Designing for long electron spin T₂ and T_m

Application of electron spins to quantum computing are enhanced by lengthening the spin-spin relaxation times, the Bloch T₂ and the experimental phase memory time T_m. Many factors contribute to T_m including electron spin concentrations, concentration of nuclear spins near and far, dynamics of the nuclear spins, and the spin-lattice relaxation time, T₁.

 

The emphasis of this presentation is on the impact on T_m of motions that take spins off resonance or modulate the resonance energy. Methyl and amino groups decrease T_m both by quantum mechanical tunneling and by classical rotation. Examples will be given for nitroxide radicals, Cr(V) complexes and V(IV) complexes. The impact on T_m of low amplitude vibrational motions (librations) increases with increasing anisotropy. These motions are strongly dependent on the extent of immobilization of the paramagnetic center by the diamagnetic host. Examples for vanadyl porphyrins in solid hosts and in solution will be discussed.

 

The numerical values cited depend on the method of measurement. Pulse powers and lengths can result in spectra diffusion and instantaneous diffusion in addition to T_m and T₁. Some T_m measurement parameters could yield values more closely approximating T₁ than T₂.