Quantum Discord-A tool for differentiating between possible solutions to Quantum Measurement Problem (in Laboratory and in Cosmic Microwave Background).

 In the context of quantum information theory, quantum discord is a measure of the quantumness or non-classicality between two bipartite subsystems of a quantum system.  It is zero only for purely classical systems. We also know that quantum mechanics, though a successful theory, fails to explain the absence of macroscopic position superpositions and probabilistic outcomes. This is commonly known as quantum measurement problem in laboratory. This loss of superposition may be caused by environmental decoherence (if supplemented by the many worlds interpretation). Alternatively the explanation may lie in Bohmian mechanics, or in fundamental decoherence induced by gravity, or it may result from collapse models which modify the Schrodinger equation. Till date the debate remains as to which model is the correct/effective one. My talk is based on a recent work where we proposed  quantum discord as a tool to  compare and contrast collapse model (Continuous Spontaneous Localization) and various  sources of decoherence (environmental and fundamental). We study these models for an experimentally demonstrated macroscopic entanglement between diamond lattices [K. C. Lee, et al., Entangling Macroscopic Diamonds at Room 
Temperature, Science, 334 (2011) 1253] and show that, provided we have long enough experimental time, one can in principle distinguish between these models. I shall also discuss a recent novel application of discord to the anisotropies of the cosmic microwave background and how this novel idea can be used to test the effectiveness of different collapse and decoherence models in causing quantum to classical transition of inflationary perturbations.