Electron-on-helium qubit

[1][2] The electron-on-helium qubit was proposed as the basic element for building quantum computers with electrons on helium by Platzman and Dykman in 1999.

The energy of the electron in this potential well is quantised in a Hydrogen-like series with the modified Rydberg constant RHe

The intrinsic low temperature of the system allowed the straightforward preparation of the qubit in the ground state.

Qubit operations were performed via the excitation of the Rydberg transition with resonant microwave fields at frequencies ~120 GHz.

In 2000, Lea and co-authors proposed that the qubit read-out could be achieved using a single electron transistor (SET) device positioned beneath the helium.

[21] A CCD-like architecture was proposed for the control of the many-qubit system with dipole-dipole interaction allowing two-qubit gate operations for adjacent spins.

Exchange interaction for adjacent qubits was proposed as a read-out scheme, as demonstrated in semiconductor double-quantum-dot devices.

It was shown that, as in many superconducting qubit systems, the resonant exchange of microwave photons between the trapped electron and the cavity could be described by the Jaynes-Cummings Hamiltonian.

In any quantum computer the decoherence of the qubit wavefunction, due to energy relaxation or dephasing effects, must be limited to a suitably low rate.

Therefore, for Rydberg and orbital states, the primary source of decoherence is expected to be the emission of ripplons or phonons in the helium substrate.