We test Lorentz invariance by searching for a time-dependent quadrupole splitting of Zeeman levels in 21 Ne. A component at twice the Earth's sidereal frequency would suggest a preferred direction whichaffects the local physics of the nucleus. The technique employs polarized 21 Ne and 3 He gases produced by spin exchange with laser optically pumped Rb. Both species are contained in the same glass cell; 3 He provides magnetometry and a monitor of systematic effects. Our data produce an upper limit (1

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We have demonstrated the first two species maser. Ensembles of 3 He and 129 Xe gas, co-located in a double-chamber glass cell, performed simultaneous maser oscillations on their nuclear spin-1 2 Zeeman transitions. This new device may be used for experiments requiring precision magnetometry combined with frequency measurement of a second free-running species operating in the same volume. For example, the 3 He maser may serve as a magnetometer, while the 129 Xe maser may be used to search for a permanent electric dipole moment of the 129 Xe atom as a test of time reversal symmetry. [S0031-9007(96)01584-0] PACS numbers: 32.80. Bx, 32.60.+i, 84.40.Ik Precision measurement of the Zeeman splitting in a twostate system is the basis for searches for permanent electric dipole moments (EDMs) in the neutron [1] and in atoms [2][3][4][5]. Such EDM searches serve as stringent tests of time reversal symmetry in elementary particle interactions [6]. Currently, two species differential EDM experiments are being performed to search for leptonic T-violation (using 205 Tl and Na) [7], and to search for T-violation in neutrons (using a 199 Hg comagnetometer) [8]. The advantage of differential measurements is that they are insensitive to common-mode systematic effects [9]. Here we report the operation of a two species noble gas maser, the first device to simultaneously sustain active maser oscillations on two distinct transitions in different atomic species ( 3 He and 129 Xe). The two species noble gas maser allows sensitive differential measurements of the noble gas Zeeman splittings. Thus one noble gas species can serve as a precision magnetometer to stabilize the system's static magnetic field, while the other species is used as a sensitive probe for new physics such as an EDM. The two species noble gas maser has an additional important feature: active maser oscillation permits arbitrarily long coherent measurement of the noble gas Zeeman frequencies. A coherent frequency measurement can achieve greater precision than the incoherent average of a set of shorter measurements made during an equivalent period of time.Predicted 129 Xe and 3 He EDMs arise from hadronic and tensor electron-nuclear interactions containing terms proportional to Z 2 and higher order in Z [6], so that a 3 He EDM is expected to be much smaller in magnitude than a 129 Xe EDM. Our planned EDM search will entail sequential applications of an electric field parallel, and then antiparallel, to a static magnetic field. The electric field's coupling to a 129 Xe EDM would produce a maser frequency shift linear in the magnitudes and signs of both the 129 Xe EDM and the electric field. The static magnetic field can be feedback stabilized by phase locking one species' maser to a stable frequency standard. The other [free-running] maser will be monitored for electric-fieldproportional frequency shifts. Either maser can be phase locked. When the 3 He maser is phase locked, a possible 129 Xe EDM͞E-field coupling would induce a frequency shift in the 129 Xe maser. When ...

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