Friday, March 03, 2006

MS+S: John Martinis

John Martinis (UC Santa Barbara) talked about high-fidelity measurements of a Josephson junction flux qubit. Their device is Al wires, SiNx insulators, an external SQUID for measurement.

They have two qubits coupled through a capacitor. They think they have proven entanglement between the two via tomography on the |10>-i|01> state.

They have done four years' work on materials. A major part of the dissipation is from the on-chip capacitor. The cap is amorphous material, sometimes atomic bonds can oscillate at uwave freq that cause problems. At high power, SiO2 looks like a good dielectric,
but at very low powers, loss is ~1%, way too high. SiNx is 20x better, they think they have some materials that might be better still. Their current device uses SiNx.

Currently at a T1 of 110nsec, hoping 500ns or more with better caps.

John had wonderful animated data on the decay of a qubit.

John is very optimistic about systems of 4-10 qubits. One of his people (sorry, I didn't catch the name) has built a very scalable, distributed control system in software, 50-100KLOC (kilo-lines of code) to do the qubit initialization, tuning, and control.

Through their coupling system, each qubit can in theory be connected to maybe 3-4 others, over moderate distances. In other words, I think it's time for me to get involved :-).

They have also done work on improved dil fridges and getting the wires in and out of the fridge, which concerns me, so I'm happy to see that.

I'm planning on visiting Santa Barbara in October, looking forward to it.


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