Electron-Spin Relaxation Measurements of Biological [2Fe-2S] Cluster System in View of Electron Spin Quantum Bits

Abstract

At 20 K, as long as \(T_m\sim 800-1000\) ns were measured for the [2Fe-2S] cluster in its intrinsic protein environment. Such relaxations are a relatively long coherence time for the low-spin \(S=1/2\) system. For this biological cluster, the phase memory time was found significantly affected by the nuclear hyperfine interactions of \(^{14}\)N with \(I=1\). When labeling the surrounding ligands with the \(^{15}\)N isotope uniformly, \(T_m\) are enhanced between \({\sim }1.1-1.4~\upmu\)s at the canonical orientations. This is already an order of magnitude longer than the duration of a single-spin qubit manipulation \({\sim }10-100\) ns. While \(T_1\) are of the order of \({\sim }130\)\(\upmu\)s at the canonical orientations, the transient nutation experiments reflect on the coherent manipulation of the electron spin.