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Optical and Quantum Sensing and Precision Metrology II

Prospects for a simultaneous atom interferometer with ultracold cadmium and strontium for fundamental physics tests

Jonathan N. Tinsley, Satvika Bandarupally, Mauro Chiarotti, Shamaila Manzoor, Leonardo Salvi, N. Poli

Published Mar 3, 2022• 6 citations
Publisher

Abstract

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.

DOI
10.1117/12.2616918

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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.
We report on the progress toward a dual-species cadmium and strontium atom interferometer for fundamental physics tests. We have developed and characterized a complete baseline laser system for cadmium, which provides the high power and narrow linewidth necessary for laser cooling and trapping and for performing atom interferometry, with upgraded systems for strontium also implemented. An overview of a design for cooling cadmium is presented, and we outline the basic design of a Cd–Sr atomic fountain, discussing atom launching techniques and the possible role of blackbody radiation. The excellent properties of cadmium and strontium, both individually and as a test pair, are discussed along with the enabled fundamental physics program of tests of the weak equivalence principle and the measurement of relativistic time dilation effects in quantum superpositions of clocks.
Atom interferometers with their extremely high sensitivity to inertial forces are an excellent method for investigating and understanding gravity and its gradients. Studying gravity using quantum mechanical test sources, such as ultra-cold atoms, is an exciting choice for probing physics at this intersection. Here work is presented towards the realization of novel atom interferometers based upon Cd and Sr atoms, which posses a common electronic structure with two valence electrons, also providing access to narrow linewidth intercombination transitions. For these experiments, a novel, high-power, tunable, narrow-linewidth VECSEL source has been developed, which acts as a master source to produce continuous light at either 461 nm or 229 nm, corresponding to the cooling transitions in Sr and Cd atoms, respectively. The laser systems for accessing the clock transition and also the inter-combination transition have also been implemented. The current design of the vacuuum chamber is presented, which involves the transfer of the prepared ultracold atomic clouds from preparatory chambers to a science chamber. Towards this, we have also simulated the generation of a cold atomic source of Cd, which is a key component in producing a high sensitivity atom interferometer.
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.
The search for a fundamental, self-consistent theoretical framework to cover phenomena over all energy scales is possibly the most challenging quest of contemporary physics. Approaches to reconcile quantum mechanics and general relativity entail the modification of their foundations such as the equivalence principle. This corner stone of general relativity is suspected to be violated in various scenarios and is therefore under close scrutiny. Experiments based on the manipulation of cold atoms are excellently suited to challenge its different facets. Freely falling atoms constitute ideal test masses for tests of the universality of free fall in interferometric setups. Moreover, the superposition of internal energy eigenstates provides the notion of a clock, which allows to perform tests of the gravitational redshift. Furthermore, as atom interferometers constitute outstanding phasemeters, they hold the promise to detect gravitational waves, another integral aspect of general relativity. In recent years, atom interferometers have developed into versatile sensors with excellent accuracy and stability, and allow to probe physics at the interface of quantum mechanics and general relativity without classical analog. In this thesis, various aspects regarding tests of general relativity with atom interferometry have been theoretically investigated. This includes the analysis of fundamental effects as well as feasibility studies of experimental configurations. The work is partially focussed on a space-borne mission scenario for a dedicated quantum test of the universality of free fall beyond state-of-the-art by dropping matter waves of different elements. To enable the target accuracy at the level of 10^(−17), a compensation scheme has been developed and discussed, mitigating the detrimental effects of imperfect test mass co-location upon release and relaxing the requirements on the source preparation by several orders of magnitude. In addition, it was demonstrated that the careful design of quantum degenerate sources is indispensable for these experiments, requiring tailored schemes to prepare miscible binary sources. The possibility to test the gravitational redshift with atom interferometers has also been examined in this thesis and connected to the ideas of clock interferometry. With the proof that closed light pulse atom interferometers without transitions between internal internal states are not sensitive to gravitational time dilation, an ongoing scientific debate has been resolved. Instead, certain configurations were shown to implement a quantum version of the special-relativistic twin paradox, for which an experiment has been proposed. Finally, requirements on atomic sources and atom optics for scenarios of gravitational wave detection on ground and in space have been investigated.
Summary form only given. Alkali-earth atoms have an electronic level structure particularly suited for applications in matter-wave interferometry and high-precision laser spectroscopy. Recently atomic strontium was the subject of active research in several fields such as all-optical cooling towards quantum degeneracy and detection of ultra-narrow optical transitions. Because of its small elastic cross-section, we show that ultra-cold88Sr in presence of a lattice potential is also particularly well suited for the realization of inertial sensors to accurately measure forces with micro-metric spatial resolution. By loading the sample into a vertical lattice potential we observe persistent Bloch oscillations with a damping time longer than 10 seconds, and from the measured Bloch frequency we determine the local gravity with a sensitivity of 5 x 10-6g. Our result has direct implications in force measurements at small distances from surfaces such as tests of possible deviations form the Newtonian gravity potential at sub-millimetre distances. We will present the status of a force measurement at distances below 20 mum from dielectric and metallic surfaces, which based on ultra-cold atoms undergoing Bloch oscillations. We will also report on the progress towards the realization of an optical frequency standard based on the highly forbidden1S0-3Po 88Sr intercombination line at 698 nm as well as the realization of a laser suited for precision spectroscopy on this transition.