Browsing by Author "Büchler, Hans Peter"

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    Absorbing state phase transition with Clifford circuits
    (2024) Makki, Nastasia; Lang, Nicolai; Büchler, Hans Peter
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    Controlled multi-photon subtraction with cascaded Rydberg superatoms as single-photon absorbers
    (2021) Stiesdal, Nina; Busche, Hannes; Kleinbeck, Kevin; Kumlin, Jan; Hansen, Mikkel G.; Büchler, Hans Peter; Hofferberth, Sebastian
    The preparation of light pulses with well-defined quantum properties requires precise control at the individual photon level. Here, we demonstrate exact and controlled multi-photon subtraction from incoming light pulses. We employ a cascaded system of tightly confined cold atom ensembles with strong, collectively enhanced coupling of photons to Rydberg states. The excitation blockade resulting from interactions between Rydberg atoms limits photon absorption to one per ensemble and rapid dephasing of the collective excitation suppresses stimulated re-emission of the photon. We experimentally demonstrate subtraction with up to three absorbers. Furthermore, we present a thorough theoretical analysis of our scheme where we identify weak Raman decay of the long-lived Rydberg state as the main source of infidelity in the subtracted photon number and investigate the performance of the multi-photon subtractor for increasing absorber numbers in the presence of Raman decay.
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    Crystalline phase for one-dimensional ultra-cold atomic bosons
    (2011) Büchler, Hans Peter
    We study cold atomic gases with a contact interaction and confined into one-dimension. Crossing the confinement induced resonance the correlation between the bosons increases, and introduces an effective range for the interaction potential. Using the mapping onto the sine-Gordon model and a Hubbard model in the strongly interacting regime allows us to derive the phase diagram in the presence of an optical lattice. We find the appearance of a phase transition from a Luttinger liquid with algebraic correlations into a crystalline phase with a particle on every second lattice site.
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    Quantum fluctuations in one-dimensional supersolids
    (2023) Bühler, Chris; Ilg, Tobias; Büchler, Hans Peter