Stability and Decay of Macrovortices in Rotating Bose Gases Beyond Mean Field

TL;DR

The paper addresses how macrovortices in a rotating Bose gas behave when quantum correlations beyond mean-field are important. It employs the multiconfigurational time-dependent Hartree method for indistinguishable bosons (MCTDH-X) up to $M$=3 orbitals to map the ground-state phase diagram and to study three quench protocols—rotation, interaction, and trap—in a 2D Mexican-hat trap, revealing how correlations stabilize macrovortices and modify phase boundaries. The key findings show that rotation and interaction quenches preserve macrovortices and excite clear, vorticity-dependent breathing modes, while trap quenches induce a universal, vortex-phonon–mediated decay with energy flowing between incompressible (vortical) and compressible (phononic) channels; this decay is accompanied by quadrupole symmetry breaking and observable density- and current-field signatures. The work has significant implications for experimental probes of vortex–phonon coupling and energy transfer in correlated quantum fluids, and it suggests potential applications in information encoding using macrovortex collective modes and controlled manipulation of topological excitations in ultracold gases.

Abstract

We study the formation, stability, and decay of macrovortices in a rotating Bose gas confined by a Mexican-hat potential with a multiconfigurational ansatz. By systematically including correlations beyond the mean-field level, we map the equilibrium phase diagram and identify regimes of coexistence between vortex lattices and multiply charge central vortices. Quench dynamics reveals that macrovortices are robust under changes in rotation or interaction strength, sustaining clean monopole oscillations with well-separated, vorticity-dependent breathing frequencies. In contrast, trap quenches trigger a universal decay process mediated by vortex-phonon coupling, in which rotational energy is progressively transferred to compressible modes until the macrovortex splits into singly quantized vortices. Our results demonstrate that macrovortex lifetimes and decay pathways can be tuned by trap confinement, providing experimentally accessible signatures of vortex-phonon interactions and collective energy transfer in correlated quantum fluids.

Figures (15)

• Figure 1: Phase diagram for $N=100$ rotating bosons in a Mexican-hat potential. The diagram is plotted as a function of angular velocity $\Omega$ and interaction strength $g_0$, plotted for (a) $M=1$ orbital (mean-field result), (b) $M=2$ orbitals, and (c) $M=3$ orbitals. The different color schemes indicate the three possible phases: vortex lattice only (blue colorbar), central macrovortex only (orange colorbar), and coexistence of the two (green colorbar). For the region where the central macrovortex coexists with a surrounding vortex lattice, the red dots additionally mark the macrovortex size. The pink arrows in panel (c) indicate the approximate extent of sudden quenches used to assess vortex stability, here only showed for a single-vortex state.
• Figure 2: Representative density distributions for the different ground states encountered in the rotating Mexican hat potential. (a) single vortex ($g_0=0.5$, $\Omega=0.5$), (b) vortex lattice ($g_0=0.9$, $\Omega=0.75$), (c) macrovortex -- here with vorticity 3 ($g_0=0.2$, $\Omega=0.7$), (c) coexistence of macrovortex -- here with vorticity 2 -- and vortex lattice ($g_0=0.95$, $\Omega=0.95$). All the densities were obtained for $N=100$ bosons and $M=3$ orbitals.
• Figure 3: Macrovortex stability in rotation and interaction quench. (a) Dynamics of monopole and quadrupole moments for a representative rotation quench with $g_0 = 0.15$, $\Omega = 0.65 \to 0.75$. (b) Dynamics of monopole and quadrupole moments for a representative interaction quench with $g_0 = 0.15 \to 0.35$, $\Omega = 0.65$. (c) Center of mass dynamics for the interaction quench in (b). (d) Dynamics of the mean cloud radius for the interaction quench in (b). (e) Fourier transform of the monopole time series in (b). (f) Breathing mode oscillation period as a function of the strength of the quenched interaction for initial states exhibiting macrovortices with different vorticity. The vertical dotted line at $g_0=0.15$ indicates the initial interaction strength. The dashed lines are quadratic fits.
• Figure 4: Density behavior after a trap quench. The panels show the initial density (left panels) and the density after decay if any (right panels) for states with initial vortices with vorticity 1 through 4. The plots were obtained for $N=100$ bosons in $M=3$ orbitals with quenched trap parameters $(p_1, p_2)=(-0.1, 0.05) \to (0.1, 0.0)$. The parameters for the initial states are (a)-(b) $g_0=0.5$, $\Omega=0.5$ (single vortex), (c)-(d) $g_0=0.2$, $\Omega=0.65$ (2-macrovortex), (e)-(f) $g_0=0.2$, $\Omega=0.7$ (3-macrovortex), (g)-(h) $g_0=0.15$, $\Omega=0.75$ (4-macrovortex).
• Figure 5: Phase behavior after a trap quench. The panels show the phase of the largest natural orbital at time $t=0$ (left panels) and after decay if any (right panels), for states with initial vortices with vorticity 1 through 4. The plots were obtained for $N=100$ bosons in $M=3$ orbitals with quenched trap parameters $(p_1, p_2)=(-0.1, 0.05) \to (0.1, 0.0)$. The parameters for the initial states are (a)-(b) $g_0=0.5$, $\Omega=0.5$ (single vortex), (c)-(d) $g_0=0.2$, $\Omega=0.65$ (2-macrovortex), (e)-(f) $g_0=0.2$, $\Omega=0.7$ (3-macrovortex), (g)-(h) $g_0=0.15$, $\Omega=0.75$ (4-macrovortex). The green dots (fuchsia squares) are a guide to the eye for vortices (antivortices). Note that at $t=0$, a number of artifact vortices appears in boundary regions where the many-body amplitude is vanishingly small.