On the quantumness of correlations in nuclear magnetic resonance

Abstract

Nuclear magnetic resonance (NMR) was successfully employed to test several protocols and ideas in quantum information science. In most of these implementations, the existence of entanglement was ruled out. This fact introduced concerns and questions about the quantum nature of such bench tests. In this paper, we address some issues related to the non-classical aspects of NMR systems. We discuss some experiments where the quantum aspects of this system are supported by quantum correlations of separable states. Such quantumness, beyond the entanglement-separability paradigm, is revealed via a departure between the quantum and the classical versions of information theory. In this scenario, the concept of quantum discord seems to play an important role. We also present an experimental implementation of an analogue of the single-photon MachZehnder interferometer employing two nuclear spins to encode the interferometric paths. This experiment illustrates how non-classical correlations of separable states may be used to simulate quantum dynamics. The results obtained are completely equivalent to the optical scenario, where entanglement (between two field modes) may be present.

Broadcasting of quantum correlations in qubit-qudit systems

“…We trace out the (2, 4) and (1,3) subsystems to obtain the local output statesρ 13 on Alice's side and ρ 24 on Bob's side respectively. Similarly, after tracing out appropriate qubits and qudits from the output state, we obtain the two plausible groups of nonlocal output states ρ 14 andρ 23 . The process is illustrated in figure (1).…”

“…However, there are separable states which preserve their separability under any nonlocal unitary action. Such states are known as absolutely separable states and their characterization is a significant problem in quantum computing especially in context to NMR quantum computing [23]. Another important feature in entanglement theory is the existence of entangled states with positive partial transpose (PPTES) [24,25].…”

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

“…An interesting way to detect it in NMR systems can be provided by an analogous of the well-known single-photon Mach-Zehnder interferometer employing two nuclear spins to encode the interferometric paths, where the experimental implementations of interferometry in NMR have already been reported in Refs. [31][32][33][34]. Due to the fact that distinct nuclei have, generally, distinct relaxation times, it is possible to study the environmentinduced phase shift between both paths [35,36].…”

Curvature detection by entanglement generation using a beam splitter

“…Recently, numerous devices have been proposed and realized experimentally to generate the quantum entanglement, such as beam splitter [2][3][4][5], cavity QED [6,7], NMR systems [8,9] and semiconductor microcavity [10]. In this paper, we concentrate on the first device, that is, the beam splitter.…”