We performed a search for neutron spin coupling to a Lorentz and CPT-violating background field using a magnetometer with overlapping ensembles of K and 3 He atoms. The co-magnetometer is mounted on a rotary platform for frequent reversal of its orientation. We measure sidereal oscillations in the signal to search for anomalous spin coupling of extra-solar origin. We determine the equatorial components of the background field interacting with the neutron spin to be b n X = (0.1 ± 1.6) × 10 −33 GeV and b n Y = (2.5 ± 1.6) × 10 −33 GeV, improving on the previous limit by a factor of 30. This measurement represents the highest energy resolution of any spin anisotropy experiment.

We studied the line shape of Rb D 1 and D 2 resonance lines in the presence of 1-10 amg of several gases: 3 He, 4 He, N 2 , and Xe. We found that the line cores are well described by the asymmetric line shape expected for a van der Waals interatomic potential. The width and shift of the lines is proportional to the density of the foreign gas with high degree of accuracy, while the asymmetry is independent of the density. The constants of proportionality for pressure broadening and shift were measured with much higher accuracy than in previous experiments. We also studied the density dependence of the oscillator strength of the transitions.

A radio-frequency tunable atomic magnetometer is developed for detection of nuclear quadrupole resonance ͑NQR͒ from room temperature solids. It has a field sensitivity 0.24 fT/ Hz 1/2 at the 423 kHz 14 N NQR frequency of ammonium nitrate. A potential application of the magnetometer is detection of nitrogen-containing explosives which is difficult with conventional tuned copper coils due to a poor signal-to-noise ratio ͑SNR͒ below a few megahertz. The NQR signal from 22 g of powdered ammonium nitrate located 2 cm away from the sensor is detected with a SNR of 9 in a 4.4-s-long multiple echo sequence, which represents an estimated order-of-magnitude improvement in sensitivity over the pickup coil detection.

We describe a 3 He-129 Xe comagnetometer using 87 Rb atoms for noble-gas spin polarization and detection. We use a train of 87 Rb π pulses and σ + /σ − optical pumping to realize a finite-field Rb magnetometer with suppression of spin-exchange relaxation. We suppress frequency shifts from polarized Rb by measuring the 3 He and 129 Xe spin precession frequencies in the dark, while applying π pulses along two directions to depolarize Rb atoms. The plane of the π pulses is rotated to suppress the Bloch-Siegert shifts for the nuclear spins. We measure the ratio of 3 He to 129 Xe spin precession frequencies with sufficient absolute accuracy to resolve the Earth's rotation without changing the orientation of the comagnetometer. A frequency resolution of 7 nHz is achieved after integration for 8 hours without evidence of significant drift.PACS numbers: 32.30. Dx, 06.30.Gv, 39.90.+d Spin comagnetometers first introduced in [1] are used for several types of fundamental physics experiments, such as tests of Lorentz, CP and CPT symmetries [2][3][4][5] and searches for spin-dependent forces [6][7][8][9][10]. They also have practical applications as inertial rotation sensors [11][12][13][14][15][16]. When two different spin ensembles occupy the same volume they experience nearly the same average magnetic field [17]. The ratio of their spin precession frequencies f r = ω He /ω Xe can then be used to measure the inertial rotation rate Ω or a spin coupling beyond the Standard Model b:( 1) where B 0 is the bias field alongẑ and γ He , γ Xe are the gyromagnetic ratios for 3 He and 129 Xe, which are well known [18]. Since I = 1/2 nuclear spins are free from quadrupolar energy shifts [19], f r provides an absolute measure of non-magnetic spin interactions-this is particularly important in searches for spin-gravity coupling [20] (where the interaction is hard to modulate), and for use as a gyroscope.An alkali-metal magnetometer provides a natural way to detect nuclear-spin signals because Rb atoms are already used to polarize the nuclear spins by spin-exchange collisions; these collisions enhance the classical dipolar field from the nuclear magnetization by a factor κ 0 [21], which is about 5 for Rb-3 He [22] and 500 for Rb-Xe [23]. However, the presence of polarized Rb atoms also causes large noble-gas frequency shifts that affect the accuracy of Eq. (1). In the past, these frequency shifts have been avoided in 3 He-129 Xe comagnetometers by detecting a smaller dipolar field outside of an alkali-free cell using an RF coil [24] or a SQUID magnetometer [25].In this Letter we describe a new method for operating the 3 He-129 Xe comagnetometer using 87 Rb readout with high sensitivity and accuracy. We develop a 87 Rb magnetometer that can operate in a finite magnetic field of about 5 mG while suppressing Rb-Rb spin-exchange relaxation to increase the magnetometer sensitivity. It

Using spin-echo NMR techniques we study the transverse spin relaxation of hyperpolarized liquid 129Xe in a spherical cell. We observe an instability of the transverse magnetization due to dipolar fields produced by liquid 129Xe, and find that imperfections in the pi pulses of the spin-echo sequence suppress this instability. A simple perturbative model of this effect is in good agreement with the data. We obtain a transverse spin relaxation time of 1300 sec in liquid 129Xe, and discuss applications of hyperpolarized liquid 129Xe as a sensitive magnetic gradiometer and for a permanent electric dipole moment search.