Ladder-type Three-level Atomic System Research Articles

Vortex beam induced spatial modulation of quantum-optical effects in a coherent atomic medium

We have studied two-dimensional absorption, gain, and corresponding refractive index profiles in a ladder-type three-level atomic system interacting with three coherent fields. One is a weak probe field considered as a plane wave, while the other two are the control fields taken as two Laguerre–Gaussian doughnut beams. Position dependence of two vortex beams induces the spatially modulated coherence at the condition of resonance, which enables us to obtain space-dependent absorption, transparency, gain without inversion (GWI), and refractive index enhancement in the present scheme. The azimuthal modulation of coherence effects is attributed to the presence of optical angular momentum of the vortex beams. Under the influence of an additional travelling wave field with the presence of two vortex beams, the present model leads us to obtain an ultra-large enhancement of refractive index at the resonant detuning of the fields. This phenomenon makes the atom-field system to play the equivalent role of a high-refractive-index prism. The role of near dipole–dipole (NDD) interaction on the modulation of position-dependent coherence effects has also been investigated. It has been shown that, without any inclusion of the travelling wave field in the system, the phenomenon of resonant enhancement of refractive index may also occur in the presence of NDD effect. The new way of generating spatially controlled GWI and nonlinear refractive index enhancement is specific to the present model. This work seems to be useful for finding its applications in spatially modulated coherence controlled electromagnetically induced transparency-based quantum devices like quantum optical memory, switches, and quantum logic gates, where the refractive index switching phenomenon is a prerequisite.

Three-photon electromagnetically induced absorption in a dressed atomic system

We present a theoretical treatment for the complete dynamics process of three-photon electromagnetically induced absorption (TPEIA). The nested-cascade doubly dressed TPEIA is considered when two counterpropagating coupling fields are tuned to the upper line in a closed-cycle ladder-type three-level atomic system. The enhancement or suppression of the TPEIA signal relies on the constructive interference between the excitation pathways of doubly dressed states, which can be controlled by changing the intensity of the coupling field. Meanwhile, two symmetrical transparency frequency windows are observed and discussed. The theoretical results and dressed-state analysis are demonstrated experimentally in the 5 S 1 / 2 ( F = 2 ) − 5 P 3 / 2 ( F ′ = 3 ) − 5 D 5 / 2 ( F ′ ′ = 4 ) transition of the 87 R b atoms.

The controllable amplitude and shape of hyperfine spectra in a ladder-type three-level atomic system

We report experimentally the properties of the hyperfine spectra in [Formula: see text]–[Formula: see text]–[Formula: see text] transitions of [Formula: see text]Rb. When the frequency of the coupling field is fixed between [Formula: see text]–[Formula: see text] transition and the probe scans the [Formula: see text]–[Formula: see text] transitions, two-photon absorption (TPA) and electromagnetically induced transparent (EIT) peaks could be investigated simultaneously, and the amplitude of the peaks can be controlled by changing the temperature of rubidium atomic vapor cell and the probe field power. In particular, the probe field power plays a dual role in controlling the amplitude of the peaks. In the [Formula: see text]–[Formula: see text]–[Formula: see text] transitions with the open intermediate state [Formula: see text], with decrease of the coupling field power, our experimental results show a crossover from a convoluted line-shape to EIT when the probe is weak whereas a transformation from a convoluted line-shape to TPA with an enhanced probe power. Formation of the convoluted line-shape is explained by virtue of the dressed energy-level diagram.

Analytical study of the spiky feature in a two-photon driven lossy ladder system

There has been an experimental report (Traverso et al 2012 Proc. Natl Acad. Sci. USA 109 15185) that oxygen lasing in ambient air exhibits a spiky feature. We theoretically explore a ladder-type three-level atomic system driven by a two-photon resonant pump pulse in a lossy medium, which corresponds to that oxygen experiment. We study the Maxwell–Bloch equations both numerically and analytically and discover that a long pump field brings competition between two mechanisms of coherent pumping and coherent emission, leading to the spiky emission, which cannot be produced using a short pump. The results indicate that atomic coherence occurs in the experiment. Our study provides a clear understanding of the oxygen experiment using a nanosecond pump laser and could lead to the potential application of this oxygen lasing in future experiments.

Dressed-state analysis of efficient three-dimensional atom localization in a ladder-type three-level atomic system

We study the control of high-precision three-dimensional (3D) atom localization by measuring the population of the excited state in a ladder-type three-level atomic system driven by a weak probe field and a control field, together with three mutually perpendicular standing-wave fields. We find that the precision of 3D atom localization in volumes depends sensitively on the frequency detuning of the probe field and the intensity of the control field. Most importantly, we show that adjusting the phase shifts associated with the standing-wave fields leads to a redistribution of the atoms and a significant change of the atomic coherence, so that the atom can be localized in volumes that are substantially smaller than a cubic optical wavelength.

A universal quantum frequency converter via four-wave-mixing processes

We present a convenient and flexible way to realize a universal quantum frequency converter by using nondegenerate four-wave-mixing processes in the ladder-type three-level atomic system. It is shown that quantum state exchange between two fields with large frequency difference can be readily achieved, where one corresponds to the atomic resonant transition in the visible spectral region for quantum memory and the other to the telecommunication range wavelength (1550nm) for long-distance transmission over optical fiber. This method would bring great facility in realistic quantum information processing protocols with atomic ensembles as quantum memory and low-loss optical fiber as transmission channel.

Condition for Doppler-free three-photon resonance in a ladder-type atomic system.

We report the essential condition for three-photon electromagnetically induced absorption (TPEIA) in a Doppler-broadened ladder-type atomic system. When the two coupling lasers operate at different frequencies, we observed Doppler-free TPEIA resonance at a counterintuitive frequency, which is the almost half-frequency detuning of the frequency difference between the two coupling fields. Considering three-photon coherence in a Doppler-broadened ladder-type three-level atomic system, the TPEIA due to the atomic group of non-zero velocity was in good agreement with the calculated TPEIA spectrum under the one-photon resonance condition of all three optical fields. From the results, we found that an atomic group with a proper velocity for ladder-type TPEIA should satisfy the one-photon resonances of all three optical fields.

Three-photon coherence in a ladder-type atomic system

We present a theoretical study of three-photon electromagnetically induced absorption for a ladder-type three-level atomic system. A probe beam was tuned to the lower line and two counterpropagating, linearly polarized coupling beams were tuned to the upper line. The system can be modeled with a three- (or five-) level scheme when the polarization directions of the coupling beams are parallel (or perpendicular). By calculating the absorption coefficients analytically for the two schemes, we found that the corresponding absorption coefficients were identical except for different transition strengths, and that the primitive scheme embedded in those schemes was a simple four-level scheme.

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.

Relationship between two- and three-photon coherence in a ladder-type atomic system.

We investigated the relationship between two- and three-photon coherence in terms of the transition routes and coupling field intensities in a Doppler-broadened ladder-type atomic system for the 5S(1/2)-5P(3/2)-5D(5/2) transition in (87)Rb atoms. Three-photon electromagnetically induced absorption (TPEIA) due to three-photon coherence was observed in the only transition route that exhibited a dominant two-photon coherence effect. We showed that two-photon coherence is a necessary condition for three-photon coherence phenomena. A comparison of the relative magnitudes of the electromagnetically induced transparency and TPEIA as a function of the coupling field intensity revealed that the increase of three-photon coherence was faster than that of two-photon coherence. Considering three-photon coherence in a Doppler-broadened ladder-type three-level atomic system, the relation between two- and three-photon coherence was numerically calculated.

Optical bistability and multistability in an open ladder-type atomic system

A novel scheme is proposed for controlling the optical bistability and multistability in an atomic system. In an open ladder-type three-level atomic system, it is shown that, by adjusting the ratio between atomic injections and exit rates from the cavity, the intensity threshold of optical bistability can be controlled. The effect of incoherent pumping field and spontaneously generated coherence (SGC) on optical bistability for different values of exit rates is also discussed. It is found that SGC makes the medium phase dependent, so the optical bistability and multistability threshold can be controlled via relative phase between applied fields. Moreover, it is shown that the optical bistability can be switched to optical multistability, which is favorable for the next generation of all-optical systems and quantum networks.

Spatial interplay of two four-wave mixing images

We investigate the interplay between the two components of the four-wave mixing (FWM) beams in a ladder-type three-level atomic system. The interplay, including the shift and splitting of the two FWM beams and their intensity modulation, depends on the frequency detuning and the angles as well as the powers of the pump fields. The x-directional splitting due to the cross-phase modulation and y-directional splitting because of electromagnetically induced gratings of FWM beams are investigated. Both the theoretical and experimental results exhibit that the spatial separation and the number of the FWM signals can be well controlled by additional dressing laser beams. Such studies not only can be very useful in better understanding the formation of spatial solitons but also have potential applications in signal processing.

Diagrammatic analysis of multiphoton processes in a ladder-type three-level atomic system

We present a diagrammatic method for complete characterization of multiphoton processes in three-level atomic systems. By considering the interaction routes of the coupling and probe photons for a ladder-type, three-level, noncycling (or cycling) atomic system, we are able to completely discriminate between the pure one-photon and the pure two-photon resonance effects, and the effect of their combination in electromagnetically induced transparency (EIT) using our diagrammatic method. We show that the proposed diagrammatic method is very useful for the analysis of multiphoton processes in ladder-type EIT.

Discrimination of one-photon and two-photon coherence parts in electromagnetically induced transparency for a ladder-type three-level atomic system

We present discrimination of the effect of one-photon and two-photon coherences in electromagnetically induced transparency for a three-level ladder-type atomic system. After the optical Bloch equations for a three-level atom, with either cycling or non-cycling transitions, were solved numerically, the solutions were averaged over the velocity distribution and finite transit time. Through this we were able to discriminate one-photon and two-photon coherence parts of the calculated spectra. We also found that the spectra showed peaks as the branching ratio of the intermediate (excited) state increased (decreased). The experimental results of previous reports [H. S. Moon, et al., Opt. Express 16, 12163 (2008); H. S. Moon and H. R. Noh, J. Phys. B 44, 055004 (2011)] could well be accounted for by this discrimination of one-photon and two-photon coherences in the transmittance signals for the simplified three-level atomic system.

The impact of decay-induced interference on transient behaviours of the dispersion and the absorption

The dynamical behaviour of the dispersion and the absorption in a nearly equispaced ladder-type three-level atomic system is investigated. It is shown that in the presence of decay-induced interference the probe dispersion and absorption are phase dependent. The required switching times for switching the group velocity of a probe field from subluminal to superluminal pulse propagation is then discussed. We find that applying an incoherent pumping field provides an additional control parameter for switching the probe absorption to probe gain.

Optical bistability and multistability via the effect of spontaneously generated coherence in a three-level ladder-type atomic system

We investigate the optical bistability (OB) behavior of a nearly equispaced ladder-type three-level atomic system contained in a unidirectional ring cavity. We consider the three-level atoms under conditions that the atomic dipole moments are nonorthogonal so that the effect of spontaneously generated coherence (SGC) is important. We find that the SGC effect significantly affects the OB behavior of such system. Within certain parameter range, OB can be realized due to the SGC effect. The bistable hysteresis cycle becomes wider with the enhancement of SGC effect. Furthermore, such system is much sensitive to the relative phase between the coupling and probe fields. This property makes it possible to switch between bistability and multistability via adjusting the relative phase.