  We study the gate-based implementation of the binary reflected Gray code
(BRGC) and binary code of the unitary time evolution operator due to the
Laplacian discretized on a lattice with periodic boundary conditions. We find
that the resulting Trotter error is independent of system size for a fixed
lattice spacing through the Baker-Campbell-Hausdorff formula. We then present
our algorithm for building the BRGC quantum circuit. For an adiabatic evolution
time $t$ with this circuit, and spectral norm error $\epsilon$, we find the
circuit cost (number of gates) and depth required are $\mc{O}(t^2 n A D
/\epsilon)$ with $n-3$ auxiliary qubits for a system with $2^n$ lattice points
per dimension $D$ and particle number $A$; an improvement over binary position
encoding which requires an exponential number of $n$-local operators. Further,
under the reasonable assumption that $[T,V]$ bounds $\Delta t$, with $T$ the
kinetic energy and $V$ a non-trivial potential, the cost of QFT (Quantum
Fourier Transform ) implementation of the Laplacian scales as
$\mc{O}\left(n^2\right)$ with depth $\mc{O}\left(n\right)$ while BRGC scales as
$\mc{O}\left(n\right)$, giving an advantage to the BRGC implementation.
