Mesoscopic physics challenges (in) superconducting quantum devices

Superconducting quantum bits, or qubits, are at the forefront of quantum
computing research. Harnessing the low loss properties of
superconductors and the nonlinearity of Josephson junctions, qubits can
be engineered to exist in quantum superposition states and they can be
entangled, promising a new paradigm in information processing. By
controlling and measuring these fragile quantum states, the community
eventually aims to implement powerful quantum algorithms. However, due
to the innate complexity of solid-state physics, superconducting qubits
still have to cope with various loss and decoherence mechanisms,
certainly to the chagrin of quantum computing scientists, but also to
the joy of mesoscopic physicists. I will discuss three mesoscopic
physics phenomena which significantly complicate the task of engineering
coherent superconducting hardware: ionizing radiation interactions with
the device substrate, long lived two level systems which imprint a
memory in the qubit's environment, and fluctuations in the transparency
of aluminum oxide tunnel barriers which are at the heart of Josephson
junctions.