A magnetometer using spin-polarized K and 3He atoms occupying the same volume is used to search for anomalous nuclear spin-dependent forces generated by a separate 3He spin source. We measure changes in the 3He spin precession frequency with a resolution of 18 pHz and constrain anomalous spin forces between neutrons to be less than 2x10(-8) of their magnetic or less than 2x10(-3) of their gravitational interactions on a length scale of 50 cm. We present new limits on neutron coupling to light pseudoscalar and vector particles, including torsion, and constraints on recently proposed models involving unparticles and spontaneous breaking of Lorentz symmetry.

We develop a new comagnetometer using 21 Ne atoms with nuclear spin I = 3/2 and Rb atoms polarized by spin-exchange with K atoms to search for tensor interactions that violate local Lorentz invariance. We frequently reverse orientation of the experiment and search for signals at the first and second harmonics of the sidereal frequency. We constrain 4 of the 5 spatial Lorentz-violating coefficients c n jk that parameterize anisotropy of the maximum attainable velocity of a neutron at a level of 10 −29 , improving previous limits by 2 to 4 orders of magnitude and placing the most stringent constrain on deviations from local Lorentz invariance.PACS numbers: 11.30. Cp, 21.30.Cb, 32.30.Dx The Michelson-Morley experiment and its successors have established that the speed of light is isotropic to a part in 10 17 [1,2]. Similarly, possible anisotropy in the maximum attainable velocity (MAV) for a massive particle [3] has been constrained by Hughes and Drever NMR experiments [4,5] and their successors to a part in 10 27[6]. These experiments form the basis for the principle of local Lorentz invariance (LLI). Together with the weak equivalence principle and the position invariance principle, they constitute the Einstein equivalence principle that is the basis of general relativity [7]. Measurements of tensor NMR energy shifts [8,9] are particularly sensitive to variation in MAV due to a finite kinetic energy of valence nucleons. They place the most stringent limits on violation of LLI within the T H µ formalism [10] describing deviations from the Einstein Equivalence Principle as well as within more general Standard Model Extension (SME) [11]. They compare favorably even to the limits on variation in MAV from ultra-high energy cosmic rays and other astrophysical phenomena [12][13][14]. It can be argued that Lorentz invariance is likely to be broken at some level by the effects of quantum gravity, which contains a dimensionfull Planck scale that is not Lorentzinvariant. Popular ideas for quantum gravity theories, such as recently proposed Hořava-Lifshitz model [15], explicitly violate Lorentz symmetry. CPT-even tensor Lorentz-violating effects, such as variation in MAV, are particularly interesting to explore because they can arise from purely kinematic violation of Lorentz invariance, do not require explicit particle spin coupling at the fundamental level, and do not suffer from fine-tuning problems associated with CPT-odd Lorentz-violating vector spin interactions [16,17].Here we describe a new comagnetometer that is sensitive to anisotropy in neutron MAV at 10 −29 level. The idea of the experiment is based on the K-3 He comagnetometer, previously used to constrain Lorentz-violating vector spin interactions [18]. The 3 He (I = 1/2) is replaced by 21 Ne (I = 3/2) to allow measurements of tensor anisotropy. In addition, since the gyromagnetic ratio of 21 Ne is about an order of magnitude smaller than that of 3 He, the comagnetometer has an order of magnitude better energy resolution for the same level of magnetic field ...

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 ³He atoms. The comagnetometer 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˜Xn=(0.1 ± 1.6) × 10⁻³³ GeV and b˜Yn=(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.

Historically, time measurements have been based on oscillation frequencies in systems of particles, from the motion of celestial bodies to atomic transitions. Relativity and quantum mechanics show that even a single particle of mass m determines a Compton frequency ω(0) = mc(2)/[formula: see text] where c is the speed of light and [formula: see text] is Planck's constant h divided by 2π. A clock referenced to ω(0) would enable high-precision mass measurements and a fundamental definition of the second. We demonstrate such a clock using an optical frequency comb to self-reference a Ramsey-Bordé atom interferometer and synchronize an oscillator at a subharmonic of ω(0.) This directly demonstrates the connection between time and mass. It allows measurement of microscopic masses with 4 × 10(-9) accuracy in the proposed revision to SI units. Together with the Avogadro project, it yields calibrated kilograms.

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.