Quantum 2025 – scientific programme

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MON: Monday Contributed Sessions

MON 1: QIP Implementations: Photons I

MON 1.3: Talk

Monday, September 8, 2025, 14:45–15:00, ZHG001

Enhanced phase sensitivity in displacement-assisted SU(1,1) interferometer with photon recycling — Taj Kumar, Aviral Kumar Pandey, Anand Kumar, and •Devendra Kumar Mishra — Department of Physics, Institute of Science, Banaras Hindu University, Varanasi-221005, Uttar Pradesh, India

In this work, we propose a novel method to improve the phase sensitivity of the displacement-assisted SU(1,1) (DSU(1,1)) interferometer (with displacement strength γ) via photon recycling. We consider vacuum and squeezed vacuum (with squeezing parameter r) states as inputs, with a phase shift φ in one of the arms. This setup is modified by re-injecting the one output mode into the input mode after a phase shift θ, and the photon loss, characterized by √1−T, where T is the transmission coefficient of a fictitious beam splitter. We determined the phase sensitivity of the photon recycled DSU(1,1) (PR-DSU(1,1)) interferometer under the single-intensity and homodyne detection schemes along with the quantum Cramér-Rao bound (QCRB). Then, we compared its performance with the conventional DSU(1,1) interferometer and found that the PR-DSU(1,1) interferometer can achieve improved phase sensitivity and a lower QCRB compared to the latter. Moreover, for both detection schemes, we observed the improvement in the phase sensitivity and QCRB of the PR-DSU(1,1) interferometer relative to the SNL, which further increases with an increase in T, g, |γ|, and r. Therefore, our work offers a novel approach to increase phase sensitivity via photon recycling. This work is based on our recent publication [APL Quantum 2, 016127 (2025)].

Keywords: Phase-sensitivity; SU(1,1) interferometer; Quantum Cramér-Rao bound (QCRB); Photon recycling; Squeezed vacuum state