# Stuttgart 2012 – wissenschaftliches Programm

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# Q: Fachverband Quantenoptik und Photonik

## Q 65: SYQM: Quantum limited measurement applications 2

### Q 65.4: Vortrag

### Freitag, 16. März 2012, 15:15–15:30, V47.01

**High Dynamic Range Magnetometry with a Single Nuclear Spin in Diamond** — •Gerald Waldherr^{1}, Johannes Beck^{1}, Philipp Neumann^{1}, Ressa S. Said^{2}, Matthias Nitsche^{1}, Jason Twamley^{3}, Fedor Jelezko^{4}, and Jörg Wrachtrup^{1} — ^{1}3. Physikalisches Institut, Universität Stuttgart, 70569 Stuttgart — ^{2}Institut für Quanten-Informationsverarbeitung, Universität Ulm, 89081 Ulm — ^{3}Centre for Engineered Quantum Systems, Faculty of Science, Macquarie University, Sydney, Australia — ^{4}Institut für Quantenoptik, Universität Ulm, 89073 Ulm

Sensors based on the nitrogen-vacancy (NV) defect in diamond are being developed to measure weak magnetic and electric fields at nanoscale. However, such sensors rely on measurements of a shift in the Lamor frequency of the defect, so an accumulation of quantum phase causes the measurement signal to exhibit a periodic modulation. This means that the measurement time is either restricted to half of one oscillation period, which limits accuracy, or that the magnetic field range must be known in advance. Moreover, the precision increases only slowly, as *T*^{−0.5}, with the measurement time *T*. We implement a quantum phase estimation algorithm on a single nuclear spin in diamond to combine both high sensitivity and high dynamic range. By achieving a scaling of the precision with time to *T*^{−0.85}, we improve the sensitivity by a factor of 7.4, for an accessible field range of 16 mT, or alternatively, we improve the dynamic range by a factor of 130 for a sensitivity of 2.5 µT/Hz^{0.5}. These methods are applicable to a variety of field detection schemes, and do not require entanglement.