  In this paper we present a novel approach to emulating a universal quantum
computer with a classical system, one that uses a signal of bounded duration
and amplitude to represent an arbitrary quantum state. The signal may be of any
modality (e.g., acoustic, electromagnetic, etc), but we focus our discussion
here on electronic signals. Unitary gate operations are performed using analog
electronic circuit devices, such as four-quadrant multipliers, operational
amplifiers, and analog filters, although non-unitary operations may be
performed as well. In this manner, the Hilbert space structure of the quantum
state, as well as a universal set of gate operations, may be fully emulated
classically. The required bandwidth scales exponentially with the number of
qubits, however, thereby limiting the scalability of the approach, but the
intrinsic parallelism, ease of construction, and classical robustness to
decoherence may nevertheless lead to capabilities and efficiencies rivaling
that of current high performance computers.
