Quantum Back-action Limits in Dispersively Measured Bose-Einstein Condensates

Most quantum technologies simultaneously require quantum limited measurements and feedback control to establish and maintain quantum coherence and entanglement, with applications ranging from quantum state preparation to quantum error correction. Large-scale applications of these capabilities hinge on understanding system-reservoir dynamics of many-body quantum systems, whose Hilbert space grows exponentially with system size. Ultracold atoms are an ideal platform for understanding the system-reservoir dynamics of many-body systems. In this talk, I will present the characterization of measurement back-action in atomic Bose-Einstein condensates, weakly interacting with a far-from resonant, i.e., dispersively interacting, laser beam. We theoretically describe this process using a quantum trajectories approach where the environment measures the scattered light and I will present our measurement model based on an ideal photodetection mechanism. Next, I will discuss our experimental quantification of the resulting wavefunction change with two observations: the contrast of a Ramsey interferometer [1] and the deposited energy [2]. These results are necessary precursors for achieving true quantum back-action limited measurements of quantum gases and open the door to quantum feedback control of ultracold atoms.

[1] E. Altuntas and I. B. Spielman, arXiv preprint arXiv:2209.04400 (2022).

[2] E. Altuntas and I. B. Spielman, arXiv preprint arXiv:2212.03431 (2022).