Heralded photonic entanglement source

A method for generating at least two entangled optical outputs from one or more heralded entanglement sources, the method comprising:

• for each of the one or more heralded entanglement sources:
• providing from a first free-running entanglement source a first optical output comprising a quantum superposition of first and second orthogonal optical modes, and a second optical output comprising a quantum superposition of third and fourth orthogonal optical modes, entangled with the first optical output;
• providing from a second free-running entanglement source a third optical output comprising a quantum superposition of fifth and sixth orthogonal optical modes, and a fourth optical output comprising a quantum superposition of seventh and eighth orthogonal optical modes, entangled with the third optical output;
• combining, using at least one beam splitter, the first optical mode and the fifth optical mode;
• combining, using at least one beam splitter, the second optical mode and the sixth optical mode;
• detecting, using two or more optical detectors, a first output of the one or more beam splitters to generate a first detection signal in a series of time slots, a second output of the one or more beam splitters to generate a second detection signal in the series of time slots, a third output of the one or more beam splitters to generate a third detection signal in the series of time slots, and a fourth output of the one or more beam splitters to generate a fourth detection signal in the series of time slots;
• and
• generating, using a trigger module, a trigger signal based on the first, second, third, and fourth detection signals to indicate one or more time slots in which the second optical output and the fourth optical output, provided from respective output ports of that heralded entanglement source, are entangled with each other.

An apparatus for generating at least two entangled optical outputs, the apparatus comprising:

• one or more heralded entanglement sources, each heralded entanglement source comprising:
• a first free-running entanglement source providing a first optical output comprising a quantum superposition of a pair of orthogonal optical modes, and a second optical output comprising a quantum superposition of a pair of orthogonal optical modes, entangled with the first optical output;
• a second free-running entanglement source providing a third optical output comprising a quantum superposition of a pair of orthogonal optical modes, and a fourth optical output comprising a quantum superposition of a pair of orthogonal optical modes, entangled with the third optical output;
• an optical module configured to perform an interferometric measurement based on optical interference between at least a portion of the first optical output and at least a portion of the third optical output, and to generate one or more detection signals based on the interferometric measurement in a series of time slots;
• and
• a trigger module configured to generate a trigger signal based on the one or more detection signals to indicate one or more time slots in which the second optical output and the fourth optical output, provided from respective output ports of that heralded entanglement source, are entangled with each other.

An apparatus for generating at least two entangled optical outputs, the apparatus comprising:

• a plurality of heralded entanglement sources, each heralded entanglement source comprising:
• a first output port providing a first optical output comprising a quantum superposition of orthogonal optical modes,
• a second output port providing a second optical output comprising a quantum superposition of orthogonal optical modes, and
• a trigger module configured to generate a trigger signal to indicate one or more time slots in which the first optical output and the second optical output are entangled with each other;
• a first optical multiplexer configured to combine first output ports of each of the heralded entanglement sources into a first multiplexed output;
• a second optical multiplexer configured to combine second output ports of each of the heralded entanglement sources into a second multiplexed output;
• and
• a controller configured to control the first and second optical multiplexers based on respective trigger signals generated by the plurality of heralded entanglement sources.