Light that barely advances can make quantum bits feel closer than they are. That is the strange, useful physics at the heart of new work from the University of Namur with collaborators at Harvard, Michigan Tech, and Sparrow Quantum, published in Light: Science & Applications.
The team describes a photonic chip design that keeps entanglement alive between diamond based emitters across about 12.5 micrometers, roughly 17 free space wavelengths. For on chip quantum hardware, that distance matters.
The trick uses near zero index media. In ordinary materials, light ripples forward with peaks and troughs. In a near zero index structure, the field becomes more uniform. Phases flatten. And when phases flatten, emitters that are physically apart can become optically close. That is where superradiance, theorized by Robert Dicke in 1954, becomes a practical tool rather than a historical footnote.
“This paper shows how near-zero refractive index photonics can transition from classical electrodynamics to the quantum regime, since superradiance is intrinsically quantum.”
So said Eric Mazur of Harvard, who has championed these materials for years. His point lands: once the field looks uniform, collective effects that normally collapse with distance can persist. The authors push that idea with a fully dielectric, mu near zero (MNZ) metamaterial tuned around the 737 nanometer line of silicon vacancy centers in diamond. That choice avoids the high losses that plague plasmonic, epsilon near zero waveguides, while keeping coupling in and out of the structure feasible. No small feat. And it keeps device engineers in the game, not just theorists.
In simulations using the Lindblad master equation and Green’s tensor calculations, the team shows transient concurrence, a standard entanglement metric, holding up past 17 wavelengths. With antisymmetric optical pumping, they also report steady state regimes where entanglement persists. The numbers are the headline here. Compared to free space, concurrence survives an order of magnitude farther. Compared to prior ENZ waveguides, the MNZ platform maintains similar or better entanglement with far less sensitivity to exact emitter placement. Turns out, a little magnetic near zero goes a long way.
There is a practical rhythm to the work. The chip is a square lattice of diamond pillars with geometry detuned from an EMNZ Dirac cone to yield a TE polarized MNZ mode and finite impedance. Translation: you can actually feed light in and get it out. The authors also stress fabrication tolerance, showing that small random variations in pillar radius still leave the effective index near zero across a useful bandwidth. For anyone who has stood at an electron beam lithography tool at 2 a.m., that last bit is not an academic detail.
And the stakes are not only scientific. If on chip entanglement holds over tens of wavelengths, you can space qubits more comfortably, route signals with less acrobatics, and design cluster states for one way quantum computing without packing everything elbow to elbow. There are commercial consequences here, from cleaner photonic layouts to more scalable repeaters for quantum networks. The authors even sketch out a measurement path with Raman transitions and tapered diamond waveguides. Not a product yet, but not vapor either.
“This is one of the major areas I’ve been studying for ten years now, and for which I was a post-doctoral fellow in Professor Eric Mazur’s team at Harvard”
That is Michaël Lobet of UNamur, staking a claim with the patience of someone who has watched this field inch forward. The real surprise came in how controlled repetition keeps paying off: near zero index, near zero index, near zero index. Flatten the phase, extend the reach, repeat. But there is still the usual caveat. The present work is theoretical and numerical. Experiments will have to pin down losses, disorder, and dephasing in real devices at low temperatures, then show that the entanglement numbers survive on a benchtop. If they do, expect a raft of chips where light barely moves, and yet everything suddenly clicks.
Explainer: Why Near Zero Index Helps Entanglement
Near zero index (NZI) materials make the wavelength inside the medium effectively very large, which flattens the phase of the light field. When phase is flat, distant emitters can behave as if they are in the same optical neighborhood. That enables collective effects like superradiance and supports entanglement over longer distances. Plasmonic ENZ devices can do some of this, but metal losses kill performance. The new study uses an all dielectric, mu near zero (MNZ) metamaterial with a TE polarized mode and finite impedance, so light can couple in and out. Using nitrogen or silicon vacancy centers in diamond as qubits, the authors simulate concurrence persisting over about 12.5 micrometers. Longer reach on chip means simpler layouts, fewer tight tolerances, and a clearer path toward scalable photonic quantum computing and networking.
Journal: Light: Science & Applications
DOI: 10.1038/s41377-025-01994-9
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