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Si us plau utilitzeu sempre aquest identificador per citar o enllaçar aquest document: https://hdl.handle.net/2445/230965
Quasi-adiabatic preparation of squeezed antiferromagnetic states
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Cavity-mediated interactions have recently been proposed as a route toward strongly correlated many-body regimes in atomic ensembles. The underlying mechanism is that an antiferromagnetic cavity-mediated interaction penalises total transverse spin fluctuations, pushing the system toward states of small total spin, where the physics is determined by the cavity fluctuations. Once the system reaches a degenerate singlet-like sector, additional spatially structured spin couplings lift the degeneracy and select specific many-body phases, such as quantum spin liquids. This thesis addresses the first of these steps: the quasi-adiabatic preparation of squeezed antiferromagnetic states in a collective cavity-QED setting. We consider two atomic sublattices initialised in a classical antiferromagnetic product state pinned by a staggered field, and ramp up
a cavity-mediated interaction that generates correlations between the sublattices, suppressing their collective transverse fluctuations. Since the cavity is intrinsically lossy, we describe the dynamics with a Lindblad master equation for collective photon loss, which introduces a competition between diabatic excitations from fast ramps and dissipative degradation from slow ones. We solve this trade-off in the minimal two-atom case, where the target is the antisymmetric Bell state, and then extend the analysis to larger ensembles using linear spin-wave theory, where the target is a two-mode squeezed antiferromagnetic state. In both regimes, the optimal protocol is not the most adiabatic one, but the one that best balances diabatic and dissipative errors. As the atom number increases, the achievable squeezing improves monotonically despite collective dissipation, approaching Heisenberg-limited scaling (∝ 1/N) in the weakdissipation regime. These results show that squeezed antiferromagnetic states
remain accessible under realistic cavity-QED conditions, supporting their role as a collective precursor toward richer, spatially structured many-body phases.
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Màster Oficial de Ciència i Tecnologia Quàntiques / Quantum Science and Technology, Facultat de Física, Universitat de Barcelona. Curs: 2025-2026. Tutors: Darrick Chang, Błażej Jaworowski
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LÓPEZ I IGLESIAS, Mar. Quasi-adiabatic preparation of squeezed antiferromagnetic states. [consulted: 25 of July of 2026]. Available at: https://hdl.handle.net/2445/230965