Dario Gerace

Digital quantum simulators in a scalable architecture of hybrid spin-photon qubits

  1. Alessandro Chiesa,
  2. Paolo Santini,
  3. Dario Gerace,
  4. James Raftery,
  5. Andrew A. Houck,
  6. and Stefano Carretta
Resolving quantum many-body problems represents one of the greatest challenges in physics and physical chemistry, due to the prohibitively large computational resources that would be
required by using classical computers. A solution has been foreseen by directly simulating the time evolution through sequences of quantum gates applied to arrays of qubits, i.e. by implementing a digital quantum simulator. Superconducting circuits and resonators are emerging as an extremely-promising platform for quantum computation architectures, but a digital quantum simulator proposal that is straightforwardly scalable, universal, and realizable with state-of-the-art technology is presently lacking. Here we propose a viable scheme to implement a universal quantum simulator with hybrid spin-photon qubits in an array of superconducting resonators, which is intrinsically scalable and allows for local control. As representative examples we consider the transverse-field Ising model, a spin-1 Hamiltonian, and the two-dimensional Hubbard model; for these, we numerically simulate the scheme by including the main sources of decoherence. In addition, we show how to circumvent the potentially harmful effects of inhomogeneous broadening of the spin systems.
arxiv pdf

YBCO microwave resonators for strong collective coupling with spin ensembles

  1. Alberto Ghirri,
  2. Claudio Bonizzoni,
  3. Dario Gerace,
  4. Samuele Sanna,
  5. Antonio Cassinese,
  6. and Marco Affronte
Coplanar microwave resonators made of 330 nm-thick superconducting YBCO have been realized and characterized in a wide temperature (T, 2-100 K) and magnetic field (B, 0-7 T) range.
The quality factor Q significantly exceeds 104 below 55 K and slightly decreases for increasing fields, remaining 90% of Q(B=0) for B=7 T and T=2 K. These features allow to coherently couple resonant photons with spin ensembles at finite temperature and magnetic field. To demonstrate this, collective strong coupling regime was achieved by using the spin ensemble of a DPPH organic radical placed at the magnetic antinode of the fundamental mode: the in-plane magnetic field is used to tune the spin frequency gap across the single-mode cavity resonance at 7.78 GHz, where clear anticrossings are observed with a splitting as large as ∼82 MHz at T=2 K. The spin-cavity collective coupling rate is shown to scale as the square root of the number of active spins in the ensemble.
arxiv pdf