Miniature Cavity-Enhanced Diamond Magnetometer

We present a highly sensitive miniaturized cavity-enhanced room-temperature magnetic-field sensor based on nitrogen-vacancy centers in diamond. The magnetic resonance signal is detected by probing absorption on the 1042-nm spin-singlet transition. To improve the absorptive signal the diamond is placed in an optical resonator. The device has a magnetic-field sensitivity of $28\mathrm{pT}/\sqrt{\mathrm{Hz}}$, a projected photon shot-noise-limited sensitivity of $22\mathrm{pT}/\sqrt{\mathrm{Hz}}$, and an estimated quantum projection-noise-limited sensitivity of $0.43\mathrm{pT}/\sqrt{\mathrm{Hz}}$ with the sensing volume of $\sim 390\mu \mathrm{m}\times 4500\mu {\mathrm{m}}^2$. The presented miniaturized device is the basis for an endoscopic magnetic-field sensor for biomedical applications.

Figure 1

(a) Relevant $\mathrm{N}\text{−}V$-center energy levels and transitions (Ref. [5]). Solid green and red lines indicate excitations, dashed lines indicate radiative transitions, and gray solid lines indicate nonradiative transitions. (b) Explosion view and 2D cross section of the cavity magnetometer. (c) Schematic of the experimental setup.

Figure 2

IR-light transmission of the cavity [$P_{\mathrm{IR},t}$ as a function of green pump power ($P_{532}$)]. The transmission is normalized to unity for zero pump power. The inset displays the ${\mathrm{TEM}}_{00}$ cavity mode at 0 mW (blue) and 500 mW of pump light power (amber).

Figure 3

IR transmission signal normalized to unity off resonance as a function of microwave frequency.

Figure 4

The cavity-transmission signal (blue) and lock-in demodulated signal (red) as a function of a central frequency $f_{\mathrm{c}}$ scanned over a magnetic resonance. The experimental data are represented with dots and the fits with solid lines. The slope of the fit is represented with a straight line.

Figure 5

The magnetic-field noise spectrum (green) represents the magnetically sensitive spectrum corresponding to an environment-limited noise floor of $37\mathrm{pT}/\sqrt{\mathrm{Hz}}$ between 60 and 90 Hz; (amber) the magnetically insensitive spectrum with a noise floor of $28\mathrm{pT}/\sqrt{\mathrm{Hz}}$; (blue) the electronic noise with a floor of $2\mathrm{pT}/\sqrt{\mathrm{Hz}}$. The shot-noise limit of the system and the spin-projection noise are also depicted with dashed lines at $22\mathrm{pT}/\sqrt{\mathrm{Hz}}$ and $0.43\mathrm{pT}/\sqrt{\mathrm{Hz}}$, respectively.