PhD

When shining classical light onto a non-linear medium, intriguing quantum states of light can be generated such as squeezed states, single photon states or complex multiphoton entangled states. In the past years, physicists have proposed to use lattices of highly non-linear resonators to engineer spatial and temporal entanglement between photons [1]. To date, a versatile and scalable experimental platform is still missing in the optical domain, where a great variety of applications are foreseen for quantum science and quantum technology.
Our group at C2N has developed a unique expertise in designing photonic lattices of coupled non-linear semiconductor microcavities. We show, in Fig. 1, some examples of assemblies of coupled microcavities where light emulates the properties of electrons in a benzene molecule or in graphene [2].
The challenge we propose to tackle during this PhD program is to engineer interactions between photons that are strong enough (at the single photon level) to enter the quantum regime. To do so, we will optimize the non-linear medium and produce a new generation of non-linear semiconductor lattices using the state-of-the art nanotechnology tools that are available in the C2N clean room.
The candidate will contribute to the exploration of these new structures by realizing optics experiments under cryogenic conditions (4 K). The goal will be to use advanced optical measurements techniques in order to quantify photon-photon interactions in the cavities
(pump-probe spectroscopy), measure the quantum correlations in trains of photons emitted through the cavity (Hanbury Brown and Twiss experiment) and evidence entanglement (measurement of the spatio-temporal correlations). Analysis of the experimental data will besupported by theoretical modeling developed by the applicant in collaboration with theoretician collaborators through our large network of international collaborators.
We are looking for a candidate with skills and interest in experimental work, as well as solid knowledge in quantum optics and solid state physics.

References:
[1] C. Ciuti, and I. Carusotto, Quantun fluids of light, Rev. Mod. Phys 85, 299 (2013).
[2] A. Amo and J. Bloch, Exciton-polaritons in lattices: A non-linear photonic simulator, C. R.
Phys. 17 (2016).

PhD

The hexagonal crystal phase of GeSi-2H (an allotrope of the standard cubic 3C structure) has emerged as a revolutionary material which brings forward exciting photonic functionalities to the silicon technology. SiGe-2H phase exhibits a direct band gap and an excellent light emission capabilities with a tuneable emission wavelength in the mid infrared between 1.8-4.2 μm by a concentration range of 0-40% of Si.
We have pioneered the growth of Au-catalyzed Ge-2H branches on wurtzite GaAs nanowires. We have shown that the Ge branches grow in the particular <1-100> direction on the (1-100) sidewalls of the GaAs trunk. They exhibit the wanted 2H crystal structure keeping an epitaxial relationship with the GaAs trunk.
We aim at investigating the growth mechanisms using in-situ and real time TEM observations at the atomic scale and compare Vapor-Solid-Solid (VSS) and Vapor-Liquid-Solid (VLS) growth modes, which can be tuned by the substrate temperature. It is important to understand nucleation of this new material system with the specific <1-100> orientation and analyse the growth interface between the branch and the catalyst. We will study the crystal structure and defect formation as well as the formation of the cubic phase lateral overgrowth on the (0001) sidewalls of the branches. This fundamental study will support the fabrication of axial Si/Ge heterostructures along the unconventional <1-100> axis.
For scalable integration, nanowires must be grown on adequate hexagonal substrates with the specific m-plane {1-100} surface. In a first attempt, we will use commercially available m-plane CdS substrates.
We will study the catalyst (Au and Sn) dewetting on CdS substrates and validate the possible growth of GeSi-2H nanowires on CdS or on GaAs/CdS.
This study is part of ONCHIPS project funded by the EU Horizon-CL4-2021. In the global project we aim at combining electronic and photonic qubits in the nanowires. We propose to grow enriched Ge quantum dots acting as light emitting diode (LED) in Si-rich hexagonal GeSi nanowire. To this end we will grow heterostructured GeSi-2H nanowires, control doping (p- & n-type), form junctions and embed heterostructure quantum dots in Si shell to facilitate conversion of carrier spin into photon polarization.

More information in the attached file