arXiv subjects

Naoki Watamura

Publications and source records attributed to Naoki Watamura.

5 recordsLinked to original sources

arXiv2022

AnaBHEL (Analog Black Hole Evaporation via Lasers) Experiment: Concept, Design, and Status

Accelerating relativistic mirror has long been recognized as a viable setting where the physics mimics that of black hole Hawking radiation. In 2017, Chen and Mourou proposed a novel method to realize such a system by traversing an ultra-intense laser through a plasma target with a decreasing density. An international AnaBHEL (Analog Black Hole Evaporation via Lasers) Collaboration has been formed with the objectives of observing the analog Hawking radiation and shedding light on the information loss paradox. To reach these goals, we plan to first verify the dynamics of the flying plasma mirror and to characterize the correspondence between the plasma density gradient and the trajectory of the accelerating plasma mirror. We will then attempt to detect the analog Hawking radiation photons and measure the entanglement between the Hawking photons and their "partner particles". In this paper, we describe our vision and strategy of AnaBHEL using the Apollon laser as a reference, and we report on the progress of our R&D of the key components in this experiment, including the supersonic gas jet with a graded density profile, and the superconducting nanowire single-photon Hawking detector. In parallel to these hardware efforts, we performed computer simulations to estimate the potential backgrounds, and derive analytic expressions for modifications to the blackbody spectrum of Hawking radiation for a perfectly reflecting, point mirror, due to the semit-ransparency and finite-size effects specific to flying plasma mirrors. Based on this more realistic radiation spectrum, we estimate the Hawking photon yield to guide the design of the AnaBHEL experiment, which appears to be achievable.

gr-qc↗

arXiv2020

Quantum Spacetime Instability and Breakdown of Semiclassical Gravity

The semiclassical gravity describes gravitational back-reactions of the classical spacetime interacting with quantum matter fields but the quantum effects on the background is formally defined as higher derivative curvatures. These induce catastrophic instabilities and classic solutions become unstable under small perturbations or their evolutions. In this paper we discuss validity of the semiclassical gravity from the perspective of the spacetime instabilities and consider cosmological dynamics of the Universe in this theory. We clearly show that the homogenous and isotropic flat Universe is unstable and the solutions either grow exponentially or oscillate even in Planckian time $t_{\rm I}=(α_{ 1 }G_N)^{1/2}\approx α_{ 1 }10^{-43}\ {\rm sec}$. The subsequent curvature evolution leads to Planck-scale spacetime curvature in a short time and causes a catastrophe of the Universe unless one takes extremely large values of the gravitational couplings. Furthermore, we confirm the above suggestion by comparing the semiclassical solutions and $Λ$CDM with the Planck data and it is found that the semiclassical solutions are not consistent with the cosmological observations. Thus, the standard semiclassical gravity using quantum energy momentum tensor $\left< { T }_{ μν} \right>$ is not appropriate to describe our Universe.

gr-qc↗

arXiv2019

Quantum Information Capsule and Information Delocalization by Entanglement in Multiple-qubit Systems

Where do entangled multiple-qubit systems store information? For information injected into a qubit, this question is nontrivial and interesting since the entanglement delocalizes the information. So far, a common picture is that of a qubit and its purification partner sharing the information quantum mechanically. Here, we introduce a new picture of a single qubit in the correlation space, referred to as quantum information capsule (QIC), confining the information perfectly. This picture is applicable for the entangled multiple-qubit system in an arbitrary state. Unlike the partner picture, in the QIC picture, by swapping the single-body state, leaving other subsystems untouched, the whole information can be retrieved out of the system. After the swapping process, no information remains in the system.

quant-ph↗

arXiv2017

Correspondence between Entanglement Growth and Probability Distribution of Quasi-Particles

We study the excess of (Renyi) entanglement entropy in various free field theories for the locally excited states defined by acting with local operators on the ground state. It is defined by subtracting the entropy for the ground state from the one for the excited state. Here the spacetime dimension is greater than or equal to 4. We find a correspondence between entanglement and a probability. The probability with which a quasi-particle exists in a subregion gives the excess of the entropy. We also propose a toy model which reproduces the excess in the replica method. In this model, a quasi-particle created by a local operator propagates freely and its probability distribution gives the excess.

hep-th↗

arXiv2016

Quantum Entanglement of Locally Excited States in Maxwell Theory

In 4 dimensional Maxwell gauge theory, we study the changes of (Renyi) entangle-ment entropy which are defined by subtracting the entropy for the ground state from the one for the locally excited states generated by acting with the gauge invariant local operators on the state. The changes for the operators which we consider in this paper reflect the electric-magnetic duality. The late-time value of changes can be interpreted in terms of electromagnetic quasi-particles. When the operator constructed of both electric and magnetic fields acts on the ground state, it shows that the operator acts on the late-time structure of quantum entanglement differently from free scalar fields.

hep-th↗