Generating Fock state exceeding 10000 excitations with near unit fidelity by adaptive generalized-parity measurement

• URL: http://arxiv.org/abs/2606.01341v1
• Date: Sun, 31 May 2026 16:47:50 GMT
• Title: Generating Fock state exceeding 10000 excitations with near unit fidelity by adaptive generalized-parity measurement
• Abstract summary: We propose an adaptive generalized-parity-measurement protocol to create macroscopic Fock states with more than $10000$ excitations.<n>Our protocol can transform a large coherent state to a large Fock state of photon numbers up to $n_t=mathcalO(104)$ within $10$ rounds of measurements.
• Score: 2.8668875019366395
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: Macroscopic Fock states provide valuable resources for quantum information processing and quantum metrology. We here propose an adaptive generalized-parity-measurement protocol to create macroscopic Fock states with more than $10000$ excitations. For a general system with a discrete spectrum, e.g., a bosonic mode, that is coupled to an ancillary qubit, we derive a construction rule of either a diagonal generalized parity measurement (GPM) or a displaced GPM with intervals adaptive to the last outcome of repeated measurements on the qubit. Different from the probabilistic protocols based on postselection, in which only a single prescribed sequence of free-evolution-measurement is survived, our protocol retains every measurement trajectory by converting the outcome randomness of the ancillary-qubit measurement to the adaptive update of GPM. Using the resonant Jaynes-Cummings (JC) model, our protocol can transform a large coherent state to a large Fock state of photon numbers up to $n_t=\mathcal{O}(10^4)$ within $10$ rounds of measurements, where the averaged fidelity reaches about $80\%$. The probability for obtaining such a large Fock state with a fidelity above $99\%$ remains about $35\%$ with respect to the ensemble sampling. Our protocol also applies to displaced thermal states, indicating its robustness against a moderate thermal mixture.

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