Optical switching by controlling the double-dark resonances in a N-tripod five-level atom

We have investigated the optical switching in a five-level atom in a novel configuration of electromagnetically induced transparency. This N-tripod type level scheme combines the attractive features of cross-phase modulation appearing in N-type atoms with the ability to slow light pulses associated with tripod atoms. The addition of a new driving field to the usual tripod configuration allows to control the double-dark resonances which appear in the four-level tripod system and thus enables to manipulate the probe absorption and dispersion properties. We have studied the temporal dynamics of two pulses, a probe pulse and a switch propagating pulse through the sample. In the presence of the switching field, a deep in the absorption at resonance due to one-photon electromagnetically induced transparency appears and the atomic system is transparent to the probe field, which propagates at a very small group velocity. By tuning the fields, one of the usual double-dark resonances appearing in tripod system can be controlled (Stark-shifted) and the medium, which is transparent in the absence of the control field, will become highly absorptive. The linear and cross-phase modulation susceptibilities have been calculated and we predict the possibility to realize two-photon switching and giant cross-phase modulation. Finally we address the question about the generation of an entangled coherent state and we show that the giant cross-phase modulation provided by this N-tripod atomic system can be used for realizing polarization quantum phase gates.     

Absorption Changes Induced by Off-Resonance Driving a Degenerate Two-Level System

The alteration of atomic absorption via quantum coherence is observed in the degenerate two-level atomic system. It is shown that when the detuning of coupling field equals to that of probe light, i.e. two-photon resonance, the reduction of atomic absorption via electromagnetically induced transparency occurs. However, when we tune the coupling field to two-photon off-resonance, the enhancement of absorption is obtained for the probe field. The influences of one-photon detuning and intensity of coupling field on absorption are also experimentally demonstrated.     

Quantum coherence effects in a four-level diamond-shape atomic system

A symmetric four-level closed-loop ? type (the diamond-shape) atomic system driven by four coherent optical fields is investigated. The system shows rich quantum interference and coherence features. When symmetry of the system is broken, interesting phenomena such as single and double-dark resonances appear. As a result, the controllable double electromagnetically induced transparency (EIT) effect is generated, which will facilitate the implementation of quantum phase gate (QPG) operation.     

Electromagnetically induced transparency and enhanced self-Kerr nonlinearity in a four-level scheme

We analyze the interaction of three laser fields with a four-level quantum system in a tripod configuration. We obtain an analytical expression for the linear susceptibility and nonlinear susceptibility of a weak-probe field and show that the properties of double electromagnetically induced transparency and the self-Kerr nonlinearity can be modified significantly by changing the ratio of the two coupling fields. We also show that a coherently prepared tripod scheme can be used for a giant self-Kerr nonlinearity generation with vanishing absorption in the case of optimal ratio. We present a physical understanding of our numerical results using the dressed-state approach and analytical explanation.     

Effects of relative phase in an open ladder system without incoherent pumping

We studied effects of the relative phase between the probe and driving fields on the absorption and dispersion properties in an open three-level ladder system with spontaneously generated coherence but without incoherent pumping. It is shown that by the phase controlling, switching from absorption to lasing without inversion (LWI) and enhancing remarkablely LWI gain can be realized; large index of refraction with zero absorption and the electromagnetically induced transparency can be obtained. We also find that varying the atomic injection and exit rates has a considerable influence on the phase dependent-absorption property of the probe field, existent of the atomic injection and exit rates gives the necessary condition of the realization of LWI, getting LWI is impossible in the corresponding closed system without incoherent pumping.     

Enhanced narrow spectral line and double electromagnetically induced two-photon transparency induced by double dark resonances

We theoretically investigate the features of two-photon absorption in a five-level atomic system with interacting dark resonances. It is found that two-photon absorption can be completely suppressed at two different frequencies due to the application of two coherent coupling fields and the atomic system exhibits double electromagnetically induced transparency windows against two-photon absorption. The position and width of the double two-photon transparency windows can be controlled via properly adjusting the frequency detuning and the intensities of the two coupling fields. In addition, one enhanced narrow central line can be observed in the two-photon absorption spectra, which may find applications in high-precision spectroscopy. Form a physical point of view, we explicitly explain these results in terms of quantum interference induced by three different two-photon excitation channels in the dressed-state picture.     

Parametric conversion and maximally entangled photon pair via collective excitations in a cycle atomic ensemble

We study the propagation of two quantized optical fields via considering the collective effects of photonic emissions and excitations of a three-level cyclic-type system (such as atomic ensemble with symmetry broken, or the chiral molecular gases, or manual “atomic” array with symmetry broken), where the quantum transitions is driven by two quantized fields and a classical one. The results show that the parametric conversion and maximally entangled photon pair generation can be achieved by means of the collective excitation of the two upper energy levels induced by the classic optical field. This investigation may be used for the generated coherent short-wavelength quantum radiation and quantum information processing.     

Effect of spontaneously generated coherence on probe response in an open system

The effect of spontaneously generated coherence on the probe response in an open ladder atomic system with equispaced levels is studied. The result shows that by adjusting the strength of spontaneously generated coherence (SGC), electromagnetically induced transparency (EIT) and high dispersion (index of refraction) with zero absorption can be realized, a much larger gain without inversion (GWI) than that without SGC can be obtained. Moreover, in the open system and for some strength of SGC, GWI without the incoherent pumping is much larger than that with the incoherent pumping; however, in the corresponding closed system, when the incoherent pumping is absent, we cannot obtain any gain (with or without inversion) for any strength of SGC. In addition, the manipulation role of the atomic exit and injection rates on SGC-dependent absorption property is analyzed for the case when the incoherence pumping does not exist.     

Ultraslow optical solitons in a four-level tripod atomic system

We investigate possible formation and propagation of localized, shape-preserving nonlinear optical pulse in a resonant, lifetime-broadened four-level tripod atomic system via electromagnetically induced transparency (EIT). We prove both analytically and numerically that although in anomalous dispersion regimes near resonance a superluminal optical soliton may appear, such soliton suffers serious absorption. However, by choosing appropriate parameters to make the system work in normal dispersion regimes and within an EIT transparency window, ultraslow optical solitons with very low light intensity can form and propagate stably in the system.     

Coherence induced by incoherent pumping field and decay process in three-level Λ type atomic system

Following the method proposed by Kozlov et al. [Victor V. Kozlov, Yuri Rostovtsev, Marlan O. Scully, Phys. Rev. A 74 (2006) 063829], we have investigated the atomic coherence induced by incoherent pump and vacuum spontaneous decay process in a Λ type three-level atomic system. The system can be in a coherent population trapping state and multi-steady states in different conditions. Interestingly, two kinds of new states are derived from the system with different pumping rate and decaying rate. They are the “robust” steady state and the “weak” steady state. Under the action of pump field and vacuum reservoir, these two kinds of states exhibit stable or unstable characteristics, respectively. Moreover, by investigating the difference between these states, we reveal the mechanism of coherence excitation and level-population transition. The special feature of the Λ atomic system will promise fruitful applications in quantum optics.     

Evolution of population in an equispaced three-level ladder-type atomic system

Transient response of nearly equispaced three-level ladder-type atomic system with a broad-band squeezed vacuum (SV) is investigated. We focus our attention in the interplay between the quantum interference and the squeezed field on the population distribution. It is shown that an atomic population inversion can be attained on one of the optical transitions due to the SV. Additionally, we show, with the proper value of the relative phase, the SV can also lead to unexpected population inversion on the transition between two different levels.     

Quantum interference effect on absorption-dispersion spectra in Λ-type three-level EIT medium interacting with a squeezed bath

A Λ-type three-level atomic system in the electromagnetically induced transparency (EIT) configuration interacting with a broadband squeezed vacuum (SV) bath is studied with quantum interference (QI) between decay channels taken into account. We formulate two sufficient critical conditions for the medium to be dispersionless or absorptionless. Computational results for the dispersion and absorption spectra show that presence of both QI and SV offers more avenues to manipulate the group velocity of probe pulse for its variation from sub-luminal to super-luminal regimes. The relative phase between the two external fields is found to act as a control knob of the atomic medium.     

From laser-induced line narrowing to electro- magnetically induced transparency: closed system analysis

The laser-induced line-narrowing effect, discovered more than thirty years ago, can also be applied to recent studies in high resolution spectroscopy based on electromagnetically induced transparency. In this paper we first present a general form of the transmission width of electromagnetically induced transparency in a homogeneously broadened medium. We then analyze a Doppler broadened medium by using a lorentzian function as the atomic velocity distribution. The dependence of the transmission linewidth on the driving field intensity is discussed and compared to the laser-induced line-narrowing effect. This dependence can be characterized by a parameter which can be regarded as “the degree of optical pumping.” Received: 17 December 2001 / Published online: 15 January 2003 RID="*" ID="*"Corresponding author. E-mail: hwang.Lee@jpl.nasa.gov RID="**" ID="**"Present address: Jet Propulsion Laboratory, MS 126-347, California Institute of Technology, Pasadena, CA 91109, USA     

On atomic analogue of Landau quantization

We have studied the physics of atoms with permanent electric dipole moment and nonvanishing magnetic moment interacting with an electric field and inhomogeneous magnetic field. This system can be demonstrated as the atomic analogue of Landau quantization of charged particles in a uniform magnetic field. This Landau-like atomic problem is also studied with space-space noncommutative coordinates.     

Ultranarrow absorptive spectral line induced by microwave field

This paper investigates the absorptive spectral lines of four-level atomic system driven by a coupling, probe and microwave fields. Due to the perturbation of the microwave field, the original electromagnetically induced transparency is changed to electromagnetically induced absorption and the absorptive spectral line can be very narrow. This ultranarrow spectral line has potential applications to the microwave atomic frequency standard and the measurement of very weak magnetic field.     

Transient gain property of a weak probe field in an asymmetric semiconductor coupled double quantum well structure

The transient gain property of a weak probe field in an asymmetric semiconductor coupled double quantum well structure is reported. The transient process of the system, which is induced by the external coherent coupling field, shows the property of no inverse gain. We find that the transient behavior of the probe field can be tuned by the change of tunneling barrier. Both the amplitude of the transient gain and the frequency of the oscillation can be affected by the lifetime broadening.     

Autler-Townes triplet spectroscopy

We study the effects of quantum interference in the spontaneous emission spectrum of a four-level driven atomic system. We use three strong laser fields to drive the atom and a weak laser field to prepare the initial state of the atom. The atomic system exhibits Autler-Townes triplet in the spectrum. The single Lorentzian peak splits into triplet and their widths are controlled by the relative strengths of the laser fields.     

Local Modulation of Double Electromagnetically Induced Transparency Spectrum

The double electromagnetically induced transparency induced by two coupling fields can be realized in a fourlevel tripod-type atom. Such double transparency spectra can be locally modulated by using the weak coherent fields to perturb the coupling transitions. These investigations within this scheme can be independent of Doppler broadening by properly orienting these fieds.     

An analytical description of the atomic information entropy in a multi-level system

We construct a complete representation of the atomic information entropy of an arbitrary multi-level system. Our approach is applicable to all scenarios in which the quantum state shared by a single particle and fields is known. As illustrations we apply our findings to a single four-level atom strongly coupled to a cavity field and driven by a coherent laser field. In this framework, we discuss connections with entanglement frustration and entropic forms. We conclude by showing how the atomic information entropy can be extended to examine entanglement in multi-level atomic systems.     

Control of the switch between optical multistability and bistability in three-level V-type atoms

We theoretically investigated a hybrid absorptive-dispersive optical bistability and multistability behaviour in a three-level V-type system using a microwave field driving a hyperfine transition between two upper excited states inside a unidirectional ring cavity. We find that the intensity and the frequency detuning of the coupling field as well as the intensity of the microwave field can affect the OM behaviour dramatically, which can be used to control the transition from OM to OB or vice versa without need to resort the effect of the quantum interference. The effects of the phase, the quantum interference and the atomic cooperation parameter on the OM are also studied. Our scheme may be used for building more efficient all-optical switches and logic-gate devices for optical computing and quantum information processing.