Novel qubits in hybrid semiconductor-superconductor nanostructures

TL;DR

This review surveys the emergence of hybrid semiconductor–superconductor qubits, focusing on gate-tunable Josephson junctions, subgap physics, and topological concepts. It integrates materials science advances (epitaxial interfaces, SOC, g-factors) with device architectures that fuse circuit-QED control and proximity-induced superconductivity. A central thread is the exploration of Andreev-bound-state–based qubits, Andreev spin qubits, and Majorana-based topological qubits, including minimal Kitaev chains, parity readout, and scalable coupling. The work highlights how bottom-up and top-down approaches complement each other, offering pathways toward protected quantum information processing and potential fault-tolerant platforms, while detailing outstanding experimental and theoretical challenges to realize practical quantum computation with hybrid qubits.

Abstract

Hybrid semiconductor-superconductor qubits have recently emerged as a promising alternative to traditional platforms, combining material advantages with device-level tunability. A defining feature is their gate-tunable Josephson coupling, enabling superconducting qubit architectures with full electric-field control and offering a path toward scalable, low-crosstalk quantum processors. This approach seeks to merge benefits of superconducting and semiconductor qubits, for instance by encoding quantum information in the spin of a quasiparticle occupying an Andreev bound state, thus combining long coherence times with fast, flexible control. Progress has accelerated through bottom-up engineering of Andreev states in coupled quantum dot arrays, leading to architectures such as minimal Kitaev chains hosting Majorana zero modes. In parallel, Hamiltonian-protected designs aim to enhance resilience against local noise and decoherence by exploiting superconducting phase dynamics and discrete charge or flux degrees of freedom. This article reviews recent theoretical and experimental advances in hybrid qubits, providing an overview of physical mechanisms, device implementations, and emerging architectures, with emphasis on their potential for (topologically) protected quantum information processing. While many designs remain at proof-of-concept stage, rapid progress suggests practical demonstrations may soon be achievable.

Figures (56)

• Figure 1: Schematics of various solid-state qubit platforms and their typical physical sizes: from the smallest, spin qubits based on semiconductor quantum dots (red circles), with typical sizes around $100nm$, to superconducting qubit realizations (blue elements) with sizes exceeding $100 \mu m$. The hybrid semiconductor-superconductor devices discussed in this review, like e.g minimal arrays of quantum dots coupled to superconductors, combine advantages of the two different platforms like the relatively small footprint of semiconductors combined with circuit-QED readout techniques of superconducting qubits.
• Figure 2: (a) Illustration of a Josephson junction. (b) False-colored scanning electron micrograph of a Josephson junction. Here, green indicates the silicon substrate, blue the niobium base-layer, and gray the aluminum that defined the junction where the two electrodes cross. The big squares of aluminum ensures good electric contact between the thin aluminum electroces and the niobium base-layer. Adapted and reprinted from Ref. colao2025mitigating.
• Figure 3: Frequency ($=$ Energy divided by $\hbar$) difference of the first three energy levels of the CPB Hamiltonian. For small $E_J$, we note the locally charge insensitive points at $N_g = \pm 1$, where we can operate the CPB as a qubit. For large values of $E_J$ compared to $E_C$, the energy levels become fully insensitive to $N_g$ and, thus, insensitive to charge noise. Adapted and reprinted from Ref. Blais2021.
• Figure 4: Progress of superconducting charge qubits over the past two decades. (a) The experimental realization of a superconducting qubit by Nakamura et al. Nakamura1999, demonstrated coherent Rabi oscillations in a superconducting qubits for the first time. (b) First-generation transmon qubit device by Houck et al. Houck2007 operating in the regime $E_J \gg E_C$. Note that the capacitor is large compared to the Josephson junction and, therefore, the Josephson junction in the center of the transmon is barely visible in the image. (c) Tantalum device from Place et al. place2021new, where coherence times were extended to several hundreds of microseconds by mitigating dielectric loss through geometric and material engineering. (d) State-of-the-art device from Bland et al. bland20252d, demonstrating qubit lifetimes exceeding 1 ms. Panels (a), (b), (c) and (d) are adapted and reprinted from Refs. Nakamura1999, Houck2007, place2021new and bland20252d, respectively.
• Figure 5: (a) Flux qubit from Ref. Chiorescu2003, which was the first flux qubit. The qubit loop is at the top of the device, indicated with an arrow, with three Josephson junctions in series. (b) and (c) Improved flux qubit from Ref. yan2016flux which shunted a flux loop with a large capacitor. (d) Fluxonium qubit from Ref. Nguyen2019. The flux loop consist of a small junction and a array of large junctions acting as a linear inductor.