Single-shot measurement of the Josephson charge qubit

Astafiev, Oleg V. and Pashkin, Yuri and Yamamoto, T. and Nakamura, Y. and Tsai, Jaw-Shen (2004) Single-shot measurement of the Josephson charge qubit. Physical review B, 69 (18): 180507. ISSN 0163-1829

Abstract

We demonstrate single-shot readout of quantum states of the Josephson charge qubit. The quantum bits are transformed into and stored as classical bits ~charge quanta! in a dynamic memory cell—a superconducting island. The transformation of state u1& ~differing form state u0& by an extra Cooper pair! is a result of a controllable quasiparticle tunneling to the island. The charge is then detected by a conventional single-electron transistor, electrostatically decoupled from the qubit. We study relaxation dynamics in the system and obtain the readout efficiency of 87% and 93% for u1& and u0& states, respectively.