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Proceedings of the Japan Academy Series B

Toward a superconducting quantum computer Harnessing macroscopic quantum coherence

Jaw-Shen Tsai

Published Jan 1, 2010• 11 citations
Publisher

Abstract

Intensive research on the construction of superconducting quantum computers has produced numerous important achievements. The quantum bit (qubit), based on the Josephson junction, is at the heart of this research. This macroscopic system has the ability to control quantum coherence. This article reviews the current state of quantum computing as well as its history, and discusses its future. Although progress has been rapid, the field remains beset with unsolved issues, and there are still many new research opportunities open to physicists and engineers.

DOI
10.2183/pjab.86.275

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Recent demonstrations of macroscopic quantum coherence in Josephson junction based electronic circuits have opened an entirely new dimension for research and applications in the established field of Josephson electronics. In this article we discuss basic Josephson circuits for qubit applications, methods of quantum description of these circuits, and circuit solutions for qubit couplings. Principles of manipulation and readout of superconducting qubits are reviewed and illustrated with recent experiments using various qubit types.
The superconducting qubit quantum computer is one of the most promising quantum computing architectures for large-scale integration due to its maturity and close proximity to the well-established semiconductor manufacturing infrastructure. From an education perspective, it also bridges classical microwave electronics and quantum electrodynamics. In this paper, we will review the basics of quantum computers, superconductivity, and Josephson junctions. We then introduce important technologies and concepts related to DiVincenzo's criteria, which are the necessary conditions for the superconducting qubits to work as a useful quantum computer. Firstly, we will discuss various types of superconducting qubits formed with Josephson junctions, from which we will understand the trade-off across multiple design parameters, including their noise immunity. Secondly, we will discuss different schemes to achieve entanglement gate operations, which are a major bottleneck in achieving more efficient fault-tolerant quantum computing. Thirdly, we will review readout engineering, including the implementations of the Purcell filters and quantum-limited amplifiers. Finally, we will discuss the nature and review the studies of two-level system defects, which are currently the limiting factor of qubit coherence time. DiVincenzo's criteria are only the necessary conditions for a technology to be eligible for quantum computing. To have a useful quantum computer, large-scale integration is required. We will review proposals and developments for the large-scale integration of superconducting qubit devices. By comparing with the application of electronic design automation (EDA) in semiconductors, we will also review the use of EDA in superconducting qubit quantum computer design, which is necessary for its large-scale integration.
Superconducting circuits based on Josephson junctions can exhibit macroscopic quantum coherence.Quantum computation with superconducting circuits is one of the most important research directions in the field of quantum information.Moreover,the study of the physical properties of superconducting circuits is an interdisciplinary area of both condensed matter physics and quantum optics.A brief overview is presented of the main results and advancements achieved so far,as well as future prospects,in the area of superconducting quantum computation.
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Research towards the realization of superconducting quantum computers is progressing rapidly. Recently, the number of integrated quantum bits (qubits) has begun to exceed 50 bits, and such quantum system has the potential capability to surpass that of any classical computer (quantum supremacy). To improve gate fidelity, research on qubits and surrounding environments are actively being studied. Which superconducting circuit will become the platform for quantum computers? What kind of technologies and theory will be used for quantum computers? In this paper, we cover many issues leading towards the realization of quantum computing systems.