arXiv subjects

Wyatt Kirkby

Publications and source records attributed to Wyatt Kirkby.

7 recordsLinked to original sources

arXiv2026

Competing triangular and stripe supersolid orders in a dipolar quantum gas

Supersolids are exotic quantum states in which long-range phase coherence coexists, and may interplay, with emergent spatial orders. A particularly rich phase diagram featuring several competing spatial orders is predicted for dipolar supersolids with two-dimensional crystals, yet the experimental observation of this structural variety has remained limited. Here we experimentally form competing triangular and stripe density-modulated states in a quantum gas of highly magnetic atoms confined in a surfboard-shaped trap by tuning contact interaction strength and dipole orientation. We define a structural order parameter and study its statistical behavior. Thereby, we identify both the triangular and stripe phases and the transition between them, the associated critical behavior being marked by enhanced non-Gaussian fluctuations. Furthermore, we observe each spatial structure in both the phase-coherent supersolid regime and the phase-incoherent insulating one, near and far from the unmodulated-to-modulated transition, respectively. Our results establish a versatile platform in which multiple phases of the two-dimensional-supersolid phase diagram, and more generally, intertwined symmetry-breaking phenomena, can be investigated.

cond-mat.quant-gas↗

arXiv2026

A Maxwell Fish-Eye Lens in a Bose-Einstein Condensate

We experimentally realize an analogue of the optical Maxwell fish-eye lens (MFEL) using phononic excitations in a Bose-Einstein condensate (BEC). A MFEL is characterized by a radially symmetric, spatially varying refractive index with the remarkable property that rays emitted from any point within the lens are perfectly focused at their antipodal points. While the implementation of such gradient-index lenses is challenging in conventional optical systems, BECs offer a highly tunable platform in which the spatially varying speed of sound of collective excitations -- phonons, the acoustic analogues of photons -- can be engineered and their dynamics observed in real time. Time-resolved measurements of phonon wavefronts reveal focusing behavior that shows good agreement with analytical theory and numerical simulations. This work provides both a geometric and physical framework for engineering effective refractive indices using ultracold atoms, and simulating wave propagation on effective spherical geometries.

cond-mat.quant-gas↗

arXiv2026

Morphological false-vacuum decay in dipolar supersolids

False-vacuum decay between two morphologically distinct supersolid phases via bubble nucleation is studied in a uniform dipolar gas confined to the plane. Starting from a metastable honeycomb state, the formation of stripe phase domains is simulated numerically by means of a stochastic projected extended Gross-Pitaevskii equation. The speed of bubble growth is analyzed in relation to the multiple speeds of sound of the supersolid, and is found to be set by the slowest of these sounds. The vacuum decay rate is numerically extracted and compared against a minimal effective model for the Coleman bounce solution connecting the two supersolid orders. Our results establish dipolar supersolids as a novel and versatile platform for studying false-vacuum decay. This setting offers a rich structure of metastable states and collective excitations that come into play in the decay. Furthermore, here, in contrast to previous studies, bubble formation occurs directly in the real-space density and can be probed with \textit{in situ} imaging.

cond-mat.quant-gas↗

arXiv2026

Quantum vortex channels as Josephson junctions

In quantum gases, weak links are typically realized with externally imposed optical potentials. We show that, in rotating binary condensates, quantized vortices in one component form hollow channels that act as self-induced weak links for the other, enabling superflow through otherwise impenetrable, phase-separated domains. This introduces a novel barrier mechanism: quantum pressure creates an effective barrier inside the vortex channel, set by the constriction width, which controls the superflow. Tuning the interspecies interaction strength drives a crossover from the hydrodynamic transport to Josephson tunneling regime. Long-range dipolar interactions further tune the weak-link properties, enabling both short links and two coupled junctions in series. Circuit models quantitatively capture the dc current-phase relations for both configurations. These results establish vortices as reconfigurable, interaction-controlled Josephson elements in superfluids.

cond-mat.quant-gas↗

arXiv2025

Kibble-Zurek scaling of the superfluid-supersolid transition in an elongated dipolar gas

We simulate interaction quenches crossing from a superfluid to a supersolid state in a dipolar quantum gas of ${}^{164}\mathrm{Dy}$ atoms, trapped in an elongated tube with periodic boundary conditions, via the extended Gross-Pitaevskii equation. A freeze-out time is observed through a delay in supersolid formation after crossing the critical point. We compute the density-density correlations at the freeze-out time and extract the frozen correlation length for the solid order. An analysis of the freeze-out time and correlation length versus the interaction quench rate allows us to extract universal exponents corresponding to the relaxation time and correlation length based on predictions of the Kibble-Zurek mechanism. Over several orders of magnitude, clear power-law scaling is observed for both the freeze-out time and the correlation length, and the corresponding exponents are compatible with predictions based on the excitation spectrum calculated via Bogoliubov theory. Defects due to independent local breaking of translational symmetry, contributing to globally incommensurate supersolid order, are identified, and their number at the freeze-out time is found to also scale as a power law. Our results support the hypothesis of a continuous transition whose universality class remains to be determined but appears to differ from that of the (1+1)D XY model.

cond-mat.quant-gas↗

arXiv2025

Ab initio Complex Langevin computation of the roton gap for a dipolar Bose condensate

We compute from first principles the dispersion relation $ω(k)$ of a dipolar Bose gas of erbium atoms close to the roton instability by employing the Complex Langevin (CL) algorithm. Other than the path integral Monte Carlo algorithm, which samples the quantum mechanical path integral in the $N$-particle basis, CL samples the field-theoretic path integral of interacting bosons and can be evaluated for experimentally realistic atom numbers. We extract the energy of roton excitations as a function of the s-wave scattering length, and compare our results to those from Gross-Pitaevskii theory, with and without quantum fluctuation corrections.

cond-mat.quant-gas↗

arXiv2023

Scaling at the OTOC Wavefront: free versus chaotic models

Out of time ordered correlators (OTOCs) are useful tools for investigating foundational questions such as thermalization in closed quantum systems because they can potentially distinguish between integrable and nonintegrable dynamics. Here we discuss the properties of wavefronts of OTOCs by focusing on the region around the main wavefront at $x=v_{B}t$, where $v_{B}$ is the butterfly velocity. Using a Heisenberg spin model as an example, we find that the leading edge of a propagating Gaussian with the argument $-m(x)\left( x-v_B t \right)^2 +b(x)t$ gives an excellent fit to the region around $x=v_{B}t$ for both the free and chaotic cases. However, the scaling in these two regimes is very different: in the free case the coefficients $m(x)$ and $b(x)$ have an inverse power law dependence on $x$ whereas in the chaotic case they decay exponentially. We conjecture that this result is universal by using catastrophe theory to show that, on the one hand, the wavefront in the free case has to take the form of an Airy function and its local expansion shows that the power law scaling seen in the numerics holds rigorously, and on the other hand an exponential scaling of the OTOC wavefront must be a signature of nonintegrable dynamics. We find that the crossover between the two regimes is smooth and characterized by an S-shaped curve giving the lifting of Airy nodes as a function of a chaos parameter. This shows that the Airy form is qualitatively stable against weak chaos and consistent with the concept of a quantum Kolmogorov-Arnold-Moser theory.

cond-mat.stat-mech↗