Oral: Optimizing quantum logic spectroscopy for molecular state control*

Quantum logic spectroscopy (QLS) is a powerful technique for precision measurements, enabling the control and non-destructive detection of molecular ion states that are challenging to manipulate otherwise[1]. While experimentally demonstrated, this method is limited by blackbody radiation exciting numerous hyperfine states, requiring a large number of measurements for state preparation and spectroscopic data collection. To address this challenge, we perform Monte Carlo simulations of a new protocol involving a two-step process. First, we couple at most half the total number of rotational states to a chosen normal mode shared between the molecular and logic ions, followed by a projective measurement of their motional state. By consistently repeating these two steps, we can gradually reduce the large state space to a single pure quantum state. The process is optimized to account for degeneracies and off-resonant couplings by observing the dynamics through the transition matrix of the Markovian state model, which encodes information about how external laser pulses affect the probability distribution of the molecular state space. Additionally, the study explores the application of optimal control theory in designing robust laser pulses. This protocol reduces the number of measurements from linear to logarithmic scaling, improving our ability to manipulate molecular states and potentially observe parity violation signatures in molecules[2], or facilitate transduction between trapped ion qubits and photons[3].

[1] Chou, Cw., Kurz, C., Hume, D. et al. Preparation and coherent manipulation of pure quantum states of a single molecular ion. Nature 545, 203–207 (2017). 

[2] Arie Landau, Eduardus, Doron Behar, Eliana Ruth Wallach, Lukáš F. Pašteka, Shirin Faraji, Anastasia Borschevsky, Yuval Shagam; Chiral molecule candidates for trapped ion spectroscopy by ab initio calculations: From state preparation to parity violation. J. Chem. Phys. 21 September 2023; 159 (11): 114307. 

[3] Lin, Y., Leibrandt, D.R., Leibfried, D. et al. Quantum entanglement between an atom and a molecule. Nature 581, 273–277 (2020).