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 $\alt 10^4$ s$^{-1}$. We also calculate the dephasing rate, which is due primarily to ripplon scattering off an electron. This rate is $\alt 10^2$ s$^{-1}$ for typical operation temperatures.