"Using weak measurements to improve interference contrast and investigate photon trajectories":
Optical interferometry has various applications in physics, such as measurements of length, optical testing and interference microscopy.
In order to make the best use of an interferometer, it has to be accurately aligned spatially and angularly.
We suggest an original method for alignment of a free-space optical Mach-Zehnder Interferometer(MZI), which is based on a master equation derived from the two-state vector formalism of quantum mecahnics. The alignment process is quick and simple, and requires only a single phase scan, acting as a weak measurement, and a single light detector.
The suggested technique was already used as a tool for photon trajectory investigation. Information about the positions through which photons pass in a complicated system of a nested MZI is retrieved from different vibration frequencies of mirrors the photons bounce off.
We present surprising experimental evidence regarding the past of photons: photons themselves tell us that they have been in a place through which they could not pass(!). From the analysis we conclude that the past of the photons is not represented by continuous trajectories, contrary to the ‘‘common sense’’.