Qubits with Electrons on Liquid Helium

We study dissipation effects for electrons on the surface of liquid helium, which may serve as qubits of a quantum computer. Each electron is localized in a 3D potential well formed by the image potential in helium and the potential from a submicron electrode submerged into helium. We estimate parameters of the confining potential and characterize the electron energy spectrum. Decay of the excited electron state is due to two- ripplon scattering and to scattering by phonons in helium. We identify mechanisms of coupling to phonons and estimate contributions from different scattering mechanisms. Even in the absence of a magnetic field we expect the decay rate to be ~10(sup 4) s(sup -1). We also calculate the dephasing rate, which is due primarily to ripplon scattering of an electron. This rate is ~10(sup 2) s(sup - 1) for typical operation temperatures. PACS numbers: 03.67.Lx, 73.21.-b, 76.60.Es, 73.63.-b