Noninvasiveness and time symmetry of weak measurements
Abstract
Measurements in classical and quantum physics are described in fundamentally different ways. Nevertheless, one can formally define similar measurement procedures with respect to the disturbance they cause. Obviously, strong measurements, both classical and quantum, are invasive—they disturb the measured system. We show that it is possible to define general weak measurements, which are noninvasive: the disturbance becomes negligible as the measurement strength goes to zero. Classical intuition suggests that noninvasive measurements should be time symmetric (if the system dynamics is reversible) and we confirm that correlations are timereversal symmetric in the classical case. However, quantum weak measurements—defined analogously to their classical counterparts—can be noninvasive but not time symmetric. We present a simple example of measurements on a twolevel system which violates time symmetry and propose an experiment with quantum dots to measure the timesymmetry violation in a thirdorder current correlation function.
 Publication:

New Journal of Physics
 Pub Date:
 February 2013
 DOI:
 10.1088/13672630/15/2/023043
 Bibcode:
 2013NJPh...15b3043B