€2M Project Targets Quantum Memories for Longer Networks
The fundamental dilemma in quantum communication is a cruel irony: the very property that makes a quantum signal secure: its inability to be copied or amplified, is also what severely limits its transmission distance. When a single photon traverses a long fiber, it inevitably experiences absorption, scattering, and loss. In traditional internet infrastructure, repeaters would simply boost the signal. However, this isn’t possible in quantum systems, as boosting requires copying, which quantum physics forbids.
A European team believes they have a solution: a device capable of holding a quantum state, pausing, and then connecting two shorter links into a single, longer one. This device is known as a quantum memory, and a three-year initiative to develop a specific type of it has just commenced.
The specifics of the new funding
According to the August 25 press release, the project, named AL FreSQO (Atom-Light Free-Space Quantum Optics networking), is led by the University of Strathclyde in Glasgow. It has secured a €2 million grant over three years, funded by QuantERA, a transnational quantum research program supported by the European Commission. Collaborating institutions include the Universities of Southampton, Padova, and Humboldt in Berlin, Sabancı University in Istanbul, and ThinkQuantum, a spinout from Padova.
It’s important to clarify what this funding represents. It supports an attempt. The complete system hasn’t yet been demonstrated, and the announcement is purely a media release. Therefore, the following details should be understood as the project’s plan, not as proven achievements.
The repeater strategy, without the cheating
The central concept, known as entanglement swapping, sounds like magic but is a tangible process.
Say you need to connect Point A to a distant Point C. Instead of sending a single, fragile photon directly across the entire span, a station is set up at Point B in the middle. You entangle A with B, and then B with C. A measurement performed at B then effectively merges these two connections, resulting in A and C becoming entangled, even though no particle has physically traveled the full distance between them. The middle station transforms from a bottleneck into a matchmaker.
The challenge lies in timing. Entangling A with B and B with C will not happen simultaneously. Photons are lost, attempts fail, and retries are necessary. This means a temporary storage location is needed for the first successful link while awaiting the second. This storage is the quantum memory, designed to store the quantum state, hold it, and release it on demand. Without it, entanglement swapping would be like trying to shake hands with two people who arrive an hour apart.
AL FreSQO’s quantum memory utilizes cold atoms, which are clouds of atoms chilled to near absolute zero. This extreme cold keeps them stable enough to reliably store and retrieve a photon’s quantum information.
The decision to bypass fiber optics
Though most quantum networking demonstrations use optical fiber, the same glass strands that carry your internet traffic, AL FreSQO is pursuing free-space optical links. This involves sending signals through open air, with future plans to extend to the vacuum of space for satellite communication.
Why this approach?
Optical fiber isn’t universally available. It doesn’t span every ocean, follow every flight path, nor can it connect to spacecraft. For aviation, shipping, rail, and satellite communications, air is the only viable transmission medium. Additionally, the project aims to reduce reliance on the bulky, power-intensive cryogenic refrigerators required by some competing memory platforms, which often occupy significant space.
Another significant technical hurdle is the wavelength mismatch between telecommunications light and the light that atoms readily absorb. Atoms are highly specific. To overcome this, the team plans to develop wavelength converters that can transform photons from telecom wavelengths to atom-friendly wavelengths and back. This would enable seamless communication between free-space and fiber networks, offering crucial flexibility. This conversion is currently the most significant engineering unknown.
Professor Daniel Oi of Strathclyde, the project coordinator, articulated the problem succinctly:
“Quantum signals are fragile and easily lost over long distances. Since they cannot be copied or amplified, we need innovative methods to extend their range. Our strategy involves using repeater devices and quantum memories to divide long links into shorter ones and reconnect them through entanglement swapping, thereby allowing information to travel much further.”
Understanding the project’s scope
This project is in its nascent stages. Some of the work is still at the experimental design phase. For example, Dr. Aidan Arnold at Strathclyde will conduct experiments on quantum non-demolition detection: detecting a photon without destroying it. This is a complex problem in itself and represents a component of the network, not the finished product.
Currently, no performance metrics exist because the system hasn’t yet been built. There are no storage times, link distances, or fidelities to report. Though cold-atom memories are a well-established platform with years of laboratory results, scaling them into a deployable free-space repeater that can withstand real-world atmospheric conditions, weather, and satellite geometries is an entirely different challenge.
Free-space links contend with turbulence and pointing errors that fiber optics do not. Wavelength conversion introduces additional loss and noise. Though each of these elements has been demonstrated in isolation, integrating them into a functional repeater is the project’s central gamble.
The vision of a future quantum internet by 2035, which aligns with the UK National Quantum Strategy, represents a target, not an achieved timeline.
What is certain today: a well-funded, credible team has a sensible architectural approach and a clear plan. What remains aspirational is the network itself. Revisit this question in three years.