Mollow Triplet Research Articles

Fate of the Mollow triplet in strongly coupled atomic arrays

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

Acceleration-induced spectral beats in strongly driven harmonic oscillators

The harmonic modulation of coherent systems gives rise to a wealth of physical phenomena, e.g., the AC-Stark effect and Mollow triplets, with important implications for coherent control and frequency conversion. Here, we demonstrate a novel regime of temporal coherence in oscillators harmonically driven at extreme energy modulation amplitudes relative to the modulation quantum. The studies were carried out by modulating a confined exciton-polariton Bose-Einstein condensate (BEC) by an acoustic wave. Features of the new regime are the appearance, in the spectral domain, of a comb of resonances termed acceleration beats with energy spacing tunable by the modulation amplitude and, in the time domain, of temporal correlations at time scales much shorter than the acoustic period, which also depend on the modulation amplitude. These features are quantitatively accounted for by a theoretical framework, which associates the beats with accelerated energy-change rates during the harmonic cycle. These observations are underpinned by the high sensitivity of the BEC energy to the acoustic driving, which simultaneously preserves the BEC’s temporal coherence. The acceleration beats are a general feature associated with accelerated energy changes: analogous features are thus also expected to appear under highly accelerated motion e.g., in connection with Cherenkov and Hawking radiation.

Unveiling the interplay of Mollow physics and perturbed free induction decay by nonlinear optical signals of a dynamically driven two-level system

Nonlinear optical signals in optically driven quantum systems can reveal coherences and thereby open up the possibility for manipulation of quantum states. While the limiting cases of ultrafast and continuous-wave excitation have been extensively studied, the time dynamics of finite pulses bear interesting phenomena. In this paper, we explore the nonlinear optical probe signals of a two-level system excited with a laser pulse of finite duration. In addition to the prominent Mollow peaks, the probe spectra feature several smaller peaks for certain time delays. Similar features have been recently observed for resonance fluorescence signals [K. Boos , ]. We discuss that the emergent phenomena can be explained by a combination of Mollow triplet physics and perturbed free induction decay effects, providing an insightful understanding of the underlying physics. Published by the American Physical Society 2024

Mollow triplet in Two-Impurity dumbbell quantum dot

The current study uses various computational methods to determine the eigenvalues and eigenvectors of a specific system—namely, a two-impurity, two-electron system within a dumbbell-shaped quantum dot. Initially, the single-electron, single-impurity problem is resolved using the effective mass approximation and the finite element method. Subsequently, a technique similar to the linear combination of atomic orbitals is applied to derive singlet–triplet states. The research work deeply investigates the key characteristics of the mentioned states, with a particular focus on their energy splitting and exchange times. Additionally, it highlights the dynamic evolution of the singlet–triplet two-level system, illustrating its manipulation through detuning and Rabi frequency. The Mollow triplet spectrum is also calculated and analyzed under various initial conditions. The findings of this research have significant implications across multiple domains, including the advancement of quantum information processing, the enhancement of optoelectronic device performance, and the development of innovative sensing and communication technologies.

Mollow triplets under few-photon excitation

Resonant excitation is an essential tool in the development of semiconductor quantum dots (QDs) for quantum information processing. One central challenge is to enable transparent access to the QD signal without post-selection information loss. A viable path is through cavity enhancement, which has successfully lifted the resonantly scattered field strength over the laser background under weak excitation. Here, we extend this success to the saturation regime using a QD-micropillar device with a Purcell factor of 10.9 and ultra-low background cavity reflectivity of just 0.0089±0.0001. We achieve a signal to background ratio of 55 and overall system responsivity of 3.01±0.08%, i.e., we detect on average 0.03 resonantly scattered single photons for every incident laser photon. Raising the excitation to the few-photon level, the QD response is brought into saturation where we observe Mollow triplets as well as the associated cascaded single photon emissions, without resorting to any laser background rejection technique. Our work offers a perspective on a QD cavity interface that is not restricted by the laser background.

Plasmon-induced quantum interference near an L-shaped nanostructure

In the near-field region of a metallic slab or metallic nanosphere, quantum interference caused by anisotropic spontaneous emission in a multilevel quantum system is a hot research topic. The research on the influence of an anisotropic plasmon nanostructure on quantum interference is expected to open the door for tunability of quantum interference. In this paper, we study an L-shaped plasmon nanostructure, which can provide a high degree of quantum interference for a three-level V-type atom. The research shows that the degree of quantum interference greatly depends on the atomic position and the separation between the atom and the nanostructure. By adjusting the atomic position, tunable peak positions and linewidths of the Mollow triplet can be achieved caused by quantum interference. The proposed system is highly versatile and has potential application in quantum single photon source and some active nanodevices.

Two-level atom dynamics induced by a spin-orbit coupled optical vortex: dressed states formulation

We consider here the interaction of a two-level atom with a tightly focused paraxial optical vortex beam in the dressed states formalism. The interaction is characterized by a term that couples the photon spin angular momentum (SAM) with its orbital angular momentum (OAM). This term affects all the physical quantities related to the dressed states, like their energies, populations, and relaxation rates among them. We also show that the Mollow triplet associated with the resonance fluorescence spectrum of a two-level atom acquires a chiral character. We give numerical examples based on experimentally accessible values of the various parameters, and we show that the chirality can give rise to observable modifications of the various physical quantities under consideration.

Vacuum Rabi Splitting and Kerr Effect of a Hybrid Spin–Magnon–Photon System

AbstractThe vacuum Rabi splitting and Kerr effect are investigated theoretically in a hybrid spin–magnon–photon system, where the nitrogen‐vacancy center in diamond driven by two light fields is coupled to a spherical micromagnet embedded in a superconducting coplanar waveguide resonator. The results indicate that the phenomenon of the Mollow triplet and vacuum Rabi splitting can appear by controlling the spin–magnon coupling and magnon–photon coupling. It is shown that the probe absorption spectrum can be adjusted effectively via the pump frequency detuning. Moreover, it is demonstrated that the optical Kerr effect can be tuned by changing the Rabi frequency. This work may provide a possibility for the applications in quantum information processing and quantum sensing of magnetic signal.

Optomechanical effects in nanocavity-enhanced resonant Raman scattering of a single molecule

In this article, we address the optomechanical effects in surface-enhanced resonant Raman scattering (SERRS) from a single molecule in a nano-particle on mirror (NPoM) nanocavity by developing a quantum master equation theory, which combines macroscopic quantum electrodynamics and electron-vibration interaction within the framework of open quantum system theory. We supplement the theory with electromagnetic simulations and time-dependent density functional theory calculations in order to study the SERRS of a methylene blue molecule in a realistic NPoM nanocavity. The simulations allow us not only to identify the conditions to achieve conventional optomechanical effects, such as vibrational pumping, non-linear scaling of Stokes and anti-Stokes scattering, but also to discovery distinct behaviors, such as the saturation of exciton population, the emergence of Mollow triplet side-bands, and higher-order Raman scattering. All in all, our study might guide further investigations of optomechanical effects in resonant Raman scattering.

Resonance fluorescence of two asymmetrically pumped and coupled two-level systems

We study a driven-dissipative duo of two-level systems in an open quantum systems approach, modelling a pair of atoms or (more generally) meta-atoms. Allowing for complex-valued couplings in the setup, which are of both a coherent and incoherent character, gives rise to a diverse coupling landscape. We consider several points on this landscape, for example where the coupling between the two coupled two-level systems is dominated by coherent, incoherent, unsymmetrical and even unidirectional interactions. Traversing the coupling terrain leads to remarkable features in the populations of the pair, correlations and optical spectra. Most notably, the famous Mollow triplet spectrum for a single atom may be superseded for a pair by a Mollow quintuplet (or even by a spectral singlet) and the setup allows for population trapping to arise, all depending upon the precise nature of the coupling between the two-level systems.

Observation of the Mollow triplet from an optically confined single atom

Resonance fluorescence from atomic systems consists of a single spectral peak that evolves into a Mollow triplet for a strong excitation field. Photons from different peaks of the triplet show distinct timing correlations that make the fluorescence a useful light source for quantum information purposes. We characterize the fluorescence of a single optically trapped $^{87}\mathrm{Rb}$ atom that is excited resonantly at different power levels. Second-order correlation measurements reveal the single photon nature of the fluorescence concurrently with Rabi oscillations of a strongly excited atom. The asymmetry in correlations between photons from two sidebands of the fluorescence spectrum when the atom is exposed to an off-resonant field indicates that there is a preferred time ordering of the emitted photons from different sidebands.

Optical susceptibility of metal nanoparticle-double quantum dot hybrid system

This work is modeling the linear optical susceptibility of a double quantum dot (DQD)–metal nanoparticle (MNP) hybrid system using density matrix equations that consider the interaction between excitons and surface plasmons. The wetting layer (WL)-QD interaction is considered.The absorption of the hybrid DQD-MNP system increases by five times compared to the bare DQD system. The absorption peak is reducing in a similar ratio of increasing MNP radius. A Mollow triplet with asymmetric sidebands appears and decreases with increasing MNP radius, which is compatible with recent experimental evidence. The susceptibility peaks at resonance for a small distance between the hybrid MNP-DQD. The susceptibility is increased by one order for the DQD system compared to a single QD. A similar result is obtained under WL-QD detuning compared to the case of the probe between DQD states. Small DQDs give high absorption and dispersion, offering more shifts from resonance.

Quantum synchronization in quadratically coupled quantum van der Pol oscillators

We implement nonlinear anharmonic interaction in the coupled van der Pol oscillators to investigate the quantum synchronization behavior of the systems. We study the quantum synchronization in two oscillator models, coupled quantum van der Pol oscillators and anharmonic self-oscillators. We demonstrate that the considered systems exhibit a high-order synchronization through coupling in both classical and quantum domains. We show that, due to the anharmonicity of the nonlinear interaction between the oscillators, the system exhibits phonon blockade in the phase-locking regime, which is a pure nonclassical effect and has not been observed in the classical domain. We also demonstrate that, for coupled anharmonic oscillators, the system shows a multiple resonance phase-locking behavior due to nonlinear interaction. We point out that the synchronization blockade arises due to strong anticorrelation between the oscillators, which leads to phonon antibunching in the same parametric regime. In the anharmonic oscillator case we illustrate the simultaneous occurrence of bunching and antibunching effects as a consequence of simultaneous negative and positive correlation between the anharmonic oscillators. We examine the aforementioned characteristic features in the frequency entrainment of the oscillators using a power spectrum where one can observe normal mode splitting and the Mollow triplet in the strong coupling regime. Finally, we propose a possible experimental realization for the considered system in the trapped ion and optomechanical setting.

Quantum trajectory theory and simulations of nonlinear spectra and multiphoton effects in waveguide-QED systems with a time-delayed coherent feedback

We study the nonlinear spectra and multi-photon correlation functions for the waveguide output of a two-level system (including realistic dissipation channels) with a time-delayed coherent feedback. We compute these observables by extending a recent quantum trajectory discretized-waveguide (QTDW) approach which exploits quantum trajectory simulations and a collisional model for the waveguide to tractably simulate the dynamics. Following a description of the general technique, we show how to calculate the first and second order quantum correlation functions, in the presence of a coherent pumping field. With a short delay time, we show how feedback can be used to filter out the central peak of the Mollow triplet or switch the output between bunched and anti-bunched photons by proper choice of round trip phase. We further show how the loop length and round trip phase effects the zero-time second order quantum correlation function, an indicator of bunching or anti-bunching. New resonances introduced through the feedback loop are also shown through their appearance in the incoherent output spectrum from the waveguide. We explain these results in the context of the waiting time distributions of the system output and individual trajectories, uniquely stochastic observables that are easily accessible with the QTDW model.

Picocavity-Controlled Subnanometer-Resolved Single-Molecule Fluorescence Imaging and Mollow Triplets

Picocavity-Controlled Subnanometer-Resolved Single-Molecule Fluorescence Imaging and Mollow Triplets

Broadband strong photon correlations of frequency-resolved single-atom resonance fluorescence generated by two equal-frequency laser fields with different amplitudes

Frequency-resolved photon statistics of resonance fluorescence generated from a two-level system driven by a strong laser field and a weak laser field with equal frequencies are studied. The frequency resolution of fluorescent radiation is described by quantum filtering dynamics, which is simulated theoretically by two single-mode quantum optical cavities with tunable frequencies to scan the incident fluorescent radiation. By calculating the two-photon intensity–intensity correlation functions in terms of the cavity modes, we demonstrate that two-color strong correlations of resonance fluorescence can be generated not only between the opposite sidebands, but also between the central band and one of the sidebands: although both sidebands are broadened due to the perturbation of the weak laser field on the strong-field dressed atom. We emphasize that these properties are in contrast to the conventional case of the standard single-atom Mollow triplet. Moreover, if the resonance frequencies of the two filtering cavities are tuned appropriately, broadband two-color strong correlations are predicted, and the physical origin is revealed from the perspective of quantum interference of photon emission dynamics. This can be considered as a feasible scheme for the design of broadband non-classical light sources, and may be beneficial to the quantum precise detection of atomic and molecular dynamics via quantum optical spectroscopy.

Quantum Mollow Quadruplet in Nonlinear Cavity QED.

We develop an exact analytical approach to the optical response of a two-level system coupled to a microcavity for arbitrary excitation strengths. The response is determined in terms of the complex amplitudes of transitions between the rungs of the Jaynes-Cummings ladder, explicitly isolating nonlinearities of different orders. Increasing the pulse area of the excitation field, we demonstrate the formation of a quantum Mollow quadruplet (QMQ), quantizing the semiclassical Mollow triplet into a coherent superposition of a large number of transitions between rungs of the ladder, with inner and outer doublets of the QMQ formed by densely lying inner and outer quantum transitions between the split rungs. Remarkably, a closed-form analytic approximation for the QMQ of any order of nonlinearity is found in the high-field low-damping limit.

Assessment of weak-coupling approximations on a driven two-level system under dissipation

The standard weak-coupling approximations associated to open quantum systems have been extensively used in the description of a two-level quantum system, qubit, subjected to relatively weak dissipation compared with the qubit frequency. However, recent progress in the experimental implementations of controlled quantum systems with increased levels of on-demand engineered dissipation has motivated precision studies in parameter regimes that question the validity of the approximations, especially in the presence of time-dependent drive fields. In this paper, we address the precision of weak-coupling approximations by studying a driven qubit through the numerically exact and non-perturbative method known as the stochastic Liouville–von Neumann equation with dissipation. By considering weak drive fields and a cold Ohmic environment with a high cutoff frequency, we use the Markovian Lindblad master equation as a point of comparison for the SLED method and study the influence of the bath-induced energy shift on the qubit dynamics. We also propose a metric that may be used in experiments to map the regime of validity of the Lindblad equation in predicting the steady state of the driven qubit. In addition, we study signatures of the well-known Mollow triplet and observe its meltdown owing to dissipation in an experimentally feasible parameter regime of circuit electrodynamics. Besides shedding light on the practical limitations of the Lindblad equation, we expect our results to inspire future experimental research on engineered open quantum systems, the accurate modeling of which may benefit from non-perturbative methods.

Photonic analog of Mollow triplet with on-chip photon-pair generation in dressed modes.

Making analogy with atomic physics is a powerful tool for photonic technology, witnessed by the recent development in topological photonics and non-Hermitian photonics based on parity-time symmetry. The Mollow triplet is a prominent atomic effect with both fundamental and technological importance. Here we demonstrate the analog of the Mollow triplet with quantum photonic systems. Photonic entanglement is generated with spontaneous nonlinear processes in dressed photonic modes, which are introduced through coherent multimode coupling. We further demonstrate the possibility of the photonic system to realize different configurations of dressed states, leading to modification of the Mollow triplet. Our work would enable the investigation of complex atomic processes and the realization of unique quantum functionalities based on photonic systems.

Multistability and Fano resonances in a hybrid optomechanical photonic crystal microcavity

We investigate the optical response of a hybrid cavity quantum-electrodynamics system consisting of a quantum dot embedded in an optomechanical photonic crystal cavity. The system is coupled to an auxiliary cavity via a waveguide that can support a single optical mode. We demonstrate the possibility of generating tunable optical bistability, double-bistabilty and tristability which can be utilized to design all-optical-switch and multi-valued logic circuits eventually forming a part of a large scale quantum communication platform. The proposed system has also found to exhibit the Mollow triplet and the Fano resonances modified by an optomechanical interaction. The optomechanically induced transparency (OMIT) is superimposed on the Fano resonance (OMIT-Fano resonance) having the transparency window occurring exactly at the point where the probe detuning becomes equal to the mechanical oscillator's resonant frequency.