A geometric framework for describing quantum particles on a possibly curved background is proposed. Natural constructions on certain distributional bundles ('quantum bundles') over the spacetime manifold yield a quantum "formalism" along any 1-dimensional timelike submanifold (a 'detector'); in the flat, inertial case this turns out to reproduce the basic results of the usual quantum field theory, while in general it could be seen as a local, "linearized" description of the actual physics.1991 MSC: 58B99, 53C05, 81Q99, 81T20