Quantum computing circuit two-level system defects and their phenomena
Kevin Osborn
Laboratory for Physical Sciences, College Park, MD
Abstract
Superconducting qubits have steadily improved their coherence time for
over a decade such that quantum information algorithms are now
implemented with an integrated circuit. However, material defects at
the requisite millikelvin temperatures, often referred to as two-level
systems (TLS), interact with the microwave photon fields and continue
to limit the coherence of qubits. These TLS also limit the
performance of astronomy photon detectors, which are made with
superconducting circuits. In this talk, I will focus on TLS which are
electrically and resonantly coupled to the microwave fields, and are
particularly troublesome for these devices. Unfortunately the
microscopic model of these low temperature defects is often unknown,
but I will argue that a particular Hydrogen-based defect recently
identified by ab-initio calculations in alumina is a likely TLS
candidate. In addition, I will show how data from resonators and a
specialized Josephson junction defect spectrometer allows one to
individual TLS. Finally I will show how the TLS dipole moment can
be measured for the first time in insulating films using a
non-equilibrium measurement. These measurements also increase our
understanding of the applicability of the standard TLS model out of
equilibrium.
Bio: Dr. Kevin D. Osborn
received his doctorate in physics from the University of Illinois at
Urbana-Champaign in 2001, with a thesis on the critical fluctuations of
the superfluid density in high-temperature superconducting films.
He then started postdoctoral research at the National Institute of
Standards and Technology in Boulder, Colorado and measured individual
InGaAs quantum dots using Al single-electron transistors. In 2004
he received a National Research Council postdoctoral associate award
which allowed him to perform studies at NIST on decoherence mechanisms
in superconducting phase qubits. In 2007 Dr. Osborn transitioned
to the Laboratory for Physical Sciences in College Park, Maryland, to
set up a new research group as a US government physicist. His
group currently studies decoherence mechanisms in superconducting
qubits, with an emphasis on condensed matter phenomena related to
two-level systems.