Mika Prunnila

Thermal resistance in superconducting flip-chip assemblies

  1. Joel Hätinen,
  2. Emma Mykkänen,
  3. Klaara Viisanen,
  4. Alberto Ronzani,
  5. Antti Kemppinen,
  6. Lassi Lehtisyrjä,
  7. Janne S. Lehtinen,
  8. and Mika Prunnila
Cryogenic microsystems that utilize different 3D integration techniques are being actively developed, e.g., for the needs of quantum technologies. 3D integration can introduce opportunities
and challenges to the thermal management of low temperature devices. In this work, we investigate sub-1 K inter-chip thermal resistance of a flip-chip bonded assembly, where two silicon chips are interconnected by indium bumps by atmospheric thermocompression bonding. The temperature dependence of the inter-chip thermal resistance follows the power law of αT−3, with α=7.7−15.4 K4 μm2/nW and a thermal contact area of 0.306 mm2. The T−3 relation indicates phononic interfacial thermal resistance, which is supported by the vanishing electrical thermal conduction due to the superconducting interconnections. Such a thermal resistance value can introduce a thermalization bottleneck, which can be detrimental for some applications, but it can also be harnessed. We provide a study of the latter case by simulating the performance of solid-state junction microrefrigerator where we use the measured thermal resistance value.
arxiv pdf

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.
arxiv pdf

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.
arxiv pdf

Dielectric losses in multi-layer Josephson junction qubits

  1. David Gunnarsson,
  2. Juha-Matti Pirkkalainen,
  3. Jian Li,
  4. Gheorghe Sorin Paraoanu,
  5. Pertti Hakonen,
  6. Mika Sillanpää,
  7. and Mika Prunnila
We have measured the excited state lifetimes in Josephson junction phase and transmon qubits, all of which were fabricated with the same scalable multi-layer process. We have compared
the lifetimes of phase qubits before and after removal of the isolating dielectric, SiNx, and find a four-fold improvement of the relaxation time after the removal. Together with the results from the transmon qubit and measurements on coplanar waveguide resonators, these measurements indicate that the lifetimes are limited by losses from the dielectric constituents of the qubits. We have extracted the individual loss contributions from the dielectrics in the tunnel junction barrier, AlOx, the isolating dielectric, SiNx, and the substrate, Si/SiO2, by weighing the total loss with the parts of electric field over the different dielectric materials. Our results agree well and complement the findings from other studies, demonstrating that superconducting qubits can be used as a reliable tool for high-frequency characterization of dielectric materials. We conclude with a discussion of how changes in design and material choice could improve qubit lifetimes up to a factor of four.
arxiv pdf