Quantum non-demolition measurement of a superconducting two-level system
Author: ["A. Lupaşcu","S. Saito","T. Picot","P. C. de Groot","C. J. P. M. Harmans","J. E. Mooij"]
Publication: Nature Physics
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Abstract
In quantum mechanics, the process of measurement is a subtle interplay between extraction of information and disturbance of the state of the quantum system. A quantum non-demolition (QND) measurement minimizes this disturbance by using a particular system—detector interaction that preserves the eigenstates of a suitable operator of the quantum system. This leads to an ideal projective measurement. We present experiments in which we carry out two consecutive measurements on a quantum two-level system, a superconducting flux qubit, by probing the hysteretic behaviour of a coupled nonlinear resonator. The large correlation between the results of the two measurements demonstrates the QND nature of the readout method. The fact that a QND measurement is possible for superconducting qubits strengthens the notion that these fabricated mesoscopic systems are to be regarded as fundamental quantum objects. Our results are also relevant for quantum-information processing for protocols such as state preparation and error correction.
Cite this article
Lupaşcu, A., Saito, S., Picot, T. et al. Quantum non-demolition measurement of a superconducting two-level system. Nature Phys 3, 119–123 (2007). https://doi.org/10.1038/nphys509
