Hyperloss from coherent spatial-mode mixing in quantum-correlated networks

TL;DR

This paper reveals that coherent spatial-mode mixing can cause hyperloss in quantum networks, severely degrading quantum resources, but it can be mitigated through phase tuning, improving the robustness of quantum technologies.

Contribution

It demonstrates experimentally that mode mismatch can lead to hyperloss, exceeding 100%, and shows how phase control can recover quantum correlations, offering new design strategies.

Findings

Hyperloss can exceed 100% due to mode mismatch.

Phase tuning can recover quantum correlations and suppress hyperloss.

Mode mismatch acts as an explicit, controllable parameter in quantum network design.

Abstract

Quantum-correlated networks distribute quantum resources such as squeezed and entangled states. These states are central to modern quantum technology, including photonic quantum computing, quantum communications, non-destructive biological sensing and gravitational-wave detection. Even for squeezed states of light - the most robust quantum-correlated resource - loss-induced decoherence remains the dominant obstacle to strong quantum advantage in in large-scale interferometric and networked quantum systems. Common design assumption in these applications is treating mismatches between spatial modes as a small, incoherent loss. Here we show that this picture can fail: coherent spatial-mode mixing with higher-order spatial modes can produce an apparent loss exceeding 100% relative to the initial squeezing, a regime we term hyperloss. We experimentally demonstrate hyperloss in a minimal two-node quantum network: with only 8% mode mismatch, a 5.8dB squeezed state is converted into an effectively thermal state with no quadrature squeezing, eliminating the quantum advantage. Because the effect is coherent, it is controllable: lost correlations can be recovered by tuning differential spatial-mode phases (e.g., Gouy-/propagation-phase). We demonstrate this recovery experimentally, not only eliminating the hyperloss, but even significantly suppressing the mode mismatch loss, with 15% geometric mismatch acting like only ~2.8% effective loss. Hyperloss is a design-limiting mechanism for all quantum networks with squeezed light, from from photonic quantum processors to large-scale interferometers and distributed quantum-sensing networks. Our results provide a practical route to avoid hyperloss and turn mode mismatch into an explicit, phase-aware design parameter for future quantum technologies.