arXiv subjects

Kazuyuki Kuroyama

Publications and source records attributed to Kazuyuki Kuroyama.

8 recordsLinked to original sources

arXiv2026

Real-time dynamics of triplet-resonant tunneling driven by nonequilibrium phonons

Driven nonequilibrium systems can host emergent functionalities beyond equilibrium, but real-time access to excited-state dynamics remains limited. Here we report real-time measurements of phonon-driven charge and spin dynamics in excited states of a double quantum dot. Under phonon irradiation, resonant inter-dot tunneling emerges at triplet resonance. Time-resolved charge sensing reveals that the resonant inter-dot tunneling is strongly modified by spin blockade. For weaker inter-dot coupling, the nonequilibrium phonon environment generates a unidirectional transport cycle along the phonon density gradient.

cond-mat.mes-hall↗

arXiv2026

Ultrastrong light-matter coupling in near-field coupled split-ring resonators revealed by photocurrent spectroscopy

Landau polaritons arising from the coupling between cyclotron resonance and terahertz split-ring resonators (SRRs) have served as a central platform for exploring ultrastrong light-matter interaction for more than a decade. Over this period, a wide variety of SRR architectures, differing in size, geometry, and even material composition, have been investigated. However, the regime of near-field coupled SRRs has remained largely unexplored. Here, we demonstrate ultrastrong coupling using photocurrent spectroscopy in two prototypical near-field configurations: a SRR dimer and a topological SRR chain. The measurements reveal hybridization not only with bright resonant modes but also with optically dark modes and topological edge modes, highlighting the exceptional sensitivity of the photocurrent spectroscopy. Moreover, the engineered near-field interactions allow the study of multi-mode ultrastrong coupling and the interplay between topological band structure and cavity quantum electrodynamics.

cond-mat.mes-hall↗

arXiv2023

Phonon-mediated spin dynamics in a two-electron double quantum dot under a phonon temperature gradient

We have theoretically studied phonon-mediated spin-flip processes of electrons in a GaAs double quantum dot (DQD) holding two spins, under a phonon temperature gradient over the DQD. Transition rates of inter-dot phonon-assisted tunnel processes and intra-dot spin-flip processes involving spin triplet states are formalized by the electron-phonon interaction accompanied with the spin-orbit interaction. The calculations of the spin-flip rates and the occupation probabilities of the spin-states in the two-electron DQD with respect to the phonon temperature difference between the dots are quantitatively consistent with our previous experiment. This theoretical study on the temperature gradient effect onto spins in coupled QDs would be essential for understanding spin-related thermodynamic physics.

cond-mat.mes-hall↗

arXiv2023

Coherent interaction of a-few-electron quantum dot with a terahertz optical resonator

We have investigated light-matter hybrid excitations in a quantum dot (QD)-terahertz (THz) optical resonator coupled system. We fabricate a gate-defined QD in the vicinity of a THz split-ring resonator (SRR) by using a AlGaAs/GaAs two-dimensional electron system (2DES). By illuminating the system with THz radiation, the QD shows a current change whose spectrum exhibits coherent coupling between the electrons in the QD and the SRR as well as coupling between the 2DES and the SRR. The latter coupling enters the ultrastrong coupling regime and the coupling between the QD and the SRR is also very close to the ultrastrong coupling regime, despite the fact that only a few electrons reside in the QD.

cond-mat.mes-hall↗

arXiv2021

Real-time observation of charge-spin cooperative dynamics driven by a nonequilibrium phonon environment

Quantum dots are recognized as a suitable platform for studying thermodynamic phenomena involving single electronic charges and spins in nano-scale devices. However, such a thermodynamic system is usually driven by electron reservoirs at different temperatures, not by a lattice temperature gradient. We report on experimental observations of charge-spin cooperative dynamics in transitions of two-electron spin states in a GaAs double quantum dot located in a non-equilibrium phonon environment. Enhancements in the spin-flip processes are observed, originating from phonon excitation combined with the spin-orbit interaction. In addition, due to the spatial gradient of phonon density between the dots, the spin-flip rate during an inter-dot electron tunnel from a hot to a cold dot is more enhanced than in the other direction, resulting in accumulation of parallel spin states in the double dot.

cond-mat.mes-hall↗

arXiv2019

Full Counting Statistics of Spin-Flip/Conserving Charge Transitions in Pauli-Spin Blockade

We investigate the full counting statistics (FCS) of spin-conserving and spin-flip charge transitions in Pauli-spin blockade regime of a GaAs double quantum dot. A theoretical model is proposed to evaluate all spin-conserving and spin-flip tunnel rates, and to demonstrate the fundamental relation between FCS and waiting time distribution. We observe the remarkable features of parity effect and a tail structure in the constructed FCS, which do not appear in the Poisson distribution, and are originated from spin degeneracy and coexistence of slow and fast transitions, respectively. This study is potentially useful for elucidating the spin-related and other complex transition dynamics in quantum systems.

cond-mat.mes-hall↗

arXiv2018

Quantum state transfer of angular momentum via single electron photo-excitation from a Zeeman-resolved light hole

Electron spins in GaAs quantum dots have been used to make qubits with high-fidelity gating and long coherence time, necessary ingredients in solid-state quantum computing. The quantum dots can also host photon qubits with energy applicable for optical communication, and can show a promising photon-to-spin conversion. The coherent interface is established through photo-excitation of a single pair of an electron and a Zeeman-resolved light-hole, not heavy-hole. However, no experiments on the single photon to spin conversion have been performed yet. Here we report on single shot readout of a single electron spin generated in a GaAs quantum dot by spin-selective excitation with linearly polarized light. A photo-electron spin generated from a Zeeman-resolved light-hole exciton is detected using an optical spin blockade method in a single quantum dot and a Pauli spin blockade method in a double quantum dot. We found that the blockade probability strongly depends on the photon polarization and the hole state, heavy- or light-hole, indicating a transfer of the angular momentum from single photons to single electron spins. Our demonstration will open a pathway to further investigation on fundamental quantum physics such as quantum entanglement between a wide variety of quantum systems and applications of quantum networking technology.

cond-mat.mes-hall↗

arXiv2017

A single eletron-photon pair generation from a single polarization-entangled photon pair

We demonstrate paired generation of a single photo-electron in a quantum dot and a single photon from a single polarization-entangled photon pair that is generated by spontaneous parametric down conversion. The electron is reated in a GaAs quantum dot via inter-band resonantexcitation by irradiating one of the paired photons on the dot, while the remaining photon is detected by a single photon counter. Because the paired photons are generated simultaneously, the photo-electron and the remaining photon should be observed as a coincident event if the traveling distance is equivalent between them. The coincidence is probabilistic due to the probabilistic generation of the paired photon. We observe the probability of finding the photon with the photo-electron detection substantially higher then that without the photo-electron detection and derive the coincident rate comparable to the emission rate of the original photon pairs.

cond-mat.mes-hall↗