  Quantum-dot cellular automata (QCA) is a low-power, non-von-Neumann,
general-purpose paradigm for classical computing using transistor-free logic.
An elementary QCA device called a "cell" is made from a system of coupled
quantum dots with a few mobile charges. The cell's charge configuration encodes
a bit, and quantum charge tunneling within a cell enables device switching.
Arrays of cells networked locally via the electrostatic field form QCA
circuits, which mix logic, memory and interconnect. A molecular QCA
implementation promises ultra-high device densities, high switching speeds, and
room-temperature operation. We propose a novel approach to the technical
challenge of transducing bits from larger conventional devices to nanoscale QCA
molecules. This signal transduction begins with lithographically-formed
electrodes placed on the device plane. A voltage applied across these
electrodes establishes an in-plane electric field, which selects a bit packet
on a large QCA input circuit. A typical QCA binary wire may be used to transmit
a smaller bit packet of a size more suitable for processing from this input to
other QCA circuitry. In contrast to previous concepts for bit inputs to
molecular QCA, this approach requires neither special QCA cells with fixed
states nor nanoelectrodes which establish fields with single-electron
specificity. A brief overview of the QCA paradigm is given. Proof-of-principle
simulation results are shown, demonstrating the input concept in circuits made
from two-dot QCA cells. Importantly, this concept for bit inputs to molecular
QCA may enable solutions to or provide insights into other challenges to the
realization of molecular QCA, such as the demonstration of molecular device
switching, the read-out of molecular QCA states, and the layout of molecular
QCA circuits.
