Graduate Lunch Talk: Luke Burkhart, Yale Physics, “Magnetic Skinholes and Copper Snares: Eliminating Decoherence from Quasiparticles in Superconducting Qubits”

Superconducting circuits, built around the non-linear inductance of the Josephson junction, are one of the most promising candidates for the building block of quantum computers. The viability of such a computer is highly dependent on the decoherence processes which scramble the quantum information stored in the individual quantum bits (qubits). One of the primary sources of decoherence in superconducting qubits is from the tunneling of excitations in the superconductor (quasiparticles) through the Josephson junction. The presence of these quasiparticles, whose minimum energy is much larger than the available thermal energy in our experiments, remains a mystery. Counterintuitively, one way to eliminate quasiparticles is by creating regions of the circuit where superconductivity is suppressed, which creates regions away from the Josephson junction where the quasiparticles can die quietly. After reviewing the basics of superconducting circuits and quasiparticles, I’ll discuss our recent work engineering protection from quasiparticles in our implementation of the superconducting qubit (the 3D transmon), both with magnetic field vortices, and most recently, with the addition of normal (non-superconducting) metal.