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arXiv:1507.00072 · Physical Review A

Detection of a weak magnetic field via cavity-enhanced Faraday rotation

Keyu Xia, Nan Zhao, Jason Twamley

Published Oct 12, 2015• 18 citations
arXivHTMLPDF

Abstract

We study the sensitive detection of a weak static magnetic field via Faraday rotation induced by an ensemble of spins in a bimodal degenerate microwave cavity. We determine the limit of the resolution for the sensitivity of the magnetometry achieved using either single-photon or multiphoton inputs. For the case of a microwave cavity containing an ensemble of nitrogen-vacancy defects in diamond, we obtain a magnetometry sensitivity exceeding $5.2\phantom{\rule{0.28em}{0ex}}\phantom{\rule{4pt}{0ex}}\mathrm{n}\mathrm{T}/\sqrt{\mathrm{Hz}}$ utilizing a single-photon probe field, while for a multiphoton input we achieve a subfemtotesla sensitivity using a coherent-probe microwave field with power of ${P}_{\text{in}}=1\phantom{\rule{0.28em}{0ex}}\mathrm{n}\mathrm{W}$.

DOI
10.1103/physreva.92.043409

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We study the sensitive detection of a weak static magnetic field via Faraday rotation induced by an ensemble of spins in a bimodal degenerate microwave cavity. We determine the limit of the resolution for the sensitivity of the magnetometry achieved using either single-photon or multiphoton inputs. For the case of a microwave cavity containing an ensemble of nitrogen-vacancy defects in diamond, we obtain a magnetometry sensitivity exceeding 5.2nT/Hz5.2\phantom{\rule{0.28em}{0ex}}\phantom{\rule{4pt}{0ex}}\mathrm{n}\mathrm{T}/\sqrt{\mathrm{Hz}}5.2nT/Hz​ utilizing a single-photon probe field, while for a multiphoton input we achieve a subfemtotesla sensitivity using a coherent-probe microwave field with power of Pin=1nW{P}_{\text{in}}=1\phantom{\rule{0.28em}{0ex}}\mathrm{n}\mathrm{W}Pin​=1nW.
Abstract We suggest a multiatom cavity quantum electrodynamics system for the detection of a weak magnetic field, based on Faraday rotation with intracavity electromagnetically induced transparency. Our study demonstrates that the collective coupling between the cavity modes and the atomic ensemble can be used to improve the sensitivity. With single-probe photon input, the sensitivity is inversely proportional to the number of atoms, and a sensitivity of 2.45 nT Hz –1/2 could be attained. With multiphoton measurement, our numerical calculations show that the magnetic field sensitivity can be improved to 105.6 aT Hz –1/2 with realistic experimental conditions.
We demonstrate 4π4π4π-steradian vector magnetic field sensing using an ensemble of nitrogen-vacancy (NV) centers in a single-crystal diamond coupled to a microwave (MW) cavity. The MW cavity enhances the spin-photon coupling which enables efficient, high-contrast spin-state readout via MW interrogation and removes the need for bulky optical collection components. An applied AC bias magnetic field lifts the zero-field degeneracy of the four crystallographic NV orientations, allowing each orientation to be individually addressed and used for vector reconstruction of the magnetic field. The resulting magnetometer has a 40\% contrast (20x higher than typical for optical spin-ensemble readout) and achieves a single-axis sensitivity of 250 pT/Hz\sqrt{\mathrm{Hz}}Hz​ which is flat from DC to 1 kHz. Noise models of the composite spin-cavity system establish MW amplitude noise as the dominant noise source and predict a thermal noise limit of 2 pT/Hz\sqrt{\mathrm{Hz}}Hz​.
The nitrogen vacancy (NV) center in diamond is a versatile color center used for magnetometry, quantum computing, and quantum communications. In this article, using a single laser beam as a pump and probe, we measure the spin states of the NV center using the Faraday effect and use such measurements to develop a novel magnetic field sensor. Using the spin-state-dependent effect on the left and right circularly polarized light, we probe and confirm the existence of spin-orbit coupling in the NV center at room temperature. The sensitivity of our magnetometer is 350 350~350 nT/Hz\sqrt{Hz}Hz​, limited by the background produced by the laser trapped inside the diamond. We argue that by using an optical cavity and a high-purity diamond, sensitivities in the femtotesla level can be achieved.
We propose using an optical cavity to enhance the sensitivity of a magnetometer relying on the detection of the spin state of a high-density nitrogen-vacancy ensemble in diamond using infrared optical absorption. The role of the cavity is to obtain a contrast in the absorption-detected magnetic resonance approaching unity at room temperature. We project an increase in the photon shot-noise limited sensitivity of two orders of magnitude in comparison with a single-pass approach. Optical losses can limit the enhancement to one order of magnitude, which could still enable room-temperature operation. Finally, the optical cavity also allows us to use less pumping power when the cavity is resonant at both the pump and the infrared probe wavelength.
We demonstrate a cavity-enhanced room-temperature magnetic field sensor based on nitrogen-vacancy centers in diamond. Magnetic resonance is detected using absorption of light resonant with the 1042 nm spin-singlet transition. The diamond is placed in an external optical cavity to enhance the absorption, and significant absorption is observed even at room temperature. We demonstrate a magnetic field sensitivity of 2.5  nT/Hz2.5\text{ }\text{ }\mathrm{nT}/\sqrt{\mathrm{Hz}}2.5  nT/Hz​, and project a photon shot-noise-limited sensitivity of 70  pT/Hz70\text{ }\text{ }\mathrm{pT}/\sqrt{\mathrm{Hz}}70  pT/Hz​ for a few mW of infrared light, and a quantum projection-noise-limited sensitivity of 250  fT/Hz250\text{ }\text{ }\mathrm{fT}/\sqrt{\mathrm{Hz}}250  fT/Hz​ for the sensing volume of $\ensuremath{\sim}90\text{ }\text{ }\mathrm{\ensuremath{\mu}}\mathrm{m}\ifmmode\times\else\texttimes\fi{}90\text{ }\text{ }\mathrm{\ensuremath{\mu}}\mathrm{m}\ifmmode\times\else\texttimes\fi{}200\text{ }\text{ }\mathrm{\ensuremath{\mu}}\mathrm{m}$.