Measuring geometric quantum discord using one bit of quantum information
Gina Passante, Osama Moussa, Raymond Laflamme · Physical Review A · 2012
We describe an efficient DQC1 (deterministic quantum computation with one quantum qubit) algorithm to quantify the amount of geometric quantum discord present in the output state of a DQC1 computation. DQC1 is a model of computation that utilizes separable states to solve a problem with no known efficient classical algorithm and is known to contain quantum correlations as measured by the discord. For the general case of a $(1+n)$-qubit DQC1 state we provide an analytical expression for the geometric quantum discord and find that its typical (and maximum) value decreases exponentially with $n$. This is in contrast to the standard quantum discord whose value for typical DQC1 states is known to be independent of $n$. We experimentally demonstrate the proposed algorithm on a four-qubit liquid-state nuclear magnetic resonance quantum information processor. In the special case of a two-qubit DQC1 model, we also provide an expression for the quantum discord that only requires the outcome of the DQC1 algorithm.