Atomic System Research Articles

Experimental Implementation of the Optical Fractional Fourier Transform in the Time-Frequency Domain.

The fractional Fourier transform (FrFT), a fundamental operation in physics that corresponds to a rotation of phase space by any angle, is also an indispensable tool employed in digital signal processing for noise reduction. Processing of optical signals in their time-frequency degree of freedom bypasses the digitization step and presents an opportunity to enhance many protocols in quantum and classical communication, sensing, and computing. In this Letter, we present the experimental realization of the fractional Fourier transform in the time-frequency domain using an atomic quantum-optical memory system with processing capabilities. Our scheme performs the operation by imposing programmable interleaved spectral and temporal phases. We have verified the FrFT by analyses of chroncyclic Wigner functions measured via a shot-noise limited homodyne detector. Our results hold prospects for achieving temporal-mode sorting, processing, and superresolved parameter estimation.

Enhanced spatially focused superbunched emission from a line of few interacting atomic dipoles

An excellent phenomenon in the realm of quantum optics and informatics is the study of radiative characteristics of a set of few identical two-level correlated systems. The system envisaged consists of a line of equidistant atoms probed by a weak resonant laser field. Collective decay and dipole-dipole interactions are incorporated due to a coupling of the atomic system to the common surrounding vacuum field. The correlation functions of the emitted field give important physical information about statistical correlations that exist between the emitting atoms. The dependence of the one-time first, second and third order correlation functions of the emitted field on the detection directions in the far-field domain in steady state has been studied. It has been found that the probability of the coincident detection of two and three photons is very large in particular directions. Interestingly, it is observed that the preferred directions for two-photon emission are the same as the favoured directions for the emission of a triplet of photons. Moreover, these directions are exactly located where the emission of a single uncorrelated photon is extremely unlikely. The variation of these directions where two or three correlated fluorescent photons are detected with high probability has been studied as a function of the magnitude of the dipole-dipole interaction between the emitting atoms. A general trend in this variation can be noted for closely-spaced interacting atoms.

Interaction of four level closed loop atomic systems in the presence of two vector beams

In this manuscript, we have theoretically studied the four level closed loop atomic systems in the presence of two vector beams. A spatially dependent transparency for the probe vector beam is obtained based on the semiclassical model. We have explicitly shown that the number of petals formed for probe absorption depends on the value of orbital angular momentum (OAM) of the constituting beams. A detailed study for absorption and dispersion of right circularly polarized (RCP) and left circularly polarized (LCP) components of the probe beam is carried out and the importance of the polarization state of the beams on Higher Order Poincare Sphere (HOPS) is highlighted. An explicit effect of the interferometer phase of the vector beam which is geometric in nature, is shown for probe beam response. Three types of four level closed loop atomic system is studied with particular emphasis given for double Λ and Diamond atomic system. A dark state analysis of the atomic system is carried out which facilitate a physical understanding of the obtained results. Our study has explored the effects of inhomogeneity in both polarization and intensity for probe and coupling beam in a closed loop atomic system which is phase dependent.

Enhanced coherent microwave-to-optics conversion based on second-order nonlinearity

An efficient microwave-optical frequency conversion scheme is proposed based on the second-order nonlinearity in the atomic system. Due to the magnetic transition driven by a microwave field, the second-order nonlinearity builds up and three-wave mixing process appears. It is interesting to find that a detuned auxiliary transition causes a large second-order nonlinearity, which contributes to the increase of conversion efficiency. The simulation results show that the conversion efficiency could be increased by five times. Other effects on the conversion efficiency are also discussed.

Manipulation of double-four-wave mixing in an atomic system under vortex-beam illumination

Manipulation of double-four-wave mixing in an atomic system under vortex-beam illumination

CFD Simulation of the Dosing Behavior within the Atomic Layer Deposition Feeding System

The effective operation of atomic layer deposition (ALD) feeding system is the premise of realizing specific ALD processes. In the present work, a detailed computational fluid dynamics (CFD) model of the feeding system has been developed and validated, which accounts for the roles of ALD valves and manifolds. A numerical simulation of the compressible fluid flow and heat/mass transfer within the feeding system was conducted. The dosing amounts and the spatiotemporal distributions of the precursors can be accurately predicted using the CFD model, as validated by experimental results. Different precursors, operating conditions, and structures of the feeding system were simulated and analyzed to examine the operating flexibility of the feeding system. The simulation results can be adopted as the upstream boundary conditions for simulations of the ALD process in the reaction chamber. The substrate-scale simulation indicates that the effect of the feeding system on the film deposition is highly related to the surface kinetics of ALD. The present work can serve as a guide for the development and optimization of different ALD-based processes via proper operation and even the design of the feeding system.

Multichannel nonreciprocal amplifications using cesium vapor

Multichannel synchronous amplifications are an inevitable key problem in quantum communication process, which can broaden the bandwidth of transmitted signals and establish correlation among different optical channels. Here we study a nonreciprocal system with four concurrent amplification channels using hot cesium atoms, both theoretically and experimentally. For the forward probe field, the double--electromagnetically induced transparency structure is formed and the phase-matching condition of the multiwave mixing process is satisfied, which are both destroyed when the probe field is reversed. In addition, the four-channel nonreciprocal amplifications are formed in the Zeeman sublevels of the system with special selection of light field polarization, which will also dramatically enhance the signal-to-noise ratio by suppressing the spontaneous emission noise of the system. In our experiment, the quadruple nonreciprocal amplifications are achieved with the maximum forward gain reaching 30 dB and the reverse suppression reaching--23 dB. The gain adjustability allows the construction of a gain-loss balanced system, providing a scheme for an atomic system to engineer a parity-time-symmetric (or -antisymmetric) structure.

Many-body spin rotation by adiabatic passage in spin-1/2 XXZ chains of ultracold atoms

Quantum many-body phases offer unique properties and emergent phenomena, making them an active area of research. A promising approach for their experimental realization in model systems is to adiabatically follow the ground state of a quantum Hamiltonian from a product state of isolated particles to one that is strongly-correlated. Such protocols are relevant also more broadly in coherent quantum annealing and adiabatic quantum computing. Here we explore one such protocol in a system of ultracold atoms in an optical lattice. A fully magnetized state is connected to a correlated zero-magnetization state (an xy-ferromagnet) by a many-body spin rotation, realized by sweeping the detuning and power of a microwave field. The efficiency is characterized by applying a reverse sweep with a variable relative phase. We restore up to of the original magnetization independent of the relative phase, evidence for the formation of correlations. The protocol is limited by the many-body gap of the final state, which is inversely proportional to system size, and technical noise. Our experimental and theoretical studies highlight the potential and challenges for adiabatic preparation protocols to prepare many-body eigenstates of spin Hamiltonians.

Tailoring population transfer between two hyperfine ground states of Rb87

In this paper, we investigate the coherent control over a complex multi-level atomic system using the stimulated Raman adiabatic passage (STIRAP). Based on the example of rubidium-87 atoms, excited with circularly-polarized light at the D1 line, we demonstrate the ability to decompose the system into three- and four-level subsystems independently interacting with light beams. Focusing on the four-level system, we demonstrate that the presence of an additional excited state significantly affects the dynamics of the system evolution. Specifically, it is shown that, through the appropriate tuning of the light beams, some of the transfer channels can be blocked, which leads to better control over the system. We also demonstrate that this effect is most significant in media free from inhomogeneous broadening (e.g., Doppler effect) and deteriorates if such broadening is present. For instance, motion of atoms affects both the efficiency and selectivity of the transfer.

Chiral spin liquid state of strongly interacting bosons with a moat dispersion: A Monte Carlo simulation

We consider a system of strongly interacting bosons in two dimensions with moat band dispersion which supports an infinitely degenerate energy minimum along a closed contour in the Brillouin zone. The system has been theoretically predicted to stabilize a chiral spin liquid (CSL) ground state. In the thermodynamic limit and vanishing densities, n→0, chemical potential, μ, of the uniform CSL state was shown to scale with n as μ∼n2log2n. Here we perform a Monte Carlo simulation to find the parametric window for particle density, n≲k0282π, where k0 is the linear size of the moat (the radius for a circular moat), for which the scaling ∼n2log2n in the equation of state of the homogeneous CSL is preserved. We variationally show that the uniform CSL state is favorable in an interval beyond the obtained scale and present a schematic phase diagram for the system. Our results offer some density estimates for observing the low-density behavior of CSL in time-of-flight experiments with a recently Floquet-engineered moat band system of ultracold atoms in Bracamontes et al. (2022), and for the recent experiments on emergent excitonic topological order in imbalanced electron–hole bilayers.

Engineering Knill–Laflamme–Milburn Entanglement via Dissipation and Coherent Population Trapping in Rydberg Atoms

We present a scheme for dissipatively preparing bipartite Knill–Laflamme–Milburn (KLM) entangled state in a neutral atom system, where the spontaneous emission of excited Rydberg states, combined with the coherent population trapping, is actively exploited to engineer a steady KLM state from an arbitrary initial state. Instead of commonly used antiblockade dynamics of two Rydberg atoms, we particularly utilize the Rydberg–Rydberg interaction as the pumping source to drive the undesired states so that it is unnecessary to satisfy a certain relation with laser detuning. The numerical simulation of the master equation signifies that both the fidelity and the purity above 98% is available with the current feasible parameters, and the corresponding steady-state fidelity is robust to the variations of the dynamical parameters.

Exploring the teleported information in two two-level atoms interacting with a deformed cavity field

The possibility of teleporting a single-qubit system in an atomic system that interacts with a deformed cavity mode is being discussed. The average fidelity is used to investigate the quality of the teleported information in either ideal or deformed cavity. The quantum Fisher information is used as an estimator for the weight and phase angle parameters of the initial input state. The study shows that maximizing/minimizing the estimation degree and fidelity depends on the initial state settings of the atomic system, dipole–dipole coupling, and the estimated parameters. To maximize the information in the presence of a deformed cavity, one has to set large values of the atomic coupling dipole subsystem and reduce the deformation parameter.

Rydberg-dressed solitons in Bose-Einstein condensates with parity-time symmetry

Generating stable bright solitons in free space has been a long-standing goal in the study of matter waves in Bose-Einstein condensates (BECs). Rydberg-induced matter wave demonstrates an excellent effect in balancing the repulsive and attractive interactions between remote atoms. Parity-time (PT) symmetric lattices have been widely studied in controlling the flow of matter waves. In this study, we theoretically investigated the localization of nonlinear matter waves in the PT-symmetric Rydberg atomic BECs system. The numerical simulation method was used to obtain the stationary solutions of the wave function by solving the Gross-Pitaevskii equation (GPE) of the Rydberg-dressed BECs system. Fundamental, higher-order solitons and vortical ones were uncovered, and their stabilities were evaluated through linear-stability analysis and direct simulation with perturbation. Furthermore, the collision of solitons exhibited a quasi-elastic feature.

Accelerating the Assembly of Defect-Free Atomic Arrays with Maximum Parallelisms

Defect-free atomic arrays have been demonstrated as a scalable and fully-controllable platform for quantum simulations and quantum computations. To push the qubit size limit of this platform further, we design an integrated measurement and feedback system, based on field programmable gate array (FPGA), to quickly assemble two-dimensional defect-free atomic array using maximum parallelisms. The total time cost of the rearrangement is first reduced by processing atom detection, atomic occupation analysis, rearrangement strategy formulation, and acousto-optic deflectors (AOD) driving signal generation in parallel in time. Then, by simultaneously moving multiple atoms in the same row (column), we save rearrangement time by parallelism in space. To best utilize these parallelisms, we propose a new algorithm named Tetris algorithm to reassemble atoms to arbitrary target array geometry from two-dimensional stochastically loaded atomic arrays. For an $L \times L$ target array geometry, the number of moves scales as $L$, and the total rearrangement time scales at most as $L^2$. We present the overall performance for different target geometries, and demonstrate a significant reduction in rearrangement time and the potential to scale up defect-free atomic array system to thousands of qubits.

Helical phase steering via four-wave mixing in a closely cycled double-ladder atomic system

This work presents a theoretical analysis of the helical phase steering via a four-wave mixing (FWM) process in a closely cycled double-ladder atomic system. Our focus is to understand the contribution of the two-photon resonant process governed by a probe field and a driving laser in the control of the helical phase. The theoretical analysis allows us to understand the helical phase can be effectively steered when the two-photon resonant condition Δ=−δ is satisfied. Moreover, we investigate the superposition modes of the FWM field and a same-frequency Gaussian beam, which testify the two-photon resonant condition Δ=−δ plays an important role in the steering of the helical phase.

Quantum Langevin theory for two coupled phase-conjugated electromagnetic waves

While loss-gain-induced Langevin noises have been intensively studied in quantum optics, the effect of a complex-valued nonlinear coupling coefficient on the noises of two coupled phase-conjugated optical fields has never been questioned before. Here, we provide a general macroscopic phenomenological formula of quantum Langevin equations for two coupled phase-conjugated fields with linear loss (gain) and complex nonlinear coupling coefficient. The macroscopic phenomenological formula is obtained from the coupling matrix to preserve the field commutation relations and correlations, which does not require knowing the microscopic details of light-matter interaction and internal atomic structures. To validate this phenomenological formula, we take spontaneous four-wave mixing in a double-$\Lambda$ four-level atomic system as an example to numerically confirm that our macroscopic phenomenological result is consistent with that obtained from the microscopic Heisenberg-Langevin theory. Finally, we apply the quantum Langevin equations to study the effects of linear gain and loss, complex phase mismatching, as well as complex nonlinear coupling coefficient in entangled photon pair (biphoton) generation, particularly to their temporal quantum correlations.

Itinerant ferromagnetism entrenched by the anisotropy of spin–orbit coupling in a dipolar Fermi gas

We investigate the itinerant ferromagnetism in a dipolar Fermi atomic system with the anisotropic spin–orbit coupling (SOC), which is traditionally explored with isotropic contact interaction. We first study the ferromagnetism transition boundaries and the properties of the ground states through the density and spin-flip distribution in momentum space, and we find that both the anisotropy and the magnitude of the SOC play an important role in this process. We propose a helpful scheme and a quantum control method which can be applied to conquering the difficulties of previous experimental observation of itinerant ferromagnetism. Our further study reveals that exotic Fermi surfaces and an abnormal phase region can exist in this system by controlling the anisotropy of SOC, which can provide constructive suggestions for the research and the application of a dipolar Fermi gas. Furthermore, we also calculate the ferromagnetism transition temperature and novel distributions in momentum space at finite temperature beyond the ground states from the perspective of experiment.

Optically polarized selective transmission of a fractional vector vortex beam by the polarized atoms with external magnetic fields.

We investigate the role of external magnetic fields and linearly polarized pump light, especially when their directions are parallel or vertical, on the propagation of the fractional vector vortex beams (FVVBs) through a polarized atomic system. Herein, the different configurations of external magnetic fields lead to various optically polarized selective transmissions of FVVBs with different fractional topological charge α caused by the polarized atoms, which is theoretically demonstrated by the atomic density matrix visualization analysis and experimentally explored by Cesium atom vapor. Meanwhile, we find that the FVVBs-atom interaction is a vectorial process due to the different optical vector polarized states. In this interaction process, the atomic optically polarized selection property provides potential for the realization of the magnetic compass based on warm atoms. For the FVVBs, due to the rotational asymmetry of the intensity distribution, we can observe some transmitted light spots with unequal energy. Compared with the integer vector vortex beam, it is possible to obtain a more precise magnetic field direction by fitting the different "petal" spots of the FVVBs.

Generation of optical -antisymmetry in a coherent N-type atomic medium

We have proposed two schemes to exhibit -antisymmetry in a four-level N-type atomic system interacting with two strong driving fields and a weak probe field. For both the schemes, the required spatially modulated coherence rendering -antisymmetry is achieved by employing a double-channel Gaussian beam for one driving field with a single channel for the other driving field in different field configurations. In each scheme, for equal and opposite detunings of the double-channel Gaussian beam, -antisymmetry can be obtained in the spatial domain. Such a way of control is unique to this model. Using the present method, it is possible to obtain -antisymmetry for both the homogeneously and inhomogeneously broadened atoms.

Optimization Strategy for Molecular Dynamics Simulations of Nanometric Cutting of Aluminium Alloy Using Molecular Modelling

Atoms constituting a metal define its molecular crystal structure (atomic system) and interact in molecular dynamics simulations of nanometric cutting of the metal. The removal of the material (metal) at nanoscale and generation of high quality surface with a nanometric finish is largely influenced by the mechanical and physical properties of the metal as it associates with the metal lattice (atomistic) structure. Improved studies of the molecular modelling (behaviour of molecules) as it creates mathematical models of molecular properties and behaviour of atomistic systems are required for condition prediction of a nanometric surface finish. In this study, atomic system of rapidly solidified aluminium (RSA) alloy, grade RSA 431, with the use of its alloying elemental compositions by weight percentage is designed and constructed with cell geometry and atom positions that are written into a data file using AtomsK program. In addition, atomic concentration influencing the structural properties of the alloying elements were calculated. Obtained microstructure depicts the spread of the elemental compositions and the data file is suitable for a code performing simulations on classical particles like the large-scale atomic/molecular massively parallel simulator (LAMMPS) software. Understanding the computer simulations (molecular dynamics) for analyzing the physical movements of atoms and molecules, and the peculiar characteristic properties of the composing alloying elements of the RSA 431 determine how much influence each of them (elements) has on the nanometric cutting surface. Hence, the nanometric surface finish of the RSA 431.