arXiv subjects

Yanda Geng

Publications and source records attributed to Yanda Geng.

4 recordsLinked to original sources

arXiv2026

Prethermal ripplons in quenched binary Bose-Einstein condensates

Prethermal states--long-lived quasi-equilibrium configurations--occur in a wide range of physical systems that exhibit fast dephasing or reconfiguration followed by slow relaxation towards thermal equilibrium. We experimentally studied the 1D interface between immiscible 2D Bose-Einstein condensates (BECs); following a quench, the interfacial capillary waves (ripplons) quickly relaxed into a long-lived prethermal state characterized by a persistent non-equipartition of energy, evoking the classic Fermi-Pasta-Ulam-Tsingou problem. We directly measured the interface's height profile as it evolved in time, identified the contribution of individual ripplon modes, and find that, though their individual amplitudes are thermally distributed, they are not in thermal equilibrium--high-momentum modes rapidly equilibrated with the bulk phonon modes of the 2D BEC, while lower momentum modes remained at elevated temperatures, forming a long-lived prethermal configuration for the whole system. We attribute this to kinematic isolation: the absence of energy- and momentum-conserving relaxation processes in our system at ultracold temperature.

cond-mat.quant-gas↗

arXiv2025

Efficient production of sodium Bose-Einstein condensates in a hybrid trap

We describe an apparatus that efficiently produces $^{23}$Na Bose-Einstein condensates (BECs) in a hybrid trap that combines a quadrupole magnetic field with a far-detuned optical dipole trap. Using a Bayesian optimization framework, we systematically optimize all BEC production parameters in modest sized batches of highly correlated parameters. Furthermore, we introduce a Lagrange multiplier-based technique to optimize the duration of different evaporation stages constrained to have a fixed total duration; this enables the progressive creation of increasingly rapid experimental sequences that still generate high quality BECs. Taken together, our techniques constitute a general approach for refining and accelerating sequence-based experimental protocols.

cond-mat.quant-gas↗

arXiv2024

The Rayleigh-Taylor instability in a binary quantum fluid

Instabilities, where small fluctuations seed the formation of large-scale structures, govern dynamics in a variety of fluid systems. The Rayleigh-Taylor instability (RTI), present from tabletop to astronomical scales, is an iconic example characterized by mushroom-shaped incursions appearing when immiscible fluids are forced together. Despite its ubiquity, RTI experiments are challenging; here, we report the observation of the RTI in an immiscible binary superfluid consisting of a two-component Bose-Einstein condensate. We force these components together to initiate the instability, and observe the growth of mushroom-like structures. The interface can also be stabilized, allowing us to spectroscopically measure the "ripplon" interface modes. Lastly, we use matter-wave interferometry to transform the superfluid velocity field at the interface into a vortex chain. These results-in agreement with our theory-demonstrate the close connection between the RTI in classical and quantum fluids.

cond-mat.quant-gas↗

arXiv2024

A compact and open-source microcontroller-based rapid auto-alignment system

Maintaining stable and precise alignment of a laser beam is crucial in many optical setups. In this work, we present a microcontroller-based rapid auto-alignment system that detects and corrects for drifts in a laser beam trajectory using a pair of two-dimensional duo-lateral position sensing detectors (PSDs) and a pair of mirror mounts with piezoelectric actuators. We develop hardware and software for interfacing with the PSDs and for controlling the motion of the piezoelectric mirrors mounts. Our auto-alignment strategy -- implemented as a state machine on the microcontroller by a FreeRTOS kernel -- is based on a simple linearized geometrical optical model. We benchmark our system using the standard case of coupling laser light efficiently into the guided mode of a single-mode fiber optic patch cable. We can recover the maximum fiber coupling efficiency in $\sim10$ seconds, even for a laser beam that was misaligned to the point of zero fiber coupling.

physics.ins-det↗