We discuss radiative corrections to an atomic two-level system subject to an intense driving laser field. It is shown that the Lamb shift of the laser-dressed states, which are the natural state basis of the combined atom-laser system, cannot be explained in terms of the Lamb shift received by the atomic bare states which is usually observed in spectroscopic experiments. In the final part, we propose an experimental scheme to measure these corrections based on the incoherent resonance fluorescence spectrum of the driven atom.
A cavity-modified master equation is derived for a coherently driven, V-type three-level atom coupled to a single-mode cavity in the bad cavity limit. We show that population inversion in both the bare and dressed-state bases may be achieved, originating from the enhancement of the atom-cavity interaction when the cavity is resonant with an atomic dressed-state transition. The atomic populations in the dressed state representation are analysed in terms of the cavity-modified transition rates. The atomic fluorescence spectrum and probe absorption spectrum also investigated, and it is found that…
We demonstrate the capability of complete thresholdless lasing operation between dressed states of a two-level atom located inside a microscopic cavity engineered in a photonic band-gap material. We distinguish between threshold and thresholdless behaves by analyzing the Mandel's Q parameter for the cavity field. We find that the threshold behave depends on whether the spontaneous emission is or is not present on the lasing transition. In the presence of the spontaneous emission, the mean photon number of the cavity field exhibits threshold behavior indicating that the system may operate as an…
We propose a theoretical approach for the interpretation of pump-probe measurements where an attosecond pulse is absorbed in the presence of an intense laser pulse. This approach is based on abstractly defined dressed bound states, which capture the essential aspects of the interaction with the laser pulse and facilitate a perturbative description of transitions induced by the attosecond pulse. Necessary properties of dressed bound states are defined and various choices are discussed and compared to accurate numerical solutions of the time-dependent Schroedinger equation.
Analytical expressions for the semiclassical dressed states and corresponding quasienergies are obtained for a two-level quantum system driven by a nonresonant and/or strong laser field in a coherent state. These expressions are of first order in a proper perturbative expansion, and already contain all the relevant physical information on the dynamical and spectroscopic properties displayed by these systems under such particular conditions. The influence of the laser field parameters on transition frequencies, selection rules, and line intensities can be easily understood in terms of the quasi…
We theoretically investigate the scattering of an attosecond electron wave packet launched by an attosecond pulse under the influence of an infrared laser field. As the electron scatters inside a spatially extended system, the dressing laser field controls its motion. We show that this interaction, which lasts just a few hundreds of attoseconds, clearly manifests itself in the spectral interference pattern between different quantum pathways taken by the outgoing electron. We find that the Coulomb-Volkov approximation, a standard expression used to describe laser-dressed photoionization, cannot…
The derivation of approximate wave functions for an electron submitted to both a coulomb and a time-dependent laser electric fields, the so-called Coulomb-Volkov (CV) state, is addressed. Despite its derivation for continuum states does not exhibit any particular problem within the framework of the standard theory of quantum mechanics (QM), difficulties arise when considering an initially bound atomic state. Indeed the natural way of translating the unperturbed momentum by the laser vector potential is no longer possible since a bound state does not exhibit a plane wave form including explicit…
We study non-classical and spectral properties of a strongly driven single-atom laser engineered within a photonic crystal that facilitates a frequency-dependent reservoir. In these studies, we apply a dressed atom model approach to derive the master equation of the system and study the properties of the dressed laser under the frequency dependent transition rates. By going beyond the secular approximation in the dressed-atom cavity field interaction, we find that if, in addition, the non-secular terms are included into the dynamics of the system, then non-linear processes can occur that lead …
A scheme to implement quantum logic gates by manipulating trapped ions through interaction with monochromatic external laser field and quantized cavity field, beyond the Lamb-Dicke regime, is presented. Characteristic times, for implementing ionic state transitions using non-resont laser pulse or quantized cavity field, shows a sharp decline for large Lamb-Dicke parameter value of $η_{L}=η_{c}=0.2$, and is seen to decrease further with increase in number of initial state vibrational quanta $m$.
Characterizing and controlling matter driven far from equilibrium represents a major challenge for science and technology. Here we develop a theory for the optical absorption of electronic materials driven far from equilibrium by resonant and non-resonant lasers. In it, the interaction between matter and the driving light is treated exactly through a Floquet analysis, while the effects of the probing light are captured to first order in perturbation theory. The resulting equations are reminiscent to those for equilibrium absorption but with the Floquet modes playing the role of the pristine ei…
We investigate spectral properties of the atomic fluorescence and the output field of the cavity-mode of a single-atom dressed-state laser in a photonic crystal. We pay a particular attention to the behavior of the spectra in the presence of the frequency dependent reservoir and search for signatures of the thresholdless lasing. Although the thresholdless behavior has been predicted by analyzing the photon statistics of the cavity field, we find that the threshold behavior still exists in the spectrum of the cavity field. We find that the structure of cavity field spectrum depends strongly on …
Electric susceptibility of a laser-dressed atomic medium is calculated for a model Lambda - like system including two lower states and a continuum structured by a presence of an autoionizing state or a continuum with a laser-induced structure. Depending on the strength of a control field it is possible to obtain a significant reduction of the light velocity in a narrow frequency window in the conditions of a small absorption. A smooth transition is shown between the case of a flat continuum and that of a discrete state serving as the upper state of a Lambda system.
We investigate the absorption line shapes of laser-dressed atoms beyond the single-atom response, by using extreme ultraviolet (XUV) attosecond pulse trains to probe an optically thick helium target under the influence of a strong infrared (IR) field. We study the interplay between the IR-induced phase shift of the microscopic time-dependent dipole moment and the resonant-propagation-induced reshaping of the macroscopic XUV pulse. Our experimental and theoretical results show that as the optical depth increases, this interplay leads initially to a broadening of the IR-modified line shape, and …
We propose a laser cooling scheme that allows to cool a single atom confined in a harmonic potential to the trap ground state $|0>$. The scheme assumes strong confinement, where the oscillation frequency in the trap is larger than the effective spontaneous decay width, but is not restricted to the Lamb-Dicke limit, i.e. the size of the trap ground state can be larger than the optical wavelength. This cooling scheme may be useful in the context of quantum computations with ions and Bose-Einstein condensation.
We discuss quantum interference effects in a three-level atom in lambda-configuration, where both transitions from the upper state to the lower states are driven by a single monochromatic laser field. Although the system has two lower states, quantum interference is possible because there are interfering pathways to each of the two lower states. The additional interference terms allow for interesting effects such as the suppression of a dark state which is present without the interference. Finally we examine a narrow spectral feature in the resonance fluorescence of the atom with quantum inter…
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.
We study laser cooling of two ions that are trapped in a harmonic potential and interact by Coulomb repulsion. Sideband cooling in the Lamb-Dicke regime is shown to work analogously to sideband cooling of a single ion. Outside the Lamb-Dicke regime, the incommensurable frequencies of the two vibrational modes result in a quasi-continuous energy spectrum that significantly alters the cooling dynamics. The cooling time decreases nonlinearly with the linewidth of the cooling transition, and the effect of trapping states which may slow down the cooling is considerably reduced. We show that cooling…
We calculate the transient absorption of an isolated attosecond pulse by helium atoms subject to a delayed infrared (\ir) laser pulse. With the central frequency of the broad attosecond spectrum near the ionization threshold, the absorption spectrum is strongly modulated at the sub-\ir-cycle level. Given that the absorption spectrum results from a time-integrated measurement, we investigate the extent to which the delay-dependence of the absorption yields information about the attosecond dynamics of the atom-field energy exchange. We find two configurations in which this is possible. The first…
We show how a broad class of lattice spin-1/2 models with angular- and distance-dependent couplings can be realized with cold alkali atoms stored in optical or magnetic trap arrays. The effective spin-1/2 is represented by a pair of atomic ground states, and spin-spin interactions are obtained by admixing van der Waals interactions between fine-structure split Rydberg states with laser light. The strengths of the diagonal spin interactions as well as the "flip-flop", and "flip-flip" and "flop-flop" interactions can be tuned by exploiting quantum interference, thus realizing different spin symm…
Cavity-mediated cooling has the potential to become one of the most efficient techniques to cool molecular species down to very low temperatures. In this paper we analyse cavity cooling with single-laser driving for relatively large cavity decay rates kappa and relatively large phonon frequencies nu. It is shown that cavity cooling and ordinary laser cooling are essentially the same within the validity range of the Lamb-Dicke approximation. This is done by deriving a closed set of rate equations and calculating the corresponding stationary state phonon number and cooling rate. For example, whe…
The dynamical behavior of entanglement between the atomic ensemble and the spontaneous emission is investigated by applying the femtosecond Gaussian pulses in double- lambda quantum system. In fact by solving the density matrix equations of motion in such a system and by using the von Neumann entropy, the degree of entanglement (DEM) could be measured in semi classical regime and in the multi-photon resonance condition. We interested in investigating the maximum value for DEM and controlled the DEM via relative phase. At first we consider three laser fields as CW optical laser fields and one f…
Two-mode squeezing and entanglement is obtained in a atom-cavity system cosisting a three-level atom and a two-mode cavity with driving laser fields. Here non-resonatn dressed-state transitions between the cavity modes and atom are used to get the effective Hamiltonian.
We propose a simple scheme for implementing quantum logic gates with a string of two-level trapped cold ions outside the Lamb-Dicke limit. Two internal states of each ion are used as one computational qubit (CQ) and the collective vibration of ions acts as the information bus, i.e., bus qubit (BQ). Using the quantum dynamics for the laser-ion interaction as described by a generalized Jaynes-Cummings model, we show that quantum entanglement between any one CQ and the BQ can be coherently manipulated by applying classical laser beams. As a result, universal quantum gates, i.e. the one-qubit rota…
Thanks to the atomic coherence in coupling laser driven atomic system, sub-Doppler absorption has been observed in Doppler-broadened cesium vapor cell via the /Lambda-type three-level scheme. The linewidth of the sub-Doppler absorption peak become narrower while the frequency detuning of coupling laser increases. The results are in agreement with the theoretical prediction by G. Vemuri et al.[PRA,Vol.53(1996) p.2842].
Charge dynamics in an ultra-cold setup involving a laser dressed atom and an ion is studied here. This transfer of charge is enabled through molecular Rydberg states that are accessed via a laser. The character of the charge exchange crucially depends on the coupling between the electronic dynamics and the vibrational motion of the atoms and ion. The molecular Rydberg states are characterized and a criterion for distinguishing coherent and incoherent regimes is formulated. Furthermore the concept is generalized to the many-body setup as the ion effectively propagates through a chain of atoms. …
We use a non-Lindbladian master equation of the Scully-Lamb laser model for the analysis of light propagation in a parity-time symmetric photonic system composed of coupled active and passive whispering-gallery microresonators. Performing the semiclassical approximation, we obtain a set of two nonlinear coupled differential equations describing the time evolution of intracavity fields. These coupled equations are able to explain the experimentally-observed light non-reciprocity [Peng {\em et al.}, Nature Physics {\bf 10}, 394 (2014), Chang {\em et al.}, Nature Photonics {\bf 8}, 524 (2014)]. W…
It is shown that strong driving of a quantum system substantially enhances the Lamb shift induced by broadband reservoirs which are typical for solid-state devices. By varying drive parameters the impact of environmental vacuum fluctuations with continuous spectral distribution onto system observables can be tuned in a distinctive way. This provides experimentally feasible measurement schemes for the Lamb shift in superconducting circuits based on Cooper pair boxes, where it can be detected either in shifted dressed transition frequencies or in pumped charge currents.
The collective interaction via the environmental vacuum is investigated for a mixture of two deviating multi-atom ensembles in a moderately intense laser field. Due to the numerous inter-atomic couplings, the laser-dressed system may react sensitively and rapidly with respect to changes in the atomic and laser parameters. We show for weak probe fields that in the absence of absorption both the index of refraction and the group velocity may be modified strongly and rapidly due to the collectivity.
We study an architecture for implementing adiabatic quantum computation with trapped neutral atoms. Ground state atoms are dressed by laser fields in a manner conditional on the Rydberg blockade mechanism, thereby providing the requisite entangling interactions. As a benchmark we study the performance of a Quadratic Unconstrained Binary Optimization (QUBO) problem whose solution is found in the ground state spin configuration of an Ising-like model. We model a realistic architecture, including details of the atomic implementation, with qubits encoded into the clock states of 133Cs, effective B…
In dense atomic gases the interaction between transition dipoles and photons leads to the formation of many-body states with collective dissipation and long-ranged forces. Despite decades of research, a full understanding of this paradigmatic many-body problem is still lacking. Here, we put forward and explore a scenario in which a dense atomic gas is weakly excited by an off-resonant laser field. We develop the theory for describing such dressed many-body ensembles and show that collective excitations are responsible for the emergence of many-body interactions, i.e. effective potentials that …
Based on the conditional quantum dynamics of laser-ion interaction, we propose an efficient theoretical scheme to deterministically generate quantum pure states of a single trapped cold ion without performing the Lamb-Dicke approximation. An arbitrary quantum state can be created by using a series of classical laser beams with selected frequencies, initial phases and durations. As special examples, we further show how to create or approximate several typical macroscopic quantum states, such as the phase state and (even/odd) coherent states. Unlike previous schemes operated in the Lamb-Dicke re…
Several sequential operations are usually needed for implementing controlled quantum gates and generating entanglement between a pair of quantum bits. Based on the conditional quantum dynamics for a two-ion system beyond the Lamb-Dicke limit, here we propose a theoretical scheme for manipulating two-qubit quantum information, i.e., implementing a universal two-qubit quantum gate and generating a two-qubit entangled state, by using a pair of simultaneous laser pulses. Neither the Lamb-Dicke approximation nor the auxiliary atomic level are required. The experimental realizability of this simple …
A simple alternative scheme for implementing quantum gates with a single trapped cold two-level ion beyond the Lamb-Dicke (LD) limit is proposed. Basing on the quantum dynamics for the laser-ion interaction described by a generalized Jaynes-Cummings model, one can introduce two kinds of elementary quantum operations i.e., the simple rotation on the bare atomic state, generated by applying a resonant pulse, and the joint operation on the internal and external degrees of the ion, performed by using an off-resonant pulse. Several typical quantum gates, including Hadamard gate, controlled-Z and co…
The dynamics of an atomic few-level system can depend on the phase of driving fields coupled to the atom if certain conditions are satisfied. This is of particular interest to control interference effects, which can alter the system properties considerably. In this article, we discuss the mechanisms of such phase control and interference effects in an atomic three-level system in $Λ$ configuration, where the upper state spontaneously decays into the two lower states. The lower states are coupled by a driving field, which we treat as quantized. This allows for an interpretation on the single ph…
While the Rydberg-blockade regime provides the natural setting for creating $W$-type entanglement with cold neutral atoms, it is demonstrated here that a scalable entanglement resource of this type can even be obtained under completely different physical circumstances. To be more precise, a special instance of twisted $W$ states -- namely, $π$-twisted ones -- can be engineered in one-dimensional arrays of cold neutral atoms with Rydberg-dressed resonant dipole-dipole interaction. In particular, it is shown here that this is possible even when a (dressed) Rydberg excitation is coupled to the mo…
We present a robust quantum optimal control framework for implementing fast entangling gates on ion-trap quantum processors. The framework leverages tailored laser pulses to drive the multiple vibrational sidebands of the ions to create phonon-mediated entangling gates and, unlike the state of the art, requires neither weak-coupling Lamb-Dicke approximation nor perturbation treatment. With the application of gradient-based optimal control, it enables finding amplitude- and phase-modulated laser control protocols that work beyond the Lamb-Dicke regime, promising gate speed at the order of micro…
We discuss a laser cooling scheme for trapped atoms or ions which is based on double electromagnetically induced transparency (EIT) and makes use of a four-level atom in tripod configuration. The additional fourth atomic state is coupled by a strong coupling laser field to the usual three-level setup of single-EIT cooling. This effectively allows to create two EIT structures in the absorption spectrum of the system to be cooled, which may be controlled by the coupling laser field parameters to cancel both the carrier- and the blue-sideband excitations. In leading order of the Lamb-Dicke expans…
We study theoretically inelastic spectrum of coherent backscattering of laser light by two atoms. For an intense laser field, there are frequency domains of not only constructive but also destructive (self-)interference of the inelastic photons. We interpret the emergent spectral features using the dressed states and considering coherent backscattering as a kind of the pump-probe experiment.
In the past few decades, many works have been devoted to the study of exceptional points (EPs), i.e., exotic degeneracies of non-Hermitian systems. The usual approach in those studies involves the introduction of a phenomenological effective non-Hermitian Hamiltonian (NHH), where the gain and losses are incorporated as the imaginary frequencies of fields and from which the Hamiltonian EPs (HEPs) are derived. Although this approach can provide valid equations of motion for the fields in the classical limit, its application in the derivation of EPs in the quantum regime is questionable. Recently…
This paper is concerned with two rather basic phenomena: the incoherent fluorescence spectrum of an atom driven by an intense laser field and the coupling of the atom to the (empty) modes of the radiation field. The sum of the many-photon processes gives rise to the inelastic part of the atomic fluorescence, which, for a two-level system, has a well-known characteristic three-peak structure known as the Mollow spectrum. From a theoretical point of view, the Mollow spectrum finds a natural interpretation in terms of transitions among laser-dressed states which are the energy eigenstates of a se…
Electromagnetically induced transparency (EIT) is an important tool for controlling light propagation and nonlinear wave mixing in atomic gases with potential applications ranging from quantum computing to table top tests of general relativity. Here we consider EIT in an atomic Bose-Einstein Condensate (BEC) trapped in a double well potential. A weak probe laser propagates through one of the wells and interacts with atoms in a three-level $Λ$ configuration. The well through which the probe propagates is dressed by a strong control laser with Rabi frequency $Ω_μ$, as in standard EIT systems. Tu…
Phase transitions of thermal systems and the laser threshold were first connected more than forty years ago. Despite the nonequilibrium nature of the laser, the Landau theory of thermal phase transitions, applied directly to the Scully-Lamb laser model (SLLM), indicates that the laser threshold is a second-order phase transition, associated with a $U(1)$ spontaneous symmetry breaking (SSB). To capture the genuine nonequilibrium phase transition of the SLLM (i.e., a single-mode laser without a saturable absorber), here we employ a quantum theory of dissipative phase transitions. Our results con…
The effect of an ac modulation on a 2-level or 3-level system is studied theoretically. The absorption spectrum is calculated by solving the optical Bloch equations and is interpreted by reference to the Floquet quasienergy spectrum. The dependence of the absorption sidebands on the intensity of the coupling laser field in Rydberg systems submitted to a radio-frequency (rf) field is analysed in detail. It is shown that for sufficiently strong coupling fields additional sidebands appear in the probe absorption spectrum in ladder 3-level systems. These additional sidebands are induced by the cou…
We report and propose a simple scheme to achieve efficient and fast coherent population transfer (CPT) by utilizing either a nonlinearly chirped Gaussian shaped few-cycle laser pulse or an unchirped sinc-shaped few-cycle laser pulse. The proposed scheme is shown to be fairly robust against the variation of the laser parameters such as temporal pulse width, chirp rates, carrier envelope phases and Rabi frequencies. We find that compared to the so-called stimulated Raman adiabatic passage (STIRAP) technique, our scheme for complete population transfer with few-cycle Gaussian shaped laser pulses …
We demonstrate the trapping of cold $^{87}Rb$ atoms in a toroidal geometry using a radio frequency (rf) dressed quadrupole magnetic trap formed by superposing a strong rf-field on a quadrupole trap. This rf-dressed quadrupole trap has the minimum potential away from the quadrupole trap centre on a circular path which facilitates trapping in toroidal geometry. In these experiments, the laser cooled atoms were first trapped in a quadrupole trap, then cooled evaporatively using a weak rf-field, and finally trapped in an rf-dressed quadrupole trap. The radius of the toroid could be varied by varyi…
In this work, robustness of controlled density of optical states in doubly driven artificial atoms is studied under phonon dissipation. By using both perturbative and polaron approaches, we investigate the influence of carrier-phonon interactions on the emission properties of a two-level solid-state emitter, simultaneously coupled to two intense distinguishable lasers. Phonon decoherence effects on the emission spectra are found modest up to neon boiling temperatures ($\sim 30$ K), as compared with photon generation at the Fourier transform limit obtained in absence of lattice vibrations (zero…
We scrutinize the behaviour of hydrogen atom's eigenvalues in a quantum plasma as it interacts with electric field directed along $θ=π$ and exposed to linearly polarized intense laser field radiation. Using the Kramers-Henneberger (KH) unitary transformation, which is semiclassical counterpart of the Block-Nordsieck transformation in the quantized field formalism, the squared vector potential that appears in the equation of motion is eliminated and the resultant equation is expressed in KH frame. Within this frame, the resulting potential and the corresponding wavefunction have been expanded i…
Bright solitons in atomic Bose--Einstein condensates are strong candidates for high precision matter-wave interferometry, as their inherent stability against dispersion supports long interrogation times. An analog to a beam splitter is then a narrow potential barrier. A very narrow barrier is desirable for interferometric purposes, but in a typical realisation using a blue-detuned optical dipole potential, the width is limited by the laser wavelength. We investigate a soliton interferometry scheme using the geometric scalar potential experienced by atoms in a spatially dependent dark state to …
Measurement-based quantum computing relies on the rapid creation of large-scale entanglement in a register of stable qubits. Atomic arrays are well suited to store quantum information, and entanglement can be created using highly-excited Rydberg states. Typically, isolating pairs during gate operation is difficult because Rydberg interactions feature long tails at large distances. Here, we engineer distance-selective interactions that are strongly peaked in distance through off-resonant laser coupling of molecular potentials between Rydberg atom pairs. Employing quantum gas microscopy, we veri…
