Quantum gates and simple quantum algorithms can be designed utilizing the
diffraction phenomena of a photon within a multiplexed holographic element. The
quantum eigenstates we use are the photon's linear momentum (LM) as measured by
the number of waves of tilt across the aperture. Two properties of quantum
computing within the circuit model make this approach attractive. First, any
conditional measurement can be commuted in time with any unitary quantum gate -
the timeless nature of quantum computing. Second, photon entanglement can be
encoded as a superposition state of a single photon in a higher-dimensional
state space afforded by LM. Our theoretical and numerical results indicate that
OptiGrate's photo-thermal refractive (PTR) glass is an enabling technology. We
will review our previous design of a quantum projection operator and give
credence to this approach on a representative quantum gate grounded on
coupled-mode theory and numerical simulations, all with parameters consistent
with PTR glass. We discuss the strengths (high efficiencies, robustness to
environment) and limitations (scalability, crosstalk) of this technology. While
not scalable, the utility and robustness of such optical elements for broader
quantum information processing applications can be substantial.Comment: 14 pages, 6 figure