Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session T4: Keithly Award Session: Precision Time and Frequency Measurements |
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Sponsoring Units: GIMS Chair: James Matey, United States Naval Academy Room: Oregon Ballroom 204 |
Wednesday, March 17, 2010 2:30PM - 3:06PM |
T4.00001: Joseph F. Keithley Award For Advances in Measurement Science Talk: Precision Noise Measurements at Microwave and Optical Frequencies Invited Speaker: The quest to detect Gravitational Waves resulted in a number of important developments in the fields of oscillator frequency stabilization and precision noise measurements. This was due to the realization of similarities between the principles of high sensitivity measurements of weak mechanical forces and phase/amplitude fluctuations of microwave signals. In both cases interferometric carrier suppression and low-noise amplification of the residual noise sidebands were the main factors behind significant improvements in the resolution of spectral measurements. In particular, microwave frequency discriminators with almost thermal noise limited sensitivity were constructed leading to microwave oscillators with more than 25dB lower phase noise than the previous state-of-the-art. High power solid-state microwave amplifiers offered further opportunity of oscillator phase noise reduction due to the increased energy stored in the high-Q resonator of the frequency discriminator. High power microwave oscillators with the phase noise spectral density close to -160dBc/Hz at 1kHz Fourier frequency have been recently demonstrated. The principles of interferometric signal processing have been applied to the study of noise phenomena in microwave components which were considered to be ``noise free''. This resulted in the first experimental evidence of phase fluctuations in microwave circulators. More efficient use of signal power enabled construction of the ``power recycled'' interferometers with spectral resolution of -200dBc/Hz at 1kHz Fourier frequency. This has been lately superseded by an order of magnitude with a waveguide interferometer due to its higher power recycling factor. A number of opto-electronic measurement systems were developed to characterize the fidelity of frequency transfer from the optical to the microwave domain. This included a new type of a phase detector capable of measuring phase fluctuations of the weak microwave signals extracted from the demodulated femtosecond light pulses with almost thermal noise limited precision. The experiments which followed showed that microwave signals of exceptional spectral purity could be generated from the frequency stabilized lasers [Preview Abstract] |
Wednesday, March 17, 2010 3:06PM - 3:42PM |
T4.00002: Toward Robust, Stable, and Accurate Single Atom Optical Clocks Invited Speaker: |
Wednesday, March 17, 2010 3:42PM - 4:18PM |
T4.00003: Optical Lattice Clocks Based on Neutral Yb Atoms Invited Speaker: Designer optical lattices are used in a variety of AMO investigations due to their ability to confine atoms under highly controllable conditions. I will describe how we use such lattices (in one or more dimensions) to produce optical atomic clocks that might one day achieve a fractional frequency precision of one part in 10$^{17}$ or better. We take advantage of the tight confinement and long interaction times provided by the lattice to perform high resolution spectroscopy on a narrow optical transition in neutral Yb (natural linewidth $\sim $ 10 mHz) to which we lock the frequency of our clock laser. By tuning the optical lattice to its magic wavelength (at which the induced light shifts are equal for the ground and excited states of the clock reference transition), we remove the effect of the lattice on the clock frequency to first order. To improve further our knowledge of the clock frequency, we evaluate potential shifts due to higher-order lattice effects, background blackbody radiation, and collision effects in over-filled lattices. Through the use of tens of thousands of trapped atoms, we have the potential to achieve high measurement precision in comparatively short averaging times. I will present results for one-dimensional lattice clocks at 578 nm based on two isotopes of Yb. The first uses Yb-171 (nuclear spin, I, =1/2) and has demonstrated an absolute fractional frequency uncertainty below one part in 10$^{15}$. The second is based on Yb-174 (I = 0) and uses the technique of magnetic-field induced spectroscopy to excite the atoms. Included will be measurements of the Yb absolute clock frequency at the sub-Hz level, new stability results, and comparisons with other optical clocks. Finally, future directions will be considered including the use of multi-dimensional lattices to isolate the individual atoms. [Preview Abstract] |
Wednesday, March 17, 2010 4:18PM - 4:54PM |
T4.00004: Tests of Lorenz and Local Position Invariance using Microwave Oscillators and Interferometers Invited Speaker: We present current work at the University of Western Australia and Paris Observatory to test fundamental physics using precision phase and frequency measurements. We describe three experiments under development. Firstly, we describe a continuously rotating cryogenic microwave oscillator constructed to test Local Lorentz Invariance. Secondly, we describe the development of a new, magnetically asymmetric, microwave interferometer with thermal noise limited readout, which will allow a sensitivity to the scalar and odd-parity coefficients for Lorentz violation in the photon sector of the Standard Model Extension Thirdly, we describe an experiment between a cryogenic sapphire oscillator and a Hydrogen maser, which is used to test fundamental constants and Local Position and Lorentz Invariance. [Preview Abstract] |
Wednesday, March 17, 2010 4:54PM - 5:30PM |
T4.00005: Modern Laser-Atomic Physics and Stable Oscillators for Real World Applications Invited Speaker: This talk will consider how, when and where modern laser/atomic physics might play a significant role in real world applications. Advances in laser technology, control systems and precision laser spectroscopy are enabling many new capabilities for measurements and instrumentation, and can improve the performance of atomic clocks, magnetometers and inertial sensors by several orders of magnitude. Initial ideas of using lasers to enhance the performance of atom-based instruments dates back to the 1960s, and those early predictions were mostly well founded and have now been demonstrated, to varying degrees, in research laboratories and environments around the world. However, 40 years later, these promises have yet to be realized in industrial, governmental or commercial applications. As an example, the technology and performance (in terms of accuracy and stability) of commercially available atomic clocks has been rather stagnate since the 1970s, whereas those in research laboratories have continued to improve so that their performance is roughly 1000x better than the commercial frequency standards. We can, and should, ask why there is such a large gap between what is possible and what is commercially available? Reasons for the large disconnect in performance are multifold, and will be discussed. Atom-Optic Inertial sensors (gyros, accelerometers) are a more recent development and application that uses the same methods of laser atomic physics. Efforts are now underway to bring these atom interferometer inertial sensors to real world applications and commercial availability. Extremely stable microwave sources are another spinoff of precision laser technology and spectroscopy. It now appears that lasers may soon find their way into high performance commercial clocks and magnetometers and other instruments. However, our community has been making such promises and predictions for decades now... [Preview Abstract] |
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