2000 character limit reached
QND measurement of a superconducting qubit in the weakly projective regime (1007.0166v1)
Published 1 Jul 2010 in cond-mat.supr-con, cond-mat.mes-hall, and quant-ph
Abstract: Quantum state detectors based on switching of hysteretic Josephson junctions biased close to their critical current are simple to use but have strong back-action. We show that the back-action of a DC-switching detector can be considerably reduced by limiting the switching voltage and using a fast cryogenic amplifier, such that a single readout can be completed within 25 ns at a repetition rate of 1 MHz without loss of contrast. Based on a sequence of two successive readouts we show that the measurement has a clear quantum non-demolition character, with a QND fidelity of 75 %.