Valentina Brosco

Flux-Tunable Regimes and Supersymmetry in Twisted Cuprate Heterostructures

  1. Alessandro Coppo,
  2. Luca Chirolli,
  3. Nicola Poccia,
  4. Uri Vool,
  5. and Valentina Brosco
Van der Waals assembly allows for the creation of Josephson junctions in an atomically sharp interface between two exfoliated Bi2Sr2CaCu2O8+δ (Bi-2212) flakes that are twisted relative
to each other. In a narrow range of angles close to 45∘, the junction exhibits a regime where time-reversal symmetry can be spontaneously broken and it can be used to encode an inherently protected qubit called flowermon. In this work we investigate the physics emerging when two such junctions are integrated in a SQuID circuit threaded by a magnetic flux. We show that the flowermon qubit regime is maintained up to a finite critical value of the magnetic field and, under appropriate conditions, it is protected against both charge and flux noise. For larger external fluxes, the interplay between the inherent twisted d-wave nature of the order parameter and the external magnetic flux enables the implementation of different artificial atoms, including a flux-biased protected qubit and a supersymmetric quantum circuit.
arxiv pdf

Superconducting qubit based on twisted cuprate van der Waals heterostructures

  1. Valentina Brosco,
  2. Giuseppe Serpico,
  3. Valerii Vinokur,
  4. Nicola Poccia,
  5. and Uri Vool
Van-der-Waals (vdW) assembly enables the fabrication of novel Josephson junctions utilizing an atomically sharp interface between two exfoliated and relatively twisted Bi2Sr2CaCu2O8+x
(Bi2212) flakes. In a range of twist angles around 45∘, the junction provides a regime where the interlayer two-Cooper pair tunneling dominates the current-phase relation. Here we propose to employ this novel junction to realize a capacitively shunted qubit that we call flowermon. The d-wave nature of the order parameter endows the flowermon with inherent protection against charge-noise-induced relaxation and quasiparticle-induced dissipation. This inherently protected qubit paves the way to a new class of high-coherence hybrid superconducting quantum devices based on unconventional superconductors.
arxiv pdf

A hybrid ferromagnetic transmon qubit: circuit design, feasibility and detection protocols for magnetic fluctuations

  1. Halima Giovanna Ahmad,
  2. Valentina Brosco,
  3. Alessandro Miano,
  4. Luigi Di Palma,
  5. Marco Arzeo,
  6. Domenico Montemurro,
  7. Procolo Lucignano,
  8. Giovanni Piero Pepe,
  9. Francesco Tafuri,
  10. Rosario Fazio,
  11. and Davide Massarotti
We propose to exploit currently available tunnel ferromagnetic Josephson junctions to realize a hybrid superconducting qubit. We show that the characteristic hysteretic behavior of
the ferromagnetic barrier provides an alternative and intrinsically digital tuning of the qubit frequency by means of magnetic field pulses. To illustrate functionalities and limitation of the device, we discuss the coupling to a read-out resonator and the effect of magnetic fluctuations. The possibility to use the qubit as a noise detector and its relevance to investigate the subtle interplay of magnetism and superconductivity is envisaged.
arxiv pdf