Engineering symmetry-selective couplings of a superconducting artificial molecule to microwave waveguides

  1. Mohammed Ali Aamir,
  2. Claudia Castillo Moreno,
  3. Simon Sundelin,
  4. Janka Biznárová,
  5. Marco Scigliuzzo,
  6. Kowshik Erappaji Patel,
  7. Amr Osman,
  8. D. P. Lozano,
  9. and Simone Gasparinetti
Tailoring the decay rate of structured quantum emitters into their environment opens new avenues for nonlinear quantum optics, collective phenomena, and quantum communications. Here
we demonstrate a novel coupling scheme between an artificial molecule comprising two identical, strongly coupled transmon qubits, and two microwave waveguides. In our scheme, the coupling is engineered so that transitions between states of the same (opposite) symmetry, with respect to the permutation operator, are predominantly coupled to one (the other) waveguide. The symmetry-based coupling selectivity, as quantified by the ratio of the coupling strengths, exceeds a factor of 30 for both the waveguides in our device. In addition, we implement a two-photon Raman process activated by simultaneously driving both waveguides, and show that it can be used to coherently couple states of different symmetry in the single-excitation manifold of the molecule. Using that process, we implement frequency conversion across the waveguides, mediated by the molecule, with efficiency of about 95%. Finally, we show that this coupling arrangement makes it possible to straightforwardly generate spatially-separated Bell states propagating across the waveguides. We envisage further applications to quantum thermodynamics, microwave photodetection, and photon-photon gates.

Qubit-compatible substrates with superconducting through-silicon vias

  1. K. Grigoras,
  2. N. Yurttagül,
  3. J.-P. Kaikkonen,
  4. E. T. Mannila,
  5. P. Eskelinen,
  6. D. P. Lozano,
  7. H.-X. Li,
  8. M. Rommel,
  9. D. Shiri,
  10. N. Tiencken,
  11. S. Simbierowicz,
  12. A. Ronzani,
  13. J. Hätinen,
  14. D. Datta,
  15. V. Vesterinen,
  16. L. Grönberg,
  17. J. Biznárová,
  18. A. Fadavi Roudsari,
  19. S. Kosen,
  20. A. Osman,
  21. J. Hassel,
  22. J. Bylander,
  23. and J. Govenius
We fabricate and characterize superconducting through-silicon vias and electrodes suitable for superconducting quantum processors. We measure internal quality factors of a million for
test resonators excited at single-photon levels, when vias are used to stitch ground planes on the front and back sides of the wafer. This resonator performance is on par with the state of the art for silicon-based planar solutions, despite the presence of vias. Via stitching of ground planes is an important enabling technology for increasing the physical size of quantum processor chips, and is a first step toward more complex quantum devices with three-dimensional integration.