担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review D  

We investigate entanglement of local spatial modes defined by a quantum field in a de Sitter universe. The introduced modes show disentanglement behavior when the separation between two regions where local modes are assigned becomes larger than the cosmological horizon. To understand the emergence of separability between these local modes, we apply the monogamy inequality proposed by S. Camalet. We embed the focusing bipartite mode defined by the quantum field in a pure four-mode Gaussian state, and identify its partner modes. Then applying a Gaussian version of the monogamy relation, we show that the external entanglement between the bipartite mode and its partner modes constrains the entanglement of the bipartite mode. Thus the emergence of separability of local modes in the de Sitter universe can be understood from the perspective of entanglement monogamy.

DOI： 10.1103/PhysRevD.108.045002

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review D  

We investigate particle creation and entanglement structure in a dispersive model with subluminal dispersion relation. Assuming the step function spatial velocity profile of the background flow, mode functions for a massless scalar field are exactly obtained by the matching method. Power spectrums of created particles are calculated for the subsonic and the trans-sonic flow cases. For the trans-sonic case, the sonic horizon exists, and created particles show the Planckian distribution for the low frequency region, but the thermal property disappears for the high frequency region near the cutoff frequency introduced by the nonlinear dispersion. For the subsonic case, although the sonic horizon does not exist, the effective group velocity horizon appears due to the nonlinear dispersion for the high frequency region, and an approximate thermal property of the power spectrum arises. The relation between particle creation and entanglement between each mode is also discussed.

DOI： 10.1103/PhysRevD.107.105005

Web of Science

Scopus

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

CiNii Research

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review D  

This study investigates the quantumness of gravity under the setup of the atomic interferometry from the viewpoint of mass-energy equivalence. We evaluated interference visibility considering a particle with internal energy levels in a harmonic trapping potential. As per the result, for a spatially superposed gravitational source mass, interference visibility exhibits collapse and revival behavior, which implies that an initial separable internal state evolves to the entangled state with respect to the degrees of freedom of the center of mass, the internal energy levels, and the external source state. In particular, it does not exhibit revival behavior when gravity is treated as a quantum interaction, while it revives with a finite period for a semiclassical treatment of gravity. We also examined the temporal behavior of entanglement negativity and found that the nonrevival behavior of visibility reflects the creation of the entanglement between the internal energy state and the external source state which is uniquely induced by the quantum interaction of gravity in accordance with the weak equivalence principle.

DOI： 10.1103/PhysRevD.106.126005

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Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Entropy  

Entanglement entropy (EE) is a quantitative measure of the effective degrees of freedom and the correlation between the sub-systems of a physical system. Using the replica trick, we can obtain the EE by evaluating the entanglement Renyi entropy (ERE). The ERE is a q-analogue of the EE and expressed by the q replicated partition function. In the semi-classical approximation, it is apparently easy to calculate the EE because the classical action represents the partition function by the saddle point approximation and we do not need to perform the path integral for the evaluation of the partition function. In previous studies, it has been assumed that only the minimal-valued saddle point contributes to the EE. In this paper, we propose that all the saddle points contribute comparably but not necessarily equally to the EE by dealing carefully with the semi-classical limit and then the (Formula presented.) limit. For example, we numerically evaluate the ERE of two disjoint intervals for the large c Liouville field theory with (Formula presented.). We exploit the BPZ equation with the four twist operators, whose solution is given by the Heun function. We determine the ERE by tuning the behavior of the Heun function such that it becomes consistent with the geometry of the replica manifold. We find the same two saddle points as previous studies for (Formula presented.) in the above system. Then, we provide the ERE for the large but finite c and the (Formula presented.) in case that all the saddle points contribute comparably to the ERE. In particular, the ERE is the summation of these two saddle points by the same weight, due to the symmetry of the system. Based on this work, it shall be of interest to reconsider EE in other semi-classical physical systems with multiple saddle points.

DOI： 10.3390/e24121758

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review D  

We consider conceptual issues of deep learning (DL) for metric detectors using test particle geodesics in curved spacetimes. Advantages of DL metric detectors are emphasized from a viewpoint of general coordinate transformations. Two given metrics (two spacetimes) are defined to be connected by a DL isometry if their geodesic image data cannot be discriminated by any DL metric detector at any time. The fundamental question of when the DL isometry appears is extensively explored. If the two spacetimes connected by the DL isometry are in superposition of quantum gravity theory, the postmeasurement state may be still in the same superposition even after DL metric detectors observe the superposed state. We also demonstrate metric-detection DL methods in 2dimensional anti-de Sitter (AdS) spacetimes to estimate the cosmological constants and Brown-Henneaux charges. In the AdS/CFT correspondence dictionary, it may be expected that such metric detectors in the AdS bulk region correspond to quantum measurement devices in the conformal field theory at the AdS boundary. +ACY-copy+ADs- 2022 American Physical Society.

DOI： 10.1103/PhysRevD.106.044051

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Scopus

記述言語：日本語   出版者・発行元：Physical Review A  

In this study, we determine a violation of the Leggett-Garg inequalities due to gravitational interaction in a hybrid system consisting of a harmonic oscillator and a spatially localized superposed particle. The violation of the Leggett-Garg inequalities is discussed using the two-time quasiprobability in connection with the entanglement negativity generated by gravitational interaction. It is demonstrated that the entanglement suppresses the violation of the Leggett-Garg inequalities when one of the two times of the quasiprobability t1 is chosen as the initial time. Further, it is shown that the Leggett-Garg inequalities are generally violated due to gravitational interaction by properly choosing the configuration of the parameters, including t1 and t2, which are the times of the two-time quasiprobability. The feasibility of detecting violations of the Leggett-Garg inequalities in hybrid systems is also discussed.

DOI： 10.1103/PhysRevA.106.012214

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Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review D  

Expanding edge experiments are promising to open new physics windows of quantum Hall systems. In a static edge, the edge excitation, which is described by free fields decoupled with the bulk dynamics, is gapless, and the dynamics preserve conformal symmetry. When the edge expands, such properties need not be preserved. We formulate a quantum field theory in 1+1-dimensional curved spacetimes to analyze the edge dynamics. We propose methods to address the following questions using edge waveforms from the expanding region: Does the conformal symmetry survive? Is the nonlinear interaction of the edge excitations induced by edge expansion? Do the edge excitations interact with the bulk excitations? We additionally show that the expanding edges can be regarded as expanding universe simulators of two-dimensional dilaton-gravity models, including the Jackiw-Teitelboim gravity model. As an application, we point out that our theoretical setup might simulate emission of analog Hawking radiation with the Gibbons-Hawking temperature from the future de Sitter horizon formed in the expanding-edge region.

DOI： 10.1103/PhysRevD.105.105009

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Scopus

arXiv

その他リンク： http://arxiv.org/pdf/2202.03731v2

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review D  

Herein, we explore superradiance for Alfvén waves (Alfvénic superradiance) in an axisymmetric rotating magnetosphere of a Kerr black hole within the force-free approximation. On the equatorial plane of the Kerr spacetime, the Alfvén wave equation is reduced to a one-dimensional Schrödinger-type equation by separating variables of the wave function and introducing a tortoise coordinate mapping the inner and outer light surfaces to -∞ and +∞, respectively, and we investigate a wave scattering problem for Alfvén waves. An analysis of the asymptotic solutions of the wave equation and conservation of the Wronskian provides the superradiant condition for Alfvén waves, and it is shown that the condition coincides with that for the Blandford-Znajek process. This indicates that when Alfvénic superradiance occurs, the Blandford-Znajek process also occurs in the force-free magnetosphere. Then, we evaluate the reflection rate of Alfvén waves numerically and confirm that Alfvénic superradiance is indeed possible in the Kerr spacetime. Moreover, we will discuss a resonant scattering of Alfvén waves, which is related to a "quasinormal mode"of the magnetosphere.

DOI： 10.1103/PhysRevD.105.064018

Scopus

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review D  

We investigate the wave optical imaging of black holes with Hawking radiation. The spatial correlation function of Hawking radiation is expressed in terms of transmission and reflection coefficients for scalar wave modes and evaluated by numerically summing over angular quantum numbers for the Unruh-Hawking state of the Kerr-de Sitter black hole. Then, wave optical images of an evaporating black hole are obtained by the Fourier transformation of the spatial correlation function. For a short wavelength, the image of the black hole with the outgoing mode of the Unruh-Hawking state has the appearance of a star with its surface given by the photon sphere. It is found that interference between incoming modes from the cosmological horizon and reflected modes due to the scattering of the black hole can enhance brightness of images in the vicinity of the photon sphere. For a long wavelength, the entire field of view is bright, and the emission region of Hawking radiation cannot be identified.

DOI： 10.1103/PhysRevD.105.045022

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Scopus

担当区分：責任著者   記述言語：英語   出版者・発行元：Universe  

We investigate the emergent time scenario in quantum cosmology based on the Page– Wotters approach. Using a quantum cosmological model with a qubit clock, it is demonstrated how the entanglement between the qubit clock and the geometry derives emergence of a time parameter, which defines evolution of the timeless quantum state of the universe. We show that the universe wave function conditioned by a qubit clock obeys the standard Schrödinger equation and the Fisher information for the clock state, which quantifies entanglement between the universe and the clock, and contributes as a negative energy density.

DOI： 10.3390/universe8020099

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Scopus

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevD.101.023003

Web of Science

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevD.100.064037

Web of Science

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevD.98.025004

Web of Science

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevLett.120.181301

Web of Science

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3390/e19090449

Web of Science

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：日本語   出版者・発行元：Astrophysical Journal  

We performed one-dimensional force-free magnetodynamic numerical simulations of the propagation of Alfvén waves along magnetic field lines around a spinning black-hole-like object, the Banados-Teitelboim-Zanelli black string, to investigate the dynamic process of wave propagation and energy transport with Alfvén waves. We considered an axisymmetric and stationary magnetosphere and perturbed the background magnetosphere to obtain the linear wave equation for the Alfvén wave mode. The numerical results show that the energy of Alfvén waves monotonically increases as the waves propagate outwardly along the rotating curved magnetic field line around the ergosphere, where energy seems not to be conserved, in the case of energy extraction from the black string by the Blandford-Znajek mechanism. The apparent breakdown of energy conservation suggests the existence of a wave induced by the Alfvén wave. Considering the additional fast magnetosonic wave induced by the Alfvén wave, the energy conservation is confirmed. Similar relativistic phenomena, such as the amplification of Alfvén waves and induction of fast magnetosonic waves, are expected around a spinning black hole.

DOI： 10.3847/1538-4357/ac47f8

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Scopus

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1103/PhysRevD.103.125007 I.

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3390/e22111297

Web of Science

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3390/universe6020033

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3390/universe5020066

Web of Science

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.74.2.0_367

CiNii Research

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1361-6382/aaeb5a

Web of Science

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3390/universe4060071

Web of Science

出版者・発行元：Proceedings of the 28th Workshop on General Relativity and Gravitation in Japan, JGRG 2018  

Scopus

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.73.1.0_446

CiNii Research

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1361-6382/aa8e31

Web of Science

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3390/universe3040071

Web of Science

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevD.95.104055

Web of Science

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1007/s10714-017-2185-z

Web of Science

DOI： 10.1088/1742-6596/880/1/012025

Web of Science

出版者・発行元：Proceedings of the 27th Workshop on General Relativity and Gravitation in Japan, JGRG 2017  

Scopus

担当区分：筆頭著者   記述言語：日本語  

担当区分：筆頭著者   記述言語：日本語  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

開催年月日： 2022年1月

記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

開催年月日： 2021年5月

記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

開催年月日： 2021年3月

記述言語：日本語   会議種別：口頭発表（招待・特別）  

開催地：名古屋大学  

開催年月日： 2020年10月

記述言語：日本語  

開催地：九州大学理学部  

開催年月日： 2018年6月

記述言語：日本語   会議種別：口頭発表（招待・特別）  

開催地：広島国際会議場  

開催年月日： 2018年2月

記述言語：日本語   会議種別：口頭発表（招待・特別）  

開催地：KEK  

開催年月日： 2018年1月

記述言語：英語   会議種別：口頭発表（基調）  

開催年月日： 2017年9月

記述言語：日本語   会議種別：口頭発表（基調）  

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：琵琶湖クラブ  

記述言語：英語   会議種別：口頭発表（基調）  

開催地：台南成功大学