Spin-orbit interaction and anomalous spin relaxation in carbon nanotube quantum dots

We study spin relaxation and decoherence in nanotube quantum dots caused by electron-lattice and spin-orbit interaction and predict striking effects induced by magnetic fields B. For particular values of B, destructive interference occurs resulting in ultralong spin relaxation times T(1) exceeding tens of seconds. For small phonon frequencies omega, we find a 1/root omega spin-phonon noise spectrum-a dissipation channel for spins in quantum dots-which can reduce T(1) by many orders of magnitude. We show that nanotubes exhibit zero-field level splitting caused by spin-orbit interaction. This enables an all-electrical and phase-coherent control of spin.