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Cold atom-based quantum technology for probing fundamental physics

Elizabeth Pasatembou

Published Aug 1, 2025• 0 citations
Publisher

Abstract

Advancing our knowledge of the universe increasingly relies on technologies capable of extremely precise measurement. Quantum sensors have emerged as promising tools for searching for new physics by pushing the boundaries of precision in measuring time, acceleration, and gravity. Two promising platforms are long-baseline atom interferometers and atomic clocks, both of which rely on cold atoms. This thesis lies at the intersection of cold-atom physics, quantum technology, and particle phenomenology. We report experimental progress from the AION project, a next-generation atom interferometer for the detection of ultra-light dark matter and mid-frequency gravitational waves. Within the collaboration, we present the first results from a red magneto-optical trap (MOT) for strontium-88 atoms. A seed–amplifier injection-locked laser system was developed to address the 1S0–3P1 transition at 689 nm, delivering 13.8 mW of light to the science chamber. Using this setup, we produced an atomic cloud at a temperature of (812 ± 4) nK in the narrowband red MOT, marking a critical milestone in the project. Secondly, the potential of next-generation atomic and molecular clocks in constraining theories that violate the weak equivalence principle (EP) is investigated. A search for variations in the electron–proton mass ratio is performed using publicly available data from UTC. A statistical framework is then developed to model clock noise and forecast sensitivity to signals arising in theories of dark matter, dark energy, unification, and other EP-violating scenarios, providing new and improved constraints. The framework is packaged into a tool that translates clock noise characteristics into constraints on fundamental physics theories. A preliminary study investigating the effect of data gaps in signal recovery shows that annual signals with amplitudes above 10⁻¹⁶ can be recovered even with up to 83% missing data.

DOI
10.25560/125148

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Advancing our knowledge of the universe increasingly relies on technologies capable of extremely precise measurement. Quantum sensors have emerged as promising tools for searching for new physics by pushing the boundaries of precision in measuring time, acceleration, and gravity. Two promising platforms are long-baseline atom interferometers and atomic clocks, both of which rely on cold atoms. This thesis lies at the intersection of cold-atom physics, quantum technology, and particle phenomenology. We report experimental progress from the AION project, a next-generation atom interferometer for the detection of ultra-light dark matter and mid-frequency gravitational waves. Within the collaboration, we present the first results from a red magneto-optical trap (MOT) for strontium-88 atoms. A seed–amplifier injection-locked laser system was developed to address the 1S0–3P1 transition at 689 nm, delivering 13.8 mW of light to the science chamber. Using this setup, we produced an atomic cloud at a temperature of (812 ± 4) nK in the narrowband red MOT, marking a critical milestone in the project. Secondly, the potential of next-generation atomic and molecular clocks in constraining theories that violate the weak equivalence principle (EP) is investigated. A search for variations in the electron–proton mass ratio is performed using publicly available data from UTC. A statistical framework is then developed to model clock noise and forecast sensitivity to signals arising in theories of dark matter, dark energy, unification, and other EP-violating scenarios, providing new and improved constraints. The framework is packaged into a tool that translates clock noise characteristics into constraints on fundamental physics theories. A preliminary study investigating the effect of data gaps in signal recovery shows that annual signals with amplitudes above 10⁻¹⁶ can be recovered even with up to 83% missing data.
Abstract Gravitational waves and ultralight dark matter are among the most compelling frontiers in fundamental physics, motivating proposals for very-long-baseline atom interferometerssuch as AION 1 , MAGIS 2 , AICE 3 and AEDGE 4 that aim to detect at frequencies at which ground-based 5 and space-borne 6 laser interferometers lose sensitivity. Very-long-baseline atom interferometers look for signals by comparing the quantum phase evolution of widely separated atomic ensembles interrogated by a common laser. However, their performance depends critically on suppressing noise sources, particularly laser phase noise. The experimental validation of such noise rejection remains an important challenge. Here we demonstrate a prototype differential atom interferometer based on the single-photon clock transition of fermionic 87 Sr. Thus, we obtain a gradiometer configuration with a species intrinsically suited to kilometre-scale and space-baseline operation. The instrument operates at the standard quantum limit 7 with no excess noise beyond atom shot noise. The differential configuration maintains quantum-limited sensitivity in the presence of several radians of artificially injected laser phase noise per shot, which emulates the conditions expected in a very-long-baseline atom interferometer. We also demonstrate the recovery of coherent oscillatory signals across a broad frequency range under fully phase-randomized conditions, a capability that is inaccessible to a single interferometer operating in the same regime. These results provide an experimental validation of the noise-immune measurement principle underlying very-long-baseline atom interferometers and mark an important step towards next-generation quantum sensors for gravitational-wave detection and searches for ultralight dark matter 8,9 .
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.
Gravitational waves and ultralight dark matter are among the most compelling frontiers in fundamental physics, motivating proposals for very-long-baseline atom interferometerssuch as AION1, MAGIS2, AICE3 and AEDGE4 that aim to detect at frequencies at which ground-based5 and space-borne6 laser interferometers lose sensitivity. Very-long-baseline atom interferometers look for signals by comparing the quantum phase evolution of widely separated atomic ensembles interrogated by a common laser. However, their performance depends critically on suppressing noise sources, particularly laser phase noise. The experimental validation of such noise rejection remains an important challenge. Here we demonstrate a prototype differential atom interferometer based on the single-photon clock transition of fermionic 87Sr. Thus, we obtain a gradiometer configuration with a species intrinsically suited to kilometre-scale and space-baseline operation. The instrument operates at the standard quantum limit7 with no excess noise beyond atom shot noise. The differential configuration maintains quantum-limited sensitivity in the presence of several radians of artificially injected laser phase noise per shot, which emulates the conditions expected in a very-long-baseline atom interferometer. We also demonstrate the recovery of coherent oscillatory signals across a broad frequency range under fully phase-randomized conditions, a capability that is inaccessible to a single interferometer operating in the same regime. These results provide an experimental validation of the noise-immune measurement principle underlying very-long-baseline atom interferometers and mark an important step towards next-generation quantum sensors for gravitational-wave detection and searches for ultralight dark matter8,9.
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.
Long-baseline atom interferometers, such as the one to be built by the AION collaboration, require ultra-cold atomic clouds. These are produced by trapping the atoms in magneto-optical traps (MOTs) using high-power, narrow-linewidth lasers. We report on the laser and optical master–slave injection-locked system used to address the 1S0–3P1 strontium transition at 689 nm and on the trapping of strontium atoms in a narrowband MOT. We demonstrate the quality of the injection through the characterization of the injection lock using an easy-to-assemble method that uses a double-pass acousto-optic modulator to generate and detect a heterodyne beatnote. The reported system is used to produce an atomic cloud at a temperature of 812(43) nK in a narrowband red MOT.
Atoms cooled and trapped using laser light have become the backbone of modern quantum physics research. Various new applications based on laser-cooled atoms are in active development. The work described in this dissertation is dedicated to this endeavor. I present experimental and numerical investigations on several fundamental properties of the laser-cooled atoms in different quantum states and how they may translate into applications within several emerging atom-based technologies. First, I describe the precision measurements of the dynamic polarizability and photo-ionization cross-section at 1064-nm light of the 5D3/25D_{3/2}5D3/2​ state in rubidium, which is of interest for the portable atomic clocks. Two different spectroscopic methods are implemented to extract the polarizability from the experimental data. The results are statistically equivalent: -524(17) [-499(59)] atomic units from the first [second] method. The photo-ionization cross section of the 5D3/25D_{3/2}5D3/2​ state at 1064~nm is measured to be 44(1) Mb. The aforementioned photo-ionization cross section is suitable for efficient ion generation and the subsequent application in cold-atom-based ion sources. This is demonstrated in the second study presented here. The ion source employs a novel method to monitor the electric microfields of the ions using the Stark effect of the highly-excited (Rydberg) atoms seeded within the origin of the ion source. Rydberg atoms are extremely sensitive to electric fields and serve as an embedded real-time sensor and tracker of the ion-source performance because of their quasicontinuous creation and detection. The principles of such ion-microfield sensing are discussed and analyzed in detail and can be utilized in any cold-atom-based focused-ion-beam source. The hyperfine structure of the 4D3/24D_{3/2}4D3/2​ state in rubidium is investigated next. The measurement utilizes two-photon optical absorption spectroscopy and a detailed analysis of light shifts. All four hyperfine components are resolved in the experimental data. The magnetic-dipole and electric-quadrupole hyperfine constants are obtained to be 7.419(45) MHz and 4.19(19) MHz, respectively. Future applications of the 4D3/24D_{3/2}4D3/2​ state in optical atomic clocks and Rydberg-atom physics are discussed. Next, I investigate a Rydberg-atom-ion molecule bound by long-range multipolar forces. The molecule is the first example of a bound state between a Rydberg atom and an ion. Strong interactions between these two particles lead to large molecular binding energy (reaching a few GHz) and large binding length (exceeding 1 mumumum). The Born-Oppenheimer approximation does not hold for the Rydberg-atom-ion molecule because the motion of the Rydberg-atom nucleus is on the same timescale as the dynamics of the ion. The Born-Huang theory is utilized to investigate the resultant nonadiabatic dynamics of the molecule and to make the first fully quantum predictions of its lifetime as a function of the vibrational state and quantum principal number of the Rydberg atom. Lastly, I present a novel technique for atom interferometry that employs uninterrupted three-dimensional confinement and manipulation during the interferometric protocol. The atoms in the existing apparatuses have to follow several-meter-long trajectories along which various detrimental effects such as wave-packet dispersion erase useful phase information. ``Tractor atom interferometry" presented here promises to suppress the harmful effects and improve the interferometers’ sensitivity; provide flexible control over the atomic trajectories; and significantly reduce the experimental footprint. The suitability of this approach for measuring background acceleration (such as due to the gravitational field) is demonstrated. The sensitivity estimations, experimental considerations, and initial laboratory work are discussed.