High-Sensitivity Atomic Magnetometer Unaffected by Spin-Exchange Relaxation

Abstract

Alkali-metal magnetometers compete with SQUID detectors as the most sensitive magnetic field sensors. Their sensitivity is limited by relaxation due to spin-exchange collisions. We demonstrate a K magnetometer in which spin-exchange relaxation is completely eliminated by operating at high K density and low magnetic field. Direct measurements of the signal-to-noise ratio give a magnetometer sensitivity of 10 fT Hz(-1/2), limited by magnetic noise produced by Johnson currents in the magnetic shields. We extend a previous theoretical analysis of spin exchange in low magnetic fields to arbitrary spin polarizations and estimate the shot-noise limit of the magnetometer to be 2x10(-18) T Hz(-1/2).

Suppression of spin-bath dynamics for improved coherence of multi-spin-qubit systems

“…For samples with a finite concentration of 13 C nuclear spin impurities, this technique revealed an orderof-magnitude suppression of the N electronic spin-bath dynamics, which can be explained by random interactions between proximal electronic and 13 C nuclear spin impurities. This spin-bath suppression enhances the efficacy of dynamical decoupling for samples with high N impurity concentration, enabling increased NV spin coherence times and thus realization of a FOM ~2×10 14 (ms cm − 3 ), which is within an order of magnitude of the state-of-the-art spin coherence FOM achieved in atomic systems 15 . Further optimization of the multi-spin-qubit FOM may be possible by engineering this spin-bath suppression, for example, with 13 C concentration higher than the natural value.…”

“…In characterizing the potential usefulness of multi-qubit systems for quantum applications, the product of the qubit density (n qb ) and the qubit coherence lifetime (T 2 ) serves as a basic figure-of-merit (FOM), FOM = n qb T 2 . For example, in quantum measurements the phase-shift sensitivity δφ scales as 1/ FOM 5,[13][14][15] . Increasing this multi-qubit FOM requires an understanding of the sources of decoherence in the system and their interplay with qubit density.…”

Optical magnetometry

“…Several mechanisms of comparable importance have been identified for such relaxation [30], but some aspects of this process remain poorly understood [31]. The measured spin-destruction cross-sections are smaller for lighter alkali-metal atoms and result in a fundamental limit on the sensitivity of a K magnetometer of about 10 −17 V −1/2 T/Hz 1/2 [32], where V is the active volume of the sensor in cm 3 .…”

Magnetic Resonance Detection of Individual Proton Spins Using Quantum Reporters

“…Nuclear magnetic resonance and magnetic resonance imaging are essential tools for both the physical and life sciences [1,2], but have been limited to the detection of large ensembles of spins due to their low sensitivity [3,4], or the macroscopic nature of sensors [5,6]. Over the past decades, significant efforts [7][8][9][10][11] have been directed toward pushing this sensitivity to its ultimate physical limit, the detection of individual nuclear spin signals localized in a small volume.…”