What is the QPU "Working Graph"?

In a D-Wave QPU, the set of qubits and couplers that are available for computation is known as the working graph.

The yield of a working graph is typically less than the total number of qubits and couplers (devices) that are fabricated and physically present in the QPU. Manufacturing variations and the need to prepare the QPU to operate at cryogenic temperatures in a low–magnetic field environment limits the yield. These variations are minimized through an extensive calibration process that attempts to bring all of these analog devices into a consistent parametric regime.

Each D-Wave 2000Q QPU is fabricated with 2048 qubits and 6016 couplers. Of this total, the number of devices, and the specific set of devices, that can be made available in the working graph changes with each system cooldown and calibration cycle. Calibrated commercial systems typically have more than 97% of fabricated qubits available in their working graphs. Yields significantly higher than this are not guaranteed.

Note: The ratio of qubits available to the total fabricated is specific to a QPU model. The ratios published for the D-Wave 2000Q system may not apply to future product generations.

See also: What are the Properties of this QPU? 

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