A new quantum optics tool for simulating quantum probability density functions resulting from the linear and nonlinear interaction of photons with atoms and with other photons is developed and presented. It can be used to design and simulate quantum optics experiments used in quantum communications, quantum computing, and quantum imaging. Examples of a photon interacting with linears systems of mirrors and beamsplitters are simulated. Nonlinear simulations of the interaction of three photons resulting in photon momentum entanglement is presented. The wavefunction is expanded in Fock states. Fock states cannot be represented by classical modeling and therefore, the results of our modeling can in general represent phenomena in both the linear and nonlinear cases which cannot be modeled by classical linear optics. The modeling presented here is more general than the classical linear optics. Models of atmospheric turbulence and their simulations are presented and demonstrate the potential for first principles physics quantum optics simulations through turbulence in realistic environments.
A new quantum optics tool for simulating quantum probability density functions resulting from the linear and nonlinear interaction of photons with atoms and with other photons is developed and presented. It can be used to design and simulate quantum optics experiments used in quantum communications, quantum computing, and quantum imaging. Examples of a photon interacting with linears systems of mirrors and beamsplitters are simulated. Nonlinear simulations of the interaction of three photons resulting in photon momentum entanglement is presented. The wavefunction is expanded in Fock states. Fock states cannot be represented by classical modeling and therefore, the results of our modeling can in general represent phenomena in both the linear and nonlinear cases which cannot be modeled by classical linear optics. The modeling presented here is more general than the classical linear optics. Models of atmospheric turbulence and their simulations are presented and demonstrate the potential for first principles physics quantum optics simulations through turbulence in realistic environments.
Quantum optics has successfully been used to test fundamental principles in quantum physics and to demonstrate the potential of quantum-enhanced technologies. Linear quantum optics, in which large quantum states of light are produced by optical interference of smaller quantum states, has proved to be particularly fruitful. Further progress will rely both on developing improved experimental tools to manipulate and measure quantum light, and on expanding and refining the range of applications of these technologies. This thesis presents our contributions towards both of these endeavours. We first focus on some of the components necessary for linear quantum optics, starting with the requirement for reconfigurable interference between several optical modes. We propose a novel design for interferometers that satisfy this requirement, which is based on a new mathematical decomposition of unitary matrices used to describe optical interference. We show that our design is more efficient than previously known designs. We also experimentally demonstrate a modular approach to building these devices, which is based on the assembly of multiple UV-written integrated photonic chips. These chips are characterised, and three of them are assembled into a structure shown to enable a wide range of optical transformations. We then study methods of photon detection, showing how photon detectors can be calibrated and discussing the operation of superconducting photon number resolving transition edge sensors. Next, we study two applications of linear optics. We examine the applicability of a proposal for simulating molecular spectroscopy using quantum optics in the presence of experimental imperfections. Our findings are illustrated with a proof of principle experiment in which we simulate part of the vibronic spectrum of the tropolone molecule. Finally, we study a class of optical devices, known as optical Ising machines, that has been shown to find solutions to difficult combinatorial problems. Describing the optical pulses in these devices in phase space as Gaussian quasi-probability distributions that evolve stochastically, we analyse the computational mechanism of these machines and show in theory that they can be simplified without affecting their performance.
Long-range quantum communication requires sending qubits, usually photonic cubits, over long distances through free space. Photons propagating through free space encounter optical turbulence, causing scattering and entanglement degradation. In recent decades, adaptive optics has been used to correct imaging errors introduced by turbulence. An atmospheric turbulence simulator has been constructed to measure the effect of optical turbulence on single photon propagation, and an adaptive optics system has been incorporated. The turbulence simulator uses two rotating phase plates to emulate the effects of random dispersive media and two afocal systems to scale long propagation distances down to lengths realizable in a laboratory. The adaptive optics system consists of a Shack-Hartman wavefront sensor used to measure wavefront error, and a deformable mirror used to correct this error. The use of adaptive optics allows us to correct wavefront errors introduced by turbulence. Adding an adaptive optics system into this simulator facilitates more robust characterization of the strength of the simulated turbulence, as well as correction of some of the negative effects the turbulence introduces. This presentation will discuss the effects of turbulence on single photon propagation when an adaptive optics system is used and how these results compare to previously measurements taken without the use of adaptive optics, allowing us to quantify the improvement adaptive optics introduces.
Photonics is a promising architecture for the realisation of quantum information processing, since the two-photon interaction, or non-linearity, necessary to build logical gates can efficiently be realised by the use of interference with ancillary photons and detection. Although single-photon sources and detectors are pivotal in realisations of such systems, clear guidelines for the required performance of realistic systems are yet to be defined. We present our detailed numerical simulation of several quantum optics circuits including sources and detectors all represented in multi-dimensional Fock-spaces, which allows us to obtain experimentally realistic performance bounds for these devices. In addition, the single-photon source based on switched parametric downconversion is studied, which in principle could reach the required performance. Three approaches for implementing the switching hierarchy of the photons are simulated, and their anticipated performance is obtained. Our results define the bar for the optical
Quantum light propagation through turbulent atmosphere has become a subject of intensive research, spanning both theoretical and experimental studies. This interest is driven by its important applications in free-space quantum communication, remote quantum sensing, and environmental monitoring. At the same time, this phenomenon itself poses an intriguing fundamental problem. A consistent theoretical description typically makes explicit assumptions about the measurement scheme at the receiver station and/or the method of quantum-information encoding. A common and straightforward approach encodes the information in quantum states of a quasi-monochromatic mode, representing a pulsed Gaussian beam. Atmospheric turbulence induces random distortions of the pulse shape and, consequently, random fluctuations of the transmittance through the receiver aperture. These fluctuations, characterized by the probability distribution of transmittance (PDT), directly affect the quantum state of the received light. In this paper we examine various analytical models of the PDT, validate them through numerical simulations, and assess their range of applicability. Furthermore, we extend the analysis beyond the standard ensemble-averaging approach, recognizing that realistic experiments typically involve time averaging. This requires a detailed examination of the underlying random process, including the study of temporal correlations and their impact on nonclassical properties of electromagnetic radiation.
Free-space quantum communications offers a promising route for securely transmitting information over long distances. However, a major challenge for these systems is atmospheric turbulence, which distorts the spatial structure of light and can severely limit the amount of information that can be reliably transmitted. In this work, we propose and demonstrate a turbulence-resilient scheme for free-space quantum communication. By leveraging the phase conjugation property of stimulated parametric down-conversion, our scheme enables all-optical dynamic correction of spatial-mode distortion induced by atmospheric turbulence, thereby enhancing the secure key rate in high-dimensional quantum key distribution. We develop a theoretical model that provides detailed guidelines for selecting the optimal basis and spatial properties needed to maximize the efficiency of the proposed scheme. Both numerical simulations and experimental results show that, even under strong turbulence, our scheme can reduce the quantum error rates well below the security threshold. These results highlight the potential of nonlinear optical approaches as powerful tools for robust quantum communication in realistic free-space environments.
In this work, we propose and demonstrate a turbulence-resilient scheme for free-space quantum communication. By leveraging the phase conjugation property of stimulated parametric down-conversion, our scheme enables all-optical dynamic correction of spatial-mode distortion induced by atmospheric turbulence, thereby enhancing the secure key rate in high-dimensional quantum key distribution. We develop a theoretical model that provides detailed guidelines for selecting the optimal basis and spatial properties needed to maximize the efficiency of the proposed scheme. Both numerical simulations and experimental results show that, even under strong turbulence, our scheme can reduce the quantum error rates well below the security threshold. These results highlight the potential of nonlinear optical approaches as powerful tools for robust quantum communication in realistic free-space environments. Our work could have important implications for the practical implementation of secure quantum channels over long free-space distances.