Experimental Feedback Control of Quantum Systems Using Weak Measurements

G. G. Gillett (1) , R.B. Dalton (1) , B.P. Lanyon (1) , M.P. Almeida (1) , Marco Barbieri (2, 1) , Geoff J. Pryde (3) , J.L. O'Brien (4) , K.J. Resch (5, 6) , S. D. Bartlett (7) , A.G. White (1)

1 Department of Physics and Centre for Quantum Computer Technology
2 Laboratoire Charles Fabry de l'Institut d'Optique / Optique quantique
3 Centre for Quantum Dynamics
4 Centre for Quantum Photonics
5 IQC - Institute for Quantum Computing [Waterloo]
6 Department of Physics and Astronomy [Waterloo]
7 School of Physics

A goal of the emerging field of quantum control is to develop methods for quantum technologies to function robustly in the presence of noise. Central issues are the fundamental limitations on the available information about quantum systems and the disturbance they suffer in the process of measurement. In the context of a simple quantum control scenario--the stabilization of nonorthogonal states of a qubit against dephasing--we experimentally explore the use of weak measurements in feedback control. We find that, despite the intrinsic difficultly of implementing them, weak measurements allow us to control the qubit better in practice than is even theoretically possible without them. Our work shows that these more general quantum measurements can play an important role for feedback control of quantum systems.

Domains: Quantum Physics [quant-ph]

G. G. Gillett, R.B. Dalton, B.P. Lanyon, M.P. Almeida, Marco Barbieri, et al.. Experimental Feedback Control of Quantum Systems Using Weak Measurements. Physical Review Letters, 2010, 104, pp.080503. ⟨10.1103/PhysRevLett.104.080503⟩. ⟨hal-00570271⟩