We propose a quantum nondemolition measurement using a kicked two-state system (qubit). By tuning the waiting time between kicks to be the qubit oscillation period, the kicking apparatus performs a nondemolition measurement. While dephasing is unavoidable, the nondemolition measurement can (1) slow relaxation of diagonal density matrix elements, (2) avoid detector back-action, and (3) allow for a large signal-to-noise ratio. Deviations from the ideal behavior are studied by allowing for detuning of the waiting time, as well as finite-time, noisy pulses. The scheme is illustrated with a double-dot qubit measured by a gate-pulsed quantum point contact.
@article{arxiv.cond-mat/0406529,
title = {Quantum Nondemolition Measurement of a Kicked Qubit},
author = {Andrew N. Jordan and Markus Buttiker},
journal= {arXiv preprint arXiv:cond-mat/0406529},
year = {2007}
}