Article abstract
Nature Physics 3, 119 - 125 (2007)
doi:10.1038/nphys509
Subject Categories: Quantum physics | Condensed-matter physics | Information theory and computation
Quantum non-demolition measurement of a superconducting two-level system
A. Lupa
cu1,
S. Saito1,2,
T. Picot1,
P. C. de Groot1,
C. J. P. M. Harmans1
and
J. E. Mooij1
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.
- Quantum Transport Group, Kavli Institute of NanoScience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
- NTT Basic Research Laboratories, NTT Corporation, 3-1, Morinosato-Wakamiya, Atsugi, Kanagawa, 243-0198, Japan
Correspondence to: A. Lupacu1
Present address: Laboratoire Kastler Brossel, Département de Physique de l'Ecole Normale Supérieure, 24 rue Lhomond, F-75231 Paris Cedex 05, France
Correspondence to: A. Lupacu1
e-mail: Adrian.Lupascu@lkb.ens.fr
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