Liquid-State Nuclear Spin Comagnetometers

We discuss nuclear spin comagnetometers based on ultralow-field nuclear magnetic resonance in mixtures of miscible solvents, each rich in a different nuclear spin. In one version thereof, Larmor precession of protons and ${}^{19}\mathrm{F}$ nuclei in a mixture of thermally polarized pentane and hexafluorobenzene is monitored via a sensitive alkali-vapor magnetometer. We realize transverse relaxation times in excess of 20 s and suppression of magnetic field fluctuations by a factor of 3400. We estimate it should be possible to achieve single-shot sensitivity of about $5\times {10}^{-9}\mathrm{Hz}$, or about $5\times {10}^{-11}\mathrm{Hz}$ in $\approx 1$ day of integration. In a second version, spin precession of protons and ${}^{129}\mathrm{Xe}$ nuclei in a mixture of pentane and hyperpolarized liquid xenon is monitored using superconducting quantum interference devices. Application to spin-gravity experiments, electric dipole moment experiments, and sensitive gyroscopes is discussed.

Figure 1

Ultralow-field (0.6 mG) NMR signal (single shot) from a mixture of pentane and hexafluorobenzene. Data are well described by the sum of two exponentially decaying sinusoids with $T_2^{\star }=13.7$ and 20.8 s. The inset shows the real part of the Fourier transform.

Figure 2

Demonstration of the operation as a comagnetometer. (a) Free precession frequency of ${}^1\mathrm{H}$ (triangles) and ${}^{19}\mathrm{F}$ (squares) nuclei is shown as a small modulation is applied to $B_z$, $\Delta B_z\approx 3.7\mu \mathrm{G}$, demonstrating that the two frequencies track each other closely. (b) Modulation is not visible in the ratio ${\nu }_f/{\nu }_h$.

Figure 3

Effects of gradients on the pentane-HFB comagnetometer. A gradient $d{B}_z/dx$ was applied and the ratio ${\nu }_f/{\nu }_h$ is plotted. The variation in the ratio of the frequencies indicates that there is some separation of the two solvents.

Figure 4

Ultralow-field NMR signals obtained in a mixture of hyperpolarized liquid xenon and pentane. These data were acquired with SQUID magnetometers in a 10 mG magnetic field. The inset shows the magnitude Fourier transform.