Quantum noise places a fundamental limit on the per photon sensitivity attainable in optical measurements. This limit is of particular importance in biological measurements, where the optical power must be constrained to avoid damage to the specimen. By using non-classically correlated light, we demonstrated that the quantum limit can be surpassed in biological measurements. Quantum enhanced microrheology was performed within yeast cells by tracking naturally occurring lipid granules with sensitivity 2.4 dB beyond the quantum noise limit. The viscoelastic properties of the cytoplasm could thereby be determined with a 64% improved measurement rate. This demonstration paves the way to apply quantum resources broadly in a biological context.
@article{arxiv.1206.6928,
title = {Biological measurement beyond the quantum limit},
author = {Michael A. Taylor and Jiri Janousek and Vincent Daria and Joachi Knittel and Boris Hage and Hans-A. Bachor and Warwick P. Bowen},
journal= {arXiv preprint arXiv:1206.6928},
year = {2014}
}