Yale University

Title: Quantum information processing with superconducting tunnel junction circuits

Abstract: Recent experiments have shown that nanoscale superconducting circuits are potential candidates for the implementation of scalable solid-state quantum bits. A crucial question is whether these systems have a sufficiently large coherence quality factor Q, which is the ratio between the decoherence time and the time needed to perform an elementary operation. Without Q>10^4, recently proposed algorithms for quantum bit error correction would not be effective. In order to assess whether such large Q's can be achieved, we have designed and operated a novel type of superconducting tunnel junction circuit which behaves as a two-level atom*. An arbitrary evolution of its quantum state can be programmed with a series of microwave pulses. A projective measurement of the state is performed by a pulsed readout sub-circuit. The quality factor of quantum coherence, as measured by a Ramsey fringe experiment, is sufficiently high that entangling several of such circuits appears possible.

* D. Vion, A. Aassime, A. Cottet, P. Joyez, H. Pothier, C. Urbina, D. Esteve, M.H. Devoret, Science 296 (2002) 886.