Experimental validation of the Kibble-Zurek Mechanism on a Digital
  Quantum Computer
The Kibble-Zurek mechanism (KZM) captures the essential physics of
nonequilibrium quantum phase transitions with symmetry breaking. KZM predicts a
universal scaling power law for the defect density which is fully determined by
the system's critical exponents at equilibrium and the quenching rate. We
experimentally tested the KZM for the simplest quantum case, a single qubit
under the Landau-Zener evolution, on an open access IBM quantum computer
(IBM-Q). We find that for this simple one-qubit model, experimental data
validates the central KZM assumption of the adiabatic-impulse approximation for
a well isolated qubit. Furthermore, we report on extensive IBM-Q experiments on
individual qubits embedded in different circuit environments and topologies,
separately elucidating the role of crosstalk between qubits and the increasing
decoherence effects associated with the quantum circuit depth on the KZM
predictions. Our results strongly suggest that increasing circuit depth acts as
a decoherence source, producing a rapid deviation of experimental data from
theoretical unitary predictions.
Santiago Higuera-Quintero Ferney J. Rodríguez Luis Quiroga Fernando J. Gómez-Ruiz