Abstract: The possibility of using small molecules for quantum computation is explored. In a quantum computer, the qubits are encoded into the normal vibration modes of a molecule, whereas the quantum gates are applied by using the femtosecond infrared laser pulses shaped adaptively to induce the desired state-to-state transitions. To study this system theoretically and computationally, we employ optimal control theory and numerical propagation of the laser-driven vibrational wave packets.
One focus of this work is on understanding how the intra- and inter-mode anharmonicities affect the accuracy of quantum gates in such a system. We demonstrate that vibrational anharmonicities help to achieve control over the interfering state-to-state transitions and obtain high-fidelity gates. Another emphasis is on achieving proper control over the relative phase of the vibrational qubit states and on the robustness of gates with respect to pulse shaping errors. Extension of this idea into ion traps will also be presented. Finally, the outcomes of recent “experimenting” with one of the first quantum annealers will be reported, where the D-Wave machine at Los Alamos was used to compute the vibrational spectra of molecules.