An amazing level of quantum control is routinely reached in modern experiments with atoms, but similar control over molecules has been an elusive goal. A method based on quantum logic spectroscopy [1] can address this challenge for a wide class of molecular ions [2,3]. We have now realized many basic aspects of these proposals.
In our demonstrations, we trap a calcium ion together with a calcium hydride ion (CaH+) that is a convenient stand-in for more general molecular ions. We laser-cool the two-ion crystal to its motional ground state and then drive stimulated Raman transitions in the molecular ion. Laser-based transitions in the molecule can deposit a single quantum of excitation in the motion of the ion pair when a motional “sideband” is driven. We can efficiently detect this single quantum of excitation with the calcium ion, which non-destructively projects the molecule into the final state of the sideband transition, a known, pure quantum state.
The molecule can be coherently manipulated after this first projection, driving further stimulated Raman, mm-wave or vibrational overtone transitions. After attempting a transition, the resulting molecular state can be read out by another quantum logic state detection. We demonstrate this by driving Rabi oscillations between different rotational and vibrational states [4, 5, 6] and by entangling the molecular ion with the logic ion [7]. Transitions in the molecule are either driven by a single, far off-resonant continuous-wave laser, by a far-off-resonant frequency comb or a single frequency comb tooth resonant with a certain vibrational overtone transition. This makes the approach suitable for quantum control and precision measurement of a large class of molecular ions. Controlled transitions to excited vibrational levels open avenues to precise characterization of the electronic ground state potential surface and to coherent dissociation along a specific bond.
[1] P.O. Schmidt, et al. Science 309, 749 (2005).
[2] S. Ding, and D. N. Matsukevich, New J. Phys. 14, 023028 (2012).
[3] D. Leibfried, New J. Phys. 14, 023029 (2012).
[4] C.-W. Chou et al., Nature 545, 203 (2017).
[5] C.-W. Chou et al., Science 367, 1458 (2020).
[6] A. L. Collopy et al., Phys. Rev. Lett. 130, 223201 (2023).
[7] Y. Lin et al., Nature 581, 273 (2020)
* Please Note: the featured seminar will begin promptly at 3pm. There will be no 10 Minute Talk.
Mallinckrodt is located at 12 Oxford Street. The entrance near the seminar room is on the left side of the building if you’re on Oxford facing the building, under the walkway that connects the Mallinckrodt and Hoffman Lab (20 Oxford Street).
If you have any trouble accessing the building, please call Samantha at (617) 384-7839.