Quantum Science Seminar #44 - Quantum Computing
"Quantum Logic Control of a Single Molecular Ion"
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  can address this challenge for a wide class of molecular ions [2,3]. We have now realized the basic elements of this proposal. In our demonstration, 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 Raman-transitions in the molecular ion, where a transition in the molecule also deposits a single quantum of excitation in the motion of the ion pair (motional "sidebands"). We can efficiently detect this single quantum of excitation with the calcium ion, which projects the molecule into the final state of the sideband transition, a known, pure quantum state. The molecule can be coherently manipulated after the projection, and its resulting state read out by another quantum logic state detection. We demonstrate this by driving Rabi oscillations between different rotational states [4, 5] and by entangling the molecular ion with the logic ion . All transitions in the molecule are either driven by a single, far off-resonant continuous-wave laser or by a far-off-resonant frequency comb. This makes the approach suitable for quantum control and precision measurement of a large class of molecular ions.
 P.O. Schmidt, T. Rosenband, C. Langer, W. M. Itano, J. C. Bergquist, and D. J. Wineland
"Spectroscopy using quantum logic"
Science 309, 749 (2005)
 S. Ding and D. N. Matsukevich
“Quantum logic for the control and manipulation of molecular ions using a frequency comb”
New Journal of Physics 14, 023028 (2012)
 D. Leibfried
"Quantum state preparation and control of single molecular ions"
 C.-w. Chou, Ch. Kurz, D. B. Hume, P. N. Plessow, D. R. Leibrandt, and D. Leibfried
"Preparation and coherent manipulation of pure quantum states of a single molecular ion"
Nature 545, 203 (2017)
 C. W. Chou, A. L. Collopy, C. Kurz, Y. Lin, M. E. Harding, P. N. Plessow, T. Fortier, S. Diddams, D. Leibfried, and D. R. Leibrandt
"Frequency-comb spectroscopy on pure quantum states of a single molecular ion"
Science 367, 1458 (2020)
 Yiheng Lin, David R. Leibrandt, Dietrich Leibfried, and Chin-wen Chou
"Quantum entanglement between an atom and a molecule"
Nature 581, 273 (2020)
Access the live talk at 17.00 CEST or the recording afterwards via this link:
Quantum Science Seminar #44 - Dietrich Leibfried
Here you can find the recording of the last lecture by Philippe Bouyer about "Quantum sensors with matter wave: from the lab to the field".