Dressed State Theory Research Articles

Effect of electronic excitation on nuclear magnetic shielding as illustrated by nuclear spin optical rotation (NSOR) in liquids

Near resonance effect of NSOR generates new resonant light shift ω well separated from the ground state optical chemical shift ω 0 , from which the shielding in the excited state can be obtained. • The near resonance effect on the optical chemical shift in NSOR is theoretically studied. • The dressed state theory is employed to explore the near resonance effect. • New optical chemical shift line in NSOR spectrum due to excited state molecule is estimated. • Possibility of detecting the new optical chemical line is discussed. Conventional NMR is generally a technique for electronic ground state molecules. In this paper, the effect of electronic excitation on nuclear magnetic shielding is theoretically illustrated by Nuclear Spin Optical Rotation (NSOR) in liquids. The near-resonance effect on the optical chemical shift in NSOR is explored by using the dressed state theory. The results indicate that in the NSOR spectrum of a molecule with nucleus I = 1/2, such effect can induce a new optical chemical shift line with the circular frequency different from that of the ground state. From it the NMR shielding of a molecule in the electronic excited state can be got directly and used to analyze excited molecule structure in liquids. For multi-nuclei molecules, the result applies to each nucleus.

Degenerate four-wave mixing-based double-channel optical gain spectrum with two frequency bands

Focusing on the frequency division multiplexing technology in the applications of large scale optical communication, the double-channel optical gain spectrum with two frequency bands is studied in this paper. The double-channel gain spectrum, named probe channel and four wave mixing channel, comes from a co-propagating degenerate four wave mixing in a hot atomic ensemble. The intention is to divide the gain spectrum into several sub frequency bands through dressed four wave mixing. When a dressed field is exerted on one transition that shares the common excited state with the degenerate four wave mixing, the excited state can experience dressed splitting. It opens two transition paths for the degenerate four wave mixing simultaneously. Because of quantum interference between the two paths, the degenerate four wave mixing are suppressed at two-photon resonance. Consequently, Autler-Townes splitting appears in the gain spectrum, i.e. spectrum is changed from single frequency band into two “M”-type bands. In this paper, the nonlinear density matrix element describing the degenerate (dressed) four wave mixing is solved through perturbation theory, and then the gain spectrum in Doppler broadening atomic medium is plotted, and its Autler-Townes splitting is analyzed by using the dressed-state theory. It shows that the Autler-Townes splitting depends on both the Rabi frequency and single photon detuning of the dressed field. Relevant experiment is performed in cesium vapor at 60 ℃, a pair of high-gain optical spectra with two frequency bands for both double channels is successfully obtained. Moreover, the Autler-Townes splitting as a function of the dressed field intensity and single photon detuning are studied quantitatively. The experimental results accord well with the theoretical predictions. Compared with the degenerate four wave mixing, the atom-field coupled system is changed from an original open two-level into a closed Λ three-level due to the external dressed field, which greatly improves the atomic population on the coherent ground state via optical pumping, and therefore enhancing the gain significantly. This work is important for the field of atom-based optical communication. It provides an optional way of conveying multi-frequency information to the two parallel channels as well as improving the gain of four wave mixing.

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.

Tunable nonlinear measurement of microwave electric fields with a dressed-state analysis

A nonlinear absorption spectrum is proposed for measuring microwave electric fields with tunable sensitivity using electromagnetically induced transparency (EIT) in Rydberg atoms. Interacting dark resonances could enhance the nonlinear absorption, which shows a linear relationship with the microwave field (MW) strength. Compared with the linear case, the nonlinear measurement of MW field improves spectrum resolution by about one order of magnitude, the nonlinearity increases the EIT peak values by about two orders of magnitude, moreover the probe sensitivity could be improved by ten times from simulation. It is found that increasing the ratio of two coupling fields can improve probe sensitivity. The maximum probe sensitivity is predicted and explained. The above results can be well understood with the aid of the dressed-state theory.

Autler–Townes doublet in single-photon Rydberg spectra of cesium atomic vapor with a 319 nm UV laser

We demonstrate the single-photon excitation spectra of cesium Rydberg atoms by means of a Doppler-free purely all-optical detection with a room-temperature vapor cell and a 319 nm ultra-violet (UV) laser. We excite atoms directly from 6S1/2 ground state to 71P3/2 Rydberg state with a narrow-linewidth 319 nm UV laser. The detection of Rydberg states is performed by monitoring the absorption of an 852 nm probe beam in a V-type three-level system. With a strong coupling light, we observe the Autler-Townes doublet and investigate experimentally the dependence of the separation and linewidth on the coupling intensity, which is consistent with the prediction based on the dressed state theory. We further investigate the Rydberg spectra with an external magnetic field. The existence of non-degenerate Zeeman sub-levels results in the broadening and shift of the spectra. It has potential application in sensing magnetic field.

Dynamic control of coherent pulses via destructive interference in graphene under Landau quantization

We analyze the destructive interference in monolayer graphene under Landau quantization in a time-dependent way by using the Bloch-Maxwell formalism. Based on this analysis, we investigate the dynamics control of an infrared probe and a terahertz (THz) switch pulses in graphene. In presence of the THz switch pulse, the destructive interference take places and can be optimized so that the monolayer graphene is completely transparent to the infrared probe pulse. In absence of the THz switch pulse, however, the infrared probe pulse is absorbed due to such a interference does not take place. Furthermore, we provide a clear physics insight of this destructive interference by using the classical dressed-state theory. Conversely, the present model may be rendered either absorbing or transparent to the THz switch pulse. By choosing appropriate wave form of the probe and switch pulses, we show that both infrared probe and THz switch pulses exhibit the steplike transitions between absorption and transparency. Such steplike transitions can be used to devise a versatile quantum interference-based solid-state optical switching with distinct wave-lengths for optical communication devices.

Mixture of Electromagnetically Induced Transparency and Autler–Townes Splitting in a Five-Level Atomic System**Supported by the National Natural Science Foundation of China under Grant Nos. 11274132, 11547208, and the Science Foundation of China Three Gorges University

Discerning electromagnetically induced transparency (EIT) from Autler–Townes splitting (ATS) is a significant issue in quantum optics and has attracted wide attention in various three-level configurations. Here we present a detailed study of EIT and ATS in a five-level atomic system considered to be composed of a four-level Y-type subsystem and a three-level Λ-type subsystem. In our theoretical calculations with standard density matrix formalism and steady-state approximation, we obtain the general analytical expression of the first-order matrix element responsible for the probe-field absorption. In light of the well-known three-level EIT and ATS criteria, we numerically show an intersection of EIT with ATS for the Y-type subsystem. Furthermore, we show that an EIT dip is sandwiched between two ATS dips (i.e., multi-dip mixture of EIT and ATS) in the absorption line for the five-level system, which can be explained by the dressed-state theory and Fano interference.

Effective hyper-Raman scattering via inhibiting electromagnetically induced transparency in monolayer graphene under an external magnetic field

We propose and analyze an effective scheme to generate hyper-Raman scattering via inhibiting electromagnetically induced transparency (EIT) in a monolayer graphene under a magnetic field. By solving the Schrödinger-Maxwell formalism, we derive explicitly analytical expressions for linear susceptibility, nonlinear susceptibility, and generated Raman electric field under the steady-state condition. Based on dressed-state theory, our results show a competition between EIT and hyper-Raman scattering, and the hyper-Raman process is totally dominant when multiphoton destructive interference is completely suppressed.

Triple-mode squeezing with dressed six-wave mixing

The theory of proof-of-principle triple-mode squeezing is proposed via spontaneous parametric six-wave mixing process in an atomic-cavity coupled system. Special attention is focused on the role of dressed state and nonlinear gain on triple-mode squeezing process. Using the dressed state theory, we find that optical squeezing and Autler-Towns splitting of cavity mode can be realized with nonlinear gain, while the efficiency and the location of maximum squeezing point can be effectively shaped by dressed state in atomic ensemble. Our proposal can find applications in multi-channel communication and multi-channel quantum imaging.

Cavity-enhanced simultaneous dressing of quantum dot exciton and biexciton states

We demonstrate the simultaneous dressing of both vacuum-to-exciton and exciton-to-biexciton transitions of a single semiconductor quantum dot in a high-Q micropillar cavity, using photoluminescence spectroscopy. Resonant two-photon excitation of the biexciton is achieved by spectrally tuning the quantum dot emission with respect to the cavity mode. The cavity couples to both transitions and amplifies the Rabi-frequency of the likewise resonant cw laser, driving the transitions. We observe strong-field splitting of the emission lines, which depend on the driving Rabi field amplitude and the cavity-laser detuning. A dressed state theory of a driven 4-level atom correctly predicts the distinct spectral transitions observed in the emission spectrum, and a detailed description of the emission spectra is further provided through a polaron master equation approach which accounts for cavity coupling and acoustic phonon interactions of the semiconductor medium.

Coherent tunneling by adiabatic process in a four-waveguide optical coupler

We numerically simulate Schrödinger-like paraxial wave equation of a four-waveguide system. The coherent tunneling by adiabatic passage in a four-waveguide optical coupler is analyzed by borrowing the dressed state theory of coherent atom system. We discuss the optical coupling mechanism and coupling efficiency of light energy in both intuitive and counterintuitive tunneling schemes and analyze the threshold condition from adiabatic to non-adiabatic regimes in intuitive scheme. The results show that this coupler can be used as power splitter under certain conditions.

激光场作用下原子系统中光学烧孔和慢光效应

Five coherent hole-burning can be simultaneously observed in the absorption spectra of four-level N-style atoms vapors. In this system they adopt a saturated laser co-propagates and two coupling lasers counter-propagate with a probe laser, and the saturated laser can not be in the destructive Doppler state with the probe light. The positions of the coherent hole-burning can be explained by Dressed-state theory. The middle narrow deep hole-burning is induced by the superposition of two coherent hole-burnings. The depth of the coherent hole-burning can be changed by adjusting the reference parameters and the Rabi frequency of the saturated laser. The positions of the coherent hole-burning can be changed by modulating the Rabi frequency of the probe light. By numerical simulation it is found that Rabi frequency of the saturated light plays an important role in slowing the propagating speed. These results may be useful in optical quantum memory and optical quantum information.

Dynamic symmetry-breaking in a simple quantum model of magneto-electric rectification, optical magnetization, and harmonic generation

The state mixings necessary to mediate three new optical nonlinearities are shown to arise simultaneously and automatically in a 2-level atom with an ℓ = 0 ground state and an ℓ = 1 excited state that undergoes a sequence of electric and magnetic dipole-allowed transitions. The treatment is based on an extension of dressed state theory that includes quantized electric and magnetic field interactions. Magneto-electric rectification, transverse magnetization, and second-harmonic generation are shown to constitute a family of nonlinear effects that can take place regardless of whether inversion is a symmetry of the initial unperturbed system or not. Interactions driven jointly by the optical electric and magnetic fields produce dynamic symmetry-breaking that accounts for the frequency, the intensity dependence, and the polarization of induced magnetization in prior experiments. This strong field quantum model explains not only how a driven 2-level system may develop nonlinear dipole moments that are forbidden between or within its stationary states, but it also broadens the class of materials suitable for optical energy conversion applications and magnetic field generation with light so as to include all transparent dielectrics.

The effect of Doppler broadening on dispersive and absorptive properties in atomic systems with two-photon interference

The effect of Doppler broadening on dispersive and absorptive properties is theoretically investigated in the hot four-level electromagnetically induced transparency (EIT) atomic systems with two different types of two-photon interference. It is found that the dispersive behavior for the probe in the ladder-type atomic system with two-photon constructive interference will be changed from anomalous in cold atoms to normal in hot atoms, and the three-peak absorptive profile is shifted to a broadened spectrum with a shallow dip at the line center; as a comparison, there is always normal dispersion at the line center for the invert-Y-type atomic system with two-photon destructive interference, but the EIT window in the absorptive profile will be narrowed to subnatural linewidth (0.01 Γ) at room temperature. The physics of those two different behaviors are discussed and compared in the dressed-state theory.

Refractive index enhancement in three-level Λ-type atom with a saturation field: a dressed state analysis

The paper reports investigations of refractive index enhancement (RIE) with zero absorption in a three-level Λ-type atom subject to a drive field, a saturation field and a probe field. As RIEs lie in the alternate points between emission and absorption peaks, one can predict their positions by employing dressed state theory and optical Bloch equations. The numerical calculations with dressed state analysis indicate that high refractive index enhancement appears mainly at two conditions: (i) off-resonance detuning of drive and saturation frequencies have the opposite sign; (ii) the saturation Rabi frequency is larger than the drive Rabi frequency. The analysis can be extended to multi-field multi-level atomic systems.

The coherent population trapping and four-wave mixing in Λ-type system employing a two-photon field

In this paper, we explore the interaction between four-wave mixing and quantum interference in a Λ-type system employing a two-photon field. The three fields interaction including coherent radiation has given rise to asymmetric coherent population trapping (CPT) profile and gain without inversion. The effect on CPT has been demonstrated by dressed state theory in detail.

Phase-conjugation in two-level atoms: comparison of quantum interference theory to exact results

The analytically derived predictions of a recently developed theory on phase conjugate four wave mixing (FWM) in two-level atoms [Phys. Rev. A 60, 1672 (1999)], which interprets many of the signal features as a consequence of quantum interference between the probability amplitudes for photon emission from relevant dressed states, is compared to the results that one obtains from a non-perturbative, numerical calculation of the density matrix equations. The results delineate the regimes and assumptions under which the perturbative results are valid, and it is shown that despite the simplifying assumptions that are invoked for the dressed state theory, many of its predictions are in qualitative agreement with the exact, numerical results.

Observations of a doubly driven V system probed to a fourth level in laser-cooled rubidium

Observations of a doubly driven V system probed to a fourth level in an N configuration are reported. A dressed-state analysis is also presented. The expected three-peak spectrum is explored in a cold rubidium sample in a magneto-optic trap. Good agreement is found between the dressed-state theory and the experimental spectra once light shifts and uncoupled absorptions in the rubidium system are taken into account.

Atomic dynamics in microcavities: absorption spectra by Green function method

The method of thermodynamic Green functions is applied to the determination of the susceptibilities and absorption spectra of atoms in microcavities. The method is introduced by its application to an atom in free space, where the well known expression for the spectrum is very simply rederived. The calculations remain simple for more complicated systems, and results are obtained for atoms in single-mode cavities with lossy mirrors and with the additional damping by emission into free-space modes that occurs in open-sided cavities. The expressions for some limiting cases of the general theory are compared with the results of previous work and contact is made with the dressed-state theory. Special consideration is given to an atom placed in a planar microcavity; it is shown that non-Lorentzian spectra may in principle occur but that the parameter values of practical cavities produce Lorentzian spectra with linewidths given by Fermi's golden rule.

Two-color study of Autler–Townes doublet splitting and ac Stark shift in multiphoton ionization spectra of CO

By using a two-color scheme, we have given a closer scrutiny to the Autler–Townes doublet splitting and ac Stark shift in the 2+2-photon ionization spectra of CO Ion A 1(v′=4)←X 1Σ+(v″=0) transition in the presence of another strong laser field, which is resonant with the transition C 1Σ+(v′=0)←A 1Π(v′=4)P10 branch. All the observations of ac Stark shift/broadening as a function of the perturbing light frequency and its spatial homogeneity strongly support our previous theoretical interpretation for one-color studies. A qualitative interpretation based on the dressed state theory, which is being quantified, for the Autler–Townes splitting as well as the ac Stark effect has been given. In particular, the magnitude of the Autler–Townes splitting is found to vary with the square root of the perturbing light intensity, in line with the dressed state theory.