Abstract: A fundamental tenet of quantum mechanics is that measurements change a system's wavefunction to that most consistent with the measurement outcome, even if no observer is present. Weak measurements---termed partial or non-destructive in different settings---produce only limited information about the system, and as a result only minimally change the system's state. Ultracold atoms - our workhorse for quantum simulation, are an ideal platform for developing back-action limited measurements and understanding system-reservoir dynamics of large-scale many-body systems. We theoretically and experimentally characterize quantum back-action in atomic Bose-Einstein condensates (BECs) ---the system---weakly measured with a far-from resonant, i.e., dispersivly interacting, probe laser beam---the reservoir. We theoretically describe this process using a quantum trajectories approach and present a measurement model based on an ideal photodetection mechanism. We experimentally quantify the resulting wavefunction change with three observations: the change in total atom number, the contrast of a Ramsey interferometer, and the deposited energy. The observed back-action is in good agreement with our measurement model, demonstrating the capability of true quantum back-action limited measurements of BECs.
Location: ATL 2400
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