Electron charge dynamics in metal-dot QCA cell using gate reflectometry

Quantum-dot cellular automata (QCA) is a field-coupled computational paradigm [C. S. Lent et al., Nanotechnology 4, 49 (1993)] that encodes binary information through the positions of single electrons within quantum-dot cells. In this work, we present experimental results obtained using RF gate reflectometry on two coupled floating metal double dots (DDs). We demonstrate that a single gate sensor can effectively capture the behavior of both DDs, providing detailed insights into their charging dynamics. The observed variations in the reflected signal directly correspond to changes in electron tunneling rates. Experiments reveal that at low temperatures (T ≈ 0.35 K), tunneling within DDs in the non-polarized state of a QCA cell becomes strongly correlated, leading to low-frequency (≤30 kHz) thermally driven random fluctuations in cell polarization. However, the cell remains capable of fast and robust switching when driven by an input signal. Furthermore, we provide the first direct experimental measurement of temperature effects on QCA switching. At elevated temperatures, where the Coulomb blockade is weakened, we observe degradation in the abruptness of the switching, which could lead to signal loss across a chain of cells unless appropriate clocking mechanisms are implemented.