Researchers at the Niels Bohr Institute have, colla­borating with the University of Münster and Ruhr-Universität Bochum, developed new technology capable of processing the enormous amounts of information quantum systems generate. Deter­ministic single photon light sources, creating quantum bits at extreme rates and speed are now coupled to specially designed, integrated photonic circuits, capable of processing quantum information with adequate speed and quality without degrading the susceptible quantum states. This means that the first steps have been taken towards the develop­ment of photonic quantum devices that can, for example, describe and simulate other complex quantum systems – like the vibrational dynamics of biological molecules.

Peter Lodahl and the research group Quantum Photonics at the Niels Bohr Institute, University of Copen­hagen, have worked in this field for nearly twenty years. In short, it is all about the use of single photons, the smallest parts of light, used to code quantum information. This is a rapidly developing field, demons­trating a single-photon encrypted communi­cation link in the autumn of 2022 and a recent record investment in the spin-out business Sparrow Quantum. At the core of it all are the photon sources developed and refined by the group over many years. Presently with unparal­leled control, precision and quality, opening the doors to new research and develop­ment in quantum technology.

Peter Lodahl says that the work done in connection with this result points in the direction of a quantum simulator. A quantum simulator is a special-purpose computer that simulates quantum systems by processing quantum infor­mation that classical computers have a hard time dealing with. “The processing of quantum information demands an exponen­tially increasing capacity on a classical computer when increasing the number of quantum bits. This means that even rather simple quantum mechanical problems cannot be solved on classical computers”, says Stefano Paesani, one of the leading researchers behind the result.

What does processing quantum information mean?  This is where a crucial interdisciplinary element comes in. Within the framework of the Novo Nordisk Foundation Project, “Solid-State Quantum Simulators for Biochemistry (SolidQ)”, photons, inter­acting in a photonic circuit, can be used to describe the charac­teristics of biochemical processes. You can use one system (photons) to learn about the other system (the biomolecule) because the photonic quantum simulator can process the complex quantum infor­mation that describes it. One of the challenges consists in under­standing the connection between the two complex quantum systems.

“We can learn about one system by studying the other – i.e. you can “map” one system to another. The initial insight into a complex system is crucial, however. For example, there is a natural mapping occurring between photons and the vibration dynamics of molecules: When a molecule vibrates its evolution is described by the same quantum mechanical operation that describes photons sent through a circuit.”, says Peter Lodahl. The challenge is to process the photons blasting away at the speed of light and in high numbers. It must happen extremely quickly and without loss. Not too many errors are allowed to happen. 

The groups have, over the last two years, developed photonic circuits capable of processing quantum bits from the photonic source – and have made the two systems fit together. The Novo Nordisk Foundation project SolidQ has been all about optimizing the processing of photons. “The colla­boration with Münster is a great example of the fact that the research community takes the first steps. Sub­sequently, we make a road map for up-scaling the technology. This platform looks very promising indeed and in working with Münster we succeeded in realizing photonic circuits adequately efficient and fast to keep up with our photon sources. “We’re opening the door to appli­cations now”, says Stefano Paesani. (Source: NBI)

Reference: P. I. Sund et al.: High-speed thin-film lithium niobate quantum processor driven by a solid-state quantum emitter, Sci. Adv. 9, adg7268 (2023); DOI: 10.1126/sciadv.adg7268

Link: Center for Hybrid Quantum Networks (Hy-Q), Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark