Fundamentals of flux-based quantum computing

M. J. Feldman

Y. Harada, H. Nakane, Naoko Miyamoto +3 more

The basic operations of a Quantum Flux Parametron Circuit (QFP) are studied by means of computer simulation and fundamental experiments, and good agreement between experimental and simulation results is obtained. From these results, the basic operations of the QFP have been experimentally confirmed for the first time.

Hafiz Md. Hasan Babu

A. Yu. Dmitriev, O. V. Astafiev

Flux qubits are among the first qubits that were ever demonstrated. They have some advantages when compared to capacitively shunted charge qubits, which are now commonly used for building prototypes of quantum processors. Specifically, flux qubits are intrinsically nonlinear systems and they remain so even with low charging energies, which is important for the suppression of large charge noise in solids. In spite of the clear advantages of flux qubits, their applications in multi-qubit devices—prototypes of quantum computers and simulators—are still limited. Flux qubits are also a very powerful tool for fundamental research. In this paper, we discuss the basic properties of flux qubits using the radio frequency superconducting quantum interference device geometry—the most fundamental realization of flux qubits. We also compare and analyze experimental realizations of flux qubits and propose further directions for research.

Marek Kuś

Siyuan Han

This chapter focuses on the application of Nb Josephson junctions (JJs) in quantum annealing (QA). It begins with a brief introduction to diffident strategies for implementing quantum computation (QC) with an emphasis on quantum annealing. The chapter presents the basic physics of the simplest superconducting flux qubit: radio frequency superconducting quantum interference devices (RF-SQUID). It gives a brief description on the design and realization of couplers, and control and measurement circuitry using Nb Josephson junctions. The chapter describes a scalable architecture upon which quantum annealing processors consisting up to 1024 superconducting flux qubits made of more than 104 Nb Josephson junctions. It discusses evidence on whether D-Wave 2X, which is the latest quantum annealing processor available, works as expected. The chapter also focuses on the physics and application of RF-SQUID flux qubits because the fundamental building blocks of the most advanced quantum annealers demonstrated so far are variations of superconducting flux qubits with one Josephson junction, a.k.a. the RF-SQUID.