On instability of charge qubit based on double quantum dot

We present numerical model for qubits made of InAs/GaAs double quantum dot (DQD). The electron/hole localization and spectral distributions of localized/delocalized states are studied. The InAs/GaAs heterostructures are described, using the effective potential model proposed given in Ref. [1]. It was shown in [2], that the electron tunneling and spectral distributions of localized/delocalized states in this binary system are extremely sensitive to the shape symmetry violation. The coupling parameter Θ, defines the delocalized (Θ ≈ π ⁄ 2) and localized (Θ∼0) states of electrons. The parameter appears to depend on the energy difference Δ in the spectrum of the left and right QDs; the difference can be caused by a shape symmetry violation. The sensitivity of the parameter Θ to small variations of Δ is estimated to be: δ(Θ⁄2)=1⁄Δ² δ(Δ) (1) Based on this approach and related findings, we propose a new interpretation for the quantum computing general problem of instability of qubits. Since the qubit is a two-level system, exactly like DQD, its extreme sensitivity is described by Eq. (1) as Δ →0; this would include any fluctuation violations, leading to loss of 'coherency' of the qubit or 'tunneling state' in the qubit. One can propose an ideal bi-stable device (with the probability of 1/2 for each state) when Δ →0. However, the model means, the more sensitive the qubit is, the more unstable the system. Results of the modeling will be given and discussed. This work is supported by the National Science Foundation grant HRD-1345219 and DMR-1523617 awards Department of Energy / National Nuclear Security Administration under Award Number NA0003979 DOD-ARO grant №W911NF-13-0165.