We reinvestigate the famous Mollow triplet and show that most of the well-known quantum characteristics of the Mollow triplet-including incoherent emission and a nonstandard dependence of the sidebands on detuning-can be recovered quantitatively using semiclassical dynamics with a classical light field. In fact, by not relying on the rotating wave approximation, a semiclassical model predicts some quantum effects beyond the quantum optical Bloch equation, including higher-order scattering and asymmetric sideband features. This Letter highlights the fact that, with strong intensities, many putatively quantum features of light-matter interactions arise from a simple balance of mean-field electrodynamics and elementary spontaneous emission, which requires minimal computational cost. Our results suggest that the application of semiclassical electrodynamics to problems with strong light-matter coupling in the fields of nanophotonics and superradiance are likely to yield a plethora of new information.
We reinvestigate the famous Mollow triplet and show that most of the well-known quantum characteristics of the Mollow triplet-including incoherent emission and a nonstandard dependence of the sidebands on detuning-can be recovered quantitatively using semiclassical dynamics with a classical light field. In fact, by not relying on the rotating wave approximation, a semiclassical model predicts some quantum effects beyond the quantum optical Bloch equation, including higher-order scattering and asymmetric sideband features. This Letter highlights the fact that, with strong intensities, many putatively quantum features of light-matter interactions arise from a simple balance of mean-field electrodynamics and elementary spontaneous emission, which requires minimal computational cost. Our results suggest that the application of semiclassical electrodynamics to problems with strong light-matter coupling in the fields of nanophotonics and superradiance are likely to yield a plethora of new information.
Subwavelength arrays of quantum two-level emitters have emerged as an interesting platform displaying prominent collective effects that can be harnessed for applications. Here, we study such arrays under strong coherent driving, realizing an open quantum many-body problem in a strongly nonlinear regime. For this we introduce an approach to this problem in terms of a dynamical mean-field theory, paving the way for further studies. We show that the spectrum of scattered light, characterized by the famous Mollow triplet for a single atom, develops a characteristic line shape with flat sidebands determined by dipolar interactions and relevant for experiments. Remarkably, this is to some extent independent of the specific geometry, but is sensitive to the ordered arrangement of the atoms. This line shape therefore characterizes atomic arrays and distinguishes them from disordered ensembles and noninteracting emitters. Published by the American Physical Society 2024
We study the general problem of matter-laser interaction within the framework of nonrelativistic quantum electrodynamics, with particular emphasis on strong laser field effects. Consequently, we formulate a well-defined approximation leading in a straightforward manner toward the conventional semiclassical mode of description. Namely, we arrive naturally to two coupled equations of motion: (i) the Schr\"odinger equation which governs the quantum dynamics of an atomic system driven by classically described radiation field (composed of an incoming laser pulse plus radiation emitted from the atom), and (ii) the classical Maxwell wave equation which describes the emission of radiation from the mentioned atomic source. Employing the formalism of adiabatic Floquet theory, we derive a simple criterion of validity of the just described semiclassical approach. It shows that the semiclassical treatment is justified in most situations. On the other hand, it turns out that the semiclassical approximation breaks down completely in certain special but realistic cases, regardless of the fact that the incoming laser pulse contains a huge number of photons. Under such special circumstances, we anticipate new effects arising due to the quantized nature of the radiation field, to be observable, for example, in harmonic generation spectra. Our considerations are illustrated more explicitly using a simple model of a two-level atom strongly driven by a laser. The quantum dynamics of this model problem is resolved within the framework of quantum electrodynamics while adopting well-defined and physically justifiable approximations. As an outcome, analytic formulas are found serving as a quantitative criterion of (non)applicability of the semiclassical approach and demonstrating the breakdown of semiclassical theory under well-defined conditions. An illustrative numerical calculation is provided.
The Mollow triplet is the definitive spectral signature of an optically dressed quantum emitter. We predict that for emitters coupled to localized phonons, this signature is not confined to the zero-phonon line. Under a strong resonant drive, we show that Mollow triplets are strikingly replicated on the associated phonon sidebands -a surprising result, given that phonon sidebands are typically viewed as incoherent, inelastic scattering pathways. These vibronic Mollow triplets are a direct fingerprint of dynamically generated dressed states that hybridize the emitter's electronic, photonic, and vibrational degrees of freedom. We develop a scalable analytical formalism to model this effect in complex, multi-mode molecular systems, such as dibenzoterrylene. Our work provides the precise driving conditions for observing these novel spectral features, establishing a new signature of coherence in vibronically coupled systems.
The Mollow triplet is a fundamental signature of quantum optics and has been observed in numerous quantum systems. Although it arises in the ``strong driving'' regime of the quantized field, where the atoms undergo coherent oscillations, it can be typically analyzed within the rotating wave approximation. Here we report the first observation of high-order effects in the Mollow triplet structure due to strong driving. In experiments, we explore the regime beyond the rotating wave approximation using concatenated continuous driving that has less stringent requirements on the driving field power. We are then able to reveal additional transition frequencies, shifts in energy levels, and corrections to the transition amplitudes. In particular, we find that these amplitudes are more sensitive to high-order effects than the frequency shifts and that they still require an accurate determination in order to achieve high-fidelity quantum control. The experimental results are validated by Floquet theory, which enables the precise numerical simulation of the evolution and further provides an analytical form for an effective Hamiltonian that approximately predicts the spin dynamics beyond the rotating wave approximation.
We study a two-level system (atom, superconducting qubit, or quantum dot) strongly coupled to a single photonic mode of a cavity, in the presence of incoherent pumping and including detuning and dephasing. This system displays a striking quantum-to-classical transition. On the grounds of several approximations that reproduce to various degrees exact results obtained numerically, we separate five regimes of operations, that we term ``linear,'' ``quantum,'' ``lasing,'' ``quenching,'' and ``thermal.'' In the fully quantized picture, the lasing regime arises as a condensation of dressed states and manifests itself as a Mollow triplet structure in the direct emitter photoluminescence spectrum, which embeds fundamental features of the full-field quantization description of light-matter interaction.
The coherent interaction between a two-level system and electromagnetic fields serves as a foundation for fundamental quantum physics and modern photonic quantum technology. A profound example is resonance fluorescence, where the non-classical photon emission appears in the form of a Mollow-triplet when a two-level system is continuously driven by a resonant laser. Pushing resonance fluorescence from a static to dynamic regime by using short optical pulses generates on-demand emissions of highly coherent single photons. Further increasing the driving strength in the dynamical regime enables the pursuit of exotic non-classical light emission in photon number superposition, photon number entanglement, and photon bundle states. However, the long-sought-after spectrum beyond the Mollow-triplet, a characteristic of dynamic resonance fluorescence under strong driving strength, has not been observed yet. Here we report the direct observation and systematic investigations of dynamic resonance fluorescence spectra beyond the Mollow-triplet in a solid-state cavity quantum electrodynamic system. The dynamic resonance fluorescence spectra with up to five pairs of side peaks, excitation detuning induced spectral asymmetry, and cavity filtering effect are observed and quantitatively modeled by a full quantum model with phonon scattering included. Time-resolved measurements further reveal that the multiple side peaks originate from interference of the emission associated with different temporal positions of the excitation pulses. Our work facilitates the generation of a variety of exotic quantum states of light with dynamic driving of two-level systems.