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 T₁ exceeding tens of seconds. For small phonon frequencies ω, we find a 1/√ω spin-phonon noise spectrum—a dissipation channel for spins in quantum dots—which can reduce T₁ 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.