It is pointed out that superconducting microstrip transmission lines operating in the kinetic-inductance limit have the potential to reduce the size and weight of microwave circuits by several orders of magnitude. Since the phase velocity of these guided wave structures is up to a hundred times less than in free space, the electrical length of distributed elements is similarly reduced. Simple transmission lines have been fabricated from both low- and high-transition-temperature superconductors while more complicated circuits, such as filters, with a good match to 50- Omega coax have been fabricated with the low-transition-temperature superconductors. Also, a novel coupled-line topology, compatible with these structures, has been studied analytically.>
Abstract Tantalum (Ta) has recently received considerable attention in manufacturing robust superconducting quantum circuits. Ta offers low microwave loss, high kinetic inductance compared to aluminium (Al) and niobium (Nb), and good compatibility with complementary metal-oxide-semiconductor (CMOS) technology, which is essential for quantum computing applications. Here we demonstrate the fabrication engineering of thickness-dependent high-quality-factor (high-
Qi ) Ta superconducting microwave coplanar waveguide resonators. All films are deposited on high-resistivity silicon substrates at room temperature without additional substrate heating. Before Ta deposition, a niobium (Nb) seed layer is used to promote a body-centred cubic lattice (
α -Ta) formation. We further engineer the kinetic inductance (
LK ) of the resonators by varying Ta film thicknesses. High
LK is a key advantage for applications because it facilitates the realisation of high-impedance, compact quantum circuits with enhanced coupling to qubits. The maximum internal quality factor
Qi of
∼ 3.6 × 10 6 in the high power regime and
Qi of
∼ 4.5 × 10 5 in the single-photon regime is achieved for 100 nm Ta which represents an improvement over previous room-temperature deposited Ta resonators on silicon substrates in the single photon regime, while the highest kinetic inductance of 0.6 pH/sq is obtained for the thinnest film, which is 40 nm. This combination of high
Qi and high
LK highlights the potential of Ta microwave circuits for high-fidelity operation of compact quantum circuits.
This research presents the integration of ultra low loss (<1dB/cm) silicon nitride waveguides with a superconducting single photon detector with photon number resolving (PNR) capability - the Microwave Kinetic Inductance Detector - introducing a new photonic integrated circuit platform. Our approach is to integrate waveguides and MKIDs on a sapphire substrate, which minimizes the two level system noise for the MKIDs and serves as a bottom cladding for waveguides. Silicon nitride is used as the core of the waveguides and either SiO2 or SiOxNy is used as the top cladding. We present findings on how the fabrications processes -- including the materials used and the method of deposition -- affect the quality of the MKIDs and waveguides. The integrated system would ultimately be used to make photon number resolving detectors for quantum information applications and high resolution spectrometers for astrophysics and metrology applications.
Developing compact, low-dissipation, cryogenic-compatible microwave electronics is essential for scaling up low-temperature quantum computing systems. In this paper, we demonstrate an ultracompact microwave directional forward coupler based on high-impedance slow-wave superconducting-nanowire transmission lines. The coupling section of the fabricated device has a footprint of $416\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}{\mathrm{m}}^{2}$. At 4.753 GHz, the input signal couples equally to the through port and forward-coupling port (50:50) at $\ensuremath{-}6.7\phantom{\rule{0.2em}{0ex}}\mathrm{dB}$ with $\ensuremath{-}13.5\phantom{\rule{0.2em}{0ex}}\mathrm{dB}$ isolation. The coupling ratio can be controlled with dc bias current or temperature by exploiting the dependence of the kinetic inductance on these quantities. The material and fabrication processes are suitable for direct integration with superconducting circuits, providing a practical solution to the signal distribution bottlenecks in developing large-scale quantum computers.
Abstract Superconducting microwave metamaterials offer enormous potential for quantum optics and information science, enabling the development of advanced quantum technologies for sensing and amplification. In the context of circuit quantum electrodynamics, such metamaterials can be implemented as coupled cavity arrays (CCAs). In the continuous effort to miniaturize quantum devices for increasing scalability, minimizing the footprint of CCAs while preserving low disorder becomes paramount. In this work, we present a compact CCA architecture using superconducting NbN thin films manifesting high kinetic inductance. The latter enables high-impedance CCA (~1.5 kΩ), while reducing the resonator footprint. We demonstrate its versatility and scalability by engineering one-dimensional CCAs with up to 100 resonators and with structures that exhibit multiple bandgaps. Additionally, we quantitatively investigate disorder in the CCAs using symmetry-protected topological SSH edge modes, from which we extract a resonator frequency scattering of
0.22−0.03+0.04% 0.2 2 − 0.03 + 0.04 % . Our platform opens up exciting prospects for analog quantum simulations of many-body physics with ultrastrongly coupled emitters.
Tantalum (Ta) has recently received considerable attention in manufacturing robust superconducting quantum circuits. Ta offers low microwave loss, high kinetic inductance compared to aluminium (Al) and niobium (Nb), and good compatibility with complementary metal-oxide-semiconductor (CMOS) technology, which is essential for quantum computing applications. Here, we demonstrate the fabrication engineering of thickness-dependent high quality factor (high-Q_i) Ta superconducting microwave coplanar waveguide resonators. All films are deposited on high-resistivity silicon substrates at room temperature without additional substrate heating. Before Ta deposition, a niobium (Nb) seed layer is used to ensure a body-centred cubic lattice (α-Ta) formation. We further engineer the kinetic inductance (L_K) resonators by varying Ta film thicknesses. High L_K is a key advantage for applications because it facilitates the realisation of high-impedance, compact quantum circuits with enhanced coupling to qubits. The maximum internal quality factor Q_i of ~ 3.6 * 10^6 is achieved at the high power regime for 100 nm Ta, while the highest kinetic inductance is obtained to be 0.6 pH/sq for the thinnest film, which is 40 nm. This combination of high Q_i and high L_K highlights the potential of Ta microwave circuits for high-fidelity operations of compact quantum circuits.