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Squeezing of Primordial Gravitational Waves as Quantum Discord

Department of Physics, Graduate School of Science, Nagoya University, Chikusa, Nagoya 464-8602, Japan
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Universe 2020, 6(2), 33; https://doi.org/10.3390/universe6020033
Received: 8 January 2020 / Revised: 12 February 2020 / Accepted: 13 February 2020 / Published: 15 February 2020
(This article belongs to the Section Cosmology)
We investigate the squeezing of primordial gravitational waves (PGWs) in terms of quantum discord. We construct a classical state of PGWs without quantum discord and compare it with the Bunch–Davies vacuum. Then it is shown that the oscillatory behavior of the angular-power spectrum of the cosmic microwave background (CMB) fluctuations induced by PGWs can be the signature of the quantum discord of PGWs. In addition, we discuss the effect of quantum decoherence on the entanglement and the quantum discord of PGWs for super-horizon modes. For the state of PGWs with decoherence effect, we examine the decoherence condition and the correlation condition introduced by C. Kiefer et al. (Class. Quantum Grav. 24 (2007) 1699). We show that the decoherence condition is not sufficient for the separability of PGWs and the correlation condition implies that the PGWs in the matter-dominated era have quantum discord. View Full-Text
Keywords: PGWs; squeezing; quantum discord; oscillatory behavior; decoherence PGWs; squeezing; quantum discord; oscillatory behavior; decoherence
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Matsumura, A.; Nambu, Y. Squeezing of Primordial Gravitational Waves as Quantum Discord. Universe 2020, 6, 33.

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