I Is a Quantum-Controlled Mirror Possible?

[Erik Ayer]

I was reading a pdf that mentioned a quantum-controlled beam splitter and wondered whether a quantum-controlled mirror exists. In the beam-splitter case, the beam splitter could either be present or absent, such that path information of photons was either preserved or not. It was controlled with a quantum event so that it's presence or absence was in a state of superposition.

For a mirror, could it be controlled by a quantum event such that it was in a superposition state of being reflective and transparent? If so, a beam could pass through it, be reflected back together, and form interference. It seems like isolation would be critical to keep the state from collapsing.

 

[mfb]

A beam splitter is doing that - it acts as mirror or let's light through, or does both at the same time.
It would be interesting to see the source for the beam splitter experiment.

 

[Erik Ayer]

Yes, a beam splitter splits the beam, but it's on an individual photon basis. If a mirror were controlled to reflect or transmit based on some quantum event, then a bunch of photons would either be reflected or transmitted. If no determination of the setting of the mirror were made (the information was not available, even in principle), then that clot of photons could then be interfered. However, if one photons was found to have been reflected, then they all would have been reflected. Would that entangle all the photons with the mirror, or possibly with the event controlling the mirror?

It would have to be a mirror, either. Anything that selects a path, like by "bending" a beam either slightly left or right, could do this as long as the "switch" were determined by a quantum event. If a light source were dimmed down to the point where one photon per second was sent, then the state of the switch could be set by the polarization in some axis, each second.

The interesting to do next would be to split the photons coming out such that some go to an interferometer to generate interference fringes, and some go elsewhere. The "elsewhere" photons would carry information as to the state of the switch and could then collapse the state to reflect/transmit or bend-left/bend-right, or that information could be erased by focusing them onto one spot on a brick (all physics experiments should involve a brick).