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  • Letter
  • Open Access

Spin squeezing with itinerant dipoles: A case for shallow lattices

David Wellnitz, Mikhail Mamaev, Thomas Bilitewski, and Ana Maria Rey
Phys. Rev. Research 6, L012025 – Published 7 February 2024
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    Abstract

    Entangled spin squeezed states generated via dipolar interactions in lattice models provide unique opportunities for quantum enhanced sensing and are now within reach of current experiments. A critical question in this context is which parameter regimes offer the best prospects under realistic conditions. Light scattering in deep lattices can induce significant decoherence and strong Stark shifts, while shallow lattices face motional decoherence as a fundamental obstacle. Here we analyze the interplay between motion and spin squeezing in itinerant fermionic dipoles in one dimensional chains using exact matrix product state simulations. We demonstrate that shallow lattices can achieve more than 5 dB of squeezing, outperforming deep lattices by up to more than 3 dB, even in the presence of low filling, loss, and decoherence. We relate this finding to SU(2)-symmetric superexchange interactions, which keep spins aligned and protect collective correlations. We show that the optimal regime is achieved for small repulsive off-site interactions, with a trade-off between maximal squeezing and optimal squeezing time.

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    • Received 4 January 2023
    • Revised 11 October 2023
    • Accepted 2 January 2024

    DOI:https://doi.org/10.1103/PhysRevResearch.6.L012025

    Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

    Published by the American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Cold and ultracold moleculesDipolar gasesDipolar moleculesEntanglement in quantum gasesQuantum metrology
    1. Techniques
    Matrix product states
    Atomic, Molecular & OpticalQuantum Information, Science & Technology

    Authors & Affiliations

    David Wellnitz1,2,*, Mikhail Mamaev1,2, Thomas Bilitewski3, and Ana Maria Rey1,2

    • 1JILA, National Institute of Standards and Technology and Department of Physics, University of Colorado, Boulder, Colorado 80309, USA
    • 2Center for Theory of Quantum Matter, University of Colorado, Boulder, Colorado 80309, USA
    • 3Department of Physics, Oklahoma State University, Stillwater, Oklahoma 74078, USA

    • *Corresponding author: david.wellnitz@colorado.edu

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    Vol. 6, Iss. 1 — February - April 2024

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    • Figure 1
      Figure 1

      (a) Schematic of the system (see text). (b) Top: Ramsey pulse sequence. Bottom: Schematic illustration of squeezing dynamics in the Sy−Sz plane. (c) Maximal squeezing ξ2 for t<10 ms versus filling fraction f and lattice depth. In x and y/z directions (Vlatt,x,Vlatt,⊥)/ER=(3,3),(3,40),(5,40),(40,40) [ER=2π2ℏ2/(mλ2) is the recoil energy] (top to bottom, see the Supplemental Material for detailed parameters [72]). The black line indicates where the system can be approximated by a spin model. The striped area indicates where squeezing is growing past 10 ms.

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    • Figure 2
      Figure 2

      Full system dynamics. Time evolution of (a) squeezing ξ2 and (b) contrast for various lattice depths [from light to dark, (Vlatt,x,Vlatt,⊥)/ER=(3,3),(3,40),(5,40),(40,40)]. Parameters: V⊥/h=40Hz, f=0.8, Γ=Ucontact/ℏ. (c), (d) Same as (a) and (b) for varying dipolar interaction strength V⊥, while keeping the on-site interaction, U, and loss rate, Γ, fixed, and (Vlatt,x,Vlatt,⊥)/ER=(3,40). See the Supplemental Material for lattice and MPS parameters [72].

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    • Figure 3
      Figure 3

      Analytic models. (a) Spin squeezing dynamics for the FH model (symbols, size encodes doublon population), real-space spin-model (continuous lines), and the OAT limit (dotted line). (b) Contrast at 10 ms for spin-wave analysis (continuous lines; blue: f=1; red: f=0.6), spin model (gray x's; f=1), and FH model (colored symbols; f=1 without losses; f=0.6 with losses). Vertical lines and text indicate stability of spin waves (see text).

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    • Figure 4
      Figure 4

      Spin squeezing ξ2 in the presence of imperfections. (a) X pulses with different pulse spacing τ protect against dephasing due to spin-dependent tunneling. We consider J↑/h=153Hz, J↓/h=131Hz compared to the no anisotropy reference with J↓/h=J↑/h=142Hz. Other parameters f=0.8, Ucontact/h=529Hz, Udd/h=−273Hz, Γ=Ucontact/ℏ, and V⊥/h=40Hz. (b) Dynamics for different filling fractions f. Inset shows the contrast decay. Parameters: J/h=153Hz, U/h=239Hz, Γ=2π×512s−1, and V⊥/h=40Hz.

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