Coherent Excitation Of Atoms Research Articles

Observation of a narrow inner-shell orbital transition in atomic erbium at 1299 nm

We report on the observation and coherent excitation of atoms on the narrow inner-shell orbital transition, connecting the erbium ground state $[\mathrm{Xe}] 4f^{12} (^3\text{H}_6)6s^{2}$ to the excited state $[\mathrm{Xe}] 4f^{11}(^4\text{I}_{15/2})^05d (^5\text{D}_{3/2}) 6s^{2} (15/2,3/2)^0_7$. This transition corresponds to a wavelength of 1299 nm and is optically closed. We perform high-resolution spectroscopy to extract the $g_J$-factor of the $1299$-nm state and to determine the frequency shift for four bosonic isotopes. We further demonstrate coherent control of the atomic state and extract a lifetime of 178(19) ms which corresponds to a linewidth of 0.9(1) Hz. The experimental findings are in good agreement with our semi-empirical model. In addition, we present theoretical calculations of the atomic polarizability, revealing several different magic-wavelength conditions. Finally, we make use of the vectorial polarizability and confirm a possible magic wavelength at 532 nm.

Quantum phases of matter on a 256-atom programmable quantum simulator

Motivated by far-reaching applications ranging from quantum simulations of complex processes in physics and chemistry to quantum information processing1, a broad effort is currently underway to build large-scale programmable quantum systems. Such systems provide insights into strongly correlated quantum matter2-6, while at the same time enabling new methods for computation7-10 and metrology11. Here we demonstrate a programmable quantum simulator based on deterministically prepared two-dimensional arrays of neutral atoms, featuring strong interactions controlled by coherent atomic excitation into Rydberg states12. Using this approach, we realize a quantum spin model with tunable interactions for system sizes ranging from 64 to 256 qubits. We benchmark the system by characterizing high-fidelity antiferromagnetically ordered states and demonstrating quantum critical dynamics consistent with an Ising quantum phase transition in (2+1) dimensions13. We then create and study several new quantum phases that arise from the interplay between interactions and coherent laser excitation14, experimentally map the phase diagram and investigate the role of quantum fluctuations. Offering a new lens into the study of complex quantum matter, these observations pave the way for investigations of exotic quantum phases, non-equilibrium entanglement dynamics and hardware-efficient realization of quantum algorithms.

Power narrowing in coherent atomic excitation by smoothly shaped pulsed fields

When atoms are excited by laser radiation the conventional wisdom dictates that the spectral excitation profile – the excited-state population vs the detuning – broadens as the radiation intensity increases. This common expectation has been shown to be incorrect in the fluorescence signal following two-photon excitation of xenon atoms by a Gaussian laser pulse, which showed almost no power broadening [T. Halfmann, T. Rickes, N.V. Vitanov, K. Bergmann, Optics Communications, 220 (2003) 353] Here we go a step further and show that for a class of pulse shapes, the falling edges of which vanish as inverse powers of time, ∝t−n (with n>1), the spectral excitation profile must exhibit power narrowing, i.e. the spectral linewidth scales as Ω0−1/(n−1), where Ω0 is the Rabi frequency of the transition. We provide a simple physical explanation based upon the notions of adiabatic evolution and coherent population return and discuss important experimental applications.

Shaping coherent excitation of atoms and molecules by a train of ultrashort laser pulses

We propose a mechanism to produce a superposition of atomic and molecular states by a train of ultrashort laser pulses combined with weak control fields. By adjusting the repetition rate of the pump pulses and the intensity of the coupling laser, one can suppress a transition while simultaneously enhancing the desired transitions. As an example, various superpositions of vibrational states of the $K_2$ molecule are shown.

Symmetries and asymmetries in coherent atomic excitation by chirped laser pulses

We analyze the effects of laser-induced Stark shift and irreversible population loss on the technique of chirped-frequency adiabatic passage, and the ensuing symmetries and asymmetries in the ionization and fluorescence signals. We find that the properties of the detection signal depend critically on the fashion in which it is collected: for example, the post-pulse populations of the ground and excited states, and the ionization signal collected during the excitation, possess different symmetry properties with respect to the frequency chirp rate and the static frequency detuning. We illustrate these features with two exactly soluble analytic models, which describe simultaneous excitation and ionization of a two-state quantum system, as it typically occurs in atomic excitation with femtosecond laser pulses. We find that the ionization signal may exhibit unexpected oscillations and derive the conditions for maximizing their contrast.

Counterintuitive transitions between crossing energy levels

We calculate analytically the probabilities for intuitive and counterintuitive transitions in a three-state system, in which two parallel energies are crossed by a third, tilted energy. The state with the tilted energy is coupled to the other two states in a chainwise linkage pattern with constant couplings of finite duration. The probability for a counterintuitive transition is found to increase with the square of the coupling and decrease with the squares of the interaction duration, the energy splitting between the parallel energies, and the tilt (chirp) rate. Physical examples of this model can be found in coherent atomic excitation and optical shielding in cold atomic collisions.

Adiabatic elimination, the rotating-wave approximation and two-photon transitions

The rotating-wave approximation (RWA) is a formalism of great utility in the description of the coherent excitation of atoms and molecules by laser light. Not only does it give results in agreement with experiment, it also provides a simple framework allowing the Hamiltonian of a system to be written down from inspection of the state-linkage diagram. Recent interest in systems with a two-photon coupling prompted an investigation of the structure of two-photon terms in RWA Hamiltonians. In carrying through the derivation, an interaction with adiabatic elimination was discovered. It is shown that adiabatic elimination must be performed before application of the RWA, else terms are dropped that ought to be retained. RWA Hamiltonians for three-state systems with one and two two-photon linkages are displayed.

Validity of rate equations for Zeeman coherences for analysis of nonlinear interaction of atoms with broadband laser radiation

In this paper we obtain the rate equations for Zeeman coherences in the broad-line approximation and steady-state balance equations directly from optical Bloch equations without the use of the perturbation theory. The broad-line approximation allows us to use the adiabatic elimination procedure in order to eliminate the optical coherences from the optical Bloch equations, but the steady-state condition allows us to derive the balance equations in a straightforward way. We compare our approach with the perturbation-theory approach as given previously and show that our approach is more flexible for analyzing various experiments. Meanwhile we also show the validity and limitations of the application of the rate equations in experiments with coherent atomic excitation when either the broad-line approximation or steady-state conditions hold. Thus we have shown the basis for modeling the coherent atomic excitation experiments by using the relatively simple rate equations, provided that certain experimental conditions hold.

Analysis of 2 Dimensional Effects on Long-Distance Propagation of Lasers in Metal Vapor

To analyze 2 dimensional effects on long-distance propagation of laser pulses, we have developed a 2 dimensional analysis code LAPCEA (LAser Propagation with Coherent Excitation of Atoms). For the case with small transition dipole moment, the 2 dimensional effects on ionization rate of resonant atom appear clearly.

The Livermore experience: Contributions of J H Eberly to laser excitation theory

This article summarizes the developing understanding of coherent atomic excitation, as gained through a collaboration of J. H. Eberly with the Laser Isotope Separation Program of the Lawrence Livermore National Laboratory, particularly aspects of coherence, population trapping, multilevel multiphoton excitation sequences, analytic solutions to multistate excitation chains, the quasicontinuum, pulse propagation, and noise. In addition to the discovery of several curious and unexpected properties of coherent excitation, mentioned here, the collaboration provided an excellent example of unexpected benefits from investment into basic research.

Atomic excitation in strongly coupled plasmas

In dense plasmas atomic excitation rates arising from scattering between atoms and surrounding plasma particles are formulated on the basis of the equations of motion for density matrices in a stochastic potential. This model enables us to treat strong transitions for which the first-order perturbation theory does not apply. Within a decorrelation approximation, which enables one to break up the higher-order correlation functions of plasma density fluctuations into the products of binary correlation functions (i.e., dynamic structure factors), the interaction is effectively summed to infinite order. This method is applied to two-level atoms in hydrogen plasmas. It is thereby demonstrated that when the plasma density is sufficiently high, low-frequency ion-density fluctuations may cause coherent atomic excitation between close lying states. Such coherent excitation cannot be described by the conventional collisional rate equations based on the first-order perturbation theory.

Coherent population transfer via the continuum.

We present a remarkable analytic result which suggests that a continuum can be used as an intermediary for a significant transfer of population from one discrete state to another discrete state in a stimulated Raman transition. The population transfer is accomplished by employing two laser pulses that overlap in time, arranged in the so-called counterintuitive order. That a continuum can be used for population transfer is shown here for the first time. It promises to open up more channels for selective coherent excitation of atoms or molecules.

Coherent Atomic Excitation in a Cavity. I. Low Density

Abstract We present a procedure for treating coherent selective excitation (and subsequent ionization) of atomic vapour in a radiation-filled cavity. Specifically, we describe a technique for solving the coupled Maxwell-Bloch equations for atoms in a one-dimensional cavity by means of a spatial quasi-Fourier expansion that introduces a sequence of increasing spatial harmonics for atomic populations and coherences. We discuss the resulting coupled equations and present examples of solutions for a simple model of stationary and moving two-state atoms in the limit of very low density. The atomic excitation exhibits a travelling wave behaviour, but with significant modulation.

Berry's phase in optical resonance.

We examine the role of Berry's geometrical phase [Proc. R. Soc. London, Ser. A 392, 45 (1984)] in the coherent excitation of atoms. The dynamics of a two-level atom prepared in a superposition of its eigenstates will be modified in a nontrivial fashion by the Berry phase. We extend Berry's formalism to treat the Liouville equation for the density matrix. This extension allows us to discuss statistical mixtures and to incorporate Berry's phase within the well-known Bloch-vector description of optical resonance. Furthermore, our density-matrix formalism provides the means of investigating Berry's phase in open, dissipative systems.

Berry's Phase in the Coherent Excitation of Atoms

Abstract The adiabatic variation of a Hamiltonian can cause the wavefunction, governed by the Hamiltonian, to acquire an unexpected phase. The existence of this phase (Berry's phase) is an additional element in the well-known quantum adiabatic theorem. Berry's phase is observable in the interference between two identically prepared systems only one of which is adiabatically varied. We show that a single quantum system prepared in a superposition of the eigenstates of its Hamiltonian leads to observable Berry phase effects at all times. We examine this principle within the context of two-level optical resonance.

On a mechanism of transient excitation produced by nonresonant laser pulses

Different mechanisms of the Rb ∗(5P 3/2) nonresonant excitation were investigated by multistep photoionization using two pulse dye lasers. It was shown that the principal mechanism is coherent excitation of atoms. The experimental data agree well with theoretical ones.

Gell-Mann dynamic symmetry for N-level quantum systems.

We present the concept of dynamic symmetry of the Gell-Mann type to the dynamical evolution of an arbitrary quantum system of N levels involving generally time-dependent interaction parameters which are of arbitrary strengths and which need not be precisely known. The most important consequence of the dynamic symmetry is the existence of a characteristic set of constants of motion which resembles the existence of a set of quantum numbers of various flavors in high-energy particle physics, and which implies various types of population trapping in the coherent excitation of atoms by lasers in intense-field electrodynamics.

Intensity correlation as a means of manifesting coherent atomic excitation

The excitation of atoms into a coherent linear superposition of states may not always be revealed by measurement of the spontaneous-emission intensity at a single detector. Correlation of the intensity at two detectors, however, can under specified circumstances reveal this coherent excitation.

The coherent excitation of atoms moving through a crystal experimental results

Experimental results concerning to discovery of coherent Coulomb excitation for the He+ ions passing through monocrystalline silver film are reported.