title: Development and application of engineered photon sources
Creators: name: Bong, Kok Wei
Publisher: name: Griffith University
Year: 2022
Subjects: subject: engineered photon sources
subject: quantum mechanics
subject: Quantum information science (QIS)

description: The history of quantum mechanics began with a series of crises in the 19th century, such as predictions of the ultra-violet catastrophe [1]. A blackbody in thermal equilibrium would emit radiation with increasing energy as the wavelength decreases, and the ideal blackbody will emit an infinite amount of energy as the radiation’s wavelength approaches ultra-violet. Max Planck partially resolved the crisis in 1900 when he proposed a solution where electromagnetic radiation can be emitted or absorbed only in discrete packets, or quanta. In 1905, Albert Einstein further theorised that the quantised electromagnetic radiation, or photon, is able to explain the experimental data from the photoelectric effect [1]. Einstein could show that electron emission depends on the frequency of light rather than its intensity, which contrasted prediction from classical electromagnetism. Since then, quantum mechanics has been instrumental in establishing the atomic structure, superconductivity, lasers and even advancing communications. Recently, new applications of quantum mechanics has began to emerge. Quantum information science (QIS) is encoding information into the state of a quantum system. QIS is concerned with extracting information from the quantum properties of systems, and quantum computation is concerned with manipulating and processing quantum information— performing logical operations—using quantum information processing techniques. QIS promises to transform information and measurement technology, providing new capabilities in ultrafast processing of complicated problems [2], absolutely secure communication [3], measurement precision at the fundamental limit [4], and more. Optics provides an excellent platform for quantum information science (QIS). Photonic quantum optics is a mature test bed for exploring novel questions in QIS. Light is an excellent system for communicating over long distances, and its bosonic nature provides unique capabilities for certain kinds of quantum simulation tasks, like BosonSam- 1 pling [5]. The aim of this project is to advance the science and technology of generating singlephotons, and applying the improved technology to important problems like experimental BosonSampling. Many believe that sampling problems like BosonSampling will be the first demonstration of a real and growing quantum advantage in processing, and that sampling problems can be related to other tasks like molecular simulations [6], metrology [7] and decision problems [8]. In this work, I will not be implementing a BosonSampling experiment. Nevertheless, the technology developed in this thesis is useful in applications that require interfering many photons, e.g. building clusters state, an essential tool for measurement-based quantum computation [9] as well as future BosonSampling implementations, Recent work by Zhong et al. [10] showed a quantum advantage over stateof- the-art simulation strategy and supercomputers with gaussian BosonSampling. The experiment uses 25 down-conversion photon sources that is sent into 100-mode ultralowloss passive interferometer. Our work in temporal multiplexing (see Section 4.2) promises improved flexibility and programmability in large BosonSampling style experiment. BosonSampling is a computational sampling problem which requires non-polynomial time to simulate on a classical computer, but theoretically promises to be faster when harnessing quantum systems. However, it requires far less experimental resources than a universal quantum computer [11]. A BosonSampling device begins with an input state consisting of n single photons or squeezed states with n average photons in m modes, where the number of modes scales quadratically with the number of photon, m = O(n2) [11]. The input state passes through a complex passive linear optics network of beam splitters and phase-shifters. The output state is a superposition of the different configurations of how the n photons could have arrived in the output modes that depend on classical and quantum interference. Results are obtained by running the experiment many times to collect the coincidence counts at the output modes and sample a statistical distribution from the measurements. Importantly, the physics and technology behind BosonSampling also has applications to a range of other quantum information science and technology goals, including ultrahigh performance photon sources. The main aim of my project is to improve on the current generation of heralded single photon sources. However, answering questions relating to the foundation of quantum mechanics can prove to be relevant. There are several precedents where fundamental theoretical studies had relevance in QIS (e.g. the application of Bell inequalities to secure random number generation [12]).