There is a common misconception that the decoherence time is the time scale over which quantum mechanics is lost in a quantum system. This is not correct. Open quantum systems can have highly quantum mechanical equilibrium states, even when the decoherence time is very short.  Under certain conditions, you can wait the lifetime of the universe and the entanglement in an open quantum system will never “go away”. These systems can have very short decoherence times.

Here is a presentation Mohammad Amin recently gave that explains why this is and how decoherence times affect AQC, and a technique we have implemented for measuring a key figure of merit for qubits used in AQC systems.

Hi everybody. I have been pretty busy over the last couple months and have let the blogging slip a bit. Apologies. I will be posting some technical content shortly but in advance here is a great clip of Craig Venter leading Richard Dawkins around one of his facilities and answering questions.

Celera has many interesting parallels to D-Wave.

Venter explains some exceptionally interesting science, how intrducing ideas of automation into biology was met with a lot of resistance, and the politics of transforming the scientific landscape with controversial ideas.

The most impressive software demo I’ve seen since Photosynth. Check out this screencast, it is absolutely amazing.

Yes one of our earlier models made the list.

[via Boing Boing]

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]

It’s been a long ride down for SGI, and now that it’s finally over, it comes almost as a relief, like when a beloved relative who has been suffering in pain for years with a terminal disease, a mere shadow of former self, finally passes. It gives us one last chance to light candles, join hands, and remember an icon that once exemplified Silicon Valley greatness.

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]

Big news in the HPC world.

Closely related to AQC, believe it or not.

This is a youtube video — a Google tech talk — with Geoff Hinton from Toronto.

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.