We demonstrate that a quantum-dot cellular automata device can be fabricated using electron beam lithographically defined gates on GaAs/AlGaAs heterostructure materials, and that by tuning the four quantum dot (J. Phys. C: Solid State Phys. 21 (1988) L893) system polarization of one double dot can lead to polarization in the neighboring double dot (Phys. Rev. B 67 (2003) 033302). The polarization is detected using a 1-D or 0-D channel defined next to one pair of double dots which acts as a non-invasive voltage probe (Phys. Rev. Lett. 70 (1993) 1311). Ultimately a cellular automata device should be isolated from reservoirs to prevent charge fluctuations caused by co-tunneling. The non-invasive voltage probe is used to show that coupled double dots isolated from reservoirs can be made to have a sharper polarization transition. By studying the broadening of the polarization signal from a coupled double dot system isolated from reservoirs, we deduce the charge dephasing times for intra dot scattering to be more than 0.2 ns (Phys. Rev. B 67 (2003) 073302). © 2004 Elsevier Ltd. All rights reserved.

We report measurements of single-electron polarization in a coupled double-quantum-dot device isolated from current probes and demonstrate that the energetics observed for this process differs from that observed in double dots coupled to reservoirs. The movement of the electrons is detected by a quantum point contact. By analyzing the energy broadening corresponding to the tunneling of a single electron from one dot to the other we estimate a minimum for the intradot scattering time to be 0.2 ns. This energy broadening follows the predicted shot-noise variation in the detector with gate voltage, but is three orders-of-magnitude higher. We speculate that two-level systems could account for the discrepancy.

We present evidence for quantum dot cellular automata action in a cell consisting of four dots defined by submicron metal gates on the top surface of a molecular-beam-epitaxy-grown GaAs/AlGaAs heterostructure in which a two-dimensional electron gas layer was formed approximately 70 nm below the surface. The four-dot cell is separated by a strong barrier in two double-dot sets. We show that by polarizing one of the double-dot sets we can polarize the other set in the cell. The polarization is detected using noninvasive voltage probe without drawing electric currents from the cell.