Atom and spin resolved imaging in a single shot

Abstract

We report on an imaging scheme for quantum gases that enables simultaneous detection of two spin states with single-atom resolution. It utilizes the polarization of the emitted photons during fluorescence by choosing appropriate internal states of lithium-6 atoms in a magnetic field. This scheme can readily be implemented to obtain in-situ spin correlations in a wide variety of experimental settings.

Figures (1)

• Figure 1: Spin and atom resolved imaging scheme a) Level structure of the $2s_{1/2}$ ground and the $2p_{3/2}$ excited state in $^6\text{Li}$ and their magnetic field dependence. The closed cycling transitions for the stretched states $\ket{3}=\ket{m_J=-1/2, m_I=-1}$ and $\ket{6}=\ket{m_J=+1/2, m_I=+1}$ are marked in red and blue, and the corresponding polarization is assigned. b) Schematic representation of the optical setup enabling simultaneous imaging of both spin states. In the collection part, the fluorescence light from an arbitrary system, here depicted as the harmonic oscillator ground state of two fermions with different spins, is collected by a lens. The overlapping left- and right-handed fluorescence light emitted from the $\sigma_+$ and $\sigma_-$ transitions is transformed into orthogonal linear polarizations by a quarter-waveplate. In the polarization-splitting section, PBS cubes are used to split the polarizations and then recombine them at slightly different angles. The half-waveplates in each path are used such that each beam is transmitted exactly once, which optimizes the extinction ratio given by the cubes and hence minimizes cross-coupling between the two images. In the detection part, the two beams are focused onto two parts of the same camera chip, where on the left (right) hand side the signal of atoms in state $\ket{3}$ ($\ket{6}$) is located. c) A rendering of the modular imaging setup used in this experiment. Technical details of the implementation into the Heidelberg Quantum Architecture are presented in Hammel2025 and referenced by the microscopy module puzzle piece. In the inset, an experimental image of the system depicted in b) is presented, namely, the ground state of a harmonic oscillator filled with two fermions of different spins. The image is post-processed as described in Bergschneider_2018: First, the image is binarized by setting each pixel to 0 or 1 based on the raw pixel value relative to a threshold. Then, the data are folded with a Gaussian to generate a low-pass image, which is subsequently analyzed using a peak-finding routine.