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Thursday, March 04, 2010
12:30 PM - 2:00 PM
T-DO Conference Room, TA-03 - Bldg 123 - Room 121

Quantum Lunch

A metastable superconducting qubit

Andrew J. Kerman
Lincoln Laboratory, Massachusetts Institute of Technology

One of the distinguishing features of Josephson-junction (JJ)-based qubits is their strong coupling to electromagnetic (EM) fields, which permits fast gate operations ( 10-100ns). However, it may also be responsible for their short excited-state lifetimes (. 4s); that is, assuming the decay process is electromagnetic, its rate depends on the same matrix element which governs intentional qubit manipulations by external fields. Unfortunately, understanding and controlling spontaneous decay of these circuits has so far proved difficult, because it also depends on their EM environment at GHz frequencies, which is strongly influenced by microscopic degrees of freedom in the substrate, surface oxides, or JJ barrier dielectrics. Although little is yet certain about the properties of these degrees of freedom, work is ongoing to study them, and to reduce their number through improved materials and fabrication. In this presentation, I will discuss a different approach: a qubit which is insensitive to highfrequency EM fluctuations by design. This is a departure from the highly successful computational architecture known as circuit QED, in which strong transverse coupling to EM fields is both a prerequisite and a figure of merit. After describing the details of this new qubit design, which is based on an RF-SQUID and nanowire kinetic inductors, I will then discuss the consequences of weak transverse EM coupling, the first and foremost of which is a (potentially) much longer excited-state lifetime. I will describe how these metastable qubits can be manipulated and coupled to each other, as well as read out and initialized. [1] This work is sponsored by the United States Air Force under Contract #FA8721-05-C-0002. Opinions, interpretations, recommendations and conclusions are those of the authors and are not necessarily endorsed by the United States Government.

Host: Gennady Berman