Uni of Washington puts gallium phosphide cavities on diamond qubits

[Tundra94]

Researchers at the University of Washington have built a chip that could make diamond based quantum networks much easier to scale. Quantum Zeitgeist reports on the work, led by first author Nicholas Yama. The chip places tiny gallium phosphide light cavities on top of a diamond containing silicon vacancy qubits

Silicon vacancy centres in diamond are promising qubits for quantum networks, because they can store quantum information and interact with light. The challenge is getting that interaction strong and reliable, which usually requires carving delicate structures into the diamond itself. That is hard to do at scale

This team took a different route. They made more than 600 gallium phosphide nanophotonic cavities using electron beam lithography, with a 99.5 percent yield, and then transferred them onto unetched diamond with a stamp method first demonstrated in 2023. That avoids having to etch the diamond at all

The results are encouraging. Laser tests showed cooperativity above one, a sign of strong light matter interaction, which means a qubit's state can be read from the light it scatters. Spin relaxation times exceeded 0.4 milliseconds, enough to support single shot readout of the electron spin. Gallium phosphide's nonlinear properties could also allow on chip switching and frequency conversion

A 99.5 percent fabrication yield is the kind of number that matters for real products. The next steps are linking several qubit devices on one chip and boosting the interaction strength further. Diamond quantum networks just took a practical step forward

Is heterogeneous integration the best path for diamond quantum networks? And how close are we to practical quantum repeaters?

GaP-on-diamond Chip Boosts Quantum Light Interactionsquantumzeitgeist.com