  Optical quantum memories, which store and preserve the quantum state of
photons, rely on a coherent mapping of the photonic state onto matter states
that are optically accessible. Here we outline a new physical mechanism to map
the state of photons onto the long-lived but optically inaccessible collective
state of noble-gas spins. The mapping employs the coherent spin-exchange
interaction arising from random collisions with alkali vapor. We analyze
optimal strategies for high-efficiency storage and retrieval of non-classical
light at various parameter regimes. Based on these strategies, we identify
feasible experimental conditions for realizing efficient quantum memories with
noble-gas spins having hours-long coherence times at room temperature and above
