arXiv subjects

Kaito Kashiwagi

Publications and source records attributed to Kaito Kashiwagi.

3 recordsLinked to original sources

arXiv2026

Gravitational effects on a dissipative two-level atom in the weak-field regime

We investigate the dissipative dynamics of a two-level atom in a weak gravitational field. Using the Feynman--Vernon influence functional formalism, we derive a quantum master equation describing the two-level atom interacting with a scalar field in a Newtonian gravitational field, and compute the energy dissipation rate of the atom. We find that the spontaneous emission rate (the dissipation rate in vacuum) is modified by the gravitational field. Specifically, this modification depends on the atom's dipole, the position of the atom relative to the source of the gravitational field, and the frequency of the scalar radiation emitted by the atom. Furthermore, we identify the parameter regimes in which the spontaneous emission rate is enhanced or suppressed by gravity. We also discuss how the modification arises from time dilation and dipole radiation in a weak gravitational field. These findings provide a theoretical basis for exploring gravitational effects in open quantum systems.

quant-ph↗

arXiv2024

Effective description of open quantum dynamics in relativistic scattering

The open dynamics of quantum particles in relativistic scattering is investigated. In particular, we consider the scattering process of quantum particles coupled to an environment initially in a vacuum state. Tracing out the environment and using the unitarity of S-operator, we find the Gorini-Kossakowski-Sudarshan-Lindblad (GKSL) generator describing the evolution of the particles. The GKSL generator is exemplified by focusing on the concrete processes: one is the decay of scalar particle ($ϕ\rightarrow χχ$), and the others are the pair annihilation and the $2\rightarrow 2$ scattering of scalar particles ($ϕϕ\rightarrow χχ$ and $ϕϕ\rightarrow ϕϕ$). The GKSL generator for $ϕ\rightarrow χχ$ has a parameter with the coupling between $ϕ$ and $χ$ and the mass of both fields. The GKSL generator associated with $ϕϕ\rightarrow χχ$ is characterized by a Lorentz-invariant function of initial momenta. Especially, in the pair annihilation process, we show that the probability of pair annihilation varies depending on the superposition state of incident scalar $ϕ$ particles. Furthermore, we observe that the GKSL generators derived in this paper have Poincaré symmetry. This means that the description by the GKSL generator with Poincaré symmetry is effective for the asymptotic behavior of open quantum dynamics in the long-term processes of interest.

quant-ph↗

arXiv2023

Markovian quantum master equation with Poincaré symmetry

We investigate what kind of Markovian quantum master equation (QME) in the Gorini-Kossakowski-Sudarshan-Lindblad (GKSL) form is realized under Poincaré symmetry. The solution of the Markovian QME is given by a quantum dynamical semigroup, for which we introduce invariance under Poincaré transformations. Using the invariance of the dynamical semigroup and applying the unitary representation of Poincaré group, we derive the Markovian QME for a relativistic massive spin-0 particle. Introducing the field operator of the massive particle and examining its evolution, we find that the field follows a dissipative Klein-Gordon equation. In addition, we show that any two local operators for spacelike separated regions commute with each other. This means that the microcausality condition is satisfied for the dissipative model of the massive particle.

quant-ph↗