Entanglement control of qubits in a photoisomerizing molecule is studied in the context of an NMR quantum computer by taking azobenzene as an example. Azobenzene has two different isomers, {\it{}trans}-azobenzene (TAB) and {\it{}cis}-azobenzene (CAB), which can be interconverted by photoisomerization. Changing molecular structure leads to change in the spin-spin coupling constant, and hence leads to change in entangling operation time. We first obtain stable structures of TAB and CAB by {\it ab initio} calculation. Then, we calculate the NMR spectra of these isomers and verify that they reproduce the chemical shift obtained experimentally with a good precision. Our result indicates that the coupling strength between a 15N and a 13C nuclei in the molecule changes by a large amount under photoisomerization.
@article{arxiv.1004.0910,
title = {Entanglement Control of Azobenzene by Photoisomerization in NMR Quantum Computer},
author = {Taiga Yasuda and Masahito Tada-Umezaki and Mikio Nakahara and Tomonari Wakabayashi},
journal= {arXiv preprint arXiv:1004.0910},
year = {2010}
}