Florent Lecocq

Fabrication and characterization of low-loss Al/Si/Al parallel plate capacitors for superconducting quantum information applications

  1. Anthony McFadden,
  2. Aranya Goswami,
  3. Tongyu Zhao,
  4. Teun van Schijndel,
  5. Trevyn F.Q. Larson,
  6. Sudhir Sahu,
  7. Stephen Gill,
  8. Florent Lecocq,
  9. Raymond Simmonds,
  10. and Chris Palmstrøm
Increasing the density of superconducting circuits requires compact components, however, superconductor-based capacitors typically perform worse as dimensions are reduced due to loss
at surfaces and interfaces. Here, parallel plate capacitors composed of aluminum-contacted, crystalline silicon fins are shown to be a promising technology for use in superconducting circuits by evaluating the performance of lumped element resonators and transmon qubits. High aspect ratio Si-fin capacitors having widths below 300nm with an approximate total height of 3μm are fabricated using anisotropic wet etching of Si(110) substrates followed by aluminum metallization. The single-crystal Si capacitors are incorporated in lumped element resonators and transmons by shunting them with lithographically patterned aluminum inductors and conventional Al/AlOx/Al Josephson junctions respectively. Microwave characterization of these devices suggests state-of-the-art performance for superconducting parallel plate capacitors with low power internal quality factor of lumped element resonators greater than 500k and qubit T1 times greater than 25μs. These results suggest that Si-Fins are a promising technology for applications that require low loss, compact, superconductor-based capacitors with minimal stray capacitance.
arxiv pdf

Observation of two-mode squeezing in a traveling wave parametric amplifier

  1. Martina Esposito,
  2. Arpit Ranadive,
  3. Luca Planat,
  4. Sebastian Leger,
  5. Dorian Fraudet,
  6. Vincent Jouanny,
  7. Olivier Buisson,
  8. Wiebke Guichard,
  9. Cécile Naud,
  10. José Aumentado,
  11. Florent Lecocq,
  12. and Nicolas Roch
Traveling wave parametric amplifiers (TWPAs) have recently emerged as essential tools for broadband near quantum-limited amplification. However, their use to generate microwave quantum
states still misses an experimental demonstration. In this letter, we report operation of a TWPA as a source of two-mode squeezed microwave radiation. We demonstrate broadband entanglement generation between two modes separated by up to 400 MHz by measuring logarithmic negativity between 0.27 and 0.51 and collective quadrature squeezing below the vacuum limit between 1.5 and 2.1 dB. This work opens interesting perspectives for the exploration of novel microwave photonics experiments with possible applications in quantum sensing and continuous variable quantum computing.
arxiv pdf