Generating photons for quantum communication

Entangled pairs of photons are generated by and propagate away from qubits placed along a waveguide. Credit: Sampson Wilcox

MIT researchers using superconducting quantum bits connected to a microwave transmission line have shown how the qubits can generate on demand the photons, or particles of light, necessary for communication between quantum processors.

The advance is an important step toward achieving the interconnections that would allow a modular quantum computing system to perform operations at rates exponentially faster than classical computers can achieve.

Superconducting qubits are a leading technology today, but they generally support only local interactions (nearest-neighbor or qubits very close by). The question is how to connect to qubits that are at distant locations.

That communication can occur via the microwave transmission line, or waveguide, as the excitations stored in the qubits generate photon pairs, which are emitted into the waveguide and then travel to two distant processing nodes. The identical photons are said to be “entangled,” acting as one system. As they travel to distant processing nodes, they can distribute that entanglement throughout a quantum network.

This paper presented the photon generation ability of the waveguide quantum electrodynamics architecture, showing that the qubits can be used as quantum emitters for the waveguide. The researchers demonstrated that quantum interference between the photons emitted into the waveguide generates entangled, itinerant photons that travel in opposite directions and can be used for long-distance communication between quantum processors.

The study has been published in Science Advances.

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