Towards an Electric Dipole Moment (EDM) with atoms and molecules in Matrix (EDMMA) – EDMMA

Instrumental Development (LAC).

A low-vibration, two-stage optical cryostat was integrated on an optical table, featuring two thermal shields and multiple ports for in situ deposition and diagnostics. Matrices (primarily Ar) were deposited on a cooled sapphire window; gas flow was controlled via a valve, while an independent Cs oven ensured controlled doping (separate Cs and rare gas lines for improved reproducibility). Diagnostics combined cameras, transmission spectrometers, and laser excitation.

Spectroscopies.

(i) Broadband transmission spectroscopy to monitor growth and extract fine structures/positions of lines associated with 6s→6p transitions; (ii) time-resolved laser irradiation experiments (relaxation under white light, irreversibilities) to probe site rearrangements and defects; (iii) excitation–emission fluorescence mapping (spectroanalyzer), including polarization anisotropy studies, to access excited-state relaxations and lattice reorganization effects; (iv) thermal cycling (annealing) to test metastability and site population evolution.

Extension to Molecular Matrices (ISMO).

The existing pH2 setup was adapted for growing hydrogen/deuterium solids doped with alkali atoms: ortho/para conversion, purity control via FTIR, thermal shielding modifications for transmission measurements during deposition, and integration of a Cs oven designed with ISMO’s mechanical workshop.

Modeling (CIMAP).

Spectra were interpreted using a diatomic-in-molecule (DIM) approach, including 6s/6p states and spin–orbit coupling, with: (i) stability analysis of trapping geometries (Td, Oh, D3h, and low-symmetry sites); (ii) absorption/emission spectrum simulations; and (iii) wave packet dynamics to estimate vibronic relaxation and population transfer in the 6p manifold.

Metrology Interfaces (LPL).

The project benefited from exchanges with LPL on FID/ESR detectors and, through a joint postdoctoral position, from a transfer of expertise from THz spectroscopy to the implementation of RF coils and spin interrogation architecture, a necessary step for subsequent metrology

Operational Experimental Platform.

LAC commissioned a two-stage optical cryostat reaching ~3.3 K, with vibration isolation and vacuum levels compatible with clean matrix growth. The deposition procedure (rare gas) and doping (separate Cs oven) was stabilized. Initial Cs/Ar data were obtained during setup (T. Battard), then systematized and expanded in S. Lahs’ thesis.

Cs Spectroscopy in Ar: Dual-Triplet Structure.

Below 16 K, absorption shows six main resonances grouped into two triplets, attributable to distinct local environments. Relative intensities depend on preparation, indicating a distribution of sites and/or disorder (polycrystallinity, defects, grain boundaries).

Dynamics Under Irradiation and Annealing.

Laser irradiation induces depletion near the pump frequency, accompanied by changes in other bands and incomplete relaxation, suggesting coupling between site families. Annealing at 32 K simplifies fluorescence, consistent with relaxation toward more symmetric configurations; returning to 6 K durably alters absorption.

Fluorescence and Low Non-Radiative Loss.

Excitation–emission mapping reveals Stokes shifts of ~3000 cm⁻¹ and, crucially, that the fluorescence integral reproduces absorption, indicating no dominant non-radiative pathways. Polarization is generally lost between excitation and emission (except for one red band), suggesting significant excited-state reorganization but also identifying a channel compatible with a highly symmetric site.

Theoretical Contribution (CIMAP).

DIM simulations and wave packet dynamics reproduce the order of magnitude of shifts and predict, for high-symmetry sites, essentially unique emission. The experimental multiplicity of peaks is interpreted as a superposition of low-symmetry site contributions (notably grain boundaries), a key point for the EDM roadmap.

Collaborations and Outlook.

Extension to pH2/oD2 matrices was initiated at ISMO (ortho/para conversion, FTIR, modifications for deposition measurements, Cs oven integration). With LPL, a joint postdoc enabled expertise transfer for RF coil implementation, a preparatory step for ESR sequences.

Valorization and Perspectives.

A joint manuscript (LAC–ISMO–CIMAP) synthesizes these results on Cs fluorescence and relaxation in Ar. The findings directly inform the follow-up ANR QUIC project and have enhanced international visibility through invitations to Les Houches (Oct. 2025) and the EDMs2026 workshop (Mar. 2026).

The EDMMA project clearly identified the physical and instrumental conditions required to envision an electric dipole moment (EDM) measurement of atoms in cryogenic matrices. The results validate the robustness of the experimental platform and precisely guide future developments.

A major perspective is the transition to spin interrogation. Spectroscopic studies show that Cs atoms trapped in solid argon exhibit favorable radiative properties, with no dominant non-radiative channels and sufficient stability under controlled irradiation. These elements make the implementation of spin polarization and readout protocols via RF/ESR techniques credible. The integration of RF coils, initiated through interactions with LPL and a joint postdoctoral position, is a key step toward accessing observables directly sensitive to an EDM.

A second structuring axis concerns the control of trapping sites. EDMMA revealed that the observed spectral complexity is linked to a distribution of low-symmetry sites, likely associated with crystalline defects and grain boundaries. Future efforts will focus on optimizing growth and annealing conditions to favor more homogeneous, high-symmetry environments better suited for precision metrology. In this context, the extension to molecular matrices (solid parahydrogen and deuterium), initiated at ISMO, appears particularly promising.

On the theoretical front, the tools developed with CIMAP pave the way for predictive modeling of local environments. The DIM approach and non-adiabatic dynamics simulations now allow linking spectroscopic signatures and site geometries and can be extended to analyze the influence of external fields and systematic effects in future EDM experiments.

These perspectives are directly aligned with the ANR QUIC project, which builds on EDMMA’s achievements to advance toward coherent spin interrogation of atoms in matrices. The international visibility gained, notably through invitations to schools and workshops dedicated to EDMs and quantum metrology (Les Houches 2025, EDMs 2026), confirms EDMMA’s role as a foundational step toward a new class of fundamental symmetry test experiments in solid-state environments.

EDMs, i.e. electric dipole moments of electrons, neutrons or nuclei are sensitive probes for new physics beyond the Standard Model of particle physics. In the present project, we propose to measure the EDM of those systems embedded in a cryogenic solid matrix of inert gas or hydrogen. Matrices offer unprecedented sample sizes while maintaining characteristics of an atomic physics experiment, such as the possibility of manipulation by lasers. An EDM experiment on molecules in inert gas matrices has the potential to reach a statistical sensitivity of the order of 1e–36 e cm; a value beyond that of any other proposed technique. With this project, in a strong collaboration between experimental (LAC, ISMO,LPL) and theoretical (CIMAP) groups, we first aim at performing a detailed investigation of all limiting effects (mainly the ones limiting the optical pumping performance and coherence time) using Cs atoms. This should provide a first proof of principle EDM measurement and set the ground for precise study of systematic effects which will allow EDMMA to reach unprecedented precision