Quantum computers are increasingly seen as a potential solution for computing problems that are difficult to solve with conventional technologies.A photon-based quantum computer is a promising technology that enables the development of large-scale, universal quantum computing at high speeds at room temperature with large-scale quantum entanglement thanks to photons' inherent characteristics.This article explores NTT's efforts to develop optical quantum computers using optical fiber communication technology.
Quantum computers are increasingly seen as a potential solution for computing problems that are difficult to solve with conventional technologies.A photon-based quantum computer is a promising technology that enables the development of large-scale, universal quantum computing at high speeds at room temperature with large-scale quantum entanglement thanks to photons' inherent characteristics.This article explores NTT's efforts to develop optical quantum computers using optical fiber communication technology.
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.
Enabling large-scale and high-speed quantum computation is a key to practical quantum computation. Continuous-variable approach in optical systems offer advantages in scalability and speed by leveraging their temporal degree of freedom and inherent large carrier frequency. In this paper, we investigate the generation and manipulation of quantum entanglement through a time-domain multiplexing approach. By employing time-domain multiplexing, we generate a two-dimensional cluster state—a universal resource for large-scale quantum computation—and perform quantum operations in the time domain with cluster state. Additionally, our ongoing research focuses on the generation and measurement of broadband optical quantum entanglement through an optical parametric oscillator, which holds potential as a foundation for high-speed quantum computing surpassing limitations of existing systems. By further engineering the quantum entanglement, we have also theoretically formulated a practical teleportation-based architectures for quantum computation in time domain. These advancements form the groundwork for the development of practical optical quantum 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 entanglement is a fundamental resource for various quantum applications and generation of large-scale entanglement is a key quantum technology. In recent years, continuous-variable optical systems have shown promising results in this direction, thanks to deterministic generation and multiplexing via rich degrees of freedom naturally occurring in the optical system. In this paper, we review the generation and applications of multipartite optical quantum entanglement. We begin with a theoretical overview of how to represent and verify multimode continuous-variable quantum states and entanglement. Then, we discuss the multiplexing technique in time, frequency, and spatial domains, and their applications in generation of large-scale entangled states. Afterward, we review the current status and development of the basic technology used in the generation of multipartite quantum entanglement. Finally, we discuss the applications of large-scale quantum entanglement and possible future perspectives. Published by the American Physical Society 2024
For more than 100 years, researchers explore quantum physics, which led to major breakthroughs, such as the laser, being today in daily use. With the increased control that is gained in recent years over quantum systems, the current advances in quantum technologies allow the exploitation and distinct control of quantum phenomena such as superposition and entanglement. These quantum phenomena enable fundamental performance advantages over normal classical procedures. They can be used for example to realize quantum-enhanced metrology, where quantum systems show the increase in sensitivity for metrological tasks, such as length measurements, as it will be exploited in the next generation of gravitational wave detection systems. Moreover, quantum physics is foreseen to enable quantum computing which could accelerate computational tasks for certain specific problems and enable entirely novel solutions with applications in drug development, material design or climate change. However current quantum computing technology is still in a prove-of-concept demonstration phase as it requires to prove scalability to large-scale quantum systems. More conceptually and technologically advanced is the use of quantum phenomena in order to realize future-prove communication systems, that means communication techniques which cannot be decrypted by future advances in mathematical concepts or computing resources. Here prove-of-concept systems in optical fiber as well as in satellite configurations and even commercial devices already exist, which require however advances with respect to multi-user operation increased transmission rates and reduced complexity.
Quantum computers harnessing the principles of quantum mechanics hold the potential to outperform classical systems. Continuous-variable quantum information processing with light offers advantages such as THz-order clock frequencies, scalability via temporal multiplexing, and compatibility with ultra-fast optical communication technologies. This type of quantum computer can be described as an ultra-fast analog quantum computer, making it particularly well-suited for applications involving continuous variables, such as neural networks and optimization problems. However, challenges in universal computation and error correction persist due to weak light-matter interactions. This presentation introduces our advancements in optical quantum computing using waveguide optical parametric amplifiers (OPAs) and non-Gaussian quantum state generation with photon-number resolving detectors (PNRDs). We also propose an all-optical scheme leveraging OPAs to achieve fault-tolerant quantum computing, enabling logical qubit generation and clock frequencies exceeding THz.