Stuttgart 2012 – wissenschaftliches Programm
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SYQM: Symposium Quantum Limited Measurement: Applications in Metrology, Biology and Solid State Research
SYQM 1: Quantum limited measurement applications 1
SYQM 1.6: Vortrag
Freitag, 16. März 2012, 12:15–12:30, V47.01
Heisenberg-limited metrology without entanglement — •Daniel Braun1,2 and John Martin3 — 1Université de Toulouse, UPS, Laboratoire de Physique Théorique (IRSAMC), F-31062 Toulouse, France — 2CNRS, LPT (IRSAMC), F-31062 Toulouse, France — 3Institut de Physique Nucléaire, Atomique et de Spectroscopie, Université de Liège, 4000 Liège, Belgium
It is common experimental practice to improve the signal-to-noise ratio by averaging many measurements of identically prepared systems. If the systems are independent, the overall sensitivity of the measurement, defined as the smallest resolvable change of the quantity under consideration, improves as 1/√N. Quantum enhanced measurements promise the possibility to improve this scaling behavior. Indeed, if the N systems are initially entangled, one may achieve in principle a 1/N scaling of the sensitivity, known as the “Heisenberg limit”. Unfortunately, decoherence has so far limited the implementation of such “quantum enhanced protocols” to small values of N. Here we show that a setup in which N quantum systems interact with a N+1st system allows one to achieve Heisenberg limited sensitivity, without using or ever creating any entanglement. Local decoherence changes only the prefactor but not the scaling with N. We present a general theoretical framework for this new kind of measurement scheme, and propose a possible application in high precision measurements of the length of an optical cavity.
[1] Braun, D. & Martin, J., Nature Comm. 2, 223, 2011.
[2] Braun, D. & Martin, J., arXiv:1005.4443.