High Frequency Atomic Magnetometer by Use of Electromagnetically Induced Transparency

Atomic magnetometers have achieved magnetic sensitivities in the subfemtotesla regime. Their bandwidth is determined by the transverse spin relaxation rate, $1/T_2$, which also determines the magnetic sensitivity. It is theoretically demonstrated that by using an electromagnetically induced transparent probe beam in a pump-probe atomic magnetometer, it is possible to operate the latter at frequencies much higher than its bandwidth, maintaining a high signal-to-noise ratio.

Figure 1

Optical Pumping Pump-Probe Magnetometer. (a) Experimental scheme. (b) Optical pumping viewed along the $\widehat{\mathbf{z}}$ quantization axis. (c) Probing viewed along the $\widehat{\mathbf{x}}$ quantization axis.

Figure 2

Inclusion of ground-state sublevels $|c⟩$, $|\overline{c}⟩$, and of the drive laser, coupling them to $|\overline{e}⟩$ and $|e⟩$, respectively. The levels are degenerate since along the $\widehat{\mathbf{x}}$ axis the magnetic field is zero.

Figure 3

Absorption (solid lines) and dispersion (dashed lines) profiles of the probe beam for the full ${}^{85}\mathrm{Rb}$ structure (thick lines) and the toy 6-level model (thin lines). Inset: Faraday rotation angle for the full (solid line) and toy model (dashed line). The optimum point of operation is indicated by the arrows. The width of the Raman resonance is a few times $1/T_2\approx 300\mathrm{Hz}$. The calculation was done for a magnetic field $B_y=1\mathrm{fT}$, and for an alkali density $[\mathrm{Rb}]=5\times {10}^{14}{\mathrm{cm}}^{-3}$. The profiles of the numerical calculation involving the full level structure of ${}^{85}\mathrm{Rb}$ broaden and shift to the right due to higher ${\Omega }_d$.

Figure 4

Enhancement factor ${\beta }_{\varphi }$ due to enhanced Faraday rotation of the probe laser polarization. Dashed line: Doppler-free case (both toy and full model); solid line: inclusion of Doppler broadening.