Study of stochastic estimates of quark loops with unbiased subtraction

Stochastic noise estimator method is a powerful tool to calculate the disconnected insertion involving quark loops. We study the variance reduction technique with unbiased subtraction. We use the complex Z2 noise to calculate the quark loops on a 16 3 × 24 lattice with � = 6.0 and � = 0.154. Unbiased subtraction method is performed by using hoping parameter expansion. We report on the variance reduction for the point-split vector current as a function of the number of subtraction terms and the number of noise used.