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 |1〉 (differing form state |0〉 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 |1〉 and |0〉 states, respectively.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - May 2004|