Suppressing relaxation in superconducting qubits by quasiparticle   pumping
  Dynamical error suppression techniques are commonly used to improve coherence in quantum systems. They reduce dephasing errors by applying control pulses designed to reverse erroneous coherent evolution driven by environmental noise. However, such methods cannot correct for irreversible processes such as energy relaxation. In this work, we investigate a complementary, stochastic approach to reducing errors: instead of deterministically reversing the unwanted qubit evolution, we use control pulses to shape the noise environment dynamically. In the context of superconducting qubits, we implement a pumping sequence to reduce the number of unpaired electrons (quasiparticles) in close proximity to the device. We report a 70% reduction in the quasiparticle density, resulting in a threefold enhancement in qubit relaxation times, and a comparable reduction in coherence variability. 
Simon Gustavsson, Fei Yan, Gianluigi Catelani, Jonas Bylander, Archana   Kamal, Jeffrey Birenbaum, David Hover, Danna Rosenb...
quant-ph cond-mat.mes-hall cond-mat.supr-con