Recent advances in hardware, algorithms and software of quantum computers
1980年, 美国科学家 Paul Benioff和前苏联科学家 Yuri Manin提出了量子计算的概念, 1981年诺贝奖费曼提出了量子模拟, 1985年 David Deutsch证明了量子计算概念的普适性. 至此,完成了建立量子计算概念的第一个阶段. 1986-1993年, 是量子计算机研究的自由探索阶段. 1994年开始, 量子算法取得重大突破, Shor大数分解算法和 Grover 搜索算法两大算法诞生, 极大地推动了量子计算研究在全世界的发展, 量子计算进入到大强度基础研究阶段. 2016年开始, 以 IBM 推出5比特量子云平台为标志的, 量子计算进入到工程研发的第四个发展阶段.
量子计算的发展受到国际的普遍关注, 为了满足广大作者和读者的需求, 进一步促进我国学者在该领域研究的学术交流和国内外影响, 《物理学报》专门组织了量子计算的专题, 邀请活跃在研究一线的学者, 贡献最新研究成果论文或综述文章, 系统全面地反映该领域的研究成果以及最新进展. 本专题得到踊跃相应, 征集到近 20篇高水平的研究论文和综述文章, 内容涵盖发展迅速的超导量子计算、量子硬件系统与模拟、光量子计算、新奇量子系统模拟、量子算法进展等五个方向, 将在《物理学报》陆续发表.
量子计算的发展受到国际的普遍关注, 为了满足广大作者和读者的需求, 进一步促进我国学者在该领域研究的学术交流和国内外影响, 《物理学报》专门组织了量子计算的专题, 邀请活跃在研究一线的学者, 贡献最新研究成果论文或综述文章, 系统全面地反映该领域的研究成果以及最新进展. 本专题得到踊跃相应, 征集到近 20篇高水平的研究论文和综述文章, 内容涵盖发展迅速的超导量子计算、量子硬件系统与模拟、光量子计算、新奇量子系统模拟、量子算法进展等五个方向, 将在《物理学报》陆续发表.
2022, 71 (7): 074207.
doi: 10.7498/aps.70.20220270
Abstract +
2022, 71 (7): 070305.
doi: 10.7498/aps.71.20212245
Abstract +
One of the most important applications of quantum computing is to crack classical cryptosystem. Previous studies showed that the number of qubits required to crack the widely used 2048-bit RSA cipher is about 20 million, which is far beyond the current technology for quantum computing. Recently, É. Gouzien and N. Sangouard of the French Alternative Energies and Atomic Energy Commission proposed a quantum computing architecture based on a two-dimensional grid of superconducting qubits and a three-dimensional multimode quantum memory. They showed that only 13k qubits are required to crack a 2048-bit RSA integer with the help of a long-lived quantum memory with 28 million spatial modes and 45 temporal modes. Their results clearly demonstrate the values of quantum memories in quantum computing and provide an alternative approach for building practically useful quantum computers. Quantum computers require quantum memories to work at microwave band, which remains an outstanding challenge. Based on a detailed analysis of atomic radiations during the quantum storage process, we recently proposed a noiseless-photon-echo protocol which can successfully eliminate the spontaneous emission noise in photon echoes. This protocol is expected to further enable microwave quantum storage and the construction of “quantum memory” quantum computers.
2022, 71 (7): 070302.
doi: 10.7498/aps.71.20212197
Abstract +
The Heisenberg uncertainty principle is one of the characteristics of quantum mechanics. With the vigorous development of quantum information theory, uncertain relations have gradually played an important role in it. In particular, in order to solved the shortcomings of the concept in the initial formulation of the uncertainty principle, we brought entropy into the uncertainty relation, after that, the entropic uncertainty relation has exploited the advantages to the full in various applications. As we all know the entropic uncertainty relation has became the core element of the security analysis of almost all quantum cryptographic protocols. This review mainly introduces development history and latest progress of uncertain relations. After Heisenberg's argument that incompatible measurement results are impossible to predict, many scholars, inspired by this viewpoint, have made further relevant investigations. They combined the quantum correlation between the observable object and its environment, and carried out various generalizations of the uncertainty relation to obtain more general formulas. In addition, it also focuses on the entropy uncertainty relationship and quantum-memory-assisted entropic uncertainty relation, and the dynamic characteristics of uncertainty in some physical systems. Finally, various applications of the entropy uncertainty relationship in the field of quantum information are discussed, from randomnesss to wave-particle duality to quantum key distribution.
2022, 71 (16): 160302.
doi: 10.7498/aps.71.20220596
Abstract +
Since the physical limit of Moore's law is being approached, many alternative computing methods have been proposed, among which quantum computing is the most concerned and widely studied. Owing to the non closeability of quantum system, the uncontrollable external factors will lead to quantum dissipation and decoherence. In order to avoid the decoherence of quantum superposition state, the fabrication of robust quantum bits has become one of the key factors. Majorana zero mode (MZM) is a quasi-particle emerging in the topological and superconducting hybrid system. It has non-Abelian statistical properties. Therefore, the topological qubit constructed by MZM has natural robustness to quantum decoherence. Despite the arduous exploration by various experimental groups, the experimental verification of MZM is still lacking. This paper reviews the history and main technical routes of quantum computing, focusing on the theory of topological superconductors, observable experimental phenomena, and the latest experimental progress. Furthermore we discuss and analyze the present status of the topological superconductor research. Finally, we prospect the future experiments and applications of topological superconductors in quantum computing.
2022, 71 (16): 160304.
doi: 10.7498/aps.71.20220433
Abstract +
As a crucial quantum resource for quantum computing and quantum information processing, cluster state has attracted extensive attention due to its unique entanglement properties and rich structures. In this work, we theoretically propose a scheme for generating four-mode entangled states based on cascaded four-wave mixing (FWM) process. The internal entanglement characteristics are studied by using the positivity under partial transposition criterion and eigenmode decomposition. In addition, the output entangled states are reconstructed and optimized by adjusting the relative phase of balanced homodyne detection and postprocessing the signal noise, and finally three four-mode cluster states with different structures are generated. Such a method can effectively reduce the excess noise induced by finite squeezing. Our theoretical results provide a reliable way of generating scalable continuous variable cluster states based on FWM process in atomic ensemble.
2022, 71 (16): 160305.
doi: 10.7498/aps.71.20220635
Abstract +
Quantum computation presents incomparable advantages over classical computer in solving some complex problems. To realize large-scale quantum computation, it is required to establish a hardware platform that is universal, scalable and fault tolerant. Continuous-variable optical system, which has unique advantages, is a feasible way to realize large-scale quantum computation and has attracted much attention in recent years. Measurement-based continuous-variable quantum computation realizes the computation by performing the measurement and feedforward of measurement results in large-scale Gaussian cluster states, and it provides an efficient method to realize quantum computation. Quantum error correction is an important part in quantum computation and quantum communication to protect quantum information. This review briefly introduces the basic principles and research advances in one-way quantum computation based on cluster states, quantum computation based on optical Schrödinger cat states and quantum error correction with continuous variables, and discusses the problems and challenges that the continuous-variable quantum computation is facing.
2022, 71 (16): 160301.
doi: 10.7498/aps.71.20220219
Abstract +
2022, 71 (13): 133701.
doi: 10.7498/aps.71.20220224
Abstract +
Ion trap system is one of the main quantum systems to realize quantum computation and simulation. Various ion trap research groups worldwide jointly drive the continuous enrichment of ion trap structures, and develop a series of high-performance three-dimensional ion trap, two-dimensional ion trap chip, and ion traps with integrated components. The structure of ion trap is gradually developing towards miniaturization, high-optical-access and integration, and is demonstrating its outstanding ability in quantum control. Ion traps are able to trap increasingly more ions and precisely manipulate the quantum state of the system. In this review, we will summarize the evolution history of the ion trap structures in the past few decades, as well as the latest advances of trapped-ion-based quantum computation and simulation. Here we present a selection of representative examples of trap structures. We will summarize the progresses in the processing technology, robustness and versatility of ion traps, and make prospects for the realization of scalable quantum computation and simulation based on ion trap system.
2022, 71 (24): 244207.
doi: 10.7498/aps.71.20221938
Abstract +
Quantum simulation is to use a controllable quantum system to simulate other complicated or hard-to-control quantum system, and to deal with some complex unknown quantum systems that cannot be simulated on classical computers due to the exponential explosion of the Hilbert space. Among different kinds of physical realizations of quantum simulation, integrated optical systems have emerged as an appropriate platform in recent years due to the advantages of flexible control, weak decoherence, and no interaction in optical systems. In this review, we attempt to introduce some of the basic models used for quantum simulation in integrated photonic systems. This review article is organized as follows. In Section 2, we introduce the commonly used material platforms for integrated quantum simulation, including the silicon-based, lithium niobate-based integrated circuits, and the femtosecond laser direct writing optical waveguides. Several integrated optical platforms such as the coupled waveguide arrays, photonic crystals, coupled resonator arrays, and multiport interferometers are also introduced. In Section 3, we focus on the analog quantum simulations in the integrated photonic platform, including Anderson localization of light in disordered systems, various kinds of topological insulators, nonlinear and non-Hermitian systems. More specifically, in Subsection 3.1, we present the integrated photonic realizations of disordered and quasi-periodic systems. In Subsection 3.2, we review the integrated photonic realizations of the topological insulators with and without time-reversal symmetry, including Floquet topological insulators, quantum spin hall system, anomalous quantum hall system, valley hall system, Su-Schrieffer-Heeger (SSH) model, and photonic topological Anderson insulators. Besides, topological insulator lasers and topologically protected quantum photon sources are briefly reviewed. In Subsection 3.3, we review the nonlinear and non-Hermitian integrated optical systems. In Section 4 we present the integrated digital quantum simulations based on the multiport interferometers, including the discrete-time quantum random walk, Boson sampling, and molecular simulation. In Section 5, we summarize the content of the article and present the outlook on the future perspectives of the integrated photonic quantum simulation. We believe that the integrated photonic platforms will continue to provide an excellent platform for quantum simulation. More practical applications will be found based on this system through combining the fields of topological photonics, laser technologies, quantum information, nonlinear and non-Hermitian physics.
2022, 71 (24): 240303.
doi: 10.7498/aps.71.20221825
Abstract +
Quantum simulation is one of the main contents of quantum information science, aiming to simulate and investigate poorly controllable or unobtainable quantum systems by using controllable quantum systems. Quantum simulation can be implemented in quantum computers, quantum simulators, and small quantum devices. Non-Hermitian systems have aroused research interest increasingly in recent two decades. On one hand, non-Hermitian quantum theories can be seen as the complex extensions of the conventional quantum mechanics, and are closely related to open systems and dissipative systems. On the other hand, both quantum systems and classical systems can be constructed as non-Hermitian systems with novel properties, which can be used to improve the precision of precise measurements. However, a non-Hermitian system is more difficult to simulate than a Hermitian system in that the time evolution of it is no longer unitary. In this review, we introduce recent research progress of quantum simulations of non-Hermitian systems. We mainly introduce theoretical researches to simulate typical non-Hermitian quantum systems by using the linear combinations of unitaries, briefly showing the advantages and limitations of each proposal, and we briefly mention other theoretical simulation methods, such as quantum random walk, space embedded and dilation. Moreover, we briefly introduce the experimental quantum simulations of non-Hermitian systems and novel phenomena in nuclear magnetic resonance, quantum optics and photonics, classical systems, etc. The recent progress of the combinations of quantum simulation and non-Hermitian physics has promoted the development of the non-Hermitian theories, experiments and applications, and expand the scope of application of quantum simulations and quantum computers.
2022, 71 (24): 240305.
doi: 10.7498/aps.71.20221824
Abstract +
Information processing technology based on the basic principle of quantum mechanics shows great potential applications in computing, sensing and other fields, and is far superior to classical technology. With the advance of experimental technology, quantum control technology develops rapidly. Compared with other quantum information processing platforms, the superconducting system based on solid materials has the advantages of accurate quantum controllability, excellent quantum coherence and the potential for large-scale integration. Therefore, superconducting quantum system is one of the most promising platforms for quantum information processing. The existing superconducting circuits, which can integrate about one hundred qubits, have already demonstrated the advantages of quantum systems, but further development is limited by system noise. In order to break through this bottleneck, quantum error correction technology, which is developed from the classical error correction technology, has attracted extensive attention. Here, we mainly summarize the research progress of quantum error correction in superconducting quantum systems including the basic principles of superconducting quantum systems, the quantum error correction codes, the related control techniques and the recent applications. At the end of the article, we summarize seven key problems in this field.
2022, 71 (24): 240302.
doi: 10.7498/aps.71.20221782
Abstract +
2023, 72 (10): 100305.
doi: 10.7498/aps.72.20222398
Abstract +
2023, 72 (10): 100304.
doi: 10.7498/aps.72.20222349
Abstract +
In this paper, we study the transport properties of quantum states in the square-lattice quantum bit model by using inductive couplers to generate the artificial gauge potential (effective magnetic flux). It is found by theoretical calculation that the eigenstates of single particle and single hole have the same eigen energy spectrum, and the average particle and hole currents, sinusoidally modulated by the effective magnetic flux, are opposite to each other with respect to the same eigen energy. For an initial single-particle or single-hole state where only one lattice site is occuplied, if the time-inversion symmetry is preserved (the effective magnetic flux is an integral multiple of 4π), the components of the time-dependent wave functions of the single particle and the single hole are equal, otherwise they are not equal. The analysis demonstrates that the above calculation results are due to the fact that the particle-hole operation for the system Hamiltonian is equivalent to the time inversion. In addition, it is found that when the effective magnetic flux is π, a single particle or a single hole is only transported between the initial bit and two adjacent bits, and when the effective magnetic flux is 0, a single particle or a single hole is transported to the diagonal bit through two adjacent bits, and then transported in reverse. Regardless of the value of effective magnetic flux, both the single-particle and single-hole states share the same average (particle or hole) current and lattice site occupation probability.
