Atom interferometers in which atoms are delocalized over macroscopic distances can provide excellent sensitivity for gravitational measurements. I will describe progress on the design and construction of a two-meter-tall strontium atomic fountain that aims to leverage such atom interferometers to search for new interactions beyond the standard model via tests of the gravitational inverse square law and to make a new measurement of Newton’s gravitational constant. Moreover, I will discuss progress on MAGIS-100, a 100-meter-tall atom interferometer being built at Fermilab to serve as a prototype gravitational wave detector in the 0.3 – 3 Hz range and to search for ultralight dark matter.
Atom interferometers in which atoms are delocalized over macroscopic distances can provide excellent sensitivity for gravitational measurements. I will describe progress on the design and construction of a two-meter-tall strontium atomic fountain that aims to leverage such atom interferometers to search for new interactions beyond the standard model via tests of the gravitational inverse square law and to make a new measurement of Newton’s gravitational constant. Moreover, I will discuss progress on MAGIS-100, a 100-meter-tall atom interferometer being built at Fermilab to serve as a prototype gravitational wave detector in the 0.3 – 3 Hz range and to search for ultralight dark matter.
The interplay between quantum mechanics and gravity is almost as mysterious today as it was half a century ago despite remarkable progress in either field. Putting aside exotic topics like quantum theories of gravity, even a purely classical quantity, such as Newton’s gravitational constant (or “big G”), has not been measured to a precision and accuracy close to that of other fundamental constants (e.g. speed of light, fine structure constant, etc.). Moreover, until recently [1], most measurements of big G have been classical in nature. Therefore, using a quantum sensor, such as an atomic gradiometer, to perform precision measurements of big G not only adds another (quantum) dimension to said measurement, but also opens a window into studying other fundamental classical gravitational phenomena, like measuring gravitational waves [2]. Furthermore, due to the quantum nature of the sensor apparatus, the interplay of gravity and quantum mechanics can be explored by studying effects such as gravitational decoherence [3]. In this talk, I will discuss ongoing progress on the construction of a 2 meter tall atom interferometer using Strontium. By virtue of the bosonic isotope (Strontium-88) having a zero nuclear spin, the demands on magnetic shielding of the apparatus are relaxed compared to (say) alkali atoms. Once operational over the 2 meter baseline, this atom interferometer will be used to perform short-distance tests (10 centimeters to 1 meter) of gravity using source (or proof) masses in the 100 kilogram range or higher. The distance between the gravitational sensor (i.e. atom interferometer) and the proof masses can be varied using appropriate translation stages. This measurement configuration will allow us to perform precision measurements of big G. [1] Rosi et al. (2014). Nature 510, 518-521. [2] Abe et al. (2021) Quantum Science and Technology 6, 044003. [3] Roura (2020). Physical Review X 10, 021014.
Abstract MAGIS-100 is a next-generation quantum sensor under construction at Fermilab that aims to explore fundamental physics with atom interferometry over a 100 m baseline. This novel detector will search for ultralight dark matter, test quantum mechanics in new regimes, and serve as a technology pathfinder for future gravitational wave detectors in a previously unexplored frequency band. It combines techniques demonstrated in state-of-the-art 10-meter-scale atom interferometers with the latest technological advances of the world’s best atomic clocks. MAGIS-100 will provide a development platform for a future kilometer-scale detector that would be sufficiently sensitive to detect gravitational waves from known sources. Here we present the science case for the MAGIS concept, review the operating principles of the detector, describe the instrument design, and study the detector systematics.
MAGIS-100 is a 100-meter atom interferometer currently being built at Fermilab and will be the worlds largest atom fountain. It will leverage modern atom optics techniques to search for dark matter, perform quantum atomic experiments, and detect gravitational waves at frequencies inaccessible to LIGO and LISA. Generation and precise control of meter-separated quantum atomic superpositions within the interferometer requires an agile laser system able to rapidly shift the optical frequency up to a rate of 100 GHz/s while maintaining a phase lock to our static frequency comb. To meet the power requirement of the experiment, the two interferometry lasers are coherently locked and must be robust to rapid frequency shifts. The interferometry laser's spatial mode is cleaned through fiber coupling and long free space propagation in vacuum with frequency noise introduced by the fiber suppressed by a PID lock. In addition to the scientific and technical hurdles in this experiment, there are complex laser safety issues. There are a total of twenty-four lasers and seven wavelengths ranging from 50mW to 100W, all within the same LCA.
We describe two experiments where atom interferometry is applied for precision measurements of gravitational effects. In the first, we measure the Newtonian gravitational constant G using an atom interferometry gravity-gradiometer which combines a rubidium fountain, a juggling scheme for fast launch of two atomic clouds, and Raman interferometry. We show that the sensor is able to detect the gravitational field produced by source masses and G is measured with better than 10-2 accuracy. In the second experiment, using ultra-cold strontium atoms in a vertical optical lattice and observing persistent Bloch oscillations for several seconds, we measure gravity acceleration with micromet-ric spatial resolution. We discuss the prospects for the study of gravitational forces at short distances and show that unexplored regions can be investigated in the search for deviations from Newtonian gravity.
Atom interferometry is a maturing quantum technology which provides one of the most precise approaches to explore fundamental physics, e.g. to search for dark matter, and one day to observe gravitational waves in the frequency range from 10 mHz - 10 Hz. Standard atom interferometers use Bragg or Raman two-photon transitions for the coherent manipulation of matter waves. In a Michelson configuration for atom-aided gravitational waves detection, two orthogonal arms are built to reject laser noise, in the same way as optical interferometers. Atom interferometers utilizing an optical clock transition for coherent manipulation are less affected by the technical noise of the laser, and as a result that single baseline detectors become feasible.At LP2N, we are building a vertical gravity-gradiometer based on atom interferometry using strontium atoms probed on such a clock transition. The final experimental setup will implement a 6-meter tall atomic fountain to realize gradiometry with two or more separated atomic clouds.In my dissertation, I present the realization of the experimental setup in all its sub-systems, and the first experiments with atoms at millikelvin temperature obtained with the first cooling stage with blue light. The laser system for the second red cooling phase and for the coherent manipulation is ready; meanwhile, we realized a dual-frequency Zeeman slower that improves the atomic flux by a factor of six. We also present a study of an original scheme to achieve pulsed and fast light-atom interaction in a narrow-linewidth cavity by exploiting the Stark shift as a high bandwidth switch; this technique could open to the use of narrow-linewidth cavities – and notably their high power buildup - in several contexts, like atom interferometry and quantum information.
In this article, we illustrate a series of experiments performed in our group in the field of atom interferometry for precision gravity measurements. We show that instruments measuring and testing gravity can be built both with rubidium and with strontium atoms, while keeping the sources of systematic error under control. The application of these devices in the test of the Weak Equivalence Principle with quantum objects, in the measurement of the Newtonian gravitational constant G and in the development of a new type atom interferometer for the detection of gravitational waves is discussed.