This project develops techniques which enable measurement of mirror-symmetry violation, using molecular ions held for long periods of time, nearly at rest, and well isolated from their environment in linear radiofrequency traps. The major challenges to be overcome are development of capabilities to control and non-destructively read out the rotational quantum state of a single trapped molecular ion. Although molecules require extra care in control and readout as compared with atoms, the principle advantage is that opposite-parity rotational levels are intrinsically nearby in energy and thereby more substantially mixed by the weak force than are electronic levels of typical atoms. Nuclear spin-dependent parity violation is important for understanding purely hadronic weak interactions of the Standard Model, and they provide a special low-energy approach for searching for new physics at TeV energy scales.
This work is motivated by nuclear spin-dependent parity-violation investigations, but other important applications of improved precision molecular spectroscopy include measurements of time-variation of the electron-proton mass ratio, study of parity violation in the structure of chiral molecules, and discovery of an electron electric dipole moment. Furthermore, the ingredients for single molecular ion spectroscopy, internal and external quantum state control and state readout developed here, could be essential elements for molecular-ion quantum information processing applications and for studies of low-temperature chemical reactions. The spectroscopic techniques being developed in this proposal have potential to impact other areas of science as diverse as atmospheric and astrophysical spectroscopy -- where there is great interest in developing improved methods and tools for molecular rotational and vibrational spectroscopy in the so-called molecular "fingerprint" region of the electromagnetic spectrum. A strong program of undergraduate and graduate education and training is maintained by the research. The current group of students in the lab is diverse and includes underrepresented minorities.
The researchers developed techniques important for studying mirror-symmetry violation using trapped molecular ions. These molecular ions are held for long periods of time, nearly at rest, and well isolated from their environment, making them excellent candidates for such precision experiments seeking to understand fundamental interactions at a deeper level. The major challenge to be overcome are development of capabilities to control and non-destructively read out the rotational quantum state of a single trapped molecular ion. During this grant cycle, the researchers demonstrated a technique to use a single broadband laser to address many excited molecular rotational levels, pumping each of them to lower states and effecting rotational cooling. The rotational cooling achieved was from room temperature (300 Kelvin) to 4 Kelvin, such that 95% of the molecules were in the ground quantum state (see Fig. 1). This efficient ground state preparation serves as an excellent starting point for future precision experiments. Intellectual Merit Nuclear spin-dependent parity violation is important for understanding purely hadronic weak interactions of the Standard Model, and they provide a special low-energy approach for searching for new physics at TeV energy scales. However, despite many observations of nuclear spin-independent parity violation, the cesium anapole measurement represents the only observation of nuclear spin-dependent parity violation to date. This proposal is motivated by nuclear spin-dependent parity-violation investigations, but other important applications of improved precision molecular spectroscopy would potentially include measurements of time-variation of the electron-proton mass ratio, study of parity violation in the structure of chiral molecules, and discovery of an electron electric dipole moment. Furthermore, the ingredients for single molecular ion spectroscopy, internal and external quantum state control and state readout to be developed here, could be essential elements for molecular-ion quantum information processing applications and for studies of low-temperature chemical reactions. Broader Impact The researchers maintained a strong program of undergraduate and graduate education and training. The group of graduate students and undergraduates in the lab was diverse and included underrepresented minorities. Furthermore, the techniques being developed in this proposal have potential to impact other areas of science as diverse as atmospheric and astrophysical spectroscopy—where there is great interest in developing improved methods and tools for molecular rotational and vibrational spectroscopy in the so-called molecular "fingerprint" region of the electromagnetic spectrum.
