Tripod-type Atomic System Research Articles

Effects of static magnetic field, driving laser strength and polarization on the coherent properties of a microwave mediated four-level tripod-type atomic system

In this theoretical work, we study the optical behaviour of a microwave driven four-level tripod-type atomic system, configured by Zeeman sub-levels in D 1 line of 87 Rb atom. The non-optical microwave field (L) reasonably assists the optical pumping by a linearly polarized (π) laser field (P1) and a right-handed circularly polarized (σ +) laser field (P2), in presence as well as absence of a static magnetic field (MF). The optical responses of the system to the left-handed circularly polarized (σ −) optical probe laser field (Pr) under three specific P1-P2 strength conditions depict substantial variations in the Doppler-free and Doppler-broadened absorption peaks, accompanied with single EIT or double EIT windows. The origin of Doppler-free Pr absorption peaks are explained by analyzing the resonant poles for the scanning Pr which attribute to the decaying-dressed-states. Perceptible changes of resonant pole positions on the complex planes of the poles w. r. t. the applied MF and L signify that one can externally alter the optical responses of the medium. The related Pr dispersion and its controllability are discussed as well. It is found that the interaction length of the Doppler-free medium has a prominent effect on the Pr absorption and transmission when both MF and L are present in the medium. Furthermore, we have shown the modifications in the Doppler-free Pr absorption profiles in presence of MF and L by considering P2 as an elliptically polarized laser field. Interestingly, Pr absorption turns into Pr gain at suitable polarization rotation angles of the elliptically polarized P2 field for different P1-P2 strength ratios.

Quantum squeezing of vector slow-light solitons in a coherent atomic system

We investigate the squeezing of two-component quantum optical solitons slowly moving in a tripod-type atomic system with double electromagnetically induced transparency (EIT). The evolution of the double probe-field envelopes is governed by a vector quantum nonlinear Schrödinger equation, derived from the coupled Heisenberg-Langevin and Maxwell equations. Quantum fluctuations of vector soliton pairs and atomic spin are analysed by means of a direct perturbation approach. Importantly, we find that the quantum squeezing of vector soliton pairs is generated by the giant Kerr nonlinearity, which is provided by EIT, and the outcome of the squeezing can be optimized by the selection of propagation distance and angle. The atomic spin squeezing is found for short propagation distances. The predicted results offer insights into soliton physics and may be useful for entanglement detection.

Coherent control of surface plasmon polariton via spontaneously generated coherence

We investigate the control over surface plasmon polaritons (SPPs) using the interface between a four-level tripod-type atomic system and a nanocomposite medium under the effect of spontaneously generated coherence (SGC). The absorption and dispersion spectra of SPPs show interesting behavior with SGC effect at the interface. Skin depth of SPPs can be controlled via strength of SGC. The ratio of nanoparticles in the medium also affects different features of SPPs. The horizontal distances traversed by SPPs were also modified with SGC. We show the quantum confinement of SPPs at the interface for different wavelengths. These results can find important practical applications in the fields of atomic spectroscopy, plasmon-based optical devices and sensors technology.

Efficient all-optical router and beam splitter for light with orbital angular momentum.

We propose an efficient scheme for realizing all-optical router or beam splitter (BS) by employing a double tripod-type atomic system, where the ground levels are coupled by two additional intensity-dependent weak microwave fields. We show that the high-dimensional probe field encoded in a degree of freedom of orbital angular momentum can be stored, retrieved, and manipulated. Due to the constructive or destructive interference between the introduced microwave fields and the atomic spin coherence, the generated stationary light pulses and the retrieved probe fields can be increased or decreased with high efficiency and fidelity in a controllable manner. On the basis of the results and a general extension, a tunable all-optical router or BS, which can split a high-dimensional probe field into two or more ones, can be achieved by actively operating the controlling fields and the microwave fields. The current scheme, integrating multiple functions and showing excellent performance, could greatly enhance the tunability and capacity for the all-optical information processing.

Slow-light soliton beam splitters

We propose a scheme to realize slow-light soliton beam splitters by using a tripod-type four-level atomic system. We show that optical solitons, which have ultraslow propagation velocity and ultralow generation power, can be generated in the system via electromagnetically induced transparency and can be stored and retrieved with high efficiency and fidelity. In particular, a nonlinear beam splitter that splits one optical soliton into two or more ones can be obtained by switching on and off of two or more control laser fields subsequently. The results reported here open a route not only for active manipulation of nonlinear optical pulses in multistate quantum systems but also for promising applications in optical information processing and transmission.

Tunable surface plasmon polaritons at the surfaces of nanocomposite media

Surface plasmon polaritons (SPPs) at the interfaces of composite media have some important properties not found in conventional SPPs, i.e., SPPs at metal-dielectric interfaces. We present a useful scheme to control basic features of SPPs at the interface between a tripod-type atomic system and a silver-silica (AgSiO2) composite film. There is some interaction between the SPPs at the interface and localized surface plasmons (LSPs) due to Ag-nanoparticles in the composite. We show that the SPP's dispersive properties are strongly dependent on the coherent driving fields applied in the atomic system. Similarly, the filling ratio of the nanoparticles in the composite and the incident wavelength also affect different features of the SPPs. Our model provides more degrees of freedom for tuning the fundamental properties of SPPs at the interfaces associated with composite media.

Enhancement of Kerr nonlinearity completely without absorption

We investigate the enhancement of the Kerr nonlinearity in a four-level tripod-type atomic system completely without absorption. We study the effect of the incoherent pumping on the nonlinear susceptibility of the probe field and show that compared with that without the incoherent pumping, the Kerr nonlinearity can be enhanced with completely suppressed absorption at two different probe frequencies. Thus, we can get a symmetrical enhanced Kerr nonlinearity. Particularly, all of our results are in the case of Doppler broadening.

Tripod型双电磁诱导透明原子系统中压缩光的传输

Tripod型双电磁诱导透明原子系统中压缩光的传输

Two-dimensional electromagnetically induced cross-grating in a four-level tripod-type atomic system

By using two orthogonal coupling standing-wave fields, we propose a scheme for a two-dimensional electromagnetically induced cross-grating (EICG) in a four-level tripod-type atomic system. Based on the electromagnetically induced transparency, the probe field will be diffracted and form the two-dimensional EICG through the interaction of the two coupling standing-wave fields. It is shown that the first-order diffraction intensity of the two-dimensional EICG depends observably on the detuning of the probe field and the Rabi frequencies of the two coupling standing-wave fields. The results may be used to develop novel photonic devices for use in quantum information processing, quantum networking and optical imaging.

Two-dimensional sub-wavelength atom localization in an electromagnetically induced transparency atomic system

We propose a scheme for high-precision two-dimensional (2D) sub-wavelength atom localization in a tripod-type atomic system. The position information of a moving atom can be obtained by measuring the probe field absorption when the atom interacts with a weak probe field and two orthogonal standing-wave fields. It is found that sub-wavelength atom localization can be obtained under the condition of two-photon resonance. Remarkably, the localization precision can be significantly improved by changing the strength of the coherent coupling fields in the presence of superposition of coherent coupling field and standing-wave field.

Electromagnetically induced grating in a four-level tripod-type atomic system

An electromagnetically induced grating in a four-level tripod-type atomic system is studied theoretically. By virtue of a weak standing-wave signal field, the phase modulation effectively diffracts a weak probe field into the first-order direction. By changing the weak signal field, the diffraction of the weak probe field can be modulated in real time, and a first-order diffraction efficiency of more than 32% can be obtained with proper parameters. Such a system has a potential application in an all-optical switch controlled by a weak optical signal.

High-precision two-dimensional atom localization via quantum interference in a tripod-type system

A scheme is proposed for high-precision two-dimensional atom localization in a four-level tripod-type atomic system via measurement of the excited state population. It is found that because of the position-dependent atom–field interaction, the precision of 2D atom localization can be significantly improved by appropriately adjusting the system parameters. Our scheme may be helpful in laser cooling or atom nanolithography via high-precision and high-resolution atom localization.

Classical analogs of double electromagnetically induced transparency

Double electromagnetically induced transparency (DEIT) in a four-level atomic system with tripod-type energy-level configuration is modeled by using two classical systems. The first is a set of three coupled harmonic oscillators subject to frictional forces and external drives and the second is a set of three coupled RLC circuits with electric resistors and alternating voltage sources. It is shown that both of the two classical systems have absorption spectra of DEIT similar to that of the four-level tripod-type atomic system. These classical analogies provide simple and intuitive physical description of quantum interference processes and can be used to illustrate experimental observations of the DEIT in quantum systems.

Gain spectrum of a laser-driven tripod-type atom dynamically induced in the presence of spontaneously generated coherence

We examine the absorption of a weak probe beam in a laser-driven tripod-type atom with three closely lying ground levels, where both the driving and probe lasers interact simultaneously with the three transitions. The effects of spontaneously generated coherence (SGC) are taken into account. We introduce dipole moments in the dressed-state picture and the Hamiltonian in terms of the dressed states describing the interaction between the probe and the atom. Gain spectrum under various conditions are presented and analyzed. We show that the spectral structure and the gain amplitude of the probe are strongly influenced by the effect of SGC and the frequency separation of the three closely lying ground levels. The tripod-type atomic system with quantum interference in spontaneous emission can be simulated in the dressed-state picture of a coherently driven four-level N-type system where no SGC effect exists.

Spatial vector solitons in a four-level tripod-type atomic system

We study the generation of weak-light spatial vector solitons in a cold tripod-type atomic system. The condition of generating spatial vector solitons is discussed by analyzing the linear and nonlinear properties of the system. Due to the balance between the enhanced self-phase and cross-phase modulation of the Kerr nonlinearity and the diffraction effect, two orthogonal polarization components of the weak-light probe field can form various spatial vector solitons in the atomic system, such as bright-bright vector solitons and dark-dark vector solitons. We also demonstrate the possibility of generating Manakov spatial vector solitons in this atomic system.

Phase control of coherent pulse propagation and switching based on electromagnetically induced transparency in a four-level atomic system

We investigate the propagation and control of a weak probe laser pulse in a tripod-type four-level atomic system with a quantum loop scheme. The propagation of the probe pulse depends sensitively on the relative phase of the driving fields. By numerically solving the coupled Maxwell–Bloch equations, it is shown that the dynamic control and switching operation of the probe pulse are possible via changing the relative phase of the driving fields. This work may provide a useful reference for designing optical switching and optical storage devices.

Highly entangled photons and rapidly responding polarization qubit phase gates in a room-temperature active Raman gain medium

We present a scheme for obtaining entangled photons and quantum phase gates in a room-temperature four-state tripod-type atomic system with two-mode active Raman gain (ARG). We analyze the linear and nonlinear optical response of this ARG system and show that the scheme is fundamentally different from those based on electromagnetically induced transparency and hence can avoid significant probe-field absorption as well as temperature-related Doppler effect. We demonstrate that highly entangled photon pairs can be produced and rapidly responding polarization qubit phase gates can be constructed based on the unique features of enhanced cross-phase modulation and superluminal probe-field propagation of the system.

Enhancement of nonlinear susceptibility in a four-level tripod scheme

We propose a scheme for the enhancement of nonlinear susceptibility in a four-level tripod-type atomic system in the presence of a microwave field. With a microwave field, nonlinear susceptibility can be enhanced. Nonlinearity can also be ulteriorly enhanced by controlling the coupling field under the optimal intensity of the microwave field. The physical mechanism of the obtained giant nonlinear susceptibility is mainly based on interactions between microwave field and coupling fields. We present a physical understanding of our numerical results using a dressed-state approach and an analytical explanation.

Interacting dark states with enhanced nonlinearity in an ideal four-level tripod atomic system

We present an experimental system to generate large cross-phase modulation (XPM) in cold rubidium atoms. By using an efficient state-preparation technique in the $^{87}\mathrm{Rb}$ $D1$ line, an ideal four-level tripod-type atomic system is formed, which generates large cross-Kerr nonlinearity via interacting dark states in this system. The induced phase shift due to XPM for the probe beam is measured for different trigger beam intensities, which is the key to achieving conditional quantum phase gates and many other applications in quantum information processing.

Ultraslow and superluminal light propagation in a four-level atomic system

We theoretically study the coherent interaction of a tripod-type atomic system with three laser fields, i.e., one probe and two coupling, or two probe and one coupling field. Our analytical and numerical results show that, when all three fields are on two-photon resonance, in addition to the Rabi frequencies of the coupling fields, the probe group velocities also depend on the spontaneous decay rates and the initial population distribution. So we can manipulate the probe pulses to achieve controllable ultraslow group velocities by preparing different initial atomic states. With an incoherent pump field applied, a narrow transparent window accompanied by abnormal dispersion may occur in the probe absorption spectrum, which then allows us to switch a probe pulse from ultraslow to superluminal propagation.