Although quantum computers have been the subject of intensive research for several years, thus far, scientists have not managed to create suitably robust systems. Researchers at Paderborn University have now success­fully constructed Europe’s largest sampling-based quantum computer. The “PaQS” (Paderborn Quantum Sampler) was built up as part of the PhoQuant funding initiative by the Federal Ministry of Education and Research (BMBF) by the researchers at Paderborn University with support from Menlo Systems, Fraunhofer IOF Jena and Swabian Instruments. The project is coordinated by Q.ANT, a German company specialising in industrial quantum techno­logies, and will soon launch a second, cloud-­accessible sampling-based quantum computer located at Fraunhofer IOF in Jena. This project, with a funding of around 50 million euros, combines expertise from 13 science and industry partners to put Germany at the international forefront of photonic quantum computing.

“Quantum computers are extremely sensitive to system imper­fections. Scientists across the globe are therefore working on a variety of experi­mental platforms. The largest photonic quantum computers currently exist in China, Singapore, France, and Canada. Every approach to realising quantum computing has its pros and cons: for example, photonic networks can operate at room temperature and be implemented in minia­turized, programmable circuits. However, they have to contend with optical losses. We are tackling this problem by drawing on Germany’s world-leading expertise in integrated photonics, and we have managed to create a Gaussian boson sampler consisting of scalable components. This required the development of many new components and highlights the amount of work that goes into building such a device. We are treading entirely new ground here. ‘This makes the process extremely complex”, explains Christine Silberhorn from the Institute for Photonic Quantum Systems (PhoQS) at Paderborn University, where the project is based.

Paderborn’s scientists have created Europe’s largest Gaussian boson sampling machine with the PaQS. In simple terms, the aim is to measure where photons exit the large photonic network. “Gaussian boson sampling is a photonic quantum computing model that has gained attention as a platform for building quantum devices”, Silberhorn says. Unlike previous implemen­tations, the team built the PaQS with a forward-looking approach to system integration and full programmability. “Specifically, this means that we are using a fully pro­grammable and integrated interferometer with which we can implement any confi­guration we choose. With this approach, light particles are distributed and directed within a network of fibre optic cables – a little like the network of switches in a shunting yard. At the output of the network, the location where the photons emerge is measured. This can for example be relevant for solving protein folding problems or calcu­lating certain molecular states as part of pharma­ceutical research”, Silberhorn notes.

Full programma­bility also means that it even allows for the implemen­tation of appli­cations arising from future investigations – creating unprecedented flexibility and a high degree of future applicability. The system is currently being expanded to enable more complex calcu­lations and serve as the basis for investigating future devices that will further increase system inte­gration. Implementing a system like this requires an in-depth under­standing of all the components involved. Quantum mechanics phenomena, such as squeezing or photon entangle­ment, create incredibly high computing power in quantum computers.

It always starts with generating a specific quantum resource. Silberhorn explains: “For Gaussian boson sampling, this resource is known as “squeezing” or “squeezed light”, the quantum mechanical properties of which can be mani­pulated and thus harnessed. The Integrated Quantum Optics working group at Paderborn University has a long tradition of using optical waveguides to develop highly optimised squeezed states. We have access to the expertise needed to produce a light source that will drive the PaQS machine.”

Photonic quantum computers use light to perform quantum calcu­lations, while alternative quantum computing platforms are based on, for example, super­conducting qubits or trapped ions. The benefits of photonic quantum computers include a clear route towards scala­bility and high clock-rate operation. However, the entire field of quantum computing techno­logy is still in its infancy. Further research is required to verify the benefits and dis­advantages of the various quantum computing platforms that are currently under investi­gation. However, the work being conducted by Paderborn's scientists is bringing inter­national quantum research a step closer to this goal. (Source: Paderborn U.)

Link: Institute for Photonic Quantum Systems (PhoQS), Pader­born Uni­ver­sity, Paderborn, Germany