Rotonium: Shaping the Future of Photonic Quantum Edge Computing
Photonic quantum computing offers unique advantages, such as room-temperature operation and high-speed processing. However, making it practical means addressing significant physical challenges.
Instead of using matter-based qubits, such as trapped ions, neutral atoms, or superconducting circuits, Rotonium encodes quantum information in light, leveraging single-photon “qudits” (explanation below) with orbital angular momentum to unlock new levels of scalability and robustness. This enables not just room-temperature operation but also novel approaches to error handling and deterministic two-qubit gates. Both are long-standing bottlenecks in photonic systems.
Founded three years ago by Roberto Siagri (CEO) and Fabrizio Tamburini (CQO), the company is developing photonic quantum processors designed for edge applications, offering high performance, energy efficiency, and robustness against jamming, all without the need for cryogenic cooling.
Rotonium raised a €1M pre-seed round a year ago, underwritten by Galaxia, the National Technology Transfer Hub for Aerospace, founded by CDP Venture Capital‘s Tech Transfer Fund in collaboration with Obloo Ventures. Now, the team is scaling up the number of qudits and miniaturizing the hardware for real-world deployment. Roberto is a serial entrepreneur and founded Eurotech, a global edge computing company. He led the company from inception to public listing.
Learn more about how photonics and orbital angular momentum could shape the future of quantum computing in our interview with Rotonium co-founder Roberto Siagri:
What Inspired You to Start Rotonium?
I spent the past 30 years in embedded, high-performance, and edge computing, experiencing the evolution of the personal computer from its early days to mass adoption. Back then, I wasn’t thinking about quantum computers. It was already challenging enough to miniaturize traditional systems. But I remember watching Superman’s Fortress of Solitude, where he interacted with light and crystals to communicate. That planted a seed: could computing with light one day become a reality?
About ten years ago, as quantum computing and photonics evolved, that dream resurfaced in my mind. I knew the timing was finally right, and I began thinking seriously about how to build these systems.
A key challenge in photonic quantum computing is designing a deterministic two-qubit gate. Since photons don’t naturally interact with each other, this kind of gate is extremely difficult to implement. That’s not the case for platforms based on superconducting qubits, trapped ions, or neutral atoms, since they’re all based on particles that naturally interact.
Editor’s note: A deterministic two-qubit gate is an operation where two quantum bits influence each other. “Deterministic” means it always executes reliably, which is a challenge for photons.
Editor’s note: Superconducting qubit circuits, trapped ions, and neutral atoms are common types of quantum platforms that rely on matter-based qubits that naturally interact and are easier to entangle than photons.
Around that time, I reconnected with Fabrizio, my current co-founder, who had been working in astrophysics and classical communication. He was experimenting with orbital angular momentum, a special property of photons that allows more information to be packed into a single channel. He is a pioneer in that area. Orbital angular momentum isn’t typically used in standard telecommunications, so his approach was quite unique.
Editor’s note: Orbital angular momentum is a property of light where the wavefront of a photon spins in a spiral shape, like a corkscrew. This twist can be used to carry more information in a single photon, which helps increase the amount of data that can be sent through a communication channel.
Fabrizio came to me with an idea: to design a kind of communication system that could survive under jamming conditions. That caught my attention. If a signal’s robustness depends on a unique property of the photon that’s independent of its other features, maybe that same principle could be applied in quantum computing.
We explored whether it might be possible to build an optimized photonic quantum computer based on these ideas. I still remember the call when he said: “Problem solved. We can design a deterministic two-qubit gate.”
That was the breakthrough moment. We realized that if we could solve one of the biggest challenges in photonic quantum computing—something no one else had done—we could build a company around it. That’s how Rotonium started.
How Is Rotonium Rethinking Quantum Computing for Edge Devices?
We’re building edge quantum computers designed for use in robots, drones, and satellites. Our goal isn’t to develop large, centralized machines but compact systems that can be embedded directly into autonomous platforms.
The key question is whether quantum computing can deliver superior efficiency when compared to computational performance in terms of space, weight, and power requirements. If these quantum processors offer more computing power per gram, watt, or cubic centimeter than classical alternatives, they become uniquely suited for edge applications. That’s the core challenge: maximizing computation within extreme physical constraints.
Most quantum platforms today—whether superconducting, ion-based, or atomic—rely on cryogenic or ultra-high-vacuum (UHV) environments. Even most photonic platforms require photon detectors at ultra-low temperatures. That might work in a lab or a data center, but not in a satellite or drone.
We wanted to go a different route. So we developed a full-stack, room-temperature quantum system, solving the problem at all levels:
- A room-temperature single-photon source
- A computation unit that operates at room temperature
- A photon detector subsystem that also works at room temperature
Editor’s note: A single-photon source emits exactly one photon at a time, enabling precise quantum operations that even a second photon would disrupt.
Editor’s note: A photon detector senses individual photons, allowing the system to read quantum information carried by light with high precision.
Our solution to deterministic two-qubit gates involves encoding more than one qubit into a single photon. Since these qubits exist within the same quantum system, they can interact deterministically, overcoming one of photonic computing’s key limitations.
The next milestones: miniaturization and scaling. Right now, we’re operating a four-qubit system in the lab. Our goal is to scale the number of qubits while continuing to shrink the system toward deployment-ready form factors.
You’re Using Single-Photon Qudits Encoded in Orbital Angular Momentum Instead of “Conventional” Qubits. What’s the Advantage?
Editor’s note: A qubit can exist in a superposition of two quantum states simultaneously, and it collapses to either of them when measured. A qudit can be in a superposition of multiple quantum states, and correspondingly collapse to more than two possible outcomes—for example, four or eight—allowing more information per unit.
The key advantage of our approach is that we can pack more than one qubit into a single photon. Currently, we can encode two qubits per photon, and we expect to reach three or even more as the technology advances. With this qudit-based technology, we achieve a simplification of the optical circuit and improved scalability. Moreover, it enables longer coherence times and facilitates the implementation of more efficient error correction schemes.
As previously mentioned, this is important because it helps us solve one of the most challenging problems in photonic quantum computing: building deterministic two-qubit gates. Normally, photons don’t interact with each other, which makes this type of gate difficult to implement. But if multiple qubits live inside the same photon, they can interact as part of the same quantum system. No extra interaction mechanism is required.
Room Temperature Is a Major Win for Photonic QPUs, but Error Correction Remains Non-trivial. What’s Your Approach to This Challenge?
This builds on the same principle discussed earlier: By encoding multiple qubits in a single photon qudit using orbital angular momentum, we gain both interaction and error-detection advantages.
In our system, the photons themselves are the qudits. They are flying qudits, constantly in motion, unlike matter-based qubits such as electrons, atoms, or ions. That changes how we approach reliability. Instead of using traditional error correction, which requires additional qubits, we employ a repeat-until-success strategy.
Because photons are fast, we can simply repeat the computation if an error is detected. This shifts the problem away from needing more qubits for correction and toward maximizing the repetition rate of our photon sources. That’s why we focus so much on developing ultra-fast, room-temperature single-photon sources. With rapid repetition, all our qubits stay dedicated to computation.
But this only works if you can tell whether the computation succeeded or not. Our method leverages the encoding of orbital angular momentum. Because orbital angular momentum-based qubits are a kind of topological qubit, relying on the spatial structure or “shape” of the photon, we can use symmetry as an indicator. If the result breaks an expected symmetry, we know it was affected by noise and needs to be repeated.
Editor’s note: A topological qubit stores information in the geometric structure of the system, making it more resistant to errors.
This way, we replace conventional error correction with fast error detection and repetition. It keeps the architecture lean: no redundant qubits, no cryogenic hardware, just fast, compact, room-temperature components.
Together with the deterministic two-qubit gates made possible by orbital angular momentum encoding, this error-detection-through-symmetry approach enables us to maintain simple, fast, and fully operational systems at room temperature. This is a key requirement for edge use cases.
What Makes Your Tech So Well-Suited for Space as Your First Use Case?
We’re especially interested in quantum satellites. This kind of hardware can significantly improve onboard image processing, sensor performance, and even secure communication. Quantum technology will be a significant upgrade for satellite capabilities, enabling improved resolution, faster data processing, and new methods for securing information.
A big part of what makes our platform viable for space is that it operates at room temperature. And by “room temperature,” we don’t mean exactly 25°C; we mean it doesn’t require cryogenic cooling. In space, thermal management is easier in some respects and more challenging in others. Without an atmosphere, there’s no conduction or convection—only radiation. That favors architectures like ours, which can operate across a wide range of temperatures. However, it poses a challenge for systems that require a constant temperature, especially near absolute zero.
Compared to quantum systems that require temperatures close to absolute zero, ours is significantly more practical for space applications. Cooling to near-zero Kelvin requires massive and heavy equipment, not something you want to launch into orbit. However, with our setup, deploying a quantum photonic processor in space is much more similar to deploying standard electronics. In fact, from a practical standpoint, it’s no more difficult than installing classical computing systems on a satellite today.
Photons are also inherently robust to space radiation. They’re not easily disturbed, unlike matter-based qubits. Most of our system is optical, which further reduces the impact of radiation.
In short, our room-temperature, photonic platform offers the performance benefits of quantum computing while remaining lightweight, robust, and compatible with existing space electronics infrastructure.
What Advice Would You Give Fellow Deep Tech Founders?
I’m not really into giving advice, but I can share two things that have been most important for us:
1) Believe in what you’re doing, and be ready for the long game. Sometimes it takes time, and it doesn’t always work on the first try. You need a dream to build something that doesn’t exist yet. It’s about taking on big challenges.
Currently, it is an ideal time for deep tech in Europe. Sure, the geopolitical situation looks messy from one angle, but from another, it creates a unique opportunity, maybe even a kind of European Renaissance.
Whatever you’re building, you have to expect it won’t work right away. You’ll make mistakes, and that’s normal. The key is to keep going and stay committed to the vision.
2) Don’t do it all yourself and build on existing research. Deep tech is impossible without science. Ultimately, it all begins there. That’s why it’s so important to work closely with research institutions. Many have already done foundational work, like experiments that help reduce error rates. So don’t try to reinvent everything. Focus on the small part that’s still unsolved and build from there.
There’s a huge amount of valuable research out there. It may not be applied to your field yet, but if you take the time to really dig through what’s been done, you can find big advantages. We’ve spent a considerable amount of time reviewing prior research, understanding which problems were already solved and which weren’t, so we could focus on just a few key areas.
Deep tech requires an incredible amount of knowledge, more than any single team can hold in-house. And you don’t need to. Collaborate with universities and research centers. That’s what we do, and it keeps our burn rate low while allowing us to move quickly.
Ultimately, deep tech isn’t just about invention but also about innovation. It’s about turning scientific breakthroughs into real-world innovation by bridging research and entrepreneurship.