量子技術のフラックスを見つける(Finding the Flux of Quantum Technology)

2023-07-06

2023-07-05 ピッツバーグ大学

◆量子ビット（qubit）は一般のビットやバイトとは異なり、量子情報を運ぶ光子であり、量子力学の領域で振る舞います。これにより、量子コンピュータは現在のコンピュータと比べて驚異的な処理速度を実現できます。また、量子ビットは左右の手のように手の性質を持ち、その性質によって量子情報が運ばれます。
◆研究チームは、異なる手性を持つ光子を効率的に分離し、さらなる処理のために効果的に活用する方法を開発しました。この研究は、量子光学における高速単一光子源の開発に貢献するものと期待されています。量子技術は銀行の情報保護や化学の模倣など、さまざまな分野で重要な役割を果たす可能性があります。

＜関連情報＞

円偏光双極子場のスピンテクスチャとキラル結合 Spin texture and chiral coupling of circularly polarized dipole field

Yu Shi and Hong Koo Kim
Nanophotonics Published:January 3, 2023
DOI:https://doi.org/10.1515/nanoph-2022-0581

$Figure 1: Spin texture and energy flow distribution of an electric dipole with circular polarization. (A) A dipole moment p = p 0 2 x ̂ + i y ̂ $\boldsymbol{p}=\frac{{p}_{0}}{\sqrt{2}}\left(\hat{\boldsymbol{x}}+i\hat{\boldsymbol{y}}\right)$ placed at the origin of spherical coordinates; the dipole axis is along the z-direction. (B) The distance (r) dependence of spin density and energy flow: the magnitudes of spin vector (S r , S θ and S φ : left panel) and Poynting vector (P r and P φ: right panel). The angular (θ, φ) distribution of spin vector (C and D) and Poynting vector (E) calculated at r = 5 nm. Spin vector plot on the circle of a cross-section of a sphere (C). Spin vectors orient orthogonal to energy flow direction revealing transverse spins at near field. (F) Spin (S r , S θ ) and Poynting (P φ ) vector distributions plotted as a function of polar angle (θ). Note a skyrmion texture (C and D) of spin vector distribution: spin flips once when scanned along the polar angle direction (θ: from 0 to π). The angular (θ, φ) distribution of spin vector (G and H) and Poynting vector (I) calculated at r = 1 μm. Spin vector plot on the circle of a cross-section of a sphere (G). Spins orient parallel (antiparallel) to energy flow direction in the polar regions, revealing longitudinal spins at far field. (J) Spin (P r) and Poynting (S r) vector distributions plotted as a function of polar angle.$

Abstract

We show that a circularly polarized electric dipole harbors a near-field concentrated wave which orbits around with an energy flux significantly larger (five orders of magnitudes at ∼1 nm radial distance) than far-field radiation. This near-field wave is found to carry transverse spins and reveal skyrmion spin texture (Néel-type). By performing electromagnetic analysis and numerical simulation, we demonstrate chiral extraction of a near-field rotational energy flux: the confined energy flow is out-coupled to surface plasmons on metal surface, whose curvature is designed to provide orbital angular momentum matched to spin angular momentum of dipole field, that is, to facilitate spin–orbit interaction. Strong coupling occurs with high chiral selectivity (∼113) and Purcell enhancement (∼17) when both linear and angular momenta are matched between dipole field and surface plasmons. Existence of a high-intensity energy flux in the deep-bottom near-field region (r ∼ 1 nm) opens up an interesting avenue in altering fundamental properties of dipole emission. For example, extracting ∼1% of this flux would result in enhancing spontaneous emission rate by ∼1000 times.

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