On the quantumness of correlations in nuclear magnetic resonance

Quantum discord and its allies: a review of recent progress

We review concepts and methods associated with quantum discord and related topics. We also describe their possible connections with other aspects of quantum information and beyond, including quantum communication, quantum computation, many-body physics, and open quantum dynamics. Quantum discord in the multiparty regime and its applications are also discussed.

Measuring bipartite quantum correlations of an unknown state

We report the experimental measurement of bipartite quantum correlations of an unknown two-qubit state. Using a liquid state Nuclear Magnetic Resonance setup and employing geometric discord, we evaluate the quantum correlations of a state without resorting to prior knowledge of its density matrix. The method is applicable to any 2 ⊗ d system and provides, in terms of number of measurements required, an advantage over full state tomography scaling with the dimension d of the unmeasured subsystem. The negativity of quantumness is measured as well for reference. We also observe the phenomenon of sudden transition of quantum correlations when local phase and amplitude damping channels are applied to the state.

Nuclear magnetic resonance quantum information processing

For the past decade, nuclear magnetic resonance (NMR) has been established as a main experimental technique for testing quantum protocols in small systems. This Theme Issue presents recent advances and major challenges of NMR quantum information possessing (QIP), including contributions by researchers from 10 different countries. In this introduction, after a short comment on NMR-QIP basics, we briefly anticipate the contents of this issue.

Dynamic evolution for liquid-state nuclear spins and Berry phase of mixed state in a magnetic resonance

Dynamic evolution for liquid-state nuclear spin in a magnetic resonance is investigated based on Bloch sphere structure under the time-dependent modified Bloch equation. We show that the magnetization is related to the magnetic field strength but approximately independent of the initial unpolarized spin state after a very short evolving time. We predict that the Berry phase transition of the nuclear spin system take place in a quasicyclic evolution for some initial states, resulting in that the evolving memory of nuclear spin polarization is kept in terms of the Berry phase. The findings provide another clue to search for quantum memory devices in such a system on the basis of the geometric phase.