How to use quantum information techniques to enhance measurement sensitivity.

Previous results: A new technique to measure very small magnetic fields: the quantum lock-in (Kotler et.al. “Single ion quantum lock-in amplifier”, Nature 473, 61 (2011)). Our technique enabled us to extend the quantum memory time (coherence) of a single ion qubit by more than a factor of a 1000, from a millisecond to more than a second. Combining this technique and the use of ideas from Quantum Error Correction, we were able to measure the magnetic field of a single electron spin, at a distance of 2.4 um (Kotler et.al. “Measurement of the magnetic interaction between two bound electrons of two separate ions”, Nature 510, 376 (2014)). We were then able to use that measurement to place bounds on dipole-dipole couplings outside the standard model (Kotler et.al. “Constraints on Exotic Dipole-Dipole Couplings between Electrons at the Micrometer Scale”, PRL 115, 081801 (2015)).