Radial Two-Dimensional Ion Crystals in a Linear Paul Trap.

We experimentally study two-dimensional (2D) Coulomb crystals in the "radial-2D" phase of a linear Paul trap. This phase is identified by a 2D ion lattice aligned entirely with the radial plane and is created by imposing a large ratio of axial to radial trapping potentials. Using arrays of up to 19 ^{171}Yb^{+} ions, we demonstrate that the structural phase boundaries of such crystals are well described by the pseudopotential approximation, despite the time-dependent ion positions driven by intrinsic micromotion.

Time base evaluation for atom gravimeters.

Time is an inevitable quantity involved in absolute gravity measurements, and 10 MHz frequency standards are usually utilized as time base. Here we investigate the influence of time base bias on atom-interferometry-based gravity measurements and present an onsite calibration of the time base bias relying on an atom gravimeter itself. With a microwave source referenced to the time base, the time base bias leads to a magnified frequency shift of the microwave source output.

Note: Directly measuring the direct digital synthesizer frequency chirp-rate for an atom interferometer.

During gravity measurements with Raman type atom interferometry, the frequency of the laser used to drive Raman transition is scanned by chirping the frequency of a direct digital synthesizer (DDS), and the local gravity is determined by precisely measuring the chip rate α of DDS. We present an effective method that can directly evaluate the frequency chirp rate stability of our DDS. By mixing a pair of synchronous linear sweeping signals, the chirp rate fluctuation is precisely measured with a frequency counter.

Note: A three-dimension active vibration isolator for precision atom gravimeters.

An ultra-low frequency active vibration isolator, simultaneously suppressing three-dimensional vibration noise, is demonstrated experimentally. The equivalent natural period of the isolator is 100 s and 12 s for the vertical and horizontal direction, respectively. The vibration noise in the vertical direction is about 50 times reduced during 0.