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.