In-situ bandaged Josephson junctions for superconducting quantum processors

Shadow evaporation is commonly used to micro-fabricate the key element of superconducting qubits—the Josephson junction. However, in conventional two-angle deposition circuit topology, unwanted stray Josephson junctions are created which contribute to dielectric loss. So far, this could be avoided by shorting the stray junctions with a so-called bandage layer deposited in an additional lithography step, which may further contaminate the chip surface. Here, we present an improved shadow evaporation technique allowing one to fabricate sub-micrometer-sized Josephson junctions together with bandage layers in a single lithography step. We also show that junction aging is significantly reduced when junction electrodes are passivated in an oxygen atmosphere directly after deposition.

[1]  A. Ustinov,et al.  Probing defect densities at the edges and inside Josephson junctions of superconducting qubits , 2021, npj Quantum Information.

[2]  P. Delsing,et al.  Simplified Josephson-junction fabrication process for reproducibly high-performance superconducting qubits , 2020, 2011.05230.

[3]  M. Weides,et al.  Coherent superconducting qubits from a subtractive junction fabrication process , 2020, 2006.16862.

[4]  A. Megrant,et al.  Resolving the positions of defects in superconducting quantum bits , 2019, Scientific Reports.

[5]  R. Barends,et al.  Electric field spectroscopy of material defects in transmon qubits , 2019, npj Quantum Information.

[6]  I. Siddiqi,et al.  Improving wafer-scale Josephson junction resistance variation in superconducting quantum coherent circuits , 2019, Superconductor Science and Technology.

[7]  Morten Kjaergaard,et al.  Superconducting Qubits: Current State of Play , 2019, Annual Review of Condensed Matter Physics.

[8]  Fei Yan,et al.  A quantum engineer's guide to superconducting qubits , 2019, Applied Physics Reviews.

[9]  M. Weides,et al.  Correlating Decoherence in Transmon Qubits: Low Frequency Noise by Single Fluctuators. , 2019, Physical review letters.

[10]  P. Delsing,et al.  Decoherence benchmarking of superconducting qubits , 2019, npj Quantum Information.

[11]  H. Neven,et al.  Fluctuations of Energy-Relaxation Times in Superconducting Qubits. , 2018, Physical review letters.

[12]  M. Weides,et al.  An argon ion beam milling process for native AlOx layers enabling coherent superconducting contacts , 2017, 1706.06424.

[13]  Austin G. Fowler,et al.  Characterization and reduction of capacitive loss induced by sub-micron Josephson junction fabrication in superconducting qubits , 2017, 1706.00879.

[14]  M. Bal,et al.  Overlap junctions for high coherence superconducting qubits , 2017, 1705.08993.

[15]  J. Cole,et al.  Towards understanding two-level-systems in amorphous solids: insights from quantum circuits , 2017, Reports on progress in physics. Physical Society.

[16]  A. Tzalenchuk,et al.  Direct Identification of Dilute Surface Spins on Al_{2}O_{3}: Origin of Flux Noise in Quantum Circuits. , 2016, Physical review letters.

[17]  I. Siddiqi,et al.  A near–quantum-limited Josephson traveling-wave parametric amplifier , 2015, Science.

[18]  Jacob Linder,et al.  Superconducting spintronics , 2015, Nature Physics.

[19]  John M. Martinis,et al.  Characterization and reduction of microfabrication-induced decoherence in superconducting quantum circuits , 2014, 1407.4769.

[20]  R. Barends,et al.  Coherent Josephson qubit suitable for scalable quantum integrated circuits. , 2013, Physical review letters.

[21]  Olivier Buisson,et al.  Junction fabrication by shadow evaporation without a suspended bridge , 2011, Nanotechnology.

[22]  I. Pop,et al.  Fabrication of stable and reproducible submicron tunnel junctions , 2011, 1105.6204.

[23]  V. V. Ryazanov,et al.  Implementation of superconductor/ferromagnet/ superconductor [pi]-shifters in superconducting digital and quantum circuits , 2010, 1005.1581.

[24]  S. Girvin,et al.  Charge-insensitive qubit design derived from the Cooper pair box , 2007, cond-mat/0703002.

[25]  I. Maasilta,et al.  Complete stabilization and improvement of the characteristics of tunnel junctions by thermal annealing , 2006, cond-mat/0611664.

[26]  M. Steffen,et al.  State tomography of capacitively shunted phase qubits with high fidelity. , 2006, Physical review letters.

[27]  Clare C. Yu,et al.  Decoherence in Josephson qubits from dielectric loss. , 2005, Physical review letters.

[28]  M. Rooks,et al.  Low stress development of poly(methylmethacrylate) for high aspect ratio structures , 2002 .

[29]  J. Baumberg,et al.  CMOS compatible fabrication methods for submicron Josephson junction qubits , 2001 .

[30]  W. H. Mallison,et al.  Dependence of critical current density on oxygen exposure in Nb-AlO/sub x/-Nb tunnel junctions , 1995, IEEE Transactions on Applied Superconductivity.

[31]  M. Sweeny,et al.  A travelling-wave parametric amplifier utilizing Josephson junctions , 1985 .

[32]  M. Gurvitch,et al.  Critical current uniformity and stability of Nb/Al‐oxide‐Nb Josephson junctions , 1984 .

[33]  G. J. Dolan,et al.  Offset masks for lift‐off photoprocessing , 1977 .

[34]  J. Niemeyer,et al.  Observation of large dc supercurrents at nonzero voltages in Josephson tunnel junctions , 1976 .