The Role of Single Qubit Decoherence Time in Adiabatic Quantum Computation

We numerically study the evolution of an adiabatic quantum computer in the presence of a Markovian ohmic environment. We consider Ising spin glass systems with up to 20 coupled qubits that are independently coupled to the environment via two conjugate degrees of freedom. We demonstrate that the required computation time in the presence of the environment is of the same order as that for an isolated system, and is not limited by the single qubit decoherence time T2*, even when the minimum gap is much smaller than temperature. We also show that the behavior of the system can be efficiently described by a two-state model with only longitudinal coupling to the environment.

The main result is summarized in the conclusions:

…we have explicitly demonstrated that the computation time in AQC can be much longer than single qubit decoherence time T2∗.

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ok, so does this mean your system can tolerate more noise and still get an answer with a high probability of success within 1 msec?

and even higher within 2msec?

Hi Joseph

The short answer to your question is yes, although the analysis doesn’t just apply to our systems, it applies to all AQC-like machines.

The robustness of the landau-zener transition probability in the presence of noise has been known in the condensed matter community for a while. This counter-intuitive (at least to me) result has major implications for QC. In the gate model, where the Hamiltonian is thought of primarily as a generator of unitary operations, the dephasing time T_2 is extremely important as errors occur on this timescale that must be actively corrected in order for a computation to proceed. In AQC the T_2 time, while not entirely irrelevant, loses its central importance because of the nature of how adiabatic algorithms work. This paper demonstrates this explicitly and shows why it’s true.

which is why you were looking to trade off the number of variable for time, which i think most of the feedback was not eazy (if at all) to do.

but if you could connect two or more AQCpu’s together in a loop feeding the output of one to the input of the next you could cut out your cool down time,

so in a scents you could handle more variable’s in the same amount of time

after thinking about it your better off getting as many bits on to one chip

“we have explicitly demonstrated that the computation time in AQC can be much longer than single qubit decoherence time T2” This is an important result. Well done Mohammad, Colin and Dima.

Geordie, please summarize and share any scholarly comments made on this paper.

Hello Goerdie. I have a bet with my sister that by 2054 someone will have solved the protein folding problem and by that time we will have precise data on how 99.9% of how human proteins fold. Does your technology apply to protein folding or does it require some other technology in addition to pure simulation?

What do you think my chances are in winning the bet? It’s only one thousand dollars after all.