Key players insights
In the last few decades, digitalisation has disrupted almost every traditional industrial sector. Digitalisation is predominantly based on increased computing power; and the next step in accelerating computing power is quantum technology, one of the most interesting and disruptive scientific fields of the 2020s. While an ordinary computer calculates using bits, or ones and zeros, a quantum computer uses qubits, which can be ones, zeros or superpositions of both, each with their own ‘weighting’ or probability. The large number of possible states and a phenomenon called entanglement allow quantum computers to achieve an astonishing computing power for certain computational tasks – provided that the qubits perform reliably. During the starting decade, quantum technologies are making the breakthrough from research laboratories to more extensive commercial use.

Quantum computing power could enable, for instance, the extraordinarily rapid development of medicines and vaccines, thereby disrupting healthcare worldwide. Modelling complex molecules, such as protein and drug molecules, is traditionally difficult due to their large size and complex interactions. Even today’s supercomputers cannot create precise molecular simulations. But since all molecular structures are determined by the laws of quantum mechanics, it has been proposed that a large quantum computer could model the structure and activity of these molecules more precisely and rapidly. In the future, we could also use large quantum computers to solve huge systemic problems. For instance, they could help to find new ways to produce sustainable energy or develop sustainable materials. Thus, quantum computing may help us meet the challenges of climate change and resource scarcity with unbelievable efficiency.

If Europe gains a foothold in quantum industrial development, we can grow a new branch of the tech industry worth billions, employing thousands of people and serving the needs of the whole world. There are several aspects of quantum technology in which European countries are advanced. Finland, for instance, has profound expertise in developing electronics, superconducting circuits and sensors. This expertise has deepened over decades in quantum and low-temperature physics laboratories, which has already led to successful quantum technology companies.

Finland’s first quantum computer

In Finland, we are taking the first steps already. VTT and Finnish startup IQM are currently co-developing Finland’s first quantum computer as part of a €20.7m public procurement project funded by the Ministry of Economic Affairs and Employment. In the first phase, we are concentrating on expanding the technical capabilities: our aim is a functioning five-qubit quantum computer which will demonstrate our expertise in building quantum computers. The overall goal of the project is to build a much larger, 50-qubit device by around 2024. We can use this computer to develop new quantum algorithms which can be applied to solve demanding problems in the future. Besides developing a quantum computer, it is important to strengthen quantum technological expertise across the board, from building the computer itself to applying algorithms and quantum computing to solve practical problems. This development will also be supported by the Finnish IT Centre for Science’s (CSC) quantum computing simulator and new supercomputer LUMI.

VTT’s quantum technology activities
The heritage

VTT and Finland are well positioned for joining, and even leading the quantum revolution. We have a long tradition of world-class research and education on quantum physics, from theoretical and computational science to experimental and applied physics. On the applied side, VTT has been developing superconducting devices for quantum applications for decades. VTT is jointly running in a 2500m2 cleanroom that includes processes for superconductive, nano and quantum devices.

The biggest success story has been the development of a stable process for Josephson junctions, which are the basis of many quantum devices even today, and in particular, the superconducting transmon qubit. Josephson junctions enabled us to build superconducting quantum interference devices (SQUIDs), a versatile type of quantum device which can be used as an amplifier, a sensor or a non-linear element. SQUID magnetometers are the most sensitive magnetic field sensors, and these are used in magnetoencephalography (MEG) for mapping brain activity by measuring weak magnetic fields that arise due to normal neural activity. VTT has been producing the SQUID magnetometers that go into these diagnostic devices for over a decade.
Furthermore, a long tradition in applied superconductivity, nano and quantum research has enabled us at VTT to develop sensitive THz, IR and X-Ray detectors for security imaging, thermal imaging and diagnostic imaging, respectively.

VTT also has a matured silicon photonics platform developed within the same cleanroom and combining that with superconductive devices allows us to develop integrated single-photon detectors and sensors. This also enables new quantum communication and sensing possibilities.

Scaling up superconducting quantum computers

In the past few years we have seen remarkable progress in the field of quantum computing, both in hardware and in algorithms. In software, especially error correction, algorithms have gained momentum. In hardware, a few different platforms have emerged, especially superconducting qubits – the platform of choice for VTT. However, there are still significant challenges in building quantum processors of sufficient size for addressing real world problems. VTT, with its strong focus on industrially relevant R&D is in a very good position to address many of these challenges. We are not too focused on large-scale production nor on academic proof-of-principle one-offs but have a more pragmatic approach to develop components that allow for scalability.

We are currently in the ‘Noisy Intermediate-Scale Quantum’ (NISQ) era – which means significant applications can be expected already in the short- and medium-term with a limited number of noisy qubits. However, it is generally agreed that universally useful quantum computers will require about one million qubits. To date, most advanced universal quantum computers are based on superconducting transmon qubits and operated at temperatures close to absolute zero, in order to minimise thermal noise. Electrical transmission lines are used to carry the electrical signals driving and reading the transmons inside the cryostat. This approach is perfectly fine when dealing with a few hundred qubits, but starts becoming challenging for thousands of qubits, and not viable anymore when approaching one million qubits, given that electrical cables come with limited bandwidth, high crosstalk, and high thermal conductivity. For these reasons, at VTT we are pioneering the next generation of communication interfaces for cryogenic qubits, using optical fibres and suitable optoelectronic cryogenic converters.

Another challenge that VTT is addressing is 3D integration of quantum systems. 3D integration of classical microsystems is broadly available technology, but for quantum it has just started and VTT is working on it, for example, in multiple European quantum flagship projects. Although current quantum error correction codes work on a 2D lattice of qubits we still need to bring in control and readout lines to each qubit. In purely 2D architectures we need to bring these lines in from the sides, which is clearly not scalable. In practice the limit is around 20 qubits. With 3D integration, we can have a 2D lattice of qubits on one chip (‘qubit chip’) and use one or more control chips for routing the auxiliary lines (control & readout), possibly with ‘interposer’ chips for setting vertical distances. The chips are connected to each other by superconducting flip chip bonding. Superconducting through-silicon-vias (TSVs) are used for electrically connecting opposite sides of the chips. Ultra-low microwave losses are crucial in order not to kill the quantumness and this is a significant technological challenge.
Another specific challenge in the scaling we address is qubit readout in large superconducting quantum processors. We are making wide-band ultra-low noise microwave amplifiers that allow frequency multiplexed readout of many qubits using a single physical output line (coaxial cable). Our approach is based on superconducting travelling-wave parametric amplifiers (TWPAs) based on Josephson junctions. The noise added by Josephson junction-based parametric amplifiers is unparalleled: in fact it is nearly quantum limited. Together with the wide bandwidth of TWPAs, they are an unmatched solution for superconducting qubit readout and near-term quantum computer scale-up. In the long-term, VTT sees tighter integration of digital electronics as an important step in scaling to larger processors. This may include both superconducting and semiconducting ASICs tailored to specific needs and the unique requirements set by cryogenic operation.

Solid state coolers developed at VTT can one day enable reducing the size of the dilution fridges currently used for the cooling down of quantum computers. With the increase of the number of qubits the size of the fridges is expected to grow. We already hear about monster fridges to be used in next generation quantum computers. VTT’s solid-state coolers can supplement the cooling capacity of existing fridges by doing the last stage of the cooling, which will minimise the need for monster fridges and can help repurpose existing fridges for a higher number of qubit machines.

Himadri Majumdar, manager of quantum technology at VTT, discusses the research centre’s role in delivering quantum technology to Finland and Europe.