Coherent momentum control of forbidden excitons

Abstract

A double-edged sword in two-dimensional material science and technology is optically forbidden dark exciton. On the one hand, it is fascinating for condensed matter physics, quantum information processing, and optoelectronics due to its long lifetime. On the other hand, it is notorious for being optically inaccessible from both excitation and detection standpoints. Here, we provide an efficient and low-loss solution to the dilemma by reintroducing photonics bound states in the continuum (BICs) to manipulate dark excitons in the momentum space. In a monolayer tungsten diselenide under normal incidence, we demonstrated a giant enhancement (~1400) for dark excitons enabled by transverse magnetic BICs with intrinsic out-of-plane electric fields. By further employing widely tunable Friedrich-Wintgen BICs, we demonstrated highly directional emission from the dark excitons with a divergence angle of merely 7°. We found that the directional emission is coherent at room temperature, unambiguously shown in polarization analyses and interference measurements. Therefore, the BICs reintroduced as a momentum-space photonic environment could be an intriguing platform to reshape and redefine light-matter interactions in nearby quantum materials, such as low-dimensional materials, otherwise challenging or even impossible to achieve.

Emissive Dark Excitons in Monoclinic Two-Dimensional Hybrid Lead Iodide Perovskites

“…Can we make the X D state emit light just by controlling the crystal structure of 2D layered hybrid perovskites? Note that the emissive dark excitons are not only interesting for fundamental properties but also important for future quantum computing like applications where spin dependent information is stored and used for readout in the form of a qubit. , …”

“…Note that the emissive dark excitons are not only interesting for fundamental properties but also important for future quantum computing like applications where spin dependent information is stored and used for readout in the form of a qubit. 9,10 The main reasons behind the X D being nonluminescent are (i) the optical transition from X D to the ground state is spinforbidden, and therefore has a long radiative lifetime, 11,12 providing ample opportunity for nonradiative recombination, and (ii) faster thermally activated depopulation of X D to X B , because of the small energy difference (ΔE) between the two states (see Figure 1b). Furthermore, the faster radiative recombination of X B also supports the population back transfer from X D to X B .…”

As‐Grown Miniaturized True Zero‐Order Waveplates Based on Low‐Dimensional Ferrocene Crystals

“…An urgent demand exists for compact optical systems to be used in dynamic polarization control, [7] optical interconnect chips, [8] onchip quantum information processing, [9] all-optical neuromorphic computing, [10] and lab-on-chip light sources. [11] Polarization control relies on the birefringence yielded by the inherent anisotropic properties of the material. An ideal miniaturized waveplate requires an ultrathin thickness (high birefringence, Δn), low loss (small extinction coefficients, 𝜅), low distortion (low dichroism, Δ𝜅), and ease of fabrication.…”

“…An urgent demand exists for compact optical systems to be used in dynamic polarization control, [ 7 ] optical interconnect chips, [ 8 ] on‐chip quantum information processing, [ 9 ] all‐optical neuromorphic computing, [ 10 ] and lab‐on‐chip light sources. [ 11 ]…”

Photonic Crystal Enhanced Fluorescence: A Review on Design Strategies and Applications

“…While label-free biosensing with PCs offers simple assay workflows, labeling of analytes with photon-emitted tags such as fluorophores offers routes toward reduced limits of detection. Therefore, in this review, we focus our discussion upon fluorescence-based applications using PCs [ 107 ].…”