Quantum register based on double quantum dots in semiconductor nanowires
An implementation of a universal solid-state quantum register based on electron space states in field-defined double quantum dots (a DQD possesses one electron in two adjacent tunnel bound dots) in an ultrathin semiconductor wire 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 universal quantum computer fabricated by advanced silicon technology. Moreover, the structure could be developed into an ensemble quantum register where an array of nanowires with common controlling electrodes and contacts is fabricated. That register is much more resistant against environment noise. It is crucial that an individual qubit consists of two DQDs. The quantum information is encoded and processed inside the Hilbert subspace without charge transfer between dots. The filling factor of each quantum dot is permanently equal to 0.5. This guarantees a linear dynamics of qubits necessary for now existing quantum algorithms. Worth noting, the dynamics of qubits with altering charge state is more or less nonlinear due to interaction with surrounding dielectrics and metals (polaron effect). The basic two-qubit operations in the system are SWAP and sqrtSWAP. The latter operation is universal as well as CNOT. The two-qubit operations are performed by Coulomb interaction. Although that kind of interaction is incessant, the strength of its action depends on mutual states of interacting DQDs (in-resonance or off-resonance). In the proposed register any quantum algorithm could be effectuated via manipulation solely with digital voltage pulses on controlling electrodes that reminds a functioning of an 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.