arXiv subjects

Carter Turnbaugh

Publications and source records attributed to Carter Turnbaugh.

7 recordsLinked to original sources

arXiv2026

Revealing Hidden Correlations in a Fermi-Hubbard system via Interaction Ramps

We observe an enhanced visibility of charge-density-wave correlations in a cold-atom realization of the attractive Hubbard model following a rapid boost of the interaction strength. The interaction boost associates nonlocal pairs into doublons which mark the center of mass of the original pairs. The enhancement is largest in the strongly correlated regime where pairing is nonlocal. We distinguish the unpaired Fermi liquid from the pseudogap phase of preformed pairs by analyzing atom-resolved spin-charge correlations after the ramp. The technique we establish here may facilitate the observation of exotic forms of pair order in spin-imbalanced systems, and of stripe order in the dual case of the doped repulsive Hubbard model.

cond-mat.quant-gas↗

arXiv2025

Competition of fermion pairing, magnetism, and charge order in the spin-doped attractive Hubbard gas

The tension between fermion pairing and magnetism affects numerous strongly correlated electron systems, from high-temperature cuprates to twisted bilayer graphene. Exotic forms of fermion pairing and superfluidity are predicted when attraction between fermions competes with spin doping. Here, we follow the evolution of fermion pairing and charge and spin order in a spin-imbalanced attractive Hubbard gas of fermionic $^{40}$K atoms, covering a wide range of densities, magnetizations, and interactions with single-atom resolution. At low spin imbalance and weak interactions, we find a mixture of nonlocal fermion pairs coexisting with itinerant excess fermions. For stronger interactions an effective hard-core Bose-Fermi mixture emerges. Spin doping drives a crossover from charge-density wave correlations to a Fermi liquid of polarons. Beyond a certain spin imbalance and interaction strength, we find evidence for the onset of combined spin- and pair-density wave order, a possible precursor for the existence of magnetized superfluidity in the attractive Hubbard system.

cond-mat.quant-gas↗

arXiv2025

In search of exotic pairing in the Hubbard model: many-body computation and quantum gas microscopy

Pair density waves and exotic superconductivity have long been of strong interest, and have attracted much recent attention. We present a joint theoretical and experimental exploration of possible signatures of fermion pairing with finite center-of-mass momentum, or the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) order. Experimentally a doped and spin-imbalanced attractive two-dimensional Hubbard model is realized with a cold atomic gas in an optical lattice, and quantum gas microscopy is used to probe its properties. Computationally we study the same model with state-of-the-art constrained-path (CP) auxiliary field quantum Monte Carlo (AFQMC). Direct comparisons between experiment and computation on various short-range magnetic and charge correlations show excellent agreement. We then investigate these correlations, as well as pairing correlation functions, systematically to low temperatures with CP-AFQMC, and determine parameter regimes in density and magnetization where signatures of FFLO order may be observed. We show that the temperature at which precursors of such orders appear is already within reach of the current experiment. We discuss routes for direct experimental detection and measurements of such states.

cond-mat.quant-gas↗

arXiv2024

Experimental timing and control using microcontrollers

Modern physics experiments rely on precise timing provided by programmable digital pulse generators. In many experimental control systems, this role is filled by custom devices built on Field Programmable Gate Arrays (FPGAs). While highly flexible and performant, these systems can be difficult to scale to very large systems due to cost and complexity. Recent advances in microcontroller systems allows these much simpler systems to fill the role of digital pulse generators. Here we demonstrate one such alternative based on the Raspberry Pi Pico microcontroller which allows for timing resolution down to 7.5 ns with a minimum pulse width of of 37.5 ns.

physics.ins-det↗

arXiv2022

Direct observation of non-local fermion pairing in an attractive Fermi-Hubbard gas

Pairing of fermions lies at the heart of superconductivity, the hierarchy of nuclear binding energies and superfluidity of neutron stars. The Hubbard model of attractively interacting fermions provides a paradigmatic setting for fermion pairing, featuring a crossover between Bose-Einstein condensation (BEC) of tightly bound pairs and Bardeen-Cooper-Schrieffer (BCS) superfluidity of long-range Cooper pairs, and a "pseudo-gap" region where pairs form already above the superfluid critical temperature. We here directly observe the non-local nature of fermion pairing in a Hubbard lattice gas, employing spin- and density-resolved imaging of $\sim$1000 fermionic ${}^{40}$K atoms under a bilayer microscope. Complete fermion pairing is revealed by the vanishing of global spin fluctuations with increasing attraction. In the strongly correlated regime, the fermion pair size is found to be on the order of the average interparticle spacing. We resolve polaronic correlations around individual spins, resulting from the interplay of non-local pair fluctuations and charge-density-wave order. Our techniques open the door toward in-situ observation of fermionic superfluids in a Hubbard lattice gas.

cond-mat.quant-gas↗

arXiv2020

High-Power Near-Concentric Fabry-Perot Cavity for Phase Contrast Electron Microscopy

Transmission electron microscopy (TEM) of vitrified biological macromolecules (cryo-EM) is limited by the weak phase contrast signal that is available from such samples. Using a phase plate would thus substantially improve the signal-to-noise ratio. We have previously demonstrated the use of a high-power Fabry-Perot cavity as a phase plate for TEM. We now report improvements to our laser cavity that allow us to achieve record continuous-wave intensities of over 450 GW/cm$^{2}$, sufficient to produce the optimal 90{\deg} phase shift for 300 keV electrons. In addition, we have performed the first cryo-EM reconstruction using a laser phase plate, demonstrating that the stability of this laser phase plate is sufficient for use during standard cryo-EM data collection.

physics.ins-det↗

arXiv2019

Observation of the relativistic reversal of the ponderomotive potential

The secular dynamics of a non-relativistic charged particle in an electromagnetic wave can be described by the ponderomotive potential. Although ponderomotive electron-laser interactions at relativistic velocities are important for emerging technologies from laser-based particle accelerators to laser-enhanced electron microscopy, the effects of special relativity on the interaction have only been studied theoretically. Here, we use a transmission electron microscope to measure the position-dependent phase shift imparted to a relativistic electron wave function when it traverses a standing laser wave. The kinetic energy of the electrons is varied between $80\,\mathrm{keV}$ and $300\,\mathrm{keV}$, and the laser standing wave has a continuous-wave intensity of $175\,\mathrm{GW/cm}^2$. In contrast to the non-relativistic case, we demonstrate that the phase shift depends on both the electron velocity and the wave polarization, confirming the predictions of a quasiclassical theory of the interaction. Remarkably, if the electron's speed is greater than $1/\sqrt{2}$ of the speed of light, the phase shift at the electric field nodes of the wave can exceed that at the antinodes. In this case there exists a polarization such that the phase shifts at the nodes and antinodes are equal, and the electron does not experience Kapitza-Dirac diffraction. Our results thus provide new capabilities for coherent electron beam manipulation.

physics.optics↗