Efficient Quantum Simulation of Variable-Coefficient Transport with Continuous Source Injection
- URL: http://arxiv.org/abs/2608.27712v1
- Date: Thu, 27 Aug 2026 21:00:39 GMT
- Title: Efficient Quantum Simulation of Variable-Coefficient Transport with Continuous Source Injection
- Abstract summary: We present an algorithm for a forced variable-coefficient advection-diffusion equation in flow-inspired skew-symmetric form.<n>A centered skew-symmetric discretization makes the advection operator strictly skew-Hermitian for arbitrary velocity profiles.<n>We show that the per-step ancilla failure probability is proportional to the instantaneous dissipation rate, making postselection cost self-regulating over a fifty-fold viscosity range.
- Score: 0.49259062564301753
- License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
- Abstract: Quantum time-marching algorithms for transport PDEs often represent variable coefficients and forcing through register-expanding dilations, block-encoding oracles, or repeated postselection. We present an alternative algorithm for a forced variable-coefficient advection-diffusion equation in flow-inspired skew-symmetric form that incorporates spatially varying velocity, viscous dissipation, and persistent source injection with a peak logical requirement of $n_q+1$ qubits. A centered skew-symmetric discretization makes the advection operator strictly skew-Hermitian for arbitrary velocity profiles, enabling an ancilla-free unitary realization using a Gray-code Trotter sequence of controlled-$R_y$ rotations. Diffusion is applied in the Fourier basis through a uniformly controlled rotation on one postselected ancilla, which is measured, reset, and reused between the two diffusion half-steps, while the source is incorporated classically through second-order Strang splitting. Statevector simulations for $N=16$ and $32$ recover second-order temporal convergence against high-accuracy classical solutions, while Richardson extrapolation gives fourth-order accuracy and reduces kernel calls by factors of four to fourteen. Independent tests through $N=256$ confirm second-order spatial consistency. We further show that the per-step ancilla failure probability is proportional to the instantaneous viscous dissipation rate, making postselection cost self-regulating over a fifty-fold viscosity range. Stable evolution is demonstrated for $5\times10^4$ time steps without observable secular error growth, while Gray-code advection accounts for $71$--$95\%$ of transpiled controlled-NOT gates. The fixed-width kernel provides a qubit-efficient building block for near-term hardware studies, although classical readout and state re-preparation remain the main obstacles to coherent multistep evolution.
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