Léo Balembois

Hyperinductance based on stacked Josephson junctions

  1. Paul Manset,
  2. José Palomo,
  3. Aurélien Schmitt,
  4. Kyrylo Gerashchenko,
  5. Rémi Rousseau,
  6. Himanshu Patange,
  7. Patrick Abgrall,
  8. Emmanuel Flurin,
  9. Samuel Deléglise,
  10. Thibaut Jacqmin,
  11. and Léo Balembois
Superinductances are superconducting circuit elements that combine a large inductance with a low parasitic capacitance to ground, resulting in a characteristic impedance exceeding the
resistance quantum RQ=h/(2e)2≃6.45kΩ. In recent years, these components have become key enablers for emerging quantum circuit architectures. However, achieving high characteristic impedance while maintaining scalability and fabrication robustness remains a major challenge. In this work, we present two fabrication techniques for realizing superinductances based on vertically stacked Josephson junctions. Using a multi-angle Manhattan (MAM) process and a zero-angle (ZA) evaporation technique — in which junction stacks are connected pairwise using airbridges — we fabricate one-dimensional chains of stacks that act as high-impedance superconducting transmission lines. Two-tone microwave spectroscopy reveals the expected n‾√ scaling of the impedance with the number of junctions per stack. The chain fabricated using the ZA process, with nine junctions per stack, achieves a characteristic impedance of ∼16kΩ, a total inductance of 5.9μH, and a maximum frequency-dependent impedance of 50kΩ at 1.4 GHz. Our results establish junction stacking as a scalable, robust, and flexible platform for next-generation quantum circuits requiring ultra-high impedance environments.
arxiv pdf

Single electron-spin-resonance detection by microwave photon counting

  1. Zhiren Wang,
  2. Léo Balembois,
  3. Milos Rančić,
  4. Eric Billaud,
  5. Marianne Le Dantec,
  6. Alban Ferrier,
  7. Philippe Goldner,
  8. Sylvain Bertaina,
  9. Thierry Chanelière,
  10. Daniel Estève,
  11. Denis Vion,
  12. Patrice Bertet,
  13. and Emmanuel Flurin
Electron spin resonance (ESR) spectroscopy is the method of choice for characterizing paramagnetic impurities, with applications ranging from chemistry to quantum computing, but it
gives access only to ensemble-averaged quantities due to its limited signal-to-noise ratio. Single-electron-spin sensitivity has however been reached using spin-dependent photoluminescence, transport measurements, and scanning-probe techniques. These methods are system-specific or sensitive only in a small detection volume, so that practical single spin detection remains an open challenge. Here, we demonstrate single electron magnetic resonance by spin fluorescence detection, using a microwave photon counter at cryogenic temperatures. We detect individual paramagnetic erbium ions in a scheelite crystal coupled to a high-quality factor planar superconducting resonator to enhance their radiative decay rate, with a signal-to-noise ratio of 1.9 in one second integration time. The fluorescence signal shows anti-bunching, proving that it comes from individual emitters. Coherence times up to 3 ms are measured, limited by the spin radiative lifetime. The method has the potential to apply to arbitrary paramagnetic species with long enough non-radiative relaxation time, and allows single-spin detection in a volume as large as the resonator magnetic mode volume ( 10 um^3 in the present experiment), orders of magnitude larger than other single-spin detection techniques. As such, it may find applications in magnetic resonance and quantum computing.
arxiv pdf