arXiv subjects

Miku Ishizaki

Publications and source records attributed to Miku Ishizaki.

4 recordsLinked to original sources

arXiv2026

Local Determinacy of Quantum Master Equations and a Mechanical Interpretation of the Multi-Mode Jaynes-Cummings and Central Spin Models

We propose a novel formulation of master equations for open systems wherein the evolution of a state is determined solely by its local behaviour at any point of time. Specifically, our formulation allows for a local interpretation of the workings of beyond-Markovian dynamics as opposed to the more common conception that non-Markovian state evolution is affected by its cumulative past history. Quite interestingly, local determinacy is found prevalent in quantum dynamics. We illustrate the advantages of our coordinate-free formulation with exact analyses on two physically relevant models.

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arXiv2026

Broadband AC Magnetic Field Sensing via Continuous wave optically detected magnetic resonance with NV Centers in diamond

The nitrogen-vacancy (NV) center in diamond has attracted considerable attention as a highly sensitive quantum sensor that can operate at room temperature. In particular, continuous-wave optically detected magnetic resonance (CW-ODMR) is promising for a wide range of applications because of its simplicity. However, conventional AC magnetic-field sensing schemes based on CW-ODMR suffer from a limited detection bandwidth: the detectable frequency is either fixed by intrinsic physical parameters of the NV center or, even when tunable, restricted to a narrow range of only a few MHz. Here, we propose a broadband AC magnetometry scheme based on CW-ODMR with NV centers using microwave-driven dressed states.Through theoretical analysis and numerical simulations, we show that the proposed scheme enables the detection of AC magnetic fields with frequencies up to the order of 100 MHz, which has been difficult to achieve using conventional CW-ODMR-based methods.

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arXiv2025

Identification of Phase Plate Properties Using Photonic Quantum Sensor Networks

Quantum sensor networks (QSNs) have been widely studied for their potential of precise measurements. While most QSN research has focused on estimating continuous variables, recent studies have explored discrete-variable estimation. Here, we propose a method for high-precision identification of phase plate properties using a photon-based QSN, which is categorized as discrete-variable estimation. We consider an interaction of a single photon with $N$ phase plates. There are some distinct properties of the phase plates, and we aim to identify such properties. Specifically, we investigate two cases: (i) distinguishing between phase plates that impart uniformly random phases in the range $[0, 2π]$ and those that impart the same phase, and (ii) distinguishing between phase plates that impart uniformly random phases in $[0, 2π]$ and those that impart phases within a narrower range $[- δ, δ]$ ($0< δ\ll 1$). For this distinction, we consider two approaches: one in which a single photon is prepared in a nonlocal state before interacting with the phase plates, and the other in which the single photon remains in a local state. Our results demonstrate that the nonlocal state enables more precise identification when $N$ is large.

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arXiv2022

Switching the function of the quantum Otto cycle in non-Markovian dynamics: heat engine, heater and heat pump

Quantum thermodynamics explores novel thermodynamic phenomena that emerge when interactions between macroscopic systems and microscopic quantum ones go into action. Among various issues, quantum heat engines, in particular, have attracted much attention as a critical step in theoretical formulation of quantum thermodynamics and investigation of efficient use of heat by means of quantum resources. In the present paper, we focus on heat absorption and emission processes as well as work extraction processes of a quantum Otto cycle. We describe the former as non-Markovian dynamics, and thereby find that the interaction energy between a macroscopic heat bath and a microscopic qubit is not negligible. Specifically, we reveal that the interaction energy is divided into the system and the bath in a region of the short interaction time and remains negative in the region of the long interaction time. In addition, a counterintuitive energy flow from the system and the interaction energy to the hot bath occurs in another region of the short interaction time. We quantify these effects by defining an index of non-Markovianity in terms of the interaction energy. With this behavior of the interaction energy, we show that a non-Markovian quantum Otto cycle can switch functions such as an engine as well as a heater or a heat pump by controlling the interaction time with the heat bath. In particular, the qubit itself loses its energy if we shorten the interaction time, and in this sense, the qubit is cooled through the cycle. This property has a possibility of being utilized for cooling the qubits in quantum computing. We also describe the work extraction from the microscopic system to a macroscopic system like us humans as an indirect measurement process by introducing a work storage as a new reservoir.

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