Propagating Quantum Microwaves: Towards Applications in Communication and Sensing

  1. Mateo Casariego,
  2. Emmanuel Zambrini Cruzeiro,
  3. Stefano Gherardini,
  4. Tasio Gonzalez-Raya,
  5. Rui André,
  6. Gonçalo Frazão,
  7. Giacomo Catto,
  8. Mikko Möttönen,
  9. Debopam Datta,
  10. Klaara Viisanen,
  11. Joonas Govenius,
  12. Mika Prunnila,
  13. Kimmo Tuominen,
  14. Maximilian Reichert,
  15. Michael Renger,
  16. Kirill G. Fedorov,
  17. Frank Deppe,
  18. Harriet van der Vliet,
  19. A. J. Matthews,
  20. Yolanda Fernández,
  21. R. Assouly,
  22. R. Dassonneville,
  23. B. Huard,
  24. Mikel Sanz,
  25. and Yasser Omar
The field of propagating quantum microwaves has started to receive considerable attention in the past few years. Motivated at first by the lack of an efficient microwave-to-optical
platform that could solve the issue of secure communication between remote superconducting chips, current efforts are starting to reach other areas, from quantum communications to sensing. Here, we attempt at giving a state-of-the-art view of the two, pointing at some of the technical and theoretical challenges we need to address, and while providing some novel ideas and directions for future research. Hence, the goal of this paper is to provide a bigger picture, and — we hope — to inspire new ideas in quantum communications and sensing: from open-air microwave quantum key distribution to direct detection of dark matter, we expect that the recent efforts and results in quantum microwaves will soon attract a wider audience, not only in the academic community, but also in an industrial environment.

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.

Quantum Gates for Propagating Microwave Photons

  1. Roope Kokkoniemi,
  2. Tuomas Ollikainen,
  3. Russell E. Lake,
  4. Sakari Saarenpää,
  5. Kuan Yen Tan,
  6. Janne I. Kokkala,
  7. Ceren B. Dağ,
  8. Joonas Govenius,
  9. and Mikko Möttönen
We report a generic scheme to implement transmission-type quantum gates for propagating microwave photons, based on a sequence of lumped-element components on transmission lines. By
choosing three equidistant superconducting quantum interference devices (SQUIDs) as the components on a single transmission line, we experimentally implement a magnetic-flux-tunable phase shifter and demonstrate that it produces a broad range of phase shifts and full transmission within the experimental uncertainty. Together with previously demonstrated beam splitters, these phase shifters can be utilized to implement arbitrary single-qubit gates. Furthermore, we theoretically show that replacing the SQUIDs by superconducting qubits, the phase shifter can be made strongly nonlinear, thus introducing deterministic photon–photon interactions. These results critically complement the previous demonstrations of on-demand single-photon sources and detectors, and hence pave the way for an all-microwave quantum computer based on propagating photons.