▶︎ CANCELED: IQIM Postdoctoral and Graduate Student Seminar

March 13 seminar has been canceled.

Note different location: this week's IQIM seminar will be in the Cahill Building, Hameetman Auditorium. Lunch will follow the talk on the Cahill Patio.

The major issue for quantum superconducting circuits is their interaction with two level system (TLS) in their environment that precludes their operation in some frequency ranges. Particularly evil is the drift of these forbidden ranges with time associated with slow change in TLS frequencies. This results in a formidable challenge for the implementation of large-scale superconducting quantum circuits. Furthermore, TLS cause noise on timescales spanning many decades.

In this talk I will focus on the theoretical picture of the microscopic phenomena in the environment of superconducting circuits. I will argue that quasiparticle poisoning and charge noise are dominated by the same mechanism inherent to the superconducting circuits. The theory that I present is based on the results of very recent experiments performed in the group of McDermott at UW-Madison (USA) and the group of T. Lindstrom at NPL (UK). The main result of the theory is that formation of the traps with very long living quasiparticles is very natural for superconducting films. These traps provide additional source of very coherent TLS dangerous for qubits.

I will argue that cosmic rays provide a mechanism that produces the quasiparticles to fill the traps. I will show that each cosmic ray is in fact a catastrophic event from the viewpoint of superconducting qubit. During this event all qubits on a chip lose their coherence, which presents a formidable challenge for error correction. These conclusions are collaborated by recent experiments of I. Pop group in Karlsruhe.