Single-shot measurement of the Josephson charge qubit

TL;DR

This paper reports a method for single-shot measurement of Josephson charge qubits by converting quantum states into classical charge states and detecting them with a single-electron transistor, achieving high readout efficiency.

Contribution

It introduces a novel single-shot readout technique for Josephson charge qubits using a superconducting island and a single-electron transistor, with high efficiency.

Findings

Readout efficiency of 87% for |1> state

Readout efficiency of 93% for |0> state

Successful transformation of quantum states into classical charge states

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 |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.