Sources of Entangled Photons

Amaal M. Ali, Natasha Bastien, Wendy-Ann Gibbons +2 more

Goswami, Abhirup

Quantum repeaters are the most promising approach for distributing entanglement over long distances. Recent approaches to develop quantum repeaters involve the use of deterministic entangled photon pair sources. On the other hand heralded entangled photon pair sources have been proposed independently both with parametric down conversion source and single photon sources. We modify the latter scheme to implement it as an on demand entangled photon pair source and analyse its performance considering inefficient detectors, inefficient quantum memories and inefficient single photon sources. We conclude that with the current state of art, generation of high fidelity deterministic entangled photon pairs is possible with moderate efficiency. We then compare the results to the deterministic entangled photon pair source obtainable using parametric down conversion source and conclude that the single photon scheme described in this thesis is more practical for such an implementation.

Krishna Thyagarajan

Andi Shahaj

Entangled photon sources have applications in such fields as quantum communications, quantum sensing and quantum computing. Of particular interest are pulsed entangled photon sources, as they provide an additional degree of freedom – the temporal degree of freedom – to manipulate entanglement properties, hence increasing the information capacity of the entangled photons they produce. An entangled photon source in the telecom wavelength typically requires a 780 nm pump laser. So far, in most cases, pulsed entangled photon sources are pumped by the Ti:Sapph mode-locked laser, which, due to its bulky size and high cost, has limited the widescale adoption of pulsed entangled photon sources. In this thesis, I demonstrate a simple, cost-effective, pulsed laser diode capable of competing with the Ti:Sapph for the purposes of entangled photon generation. The diode and driver are capable of pulsing at up to 60 MHz , with peak power exceeding 1 W and pulse energy in excess of 1 nJ , and with a spectral width narrower than 0.1 nm. I also demonstrate a pulsed, fully fiber-based, entangled photon source, with high entanglement quality (maximum concurrence of 0.985) and a high pair generation rate (0.15 pairs/pulse). The source is to our knowledge the first of its kind.

Krishna Thyagarajan

Yan Chen, Jiaxiang Zhang, Michael Zopf +4 more

Many of the envisioned quantum photonic technologies, e.g. a quantum repeater, rely on an energy- (wavelength-) tunable source of polarization entangled photon pairs. The energy tunability is a fundamental requirement to perform two-photon-interference between different sources and to swap the entanglement. Parametric-down-conversion and four-wave-mixing sources of entangled photons have shown energy tunability, however the probabilistic nature of the sources limits their applications in complex quantum protocols. Here we report a silicon-based hybrid photonic chip where energy-tunable polarization entangled photons are generated by deterministic and scalable III-V quantum light sources. This device is based on a micro-electromechanical system (MEMS) incorporating InAs/GaAs quantum dots (QDs) on a PMNPT-on-silicon substrate. The entangled photon emissions from single QDs can be tuned by more than 3000 times of the radiative linewidth without spoiling the entanglement. With a footprint of several hundred microns, our design facilitates the miniaturization and scalable integration of indistinguishable entangled photon sources on silicon. When interfaced with silicon-based quantum photonic circuits, this device will offer a vast range of exciting possibilities.