Salvy P. Russo

Atomic delocalisation as a microscopic origin of two-level defects in Josephson junctions

  1. Timothy C. DuBois,
  2. Salvy P. Russo,
  3. and Jared H. Cole
Identifying the microscopic origins of decoherence sources prevalent in Josephson junction based circuits is central to their use as functional quantum devices. Focussing on so called
„strongly coupled“ two-level defects, we construct a theoretical model using the atomic position of the oxygen which is spatially delocalised in the oxide forming the Josephson junction barrier. Using this model, we investigate which atomic configurations give rise to two-level behaviour of the type seen in experiments. We compute experimentally observable parameters for phase qubits and examine defect response under the effects of applied electric field and strain.
arxiv pdf

Delocalised oxygen as the origin of two-level defects in Josephson junctions

  1. Timothy C. DuBois,
  2. Manolo C. Per,
  3. Salvy P. Russo,
  4. and Jared H. Cole
One of the key problems facing superconducting qubits and other Josephson junction devices is the decohering effects of bi-stable material defects. Although a variety of phenomenological
models exist, the true microscopic origin of these defects remains elusive. For the first time we show that these defects may arise from delocalisation of the atomic position of the oxygen in the oxide forming the Josephson junction barrier. Using a microscopic model, we compute experimentally observable parameters for phase qubits. Such defects are charge neutral but have non-zero response to both applied electric field and strain. This may explain the observed long coherence time of two-level defects in the presence of charge noise, while still coupling to the junction electric field and substrate phonons.
arxiv pdf