Hiroaki Terashima, Masahito Ueda
A decoherence mechanism caused by spacetime curvature is discussed. The spin state of a particle is shown to decohere if only 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 is.
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The question of whether unobserved short-wavelength modes of the gravitational field can induce decoherence in the long-wavelength modes (``the decoherence of spacetime'') is addressed using a simplified model of perturbative general relativity, related to the Nordstrom-Einstein-Fokker theory, where the metric is assumed to be conformally flat. For some long-wavelength coarse grainings, the Feynman-Vernon influence phase is found to be effective at suppressing the off-diagonal elements of the decoherence functional. The requirement that the short-wavelength modes be in a sufficiently high-temp…
We give a first principles derivation of a master equation for the evolution of a quantum matter field in a linearly perturbed Minkowski spacetime, based solely on quantum field theory and general relativity. We make no additional assumptions nor introduce extra ingredients, as is often done in alternative quantum theories. When the quantum matter field is projected to a one-particle state, the master equation for a non-relativistic quantum particle in a weak gravitational field predicts decoherence in the energy basis, in contrast to most existing theories of gravitational decoherence. We poi…
We show that quantum properties of spacetime, encoded by noncommutativity at the Planck scale, lead to a generalized time evolution of quantum systems in which pure states can evolve into mixed states. Specifically, a decoherence mechanism is obtained in the form of a Lindblad-like time evolution for the density operator when the action of time translations generator is deformed by the effects of spacetime noncommutativity. The decoherence time for the evolution of a free particle is used to show that the Planck mass is the maximum allowed mass for elementary quantum systems.
Note on the local calculation of decoherence of quantum superpositions in de Sitter spacetime
本文在德西特时空中利用弯曲时空量子场论代数方法推导纠缠粒子数表达式，建立退相干与局域两点关联函数的关系，并计算标量、电磁和引力场情形，修正了引力退相干的数值前因子。
Decoherence and entropy production due to quantum fluctuations of spacetime
本研究探讨了量子时空波动如何通过引力子导致微观系统退相干和熵产，揭示了引力与量子系统相互作用的普遍性机制。
One of the biggest problems faced by those attempting to combine quantum theory and general relativity is the experimental inaccessibility of the unification scale. In this paper we show how incoherent conformal waves in the gravitational field, which may be produced by quantum mechanical zero-point fluctuations, interact with the wavepackets of massive particles. The result of this interaction is to produce decoherence within the wavepackets which could be accessible in experiments at the atomic scale. Using a simple model for the coherence properties of the gravitational field we derive an e…
With recent developments in high-precision quantum measurements, the question of whether observations of decoherence from spacetime fluctuations are accessible experimentally arises. Here we investigate the dynamics of bound states interacting with an environment of gravitons under the Markov approximation. The corresponding Lindblad master equation is presented that enables gravitational decoherence and dissipation due to zero-point spacetime fluctuations to be analyzed. Specifically, we consider a one-dimensional cavity of massless scalar particles that models a light beam with negligible sp…
Decoherence due to Spacetime Curvature
研究引力在量子退相干中的作用，推导了一般弯曲时空中复合系统的约化密度矩阵，用 Riemann 张量显式表达了退相干时间尺度，并证明自引力与外部曲率耦合无法用 $m \ o m + H_{\ m int}/c^2$ 替换描述。
It has been suggested in the literature that spatial coherence of the wave function can be dynamically suppressed by fluctuations in the spacetime geometry. These fluctuations represent the minimal uncertainty that is present when one probes spacetime geometry with a quantum probe. Two similar models have been proposed, one by Diósi [D-model] and one by Karolyhazy and collaborators [K-model], based on apparently unrelated minimal spacetime bounds. The two models arrive at somewhat different expressions for the dependence of the localization coherence length on the mass and size of the quantum …
Relativity and decoherence of spacetime superpositions
本文提出描述时空态量子叠加的框架，揭示仅相差坐标变换的叠加可改写为固定背景上的动力学，并据此澄清引力诱导纠缠与引力源退相干中的关键假设。
We investigate the effect of quantum metric fluctuations on qubits that are gravitationally coupled to a background spacetime. In our first example, we study the propagation of a qubit in flat spacetime whose metric is subject to flat quantum fluctuations with a Gaussian spectrum. We find that these fluctuations cause two changes in the state of the qubit: they lead to a phase drift, as well as the expected exponential suppression (decoherence) of the off-diagonal terms in the density matrix. Secondly, we calculate the decoherence of a qubit in a circular orbit around a Schwarzschild black hol…
Local Description of Decoherence of Quantum Superpositions by Black Holes and Other Bodies
本文提出黑洞导致量子叠加态退相干的局域描述方法，通过实验室内部量子场两点函数阐释退相干源于极低频霍金量子，并计算了不同真空和时空下的退相干差异及模拟黑洞退相干的物质体条件。
Quantum gravitational decoherence of a mechanical oscillator from spacetime fluctuations
本文研究时空涨落（源于变形对易关系或度规张量涨落）导致的机械振子动量基退相干，并用实验数据约束模型参数，同时为其他量子引力模型提供界限。
Amplification of genuine tripartite nonlocality and entanglement in the Schwarzschild spacetime under decoherence
该研究针对 Schwarzschild 黑洞背景下 Dirac 粒子的 GTN 与 GTE，证明局部滤波可在退相干中恢复并增强物理可访问 GTN/GTE，同时揭示不可访问 GTE 的产生与增强。
Decoherence from quantum spacetime noise: An open-systems framework with application to neutrino oscillations
本文提出一个开放量子系统框架，用于建模量子时空噪声引起的退相干，通过kappa-闵可夫斯基非交换几何分析，推导出退相干率与能量的四次方反比关系，并在中微子振荡中验证了该模型的适用性。
This paper describes how the entire universe might be considered an eigenstate determined by classical limiting conditions within it. This description is in the context of an approach in which the path of each relativistic particle in spacetime represents a fine-grained history for that particle, and a path integral represents a coarse-grained history as a superposition of paths meeting some criteria. Since spacetime paths are parametrized by an invariant parameter, not time, histories based on such paths do not evolve in time but are rather histories of all spacetime. Measurements can then be…
We discuss a mechanism of spin decoherence in gravitation within the framework of general relativity. The spin state of a particle moving in a gravitational field is shown to decohere due to the curvature of spacetime. As an example, we analyze a particle going around a static spherically-symmetric object.
We analyze the quantum fluctuations of vacuum stress tensors and spacetime curvatures, using the framework of linear response theory which connects these fluctuations to dissipation mechanisms arising when stress tensors and spacetime metric are coupled. Vacuum fluctuations of spacetime curvatures are shown to be a sum of two contributions at lowest orders; the first one corresponds to vacuum gravitational waves and is restricted to light-like wavevectors and vanishing Einstein curvature, while the second one arises from gravity of vacuum stress tensors. From these fluctuations, we deduce nois…
One of the biggest unsolved problems in physics is the unification of quantum mechanics and general relativity. The lack of experimental guidance has made the issue extremely evasive, though various attempts have been made to relate the loss of matter wave coherence to quantum spacetime fluctuations. We present a new approach to the gravitational decoherence near the Planck scale, made possible by recently discovered conformal structure of canonical gravity. This leads to a gravitational analogue of the Brownian motion whose correlation length is given by the Planck length up to a scaling fact…
Spacetime curvature of the Earth deforms wavepackets of photons sent from the Earth to satellites, thus influencing the quantum state of light. We show that Gaussian steering of photon pairs, which are initially prepared in a two-mode squeezed state, is affected by the curved spacetime background of the Earth. We demonstrate that quantum steerability of the state increases for a specific range of height $h$ and then gradually approaches a finite value with further increasing height of the satellite's orbit. Comparing with the peak frequency parameter, the Gaussian steering changes more for dif…
Decoherence of spin superposition state caused by a quantum electromagnetic field
本研究分析相对论量子电磁场中空间叠加的自旋-1/2中性粒子退相干，将其分为源于单轨迹关联的局域退相干与双轨迹关联的非局域退相干，分别对应相位和振幅阻尼，且热态下退相干随温度单调上升。
Nonperturbative Danielson-Satishchandran-Wald Decoherence with Unruh-DeWitt detectors
研究非微扰DSW退相干机制，利用Minkowski时空中的无隙有限时间探测器，在均匀加速路径的宇称叠加态中与质量标量场相互作用，分析退相干过程的主要因素。
Non-relativistic quantum theory of non-interacting particles in the spacetime containing a region with closed time-like curves (time-machine spacetime) is considered with the help of the path-integral technique. It is argued that, in certain conditions, a sort of superselection may exist for evolution of a particle in such a spacetime. All types of evolution are classified by the number $n$ defined as the number of times the particle returns back to its past. It corresponds also to the topological class of trajectories of the particle. The evolutions corresponding to different values of $n$ ar…
Decoherence and entropy generation at one loop in the inflationary de Sitter spacetime for Yukawa interaction
本文在暴胀 de Sitter 背景下研究 Yukawa 耦合的无质量标量–费米子开放量子系统，利用非平衡有效场论和单圈重整化 Kadanoff-Baym 方程计算标量场晚时 von Neumann 熵及参数依赖，揭示其退相干特征。
We write the curvature of spacetime in terms of the excitation probability of particle detectors ultra-rapidly coupled to a quantum field. More precisely, we provide an expansion for the excitation probability of a smeared UDW detector delta-coupled to a real scalar quantum field in a curved background. Using a short distance expansion for the Wightman function, we express the excitation probability of a detector as the transition probability in Minkowski spacetime plus correction terms written as a function of the curvature tensors and the detector size. Comparing the excitation probability i…
We study the decoherence and thermalization of an Unruh-DeWitt detector linearly coupled to the free massless scalar field in flat spacetime of arbitrary dimensions ($d\geq 2$). The initial state of the detector is chosen to be a pure state consisting of a linear superposition of ground and excited states, and we calculate the time evolution of reduced density matrix of the detector. Using perturbation method, we analytically derive the transition rate of the detector (the rate of change of the diagonal elements in the density matrix) and the decoherence rate (the rate of change of the off-dia…
Quantum fluctuations on curved spacetimes cause the emission of pairs of particles from the quantum vacuum, as in the Hawking effect from black holes. We use an optical analogue to gravity to investigate the influence of the curvature on quantum emission. Due to dispersion, the spacetime curvature varies with frequency here. We analytically calculate for all frequencies the particle flux, correlations and entanglement. We find that horizons increase the flux with a characteristic spectral shape. The photon number correlations transition from multi- to two-mode, with close to maximal entangleme…
The interplay between quantum fluctuation and spacetime curvature is shown to induce an additional quantum-curvature (QC) term in the energy-momentum tensor of fluid using the generalized framework of the stochastic variational method (SVM). The QC term is necessary to satisfy the momentum conservation but the corresponding quantum hydrodynamics is not necessarily cast into the form of the Schrödinger equation, differently from the case of the Euclidean spacetime. This seems to suggest that the existence of the Hilbert space is not a priori requirement in the quantization of curved spacetime s…
Quantum inequalities bound the extent to which weighted time averages of the renormalized energy density of a quantum field can be negative. They have mostly been proved in flat spacetime, but we need curved-spacetime inequalities to disprove the existence of exotic phenomena, such as closed timelike curves. In this work we derive such an inequality for a minimally-coupled scalar field on a geodesic in a spacetime with small curvature, working to first order in the Ricci tensor and its derivatives. Since only the Ricci tensor enters, there are no first-order corrections to the flat-space quant…
Quantum correlations and metrological advantage among Unruh-DeWitt detectors in de Sitter spacetime
针对吉本斯-霍金退相干热性质不明确的问题，研究德西特时空中自由下落UDW探测器的QFI与LQU鲁棒性，发现其最优值依赖真空扇区且随能隙增大而增加，QFI对退相干具韧性，为相对论量子计量学提供见解。
We discuss the possible role of isocurvature perturbations for the quantum decoherence of the curvature perturbation during inflation. We point out that if the inflaton trajectory in field space is curved, the adiabatic mode is generically coupled to the isocurvature mode and thus tracing out the latter can cause the curvature perturbation to decohere. We explicitly investigate this suggestion in a model of inflation with two decoupled massive fields and find that decoherence is effective for a wide range of mass ratios. In particular, we calculate the entanglement entropy for this model and s…
Entangled quantum clocks as operational probes of spacetime curvature
研究弯曲时空背景中沿类时测地线传播的两个非相对论量子粒子，通过与量子时钟耦合计算时间可观测量协方差，将协议重构成类似贝尔的实验，发现曲率可修正贝尔参数，表明纠缠量子时钟可探测时空曲率。
We provide a detailed analysis of the electronic properties of graphene-like materials with charge carriers living on a curved substrate, focusing in particular on constant negative-curvature spacetime. An explicit parametrization is also worked out in the remarkable case of Beltrami geometry, with an analytic solution for the pseudoparticles modes living on the curved bidimensional surface. We will then exploit the correspondent massless Dirac description, to determine how it affects the sample local density of states.
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