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 $^{ 15}$N and a $^{ 13}$C nuclei in the molecule changes by a large amount under photoisomerization.
Categories: quant-ph