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Discord and Decoherence
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In quantum information theory, quantum discord has been proposed as a tool to characterise the presence of "quantum correlations" between the subparts of a given system. Whether a system behaves quantum-mechanically or classically is believed to be impacted by the phenomenon of decoherence, which originates from the unavoidable interaction between this system and an environment. Generically, decoherence is associated with a decrease of the state purity, i.e. a transition from a pure to a mixed state. In this paper, we investigate how quantum discord is modified by this quantum-to-classical transition. This study is carried out on systems described by quadratic Hamiltonians and Gaussian states, with generalised squeezing parameters. A generic parametrisation is also introduced to describe the way the system is partitioned into two subsystems. We find that the evolution of quantum discord in presence of an environment is a competition between the growth of the squeezing amplitude and the decrease of the state purity. In phase space, this corresponds to whether the semi-minor axis of the Wigner ellipse increases or decreases, which has a clear geometrical interpretation. Finally, these considerations are applied to primordial cosmological perturbations, thus allowing us to investigate how large-scale structures in our universe, which are believed to arise from quantum fluctuations, can exhibit classical properties.
Forward citations
Cited by 6 Pith papers
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When the Environment Speaks: Quantum Signatures in Non-Attractor Inflation
An open quantum system treatment of curvature perturbations during Ultra-Slow-Roll inflation shows that environmental decoherence erases the interference dip, modifies the growth slope, and induces oscillatory feature...
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A Landscape of Cosmological Decoherence
Requiring decohered cosmological perturbations to admit a classical P-function forces their momentum variance above the vacuum value, and demanding a linear gravitational potential at reheating bounds that variance by...
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When inflationary perturbations refuse to classicalise: the role of non-Gaussianity in Wigner negativity
In ultra-slow-roll inflation, the Wigner function of the inflationary Goldstone field becomes negative and its negativity grows with the scale factor squared, so the perturbations do not automatically become classical.
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Inflationary Decoherence from the Gravitational Floor
Gravitational self-interactions alone decohere super-Hubble inflationary fluctuations with purity loss growing as (aH/k)^5, faster than the a^3 growth of earlier calculations.
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Manifestation of quantum entanglement between harmonic oscillators in de Sitter
In de Sitter space, two harmonic oscillators coupled by a massless scalar field develop late-time entanglement that is sizeable when frequency and separation are near the Hubble scale, and tiny otherwise.
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Probing the self-coherence of primordial quantum fluctuations with complexity
Complexity of formation, unlike complexity of purification, shows distinct and timescale-matching signatures of both decoherence and recoherence in a Gaussian two-field de Sitter model.
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