Recent improvements in materials growth and fabrication techniques may finally allow for superconducting semiconductors to realize their potential. Here, we build on a recent proposal to construct superconducting devices such as wires, Josephson junctions, and qubits inside and out-of single crystal silicon or germanium. Using atomistic fabrication techniques such as STM hydrogen lithography, heavily doped superconducting regions within a single crystal could be constructed. We describe the characteristic parameters of basic superconducting elements-a 1-D wire and a tunneling Josephson junction-and estimate the values for boron-doped silicon. The epitaxial, single-crystal nature of these devices, along with the extreme flexibility in device design down to the single-atom scale, may enable lower noise or new types of devices and physics. We consider applications for such supersilicon devices, showing that the state-of-the-art transmon qubit and the sought-after phase-slip qubit can both be realized. The latter qubit leverages the natural high kinetic inductance of these materials. Building on this, we explore how kinetic inductance-based particle detectors (e.g., photon or phonon) could be realized with potential application in astronomy or nanomechanics. We discuss supersemi devices (such as in silicon, germanium, or diamond) which would not require atomistic fabrication approaches and could be realized today.
Recent improvements in materials growth and fabrication techniques may finally allow for superconducting semiconductors to realize their potential. Here, we build on a recent proposal to construct superconducting devices such as wires, Josephson junctions, and qubits inside and out-of single crystal silicon or germanium. Using atomistic fabrication techniques such as STM hydrogen lithography, heavily doped superconducting regions within a single crystal could be constructed. We describe the characteristic parameters of basic superconducting elements-a 1-D wire and a tunneling Josephson junction-and estimate the values for boron-doped silicon. The epitaxial, single-crystal nature of these devices, along with the extreme flexibility in device design down to the single-atom scale, may enable lower noise or new types of devices and physics. We consider applications for such supersilicon devices, showing that the state-of-the-art transmon qubit and the sought-after phase-slip qubit can both be realized. The latter qubit leverages the natural high kinetic inductance of these materials. Building on this, we explore how kinetic inductance-based particle detectors (e.g., photon or phonon) could be realized with potential application in astronomy or nanomechanics. We discuss supersemi devices (such as in silicon, germanium, or diamond) which would not require atomistic fabrication approaches and could be realized today.
This article reviews recent progress in superconducting nanodevices, with particular emphasis on fabrication methods developed for superconducting nanowires and nanoscale Josephson junctions based on different barrier materials. It evaluates the future potential of superconducting nanodevices, including nano-superconducting quantum interference devices (nanoSQUIDs), in light of improvements in nanoscale fabrication and manipulation techniques, along with their likely impacts on future quantum technology and measurement. The article first considers efforts to realize devices at the physical scale of 100 nm and below before discussing different types of Josephson junction such as trilayer junctions. It also describes the use of focused ion beam milling and electron beam lithography techniques for junction fabrication at the nanoscale and the improved energy sensitivity detectable with a nanoSQUID. Finally, it looks at a range of applications for nanoSQUIDs, superconducting single photon detectors, and other superconducting nanodevices.
Superconducting qubit based on superconducting circuits consist of a superconducting capacitor and a Josephson junction with the transmon geometry is extensively used in advanced quantum processors, pursuing scalable quantum computing. The tuning of the qubit frequency of the transmon relies on magnetic flux-dependent interference between the supercurrents of two superconductor-insulator-superconductor (S-I-S) Josephson junctions in a superconducting loop. Josephson junction based on superconductor-semiconductor-superconductor (S-Sm-S) materials opens up a possibility to the gate-tunable transmon, referred to as the "gatemon", in which the qubit frequency can be tuned by electrostatic mean. Recent realizations of gatemons on III-V material platforms show impressive development on the alternative to the transmon, yet still leave a big question on the scalability. The silicon-germanium (SiGe) heterostructure is one of the potential platforms to host hybrid devices due to its high hole mobility and the low Schottky barrier at the Ge-metal interface. Additionally, the compatibility with the silicon-based semiconductor industry is a capable advantage for the scaling-up qubit platform.In this thesis, we develop gatemons based on the Al-Ge-Al Josephson junction in the SiGe heterostructure. Firstly, the robust fabrication recipe, found on a top-down approach, for Josephson Field Effect Transistors (JoFETs) is established. We perform measurements exhaustively on the JoFETs to study their properties as a function of the gate voltage, temperature, and magnetic field. The devices show gate-tunability of the critical current and the normal state resistance . The devices are estimated to have a high-transparency superconductor-semiconductor interface, as demonstrated by the high product on the SiGe heterostructure. In the finite-voltage regime, the features corresponded to multiple Andreev reflections (MARs) are observed. Then, we fabricate and characterize niobium nitride (NbN) superconducting resonators on SiGe heterostructure. We measure the resonators in the transmission mode and extract the resonant frequency , internal quality factor, and coupling quality factor from the transmission coefficient. Following that, we develop the fabrication process to integrate Al-Ge-Al junctions shunted with capacitors, or, in other words, gatemon, into the resonator scheme and perform the fabrication according to the design. We demonstrate the anticrossing feature in one of the fabricated gatemons. The resonant frequency of the gatemon is mapped using the two-tone spectroscopy technique and is found to be gate-tunable. The qubit has large spectral linewidth, implying a low coherence time. Additionally, we conduct the current-phase relationship (CPR) measurement on the junctions in the Superconducting QUantum Interference Device (SQUID) geometry. We can demonstrate that the junctions pose non-sinusoidal CPR. Further, the integer and half-integer Shapiro steps are observed in the current-voltage characteristic curves of irradiated junctions. This indicates that our junctions have the element, which can open up another possibility toward protected qubits.
Superconducting qubit based on superconducting circuits consist of a superconducting capacitor and a Josephson junction with the transmon geometry is extensively used in advanced quantum processors, pursuing scalable quantum computing. The tuning of the qubit frequency of the transmon relies on magnetic flux dependent interference between the supercurrents of two superconductor-insulator superconductor(S-I-S) Josephson junctions in a superconducting loop. Josephson junction based on superconductor-semiconductor-superconductor (S-Sm-S) materialsopens up a possibility to the gate-tunable transmon, referred to as the "gatemon", in which the qubit frequency can be tuned by electrostatic mean. Recent realizations of gatemons on III-V material platforms show impressive development on the alternative to the transmon, yet still leave a big question on the scalability. The silicon-germanium (SiGe) heterostructure is one of the potential platforms to host hybrid devices due to its high hole mobility and the low Schottky barrier at the Ge-metal interface. Additionally, the compatibility with the silicon-based semiconductor industry is a capable advantage for the scaling-up qubit platform.In this thesis, we develop gatemons based on the Al-Ge-Al Josephson junction in the SiGe heterostructure. Firstly, the robust fabrication recipe, found on a top down approach, for Josephson Field Effect Transistors (JoFETs) is established. We perform measurements exhaustively on the JoFETs to study their properties as a function of the gate voltage, temperature, and magnetic field. The devices show gate-tunability of the critical current (IC) and the normal state resistance (RN). The devices are estimated to have a high-transparency superconductor/semiconductor interface, as demonstrated by the high ICRN product on the SiGe heterostructure. In the finite-voltage regime, the features corresponded to multiple Andreev reflections (MARs) are observed. Then, we fabricate and characterize niobium nitride (NbN) superconducting resonators on SiGe heterostructure. We measure the resonators in the transmission mode and extract the resonant frequency (fr), internal quality factor (Qi), and coupling quality factor (Qc) from the transmission coefficient (S21). Following that, we develop the fabrication process to integrate Al-Ge-Al junctions shunted with capacitors, or, in other words,gatemon, into the resonator scheme and perform the fabrication according to the design. We demonstrate the anticrossing feature in one of the fabricated gatemons. The resonant frequency of the gatemon is mapped using the two-tone spectroscopy technique and is found to be gate-tunable. The qubit has large spectral linewidth, implying a low coherence time. Additionally, we conduct the current-phase relationship (CPR) measurement on the junctions in the Superconducting QUantum Interference Device (SQUID) geometry. We can demonstrate that the junctions pose non-sinusoidal CPR. Further, the integer and half-integer Shapiro steps are observed in the current-voltage characteristic curves of irradiated junctions. This indicates that our junctions have the cos 2φ element, which can open up another possibility toward protected qubits.
Superconducting and photonic qubits are the two promising platforms for quantum computation. This review investigates different materials that are being used to advance these platforms, detailing the structural, electrical, and thermal properties that influence qubit performance. The discussion on superconducting qubits covers material properties critical for achieving low-loss circuits, the impact of two-level system defects, and the engineering of Josephson junctions. In contrast, photonic qubits, which leverage light for quantum information processing, are examined through the lens of material platforms such as silicon-based photonics and III–V semiconductors. The chapter also highlights fabrication challenges, qubit coherence improvements, and recent advances in single-photon sources for scalable quantum systems. By analyzing the intersection of materials science, quantum mechanics, and device engineering, this review provides insights into the optimization of quantum hardware for future large-scale quantum computing applications.
In the upcoming decades quantum technologies, especially quantum computation, will have a strong influence on industrial, technological, economic, and social progress and are, therefore, considered to be one of the key technologies. The fundamental building blocks for quantum computation are quantum bits (qubits). The superconducting platform offers one of the most promising implementations due to its monolithic character and potential for scalability. Present research around the world primarily focusses on scaling up the number of qubits, so reliable wafer-scale fabrication technologies are mandatory. In this paper, we present our recent developments on wafer-scale fabrication of superconducting quantum circuits including Josephson junctions by the Manhattan-type technology. We discuss fabrication parameters as well as electrical characterization. For arrays out of 50 Josephson junctions with structure dimensions of 200 nm × 200 nm, we achieve a critical current standard deviation of approx. 3% on-chip and 7% on-wafer. We also show first measurement results of so fabricated transmon-type qubits with relaxation and decoherence times ofT1= 12.5 µs andT2= 15.0 µs, respectively. With an increasing number of superconducting qubits and, thus, their input and read-out lines, new challenges arise: Crosstalk between qubits, unwanted modes in the qubit environment, and required interconnections. One way to counteract is the implementation of low inductance connections across coplanar waveguides. This can be realized by aluminum air bridges. In this paper we discuss the air bridges’ fabrication parameters and the impact on the integrated circuits’ elements, e.g., Josephson junctions. We show electrical and superconducting measurements with critical temperatures and critical currents ofTc> 1.0 K andIc> 0.6 mA, respectively.
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.