Collaborative Research: PM: CeNTREX, A Search for Nuclear Time-Reversal Symmetry Violation with Quantum-State-Controlled TlF Molecules

Fundamental symmetries are at the heart of our understanding of the physical world. In particular, small-scale violations of the time-reversal (T) symmetry are necessary to explain the observed predominance of matter over antimatter, one of the most fundamental problems in modern science. New T-violating physics is likely to be mediated by particles with large masses that exceed the current reach of high-energy accelerators. This experiment will carry out a high-precision search for the nuclear Schiff moment, a charge separation in the thallium (Tl) nucleus, that would signal T-violation. Detecting a Schiff moment with a sensitivity exceeding the best current limit would provide clear evidence for physics beyond the Standard Model, while a null measurement would set a stringent constraint on theories that include sources of T violation, and potentially identify the technical goals for future particle accelerators. Experimental molecular quantum science and theoretical nuclear physics will be combined here in a new collaboration using table-top experiments and state-of-the-art calculations. The Tl Schiff moment will be measured using thallium fluoride (TlF) polar molecules that are aligned with an applied electric field in a long interaction region. The presence of a Schiff moment will be manifested by a precession of the Tl magnetic moment (spin) about the applied field. This project will broadly impact technology and education. Graduate and undergraduate students will be actively involved in research, acquiring hands-on skills that are highly valued in academia, industry, and national labs. The results of this work are expected to have a strong appeal to the media and members of the public, and will be widely disseminated.

This project applies the techniques of molecular quantum science to a measurement of time-reversal symmetry (T) violation, as part of the Cold Molecule Nuclear Time Reversal Experiment (CeNTREX). The investigators seek to improve upon previous measurements of T violation in atomic nuclei by nearly two orders of magnitude in terms of sensitivity to fundamental parameters. This level of precision will help address grand challenges such as the observed matter-antimatter asymmetry in the universe. The investigators will use a beam of cold TlF molecules in order to combine the intrinsically high sensitivity of Tl to the T-violating nuclear Schiff moment, the large effective electric field at the Tl nucleus within strongly polarized molecules, and state-of-the-art techniques for controlling individual molecular quantum states including optical cycling for laser cooling and high-fidelity detection. In parallel, they will address the theoretical question of interpreting the measurement by developing modern methods of nuclear physics to accurately calculate the dependence of the Schiff moment on the underlying nucleon-nucleon interactions and to quantify its uncertainty. This measurement will have intellectual synergy with other ongoing T violation searches; complementary experiments can identify the source of an observed symmetry violation via their different sensitivities to fundamental parameters. This project is also complementary to the Large Hadron Collider (LHC) which is poised to detect new high-energy particles and potentially identify the nature of their T-violating interactions. The measurement supported by the current award relies on long-lived coherent superpositions of molecular quantum states, and will make an impact on quantum sensing with molecules via the meticulous quantum state control of TlF, ultrahigh-precision spectroscopy including internal co-magnetometry, and radiation pressure forces applied to novel systems.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.