| Kazuhiro Yamamoto | Last modified date：2024.04.20 |
Graduate School
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Homepage
https://kyushu-u.elsevierpure.com/en/persons/kazuhiro-yamamoto-2
Reseacher Profiling Tool Kyushu University Pure
https://yamamoto445.wixsite.com/my-site
Academic Degree
Ph.D Hiroshima University
Country of degree conferring institution (Overseas)
No
Field of Specialization
Astrophysics, Cosmology, quantum field theory on curved spacetime, quantumness of gravity
ORCID(Open Researcher and Contributor ID)
https://orcid.org/0000-0002-2976-2741
Total Priod of education and research career in the foreign country
01years02months
Outline Activities
I provide education for undergraduate and graduate students focusing on physics majors, electromagnetism II, quantum mechanics I, general relativity, and cosmology. I am working on the research and education on gravity and cosmology that applies quantum science, and educational support for doctoral students as an executive committee member of the leading human resource development fellowship (quantum science area).
Research
Research Interests
Membership in Academic Society
- Theoretical studies on testing quantum nature of gravity
keyword : quantum gravity, quantum mechanics, quantum entanglement, Unruh effect
2019.04～2022.03. - Origin of accelerating Universe
keyword : Cosmology, Observational cosmology, Inflationary universe, large scale structure of the Universe, tests of gravitational theory and dark energy, quantum field theory on curved spacetime, quantum information and gravity・cosmology
2019.04～2022.03.
Papers
| 1. | Daisuke Miki, Akira Matsumura, Kazuhiro Yamamoto, Entanglement and decoherence of massive particles due to gravity, PHYSICAL REVIEW D, 10.1103/PhysRevD.103.026017, 103, 2, 2021.01, [URL], We analyze the dynamics of a gravity-induced entanglement for N massive particles. Considering the linear configuration of these particles, we investigate the entanglement between a specific pair of particles under the influence of the gravitational interaction between the massive particles. As the particle number increases, the specific particle pair decoheres more easily due to the gravitational interaction with other particles. The timescale of the gravity-induced decoherence is analytically determined. We also discuss the entanglement dynamics of initially entangled particles, which exemplify the monogamy of the gravity-induced entanglement.. |
| 2. | Akira Matsumura, Kazuhiro Yamamoto, Gravity-induced entanglement in optomechanical systems, PHYSICAL REVIEW D, 10.1103/PhysRevD.102.106021, 102, 10, 2020.11, [URL], We investigate the phenomenon of gravity-induced entanglement in optomechanical systems. Assuming photon number conservation and the Newtonian potential expanded up to the quadratic order of the oscillator positions, we exactly solve the dynamics of the optomehcanical systems. Then, we find that the phase difference due to the Newtonian gravity leads to the large entanglement of photons in separated cavities. We clarify the generating mechanism of large gravity-induced entanglements in optomechanical systems in an exact manner. We also determine the characteristic time to generate the maximal entanglement of photons. Finally, by comparing the characteristic time with the decoherence time due to photon leakage, we evaluate the range of the dissipation rate required for testing the gravity-induced entanglement.. |
| 3. | Fluctuation-dissipation and correlation-propagation relations in (1 + 3)D moving detector-quantum field systems The fluctuation-dissipation relations (FDR) are powerful relations which can capture the essence of the interplay between a system and its environment. Challenging problems of this nature which FDRs aid in our understanding include the backreaction of quantum field processes like particle creation on the spacetime dynamics in early universe cosmology or quantum black holes. The less familiar, yet equally important correlation-propagation relations (CPR) relate the correlations of stochastic forces on different detectors to the retarded and advanced parts of the radiation propagated in the field. Here, we analyze a system of N uniformly-accelerated Unruh-DeWitt detectors whose internal degrees of freedom (idf) are minimally coupled to a real, massless, scalar field in 4D Minkowski space, extending prior work in 2D with derivative coupling. Using the influence functional formalism, we derive the stochastic equations describing the nonequilibrium dynamics of the idfs. We show after the detector-field dynamics has reached equilibration the existence of the FDR and the CPR for the detectors, which combine to form a generalized fluctuation-dissipation matrix relation. We show explicitly the energy flows between the constituents of the system of detectors and between the system and the quantum field environment. This power balance anchors the generalized FDR. We anticipate this matrix relation to provide a useful guardrail in expounding some basic issues in relativistic quantum information, such as ensuring the self-consistency of the energy balance and tracking the quantum information transfer in the detector-field system.. |
| 4. | Vacuum state in de Sitter spacetime with static charts We study the free massive scalar field in de Sitter spacetime with static charts. In particular, we find positive-frequency modes for the Bunch-Davies vacuum state natural to the static charts as superpositions of the well-known positive-frequency modes in the conformally-flat chart. We discuss in detail how these modes are defined globally in the two static charts and the region in their future. The global structure of these solutions leads to the well-known description of the Bunch-Davies vacuum state as an entangled state. Our results are expected to be useful not only for studying the thermal properties in the vacuum fluctuations in de Sitter spacetime but also for understanding the nonlocal properties of the vacuum state.. |
| 5. | Large Angle CMB Anisotropy in an Open Universe in the One-Bubble inflationary Scenario We consider an alternative scenario of inflation which can account for a spatially open universe. It is similar to the old inflation in which the bubble nucleation occurs in the sea of the false vacuum, but it differs from the old inflation in that the second slow rollover inflation occurs inside a nucleated bubble. Hence, our observable universe is entirely contained in one nucleated bubble. The significance of the scenario is that apart from a variance caused by model parameters, it gives us a definite prediction on the spectrum of the primordial density perturbations, and hence it is observationally testable. Here we investigate the spectrum of cosmic microwave background anisotropies on large angular scales. We find that the contribution from peculiar modes which never appear in the usual harmonic analysis is significant in the case Ω0 ≲ 0.1.. |
- International society of relativistic quantum information
- The Physical Society of Japan
- The Astronomical Society of Japan
Educational
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