Single photon source based on IFWM

This project was conceived as the final project of my Bachelor's studies at the Department of Physics of the University of Trento. The downloadable files are the thesis itself, the LaTeX template and the presentation used for the discussion.

Integrated single photon sources are key building blocks for on-chip quantum computation, quantum information and quantum technologies in general. Single photon states can be produced through a heralding process between correlated photon pairs generated via nonlinear optical processes. On-chip heralded single photon sources based on spontaneous four wave mixing have already been demonstrated. The purpose of this thesis is to show the advantages and potentialities of intermodal four wave mixing in the single photon generation framework.

The photon source is developed on a silicon chip, the ideal platform for integrated nonlinear processes and scalable quantum devices, thanks also to its mature and cheap fabrication technology. A heralded single photon source based on an IFWM process in silicon waveguides is demonstrated here.

The first chapter covers the basics of the formation and propagation of waveguide modes, with a focus on optical multimode waveguides. Nonlinear optics is then introduced with a concise overview of the main second and third order nonlinear processes, paying particular attention to spontaneous four wave mixing and its inefficiencies in view of a single photon source application. Through this process the signal and idler photons are generated close to the wavelength of the pump, thus limiting the generation spectrum. Moreover, narrow spectral post filtering is used to increase the spectral purity, limiting the brightness and the integration of these types of sources. Intermodal four wave mixing can be used to remove the need for tight spectral filtering and to achieve broadband quantum light generation, from the near to the mid infrared.

The second chapter introduces some elements of photon statistics and deals with the basics of probabilistic single photon sources, with close attention to heralded single photon sources and the experimental metrics necessary to characterize their performance. The last part presents a heralded single photon source based on intermodal FWM on a SOI multimode waveguide, including a description of the chip, fabricated by the Centre for Materials and Microsystems of Bruno Kessler Foundation in Trento, and the experimental set-up used for characterization. The measurements were carried out by dr. Stefano Signorini and Matteo Sanna in the Nanoscience Laboratory of the Department of Physics of the University of Trento.

The analysis I carried out on the measurements is presented in the last chapter. The experimental demonstration of a silicon integrated source of heralded single photons is reported: the source exploits intermodal four wave mixing to generate the heralding idler in the near infrared and the heralded signal in the mid infrared.