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We extend Dykhne–Davis–Pechukas (DDP) approximation which describes the nonadiabatic transition probability of a two-state atom system to a three-waveguide coupler. We optimize the traditional Gaussian tunneling rate distributions of optical waveguides based on the parallel adiabatic passage (PLAP) technique which originates from the DDP scheme. The tunneling efficiency can be further improved. We explore the robustness and the tunneling transfer error of the stimulated Raman adiabatic passage (STIRAP) in optical waveguides. The results show that the DDP-optimized scheme can keep the robustness against variations in the shift of propagation constant and hence the width of the channels.

We present a Python object-oriented computer program for simulating various aspects of laser cooling physics. Our software is designed to be both easy to use and adaptable, allowing the user to specify the level structure, magnetic field profile, or the laser beams' geometry, detuning, and intensity. The program contains three levels of approximation for the motion of the atom, applicable in different regimes offering cross checks for calculations and computational efficiency depending on the physical situation. We test the software by reproducing well-known phenomena, such as damped Rabi flopping, electromagnetically induced transparency, stimulated Raman adiabatic passage, and optical molasses . We also use our software package to quantitatively simulate recoil-limited magneto-optical traps, like those formed on the narrow 1S → 3 0 P1 transition in 88Sr and 87Sr.

This paper proposes a theoretical scheme to synthesize white laser source based on the cascaded sum frequency generation (CSFG) model with stimulated Raman adiabatic passage (STIRAP). In the CSFG model, the signal laser, intermediate laser and output laser correspond to red, green and blue (RGB) lasers respectively. The results show that in general the red laser is completely converted to the blue laser, and there is no apparent intermediate green laser. Moreover, under the counterintuitive order, the pump parameters have a wider adjustment range of system conversion efficiency than the coupling delay parameters. We synthesize the white laser source through the following steps. First, we change the pump intensity to roughly adjust the conversion efficiency of the system, and then vary the coupling delay parameters to fine-tune RGB lasers output power ratio. Compared with the scheme based on frequency conversion with Stark-chirped rapid adiabatic passage to synthesize white laser source, the RGB lasers output of the new scheme can achieve better stability. The results of the investigation can provide a theoretical foundation for the research of novel optical devices.

Nuclear-state population transfer in three-level Λ-like nuclei that interact with two X-ray laser pulses using composite stimulated Raman adiabatic passage (CSTIRAP) technique is investigated theoretically. Due to the fact that the frequency of existing X-ray lasers is less than the frequency of gamma rays, so in this method the nuclei are accelerated and interact with two X-ray laser pulses with different frequencies. We use a series of pairs of delay pulses so that the phases of the pulses in each stage are different from the other one. In this method, the maximum values of the pump and Stokes laser pulses are adjusted so that the Rabi frequencies corresponding to the two pulses are equal during time evolution. We show that by properly selecting the phases as well as the order of the pulses in each stage, in single-photon and two-photon resonance cases, the population is completely transferred from the initial ground state to the final ground state. In this scheme, the number of steps is optional and as the number of steps increases, the required lasers intensities in each step decrease significantly.

We investigate the influence of nonlinear crystal’s coupling modulation on wavelength conversion based on Stark-chirped rapid adiabatic passage. The result shows that the distribution of the efficient conversion is zonal with the change of coupling delay parameter. In addition, the efficient wavelength conversion can be performed in counterintuitive and intuitive order, which can reduce the restriction on the condition of conversion process compared to the stimulated Raman adiabatic passage. When the width parameter d 1 2 is fixed, the larger the width parameter d 2 2 is, the higher the maximum conversion efficiency is and the larger the bandwidth for efficient wavelength conversion is. These findings provide a theoretical basis for the efficient acquisition of laser sources from the visible to the mid-infrared and to the ultraviolet.

We proposed a scheme to manipulate the single qubit as the superposition of two atomic ground states in a large detuned three level Λ system using double fractional stimulated Raman adiabatic passages. This single qubit evolves mainly through two high efficient passages: a dark passage and a bright passage. Then we show the demonstration of witnessing the model independent quantumness with properly designed laser sequence according to the real experiment system of cold 87Rb atomic ensemble. Finally, we discuss the effects of dephasing, laser noise and detection noise on the quantumness witness through numerical simulations.

We observed the A 1 Σ + ∼ b 3 Π → a 3 Σ + / X 1 Σ + laser-induced fluorescence (LIF) of the RbCs molecule excited from the ground X 1 Σ + state by the Ti:Sapphire laser. The LIF spectra from the common perturbed levels of the singlet-triplet A ∼ b complex was recorded by the Fourier-transform (FT) spectrometer with the instrumental resolution of 0.03 cm − 1 . The relative intensity distribution in the rotationally resolved A ∼ b → a 3 Σ + ( v a ) / X 1 Σ + ( v X ) progressions was measured, and their branching ratio was found to be about of 1 ÷ 5 × 10 − 4 in the bound region of the a 3 Σ + and X 1 Σ + states. The experiment was complemented with the scalar- and full-relativistic calculations of the A / b − X / a transition dipole moments (TDMs) as functions of internuclear distance. The relative systematic error in the resulting ab initio TDM functions evaluated for the strong A − X transition was estimated as few percent in the energy region, where the experimental LIF intensities are relevant. The relative spectral sensitivity of the FT registration system, operated with the InGaAs diode detector and CaF beam-splitter, was calibrated in the range [6 500, 12 000] cm − 1 by a comparison of experimental intensities in the long A ∼ b → X(vX) LIF progressions of the K2 and KCs molecules with their theoretical counterparts evaluated using the ab initio A − X TDMs. Both experimental and theoretical transition probabilities can be employed to improve the stimulated Raman adiabatic passage process, a → A ∼ b → X, which is exploited for a laser assembling of ultracold RbCs molecules.

We propose protocols of loop stimulated Raman shortcut-to-adiabatic passage (STIRSAP) and modified-STIRSAP to speed up the creation of arbitrary high fidelity coherent superposition states ( F ≃ 0 . 999 ). In loop- and modified-STIRSAP protocols, the nonadiabatic coupling between the dark and bright states can be canceled by an additional microwave pulse and modified pump and Stokes pulses, respectively. As a result of dark state rotation, the creation of preselected coherent superposition states can be achieved beyond the adiabatic limit. Compared with the stimulated Raman adiabatic passage (STIRAP) protocol, the evolution time of the creation of coherent superposition states can be shortened. Our numerical calculations agree well with the theoretical analysis in the partial dressed-state picture.

Preparing an arbitrary preselected coherent superposition of quantum states finds widespread application in physics, including initialization of trapped ion and superconductor qubits in quantum computers. Both fractional and integer stimulated Raman adiabatic passage involve smooth Gaussian pulses, designed to grant adiabaticity, so to keep the system in an eigenstate constituted only of the initial and final states. We explore an alternative method for discovering appropriate pulse sequences based on deep reinforcement learning algorithms and by imposing that the control laser can be only either on or off instead of being continuously amplitude-modulated. Despite the adiabatic condition is violated, we obtain fast and flexible solutions for both integer and fractional population transfer. Such method, consisting of a Digital Stimulated Raman Passage (D-STIRaP), proves to be particularly effective when the system is affected by dephasing therefore providing an alternative path towards control of noisy quantum states, like trapped ions and superconductor qubits.

We theoretically perform a dressed state approach to investigate a fast adiabatic light transfer and split in the three-waveguide coupled system. We compare the performance of the waveguide couplers based on the dressed-state method with the stimulated Raman adiabatic passage (STIRAP) couplers. We find that the dressed-state couplers can achieve a higher fidelity at a shorter device length and can be more robust against various uncertainties than the original STIRAP couplers.

Azobenzene liquid-crystal networks (LCNs) are well known for their photo-deformation, shrinking in UV light, and reverting to their original shape in visible light. Such reversible deformation is due to trans-cis photoisomerization of the azobenzene monomer, which disturbs well-aligned order of nematic LCN. In order to predict the photo-strain of azobenzene LCNs in multiple conditions (light intensity, polarization angle, and temperature), we propose using a density functional theory (DFT)-based modeling approach, which integrates stimulated Raman adiabatic passage calculations (STIRAP), non-linear Beer's law, and polymer physics. The model predicts that as the azobenzene ratio increases, the penetration depth of photo strain decreases, whereas the shrinkage ratio of the LCN in the unit cell increases. We identify that this opposite tendency of change is the reason why there is bending limit during the photo bending of azobenzene LCN films when increasing the ratio of the azobenzene monomer, which was also measured in experimental data.

The cis profile of azobenzene is a key factor in predicting the photodeformation of the nematic azobenzene liquid crystal network (LCN). An ab initio based method for predicting the photoisomerization profile of azobenzene is developed by coupling the stimulated Raman adiabatic passage (STIRAP) method with non-linear Beers law, and compared with experimental data. Using this combined method, we calculate the photoisomerization profile of azobenzene with various light input conditions. We identify the cis profile of the nematic LCN structure evolves into a step-like decaying shape when the direction of polarized light is parallel to the nematic direction.

We propose a robust scheme to prepare entangled states among two 87 Rb Bose–Einstein Condensates (BECs) via a stimulated Raman adiabatic passage (STIRAP) technique. The atomic spontaneous radiation, the cavity decay, and the fiber loss are efficiently suppressed by engineering an adiabatic passage. The simulation also shows that we can generate this entanglement state with high fidelity.

We propose and analyze a feasible scheme for achieving arbitrary geometric Berry phases based on the efficient technique of fractional stimulated Raman adiabatic passage (f-STIRAP). In a typical Λ system, we show that a combination of two reversed f-STIRAP processes may result in a preselected coherent superposition of two ground states at the middle time and a desired geometric Berry phase of one dark state at the final time. A most important controlling parameter is the mixing angle of pump and Stokes pulses, which can be accurately designed before the dynamic evolution when we adopt a circularly polarized field and an elliptically polarized field on the J = 1 ↔ J ′ = 0 transition. The accurate accumulation of arbitrary Berry phases is of interest, e.g., in quantum computation because it allows the construction of a few quantum gates.

We consider three coupled nonlinear Schrodinger equations describing atomic Bose–Einstein condensates coupled to a molecular condensate through the stimulated Raman adiabatic passage loaded in an external potential. Using a combination of the homogeneous balance principle and sub-equation expansion technique, we obtain three families of exact stationary dark state solutions for this coupled system. The results show that there exist different trapping potentials, such as double-well, periodic and double-periodic, and harmonic potentials, where the exact dark solutions can be formed via a proper choice of the nonlinear parameters. Finally, the stability of the dark state solutions are checked by direct numerical simulations.

We propose a way to prepare W state among atomic ensembles via stimulated Raman adiabatic passage (STIRAP) technique. The atomic ensembles are trapped in spatially separated cavities collectively linked to another cavity trapping a single atom by optical fibers. Our strictly numerical simulations show that, the atomic spontaneous emission, the cavity decay and the fiber loss are efficiently suppressed by the engineering adiabatic passage. The method can be generalized to prepare W state among any number of atomic ensembles. We believe that our proposal will promote development of quantum teleportation, especially quantum state engineering of multi-target-qubit collectively controlled by a qubit.

We propose a method for the creation of arbitrary superposition of N atomic states using generalized stimulated Raman adiabatic passage (STIRAP) techniques with laser fields coupling each one of N lower states to a single upper state in a ( N + 1 ) -level atomic system. ( N - 1 ) dark states that are composed of N lower states span a dark subspace. In the adiabatic limit, the dark and bright subspaces are decoupled, thus the nonadiabatic interaction within this dark subspace dominates the evolution of the system. Different from general methods to create our required coherent superposition state, in a reverse way, here we consider the required state as the starting point of evolution dynamics, and utilize laser fields to drive it into a single lower state step by step. Time reverse pulses of laser fields return the single lower state back to our required coherent superposition state based on time reversal symmetry. In principle, the computationally simple method allows the case with a large value of N . Based on the STIRAP techniques, it is robust against small variations of parameters of laser pulses and is immune to spontaneous radiation.

Stimulated Raman adiabatic passage (STIRAP) is a well established technique whereby two pulses, S preceding P, induce complete population transfer between states 1 and 3 of a three-state chain, 1–2–3. Traditionally, the S and P pulse envelopes are taken as positive (often with Gaussian form of time dependence). However, when the envelope undergoes a sign change during the pulse, as occurs with pulses in which an abrupt phase change of p occurs and whose temporal area (time-integrated Rabi frequency) is zero, then the simple population transfer need not occur. Instead there may occur multiple adiabatic passages, in which the population may ultimately be left in either state 1 (a double STIRAP) or state 3 (a triple STIRAP) or, with suitable pulse delay, in a superposition of these two states. These adiabatic changes offer possibilities to produce final-state probability amplitudes with either positive or negative signs. We here show simulated examples of such behavior, and discuss the adiabatic conditions needed for such excitation to occur.

We investigate the ultrafast control of coherent population transfer in a Λ-type three-level system with a train of pump–Stokes femtosecond pulse pairs, where the pulse sequences can be produced either by optical delay line or by pulse shaping with sinusoidal phase modulation. It is shown that when the pump and Stokes pulses in each pair are applied in the counterintuitive order, similar to that in the stimulated Raman adiabatic passage technique, due to temporal quantum interference (besides optical interference in the case of overlapped subpulses), ultrafast control of coherent population transfer can be achieved by scanning the inter-pair time delay or by changing the sinusoidal phase modulation parameters. This method has potential applications in ultrafast control of chemical reactions and quantum information processing.

Optically driving nuclear spin waves in a Tm:YAG crystal, we experimentally demonstrate the feasibility of a three-level Λ system in this material, which is a foundation step in the prospect of quantum memory investigations. Varying the spin state splitting with an external magnetic field, we show that the nuclear spin coherence lifetime remains close to 350 μ s over a wide range of variation of this splitting. Finally, we demonstrate fast coherent population transfer between the spin states.

Nanosecond time-resolved evolution of coherence between two nondegenerate ground levels has been investigated in Rb atomic vapor. Using STIRAP and fractional STIRAP, a time-dependent coherence is prepared and indirectly monitored by the generated coherent Raman scattering signal proportional to the coherence. The experimental data fit very well with numerical simulations. This technique have potential applications in nonlinear process based on atomic coherence.

Inspired by a quantum interference phenomenon known in the atomic physics community as electromagnetically induced transparency (EIT), we propose an efficient weakly radiative wireless energy transfer scheme between two identical classical resonant objects, strongly coupled to an intermediate classical resonant object of substantially different properties, but with the same resonance frequency. The transfer mechanism essentially makes use of the adiabatic evolution of an instantaneous (so called “dark”) eigenstate of the coupled 3-object system. Our analysis is based on temporal coupled mode theory (CMT), and is general enough to be valid for various possible sorts of coupling, including the resonant inductive coupling on which witricity-type wireless energy transfer is based. We show that in certain parameter regimes of interest, this scheme can be more efficient, and/or less radiative than other, more conventional approaches. A concrete example of wireless energy transfer between capacitively-loaded metallic loops is illustrated at the beginning, as a motivation for the more general case. We also explore the performance of the currently proposed EIT-like scheme, in terms of improving efficiency and reducing radiation, as the relevant parameters of the system are varied., U.S. Department of Energy, DARPA, Army Research Office, National Science Foundation

Fractional stimulated Raman adiabatic passage (f-STIRAP) is used to develop a method for preparation of a two-photon coherence between long-lived ground states of an optically thick ensemble of lambda atoms. Despite strong depletion and reshaping of preparation pulses in the course of propagation, this method provides a stable predetermined value of the coherence uniformly established along the sample, from input to the output. Both adiabatic and nonadiabatic preparation regimes are considered.

We report on the experimental implementation of stimulated Raman adiabatic passage (STIRAP), electromagnetically induced transparency (EIT) and the retrieval of light pulses in a Pr 3+ :Y 2 SiO 5 crystal. We apply coherent, adiabatic processes to control population dynamics and atomic coherences in selected hyperfine levels of the praseodymium dopants in the crystal. Our data demonstrate efficient adiabatic population transfer by conventional STIRAP as well as by an alternative transfer process, i.e. b-STIRAP. Moreover, we investigate dark resonances, driven by EIT in a A-type and in a V-type level scheme. We apply EIT to create atomic coherences in Pr3 + :Y 2 SiO 5 . The persistent coherence is monitored by delayed retrieval of light pulses from the medium.

We propose a cavity-QED scheme to effectively generate Einstein–Podolsky–Rosen polarization-entangled photon pairs. Assisted by a classical π -polarized pump field, a tripod four-level atom successively couples to two high- Q optical cavities possessing polarization degeneracy. Through stimulated Raman adiabatic passage process the polarization-entangled photon pairs can be produced.

A simple theoretical approach to stimulated Raman adiabatic passage (STIRAP) with small two-photon detunings is presented. The STIRAP process in a tripod configuration with small two-photon detunings is investigated. It is shown that the processes can be regarded as standard STIRAP processes via dark states even in the presence of the two-photon detunings. A geometrical description for these processes is also presented.

The effects of permanent dipole moments on stimulated Raman adiabatic passage (STIRAP) are considered. Analytic expressions for the Hamiltonian including the effects of permanent dipole moments are developed for the STIRAP process. The potential detrimental effect of permanent dipoles on population transfer using standard STIRAP techniques is demonstrated using model three-level systems. However, the presence of permanent dipole moments can allow the utilization of alternative multi-photon mechanisms for STIRAP. Here two-photon plus two-photon STIRAP is highlighted as a potential new mechanism.

We analyze rovibrational excitation by Stimulated Raman adiabatic passage using long pulses, with bandwidth much smaller than the rotational constant. Due to centrifugal distortion, a single pump and Stokes laser pulses cannot resonantly excite all the different rotational lines of any branch of the Raman spectra. Thus, the yield of the excitation decreases rapidly with increasing rotational temperature. With the aid of another pulse, inducing a dynamic Stark effect, we show that it is possible to improve the yield of the process at low temperatures. The Stark effect can be used as well to assist the adiabatic passage of coherent superposition of rotational states. Designing different pulse sequences, maximal control on the preparation of superposition states in excited vibrational levels is demonstrated.

We examine the effect of dissipation on the laser control of a process that transforms a state into a superposed state. We consider a two-dimensional double well of a single potential energy surface. In the context of reactivity, the objective of the control is the localization in a given well, for instance the creation of an enantiomeric form whereas for quantum gates, this control corresponds to one of the transformation of the Hadamard gate. The environment is either modelled by coupling few harmonic oscillators (up to five) to the system or by an effective interaction with an Ohmic bath. In the discrete case, dynamics is carried out exactly by using the coupled harmonic adiabatic channels. In the continuous case, Markovian and non-Markovian dynamics are considered. We compare two laser control strategies: the Stimulated Raman Adiabatic Passage (STIRAP) method and the optimal control theory. Analytical estimations for the control by adiabatic passage in a Markovian environment are also derived.

We experimentally demonstrate coherent population transfer, driven by stimulated Raman adiabatic passage (STIRAP) between two bound quantum states, coupled via a continuum of states. We present extended numerical and experimental investigations on population transfer from the metastable state 2s 1 S0 to the excited state 4s 1 S0 in metastable helium atoms. While techniques based on incoherent excitation do not permit any population transfer via rapidly decaying continuum states, our data indicate a maximum transfer efficiency of 20% in coherent excitation by STIRAP. We study the transfer efficiency with respect to the relevant experimental parameters. � 2006 Elsevier B.V. All rights reserved.

We demonstrate a controlled phase change of p in a degenerate superposition by altering a laser frequency by only 10 MHz. The method relies on the preparation of an adiabatic state involving the M = ±2 and M = 0 states of the 3 P2 (J = 2) level of metastable neon. Dependent on the frequency, the preparation proceeds either by stimulated Raman adiabatic passage (STIRAP) or by coherent population trapping (CPT). In the former case the superposition is prepared by adiabatic transfer induced in an extended tripod linkage scheme. In the latter case population is optically pumped into the Zeeman manifold of the level 3 P2. The population which does not reach a dark state decays to the ground state of neon. The amplitudes and relative phases of the dark states differ for the two cases. The phase change is monitored using the method of phase-to-population mapping. 2006 Elsevier B.V. All rights reserved.

Adiabatic passage schemes in coupled semiconductor quantum dots are discussed. For optical control, a doped double-dot molecule is proposed as a qubit realization. The quantum information is encoded in the carrier spin, and the flexibility of the molecular structure allows to map the spin degrees of freedom onto the orbital ones and vice versa, which opens the possibility for high-finesse quantum gates by means of stimulated Raman adiabatic passage. For tunnel-coupled dots, adiabatic passage of two correlated electrons in three coupled quantum dots is shown to provide a robust and controlled way of distilling, transporting and detecting spin entanglement, as well as of measuring the rate of spin disentanglement. Employing tunable interdot coupling the scheme creates, from an unentangled two-electron state, a superposition of spatially separated singlet and triplet states, which can be discriminated through a single measurement. Finally, we discuss phonon-assisted dephasing in quantum dots, and present control strategies to suppress such genuine solid-state decoherence losses.

We describe a practical implementation of a semi-deterministic photon gun based on the stimulated Raman adiabatic passage pumping and the nonlinear tuning of the photonic density of states in a photonic band-gap material. We show that this device allows deterministic and unidirectional production of single photons with a high repetition rate of the order of 100 kHz. We also discuss specific 3D photonic microstructure architectures in which our model can be realized and the feasibility of implementing such a device using Er ions that produce single photons at the telecommunication wavelength of 1.55 μ m. © 2006 Elsevier B.V. All rights reserved.

A two-step sequential method with the π pulse and the stimulated Raman adiabatic passage (STIRAP) pulse sequence is applied to the laser control of the singlet–triplet transition in Cl 2 molecule. We find four reaction pathways from the singlet ground state to the triplet excited state by investigating the spin–orbit coupling and the transition dipole moment calculated with gamess software package, and we realize the highly effective singlet–triplet transition by STIRAP method with the spin-mixed intermediate state on picosecond time scale.

We have studied the exact nonlinear dynamics underlying stimulated Raman adiabatic passage (STIRAP) for a particle in a multi-level anharmonic system (the infinite square-well) driven by two sequential laser pulses, each with constant carrier frequency. We compare two basic processes, ladder and lambda. We have found that the coherent population transfer for both cases is dependent on the nature of the Floquet eigenphase avoided crossings created by an underlying transition to chaos.

In this paper we propose the extension of stimulated Raman adiabatic passage, a popular technique in optics for population inversion in three-level systems, to the NMR regime. The technique employs two amplitude modulated pulses-the first connecting the final and intermediate states followed by a second partially overlapped in time with it and connecting the ground and intermediate states. We present computer simulations demonstrating the applicability of the technique in NMR although we are no longer dealing with "pure" states, unlike in optics. Double quantum population inversion in two- and three-spin scalar coupled systems provides experimental support to our proposal.

This paper reports the first theoretical treatment of the MgNC↔MgCN isomerization in the X 2 Σ + electronic ground state. Based on ab initio data, a global potential energy surface encompassing the MgNC and MgCN minima (which both correspond to linear geometries) has been constructed, and this surface has been used, together with global dipole moment surfaces, for calculating 24MgNC/24MgCN rotation–vibration energies and transition moments for states up to about 2150 cm−1 above the vibrational ground state of 24MgNC. The vibrational ground state of 24MgCN is found to be 651 cm−1above that of 24MgNC. The first delocalized state occurs at 2111.9 cm−1. The prospect of implementing the successive stimulated Raman adiabatic passage (STIRAP) method for optically controlling the MgNC↔MgCN isomerization is discussed.

This review of laser probing first outlines some general aspects, noting a number of topics not covered in conference LAP2002. In more detail it describes the probing of atoms (or molecules) to determine excitation properties. This leads naturally to the consideration of ways in which coherent transients affect the response of matter to laser radiation. These include stimulated Raman adiabatic passage, with associated dark state, and electromagnetically induced modifications of transparency and refractive indices.

We present a measurement scheme designed to measure the state of an exciton in a single quantum dot: the measurement is performed by employing the stimulated Raman adiabatic passage and its result is stored in a double quantum dot structure. Calculations showing that the requirements for acting as a measurement device are fulfilled by the proposed semiconductor nanostructure are presented.

We have examined the use of successive stimulated Raman adiabatic passage (STIRAP) excitations to control the isomerization reaction HCN→CNH. We show that this method generates virtually complete transfer from an arbitrary initial vibrational state of HCN to an arbitrary final vibrational state of CNH. This result is valid even in the presence of a substantial number of background states that have non-zero dipole transition moments among themselves and with the subset of STIRAP states, and when pairs of background states are in resonance with the applied field.

We examine the possibility of transfer of atomic coherence via stimulated Raman adiabatic passage (STIRAP). As a case study, we consider a five-level scheme in which the four ground states can be coupled to the common excited state by four different laser pulses. We calculate the fidelity for the preparation of the atomic system in a superposition of two ground states starting from a superposition of the other two ground states. We prove the feasibility of transfer of coherences via STIRAP and derive the necessary conditions for the sequence of laser pulses.

We describe a method for creating an arbitrary coherent superposition of two atomic states in a controlled and robust way by using a sequence of three pulses in a four-state system. The proposed technique is based on the existence of two degenerate dark states (i.e. states having no component of the excited state) and their interaction. The mixing of the dark states can be controlled by changing the relative delay of the pulses, and thus an arbitrary superposition state can be generated. It is shown that the method is robust against small variations of parameters (e.g. the area of the pulses) and is insensitive to radiative decay from the intermediate excited state. A time reversed version of the technique makes possible the determination of phase occurring in a superposition of two atomic states.

We discuss the dependence of the population transfer probability in the three-level Λ-scheme using stimulated Raman adiabatic passage on detuning from the two-photon resonance. For a large decay rate of the intermediate level we found that the two-photon lineshape is close to Gaussian with linewidth inversely proportional to the square root of the decay rate. The shift of the maximum of the two-photon line from exact two-photon resonance has been investigated.

We show how, using a combination of a radiative pulse and a pulsed quasistatic magnetic field, it is possible to obtain complete population inversion between two states in a multistate system. The population transfer occurs between states of opposite parity, and does not require either careful control of pulse area nor frequency chirp. When the pulses are applied in counter-intuitive order the method is dynamically equivalent to stimulated Raman adiabatic passage (STIRAP). Complete inversion is also possible for intuitively ordered pulses, with robustness equivalent to that of STIRAP.

We discuss theoretical procedures for using a single laser pulse, of varying linear polarization, to transfer population between sublevels of a degenerate atomic level. The method is based on application of the procedure of stimulated Raman adiabatic passage (STIRAP). We also show how, in principle, a pulsed quasistatic magnetic field can be used to improve the usual adiabatic constraints on achieving complete population transfer by means of STIRAP. The technique allows use of shorter pulses, so that population transfer can be achieved more rapidly. It diminishes, or even eliminates, diabatic loss during the population transfer.

We analyse the effect of the intermediate-level detuning on the efficiency of the stimulated Raman adiabatic passage process in three-level systems. We present an exactly solvable analytic model, involving smooth delayed pulses, as well as numerical results and an analytic approximation for Gaussian pulses. Both types of pulses demonstrate that for fixed pulse strengths, the transfer efficiency is adversely affected as the intermediate-level detuning increases because of the deteriorating adiabaticity and eventually vanishes for very large detuning. It is shown that the width of the detuning range, over which the transfer efficiency remains high, is proportional to the squared pulse area. A simple analysis suggests that this feature should be generally valid for any smooth delayed pulses.

We present an analytically solvable model for stimulated Raman adiabatic passage (STIRAP) processes in three-level systems. It involves realistic separated pulses which vanish at infinite times, whose pulse areas are finite and whose envelopes are smooth functions of time. The solution is obtained using the correspondence between three-level systems on resonance and two-level systems. The analytic model confirms the breakdown of the Dykhne-Davis-Pechukas exponential dependence of the non-adiabatic transition probability on the adiabaticity parameter found numerically recently.

The stimulated Raman adiabatic passage (STIRAP) is an effective and robust method to control the chemical reaction by means of the laser pulses, which generate the quantum coherence in molecular states. The STIRAP, however, is usually not applicable to the molecular system with two degenerate states such as optical isomers. We propose here a different strategy within the STIRAP, which generates the effective transition from one isomer to the other, and apply this method to the model system with two degenerate levels.