Timothy P. McKenna

Loss channels affecting lithium niobate phononic crystal resonators at cryogenic temperature

  1. E. Alex Wollack,
  2. Agnetta Y. Cleland,
  3. Patricio Arrangoiz-Arriola,
  4. Timothy P. McKenna,
  5. Rachel G. Gruenke,
  6. Rishi N. Patel,
  7. Wentao Jiang,
  8. Christopher J. Sarabalis,
  9. and Amir H. Safavi-Naeini
We investigate the performance of microwave-frequency phononic crystal resonators fabricated on thin-film lithium niobate for integration with superconducting quantum circuits. For
different design geometries at millikelvin temperatures, we achieve mechanical internal quality factors Qi above 105−106 at high microwave drive power, corresponding to 5×106 phonons inside the resonator. By sweeping the defect size of resonators with identical mirror cell designs, we are able to indirectly observe signatures of the complete phononic bandgap via the resonators‘ internal quality factors. Examination of quality factors‘ temperature dependence shows how superconducting and two-level system (TLS) loss channels impact device performance. Finally, we observe an anomalous low-temperature frequency shift consistent with resonant TLS decay and find that material choice can help to mitigate these losses.
arxiv pdf

Cryogenic microwave-to-optical conversion using a triply-resonant lithium niobate on sapphire transducer

  1. Timothy P. McKenna,
  2. Jeremy D. Witmer,
  3. Rishi N. Patel,
  4. Wentao Jiang,
  5. Raphaël Van Laer,
  6. Patricio Arrangoiz-Arriola,
  7. E. Alex Wollack,
  8. Jason F. Herrmann,
  9. and Amir H. Safavi-Naeini
Quantum networks are likely to have a profound impact on the way we compute and communicate in the future. In order to wire together superconducting quantum processors over kilometer-scale
distances, we need transducers that can generate entanglement between the microwave and optical domains with high fidelity. We present an integrated electro-optic transducer that combines low-loss lithium niobate photonics with superconducting microwave resonators on a sapphire substrate. Our triply-resonant device operates in a dilution refrigerator and converts microwave photons to optical photons with an on-chip efficiency of 6.6×10−6 and a conversion bandwidth of 20 MHz. We discuss design trade-offs in this device, including strategies to manage acoustic loss, and outline ways to increase the conversion efficiency in the future.
arxiv pdf