Dissipative Dynamics of Graph-State Stabilizers with Superconducting Qubits

  1. Liran Shirizly,
  2. Grégoire Misguich,
  3. and Haggai Landa
We study the noisy evolution of multipartite entangled states, focusing on superconducting-qubit devices accessible via the cloud. We experimentally characterize the single-qubit coherent
and incoherent error parameters together with the effective two-qubit interactions, whose combined action dominates the decoherence of quantum memory states. We find that a valid modeling of the dynamics of superconducting qubits requires one to properly account for coherent frequency shifts, caused by stochastic charge-parity fluctuations. We present a numerical approach that is scalable to tens of qubits, allowing us to simulate efficiently the dissipative dynamics of some large multiqubit states. Comparing our simulations to measurements of stabilizers dynamics of graph states realized experimentally with up to 12 qubits on a ring, we find that a very good agreement is achievable. Our approach allows us to probe nonlocal state characteristics that are inaccessible in the experiment. We show evidence for a significant improvement of the many-body state fidelity using dynamical decoupling sequences, mitigating the effect of charge-parity oscillations and two-qubit crosstalk.

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.