Observation of microsecond lived quantum states in carbon-based circuits

We manipulate the quantum state of a carbon nanotube double quantum dot with ferromagnetic contacts embedded in a microwave cavity. By performing quantum manipulations such as Rabi oscillations, Ramsey fringes and spin echoes, we demonstrate coherence times of the order of 1 μs, 2 orders of magnitude larger that what has been measured so far in any carbon quantum circuit and 1 order of magnitude larger than Si based quantum dots in comparable environment. This hold promises for pure isotopically purified ¹²C spin quantum bits in circuit quantum electrodynamics.