Nonlinear-ancilla aided quantum algorithm for nonlinear Schr\"odinger equations

We present an algorithm that uses a single ancilla qubit that can evolve nonlinearly, and show how to use it to efficiently solve generic nonlinear Schr\"odinger equations, including nonlocal Hartree equations and the Navier-Stokes equation for an irrotational, non-viscous flow. We propose a realization of such nonlinear qubits via spin-spin coupling of neutral atom qubits to a Bose-Einstein condensate. The results suggest that the use of nonlinear ancillas can provide substantial speedups compared to exclusively linear qubit devices.