[Paper Review] Spin Squeezing by Rydberg Dressing in an Array of Atomic Ensembles

Jacob Hines, S. Rajagopal+5 more|PubMed|Mar 15, 2023

Cold Atom Physics and Bose-Einstein Condensates68 references4 citations

TL;DR

This paper demonstrates spin squeezing in an array of 200-atom cesium ensembles using stroboscopic Rydberg dressing, achieving a metrological squeezing parameter of ξ² = 0.77(9). By applying pulsed, off-resonant 319 nm light to induce controlled, short-range Ising interactions, the method suppresses super-Poissonian loss and enables localized, optical control of entanglement across multiple spatially separated ensembles for enhanced quantum sensing and metrology.

ABSTRACT

We report on the creation of an array of spin-squeezed ensembles of cesium atoms via Rydberg dressing, a technique that offers optical control over local interactions between neutral atoms. We optimize the coherence of the interactions by a stroboscopic dressing sequence that suppresses super-Poissonian loss. We thereby prepare squeezed states of N=200 atoms with a metrological squeezing parameter ξ^{2}=0.77(9) quantifying the reduction in phase variance below the standard quantum limit. We realize metrological gain across three spatially separated ensembles in parallel, with the strength of squeezing controlled by the local intensity of the dressing light. Our method can be applied to enhance the precision of tests of fundamental physics based on arrays of atomic clocks and to enable quantum-enhanced imaging of electromagnetic fields.

Motivation & Objective

• To generate spin-squeezed states in multiple spatially separated atomic ensembles using Rydberg dressing for improved quantum metrology.
• To overcome decoherence from facilitated excitation (avalanche effects) that limits coherence in continuous dressing schemes.
• To enable local, optical control of spin squeezing strength via spatially tailored dressing light intensity across an array.
• To demonstrate scalable, multiplexed entanglement in a 1D array of microtraps for applications in atomic clocks and field sensors.
• To achieve metrologically useful squeezing while maintaining high contrast and minimizing technical noise sources.

Proposed method

• Employ a stroboscopic pulse sequence to apply off-resonant 319 nm light, suppressing super-Poissonian loss from avalanche excitation.
• Use Rydberg dressing to induce Ising-type interactions between cesium atoms in hyperfine clock states |↓⟩ and |↑⟩ via coupling to the |60P₃/₂⟩ Rydberg state.
• Implement a spin echo sequence to calibrate the effective twisting strength Q = ∫χ(t) dt, enabling precise control of the squeezing interaction.
• Utilize spatially varying laser intensity across the array to independently tune the Rabi frequency Ω and thus the interaction strength in each site.
• Apply a one-axis twisting model with Nc = 13 interacting neighbors to describe the observed squeezing, accounting for finite baseline contrast.
• Limit pulse duration to τp ≈ 600 ns to reduce contrast loss from contaminant atoms and trap-induced dephasing.

Experimental results

Research questions

• RQ1 Can stroboscopic Rydberg dressing suppress avalanche-induced decoherence to enable coherent spin squeezing in multiple atomic ensembles?
• RQ2 To what extent can local, optical control of dressing light intensity tune the strength of spin squeezing across spatially separated ensembles?
• RQ3 What is the achievable metrological squeezing parameter ξ² in a 1D array of 200-atom ensembles using this method?
• RQ4 How does the observed squeezing compare to theoretical predictions based on one-axis twisting with finite neighbor count?
• RQ5 Can this approach be scaled to three-dimensional arrays to achieve deeper squeezing beyond the current limit of ξ² ≈ 0.3?

Key findings

• The experiment achieves a minimum metrological squeezing parameter of ξ² = 0.77(9) in three spatially separated ensembles, demonstrating sub-SQL phase variance reduction.
• Squeezing increases with twisting strength Q, confirming the expected dependence on interaction strength and validating the one-axis twisting model.
• Antisqueezing in the orthogonal quadrature reaches ξ²_max = 0.77(9) at optimal phase, consistent with spin-squeezing theory and indicating strong entanglement.
• The observed squeezing is consistent with a model including Nc = 13 interacting neighbors and a small amount of technical noise (≈3% of quantum projection noise).
• Contrast loss is minimized by limiting pulse duration to τp ≈ 600 ns, and trap-induced dephasing is mitigated by shortening the total stroboscopic sequence.
• The results suggest that stronger squeezing is achievable with higher laser intensity or longer interaction times, potentially reaching ξ² ≈ 0.09 in 3D systems with ρ = 2×10¹¹ cm⁻³ and Nc ≈ 60.