Simulating the effect of weak measurements by a phase damping channel and determining different measures of bipartite correlations in nuclear magnetic resonance

Abstract

Quantum discord is a measure based on local projective measurements which captures quantum correlations that go beyond entanglement. A change in the measurement process, achieved by replacing rank-one projectors with a weak positive operator-valued measure (POVM), allows one to define a quantity termed as weak quantum discord. In this work, we experimentally simulate the effect of a weak POVM on a nuclear magnetic resonance quantum information processor. The two-qubit system under investigation is part of a three-qubit system, where one of the qubits is used as an ancillary to implement the phase damping channel. The strength of the weak POVM is controlled by varying the strength of the phase damping channel. We experimentally observed weak discord in two-qubit states and computed a cost function whose purpose is to optimally extract correlations representing the difference between weak and strong quantum discord. The resultant dynamics of the states is investigated as a function of the measurement strength.