Quantum computation with vibrationally excited polyatomic molecules: effects of rotation, level structure, and field gradients

Abstract

Accurate rotation–vibration energy levels and transition dipoles of the molecule thiophosgene are used to model the execution of quantum gates with shaped laser pulses. Qubits are encoded in 2 ⁿ vibrational computing states on the ground electronic surface of the molecule. Computations are carried out by cycling amplitude between these computing states and a gateway state with a shaped laser pulse. The shaped pulse that performs the computation is represented by a physical model of a 128–1024 channel pulse shaper. Pulse shapes are optimized with a standard genetic algorithm, yielding experimentally realizable computing pulses. The robustness of optimization is studied as a function of the vibrational states selected, rotational level structure, additional vibrational levels not assigned to the computation, and compensation for laser power variation across a molecular ensemble.

Keywords:

• Unitary transformation
• Shor's algorithm
• Asymmetric top
• Genetic algorithm
• Gateway state

Acknowledgements

This work was supported by the National Science Foundation. DW was supported by a grant from the UIUC Research Board.

Notes

†R is defined as the number of flip/add operations required to obtain the operator from the identity operator. The identity operator, no matter how many qubits it transforms, can be implemented without any pulse, so S _I  = 0 always. The ‘1+’ factor is added to our empirical scaling relationship to produce the correct behavior when the identity is approached.