October 2011

Abstracts of the QSIT Lunch Seminar, October 6, 2011

Ultrafast all-optical switching by single photons in quantum dot cavity QED

Andreas Reinhard, Quantum Photonics Group, IQE, ETH Zurich

Switching photons with single photons is an outstanding goal in quantum optics and photonics. We show that a photonic crystal nanocavity can be utilized to switch photons of one color with a single photon of another color, when the cavity electric field is strongly coupled to a single self-assembled quantum dot. Strong effective photon-photon interactions, mediated by the electronic nature of the atom-like quantum dot transitions, make the energy diagram (the so-called Jaynes-Cummings ladder) anharmonic, enabling optical non-linearities at the single photon level: When resonantly exciting a one-photon state (fundamental polariton) with a laser, we observe the photon blockade effect - the scattering of at most one photon at a time. Furthermore, this single photon conditions the capture of a second photon when we drive - at the same time - the transition from the fundamental to the second polariton manifold with a second laser. This enables the system to act as an all-optical switch with switching times of 20 ps and paves the way for the realization of a single-photon transistor.

Nonlinear Optomechanics in the single-photon regime

Andreas Nunnenkamp, Condensed Matter Theory Group, University of Basel

Optomechanical systems couple optical and mechanical degrees of freedom via radiation pressure, optical gradient and photothermal forces. Future applications may be precision measurements, quantum information setups and studies of the quantum-to-classical transition.

To date, the literature has focused on the linear regime. For example, the recently demonstrated red-sideband cooling and normal-mode splitting can both be understood with linearized equations of motion.

To describe non-Gaussian steady states, one has to go beyond this treatment. In particular, I will discuss the regime where a single photon displaces the oscillator by more than its zero-point uncertainty. I will show that the single-photon strong-coupling regime can be detected in the cavity response as well as the optical output spectrum and that the system exhibits photon blockade inducing non-Gaussian states of the mechanics and non-classical states of light.

Nunnenkamp, Borkje, and Girvin, PRL 107, 063602 (2011)

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