ダイヤモンドはすべてのもののためにある:量子技術を後押しする一般理論(Diamonds are for everything: A general theory to boost quantum tech)

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2022-12-08 オーストラリア連邦研究会議(ARC)

研究者は、ダイヤモンドにおける窒素空孔とプラズモニックナノ粒子の相互作用を説明・予測する初の一般理論を開発し、さまざまな新しい量子技術において感度と効率を高める道を切り開いた。
窒素空孔(NV)センターはダイヤモンドの欠陥の一つで、量子力学的な実験に非常に有効な物質である。磁場、電場、ひずみ、温度に感度があり、ナノスケールの分解能をもつセンサーとしても使用できる。
実験者は、金属ナノ粒子の電子振動(プラズモンとして知られている)を利用して、NVセンターを調整し、輝度と効率の向上を達成することができる。

<関連情報>

NVプラズモニクス:プラズモニック金属ナノ粒子を介したNV中心の光放射の変調 NV-plasmonics: modifying optical emission of an NV− center via plasmonic metal nanoparticles

Harini Hapuarachchi, Francesco Campaioli and Jared H. Cole
Nanophotonics  Published:October 19, 2022
DOI:https://doi.org/10.1515/nanoph-2022-0429

Figure 1: Optical model of the NV centre, example NV-MNP schematic and isolated NV emission spectra (theoretical and experimental). (A) Optical model of the NV center with n + 1 ground states {|g k⟩} with energies {ℏω k } (k ∈ {0, …, n}) and two excited states |e 0⟩ and |e 1⟩. The state |e 1⟩ is a phenomenologically defined upper excited level resonant with the angular frequency of incoming radiation ω d. Other parameters are, spontaneous photon emission rate(s) γ k , dephasing rate γ *, ground state phonon decay rate(s) γ k,k−1, effective excited state phonon decay rate γ e, and zero phonon line (ZPL) energy ℏω z. (B) An example dimer setup where the NV-MNP hybrid axis lies along the NV dipolar plane. Optical illumination is polarized along a plane perpendicular to the NV dipolar plane. E 0 and d E m + ${\boldsymbol{d}}_{\text{E}}^{\text{m}+}$ denote the positive frequency amplitudes (coefficients of e − i ω d t ${\text{e}}^{-\text{i}{\omega }_{\text{d}}t}$ ) of the external field and the MNP dipole formed by the external field, respectively. E 0 sin θ/ϵ effD and E sin θ m + ${\boldsymbol{E}}_{\sin \theta }^{\text{m}+}$ denote the screened projections of the external field and the MNP dipole response field onto the NV dipolar plane, at the NV location. (C) The experimentally measured emission spectrum of an isolated NV center in air at room temperature and the fitted Lorentzian sum reported by Albrecht et al. in [18] are denoted by the solid blue and dashed black lines. The output of our extended NV model in (A) implemented as an open quantum system is plotted in red. Individual emission lines are shown with reduced opacity. Both theoretical and experimental spectra including the fitted Lorentzians and the individual emission bands are normalized by the area of the respective total emission curve. The inset conceptually illustrates the NV center embedded in a nanodiamond.

Abstract

The nitrogen-vacancy (NV) center in diamond is very sensitive to magnetic and electric fields, strain, and temperature. In addition, it is possible to optically interrogate individual defects, making it an ideal quantum-limited sensor with nanoscale resolution. A key limitation for the application of NV sensing is the optical brightness and collection efficiency of these defects. Plasmonic resonances of metal nanoparticles have been used in a variety of applications to increase the brightness and efficiency of quantum emitters, and therefore are a promising tool to improve NV sensing. However, the interaction between NV centers and plasmonic structures is largely unexplored. In particular, the back-action between NV and plasmonic nanoparticles is nonlinear and depends on optical wavelength, nanoparticle position, and metal type. Here we present the general theory of NV-plasmonic nanoparticle interactions. We detail how the interplay between NV response, including optical and vibrational signatures, and the plasmonic response of the metal nanoparticle results in modifications to the emission spectra. Our model is able to explain quantitatively the existing experimental measurements of NV centers near metal nanoparticles. In addition, it provides a pathway to developing new plasmonic structures to improve readout efficiencies in a range of applications for the NV center. This will enable higher precision sensors, with greater bandwidth as well as new readout modalities for quantum computing and communication.

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