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Acta Physica Sinica

Preparation methods and progress of experiments of quantum microwave

Qiang Miao, Xiang Li, Dewei Wu, Junwen Luo, Tianli Wei, Haonan Zhu

Published Jan 1, 2019• 5 citations
Publisher

Abstract

Based on the characteristics of superposition, entanglement, non-locality and non-clonality of quantum mechanics, quantum information science can break through the physical limits of classical information and open up a new information processing function different from classical electromagnetic application methods. Due to the advantages of high-energy single photon in practical applications, the research and application of optical quantum information technology dominates the development of current quantum information technology. However, the free-space transmission of light waves is greatly affected by weather conditions and atmospheric particles. Comparing with other wave bands, classical microwave signal shows good penetration ability when transmitting in free space. By introducing quantum mechanics, microwave signal also exhibits non-classical merits. As quantum microwave signal inherits both classical transmission performance and quantum non-classical features, it can be utilized as a significant signal source for diverse applications in microwave domain, such as quantum communication, quantum navigation and quantum radar, which are based on quantum technologies in large scale and dynamic free space transmission. There are three main experimental platforms on which quantum microwave is studied and produced. They are cavity quantum electrodynamics(C-QED) system, circuit quantum electrodynamics(c-QED) system, and cavity electro-opto-mechanical(EOM) system, involving with several nonlinear effects such as Kerr effect, Casimir effect, three-wave mixing, etc. In this paper, the setups of these platforms and the preparation principles are introduced. Meanwhile, the preparation principles and methods of microwave single photon, entangled microwave photons, squeezed microwave fields and entangled microwave fields are summarized and analyzed in detail from three aspects. The present status of experimental progress in the relevant fields are summarized and listed as well. Besides, key problems in the application of quantum navigation in free space utilizing quantum microwave are probed. Among them, the most pressing ones are preparation ability, decoherence in transmission and detection of entangled quantum microwave signals, which are also discussed and analyzed in this paper. Finally, we look forward to the future development of quantum microwave technology. It mainly consists of manufacturing microwave detectors with high efficiency, designing thermal photon filters, and developing suitable antennas. We hope that this study can provide useful reference for scholars who are engaged in or interested in research related to quantum microwave technologies.

DOI
10.7498/aps.68.20191981

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Based on the characteristics of superposition, entanglement, non-locality and non-clonality of quantum mechanics, quantum information science can break through the physical limits of classical information and open up a new information processing function different from classical electromagnetic application methods. Due to the advantages of high-energy single photon in practical applications, the research and application of optical quantum information technology dominates the development of current quantum information technology. However, the free-space transmission of light waves is greatly affected by weather conditions and atmospheric particles. Comparing with other wave bands, classical microwave signal shows good penetration ability when transmitting in free space. By introducing quantum mechanics, microwave signal also exhibits non-classical merits. As quantum microwave signal inherits both classical transmission performance and quantum non-classical features, it can be utilized as a significant signal source for diverse applications in microwave domain, such as quantum communication, quantum navigation and quantum radar, which are based on quantum technologies in large scale and dynamic free space transmission. There are three main experimental platforms on which quantum microwave is studied and produced. They are cavity quantum electrodynamics(C-QED) system, circuit quantum electrodynamics(c-QED) system, and cavity electro-opto-mechanical(EOM) system, involving with several nonlinear effects such as Kerr effect, Casimir effect, three-wave mixing, etc. In this paper, the setups of these platforms and the preparation principles are introduced. Meanwhile, the preparation principles and methods of microwave single photon, entangled microwave photons, squeezed microwave fields and entangled microwave fields are summarized and analyzed in detail from three aspects. The present status of experimental progress in the relevant fields are summarized and listed as well. Besides, key problems in the application of quantum navigation in free space utilizing quantum microwave are probed. Among them, the most pressing ones are preparation ability, decoherence in transmission and detection of entangled quantum microwave signals, which are also discussed and analyzed in this paper. Finally, we look forward to the future development of quantum microwave technology. It mainly consists of manufacturing microwave detectors with high efficiency, designing thermal photon filters, and developing suitable antennas. We hope that this study can provide useful reference for scholars who are engaged in or interested in research related to quantum microwave technologies.
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In this thesis, experimentally relevant aspects and open questions of quantum information processing and measurement in circuit quantum electrodynamics have been investigated theoretically. Circuit quantum electrodynamics is a relatively young field combining superconducting transmission line resonators on-chip with superconducting quantum bits which serve as artificial atoms. Remarkable experiments have underlined the prospects of circuit QED as a possible architecture for quantum information processing as well as a framework within which quantum optics experiments can be performed. In contrast to their optical counterparts, these experiments reach the ultra-strong coupling limit and allow e.g. the generation of Fock states, the study of decoherence and the observation of quantum jumps. We present the physics of superconducting circuits based on the Josephson junction as a non-linear circuit element. We discuss the various types of quantum bits (qubits) before turning to an introduction on cavity QED and conclude the introduction with a brief presentation of the most relevant experiments and a short introduction to the principles and prospects of quantum information processing. Building on the pioneering theoretical and experimental work in which up to three qubits have been integrated on a chip and successfully coupled via a cavity mode, we propose a scheme to overcome the natural limits concerning scalability in these systems. Usually, scalability is severely limited by the resonance width of the qubit transitions and the attainable frequency range for both qubit transition and cavity resonance frequencies. This limits the present setups to at most ten qubits. As a possible solution, we propose and investigate a cross-bar grid layout of cavities with qubits at the intersections. It turns out that this setup, allowing for up to about 1000 qubits, offers significant advantages over e.g. nearest-neighbor coupling schemes. In addition, it can serve as a building block for a truly scalable scheme for fault-tolerant quantum information processing with superconducting circuits by combining 7x7 arrays in a staircase manner. Furthermore, we discuss and simulate different possibilities to improve upon the suggested scheme by e.g. using resonant gates and optimal control theory. Another focus of the present thesis is measurement physics. In order to investigate e.g. the possibilities of using a circuit QED system to dispersively detect single microwave photons or to generate multi-qubit entangled states, we introduce in a pedagogical manner the basics of stochastic master equations which generate quantum trajectories before turning to concrete applications. Quantum trajectories have proven to be a state-of-the-art tool to analyze measurement situations in a very realistic manner by giving access to both the measurement record as well as the internal quantum dynamics conditioned on this record. Using the method of quantum trajectories as generated by stochastic master equations, we discuss a scheme to efficiently generate multi-qubit entangled states in a very flexible way. The method is based on a collective, dispersive qubit readout. By this measurement, a suitable product state of N qubits can be reliably converted into e.g. an N-qubit Greenberger-Horne-Zeilinger or W state. We propose and discuss the scheme and investigate the effects of decoherence and parameter spread as they would be encountered in experiment. Last but not least, we propose and fully analyze a scheme to dispersively detect single itinerant microwave photons. While experiments to generate single microwave photons have already been successfully performed, their single-shot quantum non-demolition detection has not been possible so far. The scheme presented in this thesis closes this gap in the circuit QED toolbox and reaches detection efficiencies of 30% only limited by fundamental quantum mechanics in this case the Quantum Zeno effect. This detection scheme could be used in quantum communication or quantum cryptography applications.
Quantum entanglement is a peculiar phenomenon in quantum information science, characterized by nonclassical correlations between quantum states of subsystems in a quantum system. Since the proposal of the Einstein-Podolsky-Rosen (EPR) paradox by Einstein, Podolsky, and Rosen, quantum entanglement has sparked intense debates on local realism. Bell’s inequality experiment established the nonlocality of quantum mechanics. Currently, high-dimensional quantum entanglement of both deterministic and random states can be realized in systems such as photons and cold atoms. Technologies such as quantum teleportation, quantum teleportation, quantum computing, and others rely on quantum entanglement to achieve effects beyond classical limitations. Current research focuses on the implementation of macroscopic quantum entanglement and its significance in fundamental problems of quantum mechanics. Quantum entanglement opens up a new paradigm for information processing with broad application prospects. It is necessary to conduct in-depth research on the nature of quantum entanglement and its advantages in information processing. This paper reviews the theoretical foundations of quantum entanglement, methods of generation and detection, and research progress in its applications in the field of quantum information. It discusses the important applications of quantum entanglement in quantum communication, computing, and sensing and provides an outlook on the future development prospects of quantum entanglement technologies.
In the past 20 years, impressive progress has been made both experimentally and theoretically in superconducting quantum circuits, which provide a platform for manipulating microwave photons. This emerging field of superconducting quantum microwave circuits has been driven by many new interesting phenomena in microwave photonics and quantum information processing. For instance, the interaction between superconducting quantum circuits and single microwave photons can reach the regimes of strong, ultra-strong, and even deep-strong coupling. Many higher-order effects, unusual and less familiar in traditional cavity quantum electrodynamics with natural atoms, have been experimentally observed, e.g., giant Kerr effects, multi-photon processes, and single-atom induced bistability of microwave photons. These developments may lead to improved understanding of the counterintuitive properties of quantum mechanics, and speed up applications ranging from microwave photonics to superconducting quantum information processing. In this article, we review experimental and theoretical progress in microwave photonics with superconducting quantum circuits. We hope that this global review can provide a useful roadmap for this rapidly developing field.
"Along with these developments, personal microwave technology has enabled strong non-linear effects at the photon level, leading to readily observable novel parameter regimes in quantum optics. Circuit QED has opened up new opportunities to explore the rich physics of quantum information processing (QIP) and quantum optics (QO), making them scalable on the road to quantum computing. However, we must also discuss some of the challenges involved. Quantum Technologies (QT) is a cross-disciplinary field that has made great progress in recent years. Technologies that can explicitly represent individual quantum states, as well as superposition and entanglement, are now being developed to exploit the 'strange' properties of quantum mechanics. In quantum communication, individual or entangled photons are used to securely send data, while quantum simulation utilizes well-controlled quantum systems that are less accessible. Interest is growing in higher dimensional quantum states and quantum communication, as the extended availability of Hilbert space and greater information capacity, along with increased noise elasticity, offer many advantages and new research possibilities. Let's focus our attention on the benefits of higher dimensional quantum states for quantum communication, as shown by Kuditz and others. Nevertheless, it has been demonstrated that higher dimensional quantum states can also provide improvements in many other areas."