Advancements in superconducting quantum computing

Abstract

Superconducting quantum computing (SQC) has achieved remarkable progress in recent years, garnering significant scientific and technological interests. This review provides a concise overview of the historical development of SQC, detailing fabrication methodologies for superconducting quantum chips and implementations of quantum gate operations. It compiles experimental progress in SQC over the past few years, including the preparation of multi-qubit entangled states, random circuit sampling experiments, demonstrations of quantum error correction based on surface codes, error mitigation techniques and quantum simulations. This review also discusses experimental progress related to boson-encoded qubits, fluxoniums and qudits. Finally, the current challenges in scaling are analyzed, and potential solutions for addressing these limitations are explored.

Keywords: quantum error correction; quantum gate; quantum simulation; superconducting quantum computing; superconducting qubit.

Figure 1.

Energy relaxation time reported over the past years for SC qubits. The references are [17,22,24–29] for the transmon qubits, [30–33] for the fluxonium qubits and [34–37] for the bosonic qubits.

Figure 2.

Bloch-sphere representation and common operations of single-qubit gates. (a) An arbitrary single-qubit gate as a rotation in the Bloch picture. (b) List of a few common single-qubit gate operations.

Figure 3.

Weyl chamber and two-qubit gates. (a) Weyl chamber and common two-qubit gates marked with their coordinates. (b) List of selected two-qubit gate operations and corresponding unitary matrices.

Figure 4.

Advancements in cavity-based superconducting qubits. Cavity-based superconducting qubits are propelling the field of quantum information science forward with their applications in QEC and modular quantum computation. A limited set of examples is highlighted in this illustration. For QEC, cavity-based qubits are utilized in the development of bosonic codes, which enhance the fault tolerance of quantum systems. Reprinted with permission from [219–223]. Additionally, cavity-based qubits are integral to modular quantum computation, facilitating the execution of teleported CNOT gates and enabling the use of SNAIL- (superconducting non-linear asymmetric inductive element) based couplers to establish robust quantum networks. Reprinted with permission from [224–227].

Figure 5.

Full-stack architecture of a fluxonium. (a) Schematic of the fluxonium circuit, consisting of a Josephson junction (critical current ), a loop inductor (L) and a shunt capacitor (C). (b) Optical micrograph of a typical fluxonium qubit device. (c) Scanning electron microscopy (SEM) image of the qubit loop structure, highlighting the Josephson junction and junction array (blue box in (b)). (d) SEM images of the Josephson junction (orange box) and the junction array (green box). (e) Qubit eigenstate wave functions and energies are on a phase basis. (f) Transition matrix elements of the flux () and charge (Q) operators.