Emission Quantum Research Articles

High-dimensional spin-orbital single-photon sources.

Hybrid integration of solid-state quantum emitters (QEs) into nanophotonic structures opens enticing perspectives for exploiting multiple degrees of freedom of single-photon sources for on-chip quantum photonic applications. However, the state-of-the-art single-photon sources are mostly limited to two-level states or scalar vortex beams. Direct generation of high-dimensional structured single photons remains challenging, being still in its infancy. Here, we propose a general strategy to design highly entangled high-dimensional spin-orbital single-photon sources by taking full advantage of the spatial freedom to design QE-coupled composite (i.e., Moiré/multipart) metasurfaces. We demonstrate the generation of arbitrary vectorial spin-orbital photon emission in high-dimensional Hilbert spaces, mapping the generated states on hybrid-order Bloch spheres. We further realize single-photon sources of high-dimensional spin-orbital quantum emission and experimentally verify the entanglement of high-dimensional superposition states with high fidelity. We believe that the results obtained facilitate further progress in integrated solutions for the deployment of next-generation high-capacity quantum information technologies.

Probing the limits for coherent optical control of a mechanically decoupled defect center in hexagonal boron nitride

The coherent control of a two-level system is among the most essential challenges in modern quantum optics. Understanding its fundamental limitations is crucial, also for the realization of next generation quantum devices. The quantum coherence of a two-level system is fragile in particular, when the two levels are connected via an optical transition, which, at the same time, enables the manipulation of the system. When such quantum emitters are located in solids the coherence suffers from the interaction of the optical transition with the solid state environment, which requires the sample to be cooled to temperatures of a few Kelvin or below. Here, we use a mechanically isolated quantum emitter in hexagonal boron nitride to explore the individual mechanisms which affect the coherence of an optical transition under resonant drive. We operate the system at the threshold where the mechanical isolation collapses in order to study the onset and temperature-dependence of dephasing and independently of spectral diffusion. The insights on the underlying physical decoherence mechanisms reveal a limit in temperature until which coherent driving of the system is possible. This study enables to increase the operation temperature of hBN-based quantum devices, therefore reducing the need for cryogenic cooling.

Efficient coupling between photonic waveguides and III-nitride quantum emitters in the UV-visible spectral range

Efficient coupling between photonic waveguides and III-nitride quantum emitters in the UV-visible spectral range

Mono-/multi-fluorination of 1,8-naphthalimides for developing AIE/AIEE fluorophores with tuning emission wavelength

Aggregation-induced emission/aggregation-induced emission enhancement (AIE/AIEE) luminogens provides amount of highly emissive materials in density states for versatile applications. Most of the AIE/AIEEgens were designed with the multiply rotation unit, in which the additional rotation units not only extend the molecular structure but also suffer from low atom economy. Herein, a fluorination strategy was introduced to construct ten AIE/AIEEgens with 1∼3 fluorine (F) atoms at different position of phenyl ring at previous developed AIEgen, 4-phenyl-1,8-naphthalimide, which can output tuning emissive wavelength and high quantum yields in both aqueous solutions and solids. In these compounds, five AIEgens with ortho-F atom and five AIEEgens without ortho-F atom were obtained. All compounds show bright blue emissions centered at 430–485 nm in aqueous solutions and wide emissions covering visible region in solid states. We calculated the ratio of quantum yields between their aqueous solution and THF solution (Φwater/ΦTHF). The AIE luminogens show the higher ratios between 10.19 and 24.89 and the AIEEgens show the lower ratios between 1.89 and 6.40. This strategy based on changing the substituent positions of F atoms provides an efficient and convenient method for construction of novel AIE-active materials with variable photophysical properties in density states.

Recent Advances of Organic-Inorganic Hybrid Fluorescent Hyperbranched Polymer: Synthesis, Performance Regulation Strategies and Applications.

The organic-inorganic hybrid fluorescent hyperbranched polymer, including hyperbranched polysiloxane and hyperbranched polyborate, have attracted much attention due to their excellent optical properties and wide range of applications. Hyperbranched polysiloxane and polyborates, prepared by introducing Si or B elements into organic polymer chains at the molecular level through rational molecular design and novel synthesis methods, exhibit outstanding photophysical properties as an indispensable branch of organic-inorganic hybrid fluorescent materials. Herein, this review highlights the recent research progress on hyperbranched polysiloxanes and hyperbranched polyborates, including strategies for regulating their emission wavelengths, quantum yields, and fluorescence lifetimes, potential emission mechanisms, and various applications. Finally, some challenges and promising future directions in the field of organic-inorganic hybrid fluorescent polymers are summarized.

Understanding the Role of NHC Ditopic Ligand Substituents in the Molecular Diversity and Emissive Properties of Silver Complexes.

Silver bis(carbene) complexes featuring ditopic N-heterocyclic carbene (NHC) ligands have been synthesized which enable the assembly of supramolecular architectures via reaction with silver triflate. Through a systematic exploration of crystal structures and emissive properties, this study investigates the impact of the substituents on the NHC ditopic ligands [R-Im-2-Z-py], where R = Me, benzyl (Bz), or 2-naphthylmethyl (NaphCH2), and Z = H or Cl in the structural framework and emissive properties observed in the silver bis(carbene) or polynuclear species. Remarkably diverse structural motifs emerge in both of them, predominantly influenced by the choice of R wingtip and second by the Z substituent. Also the emissive quantum yield of the complexes is mostly governed by the selection of the R wingtip and further modulated by the Z substituent. Several of the mono and polynuclear complexes exhibit complex emissive profiles, including the observation of dual emission phenomena. Particularly noteworthy is the complex [Ag(NHC)]2]OTf (R = Bz, Z = Cl), which demonstrates an exceptionally intense single blue emission with a remarkable solid-state quantum yield (Φ) of 24%.

Computationally Driven Discovery of T Center-like Quantum Defects in Silicon.

Quantum technologies would benefit from the development of high-performance quantum defects acting as single-photon emitters or spin-photon interfaces. Finding such a quantum defect in silicon is especially appealing in view of its favorable spin bath and high processability. While some color centers in silicon have been emerging in quantum applications, there remains a need to search for and develop new high-performance quantum emitters. By searching a high-throughput computational database of more than 22,000 charged complex defects in silicon, we identify a series of defects formed by a group III element combined with carbon ((A-C)Si with A = B, Al, Ga, In, Tl) and substituting on a silicon site. These defects are analogous structurally, electronically, and chemically to the well-known T center in silicon ((C-C-H)Si), and their optical properties are mainly driven by an unpaired electron on the carbon p orbital. They all emit in the telecom, and some of these color centers show improved properties compared to the T center in terms of computed radiative lifetime, emission efficiency, or smaller optical linewidth. The kinetic barrier computations and previous experimental evidence show that these T center-like defects can be formed through the capture of a diffusing carbon by a substitutional group III atom. We also show that the synthesis of hydrogenated T center-like defects followed by a dehydrogenation annealing step could facilitate the formation of these defects. Our work motivates further studies on the synthesis and control of this new family of quantum defects and demonstrates the use of high-throughput computational screening to discover new color center candidates.

Dynamic control and manipulation of near-fields using direct feedback

Shaping and controlling electromagnetic fields at the nanoscale is vital for advancing efficient and compact devices used in optical communications, sensing and metrology, as well as for the exploration of fundamental properties of light-matter interaction and optical nonlinearity. Real-time feedback for active control over light can provide a significant advantage in these endeavors, compensating for ever-changing experimental conditions and inherent or accumulated device flaws. Scanning nearfield microscopy, being slow in essence, cannot provide such a real-time feedback that was thus far possible only by scattering-based microscopy. Here, we present active control over nanophotonic near-fields with direct feedback facilitated by real-time near-field imaging. We use far-field wavefront shaping to control nanophotonic patterns in surface waves, demonstrating translation and splitting of near-field focal spots at nanometer-scale precision, active toggling of different near-field angular momenta and correction of patterns damaged by structural defects using feedback enabled by the real-time operation. The ability to simultaneously shape and observe nanophotonic fields can significantly impact various applications such as nanoscale optical manipulation, optical addressing of integrated quantum emitters and near-field adaptive optics.

Collective quantum dynamics with distant quantum emitters in slow-wave nanoplasmonic waveguides

We consider a slow-wave nanoplasmonic waveguide system with spatially separated (distant) quantum emitters. Based on a nanoplasmonic waveguide quantum electrodynamic theory the emerging non-Markovian collective plasmon-polariton dynamics directly reflects the spatial positioning of the quantum emitters. A phase-space analysis allows us to distinguish between collectivity and cooperativity and the transition between these regimes. For distant emitters, temporal decoherence is reflected in anomalous phase-space evolution. In the spectral domain, collectivity emerges as a resonant single Lorentzian peak with two weak sidebands, while cooperativity manifests as a Fano-like resonance normal-mode splitting. Remarkably, even for distant quantum emitters, we achieve collective multiple quantum emitter dynamics with non-vanishing excitation and vanishing instantaneous emission, establishing an interaction-based quantum nanoplasmonic memory with key relevance in quantum nanoplasmonic networks.

Solvent mediated synthesis of multicolor narrow bandwidth emissive carbon quantum dots and their potential in white light emitting diodes

The development of efficient and environmentally sustainable materials for white light-emitting diodes (WLEDs) is of paramount importance in the field of lighting technology. In this study, we present a solvent-modulated synthesis approach for the fabrication of multicolor narrow-bandwidth emissive carbon quantum dots (CQDs) as a promising solution for constructing WLEDs. The synthesis method involves the controlled reaction of organic precursors in different solvent environments, leading to the formation of CQDs with distinct emission wavelengths with a relatively small full width at half maximum, ranging from 28 to 42 nm. Moreover, these synthesized multicolor CQDs demonstrate a remarkably high fluorescence quantum yield of up to 65%, indicating their potential for constructing efficient WLED when incorporated in polymer matrix and coated on the surface of blue light-emitting diode (LED).

Dissipative stabilization of maximal entanglement between nonidentical emitters via two-photon excitation

Two nonidentical quantum emitters, when placed within a cavity and coherently excited at the two-photon resonance, can reach stationary states of nearly maximal entanglement. In Vivas-Viaña, Martín-Cano, and Sánchez Muñoz [], we introduce a frequency-resolved Purcell effect stabilizing entangled W states among strongly interacting quantum emitters embedded in a cavity. Here we delve deeper into a specific configuration with a particularly rich phenomenology: two interacting quantum emitters under coherent excitation at the two-photon resonance. This scenario yields two resonant cavity frequencies where the combination of two-photon driving and Purcell-enhanced decay stabilizes the system into the subradiant and superradiant states, respectively. By considering the case of nondegenerate emitters and exploring the parameter space of the system, we show that this mechanism is merely one among a complex family of phenomena that can generate both stationary and metastable entanglement when driving the emitters at the two-photon resonance. We provide a global perspective of this landscape of mechanisms and contribute analytical characterizations and insights into these phenomena, establishing connections with previous reports in the literature and discussing how some of these effects can be optically detected. Published by the American Physical Society 2024

Alternative Plasmonic Materials for Fluorescence Enhancement.

Noble metals such as gold and silver have been used extensively for a range of plasmonic applications, including enhancing the fluorescence rate of a dye molecule, as evidenced by numerous experiments over the past two decades. Recently, a variety of doped semiconductors have been proposed as alternative plasmonic materials, exhibiting plasmonic resonances from ultraviolet to far-infrared. In this work, we investigate the suitability of these alternative materials for enhancing the fluorescence of a molecule. Considering nanosized spheres, we study their response under plane wave illumination and the resulting enhancement factors when coupled to a quantum emitter. Comparisons with standard plasmonic metals reveal that semiconductor materials lead to a significantly reduced, and often strongly quenched, emission of light caused by their dominant absorption, which hinders fluorescence enhancement. However, we show that enhancement may be obtained when considering poor emitting dyes and high refractive index environments. Our findings demonstrate that these alternative materials result in weaker fluorescence enhancement compared to their plasmonic counterparts. Nonetheless, there are means to compensate for this, and a reasonable enhancement can be achieved for dyes in the infrared spectrum.

Multiqubit quantum state preparation enabled by topology optimization

Using topology optimization, we inverse-design nanophotonic cavities enabling the preparation of pure states of pairs and triples of quantum emitters. Our devices involve moderate values of the dielectric constant, operate under continuous laser driving, and yield fidelities to the target (Bell and W) states approaching unity for distant qubits (several natural wavelengths apart). In the fidelity optimization procedure, our algorithm generates entanglement by maximizing the dissipative coupling between the emitters, which allows the formation of multipartite pure steady states in the driven-dissipative dynamics of the system. Our findings open the way toward the efficient and fast preparation of multiqubit quantum states with engineered features, with potential applications for nonclassical light generation, and quantum sensing and metrology.

Quantum Physical Unclonable Function Based on Multidimensional Fingerprint Features of Single Photon Emitters in Random AlN Nanocrystals

AbstractPhysical unclonable function (PUF) has emerged as a unique physical'fingerprint' that is inherently difficult to replicate. It shows tremendous application value in various hardware security areas such as identity authentication, chip anticounterfeiting, communication encryption, blockchain, etc. However, with the rapid development of 3D nanoprinting, classical PUFs constructed with disordered micro‐nanostructures face tremendous threats from physical cloning attacks. Herein, this study proposes and demonstrates the utilization of room‐temperature single‐photon emitters derived from atomic defects in randomly distributed pyramidal aluminum nitride (AlN) nanocrystals as a novel quantum PUF to resist physical cloning attacks. The fabrication of this quantum PUF on silicon (Si) wafers enables seamless integration with silicon photonic integrated circuits. The multidimensional fingerprint features of the single‐photon emitters are highly sensitive to the lattice parameters of the uneven AlN nanocrystals. Furthermore, each single photon emitter can work as a quantum random number generator to ensure the fundamental unpredictability of PUFs. The subatomic precision requirement coupled with unpredictable quantum emission behavior makes it practically impossible to attack the proposed quantum PUF, providing a promising solution for information security in the post‐quantum era.

High Efficiency Ultra-Narrow Emission Quantum Dot Light-Emitting Diodes Enabled by Microcavity.

A wide-color-gamut display enableby a narrow emission linewidth facilitates a visually immersive experience akin to the real world. Quantum dot light-emitting diodes (QLEDs) with excellent color purity and high efficiency hold great promise as future candidates for high-definition displays. However, most devices typically exhibit emission linewidths exceeding 20nm, and lack a universal strategy for further enhancing the color purity. In this study, a planar microcavity structure for realizing ultra-narrow emissions is developed by incorporating a distributed Bragg reflector into normal electroluminescent devices. By leveraging the strong optical resonance effect derived from this microcavity structure, red QLEDs are successfully fabricated with an extraordinary full width at half maximum of 11nm in the normal direction, beyond the BT.2020 color coordinates. The fabricated red-microcavity QLEDs exhibit a considerable enhancement in the external quantum efficiency, which increases from 28.2% to 35.6%, together with an extended operating lifetime. The strategy adopted herein will serve as an effective reference for achieving ultra-narrow emission and high-efficiency QLEDs.

Near-field strong coupling and entanglement of quantum emitters for room-temperature quantum technologies

In recent years, quantum nanophotonics has forged a rich nexus of nanotechnology with photonic quantum information processing, offering remarkable prospects for advancing quantum technologies beyond their current technical limits in terms of physical compactness, energy efficiency, operation speed, temperature robustness and scalability. In this perspective, we highlight a number of recent studies that reveal the especially compelling potential of nanoplasmonic cavity quantum electrodynamics for driving quantum technologies down to nanoscale spatial and ultrafast temporal regimes, whilst elevating them to ambient temperatures. Our perspective encompasses innovative proposals for quantum plasmonic biosensing, driving ultrafast single-photon emission and achieving near-field multipartite entanglement in the strong coupling regime, with a notable emphasis on the use of industry-grade devices. We conclude with an outlook emphasizing how the bespoke characteristics and functionalities of plasmonic devices are shaping contemporary research directives in ultrafast and room-temperature quantum nanotechnologies.

Mie metasurfaces for enhancing photon outcoupling from single embedded quantum emitters

Abstract Solid-state quantum emitters (QE) can produce single photons required for quantum information processing. However, their emission properties often exhibit poor directivity and polarisation definition resulting in considerable loss of generated photons. Here we propose and numerically evaluate Mie metasurface designs for outcoupling photons from an embedded and randomly-positioned QE. These Mie metasurface designs can provide over one order of magnitude enhancement in photon outcoupling with only several percent of photons being lost. Importantly, the Mie metasurfaces provide the enhancement in photon outcoupling without the need for strict QE position alignment and without affecting the intrinsic QE emission rate (Purcell enhancement). Electric dipole modes are key for achieving the enhancement and they offer a path for selective outcoupling for photons emitted with specific polarisation, including the out-of-plane polarisation. Mie metasurfaces can provide an efficient, polarisation-selective and scalable platform for QEs.

Green Synthesis of Luminescent Carbon Dots from Ficus benghalensis Aerial Roots for Bioimaging.

In this work, carbon quantum dots (CQDs) were prepared using a one-step hydrothermal green synthesis method from a low-cost and eco-friendly renewable biomass, specifically the Ficus benghalensis aerial roots (FB-AR). For the past two decades, CQDs have been noted for their tunable emission spectrum, quantum yield, biocompatibility, photostability, and unique optoelectronic properties such as photoluminescence (PL), and fluorescence. The synthesized Ficus benghalensis carbon quantum dots (FB-CQDs) were characterized for their physical, structural, and chemical properties using XRD, Raman, HRTEM, XPS, FTIR, TG-DTG, UV-visible, and photoluminance analysis. XPS analysis confirmed the presence of phytoconstituent functionalities and the composition of components. The FB-CQDs, which exhibit long-range emissions, have potential applications in various biological and therapeutic fields. Their bioimaging capability is tested in Escherichia coli bacteria. However, despite their promising characteristics, the FB-CQDs showed no antibacterial inhibition against Escherichia coli and Staphylococcus aureus, likely due to its carbonization temperature.

Nonreciprocal Photon Transport in a Chiral Optomechanical System

AbstractChiral interaction between light and quantum emitters leads to emergence development of chiral quantum optics and stimulates a wide range of practical applications in quantum regime, such as single‐photon isolation and photon unidirectional emission. Cavity optomechanics studying the interaction between optical and mechanical resonators plays an important role in the field of quantum optics. However, how to achieve the chiral interaction between light and mechanical oscillators and explore the applications of the chiral optomechanical systems are still difficult encountered in cavity optomechanics. Here, a method is proposed to achieve chiral optomechanical interaction by exploiting directional squeezed light in a multimode optomechanical system. Based on the chiral interaction between photon and phonon, the nonreciprocal photon transport at a single‐photon level can be realized. An isolation ratio of and a negligible insertion loss for the photonic isolator are obtained. This method paves the way to realize chiral optomechanical interaction for conducting chiral optomechanics and opens up the prospect of exploring and utilizing chiral photon–phonon manipulation in the quantum regime.

Spacer Twisting Strategy to Realize Ultrabright Near-Infrared II Polymer Nanoparticles for Fluorescence Imaging-Guided Tumor Phototheranostics.

Conjugated polymers are becoming popular near-infrared II (NIR-II) phototheranostic agents (PTAs) due to their numerous advantages, such as high photostability, large molar extinction coefficients, and excellent photothermal properties. However, the strong π-π interactions between the chains of the conjugated polymers resulted in their generally low NIR-II emission quantum yields (QY). Therefore, the synthesis of conjugated polymers with high QY is an interesting but challenging task. Herein, we proposed a spacer twisting strategy to realize ultrabright NIR-II polymer nanoparticles for fluorescence imaging-guided tumor phototheranostics. Theoretical calculations indicated that the polymer PY-IT has the largest dihedral angle between the largely π-conjugated skeleton and the spacer, which can effectively inhibit intermolecular π-π stacking, resulting in an improved QY as high as 16.5% in nanoparticles. In addition, PY-IT NPs can effectively perform NIR-II imaging and photothermal treatment of tumors. The work presents some valuable guides for achieving ultrabright NIR-II polymeric PTAs with high QY.