System and method for detecting correlations between two photons

A system for detecting correlations between two photons, the system comprising:

• a non-polarizing beam splitter configured to receive a first photon from a first entanglement source at a first input of the non-polarizing beam splitter and to receive a second photon from a second entanglement source at a second input of the non-polarizing beam splitter;
• a polarizing beam splitter having a first input and a second input, the polarizing beam splitter configured to receive a first output of the non-polarizing beam splitter at the first input of the polarizing beam splitter, the polarizing beam splitter configured to direct light having a first polarization to a first output of the polarizing beam splitter and to direct light having a second polarization to a second output of the polarizing beam splitter;
• a first delay line configured to receive a second output of the non-polarizing beam splitter and to output light to the second input of the polarizing beam splitter;
• a second delay line configured to receive the second output of the polarizing beam splitter having the second polarization and to output the received second output into a shared beam path, the shared beam path configured to receive the first output of the polarizing beam splitter and an output of the second delay line;
• and
• a photon detector configured to receive photons at different times depending on their path between the non-polarizing beam splitter and the photon detector.

A method for detecting a quantum state based on detection of two photons, the method comprising:

• receiving a first photon, from a first beam path, and a second photon, from a second beam path;
• splitting the first beam path and the second beam path into a first shared beam path and a second shared beam path;
• splitting the first shared beam path, using a polarizing beam splitter, into a first polarized beam path and a second polarized beam path, the second polarized beam path having a polarization orthogonal to the first polarized beam path;
• delaying the second shared beam path;
• detecting first outputs corresponding to the first polarized beam path and the second polarized beam path;
• splitting the second shared beam path, using the polarizing beam splitter, into the first polarized beam path and the second polarized beam path;
• and
• detecting second outputs corresponding to the first polarized beam path and the second polarized beam path.