Bulletin of the American Physical Society
46th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 60, Number 7
Monday–Friday, June 8–12, 2015; Columbus, Ohio
Session J2: Invited Session: Ion Spectroscopy for Tests of Fundamental Physics |
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Chair: Joseph Tan, National Institute of Standards and Technology, Gaithersburg Room: Union ABC |
Wednesday, June 10, 2015 2:00PM - 2:30PM |
J2.00001: Placing constraints on the time-variation of fundamental constants using atomic clocks Invited Speaker: Peter Nisbet-Jones Optical atomic frequency standards, such as those based on a single trapped ion of $^{171}$Yb$^{+}$, now demonstrate systematic frequency uncertainties in the $10^{-17}-10^{-18}$ range. These standards rely on the principle that the unperturbed energy levels in atoms are fixed and can thus provide absolute frequency references. A frequency standard's uncertainty is therefore limited by the uncertainty in realising the idealized unperturbed environment. There exists the possibility however that the unperturbed level spacing is not fixed. Some theories that go beyond the Standard Model involve a time-variation of the fundamental ``constants'' - such as the fine structure constant - which determine these energy levels. Measurements of spectral lines in radiation emitted from distant galaxies around 10$^{10}$~years ago are inconclusive, with some results suggesting the existence of a time-variation, and others observing nothing. By virtue of their very small measurement uncertainty atomic-clock experiments can, in timescales of only a few years, perform tests of present-day variation that are complementary to astrophysical data. Comparisons of frequency measurements between two or more atomic ``clock'' transitions that have different sensitivities to these constants enables us to directly measure any present-day time-variation. Combining recent results from the NPL $^{171}$Yb$^{+}$ clock with measurements from other experiments worldwide places upper limits on the present-day time-variation of the proton-to-electron mass ratio $\mu$ and the fine-structure constant $\alpha$ of $\dot{\mu}/{\mu} = 0.2(1.1)\times 10^{-16}$ yr$^{-1} $ and $\dot{\mu}/{\mu} = -0.7(2.1)\times 10^{-17}$ yr$^{-1} $ . [Preview Abstract] |
Wednesday, June 10, 2015 2:30PM - 3:00PM |
J2.00002: Coulomb crystallization of sympathetically cooled highly charged ions Invited Speaker: Jos\'e R. Crespo L\'opez-Urrutia Wave functions of inner-shell electrons significantly overlap with the nucleus, whereby enormously magnified relativistic, quantum electrodynamic (QED) and nuclear size effects emerge. In highly charged ions (HCI), the relative reduction of electronic correlations contributions improves the visibility of these effects. This well known facts have driven research efforts with HCI, yet the typically high temperatures at which these can be prepared in the laboratory constitutes a serious hindrance for application of laser spectroscopic methods. The solution for this, cooling HCI down to crystallization has remained an elusive target for more than two decades. By applying laser cooling to an ensemble of Be$^{+}$ ions, we build Coulomb crystals that we use for stopping the motion of HCI and for cooling them. HCI, in this case Ar$^{13+}$ ions are extracted from an electron beam ion trap with an energy spread of a few 100's of eV, due to the ion temperature within the trap. Carefully timed electric pulses in a potential-gradient decelerate and bunch the HCI. We achieve Coulomb crystallization of these HCI by re-trapping them in a cryogenic linear radiofrequency trap where they are sympathetically cooled through Coulomb interaction with the directly laser-cooled ensemble. Furthermore, we also demonstrate cooling of a single Ar$^{13+}$ ion by a single Be$^{+}$ ion, prerequisite for quantum logic spectroscopy with potentially 10$^{-19}$ relative accuracy. The strongly suppressed thermal motion of the embedded HCI offers novel possibilities for investigation of questions related to the time variation of fundamental constants, parity non-conservation effects, Lorentz invariance and quantum electrodynamics. Achieving a seven orders-of-magnitude decrease in HCI temperature, from the starting point at MK values in the ion source down to the mK range within the Coulomb crystal eliminates the major obstacle for HCI investigation with high precision laser spectroscopy and quantum computation schemes. [Preview Abstract] |
Wednesday, June 10, 2015 3:00PM - 3:30PM |
J2.00003: Spectroscopy of dipolar interactions in trapped-ion crystals Invited Speaker: Roee Ozeri I'll describe two recent experiments in which weak dipolar interactions were measured between trapped ions in linear crystals. In the first experiment the magnetic interaction between the electronic spin of two trapped-ions was measured. This measurement enabled an improvement of the bounds placed on the existence of light pseudo-scalar or axial vector bosons. In the second experiment, the collective Lamb shift was measured in an array of resonantly excited ions in crystals of up to eight ions. [Preview Abstract] |
Wednesday, June 10, 2015 3:30PM - 4:00PM |
J2.00004: Michelson-Morley test for electrons using a trapped ion decoherence-free subspace Invited Speaker: Hartmut Haeffner Lorentz symmetry is one of the corner stones of modern physics. As such it should not only hold for photons, but also for other particles such as the electron. Here we search for violation of Lorentz symmetry by performing an analogue of a Michelson-Morley experiment for electrons. We split an electron-wavepacket bound inside a calcium ion into two parts with different orientations. As the Earth rotates, the absolute spatial orientation of the wavepackets changes and anisotropies in the electron dispersion would modify the phase of the interference signal. To remove noise, we prepare a pair of ions in a decoherence-free subspace, thereby rejecting magnetic field fluctuations common to both ions. After a 23 hour measurement, we limit the energy variations to 11 mHz, verifying the isotropy of the electron's motion at the $10^{-18}$ level, a 100 times improvement over previous work. Alternatively, we can interpret our result as testing the rotational invariance of the Coulomb potential. Assuming Lorentz symmetry holds for electrons and that the photon dispersion relation governs the Coulomb force, we obtain a fivefold improved limit on anisotropies in the speed of light. [Preview Abstract] |
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