Incoherent Coupling Research Articles

(Keynote) Engineering Lead Halide Perovskite Nanocrystals for Fast Single-Particle and Collective Light Emission

Colloidal lead halide perovskite (LHP) nanocrystals (NCs), with bright and spectrally narrow photoluminescence (PL) tunable over the entire visible spectral range, are of immense interest as classical and quantum light sources. Fast (bright) and pure single-photon emission is key for many quantum technologies, from optical quantum computing to quantum key distribution and quantum imaging.The brightness of an emitter is ultimately described by Fermi’s golden rule, with a radiative rate proportional to its oscillator strength (intrinsic emitter property) times the local density of photonic states (photonic engineering, i.e. cavity). With perovskite NCs, we present a record-low sub-100 ps radiative decay time for CsPb(Br/Cl)3, almost as short as the reported exciton coherence time, by the NC size increase to 30 nm. The characteristic dependence of radiative rates on QD size, composition, and temperature suggests the formation of giant transition dipoles, as confirmed by effective-mass calculations for the case of the giant oscillator strength. Importantly, the fast radiative rate is achieved along with the single-photon emission despite the NC size being ten times larger than the exciton Bohr radius. NC self-assembly is a versatile platform for materials engineering, particularly for attaining collective phenomena with perovskite NCs, such as superfluorescence in perovskite NC superlattices. Thus far, LHP NCs have been co-assembled with building blocks that acted solely as spacers to promote the tuning of the mutual arrangement of LHP nanocubes [2]. However, the functionality of the second SL component can give rise to the enhancement of the LHP NCs properties or the emergence of new collective effects. We present the formation of multicomponent SLs made from the CsPbBr3 NCs of two different sizes. The diversity of obtained SLs encompassed the binary ABO6-, ABO3-, and NaCl-type structures, all of which contained orientationally and positionally confined NCs. For the selected model system, the ABO6-type SL, we observed efficient NC coupling and Förster-like energy transfer from strongly confined 5.3 nm CsPbBr3 NCs to weakly confined 17.6 nm CsPbBr3 NCs. Exciton spatiotemporal dynamics measurements reveal that binary SLs exhibit enhanced exciton diffusivity compared to one-component SLs across the entire temperature range (from 5 K to 298 K). Observed incoherent NC coupling and controllable excitonic transport within the solid NC SLs hold promise for potential applications in optoelectronic devices.[1]C. Zhu, S. C. Boehme, L. G. Feld, A. Moskalenko, D. N. Dirin, R. F. Mahrt, T. Stöferle, M. I. Bodnarchuk, A. L. Efros, P. C. Sercel, M. V. Kovalenko, G. Rainò. In review.[2] Ihor Cherniukh et al. Nature, 2021, 593, 535–542. [3] T. Sekh et al. Submitted

Discovering novel optical solitons of two CNLSEs with coherent and incoherent nonlinear coupling in birefringent optical fibers

Discovering novel optical solitons of two CNLSEs with coherent and incoherent nonlinear coupling in birefringent optical fibers

All-Perovskite Multicomponent Nanocrystal Superlattices.

Nanocrystal superlattices (NC SLs) have long been sought as promising metamaterials, with nanoscale-engineered properties arising from collective and synergistic effects among the constituent building blocks. Lead halide perovskite (LHP) NCs come across as outstanding candidates for SL design, as they demonstrate collective light emission, known as superfluorescence, in single- and multicomponent SLs. Thus far, LHP NCs have only been assembled in single-component SLs or coassembled with dielectric NC building blocks acting solely as spacers between luminescent NCs. Here, we report the formation of multicomponent LHP NC-only SLs, i.e., using only CsPbBr3 NCs of different sizes as building blocks. The structural diversity of the obtained SLs encompasses the ABO6, ABO3, and NaCl structure types, all of which contain orientationally and positionally locked NCs. For the selected model system, the ABO6-type SL, we observed efficient NC coupling and Förster-like energy transfer from strongly confined 5.3 nm CsPbBr3 NCs to weakly confined 17.6 nm CsPbBr3 NCs, along with characteristic superfluorescence features at cryogenic temperatures. Spatiotemporal exciton dynamics measurements reveal that binary SLs exhibit enhanced exciton diffusivity compared to single-component NC assemblies across the entire temperature range (from 5 to 298 K). The observed coherent and incoherent NC coupling and controllable excitonic transport within the solid NC SLs hold promise for applications in quantum optoelectronic devices.

Dynamics of parafermionic states in transport measurements

Advances in hybrid fractional quantum Hall (FQH)-superconductor platforms pave the way for realisation of parafermionic modes. We analyse signatures of these non-abelian anyons in transport measurements across devices with \mathbb{Z}_6ℤ6 parafermions (PFs) coupled to an external electrode. Simulating the dynamics of these open systems by a stochastic quantum jump method, we show that a current readout over sufficiently long times constitutes a projective measurement of the fractional charge shared by two PFs. Interaction of these topological modes with the FQH environment, however, may cause poisoning events affecting this degree of freedom which we model by jump operators that describe incoherent coupling of PFs with FQH edge modes. We analyse how this gives rise to a characteristic three-level telegraph noise in the current, constituting a very strong signature of PFs. We discuss also other forms of poisoning and noise caused by interaction with fractional quasiparticles in the bulk of the Hall system. We conclude our work with an analysis of four-PF devices, in particular on how the PF fusion algebra can be observed in electrical transport experiments.

Tunable couplings between location-insensitive emitters mediated by an epsilon-near-zero plasmonic waveguide.

This work demonstrates the efficient tuning of incoherent and coherent coupling between emitters embedded in an epsilon-near-zero (ENZ) waveguide coated with a multilayer graphene. As a result, a tunable two-qubit quantum phase gate based on the ENZ waveguide is realized at the cutoff frequency. Furthermore, due to the vanishingly small permittivity of the ENZ waveguide, all incoherent coupling between any two identical emitters located in the central area of the slit approaches a maximum, enabling near-ideal bipartite and multipartite entanglement. The coherent coupling between emitters is much larger at an operating frequency far from the ENZ resonance frequency than at the cutoff frequency, and the coherent coupling and resulting energy transfer efficiency can also be effectively tuned by the Fermi level of graphene. These results demonstrate an efficiently tunable electro-optical platform for quantum devices.

Hermitian Nonlinear Wave Mixing Controlled by a PT-Symmetric Phase Transition.

While non-Hermitian systems are normally constructed through incoherent coupling to a larger environment, recent works have shown that under certain conditions coherent couplings can be used to similar effect. We show that this new paradigm enables the behavior associated with the PT-symmetric phase of a non-Hermitian subsystem to control the containing Hermitian system through the coherent couplings. This is achieved in parametric nonlinear wave mixing where simultaneous second harmonic generation replaces the role of loss to induce non-Hermitian behavior that persists through a full exchange of power within the Hermitian system. These findings suggest a new approach for the engineering of dynamics where energy recovery and sustainability are of importance that could be of significance for photonics and laser science.

Coupling‐Induced Tunable Broadband Superradiance in 2D Metal‐Dielectric‐Metal Nanocavity Arrays

AbstractSubradiance/superradiance, cooperative effects causing suppressed/enhanced radiative decay, are of particular interest in plasmonic systems as they play a very important role in modulating dampings and optical properties of resonant systems. However, subradiance/superradiance are generally limited in narrow spectral range with inaccessible tunability. Realizing broadband subradiant and superradiant plasmon modes with flexible tuning is still challenging. Here, a 2D periodic multilayer metal‐dielectric‐metal (MDM) nanostructure is rationally designed and fabricated to realize a tunable superradiant mode over a broad visible range. Angle‐resolved spectroscopy combined with full quantum calculations reveal a sufficient hybridization of delocalized guided plasmons with localized plasmons and a plasmonic cavity mode, leading to an emissive superradiant hybrid mode over a broadband visible range, which can be readily tuned by controlling the spectral three‐mode overlap. Greatly shortened polariton lifetimes down to 4 fs are achieved as direct consequence of the Rabi phases and considerable incoherent coupling strengths between interacting subsystems. Such a control of plasmon damping by cooperative mode interactions paves the way toward efficient manipulation of light emission for applications requiring bright, fast‐emitting photon sources.

Imaging dynamic exciton interactions and coupling in transition metal dichalcogenides.

Transition metal dichalcogenides (TMDs) are regarded as a possible material platform for quantum information science and related device applications. In TMD monolayers, the dephasing time and inhomogeneity are crucial parameters for any quantum information application. In TMD heterostructures, coupling strength and interlayer exciton lifetimes are also parameters of interest. However, many demonstrations in TMDs can only be realized at specific spots on the sample, presenting a challenge to the scalability of these applications. Here, using multi-dimensional coherent imaging spectroscopy, we shed light on the underlying physics-including dephasing, inhomogeneity, and strain-for a MoSe2 monolayer and identify both promising and unfavorable areas for quantum information applications. We, furthermore, apply the same technique to a MoSe2/WSe2 heterostructure. Despite the notable presence of strain and dielectric environment changes, coherent and incoherent coupling and interlayer exciton lifetimes are mostly robust across the sample. This uniformity is despite a significantly inhomogeneous interlayer exciton photoluminescence distribution that suggests a bad sample for device applications. This robustness strengthens the case for TMDs as a next-generation material platform in quantum information science and beyond.

Thermal induced polarization coupling in double-cladding linearly polarized fiber lasers

In this article, a model is built to analyze the degradation of PER in linearly polarized fiber laser caused by incoherent polarization coupling during the amplification process. The model, for the first time could study the effect of heat on birefringence and the incoherent coupling process during the double-cladding linearly polarized fiber lasers’ amplification process. The model could well explain the PER degradation in our 340 W tandem pumped fiber laser and direct pumped fiber lasers in other groups’ reports. Also, the PER maintenance capability of tandem pumping and direct pumping is first analyzed.

Strong coupling between excitons in a two-dimensional atomic crystal and quasibound states in the continuum in a two-dimensional all-dielectric asymmetric metasurface

We investigate the interaction between excitons in a two-dimensional atomic crystal and quasibound states in the continuum (q-BIC) in a two-dimensional all-dielectric asymmetric metasurface. By introducing coherent and incoherent coupling terms in a coupled oscillator model, we demonstrate the coexistence of coherent and incoherent coupling processes in the strongly coupled system and the resultant sub/superradiant polariton states. Based on the multipole decomposition method and near-field analysis of full wave simulations, we study the microscopic excitation of multipole components in q-BIC and their coupling to excitons. We reveal that not only the magnetic dipole but also the interference between electric dipole and its toroidal counterpart dominate in the exciton-BIC strong coupling regime. The fractions of the magnetic and electric dipole ingredients are modulated by the topology of the two-dimensional all-dielectric metasurface, exhibiting distinctly different features in the high- and low-energy hybrid modes in the strong coupling system. Our findings are expected to be of importance for both fundamental research in TMD-based light-matter interactions and practical applications in the design of novel, tunable exciton-polariton devices with high compactibility.

Generating high-order quantum exceptional points in synthetic dimensions

Recently, there has been intense research in proposing and developing various methods for constructing high-order exceptional points (EPs) in dissipative systems. These EPs can possess a number of intriguing properties related to, e.g., chiral transport and enhanced sensitivity. Previous proposals to realize non-Hermitian Hamiltonians (NHHs) with high-order EPs have been mainly based on either direct construction of spatial networks of coupled modes or utilization of synthetic dimensions, e.g., mapping of spatial lattices to time or photon-number space. Both methods rely on the construction of effective NHHs describing classical or postselected quantum fields, which neglect the effects of quantum jumps and which, thus, suffer from a scalability problem in the quantum regime, when the probability of quantum jumps increases with the number of excitations and dissipation rate. Here, by considering the full quantum dynamics of a quadratic Liouvillian superoperator, we introduce a simple and effective method for engineering NHHs with high-order quantum EPs, derived from evolution matrices of system operator moments. That is, by quantizing higher-order moments of system operators, e.g., of a quadratic two-mode system, the resulting evolution matrices can be interpreted as alternative NHHs describing, e.g., a spatial lattice of coupled resonators, where spatial sites are represented by high-order field moments in the synthetic space of field moments. Notably, such a mapping allows correct reproduction of the results of the Liouvillian dynamics, including quantum jumps. As an example, we consider a $U(1)$-symmetric quadratic Liouvillian describing a bimodal cavity with incoherent mode coupling, which can also possess $\mathrm{anti}\text{\ensuremath{-}}\mathcal{P}\mathcal{T}$ symmetry, whose field moment dynamics can be mapped to an NHH governing a spatial network of coupled resonators with high-order EPs.

Generation of domain-wall solitons in an anomalous dispersion fiber ring laser* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11874040, 11904327, and 61905222), Foundation for Leading Talents of Minhang, Shanghai, and the Specialized Research Fund for the Doctoral Program of Zhengzhou University of Light Industry (Grant No. 0170-13501050036).

We report experimental observations performed using a net anomalous dispersion Er-doped fiber ring laser without polarization-selective elements, highlighting the domain-wall solitary pulses generated under the incoherent polarization coupling. By adjusting the pump power and the polarization state appropriately, bright and dark solitons can stably co-exist in the cavity, both centered at 1562.16 nm with a 3-dB spectral width of ∼ 0.15 nm and a repetition rate of 3.83 MHz. Moreover, the 0.8 mm long thulium-doped fiber (TDF) facilitated the mode-locking and self-starting of the laser. This is the first demonstration of a laser being used to generate bright and dark solitons synchronously while using TDF as the saturable absorber (SA). Except possessing the all-fiber structure, the laser exhibits good stability, which may have a significant influence on improvement of the pulse-laser design, and may broaden practical applications in optical sensing, optical communication, and soliton multiplexed systems.

Bounds on edge shear layer persistence while approaching the density limit

This paper details the theory of edge shear layer collapse as the density approaches the Greenwald density limit. It significantly extends earlier work, which was restricted in applicability. The zonal shear flow screening length is calculated for banana, plateau and Pfirsch–Schluter regimes. Poloidal field scaling persists in the plateau regime. Neoclassical screening and drift wave–zonal flow dynamics are combined in a theory, which is then reduced to a predator–prey model. Zonal noise, due to incoherent mode coupling, is retained. The threshold condition for edge shear layer collapse is computed, and linked to a critical value of the dimensionless parameter . Here is the ion sound radius, is the zonal flow screening length and is the equilibrium density scale length. The limiting initial edge density for shear layer collapse is derived and shown to scale favorably with the plasma current. The results are discussed in light of the density limit and Ohmic phenomenology.

Dark-bright soliton trapping in a fiber laser.

We report, to the best of our knowledge, the first experimental observation of coexistence of scalar dark and bright solitons in a fiber laser operating in the near zero-dispersion regime. We show that because of the incoherent cross coupling, under suitable conditions a bright soliton formed in the net anomalous cavity dispersion regime could bind with a dark soliton formed in the net normal cavity dispersion regime in a fiber laser. The properties of the dark and bright solitons, as well as their bound states, are experimentally investigated. The numerical simulations based on the coupled Ginzburg-Landau equations have reproduced the experimental results well.

Rogue waves of ultra-high peak amplitude: a mechanism for reaching up to a thousand times the background level

We unveil a mechanism enabling a fundamental rogue wave, expressed by a rational function of fourth degree, to reach a peak amplitude as high as a thousand times the background level in a system of coupled nonlinear Schrödinger equations involving both incoherent and coherent coupling terms with suitable coefficients. We obtain the exact explicit vector rational solutions using a Darboux-dressing transformation. We show that both components of such coupled equations can reach extremely high amplitudes. The mechanism is confirmed in direct numerical simulations and its robustness is confirmed upon noisy perturbations. Additionally, we showcase the fact that extremely high peak-amplitude vector fundamental rogue waves (of about 80 times the background level) can be excited even within a chaotic background field .

Polarization domain splitting and incoherently coupled dark-bright vector soliton formation in single mode fiber lasers

We have experimentally investigated the polarization dynamics of a weakly birefringent cavity single mode fiber laser under different laser operation conditions. We show features of polarization domain formation, domain splitting, and domain shaping into dark-bright vector solitons under incoherent cross-polarization coupling.

Enhanced coherent interaction between monolayer WS2 and film-coupled nanocube open cavity with suppressed incoherent damping pathway

Future quantum information devices will most likely rely on the realization of coherent light-matter interactions in strong coupling regime and the maintaining of the coherence with minimized incoherent damping pathways. Here, utilizing film-coupled planar nanoparticle supporting unique plasmon-induced magnetic resonance (PIMR), we theoretically study a strong coupling of a single nanocube to a monolayer of two-dimensional atomic crystal. We demonstrate that the nanocube-based planar configuration with magnetic flux passing through the dielectric layer exhibits much higher in-plane field confinement with respect to traditional plasmon electric modes, leading to an efficient coherent coupling to only a few in-plane excitonic dipoles with a record of normal mode splitting over 280 meV. Importantly, a much reduced incoherent coupling strength down to 3 meV is obtained. We reveal that the underlying mechanism lies in two main facts: (i) the small radiative damping rate of the excitonic system giving very limited contribution to the linewidth broadening of the A-exciton resonance, and (ii) the excitation of magnetic resonance provides a net electric dipole moment orientating mainly normal to the film surface, thus greatly suppressing the exchange of photons between the two subsystems via the continuum reservoir. The numerical simulations and theoretical analysis quantitatively evaluate the dependence of both the coherent and incoherent coupling strength on the thickness of the dielectric layer, revealing the fact that coherent/incoherent coupling strength can be simultaneously enhanced/suppressed with the decrease/increase of the film thickness, which can be appropriately designed to achieve the optimal coherent coupling with minimized incoherent coupling strength. Such hybrid nanostructure with simple geometry and ease of fabrication may not only offer as an attractive platform to explore light-matter interaction in the strong coupling regime but also show potential applications in realizing novel quantum and nanophotonic optical devices.

Liouvillian exceptional points of any order in dissipative linear bosonic systems: Coherence functions and switching between PT and anti- PT symmetries

Usually, when investigating exceptional points (EPs) of an open Markovian bosonic system, one deals with spectral degeneracies of a non-Hermitian Hamiltonian (NHH), which can correctly describe the system dynamics only in the semiclassical regime. A recently proposed quantum Liouvillian framework enables to completely determine the dynamical properties of such systems and their EPs (referred to as Liouvillian EPs, or LEPs) in the quantum regime by taking into account the effects of quantum jumps, which are ignored in the NHH formalism. Moreover, the symmetry and eigenfrequency spectrum of the NHH become a part of much larger Liouvillian eigenspace. As such, the EPs of an NHH form a subspace of the LEPs. Here we show that once an NHH of a dissipative linear bosonic system exhibits an EP of a certain finite order $n$, it immediately implies that the corresponding LEP can become of any higher order $m\geq n$, defined in the infinite Hilbert space. Most importantly, these higher-order LEPs can be identified by the coherence and spectral functions at the steady state. The coherence functions can offer a convenient tool to probe extreme system sensitivity to external perturbations in the vicinity of higher-order LEPs. As an example, we study a linear bosonic system of a bimodal cavity with incoherent mode coupling to reveal its higher-order LEPs; particularly, of second and third order via first- and second-order coherence functions, respectively. Accordingly, these LEPs can be additionally revealed by squared and cubic Lorentzian spectral lineshapes in the power and intensity-fluctuation spectra. Moreover, we demonstrate that these EPs can also be associated with spontaneous parity-time (${\cal PT}$) and anti-${\cal PT}$-symmetry breaking in the system studied.

Plasmon-plasmon interactions supported by a one-dimensional plasmonic crystal: Rabi phase and generalized Rabi frequency

Plasmon-plasmon interactions are key in controlling light at the nanoscale and in the development of high-performance plasmonic devices. Sophisticated design and efficient dynamic control of such devices requires a precise description of both spectral responses and ultrafast temporal dynamics in plasmon-plasmon coupling systems. Here, a microscopic model based on the Heisenberg-Langevin formalism is developed for generic plasmon-plasmon interacting systems. The validity of the model was experimentally supported by precisely reproducing the output spectra of interacting plasmons in a one-dimensional plasmonic crystal. We discussed the inheritance from an initial phase to the Rabi phase, which is accompanied by the vacuum fluctuations dephasing the incoherent coupling channel. We further derived the generalized Rabi frequency between two coupled plasmonic modes. We demonstrate that the interplay between the Rabi phase and the coupling-induced incoherent damping process modulates the ultrafast dynamics of the polariton modes, resulting in distinctly different spectral responses including the degeneracy and reversing in the polariton branches. Our model can be readily extended to any other bosonic coupling systems such as interacting nanoparticles and photonic/plasmonic cavities, thus holding great promise and potential applications in nanocircuits and cavity QED.

Dissipative dark-bright vector solitons in fiber lasers

We present detailed studies on dark-bright vector solitons formed in dispersion- and birefringence-managed fiber lasers sustained by either incoherent or coherent cross-polarization coupling. We show that even under strong influence of the gain bandwidth limitation, coupled dark-bright solitons can still be formed in a fiber laser. Unique features of the dissipative dark-bright vector solitons are studied both numerically and experimentally, and compared with those of the vector solitons formed in nonlinear Schr\odinger equation systems.