Amir Karamlou

On-Demand Directional Photon Emission using Waveguide Quantum Electrodynamics

  1. Bharath Kannan,
  2. Aziza Almanakly,
  3. Youngkyu Sung,
  4. Agustin Di Paolo,
  5. David A. Rower,
  6. Jochen Braumüller,
  7. Alexander Melville,
  8. Bethany M. Niedzielski,
  9. Amir Karamlou,
  10. Kyle Serniak,
  11. Antti Vepsäläinen,
  12. Mollie E. Schwartz,
  13. Jonilyn L. Yoder,
  14. Roni Winik,
  15. Joel I-Jan Wang,
  16. Terry P. Orlando,
  17. Simon Gustavsson,
  18. Jeffrey A. Grover,
  19. and William D. Oliver
Routing quantum information between non-local computational nodes is a foundation for extensible networks of quantum processors. Quantum information can be transferred between arbitrary
nodes by photons that propagate between them, or by resonantly coupling nearby nodes. Notably, conventional approaches involving propagating photons have limited fidelity due to photon loss and are often unidirectional, whereas architectures that use direct resonant coupling are bidirectional in principle, but can generally accommodate only a few local nodes. Here, we demonstrate high-fidelity, on-demand, bidirectional photon emission using an artificial molecule comprising two superconducting qubits strongly coupled to a waveguide. Quantum interference between the photon emission pathways from the molecule generate single photons that selectively propagate in a chosen direction. This architecture is capable of both photon emission and capture, and can be tiled in series to form an extensible network of quantum processors with all-to-all connectivity.
arxiv pdf

Hexagonal Boron Nitride (hBN) as a Low-loss Dielectric for Superconducting Quantum Circuits and Qubits

  1. Joel I.J. Wang,
  2. Megan A. Yamoah,
  3. Qing Li,
  4. Amir Karamlou,
  5. Thao Dinh,
  6. Bharath Kannan,
  7. Jochen Braumüller,
  8. David Kim,
  9. Alexander J. Melville,
  10. Sarah E. Muschinske,
  11. Bethany M. Niedzielski,
  12. Kyle Serniak,
  13. Youngkyu Sung,
  14. Roni Winik,
  15. Jonilyn L. Yoder,
  16. Mollie Schwartz,
  17. Kenji Watanabe,
  18. Takashi Taniguchi,
  19. Terry P. Orlando,
  20. Simon Gustavsson,
  21. Pablo Jarillo-Herrero,
  22. and William D. Oliver
Dielectrics with low loss at microwave frequencies are imperative for high-coherence solid-state quantum computing platforms. We study the dielectric loss of hexagonal boron nitride
(hBN) thin films in the microwave regime by measuring the quality factor of parallel-plate capacitors (PPCs) made of NbSe2-hBN-NbSe2 heterostructures integrated into superconducting circuits. The extracted microwave loss tangent of hBN is bounded to be at most in the mid-10-6 range in the low temperature, single-photon regime. We integrate hBN PPCs with aluminum Josephson junctions to realize transmon qubits with coherence times reaching 25 μs, consistent with the hBN loss tangent inferred from resonator measurements. The hBN PPC reduces the qubit feature size by approximately two-orders of magnitude compared to conventional all-aluminum coplanar transmons. Our results establish hBN as a promising dielectric for building high-coherence quantum circuits with substantially reduced footprint and, with a high energy participation that helps to reduce unwanted qubit cross-talk.
arxiv pdf