Integrated Calendar

Achieving optical nonlinear interactions at the level of single photons has been the goal of extensive efforts in the last couple of decades.
I will present our recent demonstration of deterministic, all-optical photon-photon interactions based on a single atom. This scheme performs deterministic quantum state-transfer between a photon and a single quantum emitter (a 87Rb atom, in our case). Based on passive, interference-based nonlinearity, this scheme requires no control fields, and can function as a quantum memory and even a universal quantum gate. It therefore provides a building block for scalable quantum networks based on completely passive photonic devices interconnected and activated solely by single photons.

Collective effects can be observed in pedestrian crowds, during experiments or even in everyday life. In this presentation we use the tools of statistical mechanics to study one of them, namely the formation of diagonal stripes in an intersection of two flows. The elementary building block of the model will be the TASEP. We will combine several TASEP lanes to form an intersection where self-propelled 'pedestrians' will move. In periodic boundary conditions a diagonal pattern well-known from experiments will be observed and shown to emerge from a linear stability analysis of the mean-field equations. With open boundary conditions particles will be shown to self-organize not exactly into diagonals but into 'chevrons', a slightly tilted pattern. We will provide a simple picture of this effect in terms of environment-mediated effective interactions between particles.

Elliptic de Sitter space is a maximally symmetric spacetime that isn't time-orientable. Quantum field theory in this spacetime does not exist globally, but only for individual observers. This provides a working model for Susskind's horizon complementarity principle. I motivate a recipe for translating states and observables between the world-pictures of the different observers. In particular, we recover the thermal state at the cosmological horizon temperature as a state on which all observers agree.