Hey everyone,

Thank you for being a reader for so long. We're expanding our coverage, and today's a first for us: a whole edition built around one theme, quantum computing, instead of our usual mix.

Let us know what you think of this edition, and whether you'd want to see more quantum-exclusive editions from us, in the poll below.

If you're reading this, thanks for giving it a shot with us.

Scientists Made a Quantum Link Using Only Sunlight

A quick note before this makes sense: entanglement is the odd quantum phenomenon where two particles become so deeply connected that measuring one reveals information about the other in an instant, regardless of how far away they are.

Picture two boxes, one sent to you, one sent to a friend on the other side of the world. Each box holds either a red ball or a blue ball, and nobody knows which until someone opens one. You open yours, see red, and instantly know your friend's box holds blue, no call, no signal, no waiting. That's the everyday version of entanglement, and it's also slightly wrong.

With ordinary boxes, the color was already decided the moment they were packed, you just didn't know it yet. With entangled particles, physicists have shown there's no hidden answer sitting inside beforehand waiting to be revealed, the connection itself is doing the work in a way boxes and balls can't fully capture.

Keep that distinction in mind, it's exactly what the Bell's inequality test later in this piece is built to catch.

It is the basis of quantum computing, quantum encryption and quantum communication. It has always taken a laser to make it. Now a team from the University of Ottawa and Germany's Max Planck Institute for the Science of Light did it with something far simpler: sunlight.

Why everybody thought that you needed a laser

Physicists can make entangled particles by shining light through a special crystal, in a process known as spontaneous parametric down-conversion; basically, one photon goes in and two connected photons come out.

For decades that input light had to be a laser, because lasers are coherent: every wave lines up in lockstep, all the same color, all pointed the same direction. Sunlight is the exact opposite. It's a random jumble of every color, dispersing in every direction. It was assumed that you needed order going in to get order coming out.

Lasers also aren't free. They run on electricity, need to be stabilized all the time, and waste a lot of their own power as heat. When quantum technology scales, that adds up.

What the team actually proved

This assumption has been proven false by the research group led by physicist Robert Boyd, first through theory and later with regular LED light, provided that the entanglement gets encoded in an invariant property of light, such as polarization, which is independent of color or direction.

Sunlight was the real test. "We take out the electrical-to-optical conversion part of entanglement generation," study co-lead Cheng Li said. "We go straight from light to light."

It was not physics, but engineering, which proved the more difficult part. You can't shine unfocused sunlight onto a millimeter-sized crystal and expect anything to happen.

Hanieh Fattahi's team at the Max Planck Institute built the fix: a solar concentrator with a window-sized lens that collects sunlight, funnels it through a cone-shaped glass device, and sends it out through an optical fiber thinner than a human hair, aimed precisely at the crystal, with a motor tracking the sun's position to keep the light steady.

Did it actually work?

Yes. Outdoor tests over three days yielded photon pairs that were essentially indistinguishable from a perfect entangled state, achieving roughly 94% fidelity. More importantly, they violated Bell's inequality, a statistical test that rules out ordinary optical coincidence as an explanation for the effect.

The measured number came in at 2.54, well past the threshold of 2 required to count as legitimate proof. That's the formal "yes, this really is quantum" result.

The fidelity came in only slightly worse than the best laser-based setups, but according to the team, that gap comes from imperfect optics, not from sunlight itself, in other words, an engineering problem, not a physics one.

Why bother

This is a proof-of-concept, not an actual product. But say it out loud and it makes sense immediately: sunlight is free and it's everywhere.

An early use case, Li notes, is satellites: instead of burdening a power-hungry laser into orbit, ambient sunlight could generate secure quantum encryption keys directly. More broadly, given that power grids are already strained by data centers, it's better to build quantum technology's energy problem out from the start rather than try to fix it down the road.

It's a small experiment. But it breaks a fundamental assumption the whole field has quietly built itself around: that quantum states are fragile, precious things you can only make with isolated, artificial light. Turns out the sun was enough.

Nearly Half Of Our Readers Think Quantum Breaks Bitcoin By 2035

We asked our newsletter readers whether quantum computing would break Bitcoin by 2035. Before we get to what they said, one thing happened last week that reframes the whole question: an AI model that isn't even public found a flaw in a post-quantum defense scheme that two years of human review had missed. No quantum computer was involved.

Sui Blockchain prepares for a post Quantum world

Blockchain is one of many technologies quantum computing threatens, since a powerful enough machine could eventually break the encryption that keeps it secure.

Some networks aren't waiting to find out. Sui, for example, is adding two NIST-approved post-quantum signature schemes: ML-DSA-65 as a native protocol signature for everyday accounts, and hash-based SLH-DSA-SHA2-128s inside Move smart contracts for high-value vaults.

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