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Qubit Measurement and Backaction

Backaction in Qubit Readout by Quantum-Dot Detectors

Quantum dots, used as detectors of any kind of qubit susceptible to charge-readout provide a higher sensitivity than quantum point contacts. However, the level and charge quantization of the detector requires an account of renormalization effects on the combined qubit-detector system due to fluctuations induced by the current-carrying electrodes, in particular in the limit of weak measurements. Besides relaxation and decoherence rates, the qubit is affected by coherent torques acting on the qubit-isospin – reminiscent of spin-torques in quantum dot spin-valves.

(M. Hell, M. R. Wegewijs, D. Divincenzo