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Mirror structuring setup

This experimental project deals with the development of a microstructuring setup for high-reflectivity Bragg mirrors, that are used in our photon condensate experiments. The project approach will build on a direct laser writing method that allows the imprinting of surface profiles on dielectric mirrors. The setup building will also involve a white-light interferometric experimental to measure the printed surface structure with a high precision. In this Master project you will learn to plan, implement, and align optical microscopy setups. An important ingredient will be the development of a self-programmed experiment control to iteratively imprint custom surface structures with minimum variations. Further, the efficiency of the nanostructuring process should be characterized for different writing mirror samples.

Realizing variable Couplings for photon BECs

Controlling the optical coupling between two material-filled cavities is a fundamental building block for the construction of optical analogue simulators of spin models using arrays of photon condensates. At the same time, it is a necessary ingredient for establishing optical condensates as a new physical computation platform. 

In this project you will develop a new experimental apparatus that aims at achieving a variable coupling between two neighbouring photon condensates. Usually such couplings are either in-phase (0) or out-of-phase (π). The present project aims to realize arbitrary-phase couplings between (to begin with) two modes, and explore the feasibility with fiber and intracavity based approaches. In combination with non-Hermitian properties of the system, i.e. driving an loss, the method is expected to give access to new classes of computational devices, as optical hardware random number generators.

Numerical solver for photon gases

The goal of this project is to develop and test a numerical solver that allows the modelling of photon gases in variable potentials. In particular it is of interest, to include effects of openness, for example, spatially-resolved pumping and losses, as well as absorption and emission from dye molecules into the model. The approach for this numerical project is based on a stochastic nonlinear Gross-Pitaevskii equation, with which both the steady-state and the dynamics of a quantum gas of light should be simulated. With the developed code, the project should study closely the emerging phase ordering in networks of photon condensates with variable couplings. On the other hand, it is of interest to investigate whether it is possible to observe superfluid signatures in a quantum gas, that may emerge due to the coupling to the environment. The calculations will serve as a blueprint for subsequent experimental work in this direction.

Measurement of photon-photon correlations

This experimental project is centered on the realization of a homogeneous photon gas in a box potential. In particular, the project work will focus on the spatial density-density correlations in such a gas with a uniform density, and explore how the correlation length in the system behaves in the vicinity of the phase transition to a photon BEC, which has been observed experimentally in previous work. A key observable to quantify the correlations in this project will be the second-order coherence function, known as g(2)(x),  which characterizes the likelihood to find photons at two points (x,y) and (x',y') which are spaced by a distance r. For example, it is a tool to observe bunching of photons. A central goal of the project will be to explore the behaviour of the correlation length at the critical point and study the role of grand canonical statistical conditions in this limit.

Nonlinear photon fluids

Interactions between particles are a fundamental mechanism that leads to the formation of many-body states in physics. In general, interactions between photons are notoriously weak, which makes the it hard to observe many-body states of photons. This project aims at the realization of nonlinear effects in photon gases by developing a novel cavity platform equipped with nonlinear materials. Different approaches based on coupling light to nonlinear materials, e.g. Kerr media, atomic gases, or certain solid sate materials will be numerically studied. Based on the results an experimental approach will be implemented. A key observable in this project will be the effect of optical bistabilty in a nonlinear optical cavity.