High-bandwidth electrical generation of single and entangled photons

Semiconductor quantum dots (QDs) are a promising source of quantum light, combining sub-Poissonian photon statistics, high entanglement fidelities, and compact integration. This thesis examines the temporal driving methodology of electrically-driven semiconductor QDs and its impact on the quantum optical characteristics of the emitted light. To this end, we introduce the design and fabrication of an ultra-high-bandwidth QD light-emitting diode (LED). We demonstrate fast control of charge carrier injection and tunnelling, and report generation of single photons at a record 3.05 GHz clock rate.
Importantly, we introduce a novel driving scheme for entangled-photon sources that rely on radiative cascades of atom-like few-level systems. Using a rate-equation model, we show that an early reinitialisation of the quantum system—before the radiative cascade has completed—may produce entangled photon pairs at a higher rate compared to either conventional pulsed operation or continuous driving of the system.
This is subsequently implemented in practice, demonstrating an entangled-pair rate enhanced by (21 ± 3) % compared to the same device when driven continuously. Employing this novel driving scheme, we also demonstrate the electrical generation of entangled-photons at a record 1.15 GHz clock rate with an overall entanglement fidelity of (79.5 ± 1.1) %.
Finally, we present a theoretical model describing the integration of a QD entangled-light-emitting diode (E-LED) in entanglement-based measurement-device-independent quantum key distribution (MDI-QKD). We conclude that a proof-of-principle experimental demonstration is feasible, yielding a peak bit-exchange fidelity of up to 84.3 % for a four-state BB84 protocol.
These results may particularly benefit the performance of future long-distance
quantum networks using atom-like quantum light sources. Furthermore, the ultra-high-bandwidth device and early reinitialisation scheme may be combined with other techniques to accelerate the radiative lifetime of the emitter, such as Purcell enhancement, further enhancing the quantum light emission for photonic applications.