Building Blocks of a Flip-Chip Integrated Superconducting Quantum Processor

  1. Sandoko Kosen,
  2. Hang-Xi Li,
  3. Marcus Rommel,
  4. Daryoush Shiri,
  5. Christopher Warren,
  6. Leif Grönberg,
  7. Jaakko Salonen,
  8. Tahereh Abad,
  9. Janka Biznárová,
  10. Marco Caputo,
  11. Liangyu Chen,
  12. Kestutis Grigoras,
  13. Göran Johansson,
  14. Anton Frisk Kockum,
  15. Christian Križan,
  16. Daniel Pérez Lozano,
  17. Graham Norris,
  18. Amr Osman,
  19. Jorge Fernández-Pendás,
  20. Anita Fadavi Roudsari,
  21. Giovanna Tancredi,
  22. Andreas Wallraff,
  23. Christopher Eichler,
  24. Joonas Govenius,
  25. and Jonas Bylander
We have integrated single and coupled superconducting transmon qubits into flip-chip modules. Each module consists of two chips – one quantum chip and one control chip –
that are bump-bonded together. We demonstrate time-averaged coherence times exceeding 90μs, single-qubit gate fidelities exceeding 99.9%, and two-qubit gate fidelities above 98.6%. We also present device design methods and discuss the sensitivity of device parameters to variation in interchip spacing. Notably, the additional flip-chip fabrication steps do not degrade the qubit performance compared to our baseline state-of-the-art in single-chip, planar circuits. This integration technique can be extended to the realisation of quantum processors accommodating hundreds of qubits in one module as it offers adequate input/output wiring access to all qubits and couplers.

Broadband continuous variable entanglement generation using Kerr-free Josephson metamaterial

  1. Michael Perelshtein,
  2. Kirill Petrovnin,
  3. Visa Vesterinen,
  4. Sina Hamedani Raja,
  5. Ilari Lilja,
  6. Marco Will,
  7. Alexander Savin,
  8. Slawomir Simbierowicz,
  9. Robab Jabdaraghi,
  10. Janne Lehtinen,
  11. Leif Grönberg,
  12. Juha Hassel,
  13. Mika Prunnila,
  14. Joonas Govenius,
  15. Sorin Paraoanu,
  16. and Pertti Hakonen
Entangled microwave photons form a fundamental resource for quantum information processing and sensing with continuous variables. We use a low-loss Josephson metamaterial comprising
superconducting non-linear asymmetric inductive elements to generate frequency (colour) entangled photons from vacuum fluctuations at a rate of 11 mega entangled bits per second with a potential rate above gigabit per second. The device is operated as a traveling wave parametric amplifier under Kerr-relieving biasing conditions. Furthermore, we realize the first successfully demonstration of single-mode squeezing in such devices – 2.4±0.7 dB below the zero-point level at half of modulation frequency.

Low-noise on-chip coherent microwave source

  1. Chengyu Yan,
  2. Juha Hassel,
  3. Visa Vesterinen,
  4. Jinli Zhang,
  5. Joni Ikonen,
  6. Leif Grönberg,
  7. Jan Goetz,
  8. and Mikko Möttönen
The increasing need for scaling up quantum computers operating in the microwave domain calls for advanced approaches for control electronics. To this end, integration of components
at cryogenic temperatures hosting also the quantum devices seems tempting. However, this comes with the limitations of ultra-low power dissipation accompanied by stringent signal-quality requirements to implement quantum-coherent operations. Here, we present a device and a technique to provide coherent continuous-wave microwave emission. We experimentally verify that its operation characteristics accurately follow our introduced theory based on a perturbative treatment of the capacitively shunted Josephson junction as a gain element. From phase noise measurements, we evaluate that the infidelity of typical quantum gate operations owing to this cryogenic source is less than 0.1% up to 10-ms evolution times, which is well below the infidelity caused by dephasing of the state-of-the-art superconducting qubits. Our device provides a coherent tone of 25 pW, corresponding to the total power needed in simultaneous control of thousands of qubits. Thus, together with future cryogenic amplitude and phase modulation techniques, our results may open pathways for scalable cryogenic control systems for quantum processors.

Characterizing cryogenic amplifiers with a matched temperature-variable noise source

  1. Slawomir Simbierowicz,
  2. Visa Vesterinen,
  3. Joshua Milem,
  4. Aleksi Lintunen,
  5. Mika Oksanen,
  6. Leif Roschier,
  7. Leif Grönberg,
  8. Juha Hassel,
  9. David Gunnarsson,
  10. and Russell E. Lake
We present a cryogenic microwave noise source with characteristic impedance of 50 Ω that can be installed in a coaxial line of a cryostat. The bath temperature of the noise source
is continuously variable between 0.1 K and 5 K without causing significant back-action heating on the sample space. As a proof-of-concept experiment, we perform Y-factor measurements of an amplifier cascade that includes a traveling wave parametric amplifier and a commercial high electron mobility transistor amplifier. We observe system noise temperatures as low as 680+20−200 mK at 5.7 GHz corresponding to 1.5+0.1−0.7 excess photons. The system we present has immediate applications in the validation of solid-state qubit readout lines.

Broadband Tunable Phase Shifter For Microwaves

  1. Jinli Zhang,
  2. Tianyi Li,
  3. Roope Kokkoniemi,
  4. Chengyu Yan,
  5. Wei Liu,
  6. Matti Partanen,
  7. Kuan Yen Tan,
  8. Ming He,
  9. Lu Ji,
  10. Leif Grönberg,
  11. and Mikko Möttönen
We implement a broadly tunable phase shifter for microwaves based on superconducting quantum interference devices (SQUIDs) and study it both experimentally and theoretically. At different
frequencies, a unit transmission coefficient, |S21|=1, can be theoretically achieved along a curve where the phase shift is controllable by magnetic flux. The fabricated device consists of three equidistant SQUIDs interrupting a transmission line. We model each SQUID embedded at different positions along the transmission line with two parameters, capacitance and inductance, the values of which we extract from the experiments. In our experiments, the tunability of the phase shift varies from from 0.07×π to 0.14×π radians along the full-transmission curve with the input frequency ranging from 6.00 to 6.28~GHz. The reported measurements are in good agreement with simulations, which is promising for future design work of phase shifters for different applications.

Fast control of dissipation in a superconducting resonator

  1. Vasilii Sevriuk,
  2. Kuan Yen Tan,
  3. Eric Hyyppä,
  4. Matti Silveri,
  5. Matti Partanen,
  6. Máté Jenei,
  7. Shumpei Masuda,
  8. Jan Goetz,
  9. Visa Vesterinen,
  10. Leif Grönberg,
  11. and Mikko Möttönen
We report on fast tunability of an electromagnetic environment coupled to a superconducting coplanar waveguide resonator. Namely, we utilize a recently-developed quantum-circuit refrigerator
(QCR) to experimentally demonstrate a dynamic tunability in the total damping rate of the resonator up to almost two orders of magnitude. Based on the theory it corresponds to a change in the internal damping rate by nearly four orders of magnitude. The control of the QCR is fully electrical, with the shortest implemented operation times in the range of 10 ns. This experiment constitutes a fast active reset of a superconducting quantum circuit. In the future, a similar scheme can potentially be used to initialize superconducting quantum bits.