This paper reveals that spontaneous-emission-mediated emissive multiphoton progress can efficiently enhance nonlinear-optical signal in the cascade system:1) under the same parameters,the strongest nonlinear-optical signal takes place in the cascade system nearly double than it in the Λ system at coherent-population-trapping;2)within a certain range,the pump-atoms detuning controlled in the cascade system,we can get an increase in the generated nonlinear-optical signal efficiently,which is relaxed restrictions on the resonance between pump fields and atoms,and it is easy to operate.
This paper reveals that spontaneous-emission-mediated emissive multiphoton progress can efficiently enhance nonlinear-optical signal in the cascade system:1) under the same parameters,the strongest nonlinear-optical signal takes place in the cascade system nearly double than it in the Λ system at coherent-population-trapping;2)within a certain range,the pump-atoms detuning controlled in the cascade system,we can get an increase in the generated nonlinear-optical signal efficiently,which is relaxed restrictions on the resonance between pump fields and atoms,and it is easy to operate.
In this paper we show that non-maximal coherence can lead to more efficient nonlinear frequency conversion than maximal coherence does. For this purpose we exemplify with the three-level cascade system (with no maximal coherence) to calculate the intensity of nonlinear-optical signal. A comparison is made between the Ξ system and the Λ system (with maximal coherence). The generated intensity is calculated by employing a nonperturbative approach. It is shown that under the conditions of the two-photon resonance and the same parameters, the largest intensity from the Ξ system is about twice as large as that from Λ system. The difference is analyzed in terms of dressed states. It is shown that both the spontaneous emission on the coupling transition and the spontaneous emission mediated three photon process play a contrary role for the two systems. These two processes enhance the generation of nonlinear signals for Ξ system but act contrarily for the Λ systems.
We show that spontaneous-emission-mediated emissive multiphoton transitions provide an efficient way for the generation of squeezed light. Exemplifying the doubly driven three-level system in V configuration, we find that photon fluctuations are suppressed below the shot noise limit by more than 50%. The greatest advantage of the present scheme is that spontaneous-emission-mediated emissive multiphoton transitions are conveniently controlled by adjusting driving field parameters. Good noise reduction is achievable when the decay rate at the bare state laser transition is much larger than that at the bare state auxiliary transition, which is impossible in the previous schemes.
The effect of collectivity on the loading of an atom laser via optical pumping is discussed. In our model, atoms in a beam are laser-excited and subsequently spontaneously decay into a trapping state. We consider the case of sufficiently high particle density in the beam such that the spontaneous emission is modified by the particle interaction. We show that the collective effects lead to a better population of the trapping state over a wide range of system parameters, and that the second-order correlation function of the atoms can be controlled by the applied laser field.
The nonlinear parametric process is of great significance for achieving high-quality coherent optical signals and quantum correlated photons. With the development of classical and quantum information processing, the study of the properties of parametric processes is evolving in complex scenarios of multimode, which is limited in conventional nonlinear media due to strict phase matching, e.g. nonlinear crystals. Here we study the dressing-energy-level-cascaded four-wave mixing process to generate multimode optical parametric signals. Via cascading double-Λ type configuration of 85 Rb D 1 line, the non-degenerate energy-level-cascaded FWM is constructed to generate multimode self-parametric amplification. Moreover, with the dressing effects based on atomic coherence, the spatial and frequency multimode characteristics of energy-level-cascaded FWM parametric amplification, i.e., the modes number and pattern, are actively modulated by the pump fields detuning. Also, the spatial modes from the coupling of two coexisting spontaneous parametric FWMs can be controlled to reach tremendous scalability via the atomic coherence and Kerr non-linearity. The atomic coherence effects and unique phase-matching symmetry nature allow flexible modulation of the multimode property of the generated parametric signals within a nonlinear device, which paves a way for multimode classical and quantum information processing.
In recent years, the study of quantum electrodynamics (QED) in light-matter interactions has discovered various interesting phenomenons that orient many applications. However, due to the ambient entanglement among photons and atoms, few-particle dynamics remains challenging to analyze precisely and limits the progress in several fields. In few-particle systems, different number of atoms interacting with the light field generates drastically different results, even when there is only a single photon involved in the system. The interference between individual atom’s spontaneous emission wavefunctions can cooperatively alter the effective atom-light coupling strength. Depending on the spatial distance between individual of atoms and the involved cavities in the interaction progresses, the collective spontaneous emission rate can alter drastically from superradiance, where the emission rate is enhanced to a high value proportional to the atom number, to subradiance, where the excited atom ensemble stays in a dark state with the light trapped forever. Superradiance provides a promising mechanism to create an ultra-strong light-matter coupling environment, which is an important ingredient for the design of ultra-fast optical devices, frequency comb generation and quantum mirrors. The dark state of subradiance, on the other hand, is essential for the quantum memory implementation. Also, nontrivial phenomenons also occur when multiple photons interacting with a single atom simultaneously. When a finite number of photons incidents on an atom, their scattering through an atom is highly nonlinear, and one special eigenstate component of such nonlinear process, namely photonic bound states, exhibits many interesting properties in nonlinear quantum optical systems. The photons in such state are strongly bunched with each other, as if a virtual attractive force is in effect. Also, the frequency of photons are anti-correlated so that their total frequency remains a constant value, no matter how arbitrary the frequency of any individual is. Thesefeatures benefit certain nonlinear quantum processes for quantum computing and quantum imaging. Specially for two-photon excitation imaging, the same-parity two-level fluorophore molecules suffers from extremely low excitation efficiencies due to the far off-resonant intermediate states. However, by replacing the current commonly used ultrashort laser pulse illuminations with two photon bound state photon pairs, namely photonic dimers, the efficiency can be enhanced to orders of magnitude higher. Such exceptionally high excitation efficiency can potentially bring the current in vivo deep brain imaging depth from millimeter level to several centimeters. To obtain a stable source of such photonic dimers, it is found that a laser structure with gain medium of two-photon emission materials is capable of generating the coherent state of photonic dimer and can serve as a promising light source for nonlinear quantum optical devices.
The realization of correlated multiphoton processes usually depends on the interaction between nonlinear media and atoms. However, the nonlinearity of optical materials is generally weak, making it still very challenging to achieve correlated multiphoton dynamics at the few-photon level. Meanwhile, giant atoms, with their capability for multipoint coupling, which is a novel paradigm in quantum optics, mostly focus on the single-photon field. In this work, by using the method described in Phys. Rev. Res. 6, 013279 (2024), we reveal that the ladder-type three-level giant atom spontaneously emits strongly correlated photon pairs with high efficiency by designing and optimizing the target function. In addition, by encoding local phases into the optimal coupling sequence, directional two-photon correlated transfer can be achieved. This method does not require a nonlinear waveguide and can be realized in the conventional environment. We show that the photon pairs emitted in both the bidirectional and the chiral case exhibit strong correlation properties in both time and space. Such correlated photon pairs have great potential applications for quantum information processing. For example, numerical results show that our proposal can realize the two-photon mediated cascaded quantum system.