https://link.springer.com/content/pdf/10.1016%2FS1044-0305%2802%2900384-7.pdf

A two-dimensional quadrupole ion trap mass spectrometer.

Atomic clocks have been instrumental in science and technology, leading to innovations such as global positioning, advanced communications, and tests of fundamental constant variation. Timekeeping precision at 1 part in 10 18 enables new timing applications in relativistic geodesy, enhanced Earth- and space-based navigation and telescopy, and new tests of physics beyond the standard model. Here, we describe the development and operation of two optical lattice clocks, both using spin-polarized, ultracold atomic ytterbium. A measurement comparing these systems demonstrates an unprecedented atomic clock instability of 1.6 × 10 –18 after only 7 hours of averaging.

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An atomic clock with $10^{-18}$ instability

Micromotion of ions in Paul traps has several adverse effects, including alterations of atomic transition line shapes, significant second-order Doppler shifts in high-accuracy studies, and limited confinement time in the absence of cooling. The ac electric field that causes the micromotion may also induce significant Stark shifts in atomic transitions. We describe three methods of detecting micromotion. The first relies on the change of the average ion position as the trap potentials are changed. The second monitors the amplitude of the sidebands of a narrow atomic transition, caused by the first-order Doppler shift due to the micromotion. The last technique detects the Doppler shift induced modulation of the fluorescence rate of a broad atomic transition. We discuss the detection sensitivity of each method to Doppler and Stark shifts, and show experimental results using the last technique.

Minimization of ion micromotion in a Paul trap

▪ Abstract Laser ablation of in situ metals has recently made it possible to immerse a large number of different metal atoms and ions and small clusters of metal atoms in liquid helium (He) and thus study their absorption and emission spectra in the visible region. Atoms and molecules are readily picked up by large ( ≥ 103 atoms) He droplets, and their spectra are sensitively detected through the use of either beam depletion following absorption or laser-induced fluorescence. Within the past three years, a wide variety of molecules, ranging from OCS to large organic molecules such as amino acids and a number of van der Waals complexes and even large metal clusters, have been embedded in He droplets and studied either in infrared or in the visible region. These results are discussed here in detail, and the evidence for the effect of superfluidity on the spectral features is reviewed.

Spectroscopy of atoms and molecules in liquid helium

Characteristics of mass selective axial ion ejection from a linear quadrupole ion trap in the presence of an auxiliary quadrupole field are described. Ion ejection is shown to occur through coupling of radial and axial motion in the exit fringing fields of the linear ion trap. The coupling is efficient and can result in extraction of as much as 20% of the trapped ions. This, together with the very high trapping efficiencies, can yield high sensitivity mass spectral responses. The experimental apparatus is based on the ion path of a triple quadrupole mass spectrometer allowing either the q2 collision cell or the final mass analysis quadrupole to be used as the linear trap. Space charge induced distortions of the mass resolved features while using the pressurized q2 linear ion trap occur at approximately the same ion density as reported for conventional three-dimensional ion traps. These distortions are, however, much reduced for the lower pressure linear trap possibly owing to the proposed axial ejection mechanism that leads to ion ejection only for ions of considerable radial amplitude. RF heating due to the high ejection q-value and the low collision frequency may also contribute. Two hybrid RF/DC quadrupole-linear ion trap instruments are described that provide high sensitivity product ion scanning while operated in the linear ion trap mode while also retaining all conventional triple quadrupole scan modes such as precursor ion and neutral loss scan modes. Copyright © 2002 John Wiley & Sons, Ltd.

A new linear ion trap mass spectrometer

The critical rf magnetic field H/sub c//sup rf/ of several type-I and type-II superconductors has been measured between 90 and 300 MHz and near T/sub c/ has been found to approach the ideal superheating field in nearly all cases. However, in the same samples the dc critical field shows little evidence of superheating. The temperature dependence of H/sub c//sup rf/ suggests that rf-stimulated vortex nucleation occurs in the type-I materials.

Critical rf magnetic fields for some type-I and type-II superconductors

We discuss the implications of using high-power microwave tests in a fountain frequency standard to measure the frequency bias resulting from distributed cavity-phase shifts. We develop a theory which shows that the frequency bias from distributed cavity phase depends on the amplitude of the microwave field within the cavity. The dependence leads to the conclusion that the frequency bias associated with the distributed cavity phase is typically both misestimated and counted twice within the error budget of fountain frequency standards.

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Power dependence of distributed cavity phase-induced frequency biases in atomic fountain frequency standards

A microprocessor-based feedback system has been designed, built and tested to provide phase and amplitude stabilization of a 150 MHz superconducting splitring accelerating resonator for heavy ions. This system has a bandwidth of 400 kHz and can operate with positive feedback as a limiter or with negative feedback locking to an external reference. Direct negative feedback has already been used to stabilize the phase of a split-loop resonator to an accuracy of 0.01 radian at 2 MV/m.1 All of the parameters of the system: gains, phase shifts, level reference, phase reference and frequency of the synthesizer are digitally controlled either manually or by the microprocessor. The advantages of this control system include automatic operation of the accelerator, pre-warning of an eventual breakdown of a resonator, and automatic recovery from such a breakdown.

A Microprocessor-Based Feedback System for Phase and Amplitude Stabilization of Superconducting Resonators

Energy stored in a superconducting resonator has been switched to an external load producing a pulse of microwave power. The peak power in the pulse was nine times that of the source feeding the cavity, and the pulse was observed to be phase locked to the source.

Microwave power gain utilizing superconducting resonant energy storage

Measurements on a superconducting cavity maser oscillator are presented which show a frequency stability of parts in 10/sup 15/ for times from 1 second to 1000 seconds. A phase noise of approximately -80 dB/f/sup 3/, where f is frequency, is shown. The measured stability at a 1 second interval is 10 times better than that of a hydrogen maser, and phase noise at 8 GHz is more than 20 dB below that of a multiplied quartz crystal oscillator. >

G.J. Dick

Papers

Critical rf magnetic fields for some type-I and type-II superconductors

Power dependence of distributed cavity phase-induced frequency biases in atomic fountain frequency standards

A Microprocessor-Based Feedback System for Phase and Amplitude Stabilization of Superconducting Resonators

Microwave power gain utilizing superconducting resonant energy storage

Improved performance of the superconducting cavity maser at short measuring times (atomic frequency standards)