Almost all quantum states have nonclassical correlations

By Alessandro Ferraro, Leandro Aolita, Daniel Cavalcanti, F. Cucchietti, Antonio Acín. 2009

424 citations recorded by the source corpus.

Quantum discord quantifies nonclassical correlations in a quantum system including those not captured by entanglement. Thus, only states with zero discord exhibit strictly classical correlations. We prove that these states are negligible in the whole Hilbert space: typically a state picked out at random has positive discord and, given a state with zero discord, a generic arbitrarily small perturbation drives it to a positive-discord state. These results hold for any Hilbert-space dimension and have direct implications for quantum computation and for the foundations of the theory of open systems. In addition, we provide a simple necessary criterion for zero quantum discord. Finally, we show that, for almost all positive-discord states, an arbitrary Markovian evolution cannot lead to a sudden, permanent vanishing of discord.

Subfields: Artificial Intelligence, Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/c34338378905a7527141998a4fab97486a02d743

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In Artificial Intelligence

In Atomic and Molecular Physics, and Optics

Citations in the corpus

Quantum-enhanced measurements without entanglement (2017, background): “Every entangled state is also discordant, but the converse is not true; in fact, almost all separable states still exhibit nonzero discord (Ferraro et al., 2010).”
The classical-quantum boundary for correlations: Discord and related measures (2011, methodology): “(Ferraro et al., 2010) give a formal proof that interaction with any (local or common) Markovian bath can never lead to a sudden and permanent vanishing of discord (unless the infinite-time limit is reached).”