Quantum Light Sources Based on Superconductor-Semiconductor Structures

Superconductor-semiconductor device research is a rapidly evolving field, combining the technologically mature field of semiconductors with the exotic properties of superconductors. Notably, the electrically driven Cooper pair recombination in superconducting light emitting diodes (SLEDs) has been theoretically shown to produce polarization-entangled photon pairs.
In this work, we explore new device designs and develop theories for quantum-optical phenomena in the SLED, which consists of a superconducting contact placed above a PIN junction semiconductor stack.
Utilizing a novel SLED design with an optically transparent NbTiN superconductor, we developed a new contact fabrication process to enable emission from the entire superconducting contact, compared to previous designs where the superconductor was opaque and blocked the emission. We observed Andreev reflection in differential conductance measurements, and for the first time, we demonstrated broad-spectrum enhancement of the electroluminescence (EL) below the critical temperature (Tc). Furthermore, spatially resolved EL measurements support unexpected findings of reduced emission below Tc in previous works.
Another avenue of this research is the theoretical study of quantum-optical phenomena in hybrid devices. Utilizing second-order perturbation theory, we developed an effective Hamiltonian to show that the nonlinear optical interaction of Cooper-pair recombination can be utilized to generate squeezed light, when inputting a coherent state into a hybrid superconductor-semiconductor waveguide. We found the squeezing strength to be proportional to the superconducting energy gap squared and device length, as well as increasing with applied voltage. For practical device dimensions, we showed a maximal squeezing of 10 dB can be achieved below Tc.
This work presents a step towards the experimental demonstration of quantum-optical phenomena in the device and can pave the way toward realization of new quantum light sources.

M.Sc. student under the supervision of Prof. Alex Hayat.