Superconducting circuit stitches small groups of photons into larger entangled states

[Niamh_52]

Phys.org reports on a superconducting circuit that links smaller groups of photons into larger entangled states. As far as I can tell, the underlying work is a Nature Physics paper from Tsinghua University and the Hefei National Laboratory, titled Deterministic and programmable fusion for the scalable generation of photonic graph states. Authors include Yan Li, Yunfan Yang, Luyan Sun and Luming Duan. Graph states, also called cluster states, are large webs of entangled photons that can power measurement based quantum computing and quantum repeaters

The usual problem is that building big graph states is a game of chance. Joining small entangled states together with ordinary optics only works some of the time. Every failure has to be detected and corrected, which needs lots of extra hardware and fast feedback. As the states get bigger, the odds of success fall quickly

This team made the joining step deterministic on a superconducting chip. Small cluster states of flying microwave photons are generated on demand. Pairs of photons are then measured in a way that does not destroy them and projected into Bell states, which stitches the small states together into larger ones. The resulting graph states are reconfigurable, and the team reused qubits by actively resetting them to fight decoherence

They reported entanglement shared across all 13 photonic qubits at once. They also built a five vertex caterpillar shaped state, showing that different layouts are possible. Thirteen photons is not a huge number. The point is that the method scales without relying on luck at every step

I like this kind of work because it tackles the plumbing rather than the headline qubit count. Measurement based quantum computing needs big, reliable entangled states, and making them on demand is a key step. Microwave photons are not much use for long distance links on their own, but they suit links between chips in the same fridge. Reliable internal links will matter as much as the qubits themselves

Is measurement based quantum computing a serious alternative to gate based machines? And how far could this approach scale?

Superconducting Circuit Links Smaller Photonphys.org