Superconducting quantum devices provide excellent connectivity and controllability, while semiconductor spin qubits stand out with their long-lasting quantum coherence, fast control, and potential for miniaturization and scaling. In the last few years, remarkable progress has been made in combining superconducting circuits and semiconducting devices into hybrid quantum systems that benefit from the physical properties of both constituents. Superconducting cavities can mediate quantum-coherent coupling over long distances between electronic degrees of freedom such as the spin of individual electrons on a semiconductor chip and, thus, provide essential connectivity for a quantum device. Electron spins in semiconductor quantum dots have reached very long coherence times and allow for fast quantum gate operations with increasing fidelities. We summarize recent progress and theoretical models that describe superconducting–semiconducting hybrid quantum systems, explain the limitations of these systems, and describe different directions where future experiments and theory are headed.
Superconducting quantum devices provide excellent connectivity and controllability, while semiconductor spin qubits stand out with their long-lasting quantum coherence, fast control, and potential for miniaturization and scaling. In the last few years, remarkable progress has been made in combining superconducting circuits and semiconducting devices into hybrid quantum systems that benefit from the physical properties of both constituents. Superconducting cavities can mediate quantum-coherent coupling over long distances between electronic degrees of freedom such as the spin of individual electrons on a semiconductor chip and, thus, provide essential connectivity for a quantum device. Electron spins in semiconductor quantum dots have reached very long coherence times and allow for fast quantum gate operations with increasing fidelities. We summarize recent progress and theoretical models that describe superconducting–semiconducting hybrid quantum systems, explain the limitations of these systems, and describe different directions where future experiments and theory are headed.
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.
Semiconductor qubits rely on the control of charge and spin degrees of freedom of electrons or holes confined in quantum dots (QDs). Typically, semiconductor qubit-qubit coupling is short range, effectively limiting qubit distance to the spatial extent of the wavefunction of the confined particle (a few hundred nanometers). This is a significant constraint towards scaling of QD-based architectures to realize dense 1D or 2D arrays of QDs. Inspired by techniques originally developed for circuit QED, we recently demonstrated the strong coupling of individual electrons confined in GaAs quantum dots to individual microwave photons, making use of the enhanced electric component of the vacuum fluctuations of a resonator with impedance beyond the typical 50 Ohm of standard coplanar waveguides. In this hybrid technology, we recently realized a proof of concept experiment, where the coupling between a transmon and a double QD (DQD) is mediated by virtual microwave photon excitations in a high impedance SQUID array resonator, which acts as a quantum bus enabling long-range coupling between dissimilar qubits. Similarly, we achieved coherent coupling between two DQD charge qubits separated by approximately 50 um. In the dispersive regime, we spectroscopically observed qubit-qubit coupling as an avoided-crossing in the energy spectrum of the DQD charge qubits. The methods and techniques developed in this work are transferable to QD devices based on other material systems and can be beneficial for spin based hybrid systems.
Hybrid systems comprising superconducting and semiconducting materials are promising architectures for quantum computing. Superconductors induce long-range interactions between the spin degrees of freedom of semiconducting quantum dots. These interactions are widely anisotropic when the semiconductor material has strong spin-orbit interactions. We show that this anisotropy is tunable and enables fast and high-fidelity two-qubit gates between singlet-triplet (ST) spin qubits. Our design is immune to leakage of the quantum information into noncomputational states and removes always-on interactions between the qubits, thus resolving key open challenges for these architectures. Our ST qubits do not require additional technologically demanding components nor fine-tuning of parameters. They operate at low magnetic fields of a few millitesla and are fully compatible with superconductors. By suppressing systematic errors in realistic devices, we estimate infidelities below ${10}^{\ensuremath{-}3}$, which could pave the way toward large-scale hybrid superconducting-semiconducting quantum processors.
Coupling single spins to superconducting circuits represents a powerful route toward scalable hybrid quantum technologies. At the intersection of quantum information processing, nanoscale sensing, and condensed matter physics, this emerging research direction aims to unite the best qualities of two very different quantum systems. Spins—whether associated with electrons, nuclei, or defects—are among the most coherent quantum systems known, with coherence times that can exceed seconds. However, their weak interaction with electromagnetic fields makes them notoriously difficult to control and read out individually. Superconducting circuits, on the other hand, offer exceptional control, scalability, and strong coupling to electromagnetic fields, but they tend to suffer from shorter coherence times. Bridging these two platforms can yield hybrid quantum systems that harness the best of both worlds: the long-lived quantum memory of spins and the fast, flexible control of superconducting devices. An additional key motivation for integrating single spins with superconducting circuits is the ability to perform spectroscopy at the nanoscale, enabling the investigation of quantum systems with unprecedented spatial and energy resolution. Spins, due to their sensitivity to magnetic and electric fields, serve as exquisite local probes of their environment. This synergy not only offers powerful tools for probing quantum phenomena at the nanoscale but also opens the possibility of hybrid quantum processors combining long-lived spin states with fast superconducting-circuit control.
Quantum computing is the outcome of the size of semiconductor chips breaking the limits of classical physics, and is a landmark technology in the post-Moore's law era. Making use of the quantum properties of electrons in semiconductor quantum dots is believed to be one of the most promising candidates for the realization of quantum computing. In recent years, a series of breakthroughs have been made, including the preparation and readout of qubits, and the manipulation of quantum logic gates. This paper first introduces the background and significance of research on semiconductor quantum dot-based quantum computing and then provides an overview of the developments regarding spin-, charge-, and few-electron-based qubits, as well as the long distance coherent coupling of qubits. Finally, we discuss future trends in semiconductor-based quantum computing.
Physics
Today's (very rudimentary) quantum computers come in different guises, each with their own set of pros and cons. A growing trend has been to put two different technologies together in hybrid architectures in order to have the best of both worlds. One of the aims of such initiatives is to realize long-distance coupling between spin qubits (quantum bits based on electron spins) in quantum dots (zero-dimensional semiconductor nanostructures that allow controlled coupling of one or more electrons) via interactions with a superconducting microwave cavity. Petersson et al. made progress toward that goal by coupling a double quantum dot in an InSb nanowire to the electric field of a cavity, taking advantage of the strong spin-orbit interaction of InSb. The coupling was demonstrated by using a pulse sequence to electrically control the spin state, which was then read out in the phase response of the cavity. The estimated spin-cavity coupling is still shy of the strong limit required for two distant spin qubits to communicate; however, it is expected that improving the quality of the cavity and the coherence of the qubit, and/or using a material with stronger spin-orbit interactions, will bring physicists closer to that goal.
Nature 490 , 380 (2012).