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arXiv:2609.38804

Entangling Atomic Quantum Memories Using High-Order Modulated Coherent States

Chaohan Cui, Prajit Dhara, Saikat Guha

quant-phSubmitted Sep 30, 2026• Announced Oct 1, 2026• 0 citations
v1 · Sep 30, 2026v2 · Oct 1, 2026
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Abstract

High-order coherent-state modulation with reflective cavity-coupled atomic memories can distribute multiple heralded ebits per transmitted optical mode, but requires a collective midpoint POVM optimized for maximum distillable entanglement rather than minimum-error state discrimination. An SRM-inspired 16-QAM receiver reaches $1.75$ ebits per mode at $0.5$~dB end-to-end loss, $3.8$~dB below the half-link capacity benchmark. For 4-QAM, a variational POVM with more outcomes than constellation points improves the SRM rate by $4.0\%$ yet remains below capacity, revealing measurement-design headroom. The advantage over single-qubit-per-mode midpoint protocols persists for per-interface loss $<0.2$~dB and calibrated phase error $<0.2π$.

Comments
8 pages, 5 figures

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