Magdalena Stobinska, University of Gdańsk/Polish Academy of Sciences, Warsaw
We discuss a device capable of filtering out two-mode states of light with mode populations differing by more than a certain threshold, while not revealing which mode is more populated. It would allow engineering of macroscopic quantum states of light in a way which is preserving specific superpositions. As a result, it would enhance optical phase estimation with these states. We propose an optical scheme, which is a relatively simple, albeit non-ideal, operational implementation of such a filter.
As a side remark, we show that the principle of action of the device allows to demonstrate a quantum walk with many steps avoiding beam splitter cascades.