Superconducting Quantum Interference Devices based on InSb nanoflag Josephson junctions

  1. Andrea Chieppa,
  2. Gaurav Shukla,
  3. Simone Traverso,
  4. Giada Bucci,
  5. Valentina Zannier,
  6. Samuele Fracassi,
  7. Niccolo Traverso Ziani,
  8. Maura Sassetti,
  9. Matteo Carrega,
  10. Fabio Beltram,
  11. Francesco Giazotto,
  12. Lucia Sorba,
  13. and Stefan Heun
Planar Josephson junctions (JJs) based on InSb nanoflags have recently emerged as an intriguing platform in superconducting electronics. This letter presents the fabrication and investigation
of superconducting quantum interference devices (SQUIDs) employing InSb nanoflag JJs. We provide measurements of interference patterns in both symmetric and asymmetric geometries. The interference patterns in both configurations can be modulated by a back-gate voltage, a feature well reproduced through numerical simulations. The observed behavior aligns with the skewed current-phase relations of the JJs, demonstrating significant contributions from higher harmonics. We explore the magnetic field response of the devices across a wide range of fields (±30 mT), up to the single-junction interference regime, where a Fraunhofer-like pattern is detected. Finally, we assess the flux-to-voltage sensitivity of the SQUIDs to evaluate their performance as magnetometers. A magnetic flux noise of S1/2Φ=4.4×10−6Φ0/Hz‾‾‾√ is identified, indicating potential applications in nanoscale magnetometry.

The quartic Blochnium: an anharmonic quasicharge superconducting qubit

  1. Luca Chirolli,
  2. Matteo Carrega,
  3. and Francesco Giazotto
The quasicharge superconducting qubit realizes the dual of the transmon and shows strong robustness to flux and charge fluctuations thanks to a very large inductance closed on a Josephson
junction. At the same time, a weak anharmonicity of the spectrum is inherited from the parent transmon, that introduces leakage errors and is prone to frequency crowding in multi-qubit setups. We propose a novel design that employs a quartic superinductor and confers a good degree of anharmonicity to the spectrum. The quartic regime is achieved through a properly designed chain of Josephson junction loops that avoids strong quantum fluctuations without introducing a severe dependence on the external flux.

Novel architectures for noise-resilient superconducting qubits

  1. Alessio Calzona,
  2. and Matteo Carrega
Great interest revolves around the development of new strategies to efficiently store and manipulate quantum information in a robust and decoherence-free fashion. Several proposals
have been put forward to encode information into qubits that are simultaneously insensitive to relaxation and to dephasing processes. Among all, given their versatility and high-degree of control, superconducting qubits have been largely investigated in this direction. Here, we present a survey on the basic concepts and ideas behind the implementation of novel superconducting circuits with intrinsic protection against decoherence at a hardware level. In particular, the main focus is on multi-mode superconducting circuits, the paradigmatic example being the so-called 0−π circuit. We report on their working principle and possible physical implementations based on conventional Josephson elements, presenting recent experimental realizations, discussing both fabrication methods and characterizations.

Evidence of Josephson coupling in a few-layer black phosphorus planar Josephson junction

  1. Francesca Telesio,
  2. Matteo Carrega,
  3. Giulio Cappelli,
  4. Andrea Iorio,
  5. Alessandro Crippa,
  6. Elia Strambini,
  7. Francesco Giazotto,
  8. Manuel Serrano-Ruiz,
  9. Maurizio Peruzzini,
  10. and Stefan Heun
Setting up strong Josephson coupling in van der Waals materials in close proximity to superconductors offers several opportunities both to inspect fundamental physics and to develop
novel cryogenic quantum technologies. Here we show evidence of Josephson coupling in a planar few-layer black Phosphorus junction. The planar geometry allows us to probe the junction behavior by means of external gates, at different carrier concentrations. Clear signatures of Josephson coupling are demonstrated by measuring supercurrent flow through the junction at milli Kelvin temperatures. Manifestation of Fraunhofer pattern with a transverse magnetic field is also reported, confirming the Josephson coupling. These findings represent the first evidence of proximity Josephson coupling in a planar junction based on a van der Waals material beyond graphene and open the way to new studies, exploiting the peculiar properties of exfoliated black phosphorus thin flakes.