Spontaneous Emission Dynamics Research Articles

Geometrical parameter dependency of non-Markovian and quantum speed limit measures in the spontaneous emission dynamics of a qubit near a plasmonic nanodisk

Geometrical parameter dependency of non-Markovian and quantum speed limit measures in the spontaneous emission dynamics of a qubit near a plasmonic nanodisk

Spontaneous emission dynamics of giant atom controlled by quantum coherent feedback

Spontaneous emission dynamics of giant atom controlled by quantum coherent feedback

Strong Coupling Dynamics of a Quantum Emitter near a Topological Insulator Nanoparticle.

We study the spontaneous emission dynamics of a quantum emitter near a topological insulator Bi2Se3 spherical nanoparticle. Using the electromagnetic Green's tensor method, we find exceptional Purcell factors of the quantum emitter up to 1010 at distances between the emitter and the nanoparticle as large as half the nanoparticle's radius in the terahertz regime. We study the spontaneous emission evolution of a quantum emitter for various transition frequencies in the terahertz and various vacuum decay rates. For short vacuum decay times, we observe non-Markovian spontaneous emission dynamics, which correspond perfectly to values of well-established measures of non-Markovianity and possibly indicate considerable dynamical quantum speedup. The dynamics turn progressively Markovian as the vacuum decay times increase, while in this regime, the non-Markovianity measures are nullified, and the quantum speedup vanishes. For the shortest vacuum decay times, we find that the population remains trapped in the emitter, which indicates that a hybrid bound state between the quantum emitter and the continuum of electromagnetic modes as affected by the nanoparticle has been formed. This work demonstrates that a Bi2Se3 spherical nanoparticle can be a nanoscale platform for strong light-matter coupling.

Observation of electronic spectra modulation in a CH3NH3PbBr3 crystal by utilizing transient absorption microscopy

Organic–inorganic lead halide perovskite materials have attractive properties not only for solar cells but also for LED because of their high performance and wavelength tunability. Such an efficient light-emitting and lasing nature are indispensable for their applications, and the essential needs are miniaturization and low lasing threshold. One material that satisfies these requirements is lead halide perovskite. To understand the time evolution of the interaction between light and matter in a perovskite crystal system, it is necessary to reveal the carrier dynamics in each crystal. In this study, the transient absorption spectra of CH3NH3PbBr3 crystals were measured using a femtosecond transient absorption microscopy. Surprisingly, strong spectra modulation has been observed and these results indicate the charge separation on the surface of the crystal. Amplified spontaneous emission dynamics were also observed in the transient absorption spectra.

Collective photon emission of two correlated atoms in free space

By preparing two distant emitters in entangled Dicke states via detection of a single photon, the subsequent spatiotemporal photon emission is investigated. Depending on the parity of the established quantum state, emission patterns for the second scattered photon are observed featuring spatial superradiance as well as subradiance. We employ ultrafast single-photon resolving cameras with high spatial resolution disclosing the spatiotemporal emission characteristics. By recording the first photon in one direction and the second photon in another, revealing the spatial two-photon cross-correlation function ${g}^{(2)}({\mathbf{r}}_{1},{\mathbf{r}}_{2})$, we characterize the collective spontaneous emission behavior of two ions in free space. We explain the observed contrast of ${g}^{(2)}({\mathbf{r}}_{1},{\mathbf{r}}_{2})$ considering independently derived experimental parameters. Our results show how the detection of a single photon can profoundly modify the collective spontaneous emission dynamics of an atomic ensemble.

Generalized transfer matrix model for dipole radiation-dynamics modification in layered media: application to incoherent light-emitting structures in thin film geometry

Incoherent light-emitting structures are of key interest for many fields in optoelectronics and spontaneous emission is the physical phenomenon underlying their light emission process. In this paper, we propose a novel full-matrix algebraic framework for modeling spontaneous emission modification from radiating electric dipoles in layered media. This formalism generalizes the standard 2 × 2 transfer-matrices into a compact 3 × 3 framework, which thus allows to treat dipole radiation directly into the matrix formulation as a source matrix. Its accuracy has been confirmed by incoherent 3D-FDTD. It has then been extended to complex emitter regions with both spectral and spatial distributions using incoherent combination. Finally, we applied this approach to various examples to demonstrate its applicability. Since it only requires modest computational efforts, we hope that this model can help better understand spontaneous emission dynamics in layered media and thus pave the way to novel design guidelines for devices in many fields of optoelectronics.

Anomalous spontaneous emission dynamics at chiral exceptional points.

An open quantum system operated at the spectral singularities where dimensionality reduces, known as exceptional points (EPs), demonstrates distinguishing behavior from the Hermitian counterpart. Here, we present an analytical description of local density of states (LDOS) for microcavity featuring chiral EPs, and unveil the anomalous spontaneous emission dynamics from a quantum emitter (QE) due to the non-Lorentzian response of EPs. Specifically, we reveal that a squared Lorentzian term of LDOS contributed by chiral EPs can destructively interfere with the linear Lorentzian profile, resulting in the null Purcell enhancement to a QE with special transition frequency, which we call EP induced transparency. While for the case of constructive interference, the squared Lorentzian term can narrow the linewidth of Rabi splitting even below that of bare components, and thus significantly suppresses the decay of Rabi oscillation. Interestingly, we further find that an open microcavity with chiral EPs supports atom-photon bound states for population trapping and decay suppression in long-time dynamics. As applications, we demonstrate the advantages of microcavity operated at chiral EPs in achieving high-fidelity entanglement generation and high-efficiency single-photon generation. Our work unveils the exotic cavity quantum electrodynamics unique to chiral EPs, which opens the door for controlling light-matter interaction at the quantum level through non-Hermiticity, and holds great potential in building high-performance quantum-optics devices.

Radiative properties of an artificial atom coupled to a Josephson-junction array

We study the radiative properties -- the Lamb shift, Purcell decay rate and the spontaneous emission dynamics -- of an artificial atom coupled to a long, multimode cavity formed by an array of Josephson junctions. Introducing a tunable coupling element between the atom and the array, we demonstrate that such a system can exhibit a crossover from a perturbative to non-perturbative regime of light-matter interaction as one strengthens the coupling between the atom and the Josephson junction array (JJA). As a consequence, the concept of spontaneous emission as the occupation of the local atomic site being governed by a single complex-valued exponent breaks down. This breakdown, we show, can be interpreted in terms of formation of hybrid atom-resonator modes with radiative losses that are non-trivially related to the effective coupling between individual modes. We develop a singular function expansion approach for the description of the open quantum system dynamics in such a multimode non-perturbative regime. This modal framework generalizes the normal mode description of quantum fields in a finite volume, incorporating exact radiative losses and incident quantum noise at the delimiting surface. Our results are pertinent to recent experiments with Josephson atoms coupled to high impedance Josephson junction arrays.

Memory effects and quantum speedup for a quantum emitter near a molybdenum disulfide nanodisk

We study memory effects (non-Markovian evolution) in the spontaneous emission dynamics of a quantum emitter near a molybdenum disulfide nanodisk by going beyond the analysis of the reversible population dynamics of the excited state and considering the dynamics of the non-Markovian open system. Specifically, we quantify the non-Markovian spontaneous emission dynamics using different non-Markovianity measures and also investigate the potential quantum speed up of the dynamics in relation to its non-Markovian features. We find that the values of the non-Markovianity measures and of the potential quantum speed up are large under strong coupling conditions, while in both cases the non-Markovianity measures and the quantum speed up decreases as the coupling between the emitter and the nanodisk becomes weaker. A comparison of the different non-Markovianity measures is also presented for the system under study. • Memory effects in the photon emission of a quantum emitter next to a MoS 2 nanodisk are analyzed. • The system is treated as a non-Markovian open quantum system . • For obtaining the results, we use a combination of quantum dynamics calculations with electromagnetic calculations. • Results for different non-Markovianity measures are presented. • The quantum speed limit of the quantum emitter next to the MoS 2 nanodisk is also calculated.

Control of spontaneous emission dynamics in microcavities with chiral exceptional surfaces

The authors show how chiral exceptional surfaces can be used to tune the spontaneous emission rate from a single quantum emitter inside an optical microcavity, from total suppression to a two fold enhancement compared to a similar cavity operating at a diabolic point.

Spontaneous emission dynamics of Eu3+ ions coupled to hyperbolic metamaterials

Sub-wavelength nanostructured systems with tunable electromagnetic properties, such as hyperbolic metamaterials (HMMs), provide a useful platform to tailor spontaneous emission processes. Here, we investigate a system comprising Eu3+(NO3)3·6H2O nanocrystals on an HMM structure featuring a hexagonal array of Ag nanowires in a porous Al2O3 matrix. The HMM-coupled Eu3+ ions exhibit up to a 2.4 fold increase in their decay rate, accompanied by an enhancement of the emission rate of the 5D0 → 7F2 transition. Using finite-difference time-domain modeling, we corroborate these observations with the increase in the photonic density of states seen by the Eu3+ ions in the proximity of the HMM. Our results indicate that HMMs can serve as a valuable tool to control the emission from weak transitions and, hence, hint at a route toward more practical applications of rare-earth ions in nanoscale optoelectronics and quantum devices.

Cavity-enhanced light–matter interaction in Vogel-spiral devices as a platform for quantum photonics

Enhancing light–matter interactions on a chip is of paramount importance for classical and quantum photonics, sensing, and energy harvesting applications. Several photonic geometries have been developed, allowing high extraction efficiencies, enhanced light–matter interactions, and control over the spontaneous emission dynamics of solid-state quantum light sources. To this end, a device geometry resilient to nanofabrication imperfections, providing high-quality light confinement and control over the emitted light properties, would be desirable. We demonstrate that aperiodic arrangements, whose geometry is inspired by natural systems where scattering elements are arranged following Fibonacci series, represent a platform for enhancing the light–matter interaction in on-chip nanophotonic devices, allowing us to achieve efficient visible light confinement. We use optically active defect centers in silicon nitride as internal light sources to image and characterize, by means of microphotoluminescence spectroscopy, the individual optical modes confined by photonic membranes with Vogel-spiral geometry. By studying the statistics of the measured optical resonances, in combination with rigorous multiple scattering theory, we observe lognormal distributions and report quality factors with values as high as 2201 ± 443. Our findings improve the understanding of the fundamental physical properties of light-emitting Vogel-spiral systems and show their application to active nanophotonic devices. These results set the basis for further development of quantum devices that leverage the unique properties of aperiodic Vogel spiral order on a chip, including angular momentum states, thus producing mode structures for information processing and communications.

Cavity quantum electro-dynamics with solid-state emitters in aperiodic nano-photonic spiral devices

Integrated quantum devices are at the basis of the realization of scalable, high-performance quantum technology, including quantum computers and quantum communication schemes, where single photons are emitted, guided, manipulated, and detected on a chip. Engineered nano-devices enable the efficient confinement of light and, ultimately, the control of the spontaneous emission dynamics of single emitters, which is crucial for cavity quantum electrodynamics experiments and for the development of classical and quantum light sources. Here, we report on the demonstration of enhanced light-matter interaction and Purcell effects on a chip, based on bio-inspired aperiodic devices fabricated in gallium arsenide. Indium arsenide single quantum dots are used as internal light sources to image, by means of micro-photoluminescence spectroscopy, the optical modes supported by photonic membranes with Vogel-spiral geometry. These emitters are also used to probe the density of optical states, modified by the aperiodic devices, by means of time-resolved spectroscopy. Our results show cavity quantum electrodynamics effects providing strong modifications of the spontaneous emission decay of single optical transitions. In particular, thanks to the significant modification of the density of optical states demonstrated in Vogel-spiral photonic structures, we show control of the decay lifetime of single emitters with a dynamic range reaching 20, thus opening the path to the implementation of aperiodic geometries in active classical and quantum devices.

Non-Markovian Spontaneous Emission Dynamics of a Quantum Emitter Near a Transition-Metal Dichalcogenide Layer

We investigate the spontaneous emission dynamics of a two-level quantum emitter near a transition-metal dichalcogenide layer, specifically, a tungsten disulfide (WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) layer. The optical response of the WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer is obtained by electromagnetic calculations using parameters by experimental data. We find that depending on the distance between the quantum emitter, and the WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer the spontaneous decay can be enhanced up to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> compared with its free-space value for an emitter with transition dipole moment oriented perpendicular or tangential to the layer. We also perform quantum dynamical calculations, which indicate that the emitter's spontaneous emission dynamics changes from Markovian to weakly non-Markovian to clearly non-Markovian, featuring decaying population oscillations, as the coupling grows from relatively weak to strong, depending on the distance of the emitter to the layer, and the emitter's free-space decay rate. For quantum emitters with fast free-space decay times placed at close distances to the WS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer, the ultrastrong coupling regime can be reached, and we find that a significant amount of the initial population of the quantum emitter can remain trapped in it. We also quantify non-Markovianity using different measures. Similar results can also be obtained for other transition-metal dichalcogenide layers, like a tungsten diselenide (WSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) layer.

Spontaneous decay processes in a classical strong low-frequency laser field

The spontaneous emission of an excited two-level emitter driven by a strong classical coherent low-frequency electromagnetic field is investigated. We find that for relatively strong laser driving, multi-photon processes are induced, thereby opening additional decay channels for the atom. We analyze the interplay between the strong low-frequency driving and the interfering multiphoton decay channels, and discuss its implications for the spontaneous emission dynamics.

Investigation of spontaneous emission dynamics of dye molecules coupled into transverse Anderson localized cavities in a hyperbolic waveguide

Spontaneous emission dynamics of rhodamine 6G molecules coupled into transverse Anderson localized modes in a hyperbolic waveguide is investigated using time-resolved experiments. Four hyperbolic waveguides are simultaneously formed inside a deltoid-shaped fused-silica microtube via the capillary effect. The disordered photonic environment consisting of a rhodamine-doped polymeric material with randomly distributed air inclusions is attributed to localize photons at various resonant wavelengths of the quasi-optical cavities, randomly positioned throughout the guiding medium. The hyperbolic waveguides allow obtaining a single, double, and multimode resonant structures, trapping photons at various frequencies as explored in the form of sharp spectral resonances within the photoluminescence spectrum bandwidth of the dye molecules. Experimental results reveal that the coupling of the fluorescent emitters into multimode localizations in each hyperbolic waveguide corresponds to obtaining quasi-optical cavities at various resonant frequencies, which alter the emission characteristics of the emitters distinctively. The spontaneous emission rate of the dye molecules coupled into the isolated transverse Anderson localized modes is observed to increase by a factor of up to 6.7; thus, the vacuum fluctuations at certain resonant wavelengths are considerably enhanced.

Non-Markovian spontaneous emission dynamics of a quantum emitter near a MoS2 nanodisk

We introduce a photonic nanostructure made of two dimensional materials that can lead to non-Markovian dynamics in the spontaneous emission of a nearby quantum emitter. Specifically, we investigate the spontaneous emission dynamics of a two-level quantum emitter with picosecond free-space decay time, modelling J-aggregates, close to a MoS$_2$ nanodisk. Reversible population dynamics in the quantum emitter is obtained when the emitter's frequency matches the frequency of an exciton-polariton resonance created by the nanodisk. When such isolated resonances exist, decaying Rabi oscillations may occur. The overlapping of exciton-polariton resonances also affects strongly the decay dynamics at close distances to the nanodisk, giving rise to complex decaying population oscillations. At very close distances of the emitter to the nanodisk the ultrastrong coupling regime appears, where after a very fast oscillatory partial decay of the initial population, the emitter rest population remains constant over long times and population trapping occurs. The size and material quality of the nanodisk is shown to be of lesser influence on the above results.

Accelerating spontaneous emission in open resonators

Strength of light‐matter interactions and radiative dynamics of emitters could be controlled with structuring of electromagnetic environment. While local and cross density of electromagnetic states are routinely used for predicting total and radiative decay rates in the weak coupling regime, resonant nanostructures offer going beyond this description, giving rise to new phenomena. Correlated time‐evolution of a strongly coupled emitter‐nanoresonator system and nonradiative channels are shown here to predefine the radiative decay dynamics and lead to substantial shortening in characteristic emission times. Quantum formalism, based on stochastic Hamiltonian treatment of radiative and nonradiative processes, was generalized for describing light‐matter interactions in vicinity of open nano‐resonators. The developed theory was subsequently applied to spontaneous emission dynamics of emitters, situated next to metal surfaces, supporting stopped light resonant conditions. Over four orders of magnitude lifetime shortening was predicted to be detectable in the far‐field. The interplay between strong and weak coupling regimes, enabled by resonant nanostructures, could serve as a platform for ultrafast opto‐electronic components, fluorescent labels and others.

Giant gain enhancement in photonic crystals with a degenerate band edge

We propose a new approach leading to giant gain enhancement. It is based on unconventional slow-wave resonance associated with a degenerate band edge (DBE) in the dispersion diagram for a special class of photonic crystals supporting four modes at each frequency. We show that the gain enhancement in a Fabry-P\'erot cavity (FPC) when operating at the DBE is several orders of magnitude stronger when compared to a cavity of the same length made of a standard photonic crystal with a regular band edge (RBE). The giant gain condition is explained by a significant increase in the photon lifetime and in the local density of states. We have demonstrated the existence of DBE operated special cavities that provide for superior gain conditions for solid-state lasers, quantum cascade lasers, traveling wave tubes, and distributed solid-state amplifiers. We also report the possibility to achieve low-threshold lasing in FPC with DBE compared to RBE-based lasers.

Efficient computation of spontaneous emission dynamics in arbitrary photonic structures

Defining a quantum mechanical wavefunction for photons is one of the remaining open problems in quantum physics. Thus quantum states of light are usually treated within the realm of second quantization. Consequently, spontaneous emission (SE) in arbitrary photonic media is often described by Fock space Hamiltonians. Here, we present a real space formulation of the SE process that can capture the physics of the problem accurately under different coupling conditions. Starting from first principles, we map the unitary evolution of a dressed two-level quantum emitter onto the problem of electromagnetic radiation from a self-interacting complex harmonic oscillator. Our formalism naturally leads to an efficient computational scheme of SE dynamics using finite difference time domain method without the need for calculating the photonic eigenmodes of the surrounding environment. In contrast to earlier investigations, our computational framework provides a unified numerical treatment for both weak and strong coupling regimes alike. We illustrate the versatility of our scheme by considering several different examples.