Rabi Frequency Of Coupling Field Research Articles

Optical-density enhanced quantum entanglement via four-wave mixing process.

We theoretically propose a scheme to generate a strong continuous-variable quantum entangled light source in four-wave mixing (FWM) process by increasing the optical density of atomic medium. By properly choosing the input coupling field Rabi frequency and detuning, the optimized entanglement can be achieved to be better than -17 dB at an optical density of approximately 1, 000, which has been realized in atomic media. Besides, with the optimized one-photon detuning and coupling Rabi frequency, the optimum entanglement degree can be greatly enhanced with the increment of optical density. We also examine the effects of atomic decoherence rate and two-photon detuning on entanglement in a realistic setting, and evaluate the experimental feasibility. We find that the entanglement can be further improved by considering two-photon detuning. In addition, with optimum parameters the entanglement is robust against the decoherence. The strong entanglement provides a promising applications in continuous-variable quantum communications.

Distinction of electromagnetically induced transparency and Autler-Towners splitting in a Rydberg-involved ladder-type cold atom system.

Electromagnetically induced transparency (EIT) and Autler-Townes splitting (ATS) are two similar quantum coherent phenomena but have different mechanisms and applications. Akaike information criteria (AIC), an objective method to discriminate EIT and ATS from an experimental viewpoint, has been employed in a variety of systems. Here we use AIC method to quantitively discriminate a series of spectra of cold atoms in a Rydberg-involved upper-driving ladder-type. The derived weights of EIT and ATS reflect that our spectra change from EIT-ATS intermediate region to ATS-dominated region along Rabi frequency of coupling field increases. We find that there are two factors affecting EIT-ATS weights in a Rydberg-involved three-level system: dephasing rate, induced by the interactions among Rydberg atoms, makes the EIT-ATS crossover move to the direction of low Rabi frequency of coupling field and the experimental noise makes the difference between EIT and ATS weights reduce at elsewhere. Our investigation could provide a meaningful reference for the observations and applications of Rydberg-involved quantum coherent spectroscopy.

Selective reflection spectrum in a quasi-lambda four-level atomic system

Selective reflection (SR) from the interface between transparent medium and dilute vapour is caused by the atomic vapor near the interface. The sub-Doppler structure in SR is due to the deexcitation caused by the collision between atomic vapor and the wall. Beacuse the interaction region between atomic vapor and incident light is on the order of a few hundred nanometers, SR has low optical loss and high spatial resolution. The experimental device of SR is simple. Because of the above characteristics, the SR has been widely studied and applied. The nonlinear SR spectrum of quasi lambda-type four-level system at gas-solid interface is studied theoretically in this paper. By sloving the density matrix equations, the approximate analytic solution of the matrix element associated with the probe field is obtained at normal incidence when the intensity of the probe field is very weak. The effect of the Rabi frequency, the detuning of the signal field and the detuning of the coupling field on the lineshape are analyzed by numerical simulation, respectively. Three peaks and two transparent windows appear in SR spectrum when the detuning of coupling field and signal field are both zero. The middle peak is generated due to the participation of signal field, and the other two peaks are caused by the other two fields. The linewidth and the amplitude of the middle peak can be changed by varying the Rabi frequency of signal field, and the other two peaks have little effect on the Rabi frequency of signal field. The signal generated due to the participation of signal field can be transformed from peak to transparent window when the detuning value of the signal field is equal to the Rabi frequency of coupling field. When the detuning value of the signal field is not equal to the Rabi frequency of coupling field, a dispersion-like signal between reflection peak and transparent window is generated due to the participation of signal field. The position of peak and transparent window can be manipulated by controlling the detuning value of the coupling field. When the detuning value of coupling field decreases from zero, three peaks all shift to red detuning direction. When the detuning value of coupling field is blue-detuned and increases, three peaks all shift to blue detuning direction. The numerical results can be explained by using the various electric transition pathways and dressed state theory. This study is helpful in investigating quantum coherence and dynamic process of atoms at gas-solid interface.

Quantum interference manipulation and enhancement with fluctuation-correlation-induced dephasing in an atomic system

We investigate the manipulation of the quantum interference (QI) in an electromagnetically induced transparency (EIT) system via phase fluctuations and their correlation of interacting fields. We show that the field fluctuation correlation and atomic dephasing rate have a similar effect to atomic coherence, and furthermore that QI is dependent on the fluctuation and correlation. Using the theoretical model in a dressed-state representation, the contribution of QI and Autler-Townes splitting (ATS) to probe absorption can be expressed in separate terms, such that the obvious enhancement of QI is found with highly correlated fields while ATS remains unchanged. In particular, when the relative large Rabi frequency of coupling field is applied, in which case the ATS plays a more prominent role than QI, we can still modulate the QI to be higher than ATS with correlated fields. This result could allow the strict EIT condition to be relaxed and be easily realized, or it may be a method to get a narrow EIT window for applications in efficient light storage and quantum interface.

Managing optical bistability and multistability by embedding quantum dot nanostructures in a photonic crystal

The optical bistability and multistability properties are studied in a defect slab doped with acceptor and donor quantum dots embedded in a nonlinear photonic crystal. It is shown that the intensity threshold of optical bistability can be controlled via the corresponding controllable parameters, such as Rabi frequency of coupling field and the thickness of the slab. It is found that the switching from optical bistability to multistability can be obtained by enhancing the Rabi frequency of the coupling field. Moreover, it is observed that the dipole-dipole interaction between acceptor and donor quantum dots can lead to modifying the behaviors of optical bistability and multistability. Also, it is demonstrated that the optical thickness of the slab can be used as a potential parameter to control the intensity threshold of optical bistability and multistability. It is found that, by decreasing or increasing the optical thickness parameter, the threshold of optical bistability or multistability can be decreased or increased, correspondingly. We hope that our proposed model can be used for developing the future all-optical systems based on photonic materials doped with nanoparticles.

Phase and thickness control of optical bistability and multistability in a defect slab with a single layer of graphene

In this letter, controllable optical bistability (OB) and optical multistability (OM) in a defect slab doped with a single-layer graphene nanostructure are proposed. Our numerical results show that it is easy to control OB by Rabi frequencies of coupling fields, detuning of coherent fields, and relative phase of applied fields. Moreover, the thickness effect of the slab is considered as a new parameter for controlling the OB behaviors. It is found that the transition from OB to OM or vice versa can be made possible by the thickness of the slab and relative phase of the applied fields. We hope that our results will have potential applications in quantum information science and technology based nanoscale devices.

Electromagnetically induced transparency and ultra-narrow absorption in a ladder-type three-level atomic system

The absorption feature of a ladder-type three-level atomic system associated with double-color laser fields is investigated by adopting the theory of density matrix equation. It is shown that due to quantum coherence caused by the interaction between coupling field and atom, transparency of probe absorption appears at the position of resonant absorption when the Rabi frequency of the coupling field is comparable to the one of the probe field. The depth and width of transparency window increase with the intensity of the coupling field. The phenomena of ultra-narrow absorption can appear by adjusting the intensity and resonance detuning of the coupling field. It is particularly worth mentioning that if the Rabi frequency of coupling field is smaller than the optical relaxation rate, we can achieve a transformation from electromagnetically induced transparency (EIT) to absorption by changing the resonance detuning of the coupling field from negative to positive. Both EIT and absorption have ultra-narrow linewidth. At the same time, quantum coherence makes a dispersion-like absorption and we can design an optical switch based on this point.

Hartman effect in one-dimensional photonic crystals with a three-level atomic defect layer

The Hartman effect in one-dimensional photonic crystals contained a defect layer doped with two-level, and three-level atoms is discussed. It is shown that the transmitted phase time in one-dimensional photonic crystals contained a defect layer reaches to a positive constant as the periodic number N increases. However, for a defect layer doped by two-level atoms, the transmitted phase time reaches to negative constant by increasing periodic number N. In addition, for defect layer doped by three-level atoms, the transmitted phase time can be controlled from positive to negative just by the Rabi-frequency of coupling field.

Electromagnetically induced transparency in cold 85Rb atoms trapped in the ground hyperfine F = 2 state

We report electromagnetically induced transparency (EIT) in cold 85Rb atoms, trapped in the lower hyperfine level F = 2, of the ground state 52S1/2 (Tiwari V B et al 2008 Phys. Rev. A 78 063421). Two steady-state Λ-type systems of hyperfine energy levels are investigated using probe transitions into the levels F′ = 2 and F′ = 3 of the excited state 52P3/2 in the presence of coupling transitions F = 3 → F′ = 2 and F = 3 → F′ = 3, respectively. The effects of uncoupled magnetic sublevel transitions and coupling field's Rabi frequency on the EIT signal from these systems are studied using a simple theoretical model.

Spectral feature with sub-natural linewidth due to quantum interference in a four-level system

This paper studies the narrow spectral feature appearing in a four-level system coupled by two strong coherent fields and probed by a weak laser field. The linewidth is examined as a function of the Rabi frequencies of coupling fields, and the result is explained by using the dressed-state formalism.

Designing molecular eigenstates in a four-levelΛsystem

The interaction of single cw laser (coupling) field with a four-level $\ensuremath{\Lambda}$ system containing two closely spaced upper levels ($a$ and $b$) is studied as a means to attain quantum control. By adjusting the coupling field Rabi frequency and detuning, it is possible to create target states of a prescribed admixture of states $a$ and $b$ within a dressed state representation. An electromagnetically induced transparency of an additional probe beam is also studied. The four-level $\ensuremath{\Lambda}$ system gives rise to generally two dark resonances for a given coupling field detuning. When the resonances are degenerate EIT is enhanced.