Photons provide low-noise quantum systems which are ideal for the fundamental studies of the quantum world and for developing new quantum technologies which promise to transform the way we process, transmit and acquire information. The development of the eld of quantum information processing, broadly dened, represents one of the most important scientic and technical challenges of the 21st Century. Photons have been used in demonstrations of basic quantum logic, secure communication tasks, precision measurements and the fundamental studies of quantum mechanics. In order to apply these systems and technologies in an ever increasing scale, it is necessary to develop new methods for eciently manipulating the quantum state of light. This is one of the main goals of this study which experimentally demonstrates new techniques for realising multi-qubit logic gates as well as a new method for amplifying quantum states of light noiselessly.
Photons provide low-noise quantum systems which are ideal for the fundamental studies of the quantum world and for developing new quantum technologies which promise to transform the way we process, transmit and acquire information. The development of the eld of quantum information processing, broadly dened, represents one of the most important scientic and technical challenges of the 21st Century. Photons have been used in demonstrations of basic quantum logic, secure communication tasks, precision measurements and the fundamental studies of quantum mechanics. In order to apply these systems and technologies in an ever increasing scale, it is necessary to develop new methods for eciently manipulating the quantum state of light. This is one of the main goals of this study which experimentally demonstrates new techniques for realising multi-qubit logic gates as well as a new method for amplifying quantum states of light noiselessly.
Photons have been a flagship system for studying quantum mechanics, advancing quantum information science, and developing quantum technologies. Quantum entanglement, teleportation, quantum key distribution, and early quantum computing demonstrations were pioneered in this technology because photons represent a naturally mobile and low-noise system with quantum-limited detection readily available. The quantum states of individual photons can be manipulated with very high precision using interferometry, an experimental staple that has been under continuous development since the 19th century. The complexity of photonic quantum computing devices and protocol realizations has raced ahead as both underlying technologies and theoretical schemes have continued to develop. Today, photonic quantum computing represents an exciting path to medium- and large-scale processing. It promises to put aside its reputation for requiring excessive resource overheads due to inefficient two-qubit gates. Instead, the ability to generate large numbers of photons—and the development of integrated platforms, improved sources and detectors, novel noise-tolerant theoretical approaches, and more—have solidified it as a leading contender for both quantum information processing and quantum networking. Our concise review provides a flyover of some key aspects of the field, with a focus on experiment. Apart from being a short and accessible introduction, its many references to in-depth articles and longer specialist reviews serve as a launching point for deeper study of the field.
Photonics is an effective platform for engineering quantum states of many photons that can be harnessed for applications in information processing tasks, ranging from secure communications to enhanced sensors to efficient simulation of physical or other systems. I will discuss recent developments and some challenges to achieving this promise. Building and measuring multi-photon quantum states suitable for these applications demands a means for them to interfere and for detection at the level of individual photons. Photonic integrated circuits are well suited to these tasks at a scale that is not possible by other means. Advances in the design and utilization of circuits and detectors enable quantum advantage, and indeed provide new opportunities for classical optical systems.
Quantum information has been witnessing great science value and latent application since 1980's. The research work presented here consist of mainly two important parts: manipulations of multiphoton entanglement and atomic ensembles based quantum memory. In first part, the experimental technique multi-photon entanglement is further developed to study fundamental issues in quantum mechanics, remarkable applications to quantum communication and quantum computation. Specifically, we have demonstrated a bit-flip error-free transfer of quantum information, violation of Bell's inequality beyond Tsirelson's bound, teleportation of a two-qubit composite system, as well as the one-way computing by two-photon-four-qubit cluster state. To overcome un-scalability problem due to probabilistic feature in linear optical quantum information processing, we investigated in the second part the physics of atomic ensembles based quantum memory. We show that theoretically, entanglement between distant locations can be deterministically generated. The experimental work has thoroughly developed the necessary techniques and we have achieved deterministic single photon source, and interference of the photons from independent atomic ensembles, teleportation between photonic and atomic qubits, a novel way to create a robust entanglement between an atomic and a photonic qubit, and memory based entanglement swapping. We believe, the developed techniques here would dramatically facilitate progresses in many fields including global quantum communication, linear optical quantum computation and the foundations of quantum mechanics etc.
Quantum information processing opens up completely new possibilities in communication and computation, that would be impossible in the realms of classical physics. While the benefits of quantum information processing are well understood in theory, it remains a formidable challenge to experimentally implement even simple quantum information processing tasks. Numerous physical architectures have been proposed for preparing and coherently manipulating quantum information. Amongst these, quantum optics has been identified as a particularly promising candidate. In particular this arises from the long decoherence times of single photon states, which can be used to encode logical qubits in a variety of ways. Nonetheless, there remain formidable challenges to implementing large scale quantum information processing using optical qubits. Most notably these include: the preparation of pure indistinguishable photons; efficient number-resolving photo-detection; mode-matching; photon loss; and the non-determinism of entangling gates. Any future large scale implementation of optical quantum information processing protocols will require significant advances on most, if not all these fronts. In this thesis we aim to present a comprehensive overview of the major requirements for optical quantum information processing, understand the effects they have, and how they can be modeled. From this we aim to understand what the realistic technological requirements are to achieve scalable optical quantum information processing, and, where possible, suggest means by which to help achieve these goals.
Quantum technologies harness the properties of controlled quantum mechanical systems for applications in computation, communication and metrology, and enable us to further our understanding of fundamental physics. Quantum hardware is designed to manipulate complex and fragile many-particle quantum states, which requires exquisite control machinery, advanced software and near-complete isolation from the surrounding environment. With sufficient capabilities, quantum computers with large registers of quantum bits will perform classically intractable calculations such as quantum chemistry simulations. Quantum key distribution will provide completely secure communications across the world and quantum metrology will enable measurement precision beyond today's capabilities. While quantum technologies are far from surpassing classical hardware today, the vision and potential impact has sparked a world-wide research effort, both theoretical and experimental, to develop a quantum computer. The most sophisticated current quantum technologies have control over small numbers of quantum bits and are limited by environmental decoherence processes. While progress in developing quantum hardware is ongoing, designing and demonstrating new algorithms and protocols for quantum information is a thriving research field. Photonics provides an ideal platform for small-scale proof-of-concept quantum experiments, which are the focus of this thesis. In the coming decades, we will see the realisation of quantum hardware capable of applications that outperform any classical computer. In this thesis, I present several protocols and algorithms for quantum information science and technology, which are implemented in quantum photonic experiments. The applications of these works include robust quantum tomography, quantum state relocation, quantum enhanced data recovery and probing fundamental causality in quantum mechanics. The works presented here are based on two photon experiments from a prototypical spontaneous parametric down-conversion source, which provides an excellent test-bed for quantum information experiments. Photons can be used to encode quantum information in a range of different degrees of freedom. This versatility, along with compatibility with existing technology gives photonics a great advantage in the development of quantum hardware.
(100 Word Limit): Quantum information science promises profoundly disruptive information and communication technologies. Photons are ideal carriers of quantum information: Their low noise, high speed transmission, and ease of manipulation at the single photon level make them indispensable for quantum communication, which offers security based on the laws of physics, quantum metrology, which promises the ultimate precision measurements, and quantum information processing, which promises exponentially greater computational power for particular tasks. Recently integrated optical devices have been applied to these technologies. We give an overview of quantum technologies and progress towards their realisation in integrated optics. Presenter Bio (100 Word Limit): O’Brien is director of the Centre for Quantum Photonics, University of Bristol. His Ph.D. from the University of New South Wales in 2002 was for experimental work on correlated and confined electrons in organic conductors, superconductors and semiconductor nanostructures, and progress towards silicon quantum computing. At the University of Queensland (2001-2006) he worked on quantum optics and quantum information science with photons. CQP’s efforts are focused on the fundamental and applied quantum mechanics at the heart of quantum information science and technology, from prototypes for scalable quantum computing to quantum communication, and quantum metrology.