Emanuele G. Dalla Torre

Optimal Calibration of Qubit Detuning and Crosstalk

  1. David Shnaiderov,
  2. Matan Ben Dov,
  3. Yoav Woldiger,
  4. Assaf Hamo,
  5. Eugene Demler,
  6. and Emanuele G. Dalla Torre
Characterizing and calibrating physical qubits is essential for maintaining the performance of quantum processors. A key challenge in this process is the presence of crosstalk that
complicates the estimation of individual qubit detunings. In this work, we derive optimal strategies for estimating detuning and crosstalk parameters by optimizing Ramsey interference experiments using Fisher information and the Cramer-Rao bound. We compare several calibration protocols, including measurements of a single quadrature at multiple times and of two quadratures at a single time, for a fixed number of total measurements. Our results predict that the latter approach yields the highest precision and robustness in both cases of isolated and coupled qubits. We validate experimentally our approach using a single NV center as well as superconducting transmons. Our approach enables accurate parameter extraction with significantly fewer measurements, resulting in up to a 50\% reduction in calibration time while maintaining estimation accuracy.
arxiv pdf

Simulating long-range hopping with periodically-driven superconducting qubits

  1. Mor M. Roses,
  2. Haggai Landa,
  3. and Emanuele G. Dalla Torre
Quantum computers are a leading platform for the simulation of many-body physics. This task has been recently facilitated by the possibility to program directly the time-dependent pulses
sent to the computer. Here, we use this feature to simulate quantum lattice models with long-range hopping. Our approach is based on an exact mapping between periodically driven quantum systems and one-dimensional lattices in the synthetic Floquet direction. By engineering a periodic drive with a power-law spectrum, we simulate a lattice with long-range hopping, whose decay exponent is freely tunable. We propose and realize experimentally two protocols to probe the long tails of the Floquet eigenfunctions and to identify a scaling transition between weak and strong long-range couplings. Our work offers a useful benchmark of pulse engineering and opens the route towards quantum simulations of rich nonequilibrium effects.
arxiv pdf