Entangled Photons Display 97.1 Per Cent Interference with New Chip Design
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A high-visibility Franson interference is achieved using photonic integrated circuits at telecom wavelengths. Ramin Emadi and colleagues at CNR, INO, in a collaboration between CNR, INO, LENS, the University of Florence, and QTI srl, have created a compact and stable system for generating and analysing entangled photons. The system delivers a two-photon interference visibility of 97.1%, alongside a coincidence-to-accidental ratio exceeding 1000, with 1.7mW of pump power. This represents a sharp advance in photonic quantum information processing, offering one of the key Franson-interference visibilities reported for a fully passive, fibre-integrated platform. High-visibility entanglement via passively-stabilised integrated photonics Entanglement measures now demonstrate a Franson interference visibility of 97.1%, a substantial improvement over previous systems which struggled to exceed 95% without active stabilisation. This threshold is important for reliable quantum key distribution and advanced quantum networks, previously hampered by the instability of maintaining such high visibility. The new system achieves this landmark result using a compact, passively-stabilised platform integrating cascaded periodically poled lithium niobate waveguides with photonic integrated circuits. The new design eliminates the need for complex active phase control, simplifying operation and reducing system size. It maintains a coincidence-to-accidental ratio exceeding 1000 at a pump power of 1.7mW. A narrow-linewidth continuous-wave pump and dense wavelength-division multiplexing, a technique for transmitting multiple signals over fibre optics, have enabled a heralding efficiency of 4.8% in generating energy-time entangled photon pairs. The system maintains a coincidence-to-accidental ratio exceeding 1000 at a pump power of only 1.7mW, indicating a strong signal amidst background noise. Relying instead on thermal tuning for phase scanning simplifies the platform’s design and improves stability. Following sinusoidal fringe fitting, the resulting Franson interference visibility reached 97.1%, representing a sharp step towards practical quantum communication networks, though this figure currently reflects performance within a laboratory setting and does not yet account for losses incurred in long-distance fibre deployment. Passive stabilisation delivers high-fidelity entanglement despite photon loss Establishing a stable and compact source of entangled photons represents a key step towards building practical quantum networks, promising secure communication and enhanced computing power. Traditionally, achieving high entanglement quality, as measured by Franson interference, has demanded intricate and power-hungry systems reliant on active stabilisation of optical components. This work elegantly sidesteps that complexity with a passively-stabilised chip, yet a heralding efficiency of 4.8 percent suggests significant photon loss remains a limiting factor. A heralding efficiency of only 4.8 percent does indicate substantial photon loss within the system, hindering immediate scalability for complex networks, though incremental improvements to photon collection will be vital. This integrated photonic circuit demonstrates a new level of stability in generating entangled photons, fundamental particles linked regardless of distance. The system creates these pairs by utilising a cascaded periodically poled lithium niobate waveguide, without requiring active adjustments to maintain performance; thermal tuning passively controls the necessary phase shifts. Achieving 97.1% visibility in Franson interference, a key indicator of entanglement quality, alongside a high coincidence-to-accidental ratio, confirms the strong performance of this approach. Operating at telecommunications wavelengths, this passively-stabilised platform moves quantum key distribution closer to practical implementation. The researchers demonstrated high-fidelity Franson interference, 97.1% visibility, using a passively-stabilised photonic integrated circuit fabricated from periodically poled lithium niobate. This matters because stable, compact sources of entangled photons are essential for developing practical quantum communication networks offering enhanced security. Although current heralding efficiency stands at 4.8%, indicating photon loss, this work paves the way for further optimisation of photon collection and integration with fibre optic cables. Future development could focus on reducing these losses to enable longer-distance quantum key distribution and more complex quantum networks. 👉 More information 🗞 High-Visibility Franson Interference Enabled by Passive Photonic Integrated Interferometers at Telecom Wavelengths 🧠 ArXiv: https://arxiv.org/abs/2603.26355 Tags: Rohail T. As a quantum scientist exploring the frontiers of physics and technology. My work focuses on uncovering how quantum mechanics, computing, and emerging technologies are transforming our understanding of reality. I share research-driven insights that make complex ideas in quantum science clear, engaging, and relevant to the modern world. Latest Posts by Rohail T.: Quantum Computers Threaten Current Online Security, Study Confirms March 31, 2026 Magnets Unlock More Efficient Nanoscale Energy Conversion Via Novel Cycles March 31, 2026 Fewer Measurements Unlock Faster Quantum Processor Development March 31, 2026