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arXiv:2301.01418 · Physical review. B./Physical review. B

Magnetic light amplification by stimulated emission of radiation in subwavelength systems of a dielectric cavity and magnetic quantum emitters

Zhong‐Jian Yang, Xiao-Jing Du, Ma-Long Hu, Jun He

Published May 22, 2023• 5 citations
arXivHTMLPDF

Abstract

We propose a magnetic laser in a subwavelength system consisting of a high-refractive-index dielectric cavity and an active medium formed by magnetic quantum emitters. Stimulated emissions of magnetic quantum emitters induced by their coherent interactions with quantized magnetic fields of a cavity are theoretically considered. The condition to achieve such a magnetic laser is obtained. Numerical results show that magnetic lasers are feasible in some realistic systems, for example, a silicon disk of high-quality whispering gallery modes with embedded emitters. Furthermore, the competitions between the electric interaction and magnetic one in terms of their Purcell factors are also considered in some magnetic laser achievable systems. In a wavelength-scale silicon block of a high-order magnetic mode, the ratio of magnetic Purcell factor to the electric one can reach more than $\ensuremath{\sim}{10}^{3}$ large. Our results open up ways to enhanced magnetic light-matter interactions.

DOI
10.1103/physrevb.107.195140

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We propose a magnetic laser in a subwavelength system consisting of a high-refractive-index dielectric cavity and an active medium formed by magnetic quantum emitters. Stimulated emissions of magnetic quantum emitters induced by their coherent interactions with quantized magnetic fields of a cavity are theoretically considered. The condition to achieve such a magnetic laser is obtained. Numerical results show that magnetic lasers are feasible in some realistic systems, for example, a silicon disk of high-quality whispering gallery modes with embedded emitters. Furthermore, the competitions between the electric interaction and magnetic one in terms of their Purcell factors are also considered in some magnetic laser achievable systems. In a wavelength-scale silicon block of a high-order magnetic mode, the ratio of magnetic Purcell factor to the electric one can reach more than \ensuremath∼103\ensuremath{\sim}{10}^{3}\ensuremath∼103 large. Our results open up ways to enhanced magnetic light-matter interactions.
We investigate theoretically the light amplification by stimulated emission of radiation (laser) in the ultrastrong light-matter interaction regime under the two-level and single-mode approximations. The conventional picture of the laser is broken under the ultrastrong interaction. Instead, we must explicitly discuss the dynamics of the electric field and of the magnetic one distinctively, which make the ``laser'' qualitatively different from the conventional laser. We found that the laser generally accompanies odd-order harmonics of the electromagnetic fields both inside and outside the cavity and a synchronization with an oscillation of atomic population. A bistability is also demonstrated. However, since our model is quite simplified, we got quantitatively different results from the Hamiltonians in the velocity and length forms of the light-matter interaction, while the appearance of the multiple harmonics and the bistability is qualitatively reliable.
Abstract Inhibition and enhancement of spontaneous emission rate, first proposed by Purcell, is discussed in terms of altered density-of-modes in various types of solid-state cavities and the Purcell factor is derived for two-level atomic system. The conditions for observing Purcell factor and experimental findings in micropillars embedded with Quantum Dots (QD)s are discussed. The strong interaction between photons and matter in the form of QD excitons, dispersion relations for ground and excited states separated by Rabi splitting are discussed. Experimental photoluminescence spectra showing anticrossing of exciton lines and cavity lines by temperature and other tuning methods are used to illustrate the strong light-matter interaction. The Jayness–Cummins model based on second quantization is presented to point out Rabi oscillation, Purcell effect, and other novel features. Microcavity structures for observing cavity quantum electrodynamics effects are mentioned. Microcavity lasers predicting thresholdless operation for unity spontaneous emission coupling factors are discussed.
Abstract Tailoring of electromagnetic spontaneous emission predicted by E. M. Purcell more than 50 years ago has undoubtedly proven to be one of the most important effects in the rich areas of quantum optics and nanophotonics. Although during the past decades the research in this field has been focused on electric dipole emission, the recent progress in nanofabrication and study of magnetic quantum emitters, such as rare‐earth ions, has stimulated the investigation of the magnetic side of spontaneous emission. Here, we review the state‐of‐the‐art advances in the field of spontaneous emission enhancement of magnetic dipole quantum emitters with the use of various nanophotonics systems. We provide the general theory describing the Purcell effect of magnetic emitters, overview realizations of specific nanophotonics structures allowing for the enhanced magnetic dipole spontaneous emission, and give an outlook on the challenges in this field, which remain open to future research. image
In the context of quantum strong coupling, the magnetic dipole (MD) emitters are largely overlooked due to the rarity of MD source and the non-magnetic nature of matters at high frequencies. Based on a semi-classic model, we theoretically demonstrate magnetic strong coupling between an MD cluster (Er 3+ : 4 / 13/2 → 4 / 15/2 transition at 1,550 nm) and an antenna-in-cavity structure. It is found that placing the plasmonic diabolo/s-diabolo nanoantenna, which supports strong electric/magnetic dipole mode, inside a dielectric cavity could largely improve the strong coupling coefficient while suppressing the cavity loss rate compared to the bare nanoantenna counterparts, empowering the magnetic quantum strong coupling at a level of 10 4 emitters, which is remarkable considering the weak MD dipole momentum and small hotspot region at high frequency. Furthermore, the two Rabi resonance branches undergo highly asymmetrical changes upon a small variation on the environmental refractive index, which leads to an exotic exponential sensitivity profile by tracing the ratio between the two resonances widths. The proposed magnetic strong coupling for nonlinear refractive index sensing may add a new category to quantum plasmonic sensors.
Inspired by the remarkable ability of plasmons to boost radiative emission rates, we propose leveraging acoustic graphene plasmons (AGPs) to realize tunable, giant Purcell enhancements for single-photon, entangled-photon, and multipolar quantum emitters. These AGPs are localized inside a cavity defined by a graphene sheet and a metallic nanocube and filled with a dielectric of thickness of a few nanometers and consisting of stacked layers of 2D materials, containing impurities or defects that act as quantum light emitters. Through finite-difference time domain (FDTD) calculations, we show that this geometry can achieve giant Purcell enhancement factors over a large portion of the infrared (IR) spectrum, up to 6 orders of magnitude in the mid-IR and up to 4 orders of magnitude at telecommunications wavelengths, reaching quantum efficiencies of 95\% and 89\%, respectively, with high-mobility graphene. We obtain Purcell enhancement factors for single-photon electric dipole (E1), electric quadrupole (E2), and electric octupole (E3) transitions and two-photon spontaneous emission (2PSE) transitions, of the orders of 10410^{4}104, 10710^{7}107, 10910^{9}109, and 10910^9109, respectively, and a quantum efficiency of 79\% for entangled-photon emission with high-mobility graphene at a wavelength of λ=1.55λ=1.55λ=1.55 μμμm. Importantly, AGP mode frequencies depend on the graphene Fermi energy, which can be tuned via electrostatic gating to modulate fluorescence enhancement in real time. As an example, we consider the Purcell enhancement of spontaneous single- and two-photon emissions from an erbium atom inside single-layer (SL) WS2_22​. Our results could be useful for electrically tunable quantum emitter devices with applications in quantum communication and quantum information processing.
We analyze the interaction of a nanomagnet (ferromagnetic) with a single photonic mode of a cavity in a fully quantum-mechanical treatment and find that exceptionally large quantum-coherent magnet-photon coupling can be achieved. Coupling terms in excess of several THz are predicted to be achievable in a spherical cavity of approximately 1 mm radius with a nanomagnet of approximately 100 nm radius and ferromagnetic resonance frequency of approximately 200 GHz. Eigenstates of the magnet-photon system correspond to entangled states of spin orientation and photon number, in which over 10{5} values of each quantum number are represented; conversely, initial (coherent) states of definite spin and photon number evolve dynamically to produce large oscillations in the microwave power (and nanomagnet spin orientation), and are characterized by exceptionally long dephasing times.