REDRUM: searching for new CP-violating physics with highly ionic ultracold ²²¹FrAg molecules

We are developing an experiment (REDRUM) to measure the nuclear Schiff moment of francium-221 to search for CP-violating physics beyond the standard model. The nucleus of ²²¹Fr (t_1/2 = 4.9 min) has a static octupole deformation [1] that makes it very sensitive to CP-violating physics. The highly ionic bond of the francium-silver (FrAg) molecule provides near-maximal energy shifts due to the ²²¹Fr Schiff moment when polarized in an electric field [2]. We will use standard bi-alkali molecule assembly techniques [3] to form FrAg molecules [4] trapped in their electronic and rovibrational ground state. A precision measurement with this system would offer unprecedented sensitivity to hadronic CP violation [3], probing new physics at mass scales exceeding 100 TeV. We will present progress in the overall plan for REDRUM, including several important experimental developments and a decision to use ²²¹Fr rather than ²²³Fr as was originally planned.

[1] V. V. Flambaum and A. J. Mansour. Enhanced nuclear Schiff and electric dipole moments in nuclei with octupole deformation. Phys. Rev. C, 111:055501, May 2025.

[2] Aurélien Marc, Mickaël Hubert, and Timo Fleig. Candidate molecules for next-generation searches of hadronic charge-parity violation. Phys. Rev. A, 108:062815, Dec 2023.

[3] Tim Langen, Giacomo Valtolina, Dajun Wang, and Jun Ye. Quantum state manipulation and cooling of ultracold molecules. Nat. Phys., 20(5):702–712.

[4] Jacek Kłos, Hui Li, Eite Tiesinga, and Svetlana Kotochigova. Prospects for assembling ultracold radioactive molecules from laser-cooled atoms. New Journal of Physics, 24(2):025005, Feb 2022.