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 measure 31,908,131.25(30) kHz for the 2(3)}P J=0 to 2 fine structure interval in helium. The difference between this and theory to order mα7 (20 Hz numerical uncertainty) implies 0.22(30) kHz for uncalculated terms. The measurement is performed by using atomic beam and electro-optic laser techniques. Various checks include a 3He 2{3}S hyperfine measurement. We can obtain an independent value for the fine structure constant α with a 5 ppb experimental uncertainty. However, dominant mα8 terms (potentially 1.2 kHz) limit the overall uncertainty to a less competitive 20 ppb in α.

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Resonator Fiber-Optic Gyroscope (RFOG) performance has hitherto been limited by non-linearity, modal impurity, and backscattering in the sensing fibers. The use of hollow-core fiber (HCF) effectively reduces non-linearity, but the complex interplay among glass and air-guided modes in conventional HCF technologies can severely exacerbate RFOG instability. By employing high-performance nested anti-resonant nodeless fiber, we demonstrate long-term stability in a hollow-fiber RFOG of 0.05 deg/hr, nearing the levels required for civil aircraft navigation. This represents a 3X improvement over any prior hollow-core RFOG and a factor of 500X over any prior result at integration times longer than 1 hour.

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