Neutral atom systems are promising platforms for quantum simulation and computation, owing to their long coherence times. However, their intrinsically weak ground-state interactions pose a major limitation to the advancement of scalable quantum simulation and computation. To address this challenge, we propose an approach to enhancing the ground-state interaction strength of neutral atoms via Floquet modulation of a Rydberg atomic ensemble. Each Floquet period consists of ground-state coupling followed by a pulse driving the transition from the ground state to the Rydberg state. Theoretical analysis and numerical simulations demonstrate that after a defined evolution time, neutral atoms within Rydberg ensembles can collectively form a
W state in the ground-state manifold. Even when the Rydberg interaction strength is far below the blockade regime, the fidelity remains remarkably high. Finally, we analyze the application of this scheme in the preparation of single-photon sources. In general, our proposed mechanism offers an efficient and highly controllable method for quantum state preparation within the Rydberg atomic ensembles, significantly enhancing the accuracy and stability of quantum state engineering while providing a well-controlled quantum environment for single-photon generation.
Neutral-atom systems are promising platforms for quantum simulation and computation, owing to their long coherence times. However, their intrinsically weak ground-state interactions pose a major limitation to the advancement of scalable quantum simulation and computation. To address this challenge, we propose an approach to enhancing the ground-state interaction strength of neutral atoms via Floquet modulation of a Rydberg atomic ensemble. Each Floquet period consists of ground-state coupling followed by a pulse driving the transition from the ground state to the Rydberg state. Theoretical analysis and numerical simulations demonstrate that after a defined evolution time, neutral atoms within Rydberg ensembles can collectively form a W state in the ground-state manifold. Even when the Rydberg interaction strength is far below the blockade regime, the fidelity remains remarkably high. Finally, we analyze the application of this scheme in the preparation of single-photon sources. In general, our proposed mechanism offers an efficient and highly controllable method for quantum state preparation within the Rydberg atomic ensembles, significantly enhancing the accuracy and stability of quantum state engineering while providing a well-controlled quantum environment for single-photon generation.
This thesis reports progress towards using hyperfine-encoded neutral atomic ensembles for quantum information applications. Ensemble qubits are alternative building blocks to process quantum information, while circumventing the challenges preparing a low-entropy single-atom qubit register. While ensemble approach inherits the single-atom quantum gate protocols, cooperative atom-light interaction makes it favorable platform to implement atom-photon interface, such as quantum memory. We have demonstrated semi-deterministic preparation of W-state, which we use as an ensemble qubit. Observed 50–60% preparation fidelity shows discrepancy to expected > 80% fidelity including known imperfections. We suspect Ground-Rydberg and Rydberg-Rydberg molecular interactions within the ensemble modify the dynamics. State tomography and Ramsey experiment clearly identified that majority of constituents in an ensemble are indeed entangled. We report the first measurement of W-state coherence time as 2.6ms for 7.6 atoms, which is long enough to perform 2600 Rydberg-mediated quantum gate operations. The first demonstration of Rydberg blockade between two ensembles happened in the same apparatus. We observe blockade fidelity of 0.89 (uncorrected) and near unity when post-selected on successful N = 1 Fock state preparation of Control ensemble. For weakly blockaded cases, Target ensemble remained as a perturber inhibiting Control ensemble from de-excitation. We discuss the efficacy of optical lattice insertion to suppress molecular interactions that might have been affecting the Rydberg dynamics. High fidelity, parallel, low loss fluorescence detection of hyperfine ground state of rubidium atoms is presented. Enforced cycling transition scattering minimally alters the internal states. We achieve mean state detection fidelity of 97% (uncorrected) and 98.7% (SPAM error corrected), with atom loss rate < 2% and hyperfine-changing rate < 2%. This scalable technique is also compatible with ensemble qubits and error correcting schemes. Technical developments on apparatus, lasers, supporting hardware and software are discussed. Automatic beam alignment system is implemented to correct long term drift of tightly focused addressing beams. Achieved pointing stability of 60 nm. Two home-made, high performing, cavity-enhanced frequency doubling systems were constructed to meet experimental demand. We observe 960/480 system output as high as 180 mW with 600 mW fundamental, and 1540/770 system output as high as 13.97 W from 19 W fundamental.