Quantum squeezing, an irreducible resource for quantum communication and quantum metrology, is very fragile and can be lost due to classical noise produced by an environment. We show that a classical correlation between the squeezed signal and the classical probe partially monitoring noise from the environment can be used as a resource to restore the lost squeezing. Two basic methods, the feed-forward restoration and the unitary decoupling, are proposed to exploit this classical correlation. They are mutually compared for high and low squeezing and also in the different regimes of correlated classical noise. On one side, a robustness against classical probe noise to restore at least nonzero squeezing is discussed, and on the other side, a complete revealing of the high squeezing by a squeezed probe and unitary decoupling is proposed.

• Received 29 January 2010

DOI:https://doi.org/10.1103/PhysRevA.81.032330