  Rendering on conventional computers is capable of generating realistic
imagery, but the computational complexity of these light transport algorithms
is a limiting factor of image synthesis. Quantum computers have the potential
to significantly improve rendering performance through reducing the underlying
complexity of the algorithms behind light transport. This paper investigates
hybrid quantum-classical algorithms for ray tracing, a core component of most
rendering techniques. Through a practical implementation of quantum ray tracing
in a 3D environment, we show quantum approaches provide a quadratic improvement
in query complexity compared to the equivalent classical approach. Based on
domain specific knowledge, we then propose algorithms to significantly reduce
the computation required for quantum ray tracing through exploiting image space
coherence and a principled termination criteria for quantum searching. We show
results for both Whitted style ray tracing, and for accelerating ray tracing
operations when performing classical Monte Carlo integration for area lights
and indirect illumination.
