Session P6: Atom Interferometry and Precision Measurements

Simultaneous Dual Species Matter Wave Interferometry

We report on the first realization of a simultaneous $^{39}$K-$^{87}$Rb-dual species matter wave interferometer measuring gravitational acceleration with the aim to test Einstein's Equivalence Principle (EEP). Compared to classical tests such as torsion pendulum experiments and Lunar Laser Ranging, chemical elements suitable for performing matter wave interferometry can provide complementary information. We show the performance of our apparatus and discuss current limitations and future improvements towards highly sensitive matter wave tests of EEP.   

Interacting sources for high-precision atom interferometry - a theoretical study

We theoretically study the possibilities to use binary quantum mixtures as sources for high-precision atom interferometers with interferometry times ranging over several seconds. Such schemes are of timely interest in the context of inertial navigation or fundamental physics laws tests. The mixture expansion dynamics are solved by integrating a set of two coupled Gross-Pitaevskii equations. In order to satisfy the severe requirements of a precise differential interferometer, a common delta-kick cooling stage is applied to the two ensembles simultaneously to induce ultra-slow expansion ($\sim$ 50 pk regime). Other systematic effects are analysed and mitigation strategies identified. To illustrate this study, we consider the case of three mixtures of $^{87}$Rb/$^{85}$Rb, $^{87}$Rb/$^{39}$K and $^{87}$Rb/$^{41}$K widely used in atom interferometry measurements. The advantages and drawbacks of every pair are highlighted and discussed.   

The non-linear Sagnac effect and potential limitations to matter wave inertial navigation

The classical Sagnac effect relates the phase shift in a separated paths, area-enclosing interferometer to the rotation rate of the platform to which the interferometer is attached [1]. In the case of a Sagnac interferometer that employs matter waves (e.g. laser cooled atoms)[2], the separated path waves are not only shifted in phase relative to each other, but also spatially deflected relative to each other and relative to the platform. The displacement of the matter-waves leads to corrections to the Sagnac effect resulting in nonlinearity in rotation rate. This effect has significant repercussions to the design of inertial navigation devices that use matter waves and may limit the sensitivity of inertial measurement in some circumstances. \\[4pt] [1] Sagnac, Georges. Comptes Rendus 157, 708-710 (1913).\\[0pt] [2] Cronin, A.D. et al. Rev. Mod. Phys. 81, 1051-1129 (2009)   

The development of atom-interferometry-based instruments for space missions

The development of quantum sensors based on atom interferometry is being pursued both in academic research settings and applied research laboratories. Applications of interest range from fundamental problems, such as the precise determination of the gravitational constant, G, the direct detection of gravitational waves and the experimental verification of Einstein's equivalence principle in the quantum regime, to applied solutions, including the quantum-sensitive accelerometers, rotation sensors and gravity gradiometers. Atom interferometers of all flavors rely on the interrogation of atoms under free fall to realize their measurement. On earth, therefore, measurement sensitivity, which scales with the square of the interrogation time, must be balanced with the system size needed for the free fall trajectory of atoms. In space, however, the microgravity environment allows for quantum-sensitive measurements with compact designs, making atom interferometry an attractive technology. In this talk, we report on the development of two atom-interferometry-based instruments at the Jet Propulsion Laboratory aimed at improving gravity measurements of planetary bodies. The development and performances of these instruments will be discussed, as well as current scientific results and remaining technical challenges.   

Atom interferometery on ground and in space

We give a brief survey on our latest activities in atom interferometry. This included the first quantum test of the principle of equivalence with two different species, namely potassium and rubidium. We have also shown that interferometers equipped with atom-chip based sources allow to realise compact quantum gravimeters for ground based measurements. These devices allow to achieve a high flux of ultra-cold atoms, extremely low expansion rates of these wave packets and make it possible to realise new interferometers. Last but not least, in 2014, we currently work on testing these devices in the catapult and on a sounding rocket mission to extend atom interferometry to unprecedented time scales.\\[4pt] This project is supported by the German Space Agency Deutsches Zentrum f\"ur Luft- und Raumfahrt (DLR) with funds provided by the Federal Ministry of Economics and Technology (BMWI) under grant number DLR 50 WM 0346. We thank the German Research Foundation for funding the Cluster of Excellence QUEST Centre for Quantum Engineering and Space-Time Research.   

Weak interaction studies with laser trapped $^{6}$He

$^{6}$He beta decay is an interesting case to test the nature of the weak interaction through the precise measurement of the beta-neutrino angular correlation parameter $a$. According to the Standard Model, its pure Gamow-Teller decay should be ruled by an axial-vector interaction only, which leads to $a=$\textit{-1/3}. Any deviation to this value would indicate new physics beyond the Standard Model. The high precision goal of this experiment, $\Delta a/a=$\textit{0.1{\%}}, requires a large statistic along with small and well known systematic errors. To satisfy these constraints, $^{6}$He atoms are trapped in a magneto-optical trap (MOT) which allows observation of the decay products with minimal perturbations. The setup is optimized to have a high capture efficiency, a low background and a high detection efficiency. $^{6}$He (T$_{1/2}=$807 ms) is produced on-line through the $^{7}$Li(d,$^{3}$He)$^{6}$He nuclear reaction. The $^{6}$He atoms are then loaded into a first MOT via a Zeeman slower. Subsequently, they are pushed toward a second MOT chamber dedicated to the decay detection. $a$ is obtained by detecting the $^{6}$Li$^{+}$ recoiling ions in coincidence with the beta particle. The details of the setup and preliminary results will be presented. This work is supported by DOE, Office of Nuclear Physics, under contract nos. DE-AC02-06CH11357 and DE-FG02-97ER41020.   

Searching for spin-dependent short-range forces using nuclear magnetic resonance

Axions are particles predicted to exist in order to explain the apparent smallness of the neutron electric dipole moment. While also being a promising candidate for dark matter, in tabletop experiments axions can mediate novel macroscopic forces between matter objects. I will describe a new method for detecting short-range forces from axion-like particles based on nuclear magnetic resonance in hyperpolarized Helium-3. The method can potentially improve previous experimental bounds by several orders of magnitude and can probe deep into the theoretically interesting regime for the QCD axion.   

What Phase Matters for Diffraction?

Young's double-slit experiment for matter is often compared to that of optics. In rudimentary explanations of the locations of the diffraction maxima and minima far from the slits, paths are sometimes superimposed over waves drawn from the two slits to the detection screen, leading to a phase difference of $\Delta \phi =2\pi \Delta L/\lambda_{dB} $ between paths. Despite the intuitive connection of the two kinds of wave phenomena, this approach can lead to a misunderstanding of the theory for matter waves. The Feynman path-integral formalism [1] justifies the use of paths to determine the phase difference; however, the phase accumulated along single free-particle paths according to the formalism is not $\phi =2\pi L/\lambda _{dB} $, even though the expression for the phase difference is correct. The resulting factor of 2 difference in the single path phase from the intuitive value arises from the particular treatment of time-dependence in interpreting the problem [2]. The nature of this misunderstanding will be discussed, and a possible resolution proposed based on the quantum mechanical principle of indistinguishability: the time duration of all interfering paths must be equal.\\[4pt] [1] R. P. Feynman, Rev. Mod. Phys. \textbf{20}, 367-387 (1948).\\[0pt] [2] J. Schmiedmayer \textit{et al}., in \textit{Atom Interferometry}, edited by P. R. Berman (Academic Press, 1997), p. 20.   

Warm Vapor Atom Interferometer

We present a light pulse atom interferometer using room temperature rubidium vapor. Doppler sensitive stimulated Raman transitions forming the atom optical elements inherently select a cold velocity group for the interferometer. The interferometer is configured to be sensitive to accelerations. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.   

Precise and Stable Frequency Source, and Measurement of $^{130}$Te$_2$ Reference Lines from 443 to 451~nm

A precise, repeatable and stable optical frequency source is required for many modern spectroscopy experiments. Frequency combs have proven invaluable to many, but are not obtainable for others due to their high cost. Using a GPS disciplined oscillator, a stabilized Fabry-P\`{e}rot cavity, a relatively low-cost wavemeter and standard RF equipment, we have achieved a reliable laser system with a $10^{-9}$ or better frequency uncertainty at a fraction of the cost. With this system we have measured approximately 3000 transitions in $^{130}$Te$_2$ continuously between 664 and 676~THz to $\sim~0.0001$~cm$^{-1}$ precision. The system is described in detail, and the possibility of improving our knowledge of the excited states of $^{130}$Te$_2$ is considered.