arXiv subjects

Naotomo Takemura

Publications and source records attributed to Naotomo Takemura.

8 recordsLinked to original sources

arXiv2022

Probing the Ginzburg-Landau Potential for Lasers Using Higher-order Photon Correlations

Lasing transition is known to be analogous to the second-order phase transition. Furthermore, for some cases, it is possible to define the Ginzburg-Landau (GL) potential, and the GL theory predicts the photon statistical properties of lasers. However, the GL potential for lasers is surprising, because lasers are operating far from equilibrium. In this paper, we theoretically examine the validity of the GL theory for lasers in terms of various parameters, particularly, the ratio between photon and carrier lifetimes. For this purpose, we use stochastic rate equations and higher-order photon correlation functions. With higher-order photon correlation measurements, we can check whether or not laser dynamics are described by the GL theory. We demonstrate that, for low-$β$ lasers, the GL theory is applicable even when the photon lifetime is comparable to the carrier lifetime and that photon-carrier relaxation oscillation is the fundamental origin of the breakdown of the GL theory, which can be understood in the framework of center manifold reduction.

cond-mat.mes-hall↗

arXiv2021

Emulating the local Kuramoto model with an injection-locked photonic crystal laser array

The Kuramoto model is a mathematical model for describing the collective synchronization phenomena of coupled oscillators. We theoretically demonstrate that an array of coupled photonic crystal lasers emulates the Kuramoto model with non-delayed nearest-neighbor coupling (the local Kuramoto model). Our novel strategy employs indirect coupling between lasers via additional cold cavities. By installing cold cavities between laser cavities, we avoid the strong coupling of lasers and realize ideal mutual injection-locking with effective non-delayed dissipative coupling. First, after discussing the limit cycle interpretation of laser oscillation, we demonstrate the synchronization of two indirectly coupled lasers by numerically simulating coupled-mode equations. Second, by performing a phase reduction analysis, we show that laser dynamics in the proposed device can be mapped to the local Kuramoto model. Finally, we briefly demonstrate that a chain of indirectly coupled photonic crystal lasers actually emulates the one-dimensional local Kuramoto chain. We also argue that our proposed structure, which consists of periodically aligned cold cavities and laser cavities, will best be realized by using state-of-the-art buried multiple quantum well photonic crystals.

physics.optics↗

arXiv2021

Low- and high-$β$ lasers in Class-A limit: photon statistics, linewidth, and the laser-phase transition analogy

Nanocavity lasers are commonly characterized by the spontaneous coupling coefficient $β$ that represents the fraction of photons emitted into the lasing mode. While $β$ is conventionally discussed in semiconductor lasers where the photon lifetime is much shorter than the carrier lifetime (class-B lasers), little is known about $β$ in atomic lasers where the photon lifetime is much longer than the other lifetimes and only the photon degree of freedom exists (class-A lasers). We investigate the impact of the spontaneous coupling coefficient $β$ on lasing properties in the class-A limit by extending the well-known Scully-Lamb master equation. We demonstrate that, in the class-A limit, all the photon statistics are uniquely characterized by $β$ and that the laser phase transition-like analogy becomes transparent. In fact, $β$ perfectly represents the "system size" in phase transition. Finally, we investigate the laser-phase transition analogy from the standpoint of a quantum dissipative system. Calculating a Liouvillian gap, we clarify the relation between $β$ and the continuous phase symmetry breaking.

cond-mat.mes-hall↗

arXiv2020

Designs toward synchronization of optical limit cycles with coupled silicon photonic crystal microcavities

A driven high-Q Si microcavity is known to exhibit limit cycle oscillation originating from carrier-induced and thermo-optic nonlinearities. We propose a novel nanophotonic device to realize synchronized optical limit cycle oscillations with coupled silicon (Si) photonic crystal (PhC) microcavities. Here, coupled limit cycle oscillators are realized by using coherently coupled Si PhC microcavities. By simulating coupled-mode equations, we theoretically demonstrate mutual synchronization (entrainment) of two limit cycles induced by coherent coupling. Furthermore, we interpret the numerically simulated synchronization in the framework of phase description. Since our proposed design is perfectly compatible with current silicon photonics fabrication processes, the synchronization of optical limit cycle oscillations will be implemented in future silicon photonic circuits.

physics.optics↗

arXiv2017

Giant paramagnetism induced valley polarization of electrons in charge-tunable monolayer MoSe2

For applications exploiting the valley pseudospin degree of freedom in transition metal dichalcogenide monolayers, efficient preparation of electrons or holes in a single valley is essential. Here, we show that a magnetic field of 7 Tesla leads to a near-complete valley polarization of electrons in MoSe2 monolayer with a density 1.6x10^{12} cm^{-2}; in the absence of exchange interactions favoring single-valley occupancy, a similar degree of valley polarization would have required a pseudospin g-factor exceeding 40. To investigate the magnetic response, we use polarization resolved photoluminescence as well as resonant reflection measurements. In the latter, we observe gate voltage dependent transfer of oscillator strength from the exciton to the attractive-Fermi-polaron: stark differences in the spectrum of the two light helicities provide a confirmation of valley polarization. Our findings suggest an interaction induced giant paramagnetic response of MoSe2, which paves the way for valleytronics applications.

cond-mat.mes-hall↗

arXiv2015

Dephasing effects on coherent exciton-polaritons and the breaking of the strong coupling regime

Using femtosecond pump-probe spectroscopy, we identify excitation induced dephasing as a major mechanism responsible for the breaking of the strong-coupling between excitons and photons in a semiconductor microcavity. The effects of dephasing are observed on the transmitted probe pulse spectrum as a density dependent broadening of the exciton-polariton resonances and the emergence of a third resonance at high excitation density. A striking asymmetry in the energy shift between the upper and the lower polaritons is also evidenced. Using the excitonic Bloch equations, we quantify the respective contributions to the energy shift of many-body effects associated with Fermion exchange and photon assisted exchange processes and the contribution to collisional broadening.

cond-mat.mes-hall↗

arXiv2014

Polaritonic Feshbach Resonance

A Feshbach resonance occurs when the energy of two interacting free particles comes to resonance with a molecular bound state. When approaching this resonance, dramatic changes in the interaction strength between the particles occur. Feshbach resonances have been an essential tool to control the atom interactions, which can even be switched from repulsive to attractive [1-4]. Thanks to Feshbach resonances many effects in ultracold atomic gases could be explored [5, 6]. Here we demonstrate a Feshbach resonance based on polariton spinor interactions that characterize the fundamental interaction process in polariton quantum systems. We show the clear enhancement of attractive interactions and the prompt change to repulsive interaction by tuning the energy of two polaritons with anti-parallel spins across the biexciton bound state energy. A mean field two-channel model quantitatively reproduces the experimental results. This observation paves the way for a new tool to tune the polariton interactions and to move forward into quantum correlated polariton physics.

cond-mat.mes-hall↗

arXiv2014

Heterodyne Spectroscopy of Polariton Spinor Interactions

We report on spinor polariton interactions in GaAs based microcavities. This investigation is carried out by means of heterodyne polarized pump-probe spectroscopy. We show the dependence of the energy renormalization of the lower and upper polariton resonances with cavity detuning for different polariton densities. We use the exciton-photon based Gross-Pitaevskii equation to model the experiment for both lower and upper polariton modes. The theoretical results reproduce qualitatively the experimental observations revealing the magnitude and the sign of the parallel and anti-parallel spin interaction strength. We evidence the strong influence of the biexciton resonance on the anti-parallel spin polariton energy shift and provide the exciton-biexciton coupling constant. We derive our results in the lower polariton basis using Gross-Pitaevskii equation from which, we express analytically the spinor polariton interactions and identify the clear role of the biexciton resonance.

cond-mat.mes-hall↗