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.

Challenges in Open-air Microwave Quantum Communication and Sensing

  1. Mikel Sanz,
  2. Kirill G. Fedorov,
  3. Frank Deppe,
  4. and Enrique Solano
Quantum communication is a holy grail to achieve secure communication among a set of partners, since it is provably unbreakable by physical laws. Quantum sensing employs quantum entanglement
as an extra resource to determine parameters by either using less resources or attaining a precision unachievable in classical protocols. A paradigmatic example is the quantum radar, which allows one to detect an object without being detected oneself, by making use of the additional asset provided by quantum entanglement to reduce the intensity of the signal. In the optical regime, impressive technological advances have been reached in the last years, such as the first quantum communication between ground and satellites, as well as the first proof-of-principle experiments in quantum sensing. The development of microwave quantum technologies turned out, nonetheless, to be more challenging. Here, we will discuss the challenges regarding the use of microwaves for quantum communication and sensing. Based on this analysis, we propose a roadmap to achieve real-life applications in these fields.

Digital-Analog Quantum Simulations with Superconducting Circuits

  1. Lucas Lamata,
  2. Adrian Parra-Rodriguez,
  3. Mikel Sanz,
  4. and Enrique Solano
Quantum simulations consist in the intentional reproduction of physical or unphysical models into another more controllable quantum system. Beyond establishing communication vessels
between unconnected fields, they promise to solve complex problems which may be considered as intractable for classical computers. From a historic perspective, two independent approaches have been pursued, namely, digital and analog quantum simulations. The former usually provide universality and flexibility, while the latter allows for scalability. Here, we review recent literature merging both paradigms in the context of superconducting circuits, yielding: digital-analog quantum simulations. In this manner, we aim at getting the best of both approaches in the most advanced quantum platform involving superconducting qubits and microwave transmission lines. The discussed merge of quantum simulation concepts, digital and analog, may open the possibility in the near future for outperforming classical computers in relevant problems, enabling the reach of quantum supremacy.