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

Superconductor Science and Technology

Weak link nanobridges as single flux quantum elements

Connor D. Shelly, Patrick See, Jane Ireland, Edward J. Romans, Jonathan M. J. Williams

Published Jul 19, 2017• 15 citations
Publisher

Abstract

This paper investigates the feasibility of using weak link nanobridges as Josephson junction elements for the purpose of creating Josephson circuits. We demonstrate the development of a single-step electron beam lithography procedure to fabricate niobium nanobridges with dimensions down to . The single-step process facilitates fabrication that is scalable to complex circuits that require many junctions. We measure the IV -characteristics (IVC) of the nanobridges between temperatures of and and find agreement with numerical simulations and the analytical resistively shunted junction (RSJ) model. Furthermore, we investigate the behaviour of the nanobridges under rf irradiation and observe the characteristic microwave-induced Shapiro steps. Our simulated IVC under rf irradiation using both the RSJ model and circuit simulator JSIM are in agreement with the experimental data. As a potential use of nanobridges in circuits requiring many junctions, we investigate the theoretical performance of a nanobridge-based Josephson comparator circuit using JSIM .

DOI
10.1088/1361-6668/aa80cd

Related papers

Superconducting Nb Nanobridges for Reduced Footprint and Efficient Next-Generation Electronics

Jonathan A. Collins, Calum Rose, A. Casaburi

We optimized a process to reliably fabricate thin Nb nanobridge weak links having a physical size comparable with Nb coherence length ξ(4.2K) ∼16 nm, controlled degraded superconductivity with respect to the electrodes, and excellent edge roughness. We then investigated the feasibility to use these nanobridges as the Josephson element for reduced footprints and efficient next-generation single flux quantum (SFQ) logic electronics. First of all, we demonstrated that in such thin Nb nanobridges, there is no thermal hysteresis in the current–voltage characteristics (IVC) that instead is usually observed in other weak links and prevents their use in SFQ electronics. We fitted the experimental IVCs of nanobridges with the resistively shunted junction model implemented with piecewise linear current–phase relation (CPR) finding a very good agreement with data. This allowed us to infer the CPR parameters and evaluate the product of critical current and normal resistance,IcRn∼mV, at varying temperatures. Using these data, we simulated the generation of voltage pulses at varying CPRs and verified that they still have a quantized area equal to the magnetic flux quantum Φ0and the productIcRnallows for speed of operationIcRN/ Φ0$\gg $100 GHz. Moreover, their critical currentIc$\approx $100$\mu $A, comparable with that of tunnel Josephson junctions (JJs) used in SFQ electronics, is orders of magnitude larger than thermal current noiseITN= (2π / Φ0)kBT$\approx $0.2$\mu $A at temperatureT= 4.2 K, for stable and, at the same time, efficient operation with energy per switch of onlyEJ≈ICΦ0$\mathbin{\hbox{$\buildrel<\over {\smash{\scriptstyle \sim}\vphantom{_x}}$}} $1 aJ. To assess the potential use of these nanobridges in SFQ logic electronics with a large number of elements, we used an open-source simulation software (JSim) to simulate the behavior of a standard DC-to-SFQ converter circuit. From the simulation made by implementing the CPR inferred from experimental data, we observed that the circuit behaves exactly as intended. Our results strongly suggest that these nanobridges can be used to develop large-scale SFQ electronics with several advantages over tunnel JJs. The reduced footprint, just one-third or less than standard tunnel JJs, and simplified fabrication process, with only 2 steps involved against typically ∼20 for tunnel JJs, could allow for a better fabrication tolerance, higher control on operation parameters, higher circuit density, and easier integration with other technology platforms. These characteristics could be very appealing also to replace tunnel JJs in quantum technology devices like transmon qubits and superconducting parametric amplifiers.

IEEE Transactions on Applied Superconductivity•Nov 4, 2022•8 citations

Investigating the feasibility of using nanobridge weak links as the active Josephson element in Rapid Single Flux quantum circuitry

Abubakar Adan

Josephson junctions are used in present day voltage standards. To extend their use to AC voltage standards a high bandwidth, low-noise detector is required. A candidate component for this detector is a superconducting comparator based on Rapid Single Flux Quantum (RSFQ) circuits. The work presented here is a study to determine if nanobridge weak links can be used as the active Josephson element in these circuits. In order to achieve this an understanding of the nanobridge properties and in particular their critical currents is fundamental. We present simulations of a simple comparator using the circuit simulation software JSIM in order to study the effect of varying nanobridge parameters such as width, length, and loop area. These geometrical variables have an affect on the critical currents and loop inductances which subsequently effect device performance. Particular emphasis is given to investigation of how these parameters affect a key figure of merit, the grey zone width.

•Mar 28, 2018•0 citations

Fabrication of Niobium Nanobridge Josephson Junctions

Takashi Tachiki, Kenji Horiguchi, Takashi Uchida

To realize antenna-coupled Josephson detectors for microwave and millimeter-wave radiation, planar-type Nb nanobridge Josephson junctions were fabricated. Nb thin films whose thickness, the root mean square roughness and the critical temperature were 20.0 nm, 0.109 nm and 8.4 K, respectively were deposited using a DC magnetron sputtering at a substrate temperature of 700°C. Nanobridges were obtained from the film using 80-kV electron beam lithography and reactive ion-beam etching in CF 4 (90%) + O2 (10%) gases. The minimum bridge area was 65 nm wide and 60 nm long. For the nanobridge whose width and length were less than 110 nm, an I-V characteristic showed resistively-shunted-junction behaviour near the critical temperature. Moreover, Shapiro steps were observed in the nanobridge with microwave irradiation at a frequency of 6 – 30 GHz. The Nb nanobridges can be used as detectors in the antenna-coupled devices.

Journal of Physics Conference Series•May 12, 2014•1 citation

Development of Flux-Tuneable Inductive Nanobridge SQUIDs for Quantum Technology Applications

Laith Meti, George Long, Tom Godfrey +6 more

Niobium nanobridge SQUIDs have shown exceptional noise performance with potential applications in quantum information processing, weak signal detection and single spin detection where the nanobridge geometry should enable efficient electromagnetic coupling to implanted spins. Combining such devices with dispersive microwave readout circuitry allows the spin sensitivity to be further improved by overcoming the standard thermal limit. Here we report on the fabrication and dispersive microwave readout of an array of niobium nanobridge rf SQUIDs incorporated into a superconducting resonator, including the optimization of the nanobridge fabrication process by electron beam lithography. We show the measured flux-tuneability of the resonance is in good agreement with theory, and we also discuss how the nonlinearity of the weak-link in the resonator structure allows for the mediation of parametric effects to enhance performance.

IEEE Transactions on Applied Superconductivity•Feb 17, 2023•3 citations

Gap Engineered Superconducting Multilayer Nanobridge Josephson Junctions

Giuseppe Colletta, Susan Johny, Hua Feng +3 more

We report the realization of multilayer three-dimensional nanobridge Josephson junctions based on Nb/NbN and Nb/TiN superconducting stacks fabricated using electron-beam lithography and chlorine-based dry etching. In this architecture, a high-resistivity nitride layer defines the geometrical weak link, while the top Nb layer sets the overall critical temperature and film quality of the stack. This multilayer design enables engineering of the superconducting gap and proximity effects without relying on focused ion beam milling or oxide tunnel barriers. The devices are successfully integrated into dc SQUIDs, demonstrating reliable circuit-level operation. By combining material selectivity with three-dimensional geometry, this platform provides a scalable route toward oxide-free Josephson junctions suitable for superconducting electronics.

cond-mat.supr-conCross-listedarXiv:2603.20757•Mar 24, 2026•0 citations

Niobium Quantum Interference Microwave Circuits with Monolithic Three-Dimensional (3D) Nanobridge Junctions

Kevin Uhl, Daniel Hackenbeck, Janis Peter +3 more

Nonlinear microwave circuits are key elements for many groundbreaking research directions and technologies, such as quantum computation and quantum sensing. The majority of microwave circuits with Josephson nonlinearities to date is based on aluminum thin films, and therefore they are severely restricted in their operation range regarding temperatures and external magnetic fields. Here, we present the realization of superconducting niobium microwave resonators with integrated, three-dimensional (3D) nanobridge-based superconducting quantum interference devices. The 3D nanobridges (constriction weak links) are monolithically patterned into pre-fabricated microwave LC circuits using neon ion beam milling, and the resulting quantum interference circuits show frequency tunabilities, flux responsivities and Kerr nonlinearities on par with comparable aluminum nanobridge devices, but with the perspective of a much larger operation parameter regime. Our results reveal great potential for application of these circuits in hybrid systems with e.g. magnons and spin ensembles or in flux-mediated optomechanics.

arXiv:2305.16276•May 25, 2023•0 citations
This paper investigates the feasibility of using weak link nanobridges as Josephson junction elements for the purpose of creating Josephson circuits. We demonstrate the development of a single-step electron beam lithography procedure to fabricate niobium nanobridges with dimensions down to . The single-step process facilitates fabrication that is scalable to complex circuits that require many junctions. We measure the IV -characteristics (IVC) of the nanobridges between temperatures of and and find agreement with numerical simulations and the analytical resistively shunted junction (RSJ) model. Furthermore, we investigate the behaviour of the nanobridges under rf irradiation and observe the characteristic microwave-induced Shapiro steps. Our simulated IVC under rf irradiation using both the RSJ model and circuit simulator JSIM are in agreement with the experimental data. As a potential use of nanobridges in circuits requiring many junctions, we investigate the theoretical performance of a nanobridge-based Josephson comparator circuit using JSIM .
We optimized a process to reliably fabricate thin Nb nanobridge weak links having a physical size comparable with Nb coherence length ξ(4.2K) ∼16 nm, controlled degraded superconductivity with respect to the electrodes, and excellent edge roughness. We then investigated the feasibility to use these nanobridges as the Josephson element for reduced footprints and efficient next-generation single flux quantum (SFQ) logic electronics. First of all, we demonstrated that in such thin Nb nanobridges, there is no thermal hysteresis in the current–voltage characteristics (IVC) that instead is usually observed in other weak links and prevents their use in SFQ electronics. We fitted the experimental IVCs of nanobridges with the resistively shunted junction model implemented with piecewise linear current–phase relation (CPR) finding a very good agreement with data. This allowed us to infer the CPR parameters and evaluate the product of critical current and normal resistance,IcRn∼mV, at varying temperatures. Using these data, we simulated the generation of voltage pulses at varying CPRs and verified that they still have a quantized area equal to the magnetic flux quantum Φ0and the productIcRnallows for speed of operationIcRN/ Φ0$\gg 100GHz.Moreover,theircriticalcurrentIc100 GHz. Moreover, their critical currentIc100GHz.Moreover,theircriticalcurrentIc\approx 100100100\mu A,comparablewiththatoftunnelJosephsonjunctions(JJs)usedinSFQelectronics,isordersofmagnitudelargerthanthermalcurrentnoiseITN=(2π/Φ0)kBTA, comparable with that of tunnel Josephson junctions (JJs) used in SFQ electronics, is orders of magnitude larger than thermal current noiseITN= (2π / Φ0)kBTA,comparablewiththatoftunnelJosephsonjunctions(JJs)usedinSFQelectronics,isordersofmagnitudelargerthanthermalcurrentnoiseITN=(2π/Φ0)kBT\approx 0.20.20.2\mu AattemperatureT=4.2K,forstableand,atthesametime,efficientoperationwithenergyperswitchofonlyEJ≈ICΦ0A at temperatureT= 4.2 K, for stable and, at the same time, efficient operation with energy per switch of onlyEJ≈ICΦ0AattemperatureT=4.2K,forstableand,atthesametime,efficientoperationwithenergyperswitchofonlyEJ≈ICΦ0\mathbin{\hbox{$\buildrel<\over {\smash{\scriptstyle \sim}\vphantom{_x}}$}} $1 aJ. To assess the potential use of these nanobridges in SFQ logic electronics with a large number of elements, we used an open-source simulation software (JSim) to simulate the behavior of a standard DC-to-SFQ converter circuit. From the simulation made by implementing the CPR inferred from experimental data, we observed that the circuit behaves exactly as intended. Our results strongly suggest that these nanobridges can be used to develop large-scale SFQ electronics with several advantages over tunnel JJs. The reduced footprint, just one-third or less than standard tunnel JJs, and simplified fabrication process, with only 2 steps involved against typically ∼20 for tunnel JJs, could allow for a better fabrication tolerance, higher control on operation parameters, higher circuit density, and easier integration with other technology platforms. These characteristics could be very appealing also to replace tunnel JJs in quantum technology devices like transmon qubits and superconducting parametric amplifiers.
Josephson junctions are used in present day voltage standards. To extend their use to AC voltage standards a high bandwidth, low-noise detector is required. A candidate component for this detector is a superconducting comparator based on Rapid Single Flux Quantum (RSFQ) circuits. The work presented here is a study to determine if nanobridge weak links can be used as the active Josephson element in these circuits. In order to achieve this an understanding of the nanobridge properties and in particular their critical currents is fundamental. We present simulations of a simple comparator using the circuit simulation software JSIM in order to study the effect of varying nanobridge parameters such as width, length, and loop area. These geometrical variables have an affect on the critical currents and loop inductances which subsequently effect device performance. Particular emphasis is given to investigation of how these parameters affect a key figure of merit, the grey zone width.
To realize antenna-coupled Josephson detectors for microwave and millimeter-wave radiation, planar-type Nb nanobridge Josephson junctions were fabricated. Nb thin films whose thickness, the root mean square roughness and the critical temperature were 20.0 nm, 0.109 nm and 8.4 K, respectively were deposited using a DC magnetron sputtering at a substrate temperature of 700°C. Nanobridges were obtained from the film using 80-kV electron beam lithography and reactive ion-beam etching in CF 4 (90%) + O2 (10%) gases. The minimum bridge area was 65 nm wide and 60 nm long. For the nanobridge whose width and length were less than 110 nm, an I-V characteristic showed resistively-shunted-junction behaviour near the critical temperature. Moreover, Shapiro steps were observed in the nanobridge with microwave irradiation at a frequency of 6 – 30 GHz. The Nb nanobridges can be used as detectors in the antenna-coupled devices.
Niobium nanobridge SQUIDs have shown exceptional noise performance with potential applications in quantum information processing, weak signal detection and single spin detection where the nanobridge geometry should enable efficient electromagnetic coupling to implanted spins. Combining such devices with dispersive microwave readout circuitry allows the spin sensitivity to be further improved by overcoming the standard thermal limit. Here we report on the fabrication and dispersive microwave readout of an array of niobium nanobridge rf SQUIDs incorporated into a superconducting resonator, including the optimization of the nanobridge fabrication process by electron beam lithography. We show the measured flux-tuneability of the resonance is in good agreement with theory, and we also discuss how the nonlinearity of the weak-link in the resonator structure allows for the mediation of parametric effects to enhance performance.
We report the realization of multilayer three-dimensional nanobridge Josephson junctions based on Nb/NbN and Nb/TiN superconducting stacks fabricated using electron-beam lithography and chlorine-based dry etching. In this architecture, a high-resistivity nitride layer defines the geometrical weak link, while the top Nb layer sets the overall critical temperature and film quality of the stack. This multilayer design enables engineering of the superconducting gap and proximity effects without relying on focused ion beam milling or oxide tunnel barriers. The devices are successfully integrated into dc SQUIDs, demonstrating reliable circuit-level operation. By combining material selectivity with three-dimensional geometry, this platform provides a scalable route toward oxide-free Josephson junctions suitable for superconducting electronics.
Nonlinear microwave circuits are key elements for many groundbreaking research directions and technologies, such as quantum computation and quantum sensing. The majority of microwave circuits with Josephson nonlinearities to date is based on aluminum thin films, and therefore they are severely restricted in their operation range regarding temperatures and external magnetic fields. Here, we present the realization of superconducting niobium microwave resonators with integrated, three-dimensional (3D) nanobridge-based superconducting quantum interference devices. The 3D nanobridges (constriction weak links) are monolithically patterned into pre-fabricated microwave LC circuits using neon ion beam milling, and the resulting quantum interference circuits show frequency tunabilities, flux responsivities and Kerr nonlinearities on par with comparable aluminum nanobridge devices, but with the perspective of a much larger operation parameter regime. Our results reveal great potential for application of these circuits in hybrid systems with e.g. magnons and spin ensembles or in flux-mediated optomechanics.