The assumption that optical or analog will be more efficient for a given accuracy though is not grounded. Any non-linear optical phenomenon requires multiple photons interacting in matter, or interacting sequentially with the same matter, and this requires high intensities of (almost always coherent) light in order to make the interaction happen frequently enough.
e.g for a Mach-Zehnder interferometer measuring the phase shifts requires many photons. A single photon arrives or doesn't arrive at the detector. Even if you could perfectly ensure it hits detector at the same time as the reference photon and subsequently detect with 100% quantum efficiency, that still only gives you 1 bit of phase information, not an analog value.
Digital can be done more efficiently with adiabatic or asynchronous circuits. The limiting factor then is speed and chip area rather than joules-per-and-gate.
Comments
The assumption that optical or analog will be more efficient for a given accuracy though is not grounded. Any non-linear optical phenomenon requires multiple photons interacting in matter, or interacting sequentially with the same matter, and this requires high intensities of (almost always coherent) light in order to make the interaction happen frequently enough.
e.g for a Mach-Zehnder interferometer measuring the phase shifts requires many photons. A single photon arrives or doesn't arrive at the detector. Even if you could perfectly ensure it hits detector at the same time as the reference photon and subsequently detect with 100% quantum efficiency, that still only gives you 1 bit of phase information, not an analog value.
Digital can be done more efficiently with adiabatic or asynchronous circuits. The limiting factor then is speed and chip area rather than joules-per-and-gate.