Optical clock comparison for Lorentz symmetry testing

Overview of the Phenomenology of Lorentz and CPT Violation in Atomic Systems

This is an overview of recent publications on the prospects of searching for nonminimal Lorentz-violating effects in atomic spectroscopy experiments. The article discusses the differences in the signals for Lorentz violation in the presence of minimal and nonminimal operators and what systems are more sensitive to certain types of Lorentz-violating operators.

Highly Polarizable Rydberg Ion in a Paul Trap

Usually the influence of the quadratic Stark effect on an ion's trapping potential is minuscule and only needs to be considered in atomic clock experiments. In this work we excite a trapped ion to a Rydberg state with polarizability ∼8 orders of magnitude higher than a low-lying electronic state; we find that the highly polarizable ion experiences a vastly different trapping potential owing to the Stark effect. We observe changes in trap stiffness, equilibrium position, and minimum potential, which can be tuned using the trapping electric fields. These effects lie at the heart of several proposed studies, including a high-fidelity submicrosecond entangling operation; in addition we demonstrate these effects may be used to minimize ion micromotion. Mitigation of Stark effects is important for coherent control of Rydberg ions; we illustrate this by carrying out the first Rabi oscillations between a low-lying electronic state and a Rydberg state of an ion.

Engineering Quantum States of Matter for Atomic Clocks in Shallow Optical Lattices

We investigate the effects of stimulated scattering of optical lattice photons on atomic coherence times in a state-of-the art ^{87}Sr optical lattice clock. Such scattering processes are found to limit the achievable coherence times to less than 12 s (corresponding to a quality factor of 1×10^{16}), significantly shorter than the predicted 145(40) s lifetime of ^{87}Sr's excited clock state. We suggest that shallow, state-independent optical lattices with increased lattice constants can give rise to sufficiently small lattice photon scattering and motional dephasing rates as to enable coherence times on the order of the clock transition's natural lifetime. Not only should this scheme be compatible with the relatively high atomic density associated with Fermi-degenerate gases in three-dimensional optical lattices, but we anticipate that certain properties of various quantum states of matter-such as the localization of atoms in a Mott insulator-can be used to suppress dephasing due to tunneling.

Phase noise of frequency doublers in optical clock lasers

Frequency doublers are widely used in high-resolution spectroscopy to shift the operation wavelength of a laser to a more easily accessible or otherwise preferable spectral region. We investigate the use of a periodically-poled lithium niobate (PPLN) waveguide frequency doubler in an optical clock. We focus on the phase evolution between the fundamental (1396 nm) and frequency-doubled (698 nm) light and its effect on clock performance. We find that the excess phase noise of the doubler under steady-state operation is at least two orders of magnitude lower than the noise of today's best interrogation lasers. Phase chirps related to changes of the optical power in the doubler unit and their influence on the accuracy of optical clocks are evaluated. We also observe substantial additional noise when characterizing the doubler unit with an optical frequency comb instead of using two identical waveguide doublers.

Improved Test of Local Lorentz Invariance from a Deterministic Preparation of Entangled States

The high degree of control available over individual atoms enables precision tests of fundamental physical concepts. In this Letter, we experimentally study how precision measurements can be improved by preparing entangled states immune to the dominant source of decoherence. Using ^{40}Ca^{+} ions, we explicitly demonstrate the advantage from entanglement on a precision test of local Lorentz invariance for the electron. Reaching the quantum projection noise limit set by quantum mechanics, we observe, for bipartite entangled states, the expected gain of a factor of two in the precision. Under specific conditions, multipartite entangled states may yield substantial further improvements. Our measurements improve the previous best limit for local Lorentz invariance of the electron using ^{40}Ca^{+} ions by a factor of two to four to about 5×10^{-19}.