# Intersample Correlation Control¶

One of the main sources of environmental noise affecting the qubit is magnetic fluctuations from an ensemble of spins local to the qubit wiring. In addition, the persistent current flowing in the qubit body during the quantum annealing algorithm produces a magnetic field that can partially align or polarize this ensemble of spins. For more information on this effect, see Technical Description of the D-Wave QPU.

This partially polarized environment may bias the body of the qubit. This phenomenon may manifest, for example, in measurements of single qubit transition widths (the width of qubit population versus h bias). For very long anneal times, the polarized environment may add to the external h bias, producing a transition width that is narrower than the width expected from a thermal distribution. The partially polarized environment can also produce sample-to-sample correlations, biasing the QPU towards previously achieved spin configurations.

The reduce_intersample_correlation parameter reduces sample-to-sample correlations by adding a optimal delay times to the anneal-read cycle.

## Release Introduced¶

Solver API Release 3.0, January 2018

User parameter: