PT Journal
AU Prevedel, R
   Hamel, DR
   Colbeck, R
   Fisher, K
   Resch, KJ
TI Experimental investigation of the uncertainty principle in the presence of quantum memory and its application to witnessing entanglement
SO Nature Physics
JI Nat. Phys.
PY 2011
BP 757
EP 761
VL 7
IS 10
DE fromIPMRAS
AB Heisenberg's uncertainty principle provides a fundamental limitation on the ability of an observer holding classical information to predict the outcome when one of two measurements is performed on a quantum system. However, an observer with access to a particle (stored in a quantum memory) which is entangled with the system generally has a reduced uncertainty: indeed, if the particle and system are maximally entangled, the observer can perfectly predict the outcome of whichever measurement is chosen. This effect has recently been quantified in a new entropic uncertainty relation. Here we experimentally investigate this relation, showing its effectiveness as an efficient entanglement witness. We use entangled photon pairs, an optical delay line serving as a simple quantum memory and fast, active feed-forward. Our results quantitatively agree with the new uncertainty relation. Our technique acts as a witness for almost all entangled states in our experiment as we obtain lower uncertainties than would be possible without the entangled particle.
ER