced by a factor (1+F_p)², F_p being the Purcell factor of the quantum dot. The field is then reflected by the dipole, which corresponds to a thin dip in the transmission function. The expected visibility of the signal is 80% for realistic parameters. From now on we focus on the resonant case and we gradually increase the intensity of the pump. The saturation in the atomic population induces a saturation in the optical transmission of the {atom+cavity} system, which leads to the non-linear jump represented in figure lb. For weak intensities the transmission is low as it was just seen, for strong intensities the quantum dot is unable to prevent the light from crossing the micropillar and we recover the transmission of an empty cavity. The critical intensity Ic typically corresponds to one forth of photon per atomic lifetime, which is the signature of a giant non-linearity at the single-photon level. These two striking optical features should be observable using state of the art quantum dots and micropillars. In this talk we will recall the theoretical results and present the on-going experiments to demonstrate these effects.

© 2007 IEEE