Silicon Photonics for Quantum Information

Quantum information science and technology (QIST) combines principles of quantum mechanics and information theory to develop new approaches for processing, transmitting, and sensing information. Practical realization of applications in QIST requires generation and validation of a significant amount of entanglement, which is not only a property but a logical resource. Silicon photonic integrated circuits (PICs) are an attractive platform for applications in QIST and for generating the entanglement resource because they are foundry-fabricated, are compatible with existing fiber optic infrastructure, have a small spatial footprint, and afford access to several high-dimensional (HD) degrees of freedom. This dissertation covers three projects that contribute to the development of silicon PICs for applications in QIST. We focus on the entanglement resource and how it can be more readily generated, characterized, and manipulated using the silicon PIC platform. First, we examine an interferometrically coupled single-bus microring resonator (MRR) as a source of entangled photon pairs generated by spontaneous four-wave mixing (SFWM). By modeling the device’s transmission spectrum, we show how the design of its interferometric coupling section can enhance SFWM. Based on this model, we design, fabricate, and characterize a PIC. We report a pair generation rate of 368 ± 4 kHz/mW$^2$ and measure antibunching dips below the $g^{(2)}_H(0)< 0.5$ criterion for heralded single photon pair sources. Next, we use an array of 4 MRR photon pair sources to generate and quantify HD entanglement in the path basis. We model the joint coincidence distribution and two-photon interference experiments that partially characterize the system's density matrix. With a foundry-fabricated, fully-packaged system, we perform these measurements and analyze the data with an entanglement measure. We calculate a lower bound for the system's entanglement of formation of $E_F(\hat{\rho}) \geq 1.45 \pm 0.15$ ebits. Finally, we investigate a new approach for manipulating quantum states of light in the path basis. This approach incorporates the star coupler, an integrated diffractive element that approximates a discrete Fourier transform (DFT) in the optical path basis. Using Ansys Lumerical we simulate many star couplers with different geometries and evaluate their fidelity to a DFT, their transmission and their mixing entropy. We discuss their suitability as circuit elements for larger PICs.