Entangled dark state mediated by a dielectric cavity within epsilon-near-zero materials

Two emitters can be entangled by manipulating them through optical fields within a photonic cavity. However, maintaining entanglement for a long time is challenging due to the decoherence of the entangled qubits, primarily caused by cavity loss and atomic decay. Here, we found the entangled dark state between two emitters mediated by a dielectric cavity within epsilon-near-zero (ENZ) materials, ensuring entanglement maintenance over an extended period. To obtain the entangled dark state, we derived an effective model with degenerate mode modulation. In the dielectric cavities within ENZ materials, the decay rate of emitters can be regarded as 0, which is the key to achieving the entangled dark state. Meanwhile, the dark state immune to cavity loss exists when two emitters are in symmetric positions in the dielectric cavity. Additionally, by adjusting the emitters to specific asymmetric positions, it is possible to achieve transient entanglement with higher concurrence. By overcoming the decoherence of the entangled qubits, this study demonstrates stable, long-term entanglement with ENZ materials, holding significant importance for applications such as nanodevice design for quantum communication and quantum information processing.

Tetrazine-Isonitrile Bioorthogonal Fluorogenic Reactions Enable Multiplex Labeling and Wash-Free Bioimaging of Live Cells

Developing fluorogenic probes for simultaneous live cell labeling of multiple targets is crucial for understanding complex cellular events. The emerging [4+1] cycloaddition between tetrazine and isonitriles holds promise as a bioorthogonal tool, yet existing tetrazine probes lack reactivity and fluorogenicity. Here, we present the development of a series of tetrazine-functionalized bioorthogonal probes. By incorporating pyrazole adducts into the fluorophore scaffolds, the post-reacted probes displayed remarkable fluorescence turn-on ratios, up to 3184-fold. Moreover, these modifications are generalizable to various fluorophores, enabling a broad emission range from 473 to 659 nm. Quantum chemical calculations further elucidate the turn-on mechanisms. These probes enable the simultaneous labeling of multiple targets in live cells, without the need for a washing step. Consequently, our findings pave the way for advanced multiplex imaging and detection techniques for cellular studies.

Population and Energy Transfer Dynamics in an Open Excitonic Quantum Battery

In a previous study, we proposed an open quantum network model of a quantum battery (QB) that possesses dark states owing to its structural exchange symmetries. While in a dark state, the QB is capable of storing an exciton without any environment-induced population losses. However, when the structural exchange symmetry is broken, the QB begins to discharge the exciton towards its exit site. In this article, we start by demonstrating that this QB is not only loss-free with respect to exciton population during the storage phase, but also with respect to the QB energy. We then explore the exciton population and energy transfer dynamics of the QB during the discharge phase over a wide range of site energies, bath temperatures, and bath reorganization energies. Our results shed light on how to optimize the QB's population and energy transfer dynamics for different purposes.

Spectroscopically dark phosphate features revealed by chemical exchange saturation transfer

Phosphate is an essential anion in the human body, comprising approximately 1% of the total body weight, and playing a vital role in metabolism, cell membranes, and bone formation. We have recently provided spectroscopic, microscopic, and computational evidence indicating that phosphates can aggregate much more readily in solution than previously thought. This prior work provided indirect evidence through the observation of unusual31 P NMR relaxation and line-broadening effects with increasing temperature. Here, we show that, under conditions of slow exchange and selective RF saturation, additional features become visible in chemical exchange saturation transfer (CEST) experiments, which appear to be related to the previously reported phosphate clustering. In particular, CEST shows pronounced dips several ppm upfield of the main phosphate resonance at low temperatures, while direct31 P spectroscopy does not produce any signals in that range. We study the pH dependence of these new spectroscopic features and present exchange and spectroscopic parameters based on fitting the CEST data. These findings could be of importance in the investigation of phosphate dynamics, especially in the biological milieu.

Switching Singlet Exciton to Triplet for Efficient Pure Organic Room-Temperature Phosphorescence by Rational Molecular Design

The design and regulation of phosphors are attractive but challenging because of the spin-forbidden intersystem crossing (ISC) process. Here, a new perspective on the enhancement of the ISC is proposed and demonstrated. Different from current strategies, the ISC yield (Φ_ISC) is enhanced by decreasing the fluorescence radiative transition rate constant (k_F) via rational molecular designing rather than boosting the spin-orbit coupling by decorating the molecular skeleton with a heavy atom, heteroatom, or carbonyl. The k_F of the designed molecule in this case is associated with the substituent position of the methoxy group, which alters the distribution of the front orbitals. The S₀ → S₁ transition of these compounds evolves from a bright state to a dark state gradually with the variation of the substituent position, accompanied by the decrease of k_F and increase of Φ_ISC. The fluorescence emission is switched to phosphorescence emission successfully by regulating the k_F. This work provides an alternative strategy to design efficient room-temperature phosphorescence material.

Fluorinated graphene grating metasurface for terahertz dark state excitation

We propose an original technique for the grating metasurfaces fabrication by low-power ultraviolet laser treatment of fluorinated graphene (FG) films with the focus on terahertz applications. The laser treatment reduces dielectric FG to its conductive counterparts, increasing DC conductivity to 170 S·m^-1for treated areas. The electromagnetic response of the grating metasurfaces studied by THz time-domain spectroscopy in the 100 GHz-1 THz frequency range demonstrates enhanced resonant transmittance through metasurfaces. The intensity and position of transmittance peak could be tuned by changing the metasurface geometry, i.e. the period of the structure and width of the reduced and unreduced areas. In particular, the decrease of the reduced FG area width from 400 to 170μm leads to the shift of the resonance peak from 0.45 THz to the higher frequencies, 0.85 THz. Theoretical description based on the multipole theory supported by finite element numerical calculations confirms the excitation of the dark state in the metasurface unit cells comprising reduced and unreduced FG areas at resonance frequency determined by the structure geometrical features. Fabricated metasurfaces have been proved to be efficient narrowband polarizers being rotated by 50° about the incident THz field vector.

Phosphates form spectroscopically dark state assemblies in common aqueous solutions

Phosphates and polyphosphates play ubiquitous roles in biology as integral structural components of cell membranes and bone, or as vehicles of energy storage via adenosine triphosphate and phosphocreatine. The solution phase space of phosphate species appears more complex than previously known. We present nuclear magnetic resonance (NMR) and cryogenic transmission electron microscopy (cryo-TEM) experiments that suggest phosphate species including orthophosphates, pyrophosphates, and adenosine phosphates associate into dynamic assemblies in dilute solutions that are spectroscopically "dark." Cryo-TEM provides visual evidence of the formation of spherical assemblies tens of nanometers in size, while NMR indicates that a majority population of phosphates remain as unassociated ions in exchange with spectroscopically invisible assemblies. The formation of these assemblies is reversibly and entropically driven by the partial dehydration of phosphate groups, as verified by diffusion-ordered spectroscopy (DOSY), indicating a thermodynamic state of assembly held together by multivalent interactions between the phosphates. Molecular dynamics simulations further corroborate that orthophosphates readily cluster in aqueous solutions. This study presents the surprising discovery that phosphate-containing molecules, ubiquitously present in the biological milieu, can readily form dynamic assemblies under a wide range of commonly used solution conditions, highlighting a hitherto unreported property of phosphate's native state in biological solutions.

Molecular Origins of Heteroatom Engineering on the Emission Wavelength Tuning, Quantum Yield Variations and Fluorogenicity of NBD-like SCOTfluors

Molecular engineering of fluorophore scaffolds, especially heteroatom replacement, is a promising method to yield novel fluorophores with tailored properties for various applications. Yet, molecular origins of the distinct fluorescent properties in newly developed SCOTfluors, i. e., varied emission wavelengths, distinct quantum yields, and fluorogenicity, remain elusive. Such understanding, however, is critical for the rational molecular engineering of high-performance fluorophores. Herein, we employed quantum chemical calculations to understand the structure-property relationships of nitrobenzoxadiazole (NBD)-like SCOTfluors. Our findings are important not only for the rational deployment of SCOTfluors, but also for the effective modifications of other fluorophore scaffolds, for satisfying the increasingly diversified requirements of bioimaging and biosensing applications.

Creation of Single-Photon Emitters in WSe2 Monolayers Using Nanometer-Sized Gold Tips

Due to their tunable bandgaps and strong spin-valley locking, transition metal dichalcogenides constitute a unique platform for hosting single-photon emitters. Here, we present a versatile approach for creating bright single-photon emitters in WSe₂ monolayers by the deposition of gold nanostars. Our molecular dynamics simulations reveal that the formation of the quantum emitters is likely caused by the highly localized strain fields created by the sharp tips of the gold nanostars. The surface plasmon modes supported by the gold nanostars can change the local electromagnetic fields in the vicinity of the quantum emitters, leading to their enhanced emission intensities. Moreover, by correlating the emission energies and intensities of the quantum emitters, we are able to associate them with two types of strain fields and derive the existence of a low-lying dark state in their electronic structures. Our findings are highly relevant for the development and understanding of single-photon emitters in transition metal dichalcogenide materials.

Competition between Factors Determining Bright versus Dark Atomic States within a Laser Mode

We observe bimodal fluorescence patterns from atoms in a fast atomic beam when the laser excitation occurs in the presence of a magnetic field and the atoms sample only a portion of the laser profile. The behavior is well explained by competition between the local intensity of the laser, which tends to generate a coherent-population-trapping (CPT) dark state in the J = 1 to J' = 0 system, and the strength of an applied magnetic field that can frustrate the CPT process. This work is relevant for understanding and optimizing the detection process for clocks or other coherent systems utilizing these transitions and could be applicable to in situ calibration of the laser-atom interaction, such as the strength of the magnetic field or laser intensity at a specific location.

The origin of the dark S1 state in carotenoids: a comprehensive model

In carotenoids, by analogy to polyenes, the symmetry of the π-electron system is often invoked to explain their peculiar electronic features, in particular the inactivity of the S₀ → S₁ transition in one-photon excitation. In this review, we verify whether the molecular symmetry of carotenoids and symmetry of their π-electron system are supported in experimental and computational studies. We focus on spectroscopic techniques which are sensitive to the electron density distribution, including the X-ray crystallography, electronic absorption, two-photon techniques, circular dichroism, nuclear magnetic resonance, Stark and vibrational spectroscopies, and on this basis we seek for the origin of inactivity of the S₁ state. We come across no experimental and computational evidence for the symmetry effects and the existence of symmetry restrictions on the electronic states of carotenoids. They do not possess an inversion centre and the C_2h symmetry approximation of carotenoid structure is by no means justified. In effect, the application of symmetry rules (and notification) to the electronic states of carotenoids in this symmetry group may lead to a wrong interpretation of experimental data. This conclusion together with the results summarized in the review allows us to advance a consistent model that explains the inactivity of the S₀ → S₁ transition. Within this model, S₁ is never accessible from S₀ due to the negative synergy of (i) the contributions of double excitations of very low probability, which elevate S₁ energy, and (ii) a non-verticality of the S₀ → S₁ transition, due to the breaking of Born-Oppenheimer approximation. Certainly, our simple model requires a further experimental and theoretical verification.

Composition-Dependent Energy Splitting between Bright and Dark Excitons in Lead Halide Perovskite Nanocrystals

Perovskite semiconductor nanocrystals with different compositions have shown promise for applications in light-emitting devices. Dark excitonic states may suppress light emission from such nanocrystals by providing an additional nonradiative recombination channel. Here, we study the composition dependence of dark exciton dynamics in nanocrystals of lead halides by time-resolved photoluminescence spectroscopy at cryogenic temperatures. The presence of a spin-related dark state is revealed by magneto-optical spectroscopy. The energy splitting between bright and dark states is found to be highly sensitive to both halide elements and organic cations, which is explained by considering the effects of size confinement and charge screening, respectively, on the exchange interaction. These findings suggest the possibility of manipulating dark exciton dynamics in perovskite semiconductor nanocrystals by composition engineering, which will be instrumental in the design of highly efficient light-emitting devices.

¹³Cα decoupling during direct observation of carbonyl resonances in solution NMR of isotopically enriched proteins

Direct detection of (13)C can be advantageous when studying uniformly enriched proteins, in particular for paramagnetic proteins or when hydrogen exchange with solvent is fast. A scheme recently introduced for long-observation-window band-selective homonuclear decoupling in solid state NMR, LOW-BASHD (Struppe et al. in J Magn Reson 236:89-94, 2013) is shown to be effective for (13)C(α) decoupling during direct (13)C' observation in solution NMR experiments too. For this purpose, adjustment of the decoupling pulse parameters and delays is demonstrated to be important for increasing spectral resolution, to reduce three-spin effects, and to decrease the intensity of decoupling side-bands. LOW-BASHD then yields (13)C' line widths comparable to those obtained with the popular IPAP method, while enhancing sensitivity by ca 35 %. As a practical application of LOW-BASHD decoupling, requiring quantitative intensity measurement over a wide dynamic range, the impact of lipid binding on the (13)C'-detected NCO spectrum of the intrinsically disordered protein α-synuclein is compared with that on the (1)H-detected (1)H-(15)N HSQC spectrum. Results confirm that synuclein's "dark state" behavior is not caused by paramagnetic relaxation or rapid hydrogen exchange.