We report on the the first realization of an atom interferometer based on alkali-earth atoms, namely strontium, using Bragg diffraction. The present status of the project and future prospects towards high precision tests in gravitational physics are discussed.
Atom interferometry is a formidable tool to explore both fundamental and applied physics. While earlier research mainly concentrated on alkali atoms, there has been a rising interest in leveraging the clock transition of alkaline-earth-like atoms, specifically strontium. Consequently, a few atom interferometers utilizing strontium have been established worldwide in the last years.The primary focus of this work is twofold: firstly, to develop a compact and high-flux source of cold 88Sr atoms utilizing a novel Zeeman slower, a technique that efficiently decelerates the atomic thermal beam produced by an oven using lasers and magnetic fields. Secondly, the study explores the foundational aspects of an atom interferometer based on 88Sr.
We report on an atom interferometer based on Bragg diffraction in a fountain of alkaline-earth-metal atoms, namely 88Sr. We demonstrate large momentum transfer to the atoms up to eight photon recoils and the use of the interferometer as a gravimeter with a sensitivity $\ensuremath{\delta}g/g=4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$. Thanks to the special characteristics of strontium atoms for precision measurements, this result introduces alternate possibilities for experiments in fundamental and applied physics.
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.
Matter-wave interferometers operating as clocks and gravimeters allow for precision measurements of time and gravity at unprecedented levels. In all these sensors, the exquisite control of both the internal (electronic) and external (center-of-mass motion) degrees of freedom of ultracold atomic samples enable interactions at their most basic, quantum level to be studied, paving the way for new tests of fundamental physics. For all these applications, novel interferometric schemes based on the narrow intercombination transitions of alkali-earth (and alkali-earth like) atoms have recently gained considerable attention. Here we present the work towards the realization of a simultaneous atom interferometer with cadmium and strontium atoms and the potential physics such a system could explore, along the idea of the ERC - “TICTOCGRAV” EU research project. In particular, we present the design and implementation of the high-power UV laser sources necessary for performing atom interferometry with cadmium and the prospects for developing a high-flux, cold source of cadmium. Potential applications of a simultaneous cadmium and strontium atom interferometer, including to weak equivalence principle and quantum time dilation tests, are discussed.
Atom interferometry is a quantum sensor technology that uses ultra-cold atoms placed in entangled quantum states to detect minute changes in local fields arising from gravitational waves and ultra-light dark matter. Their extreme sensitivity to accelerations has been demonstrated for measurements of Newton’s gravitation constant, tests of the Equivalence Principle, and measurement of local gravity gradients. The search for ultra-light dark matter and measurements of gravitational waves requires interferometer baselines greater than approximately 100 m. In understanding the fundamental systematics and backgrounds of these detectors, we have discovered that atmospheric and seismic effects, even though physically decoupled from the atoms which are in vacuum and free-fall, are still detectable by the quantum phase of the atoms. From a different perspective these “noise” sources are also interesting signals that we may be able to understand better with these sensor platforms leading to cross-disciplinary studies in Earth sciences.
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.