Quantum register based on double quantum dots in semiconductor nanowires

Abstract

An implementation of a universal solid-state quantum register based on electron space states in field-defined double quantum dots (DQD possesses one electron in two adjacent tunnel bound dots) in an ultrathin semiconductor nanowire is discussed. To some extent, the structure resembles that of a field-effect transistor with multiple controlling electrodes (gates). Scalability is audible and it opens up a possibility of large-scale quantum computer fabricated by advanced silicon technology. Moreover, the structure could be developed into an ensemble quantum register where instead of single nanowire an array of them with common controlling electrodes and contacts is fabricated. This ensemble register is much more resistant against environment noise caused by phonons and stray charges due to averaging and compensation. It is crucial that an individual qubit consists of two DQDs. The basic states of that qubit correspond to symmetric state of one DQD and antisymmetric state of another, and vice versa. Then the quantum information can be encoded and processed without charge transfer between dots. The probability to find an electron in a dot constantly equals 1/2 thus the Coulomb interaction between DQDs is also constant. Although the Coulomb interaction is incessant, the strength of its action depends on mutual states of interacting DQDs (in-resonance or off-resonance). Therefore, a quantum algorithm could be effectuated via manipulation solely with steady and pulse gate potentials that reminds an operation of a digital integrated circuit. The final read-out of the register is performed after decoding into charge states of DQDs and a transmission of current through the wire.