1211.3983 (Amrit Poudel et al.)

Relaxation in quantum dots due to evanescent-wave Johnson noise from a
metallic backgate    [PDF]

Amrit Poudel, Luke Langsjoen, Maxim Vavilov, Robert Joynt

We present our study of decoherence in charge (spin) qubits due to evanescent-wave Johnson noise (EWJN) in a laterally coupled double quantum dot (single quantum dot). The high density of evanescent modes in the vicinity of metallic gates causes energy relaxation and a loss of phase coherence of electrons trapped in double quantum dots (DQDs). We derive an expression for the energy relaxation rate of a single electron trapped in a DQD. We then calculate the spin and charge relaxation rates for a variety of dot geometries. Previous studies in this field approximated a charge or spin qubit by a point dipole, which ignored the finite size of the quantum dot and were limited to dipole coupling between the fluctuating electromagnetic fields and the qubit. This leads to a spurious divergence in the relaxation rate as the qubit approaches the metal. Here we go beyond the dipole approximation and remedy the unphysical divergence by taking into account the finite size of the quantum dot.

View original: http://arxiv.org/abs/1211.3983