Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2411.11155 · Physical review. B./Physical review. B

Theory of three-terminal Andreev spin qubits

Aleksandr E. Svetogorov, Kiryl Piasotski, Wolfgang Belzig, Mikhail Pletyukhov

Published Sep 15, 2025• 1 citation
arXivHTMLPDF

Abstract

In this Letter, we introduce a next generation of Andreev spin qubits—three-terminal Andreev spin qubits. These qubits outperform two-terminal devices in the speed of two-qubit gates, benefiting from enhanced spin splitting. Our theoretical analysis reveals increased tunability and interqubit coupling mediated by the supercurrent. Furthermore, it provides a comprehensive explanation for the results of a recent experiment on a three-terminal device [M. Coraiola , ]. We identify the optimal operational regime for single- and two-qubit gates. Moreover, our concise theoretical framework for the equilibrium multiterminal Josephson effect offers significant potential for exploring nontrivial physics in the artificial dimensions of superconducting phase differences–—a rapidly growing field of research.

DOI
10.1103/55xn-c574

Related papers

Coupled superconducting spin qubits with spin-orbit interaction

Maria Spethmann, Xianpeng Zhang, Jelena Klinovaja +1 more

Superconducting spin qubits, also known as Andreev spin qubits, promise to combine the benefits of superconducting qubits and spin qubits defined in quantum dots. While most approaches to control these qubits rely on controlling the spin degree of freedom via the supercurrent, superconducting spin qubits can also be coupled to each other via the superconductor to implement two-qubit quantum gates. We theoretically investigate the interaction between superconducting spin qubits in the weak tunneling regime and concentrate on the effect of spin-orbit interaction (SOI), which can be large in semiconductor-based quantum dots and thereby offers an additional tuning parameter for quantum gates. We find analytically that the effective interaction between two superconducting spin qubits consists of Ising, Heisenberg, and Dzyaloshinskii-Moriya interactions and can be tuned by the superconducting phase difference, the tunnel barrier strength, or the SOI parameters. The Josephson current becomes dependent on SOI and spin orientations. We demonstrate that this interaction can be used for fast controlled phase-flip gates with a fidelity >99.99%. We propose a scalable network of superconducting spin qubits which is suitable for implementing the surface code.

arXiv:2205.03843•Physical review. B./Physical review. B•Sep 12, 2022•21 citations

Novel qubits in hybrid semiconductor-superconductor nanostructures

Marta Pita-Vidal, Rubén Seoane Souto, Srijit Goswami +4 more

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.

cond-mat.mes-hallCross-listedarXiv:2512.23336•Dec 30, 2025•1 citation

Superconducting singlet-triplet qubits

Anatoliy Lotkov, Maria Spethmann, Daniel Loss

Hybrid devices integrating quantum dots with Josephson junctions are gaining interest because they combine spin-based quantum computing with circuit quantum electrodynamics (circuit QED) methods. In particular, Andreev spin qubits have shown significant experimental progress including strong two-qubit coupling, and are predicted to exhibit all-to-all connectivity. Here we propose superconducting singlet-triplet (SST) qubits that rely on parallel-aligned double quantum dots in Josephson junctions. While Andreev spin qubits require spin-orbit interaction to unlock the spin degree-of-freedom, SST qubits do not require spin-orbit interaction, making the advantages of hybrid devices available to a wider range of materials. Similar to Andreev spin qubits, the qubit states couple to the superconducting phase across the junction, which allows for control and readout using circuit QED, and supports all-to-all connectivity. Only $N$ flux lines are required to perform any single- and two-qubit gate among $N$ qubits, and thus the overhead of control lines is small. Finally, linear protection from charge or flux noise makes these qubits interesting candidates for a future quantum processor.

quant-pharXiv:2607.09508•Jul 13, 2026•0 citations

Theoretical proposal for superconducting spin qubits

Ciprian Padurariu, Yuli V. Nazarov

We propose and theoretically investigate superconducting spin qubits. Superconducting spin qubit consists of a single spin confined in a Josephson junction. We show that owing to spin-orbit interaction, superconducting phase difference across the junction can polarize this spin. We demonstrate that this enables single-qubit operations and more complicated quantum gates, where spins of different qubits interact via a mutual inductance of the superconducting loop where the junctions are embedded. Recent experimental realizations of Josephson junctions made of semiconductor quantum dots in contact with superconducting leads have shown that the number of electrons in the quantum dot can be tuned by a gate voltage. Superconducting spin qubit is realized when the number of electrons is odd. We discuss the qubit properties at phenomenological level. We present a microscopic theory that enables us to make accurate estimations of the qubit parameters by evaluating the spin-dependent Josephson energy in the framework of fourth-order perturbation theory.

arXiv:0912.3910•Physical Review B•Apr 29, 2010•108 citations

Fast readout of quantum dot spin qubits via Andreev spins

Anonymous, Katharina Laubscher, Patrick Del Vecchio +3 more

Spin qubits in semiconducting quantum dots are currently limited by slow readout processes, which are orders of magnitude slower than gate operations. In contrast, Andreev spin qubits benefit from fast measurement schemes enabled by the large resonator couplings of superconducting qubits but suffer from reduced coherence during qubit operations. Here, we propose fast and high-fidelity measurement protocols based on an electrically tunable coupling between quantum dot and Andreev spin qubits. In realistic devices, this coupling can be made sufficiently strong to enable high-fidelity readout well below microseconds, potentially enabling mid-circuit measurements. Crucially, the electrical tunability of our coupler permits to switch it off during idle periods, minimizing crosstalk and measurement back-action. Our approach is fully compatible with germanium-based devices and paves the way for scalable quantum computing architectures by leveraging the advantages of heterogeneous qubit implementations.

arXiv:2506.19762•Physical Review Applied•Aug 5, 2026•0 citations

Inductively-protected Andreev (IPA) spin qubit

J. L. del Olmo N., F. J. Matute-Cañadas, A. Levy Yeyati +2 more

The spin of a quasiparticle trapped in a quantum dot Josephson junction forms the basis of an Andreev spin qubit (ASQ): a semiconductor-superconductor device where the interplay between a localized spin degree of freedom and superconductivity leads to a spin-resolved Josephson potential. In this work, we show that shunting an ASQ with a linear inductor enhances its relaxation time by separating the spin-qubit states into distinct potential wells in phase space, nearly eliminating wavefunction overlap. The resulting inductively protected Andreev (IPA) spin qubit is equivalent to two fluxoniums in the heavy regime, one for each spin. Thus, the IPA qubit combines the long coherence times, low-frequency ground-state manifold, and large anharmonicity of a protected superconducting qubit with the operational advantages of a spin degree of freedom.

cond-mat.mes-hallCross-listedarXiv:2608.13530•Aug 14, 2026•0 citations
In this Letter, we introduce a next generation of Andreev spin qubits—three-terminal Andreev spin qubits. These qubits outperform two-terminal devices in the speed of two-qubit gates, benefiting from enhanced spin splitting. Our theoretical analysis reveals increased tunability and interqubit coupling mediated by the supercurrent. Furthermore, it provides a comprehensive explanation for the results of a recent experiment on a three-terminal device [M. Coraiola , ]. We identify the optimal operational regime for single- and two-qubit gates. Moreover, our concise theoretical framework for the equilibrium multiterminal Josephson effect offers significant potential for exploring nontrivial physics in the artificial dimensions of superconducting phase differences–—a rapidly growing field of research.
Superconducting spin qubits, also known as Andreev spin qubits, promise to combine the benefits of superconducting qubits and spin qubits defined in quantum dots. While most approaches to control these qubits rely on controlling the spin degree of freedom via the supercurrent, superconducting spin qubits can also be coupled to each other via the superconductor to implement two-qubit quantum gates. We theoretically investigate the interaction between superconducting spin qubits in the weak tunneling regime and concentrate on the effect of spin-orbit interaction (SOI), which can be large in semiconductor-based quantum dots and thereby offers an additional tuning parameter for quantum gates. We find analytically that the effective interaction between two superconducting spin qubits consists of Ising, Heisenberg, and Dzyaloshinskii-Moriya interactions and can be tuned by the superconducting phase difference, the tunnel barrier strength, or the SOI parameters. The Josephson current becomes dependent on SOI and spin orientations. We demonstrate that this interaction can be used for fast controlled phase-flip gates with a fidelity >99.99%. We propose a scalable network of superconducting spin qubits which is suitable for implementing the surface code.
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.
Hybrid devices integrating quantum dots with Josephson junctions are gaining interest because they combine spin-based quantum computing with circuit quantum electrodynamics (circuit QED) methods. In particular, Andreev spin qubits have shown significant experimental progress including strong two-qubit coupling, and are predicted to exhibit all-to-all connectivity. Here we propose superconducting singlet-triplet (SST) qubits that rely on parallel-aligned double quantum dots in Josephson junctions. While Andreev spin qubits require spin-orbit interaction to unlock the spin degree-of-freedom, SST qubits do not require spin-orbit interaction, making the advantages of hybrid devices available to a wider range of materials. Similar to Andreev spin qubits, the qubit states couple to the superconducting phase across the junction, which allows for control and readout using circuit QED, and supports all-to-all connectivity. Only NNN flux lines are required to perform any single- and two-qubit gate among NNN qubits, and thus the overhead of control lines is small. Finally, linear protection from charge or flux noise makes these qubits interesting candidates for a future quantum processor.
We propose and theoretically investigate superconducting spin qubits. Superconducting spin qubit consists of a single spin confined in a Josephson junction. We show that owing to spin-orbit interaction, superconducting phase difference across the junction can polarize this spin. We demonstrate that this enables single-qubit operations and more complicated quantum gates, where spins of different qubits interact via a mutual inductance of the superconducting loop where the junctions are embedded. Recent experimental realizations of Josephson junctions made of semiconductor quantum dots in contact with superconducting leads have shown that the number of electrons in the quantum dot can be tuned by a gate voltage. Superconducting spin qubit is realized when the number of electrons is odd. We discuss the qubit properties at phenomenological level. We present a microscopic theory that enables us to make accurate estimations of the qubit parameters by evaluating the spin-dependent Josephson energy in the framework of fourth-order perturbation theory.
Spin qubits in semiconducting quantum dots are currently limited by slow readout processes, which are orders of magnitude slower than gate operations. In contrast, Andreev spin qubits benefit from fast measurement schemes enabled by the large resonator couplings of superconducting qubits but suffer from reduced coherence during qubit operations. Here, we propose fast and high-fidelity measurement protocols based on an electrically tunable coupling between quantum dot and Andreev spin qubits. In realistic devices, this coupling can be made sufficiently strong to enable high-fidelity readout well below microseconds, potentially enabling mid-circuit measurements. Crucially, the electrical tunability of our coupler permits to switch it off during idle periods, minimizing crosstalk and measurement back-action. Our approach is fully compatible with germanium-based devices and paves the way for scalable quantum computing architectures by leveraging the advantages of heterogeneous qubit implementations.
The spin of a quasiparticle trapped in a quantum dot Josephson junction forms the basis of an Andreev spin qubit (ASQ): a semiconductor-superconductor device where the interplay between a localized spin degree of freedom and superconductivity leads to a spin-resolved Josephson potential. In this work, we show that shunting an ASQ with a linear inductor enhances its relaxation time by separating the spin-qubit states into distinct potential wells in phase space, nearly eliminating wavefunction overlap. The resulting inductively protected Andreev (IPA) spin qubit is equivalent to two fluxoniums in the heavy regime, one for each spin. Thus, the IPA qubit combines the long coherence times, low-frequency ground-state manifold, and large anharmonicity of a protected superconducting qubit with the operational advantages of a spin degree of freedom.