Generation of entangled qubit states

A method, comprising:

• receiving a plurality of qubit pairs, each qubit pair being in a Bell state and including a first qubit and a second qubit that is distinct and separate from the first qubit;
• and
• obtaining a plurality of qubits comprising at least six qubits in a Greenberger-Horn-Zeilinger (GHZ) state by:
• providing qubits of the plurality of qubit pairs to a plurality of beam splitters, including:
• providing a first mode of a first qubit pair as a first input to a first beam splitter and a first mode of a second qubit pair as a second input to the first beam splitter, wherein the first beam splitter is coupled with a first output channel of the first beam splitter and a second output channel of the first beam splitter;
• and
• providing a first mode of a third qubit pair as a first input to a second beam splitter and a first mode of a fourth qubit pair as a second input to the second beam splitter that is distinct from the first beam splitter, wherein the second beam splitter is coupled with a first output channel of the second beam splitter and a second output channel of the second beam splitter;
• and
• providing a mode output from the first beam splitter in the second output channel of the first beam splitter as a first input to a first detector and a mode output from the second beam splitter in the first output channel of the second beam splitter as a second input to the first detector.

A method, comprising:

• receiving, by a set of 16 qubit inputs, four qubit pairs, each qubit pair being in a Bell state and each Bell state including respective four of the 16 qubit inputs;
• coupling four modes, one from each of the four pairs of Bell states;
• detecting at least two photons in no less than two of the four coupled modes;
• and
• outputting, on a subset of 12 of 16 waveguides, a plurality of qubits comprising at least six qubits in a Greenberger-Horn-Zeilinger (GHZ) state.