Recently, Rydberg atoms appeared as a viable alternative to the quantum gates built on atomic or molecular ions. The lifetimes of the circular Rydberg states can be in the millisecond range. That prevents inherent metastability of the Rydberg atoms to influence computation at the typical decoherence times, which are now being achieved in the range of 1 ms. The paper proposes to use a pinning potential of an image charge on a cryogenic substrate (liquid He, in particular) to confine large densities of Rydberg atoms to dielectric surfaces. The substrate can also act as a natural cooler medium. A design of the computer (quantum abacus) based on these ideas is briefly sketched in the paper.