rose.blog

We have designed, fabricated and tested an XY addressable readout architecture for superconducting flux qubits in an integrated circuit designed to enable adiabatic quantum optimization algorithms. The readout architecture for an N-qubit system comprises N hysteretic dc SQUIDs and N rf SQUID latches controlled with wires. The latching elements are coupled to the qubits and provide exceptional readout fidelity. The dc SQUIDs are then coupled to the latches to provide coarse readout. A key advantage of this architecture is that the latches are unaffected by the ac currents generated in the dc SQUIDs during switching. We place a lower bound on the readout fidelity of 99.9999% in an 8 qubit test system.

[soon to be arxiv:0905.0891]

This is the device used to couple qubits in the current design. It is used in the 128-qubit systems currently under test.

An improved tunable coupling element for building networks of coupled rf-SQUID flux qubits has been experimentally demonstrated. This new form of coupler, based upon the compound Josephson junction rf-SQUID, provides a sign and magnitude tunable mutual inductance between qubits with minimal nonlinear crosstalk from the coupler tuning parameter into the qubits. Quantitative agreement is shown between an effective one-dimensional model of the coupler’s potential and measurements of the coupler persistent current and susceptibility.

[arXiv:0904.3784]

Putting all of these qubits into superposition states — the initial Hamiltonian in the adiabatic algorithm — gives simultaneously held states.  Not quite the number of atoms in the earth, but close.

Here is a picture of a 128 qubit Rainier chip in the process of being wirebonded. More to follow.