Freezer Electronics For The Supercomputer – Fraunhofer Technology Makes Quantum Computers Suitable For Industrial Use

Quantum computers are highly energy-efficient supercomputers. In order for these to be able to exploit their full potential in future applications, such as artificial intelligence or machine learning, research on the underlying readout electronics is in full swing. Researchers at Fraunhofer IZM are working on superconducting connections that are just 10 micrometers thick and are thus taking a big step closer to the implementation of commercially usable quantum computers.

With their high computing power, quantum computers promise to become the driving force behind modern technologies in all industrial sectors. Unlike conventional digital computers, they do not calculate with bits, but with qubits: Due to their special properties - superposition and entanglement - these particles can assume far more than just the binary states 1 or 0. This logic gives the quantum computer a radical lead in terms of speed, performance and possible complexity of the computing operations. The following applies: the more qubits the supercomputer has available, the faster and more valuable the calculations will be.

The potential uses of a quantum computer are extremely diverse: Wherever complex calculations of massive data sets, simulations or probabilities have to be carried out, they could solve problems in a matter of seconds. An optimized logistics and transport system through highly accurate forecasts, efficient development of medical agents by means of lifelike replicas of molecules or meticulous encryption for banking are just a few examples.

But the quantum leap into the new technological age is by no means easy: so far, quantum computers of the first two generations have made it possible to gain fundamental insights into how the device works. Functional pioneers, for example at the Jülich Research Center, currently have an impressive 5,000 qubits in operation, i.e. 2,5000potential states for each individual quantum particle. However, these initial achievements also pose hurdles: the complex network of overlapping qubits is sensitive, which means that errors can sometimes creep into the calculations. Therefore, an error correction has to perfect the solutions, which in turn requires many times the qubits that were necessary for the actual calculation. For example, researchers are aiming for a size of at least 100,000 up to 1 million units for a single device.

In order to achieve such a high qubit density in a system, new integrated circuits and lines must be manufactured with extreme miniaturization. At the same time, they have to be able to withstand temperatures down to -273°C; because it is only in such frosty environments that the lattice vibrations in the solids slow down enough that the qubits remain entangled longer and can therefore be manipulated or read more easily. Loss-free superconductors are used at low temperatures to prevent self-heating from electrical currents. The team around Dr.-Ing. Hermann Oppermann at the Fraunhofer IZM in Berlin.

The researchers developed a new indium-based technology for efficient connection technology at extremely low temperatures using solder contacts, the so-called bumps. The material is superconductive below 3.4 Kelvin and proves to be robust even close to absolute zero. To create electronic structures from indium, it is galvanically deposited using a special electrolyte. For this purpose, the indium had to be transferred from the nickel base that is usual for these structure widths to an alternative base. Replacing this base was necessary because nickel's properties produce large magnetic fields, which would lead to disruption of the qubits. With the new metallic transition, a compatible starting layer is created for the subsequent indium deposition.

The construction of extremely low-loss and superconducting compounds made of niobium and niobium nitride is also remarkable: Using a newly developed method, the niobium materials were applied over a large area and etched with an ion beam. This results in compact cryo-suitable connections that allow high current densities due to their outstanding alloy. After the construction of the indium bumps and the superconducting circuit carrier, the elements were successfully tested in a cryogenic test stand at temperatures down to below 3 Kelvin.

As part of the InnoPush project "HALQ - Semiconductor-based Quantum Computing", a comprehensive platform was set up together with the project partners, which makes microelectronic technologies accessible for use in highly scalable quantum computers. Fraunhofer IPMS, Fraunhofer ITWM, Fraunhofer EMFT, Fraunhofer FHR, Fraunhofer IIS, Fraunhofer IISB, Fraunhofer ILT, Fraunhofer ISIT, Fraunhofer IOF, Fraunhofer ENAS and Fraunhofer IAF were involved in the project.