1. 1 Quantum Enabling Technology Materials Research for Superconducting Quantum Computing Materials P.I. - D. P. Pappas Affiliates: Jeff Kline Fabio da Silva Students:Will Kindel Teresa Osminer Postdocs*David Wisbee

2. 2 Anatomy of a superconducting qubit Substrate Insulator (if subs. conductive) Bottom electrode Junction - Tunnel barrier Insulator Wiring Top electrode

3. Materials development – can we reduce decoherence? Absorption in dielectric & junction (a-SiO 2 ) & (a-AlO 2 ) Si a-SiO x Al Focus on: Insulators: along traces & around junction in substrate crossovers Tunnel barrier: Between top and bottom electrode Electrode surfaces: Flux noise from surface spins AlOx

4. => With & without SiO2 over the capacitor C/2 L Dissipation is in SiO2 dielectric of the capacitor! ~P out Resonant circuits have low Q at low T, P

5. Qubit spectroscopy splittings due to two-level systems in Junction tunnel barrier Increase the bias voltage (tilt) Frequency of |0> => |1> transition goes down Resonances Increase bias

6. DC SQUIDs: S  1/2 (1Hz) vs. T At low T: S  1/2 (1Hz) ≈ 7 ± 3  0 Hz -1/2 Loop materials: Nb (A1-4, F1) Pb (C2) PbIn (A5, B1, C1, E1,2) Loop effective areas: 1,400  m 2 – 200,000  m 2 ( Wellstood, Urbina and Clarke (1987)

7. Superconducting JJ qubits – mtls. & meas. Primary NIST differentiator – Crystalline junction material Secondary differentiator – Crystalline bottom electrodes UHV & processing combination Enabling development: Substrate preparation Development of low loss insulators priority – a-Si:H, a-C:H, Si(111) Benchmarks – a-SiOx, a-SiN Facilities ADR with I/V and RF capablility RF capability on PPMS

8. Original Statement of Work Tasks: 1)Substrate preparation 2)Bottom electrode 3)Epitaxial barrier development 4)Top Electrode 5)Dielectric layers 6)Top & bottom wiring layers

9. Progress Studied substrates from different vendors ( collaboration w/LL, DARPA) - Task 1 – Obtained 3” wafers of Sapphire (0001) – Measured roughness using AFM Developed Qubit test platform for junction tests - Task 1-6 – 12 qubit test die – quickly find optimized junctions – Devices fabricated here – Measurements done– 500 ns T1!! Developed insulator test platform – Task 1-6 – Make simple structure to test loss in various dielectrics – new set of dies – Devices fabricated here – Measurements show absorption – sent to JPL Fabricated SQUIDs and measure noise – Task 1-6 – Various widths & flux trapping conditions – Fabricated Ru capped washers – Added Fe – Measured - Same noise level with Ru as Al & Re, reduced by factor of 2 0.2 ML Fe Measure junctions in-house for quality control – Task 1-6 – ADR test facility built up – – Tested first junctions here last week Commissioned 3” chamber for epi Si(111)/Al(111)/Al2O3/Al(111) - Task 1-4

10. Task 1 - Wafer substrate AFM analysis CG wafer surfaceES wafer surfaceSG wafer surface Acquired wafers from 3 manufacturers Epi-stone (ES) & Saint Gobain (SG), and Crystal GmbH (CG) Conducted AFM on them in collaboration with LL under DARPA CG & ES wafers looked best – show atomic steps SG wafer surface looked poor, lots of scratches, no steps. Note – Growth of Re on SG wafers actually show the best RHEED!

11. Progress Studied substrates from different vendors ( collaboration w/LL, DARPA) - Task 1 – Obtained 3” wafers of Sapphire (0001) – Measured roughness using AFM Developed Qubit test platform for junction tests - Task 1-6 – 12 qubit test die – quickly find optimized junctions – Devices fabricated here – Measurements done– 500 ns T1!! Developed insulator test platform – Task 1-6 – Make simple structure to test loss in various dielectrics – new set of dies – Devices fabricated here – Measurements show absorption – sent to JPL Fabricated SQUIDs and measure noise – Task 1-6 – Various widths & flux trapping conditions – Fabricated Ru capped washers – Added Fe – Measured - Same noise level with Ru as Al & Re, reduced by factor of 2 0.2 ML Fe Measure junctions in-house for quality control – Task 1-6 – ADR test facility built up – – Tested first junctions here last week Commissioned 3” chamber for epi Si(111)/Al(111)/Al2O3/Al(111) - Task 1-4

12. Task 3 - 12 Qubit Die Layout Bias coil Qubit loop DC-SQUID Allows us to test a wide range of junction sizes even with low yield!

13. Progress Studied substrates from different vendors ( collaboration w/LL, DARPA) - Task 1 – Obtained 3” wafers of Sapphire (0001) – Measured roughness using AFM Developed Qubit test platform for junction tests - Task 1-6 – 12 qubit test die – quickly find optimized junctions – Devices fabricated here – Measurements done– 500 ns T1!! Developed insulator test platform – Task 1-6 – Make simple structure to test loss in various dielectrics – new set of dies – Devices fabricated here – Measurements show absorption – sent to JPL Fabricated SQUIDs and measure noise – Task 1-6 – Various widths & flux trapping conditions – Fabricated Ru capped washers – Added Fe – Measured - Same noise level with Ru as Al & Re, reduced by factor of 2 0.2 ML Fe Measure junctions in-house for quality control – Task 1-6 – ADR test facility built up – – Tested first junctions here last week Commissioned 3” chamber for epi Si(111)/Al(111)/Al2O3/Al(111) - Task 1-4

14. Task 5 - Quantum Materials: Low loss insulators Test platform do develop low loss insulators – Collaborating with Ben Mazin to design antenna test platform – Measurements made on a-SiOx as a reference Q ~ 1000 – Just started making measurments on a-ALD-AlOx, – While measurements in progress, preparing SiN, a-C, a-Ge

15. Progress Studied substrates from different vendors ( collaboration w/LL, DARPA) - Task 1 – Obtained 3” wafers of Sapphire (0001) – Measured roughness using AFM Developed Qubit test platform for junction tests - Task 1-6 – 12 qubit test die – quickly find optimized junctions – Devices fabricated here – Measurements done– 500 ns T1!! Developed insulator test platform – Task 1-6 – Make simple structure to test loss in various dielectrics – new set of dies – Devices fabricated here – Measurements show absorption – sent to JPL Fabricated SQUIDs and measure noise – Task 1-6 – Various widths & flux trapping conditions – Fabricated Ru capped washers – Added Fe – Measured - Same noise level with Ru as Al & Re, reduced by factor of 2 0.2 ML Fe Measure junctions in-house for quality control – Task 1-6 – ADR test facility built up – – Tested first junctions here last week Commissioned 3” chamber for epi Si(111)/Al(111)/Al2O3/Al(111) - Task 1-4

16. Task 6 - Flux noise vs. F on Ru capped Al with 0.2 ML Fe on top Red curve – SQUID washer w/ Ru cap Blue Curve – Same SQUID washer w/ Ru cap + 0.2 ML Fe on top Factor of 2 reduction in noise due to Fe!! (rather than increasing noise)

17. Progress Studied substrates from different vendors ( collaboration w/LL, DARPA) - Task 1 – Obtained 3” wafers of Sapphire (0001) – Measured roughness using AFM Developed Qubit test platform for junction tests - Task 1-6 – 12 qubit test die – quickly find optimized junctions – Devices fabricated here – Measurements done– 500 ns T1!! Developed insulator test platform – Task 1-6 – Make simple structure to test loss in various dielectrics – new set of dies – Devices fabricated here – Measurements show absorption – sent to JPL Fabricated SQUIDs and measure noise – Task 1-6 – Various widths & flux trapping conditions – Fabricated Ru capped washers – Added Fe – Measured - Same noise level with Ru as Al & Re, reduced by factor of 2 0.2 ML Fe Measure junctions in-house for quality control – Task 1-6 – ADR test facility built up – – Tested first junctions here last week Commissioned 3” chamber for epi Si(111)/Al(111)/Al2O3/Al(111) - Task 1-4

18. I-V curve from epitaxial barrier

19. Results of our junctions: R (1/G) vs. T for Al/AlO x /Al tunnel jctn. Signatures of quantum tunneling – R increases as T decreases – Zero slope at low T Zero-bias resistance In collaboration with Oh et al (Rutgers)

20. Progress Studied substrates from different vendors ( collaboration w/LL, DARPA) - Task 1 – Obtained 3” wafers of Sapphire (0001) – Measured roughness using AFM Developed Qubit test platform for junction tests - Task 1-6 – 12 qubit test die – quickly find optimized junctions – Devices fabricated here – Measurements done– 500 ns T1!! Developed insulator test platform – Task 1-6 – Make simple structure to test loss in various dielectrics – new set of dies – Devices fabricated here – Measurements show absorption – sent to JPL Fabricated SQUIDs and measure noise – Task 1-6 – Various widths & flux trapping conditions – Fabricated Ru capped washers – Added Fe – Measured - Same noise level with Ru as Al & Re, reduced by factor of 2 0.2 ML Fe Measure junctions in-house for quality control – Task 1-6 – ADR test facility built up – – Tested first junctions here last week Commissioned 3” chamber for epi Si(111)/Al(111)/Al2O3/Al(111) - Task 1-4

21. Lesker 3” deposition chamber

22. Note: Test devices include all/most layers => Hard to separate original tasks! Re-parse SOW Tasks to reflect project goals. 1)Substrate preparation 2)Bottom electrode 3)Epitaxial barrier dev. 4)Top Electrode 5)Dielectric layers 6)Top & bottom wiring 1)Understand tunneling process 2)Devices on alternative substrates 3)Develop high Q circuits 4)Study noise in devices 5)Test coherence advances Still the same scope of work. Allows us to make Gantt chart directly from SOW.

23. Detailed subtasks 1.Understand tunnel process in epi-barriers 1.Tool up to measure I-V curves in-house with ADR 2.Measurement of samples at low temperature 3.Reduce spectroscopy splitting further using different tunnel barriers 4.Study materials doping in barriers 5.Study device/junction failure 2.Develop alternative substrates 1.Research & indentify new systems 2.Tool up 3” chamber in clean room for identified system 3.Prepare substrates 4.Prepare bottom electrode 5.Prepare barriers 6.Prepare top electrode 7.Fabricate into test junctions 3.Develop high Q materials for low T, P applications 1.Tool up for measurements at 1.7 K and 60 mK 2.Fabricate L-C circuits & test with SiO2 3.Tool up to grow a-Si dielectrics 4.Investigate new materials 5.Complete work with antenna resonators 4.Study noise due to surfaces & interfaces 1.Fabrication of SQUID devices 2. Identify source of decoherence loss 5.Test Coherence advances 1.Fabricate 12 qubit dies using optimal materials from above 2.Integrate & optimize all improvements into single qubit & measure

24. Gantt Chart