Jonathan Dowling, a theoretical physicist at Louisiana State University in the US, says that the latest work could also help in the search for gravitational waves. Researchers hope to register gravitational waves' distortion of space time by measuring the difference in path length experienced by laser beams traveling in the two orthogonal pipes of an interferometer. Dowling says that if the American LIGO detector could operate with a sensitivity that scales as 1/N3/2 rather than as 1/N1/2 then either its sensitivity could be greatly increased or its laser power enormously reduced, which would avoid potential heating and deformation of the facilities' optics. "This opens up a whole new ball game in nonlinear interferometry," he adds.
However, Barry Sanders, a quantum physicist at the University of Calgary in Canada, urges caution. "The experiment demonstrates that the Heisenberg limit can be beaten in the real world," he says. "But practical applications are not likely in the near future because of the technical challenges that need to be overcome, especially noise. We are still exploring the basic physics of using quantum resources for precise measurements."