Electron Dynamics in Quantum Dots on Helium Surface

We study single-electron quantum dots on a helium surface created by electrodes submerged into the helium. The parameters of the dots are electrostatically controlled. We find the electron energy spectrum and identify relaxation mechanisms. The in-plane confinement significantly slows down electron relaxation. The energy relaxation is due primarily to coupling to phonons in helium. The dephasing is determined by thermally excited ripplons and by the noise from underlying electrodes. The decay rate can be further suppressed by a magnetic field normal to the helium surface. Slow relaxation in combination with control over the energy spectrum make localized electrons appealing as potential qubits of a quantum computer.