Raphaël Proux

Research activities

PhD title : Generation of indistinguishable photons in resonantly excited semiconductor quantum dots.

Single indistinguishable photons are a key to the implementation of quantum information networks. Quantum dots being close to an ideal two-level system and easy to integrate in a device, they are good candidates for these applications. My PhD work focuses on the indistinguishability properties of the photons emitted by an individual semiconductor quantum dot excited resonantly. The quantum dots we study are made of InAs, by Molecular Beam Epitaxy (MBE). Typically, they emit around 1.3 eV (950 nm).

Quantum dots resonance excitation scheme.

To resonantly drive the quantum dots, they are embedded in a planar microcavity, and the excitation laser is injected through the edge using an optical fiber (see figure on the right hand side). This setup has two advantages: it guides the excitation laser to the quantum dot without blinding the detection system, and it redirects the resonance emission in a microcavity mode, improving the collection efficiency. Besides, under resonant excitation, epitaxial quantum dots can have excellent coherence properties, close to the radiative limit, which allow for quantum optics experiments such as statistics and indistinguishability measurements.

These measurements use different kinds of interferometers, in particular the Hanbury Brown – Twiss (HBT) setup which allows us to measure the statistics of the photons emitted by the dots, and the Hong – Ou – Mandel (HOM) interferometer which allows us to observe the coalescence of the photons, a phenomenon directly linked to their indistinguishability and thus to their coherence.

Whereas the literature is more focused on how low the HOM dip goes, we have published a comprehensive study on the temporal dynamics of indistinguishability with quantum dots excited resonantly. These dynamics are of first importance because they take into account the response time of the detectors and allow for better comparison between emitters. This work explores the resonant Rayleigh scattering regime, which is achieved at very low excitation power and is very difficult to observe because of the weak signal. In this regime, the light scattered by the quantum dot is as coherent as the excitation laser, which allows to obtain a very coherent single photon source. Moreover, these measurements are experimental observations of the direct link between coherence and indistinguishability of the photons.

The last year of my PhD should focus on a new sample structure with electrical contacts to control the electrostatic environment of the quantum dots in order to reduce the dephasing processes.

Publications and conferences

Articles

Please note two other articles about two-photon interference with quantum dots are being written.

Invited talks

Talks

Posters

Educational qualifications