Free-orbit experiment with laser interferometry X-rays

Later revised to take place as a tabletop experiment,[2][3] if successful, it is estimated that a mass of roughly 1014 atoms would have been superposed, approximately nine orders of magnitude more massive than any superposition observed to that date (2003).

The purpose is to vary the size of the mirror to investigate the effect of the mass on the time it takes for the quantum system to collapse.

Originally the arms of the interferometer had to stretch into the hundreds of thousands of kilometers to achieve a photon roundtrip-time comparable to the oscillator's period, but that meant that the experiment had to take place in-orbit, reducing its viability.

The revised proposal[2] requires that the mirrors be placed into high-finesse optical cavities that will trap the photons long enough to achieve the desired delay.

Various elaborate electromagnetic mechanisms have been proposed to "reset" the cavities to a stable state before each repetition of the experiment.