Editor's Summary
15 November 2007
Heisenberg's the limit
At the fundamental level, measurement precision is limited by the number of quantum resources (such as photons) involved, and standard phase measurement schemes lead to an uncertainty (the standard quantum limit) that scales with this number. In theory, it should be possible to achieve a precision limited only by the Heisenberg uncertainty principle. A few experiments have beaten the standard quantum limit, but none have achieved Heisenberg-limited scaling until now, largely due to the need for difficult-to-generate exotic quantum entangled states. Higgins et al. adopted an alternative approach using unentangled single-photon states, allowing them to achieve Heisenberg-limited phase estimation. This marks a drastic reduction in the complexity of achieving quantum-enhanced measurement precision.
News and Views: Quantum optics: Kittens catch phase
The most sensitive phase-measuring instrument yet uses quantum trickery and a scaled-down version of the notorious Schrödinger's cat. It means that more sensitive devices for metrology and imaging could be on the way.
Jonathan P. Dowling
doi:10.1038/450362b
Letter: Entanglement-free Heisenberg-limited phase estimation
B. L. Higgins, D. W. Berry, S. D. Bartlett, H. M. Wiseman & G. J. Pryde
doi:10.1038/nature06257
