arXiv subjects

Callum L. Welsh

Publications and source records attributed to Callum L. Welsh.

3 recordsLinked to original sources

arXiv2026

Creating and Probing Spin-Squeezed States of Molecules

Polar molecules are a promising platform for quantum-enhanced sensing and precision tests of fundamental physics, owing to their strong long-range dipolar interactions, broad sensitivity to electromagnetic fields, and sensitivity to potential physics beyond the Standard Model. However, the creation of metrologically useful entangled states in molecular systems has remained elusive. Here, we report the first observation of a class of metrologically useful entangled states - spin-squeezed states - in polar CaF molecules trapped in an optical tweezer array. The spin degree of freedom is encoded in rotational levels which are directly coupled by dipolar exchange interactions. By harnessing appropriate dynamical decoupling schemes we observe up to 3.0(3)dB of metrological gain, (2.2(3)dB without measurement correction) from direct exchange interactions. Using Floquet engineering, we further realize richer Hamiltonians that preserve spin squeezing while enabling the development of longer-range quantum correlations. Using site- and spin-resolved measurements we demonstrate that these entangled states enhance sensitivity to both homogeneous and spatially varying fields, and reveal strong non-classical correlations, including bipartite entanglement and Einstein-Podolsky-Rosen steering. Finally, we transfer the spin-squeezed states into long-lived and non-interacting hyperfine states, where the metrological enhancement persists for up to 100ms. Our results establish molecular optical tweezer arrays as a scalable platform for generating, controlling, characterizing, and storing entangled states of molecules, opening new opportunities for quantum-enhanced sensing and precision tests of fundamental physics.

physics.atom-ph↗

arXiv2026

Probing Coherent Many-Body Spin Dynamics in a Molecular Tweezer Array Quantum Simulator

Models of interacting quantum spins are used in many areas of physics ranging from the study of magnetism and strongly correlated materials to quantum sensing. In this work, we study coherent many-body dynamics of interacting spin models realized using polar molecules trapped in rearrangeable optical tweezer arrays. Specifically, we encode quantum spins in long-lived rotational states and use the electric dipolar interaction between molecules, together with Floquet Hamiltonian engineering, to realize $1/r^3$ XXZ and XYZ models. We microscopically probe several types of coherent dynamics in these models, including quantum walks of single spin excitations, the emergence of magnon bound states, and coherent creation and annihilation of magnon pairs. Our results establish molecular tweezer arrays as a new quantum simulation platform for interacting quantum spin models.

cond-mat.quant-gas↗

arXiv2024

Demonstration of Erasure Conversion in a Molecular Tweezer Array

Programmable optical tweezer arrays of molecules are an emerging platform for quantum simulation and quantum information science. For these applications, reducing and mitigating errors that arise during initial state preparation and subsequent evolution remain major challenges. In this paper, we present work on site-resolved detection of internal state errors and quantum erasures, which are qubit errors with known locations. First, using a new site-resolved detection scheme, we demonstrate robust and enhanced tweezer array preparation fidelities. This enables creating molecular arrays with low defect rates, opening the door to high-fidelity simulation of quantum many-body systems. Second, for the first time in molecules, we demonstrate mid-circuit detection of erasures using a composite detection scheme that minimally affects error-free qubits. We also demonstrate mid-circuit conversion of blackbody-induced errors into detectable erasures. Our demonstration of erasure conversion, which has been shown to significantly reduce overheads for fault-tolerant quantum error correction, could be useful for quantum information processing in molecular tweezer arrays.

quant-ph↗