Sandeep Gautam

Indian Institute of Technology Ropar | Indian Institute of Technology Punjab · Department of Physics

We present a theoretical study of the collective excitations of the supersolid annular stripe phase of a spin-orbital-angular-momentum-coupled (SOAM-coupled) spin-1 Bose-Einstein condensate. The annular stripe phase simultaneously breaks two continuous symmetries, namely rotational and $U(1)$ gauge symmetry, and is more probable in the condensates...

We study the collective excitation spectrum of a Raman-induced spin-orbit-coupled spin-1 Bose-Einstein condensates confined in a quasi-one-dimensional harmonic trap while varying either the Raman coupling or quadratic Zeeman term by using the Bogoliubov approach. A few low-lying modes, which can be used to delineate the phase boundaries, are identi...

Close to the superfluid plane-wave (PW)–supersolid stripe (ST) phase transition point of a zero-temperature quasi-one-dimensional spin-orbit-coupled Bose gas, we find that an increase in temperature induces a phase transition to the supersolid phase with a broken translational symmetry from the superfluid plane-wave phase. We use the Hartree-Fock-B...

We examine the quench dynamics across quantum phase transitions from a Mott insulator (MI) to a superfluid (SF) phase in a two-component bosonic mixture in an optical lattice. We show that two-component Bose mixtures exhibit qualitatively different quantum dynamics than one-component Bose gas. In addition to second-order MI-SF transitions, we inves...

Motivated by recent experiments [Chen et al., Phys. Rev. Lett. 121, 113204 (2018); Chen et al., Phys. Rev. Lett. 121, 250401 (2018)], we investigate the low-lying excitation spectrum of the ground-state phases of spin-orbital-angular-momentum-coupled (SOAM-coupled) spin-1 condensates. At vanishing detuning, a ferromagnetic SOAM-coupled spin-1 Bose-...

We study ultracold superfluid Bose-Fermi mixtures in three dimensions, with stronger confinement along one or two directions, using a non-perturbative beyond-mean-field model for bulk chemical potential valid along the weak-coupling to unitarity crossover. Although bosons are considered to be in a superfluid state, we consider two possibilities for...

We study ultracold superfluid Bose-Fermi mixtures in three dimensions, with stronger confinement along one or two directions, using a non-perturbative beyond-mean-field model for bulk chemical potential valid along the weak-coupling to unitarity crossover. Although bosons are considered to be in a superfluid state, we consider two possibilities for...

We examine the quench dynamics across quantum phase transitions from a Mott insulator (MI) to a superfluid (SF) phase in a two-component bosonic mixture in an optical lattice. We show that two-component Bose mixtures exhibit qualitatively different quantum dynamics than one-component Bose gas. Besides second-order MI-SF transitions, we also investi...

Motivated by the recent experiments [Chen et al., Phys. Rev. Lett 121, 113204 (2018), Chen et al., Phys. Rev. Lett. 121, 250401 (2018)], we investigate the low-lying excitation spectrum of the ground-state phases of spin-orbital-angular-momentum-coupled (SOAM-coupled) spin-1 condensates. At vanishing detuning, a ferromagnetic SOAM-coupled spin-1 BE...

We theoretically study the stationary-state vortex lattice configurations of rotating spin-orbit- and coherently-coupled spin-1 Bose-Einstein condensates trapped in quasi-two-dimensional harmonic potentials. The combined effects of rotation, spin-orbit and coherent couplings are analyzed systematically from the single-particle perspective. Through...

We demonstrate spontaneous generation of spatially-periodic supersolid-like super-lattice and stripe solitons in Rashba spin-orbit (SO) coupled spin-1 and spin-2 quasi-two-dimensional nonmagnetic Bose-Einstein condensates (BECs). The solitons in a weakly SO-coupled spin-1 BEC are circularly-symmetric of $(-1, 0, +1)$ and $(0, +1, +2)$ types and hav...

We demonstrate spontaneous generation of spatially-periodic supersolid-like super-lattice and stripe solitons in Rashba spin-orbit (SO) coupled spin-1 and spin-2 quasi-two-dimensional nonmagnetic Bose-Einstein condensates (BECs). The solitons in a weakly SO-coupled spin-1 BEC are circularly-symmetric of (−1,0,+1) and (0,+1,+2) types and have inhere...

We study theoretically the collective excitations of a spin-orbit-coupled spin-1 Bose-Einstein condensate with antiferromagnetic spin-exchange interactions in a cigar-shaped trapping potential at zero and finite temperatures using the Hartree-Fock-Bogoliubov theory with Popov approximation. The collective modes at zero temperature are corroborated...

We provide here the updated versions of OpenMP parallelized FORTRAN 90/95 programs to numerically study the ground states and/or the dynamics of homogeneous or trapped spin-1 or spin-2 Bose-Einstein condensates (BECs) with anisotropic spin-orbit (SO) coupling. The coupled sets of three or five Gross-Pitaevskii (GP) equations, respectively, for a sp...

We theoretically study the collective excitations of a spin-orbit-coupled spin-1 Bose-Einstein condensate with antiferromagnetic spin-exchange interactions in a cigar-shaped trapping potential at zero and finite temperatures using the Hartree-Fock-Bogoliubov theory with Popov approximation. The collective modes at zero temperature are corroborated...

We study supersolid-like crystalline structures emerging in the stationary states of a quasi-two-dimensional spin-orbit (SO)-coupled spin-2 condensate in the ferromagnetic, cyclic, and antiferromagnetic phases by solving a mean-field model. Interplay of different strengths of SO coupling and interatomic interactions gives rise to a variety of nontr...

We study supersolid-like crystalline structures emerging in the stationary states of a quasi-two-dimensional spin-orbit (SO)-coupled spin-2 condensate in the ferromagnetic, cyclic, and antiferro-magnetic phases by solving a mean-field model.Interplay of different strengths of SO coupling and interatomic interactions gives rise to a variety of non-t...

We investigate the quantum phase transitions of a two-dimensional Bose-Hubbard model in the presence of a Rashba spin-orbit coupling with and without thermal fluctuations. The interplay of single-particle hopping, strength of spin-orbit coupling, and interspin interaction leads to superfluid phases with distinct properties. With interspin interacti...

The spin-orbit and coherent couplings along with rotation can combine together to result in scalar potentials which can modify the trapping potential to yield a variety of effective potentials experienced by a particle. The bosons in these rotating SO- and coherently-coupled Bose-Einstein condensates (BECs) can thus be subjected to rotating effecti...

We develop time-splitting finite-difference methods, using an implicit Backward–Euler and a semi-implicit Crank–Nicolson discretization schemes, to study the spin-orbit-coupled (SO-coupled) spinor Bose–Einstein condensates with coherent coupling in quasi-one- and quasi-two-dimensional traps. The split equations involving kinetic energy and spin-orb...

We develop time-splitting finite difference methods, using implicit Backward-Euler and semi-implicit Crank-Nicolson discretization schemes, to study the spin-orbit coupled spinor Bose Einstein condensates with coherent coupling in quasi-one and quasi-two-dimensional traps. The split equations involving kinetic energy and spin-orbit coupling operato...

We investigate the quantum phase transitions of a two-dimensional Bose-Hubbard model with Rashba spin-orbit coupling with and without thermal fluctuations. The interplay of the single-particle hopping, the strength of spin-orbit coupling, and interspecies interaction leads to superfluid phases with distinct properties. With interspecies interaction...

Here, we present simple and efficient numerical scheme to study static and dynamic properties of spin-1 Bose–Einstein condensates (BECs) with spin–orbit (SO) coupling by solving three coupled Gross–Pitaevskii equations (CGPEs) in three-, quasi-two and quasi-one dimensional systems. We provide a set of three codes developed in FORTRAN 90/95 programm...

We provide here a set of three OpenMP parallelized FORTRAN 90/95 programs to compute the ground states and the dynamics of trapped spin-2 Bose-Einstein condensates (BECs) with anisotropic spin-orbit (SO) coupling by solving a set of five coupled Gross-Pitaevskii equations using a time-splitting Fourier spectral method. Depending on the nature of th...

After the pioneering studies on spinor Bose-Einstein condensate (BEC) and after the realization of spin-orbit (SO) coupling in a spinor BEC of 87Rb and 23Na atoms, it is now realized that an SO-coupled BEC may reveal new physical phenomena not possible in a scalar BEC. For example, a new class of two- or three-dimensional vector soliton can be stab...

We develop a FORTRAN code to compute fluctuations in atomic condensates (FACt) by solving the Bogoliubov-de Gennes (BdG) equations for two component Bose–Einstein condensate (TBEC) in quasi-two dimensions. The BdG equations are recast as matrix equations and solved self consistently. The code is suitable for handling quantum fluctuations as well as...

Here, we present simple and efficient numerical scheme to study static and dynamic properties of spin-1 Bose-Einstein condensates (BECs) with spin-orbit (SO) coupling by solving three coupled Gross-Pitaevskii equations (CGPEs) in three-, quasi-two and quasi-one dimensional systems. We provide a set of three codes developed in FORTRAN 90/95 programm...

The usual treatment of a Bose-Fermi mixture relies on weak-coupling Gross-Pitaevskii (GP) and density-functional (DF) Lagrangians, often including the more realistic perturbative Lee-Huang-Yang (LHY) corrections. We suggest analytic non-perturbative beyond-mean-field Bose and Fermi Lagrangians valid along the crossover from weak- to strong-coupling...

The perturbative Lee–Huang–Yang (LHY) interaction proportional to n3∕2, where n is the density, creates an infinitely repulsive potential at the center of a Bose–Einstein condensate (BEC) with net attraction, which stops the collapse to form a self-bound state in a dipolar BEC and in a binary BEC. However, recent microscopic calculations of the non...

We study numerically mixing-demixing and spontaneous symmetry breaking in Bose-Fermi mixtures in spherically-symmetric and quasi-one-dimensional traps while the intra-species Bose and Fermi interactions are varied from weak-coupling to strong-coupling limits. The usual treatment of a Bose-Fermi mixture relies on weak-coupling Gross-Pitaevskii (GP)...

We study the formation of a stable self-trapped spherical quantum ball in a binary Bose-Einstein condensate (BEC) with two-body inter-species attraction and intra-species repulsion employing the beyond-mean-field Lee-Huang-Yang and the three-body interactions. We find that either of these interactions or a combination of them can stabilize the bina...

We study the formation of a stable self-trapped spherical quantum ball in a binary Bose-Einstein condensate (BEC) with two-body inter-species attraction and intra-species repulsion employing the beyond-mean-field Lee-Huang-Yang and the three-body interactions. We find that either of these interactions or a combination of these can stabilize the bin...

We develop a FORTRAN code to compute fluctuations in atomic condensates (FACt) by solving the Bogoliubov-de Gennes (BdG) equations for two component Bose-Einstein condensate (TBEC) in quasi two dimensions. The BdG equations are recast as matrix equations and solved self consistently. The code is suitable for handling quantum fluctuations as well as...

We demonstrate stable and metastable vortex-bright solitons in a three-dimensional spin-orbit-coupled three-component hyperfine spin-1 Bose-Einstein condensate (BEC) using numerical solution and variational approximation of a mean-field model. The spin-orbit coupling provides attraction to form vortex-bright solitons in both attractive and repulsiv...

We study the vortex-bright solitons in a quasi-two-dimensional spin-orbit-coupled (SO-coupled) hyperfine spin-1 three-component Bose-Einstein condensate (BEC) using variational method and numerical solution of a mean-field model. The ground state of these vortex-bright solitons is radially symmetric for weak ferromagnetic and polar interactions. Fo...

We theoretically and numerically investigate the generation of fractional-charge vortex dipoles in spinor condensates with non-zero magnetization. We find that in the antiferromagnetic phase of spin-1 and spin-2 and the cyclic phase of spin-2 condensate with non-zero magnetization coupling of the density (phonon) and a spin-excitation mode results...

We classify all possible fractional charge vortices of charge less than unity in spin-1 and spin-2 polar and cyclic Bose-Einstein condensates (BECs) with zero magnetization. Statics and dynamics of these vortices in quasi-two-dimensional spinor BECs are studied employing accurate numerical solution and a Lagrange variational approximation. The resu...

We demonstrate that the ground state of a trapped spin-1 and spin-2 spinor ferromagnetic Bose-Einstein condensate (BEC) can be well approximated by a single decoupled Gross-Pitaevskii (GP) equation. Useful analytic models for the ground-state densities of ferromagnetic BECs are obtained from the Thomas-Fermi approximation (TFA) to this decoupled eq...

Five-component minimum-energy bound states and mobile vector solitons of a spin-orbit-coupled quasi-one-dimensional hyperfine-spin-2 Bose-Einstein condensate are studied using the numerical solution and variational approximation of a mean-field model. Two distinct types of solutions with single-peak and multi-peak density distribution of the compon...

We study the formation of bound states and three-component bright vector solitons in a quasi-one-dimensional spin-orbit-coupled hyperfine spin $f=1$ Bose-Einstein condensate using numerical solution and variational approximation of a mean-field model. In the antiferromagnetic domain, the solutions are time-reversal symmetric, and the component dens...

We show that the third Goldstone mode in the two-species condensate mixtures, which emerges at phase-separation, gets hardened when the confining potentials have separated trap centers. The {\em sandwich} type condensate density profiles, in this case, acquire a {\em side-by-side} density profile configuration. We use Hartree-Fock-Bogoliubov theory...

We study the ground-state density profile of a spin-orbit coupled $f=2$ spinor condensate in a quasi-one-dimensional trap. The Hamiltonian of the system is invariant under time reversal but not under parity. We identify different parity- and time-reversal-symmetry-breaking states. The time-reversal-symmetry breaking is possible for degenerate state...

We study the merging and splitting of quasi two-dimensional Bose-Einstein condensates with strong dipolar interactions. We observe that if the dipoles have a non-zero component in the plane of the condensate, the dynamics of merging or splitting along two orthogonal directions, parallel and perpendicular to the projection of dipoles on the plane of...

We study a spin-orbit (SO) coupled hyperfine spin-1 Bose-Einstein condensate (BEC) in a quasi-one-dimensional trap. For a SO-coupled BEC in a one-dimensional box, we show that in the absence of the Rabi term, any non-zero value of SO coupling will result in a phase separation among the components for a ferromagnetic BEC, like $^{87}$Rb. On the othe...

We study the dynamics of a single and a corotating vortex pair in a dipolar Bose-Einstein condensate in the framework of dissipative Gross-Pitaevskii equation. This simple model enables us to simulate the effect of finite temperature on the vortex dynamics. We study the effect of dipolar interactions on the dynamics of a single vortex in the presen...

Vortex reconnections plays an important role in the turbulent flows associated with the superfluids. To understand the dynamics, we examine the reconnections of vortex rings in the superfluids of dilute atomic gases confined in trapping potentials using Gross-Petaevskii equation. Further more we study the reconnection dynamics of coreless vortex ri...

We show that the third Goldstone mode, which emerges in binary condensates at phase-separation, persists to higher inter-species interaction for density profiles where one component is surrounded on both sides by the other component. This is not the case with symmetry-broken density profiles where one species is to entirely to the left and the othe...

We examine the Goldstone or zero energy modes of the quasi-1D binary condensate of Rb and Cs at T=0 as a function of the interspecies interaction. At phase-separation, an additional Goldstone mode appears in the system and persists at higher interspecies interaction for symmetric density profiles. This is not the case for binary condensates with as...

We study the dynamics of a single and a pair of vortices in quasi two-dimensional Bose-Einstein condensates at finite temperatures. We use the stochastic Gross-Pitaevskii equation, which is the Langevin equation for the Bose-Einstein condensate, to this end. For a pair of vortices, we study the dynamics of both the vortex-vortex and vortex-antivort...

We theoretically explore the annihilation of vortex dipoles, generated when an obstacle moves through an oblate Bose-Einstein condensate, and examine the energetics of the annihilation event. We show that the gray soliton, which results from the vortex dipole annihilation, is lower in energy than the vortex dipole. We also investigate the annihilat...

We theoretically investigate the generation of the vortex dipoles in superfluid Fermi gas in the BCS limit. The vortex dipoles are generated in superfluid either by moving an obstacle above a critical speed or due to the decay of the shock waves obtained on the sudden mixing of two superfluid fragments. We observe that in pancake-shaped traps, the...

We examine the generation and subsequent evolution of Rayleigh Taylor instability in anisotropic binary Bose-Einstein condensates. Considering a pancake-shaped geometry, to initiate the instability we tune the intraspecies interaction and analytically study the normal modes of the interface in elliptic cylindrical coordinates. The normal modes are...

We investigate the initiation and subsequent evolution of Crow instability in an inhomogeneous unitary Fermi gas using zero-temperature Galilei-invariant non-linear Schr\"odinger equation. Considering a cigar-shaped unitary Fermi gas, we generate the vortex-antivortex pair either by phase-imprinting or by moving a Gaussian obstacle potential. We ob...

Vortex dipoles are generated when an obstacle moves through a superfluid above a critical speed. In the case of phase-separated binary condensates, with appropriate interaction parameters in pancake-shaped traps, we show that coreless vortex dipoles are created when a Gaussian obstacle beam traverses across them above a critical speed. As the obsta...

We study the motion of the Gaussian obstacle potential created by blue detuned laser beam through a phase-separated binary condensate in pancake-shaped traps. For the velocity of the obstacle above a critical velocity, we observe the generation of vortex dipoles in the outer component which can penetrate the inner component. This is equivalent to f...

We show that quasi-one dimensional Bose-Einstein condensate under suitable conditions can exhibit a Berezinskii-Kosterlitz-Thouless phase transition. The role played by quantized vortices in two dimensional case, is played in this case by dark solitons. We find that the critical temperature for this transition lies in nano Kelvin range and below, f...

Vortex dipoles are generated when an obstacle moves through a superfluid. In case of phase-separated binary condensates, with appropriate interaction parameters in pan-cake shaped traps, we show that coreless vortex dipoles are created when a Gaussian obstacle beam traverses across them above a critical speed. As the obstacle passes through the inn...

We examine the density profiles of the quantum degenerate Bose-Fermi mixture of $^{174}$Yb-$^{173}$Yb, experimental observed recently, in the mean field regime. In this mixture there is a possibility of tuning the Bose-Bose and Bose-Fermi interactions simultaneously using two well separated optical Feshbach resonances, and it is a good candidate to...

We propose a modified Gaussian ansatz to study binary condensates, trapped in harmonic and optical lattice potentials, both in miscible and immiscible domains. The ansatz is an apt one as it leads to the smooth transition from miscible to immiscible domains without any {\em a priori} assumptions. In optical lattice potentials, we analyze the squeez...

We examine the use of the WKB approximation to determine the p-wave scattering length. For this we solve the p partial wave Schrödinger equation and analyse the validity of adopting the semiclassical solution to evaluate the constant factors in the solution. We also calculate the p-wave scattering lengths of 6Li and 40K for the a3Σ+u and X1Σ+g stat...

We show that the ground state interface geometry of binary condensates in the phase separated regime undergoes a smooth transition from planar to ellipsoidal to cylindrical geometry. This occurs for condensates with repulsive interactions as the trapping potential is changed from prolate to oblate. The correct ground state geometry emerges when the...

We propose a scheme to initiate and examine Rayleigh-Taylor instability in the two species Bose-Einstein condensates. We identify $^{85}$Rb-$^{87}$Rb mixture as an excellent candidate to observe it experimentally. The instability is initiated by tuning the $^{85}$Rb-$^{85}$Rb interaction through magnetic Feshbach resonance. We show that the observa...

The quartic confining potential has emerged as a key ingredient to obtain fast rotating vortices in BEC as well as observation of quantum phase transitions in optical lattices. We calculate the critical temperature Tc of bosons at which normal to BEC transition occurs for the quartic confining potential. Further more, we evaluate the effect of fini...