Nonlinear Atomic Interaction Research Articles

Information measures on matter-wave solitons in Bose–Einstein condensates

We consider quasi-one-dimensional Bose–Einstein condensates and study the properties of matter-wave bright solitons within the framework information theoretic approach. In the limit of negligible trapping effect, we calculate Shannon entropy, Fisher information, and Rényi entropy for different mean-field interactions, and study the interplay between group velocity dispersion and nonlinear atomic interaction. We see that information theoretic approach can clearly reveal localization and delocalization properties of matter-wave density distribution. In all the cases, entropic uncertainties are found to be satisfied.

Improving sensitivity of an amplitude-modulated magneto-optical atomic magnetometer using squeezed light

We experimentally demonstrate that a squeezed probe optical field can improve the sensitivity of magnetic field measurements based on nonlinear magneto-optical rotation (NMOR) with an amplitude-modulated pump when compared to a coherent probe field under identical conditions. To realize an all-atomic magnetometer prototype, we utilize a nonlinear atomic interaction, known as polarization self-rotation, to produce a squeezed probe field. An independent pump field, amplitude-modulated at the Larmor frequency of the bias magnetic field, allows us to extend the range of most sensitive NMOR measurements to sub-Gauss magnetic fields. While the overall sensitivity of the magnetometer is rather low ( > --> 250 p T / H z ), we clearly observe a 15 % sensitivity improvement when the squeezed probe is used. Our observations confirm the recently reported quantum enhancement in a modulated atomic magnetometer [Phys. Rev. Lett. 127, 193601 (2021)PRLTAO0031-900710.1103/PhysRevLett.127.193601].

SU(1, 1) squeezed state

SU(1, 1) coherent and squeezed states have been widely studied in optical, hybrid atom–light, and spinor Bose–Einstein condensate experiments. Traditionally, the definition of SU(1, 1) squeezing refers to the uncertainty relationship, which implies that the SU(1, 1) coherent state is already squeezed if it is placed in an appropriate system of coordinates. In this report we investigate the basic concept of SU(1, 1) squeezing and discuss the principle for the generation of squeezed states. We establish a new definition of the squeezing criterion for the SU(1, 1) states. We study the dynamical properties in an atom–molecule system and show that the SU(1, 1) squeezed state can be generated with a nonlinear atomic interaction, which is similar to the one-axis twisting mechanism in spin squeezing. We also discuss the effect of the atomic number on squeezing, and show that the optimal squeezing and optimal squeezing angle exhibit a sudden transition at a fixed atomic number value.

Interaction induced localization of a spin–orbit-coupled Bose-Einstein condensate in a double-well potential

We investigate atomic interaction induced localization of a spin–orbit coupled Bose-Einstein condensate loaded in a double-well potential. We confirm the existence of the localization in the presence of the spin–orbit coupling for differences between the spin-dependent nonlinear atomic interaction strength between intraspin and interspin. We find a quantum phase transition from spin balance to spin localization for the different strengths of nonlinear atomic interaction strength. We also obtain the parametric dependence of the transitions to spin localization. The results play a constructive role to control spin localization of spin–orbit coupled Bose-Einstein condensate in a double-well potential.

Adiabatically tuning quantized supercurrents in an annular Bose-Einstein condensate

The ability to generate and tune quantized persistent supercurrents is crucial for building superconducting or atomtronic devices with novel functionalities. In ultracold atoms, previous methods for generating quantized supercurrents are generally based on dynamical processes to prepare atoms in metastable excited states. Here we show that arbitrary quantized circulation states can be adiabatically prepared and tuned as the ground state of a ring-shaped Bose-Einstein condensate by utilizing spin-orbital-angular-momentum (SOAM) coupling and an external potential. There exists superfluid hysteresis for tuning supercurrents between different quantization values with nonlinear atomic interactions, which is explained by developing a nonlinear Landau-Zener theory. Our work will provide a powerful platform for studying SOAM coupled ultracold atomic gases and building novel atomtronic circuits.

Effect of optomechanical coupling on squeezed-spin states

We investigate the effect of optomechanical coupling on the squeezed-spin states for a Bose-Einstein Condensate embedded within the lossless optomechanical cavity for the three special cases of initial states of cavity field, namely, a coherent state, a squeezed vacuum state and a squeezed state. We show that the radiation pressure or pondermotive force acting on the cavity end mirror plays a significant role in producing the atomic-squeezed states by producing squeezed states of the cavity field which is then transferred to the condensate. We further show that the maximum spin-squeezing along the x-direction is obtained in the presence of optomechanical coupling for the initial cavity field prepared in the amplitude squeezed state, whereas, squeezing along the y-direction reaches a maximum value in the absence of optomechanical coupling for the initial coherent cavity field. We also study the additional effect of nonlinear atomic interaction on spin-squeezing.

High-fidelity fast quantum driving in nonlinear systems

We investigate high-fidelity quantum driving in a nonlinear two-level system and find that nonlinear atomic interaction can break the speed limit of the linear model. We show that repulsive atomic interaction can decrease the minimal time requested for reaching target state even to zero, while attractive atomic interaction tends to increase the minimal time. There exists a critical attractive interaction beyond which the target state cannot be reached with high fidelity. Possible experimental observation of the nonlinear effects using a Bose-Einstein condensate in an accelerating optical lattice is discussed.

Klein tunneling in spin-orbit coupled Bose-Einstein condensate scattered by cusp barrier

The scattering process when spin-orbit coupled Bose-Einstein condensate gets through cusp barrier is numerically simulated by adopting time-split spectrum method; the Klein tunneling phenomena exist in the scattering process. The regions of Klein block and Klein tunneling will appear at higher barrier height as compared to the scattering process on getting through Gaussian barrier. In the Klein tunneling region, the transmission coefficient oscillates with the barrier height, and the oscillation amplitude decreases with increasing barrier height. Besides, the effect of non-linear atomic interaction has been discussed for different barrier heights as well.

Bifurcation, response scenarios and dynamic integrity in a single-mode model of noncontact atomic force microscopy

The nonlinear dynamical behavior of a single-mode model of noncontact AFM is analyzed in terms of attractors robustness and basins integrity. The model considered for the analyses, proposed in (Hornstein and Gottlieb in Nonlinear Dyn. 54:93–122, 2008), consistently includes the nonlinear atomic interaction and is studied under scan excitation (which appears as parametric excitation) and vertical excitation (which is prevalently external). Local bifurcation analyses are carried out to identify the overall stability boundary in the excitation parameter space as the envelope of system local escapes, to be compared with the one obtained via numerical simulations. The dynamical integrity of periodic bounded solutions is studied, and basin erosion is evaluated by means of two different integrity measures. The obtained erosion profiles allow us to dwell on the possible lack of homogeneous safety of the stability boundary in terms of robustness of the attractors, and to identify practical escape thresholds ensuring an a priori design safety target.

Bifurcations, basin erosion and dynamic integrity in a single-mode model of noncontact atomic force microscopy

The nonlinear dynamical behavior of a single-mode model of noncontact AFM is analyzed in terms of attractors robustness and basin integrity. The model considered for the analyses, proposed by Hornstein and Gottlieb (7), consistently includes the nonlinear atomic interaction and the scan control, which appears as parametric excitation. Local bifurcation analyses are carried out to define the overall stability boundary in the excitation parameter space as the envelope of system local escapes, to be compared with the one obtained via numerical simulations. The dynamical integrity of the periodic bounded solutions is studied, and basin erosion is evaluated by means of IF and GIM integrity measures. The obtained erosion profiles allow us to dwell on the possible lack of homogeneous safeness of the stability boundary in terms of attractors robustness and to identify practical escape thresholds ensuring an a priori design safety target.

Influence of nonlinear atomic interaction on excitation of intrinsic localized modes in carbon nanotubes

Excitation of intrinsic localized modes (ILMs) in carbon nanotubes (CNTs) with different chiral structures was investigated by molecular dynamics simulations. For CNTs with a chiral angle less than or equal to 30 ∘, energy concentration that continued for more than 200 fs was found in a localized area, where a pair of neighboring atoms strongly oscillated with a higher vibrational frequency than the upper bound of phonon bands. This evidently indicates excitation of the ILM. On the other hand, the ILM was not excited in CNTs with a chiral angle greater than or equal to 41 ∘. Analyzing the nonlinearity of the interaction between excited atoms in the ILM vibration mode, we elucidated that nonlinearity predominates the selective ILM excitation. Furthermore, stronger nonlinearity excites ILMs with both higher frequency and longer lifetime.

Dynamic scheme for generating number squeezing in Bose-Einstein condensates through nonlinear interactions

We develop a scheme to generate number squeezing in a Bose-Einstein condensate by utilizing interference between two hyperfine levels and nonlinear atomic interactions. We describe the scheme using a multimode quantum field model and find agreement with a simple analytic model in certain regimes. We demonstrate that the scheme gives strong squeezing for realistic choices of parameters and atomic species. The number squeezing can result in noise well below the quantum limit, even if the initial noise on the system is classical and much greater than that of a poisson distribution.

On the stability of boundary conditions for molecular dynamics

We study the stability of boundary conditions for molecular dynamics simulations. A general stability criterion is established. We first consider a one-dimensional model with nearest neighbor interaction and multiple-neighbor interactions. We then generalize the results to more realistic models in 3D with nonlinear atomic interaction.

Vortex replication in Bose-Einstein condensates trapped in double-well potentials

In this work we demonstrate, by means of numerical simulations, the possibility of replicating matter-wave vortices in a Bose-Einstein condensate trapped in a double-well potential. The most remarkable result is the generation of replicas of an initial vortex state located in one side of the double potential, which evolves into two copies, each one located in one of the potential minima. A simple linear theory gives the basic explanation of the phenomenon and predicts experimental realistic conditions for observation. A complementary strategy of easy experimental implementation to dramatically decrease the replication time is presented and numerically tested for the general case of nonlinear atomic interactions.

Quantum Spin Dynamics of Mode-Squeezed Luttinger Liquids in Two-Component Atomic Gases

We report on the observation of many-body spin dynamics of interacting, one-dimensional (1D) ultracold bosonic gases with two spin states. By controlling the nonlinear atomic interactions close to a Feshbach resonance we are able to induce a phase diffusive many-body spin dynamics of the relative phase between the two components. We monitor this dynamical evolution by Ramsey interferometry, supplemented by a novel, many-body echo technique, which unveils the role of quantum fluctuations in 1D. We find that the time evolution of the system is well described by a Luttinger liquid initially prepared in a multimode squeezed state. Our approach allows us to probe the nonequilibrium evolution of one-dimensional many-body quantum systems.

Soliton Atom Laser with Quantum State Transfer Property

We study the nonlinear effects in the quantum states transfer techniquefrom photons to matter waves in the three-level case, which may providethe formation of a soliton atom laser with nonclassical atoms. Thevalidity of quantum transfer mechanism is confirmed in the presence ofthe intrinsic nonlinear atomic interactions. The accompanied frequencychirp effect is shown to have no influence on the grey solitons formedby the output atom laser and the possible quantum depletion effect isalso briefly discussed.

Dynamics of the spin-2 Bose condensate driven by external magnetic fields

Dynamic response of the F=2 spinor Bose-Einstein condensate (BEC) under the influence of external magnetic fields is studied. A general formula is given for the oscillation period to describe population transfer from the initial polar state to other spin states. We show that when the frequency and the reduced amplitude of the longitudinal magnetic field are related in a specific manner, the population of the initial spin-0 state will be dynamically localized during time evolution. The effects of external noise and nonlinear spin exchange interaction on the dynamics of the spinor BEC are studied. We show that while the external noise may eventually destroy the Rabi oscillations and dynamic spin localization, these coherent phenomena are robust against the nonlinear atomic interaction.

Routes to chaos for driven Bose–Einstein condensates: from fast to slow crossing regimes

Experiments with ultracold atoms periodically kicked in a phase-modulated lattice have clearly shown the emergence of chaotic behaviour and realized the transition from classical to quantum chaos, in agreement with the predictions of numerical calculations. We turn our attention to Bose–Einstein condensates (BEC), presenting a systematic study of the signatures which define the dynamical transition of periodically kicked BECs to classical and quantum chaos, pointing out the role of coherence. The same type of numerical experiments are performed and analyzed for a BEC following a different route to chaos under slow, adiabatic periodical driving. Preliminary comments are then devoted to the consequences of the nonlinear atomic interactions on the phase decoherence. Our results can be relevant to current experiments with BECs.

Coherent atomic oscillations and resonances between coupled Bose-Einstein condensates with time-dependent trapping potential

We study the quantum coherent-tunneling between two Bose-Einstein condensates separated through an oscillating trap potential. The cases of slowly and rapidly varying in time trap potential are considered. In the case of a slowly varying trap we study the nonlinear resonances and chaos in the oscillations of the relative atomic population. Using the Melnikov function approach, we find the conditions for chaotic macroscopic quantum-tunneling phenomena to exists. Criteria for the onset of chaos are also given. We find the values of frequency and modulation amplitude which lead to chaos on oscillations in the relative population, for any given damping and the nonlinear atomic interaction. In the case of a rapidly varying trap we use the multiscale expansion method in the parameter epsilon = 1/Omega, where Omega is the frequency of modulations and we derive the averaged system of equations for the modes. The analysis of this system shows that new macroscopic quantum self trapping regions, in comparison with the constant trap case, exist.