Dynamic optical interferometer locking using entangled photons

A method comprising:

• emitting first photons along a first optical path towards a first remote reflector and second photons along a second optical path towards a second remote reflector, wherein the first photons and the second photons are entangled photons;
• receiving the first photons along the first optical path and the second photons along the second optical path;
• combining the received first photons and the received second photons in a mode combiner having a first output port and a second output port;
• detecting a first output from the first output port at a first photodetector and a second output from the second output port at a second photodetector;
• performing coarse adjustments such that a difference in length of the first optical path and the second optical path is within a fine adjustment range;
• performing fine adjustments to a length of one of the first optical path and the second optical path such that a portion of the first photons and the second photons recombine before detection;
• detecting a change in the difference in length of the first optical path and the second optical path that causes a coincidence rate of the first photons and the second photons to move away from a Hong-Ou-Mandel dip;
• and
• making at least one of additional fine adjustments and additional coarse adjustments to bring the coincidence rate of the first photons and the second photons to be within the Hong-Ou-Mandel dip.

A system comprising:

• an optical source for generating a pair of simultaneously produced photons;
• a first emitter/receiver that emits a first photon in the pair of simultaneously produced photons towards a remote reflector and receives a reflected first photon along a first optical path;
• a second emitter/receiver that emits a second photon in the pair of simultaneously produced photons towards a remote reflector and receives a reflected second photon along a second optical path;
• a mode combiner which combines the reflected first photon from the first optical path and the reflected second photon from the second optical path;
• a plurality of photodetectors that detect a first output from a first output port of the mode combiner and a second output from a second output port of the mode combiner;
• a coarse adjuster that performs coarse adjustments to at least one of the first optical path and the second optical path based on a difference in arrival times of signals from the plurality of photodetectors to bring the difference in length of the first optical path and the second optical path to be within a fine adjustment range;
• and
• a fine adjuster that performs fine adjustments to at least one of the first optical path and the second optical path based on a coincidence rate of the reflected first photon and the reflected second photon to cause the coincidence rate to be within a Hong-Ou-Mandel dip;
• wherein at least one of the fine adjuster and the coarse adjuster make additional adjustments to at least one of the first optical path and the second optical path when the coincidence rate moves away from the Hong-Ou-Mandel dip to maintain the coincidence rate within the Hong-Ou-Mandel dip.