Amita Deb (University of Birmingham)

Optical response of a quantum degenerate gas

I will report our measurements on the interaction of off-resonant light with ultracold ensembles of fermionic atoms [1]. For Fermi gases of potassium atoms in the quantum degenerate regime, we observe a marked suppression in light scattering and enhancement of transmission of light as compared to a similarly prepared thermal Bose gas of rubidium atoms. We attribute these observations to Pauli blocking, where Fermi-Dirac statistics causes atoms to occupy a large region of the momentum space and thereby limits the number of accessible states for a scattering atom. While Pauli blocking suppress the scattering of light out of a probe laser beam mode, a largely unmodified dispersive light-matter interaction is predicted, and we verify this experimentally by measuring the phase shift of transmitted light. I will discuss two theoretical approaches which explain these results, one based on the Fermi golden rule [2] and another based on the coherent optical response of quantum gases [3]. Our work confirms a longstanding theoretical result in the theory of the optical response of quantum gases. Independent experiments from JILA and MIT groups have also reported suppression of incoherently scattered photons from Fermi gases of strontium [4] and lithium [5], and I will discuss these experiments. Our measurements also showed enhanced scattering near the critical temperature of a Bose gas which was later confirmed as Bosonic enhancement of light scattering by experiments in MIT [6].


[1] A.B. Deb and N. Kjærgaard. Observation of Pauli blocking in light scattering from quantum degenerate fermions. Science 374, 972 (2021).

[2] B. DeMarco and D. S. Jin, Exploring a quantum degenerate gas of fermionic atoms. Phys. Rev. A 58, R4267 (1998).

[3] O. Morice, Y. Castin and J. Dalibard, Refractive index of a dilute Bose gas. Phys. Rev. A 51, 3896–3901 (1995).

[4] C. Sanner Lindsay Sonderhouse, Ross B. Hutson, Lingfeng Yan, William R. Milner and Jun Ye, Pauli blocking of atom-light scattering. Science 374, 979 (2021).

[5] Y. Margalit, Y. Lu, F. C. Top and W. Ketterle, Pauli blocking of light scattering in degenerate fermions. Science 374, 976 (2021).

[6] Y.-K. Lu, Y. Margalit and W. Ketterle, Bosonic stimulation of atom-light scattering in an ultracold gas. Nature Physics 19, 210 (2023).