Many of the proof-of-principle experiments in quantum optics have been carried out using table-top free-space optics. While they provide good testbeds for optical quantum optics experiments, to build actual devices and quantum computers, we have to move to the integrated optics where reproducibility and stability are more reliable. In this chapter, we review the developments of the integrated optics for optical quantum computer with the main focus on their applications in continuous-variable optical quantum computation.
Many of the proof-of-principle experiments in quantum optics have been carried out using table-top free-space optics. While they provide good testbeds for optical quantum optics experiments, to build actual devices and quantum computers, we have to move to the integrated optics where reproducibility and stability are more reliable. In this chapter, we review the developments of the integrated optics for optical quantum computer with the main focus on their applications in continuous-variable optical quantum computation.
Integrated photonic quantum chips have emerged as a promising platform for realizing fault-tolerant photonic quantum computers. Compared with bulk-optics systems, integrated photonics offer compact device footprints, enhanced programmability, and exceptional stability, attributes that are essential for executing large-scale and computationally demanding quantum tasks. In this review, we provide a comprehensive overview of recent advances in both discrete-variable and continuous-variable universal photonic quantum computation. We survey progress in fault-tolerant architectures and state-of-the-art integrated platforms and highlight the key challenges that must be addressed to scale photonic systems toward full fault tolerance. Finally, we outline future opportunities and research directions aimed at bridging the gap between current proof-of-principle demonstrations and fully scalable quantum microprocessors.
Abstract Realizing a large-scale quantum computer requires hardware platforms that can simultaneously achieve universality, scalability, and fault tolerance. As a viable pathway to meeting these requirements, quantum computation (QC) based on continuous-variable optical systems has recently gained more attention due to its unique advantages and approaches. This review introduces several topics of recent experimental and theoretical progress in the optical continuous-variable QC that we believe are promising. In particular, we focus on scaling-up technologies enabled by time multiplexing, bandwidth broadening, and integrated optics, as well as hardware-efficient and robust bosonic quantum error-correction schemes.
Under the label of optical quantum computing, there are a variety of protocols and experiments that use the quantum properties of light to achieve a computational advantage over classical computing machines. In this review, we describe some of the main implementations, which differ in the type of encoding and in how the computation is performed, whether using gates or cluster states. For each protocol, we describe advantages and challenges with an overview of the experimental results obtained, summarized in tables. Because of the great relevance achieved in this field, there is a section dedicated to non-universal quantum computation with photons, where boson sampling, variational quantum eigensolvers, and quantum machine learning applications are described. The aim is to give the reader the broadest overview of the applications where photons and their quantum properties play a key role in computation.
Quantum computing, based on the inherent superposition and entanglement properties of quantum states, can break through the limits of classical computing power. However, under the present technical conditions, the number of qubits that can be manipulated is still limited. In addition, the preparation of high-precision quantum gates and additional quantum error correction systems requires more auxiliary bits, which leads to extra cost. Therefore, it seems to be a long-term goal to realize a universal fault-tolerant quantum computer. The development of analog quantum computing is a transition path that can be used to simulate many-body physics problems. Quantum walk, as the quantum counterpart of classical random walks, is a research hotspot in analog quantum computing. Owing to the unique quantum superposition characteristics, quantum walk exhibits the ballistic transport properties of outward diffusion, so quantum walk provides acceleration in computing power for various algorithms. Based on quantum walk, different computing models are derived to deal with practical physical problems in different fields, such as biology, physics, economics, and computer science. A large number of technical routes are devoted to the experiments on realizing quantum walk, including optical fiber networks, superconducting systems, nuclear magnetic resonance systems, and trapped ion atom systems. Among these routes, photons are considered as the reliable information carriers in the experiments on quantum walking due to their controllability, long coherence time. and fast speed. Therefore, in this review, we focus on different quantum walk theories and experimental implementations in optical versions, such as traditional optical platforms, optical fiber platforms, and integrated optical quantum platform. In recent years, the rapid development of integrated optical quantum platforms has driven the experiments on quantum walk to move towards the stage of integration and miniaturization, and at the same time, the experimental scale and the number of qubits have gradually increased. To this end, we summarize the technological progress of integrated optical quantum computing, including various integrated optical quantum experimental platforms and their applications. Secondly, we specifically discuss the experiment on quantum walk and practical applications based on integrated optical quantum platforms. Finally, we briefly describe other quantum algorithms and corresponding experimental implementations. These quantum computing schemes provide computational speedups for specific physical problems. In the future, with the further development of integrated optical quantum technology, along with the increase in the number of controllable qubits and the realization of the supporting quantum error correction system, a larger-scale many-body physical system can be constructed to further expand these algorithms and move towards the field of optical quantum computing, a new stage.
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.
We introduce basic ideas and contexts of quantum computation. The idea of the quantum computation is based on quantum mechanics which is a set of ideas that greatly differs from our daily-life intuitions. To encode information in quantum computation, there are two main approaches: discrete-variable (qubit) approach and continuous-variable (mode) approach. In this book, we will be focusing on continuous-variable quantum computation which uses wave functions to encode the information. For an actual physical system, we describe optical system. We give a brief comparison between optical classical computer and optical quantum computer.