Taking the Quantum Kicked Rotor Through the BEC-BCS Crossover: Signatures of Pairing and Spectral Modifications

The quantum kicked rotor (QKR) is a paradigmatic model for quantum chaos which bridges concepts in interferometry and transport. Prior works with bosons have addressed te effects of weak interactions on the QKR in 1D and 3D, and strong interactions have been used in 1D to observe many-body dynamical localization in a Tonks gas [1,2,3,4]. Generally, stronger interactions have led to decreasing experiment lifetimes due to three-body losses. In the following extension to QKR, we employ fermionic lithium-6 to access strong tunable interactions protected from three-body losses via a magnetic Feshbach resonance, using a balanced spin mixture of the two lowest hyperfine states across the BEC-BCS crossover. In addition to probing QKR physics at the unitarity limit of interactions, we also subject paired particles to the QKR for the first time. By sweeping the pulse period, we construct QKR energy spectra exhibiting mass-dependent structures which shed light on the pairing and interaction between particles. We will report on i) the QKR spectral signature of fermion pairing at unitarity, ii) observed shifts of resonances depending on interaction sign and strength, and iii) modifications to the spectral shape for different pair fractions and interaction signs.

[1] J. H. See Toh et al. Nature Physics 18 1297 (2022)

[2] A. Cao et al. Nature Physics 18 1302 (2022)

[3] J. H. See Toh et al. PRL 133 076301 (2024)

[4] Y. Guo et al. Science 389 6761 (2025)