Probing Gravity and Small Forces with Torsion Balances
Blayne Heckel University of Washington
PIRSA:14060018
Displaying 2569 - 2580 of 4881
Format results
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Resonant Detection of Short-Range Gravitational Forces
Eli Levenson-Falk University of Southern California
PIRSA:14060046 -
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Fundamental physics with atom interferometry
Jason Hogan Stanford Law School - The Bill Lane Centre for the American West
PIRSA:14060016 -
Precision gravity measurements with cold atom interferometry
Guglielmo Tino National Institute for Nuclear Physics
PIRSA:14060015 -
Atomic Clocks Monitored to 0.2 ns using Satellite Geodesy
Geoff Blewitt University of Nevada Reno
PIRSA:14060014 -
Free Discussion
PIRSA:14060013 -
Spectroscopic constrains on variation of fundamental constants in astrophysics.
Mikhail Kozlov University of Turku
PIRSA:14060012 -
Time and frequency metrology at NIST
Jeff Sherman National Institute of Standards & Technology - Time and Frequency Division
PIRSA:14060011 -
Frequency comparison of cryogenic optical lattice clocks
Hidetoshi Katori University of Tokyo
PIRSA:14060010 -
Zen and the art of atomic time-keeping (Tutorial on atomic clocks for particle theorists)
Andrei Derevianko University of Nevada Reno
PIRSA:14060009 -
Atomic Clocks and Tests of Fundamental Physics
Ekkehard Peik Physikalisch-Technische Bundesanstalt (PTB)
PIRSA:14060008
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Probing Gravity and Small Forces with Torsion Balances
Blayne Heckel University of Washington
PIRSA:14060018The EotWash group at the University of Washington has developed a set of torsion balance
instruments to probe the properties of gravity and to search for new weak forces. Current efforts
focus on improved tests of the principle of equivalence, the inverse square law at short distances,
and spin-coupled interactions. These experiments and prospects for the future will be discussed.
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Resonant Detection of Short-Range Gravitational Forces
Eli Levenson-Falk University of Southern California
PIRSA:14060046Some theories predict a short-range component to the gravitational force, typically modeled as a Yukawa modification of the gravitational potential. This force is usually detected by measuring the motion of a mechanical oscillator driven by an external mass. In this talk I will discuss such an apparatus optimized for use in the 10-100 micron distance range. The setup consists of a cantilever-style silicon nitride oscillator suspended above a rotating drive mass. Periodic density variations in the drive mass cause an oscillatory gravitational force on the cantilever, whose position is read out using optical interferometry. In order to drive the cantilever precisely on resonance, it must have a broad resonant peak; however, lower quality factors reduce force sensitivity by reducing the amplitude of oscillation for a given drive force. We solve this problem by implementing an effective damping on the oscillator by use of optical feedback. I will discuss further applications of this feedback technique, as well as improvements to the apparatus and future experiments. -
f(R) Gravity and Cosmology
Valerio Faraoni Bishop's University
PIRSA:14060045A popular alternative to dark energy in explaining the current acceleration of the universe discovered with type Ia supernovae is modifying gravity at cosmological scales. But this is risky: even when everything is well for cosmology, other fundamental and experimental aspects of gravity must be checked in order for the theory to be viable. The successes of modified gravity and its challenges, which have generated a large body of literature in the past ten years, will be reviewed. -
Fundamental physics with atom interferometry
Jason Hogan Stanford Law School - The Bill Lane Centre for the American West
PIRSA:14060016Precision atom interferometry is poised to become a powerful tool for discovery in fundamental physics. Towards this end, I will describe recent, record-breaking atom interferometry experiments performed in a 10 meter drop tower that demonstrate long-lived quantum superposition states with macroscopic spatial separations. The potential of this type of sensor is only beginning to be realized, and the ongoing march toward higher sensitivity will enable a diverse science impact, including new limits on the equivalence principle, probes of quantum mechanics, and detection of gravitational waves. Gravitational wave astronomy is particularly compelling since it opens up a new window into the universe, collecting information about astrophysical systems and cosmology that is difficult or impossible to acquire by other methods. Atom interferometric gravitational wave detection offers a number of advantages over traditional approaches, including simplified detector geometries, access to conventionally inaccessible frequency ranges, and substantially reduced antenna baselines. -
Precision gravity measurements with cold atom interferometry
Guglielmo Tino National Institute for Nuclear Physics
PIRSA:14060015I will discuss experiments we are conducting for precision tests of gravitational physics using cold atom interferometry. In particular, I will report on the measurement of the gravitational constant G with a Rb Raman interferometer, and on experiments based on Bloch oscillations of Sr atoms confined in an optical lattice for gravity measurements at small spatial scales and for testing Einstein equivalence principle. -
Atomic Clocks Monitored to 0.2 ns using Satellite Geodesy
Geoff Blewitt University of Nevada Reno
PIRSA:14060014Satellite geodesy uses the timing of photons from satellites to determine the Earth’s time varying shape, gravity field, and orientation in space, with accuracies of <1 part per billion, or millimeters at the Earth’s surface, and centimeters at satellite altitude. Implicit in mm-level GPS positioning is the modeling of widely separated atomic clocks with sub-ns precision. The precise monitoring of the relative timing phases between widely separated atomic clocks forms the metrological basis of a recently proposed approach to detect topological dark matter of a type that affects fundamental constants. Relative clock time can be updated as often as every second using the current global network of geodetic GPS stations that record data at that rate, though many more geodetic GPS stations record data every 30 seconds. Thus GPS could be used as the world’s largest dark matter detector, potentially sensitive to dark matter structures sweeping through the entire system >100 seconds, corresponding to speeds <500 km s¬-1 relative to the solar system. Here it is shown that relative timing phases can be determined to ~0.2 ns between the global network of atomic clocks at many geodetic GPS stations on the Earth’s surface separated as far as ~12,000 km, plus those aboard the 30 GPS satellites separated as far as ~50,000 km. Available atomic clock types include caesium (Cs), rubidium (Rb), and (on the ground) hydrogen maser (Hm). Achieving sub-ns relative timing precision requires (1) dual-frequency carrier phase data measured at the few mm level, (2) rigorous modeling of many aspects of the Earth system and GPS satellite dynamics, and (3) stochastic estimation of biases in the system. For example, solar radiation pressure from momentum exchange with photons hitting the satellites perturbs orbits at the few-meter level. Imperfect modeling, such as knowledge of the satellite attitude, requires us to estimate orbit acceleration biases as they slowly vary in time. For mm-level positioning applications, clock phases are considered to be unknown biases to be estimated as a white noise process, that is, estimated independently at every data epoch without constraint. By virtue of the common view of satellites simultaneously by multiple ground stations, relative clock time can be determined between all clocks in the entire satellite-ground system by estimating all biases in a global inversion. Since the timing phase between Hm clocks can be accurately extrapolated forward in time, they set the standard by which upper limits can be set on the precision of timing at any specific instant. As a feasibility study, a custom analysis of original raw GPS phase data was designed using the GIPSY OASIS II software (from NASA JPL), processing data from ~40 ground stations of various atomic clock type. An analysis of data from GPS stations that are positioned at the few-millimeter level every day indicates that Hm clock time is determined at to ~0.2 ns. Since the smoothness of Hm clocks is not assumed anywhere in the modeling, and that station clock type has no influence on positioning precision, one can infer that timing at the 0.2 ns level is also the case for less predictable atomic clocks such as Rb and Cs, thus providing a window into possibly different coupling of dark matter with different clock types. -
Free Discussion
PIRSA:14060013 -
Spectroscopic constrains on variation of fundamental constants in astrophysics.
Mikhail Kozlov University of Turku
PIRSA:14060012I will discuss present limits on the variation of the fine structure constant and the electron to proton mass ratio from the astrophysical data on the spectra from the interstellar gas medium. The emphasis will be made on the infrared and microwave spectra. Such spectra may be 2 - 3 orders of magnitude more sensitive to the variation of constants than optical spectra. -
Time and frequency metrology at NIST
Jeff Sherman National Institute of Standards & Technology - Time and Frequency Division
PIRSA:14060011Official U.S. time is currently realized by an ensemble of commercial cesium-beam atomic clocks and hydrogen masers. Cesium-fountain devices presently serve as ultimate frequency references and help to define the SI second. The present quandary is: these microwave-based standards are rapidly becoming outmatched by new optical atomic frequency references---by a factor of 1,000 in stability, and perhaps a factor of 100 in accuracy. I will survey the ongoing optical atomic clock projects at NIST and highlight related work in optical time and frequency measurement and transfer. -
Frequency comparison of cryogenic optical lattice clocks
Hidetoshi Katori University of Tokyo
PIRSA:14060010We report frequency comparison of two Sr optical lattice clocks operated at cryogenic temperature to dramatically reduce blackbody radiation shift. After 11 measurements performed over a month, the two cryo-clocks agree to within (-1.1±1.6)×〖10〗^(-18).
Current status of a frequency ratio measurement of Hg/Sr clocks and a remote comparison of cryo-clocks located at Riken and University of Tokyo will be mentioned. -
Zen and the art of atomic time-keeping (Tutorial on atomic clocks for particle theorists)
Andrei Derevianko University of Nevada Reno
PIRSA:14060009 -
Atomic Clocks and Tests of Fundamental Physics
Ekkehard Peik Physikalisch-Technische Bundesanstalt (PTB)
PIRSA:14060008The precision of atomic clocks continues to improve at a rapid pace: While caesium clocks now reach relative systematic uncertainties of a few 10-16, several optical clocks based on different atomic systems are now reported with uncertainties in the 10-18 range. This variety of precise clocks will allow for improved tests of fundamental physics, especially quantitative tests of relativity and searches for variations of constants. Laser-cooled and trapped ions permit the study of strongly forbidden transitions with extremely small natural linewidths and long coherence times. The frequency of the electric octupole transition S1/2 - F7/2 at 467 nm in 171Yb+ with a natural linewidth in the nHz range is remarkably insensitive against external electric and magnetic fields. We evaluate the systematic uncertainty of a frequency standard that is based on this transition as 4*10-18 at present. An even better isolation from external perturbations can be expected for the nuclear transition in 229Th3+ at about 160 nm with an expected linewidth in the mHz range. In order to excite the so far only indirectly observed nuclear transition using electronic bridge processes, we investigate the dense electronic level structure of Th+. Both transitions, in Yb+ and 229Th, are predicted to be highly sensitive to changes in the fine structure constant. I will give an update on limits on variations of constants as obtained from atomic clock comparisons.