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arXiv:quant-ph/0312064 · Journal of Physics A Mathematical and General

Spin decoherence by spacetime curvature

Hiroaki Terashima, Masahito Ueda

Published Feb 16, 2005• 28 citations
arXivHTMLPDF

Abstract

A mechanism of spin decoherence caused by spacetime curvature in general relativity is discussed. The spin state of a particle is shown to decohere only if the particle moves in a curved spacetime. In particular, when a particle is near the event horizon of a black hole, an extremely rapid spin decoherence occurs for an observer who is static in a Killing time, however slow the particle's motion.

DOI
10.1088/0305-4470/38/9/013

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A mechanism of spin decoherence caused by spacetime curvature in general relativity is discussed. The spin state of a particle is shown to decohere only if the particle moves in a curved spacetime. In particular, when a particle is near the event horizon of a black hole, an extremely rapid spin decoherence occurs for an observer who is static in a Killing time, however slow the particle's motion.
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The effect of a classical gravitational field on the spin entanglement of a system of two spin- particles moving in the curved spacetime is discussed. The system is described by a two-particle Gaussian wave packet represented in the momentum space and both the acceleration of the system and the curvature of the spacetime produce a Wigner rotation acting on the wave packet as it moves along a path in the curved spacetime. By calculating the reduced density operator at a final point, we focus on the spin entanglement of the system. In a spherically symmetric and static gravitational field, for example a charged black hole, there can be particular paths on which the Wigner rotation is trivial and so the initial reduced density matrix remains intact. This causes the spin entanglement to be invariant during the motion. The spin entanglement descends to zero by increasing the angular velocity of the mean centroid of the system as well as increasing the proper time during which the centroid moves on its circular path around the center.
Previous studies have shown that the decoherence of environments generally negatively influences the quantum correlations in the Schwarzschild black hole . In our paper, we find that the decoherence of the generalized amplitude damping (GAD) channel has both positive and negative effects on the quantum coherence of Dirac fields, which means that the decoherence of environments can not only reduce the quantum coherence but also increase the quantum coherence in Schwarzschild spacetime. This result banishes the widespread belief that the decoherence of the environment can only destroy the quantum coherence in curved spacetime. Furthermore, another novel phenomenon has been observed for the first time: with increasing Hawking temperature T, the QFI of physically inaccessible modes rapidly decays from infinity to 0, which may provide a way to detect whether the particles enter the physically inaccessible region or not. This result may provide a new perspective for exploring and analyzing black holes.
Abstract As a combination of the microscopic structure of spacetime and the principle of quantum superposition, the study of spacetime superposition provides a fundamental bottom-up approach to a comprehensive understanding of relativity and quantum theory. In this paper, we study how quantum gravitational effects generated by the superposition of the black hole’s masses affect the many-body entanglement for Dirac fields. The main obstacle to performing quantum information processing tasks near a classical black hole is the inevitable entanglement degradation caused by the Unruh–Hawking thermal bath. Fortunately, here we find that the many-body quantum system near a black hole with superposing masses exhibits more entanglement compared to those in the classical black hole background. The superposition properties of spacetime are found to provide additional quantum resources for mitigating gravitationally induced quantum decoherence and improving the efficiency of quantum information tasks in curved spacetime. In addition, the greatest quantum advantage for the recovery of entanglement in the curved spacetime can be obtained by preparing an optimal initial state.