Quantum materials research in Luxembourg is set to develop quantum chips, which may revolutionise the quantum internet and quantum computers.
Florian Kaiser, Head of the Quantum Materials research group in Luxembourg, has investigated a dedicated research strategy towards scalable quantum chips based on standard semiconductor technology. This ambitious programme targets the development of a ‘Quantum System-on-Chip’, which could boost performance while offering the possibility for cost-effective production at semiconductor foundries.
The promises of quantum technologies
By harnessing and controlling the intricate properties of quantum mechanics, it becomes possible to unleash new digital technologies with a potential stretching far beyond today’s standards.
Quantum computers can solve complex mathematical problems that are intractable by classical machines. Quantum simulators can help us discover new smart and efficient materials to enable a sustainable society. Quantum sensors can achieve unparalleled sensitivity for investigations on the smallest scale (nano-MRI) to the largest scale (gravitational wave detection). And quantum communication can enable a perfectly secure internet, including services in the quantum cloud.
The quantum technology challenge
On a fundamental basis, all these quantum technology pillars have already demonstrated their potential and capabilities. New breakthroughs are reported daily on the academic and startup levels.
Two of the biggest hurdles towards transitioning quantum technologies to the market are:
- Scaling up the number of qubits, especially combining qubits that exceed in quantum processing tasks with excellent quantum memories.
- Reducing the cost of quantum systems by using non-exotic materials and benefiting from established classical production lines.
A blueprint for advancing quantum technology beyond its current state
The issues with current-state quantum technology may sound familiar. Classical computers of the first generation from the late 1930s were based on hundreds to thousands of vacuum tubes, were unreliable and required permanent maintenance, and consumed hundreds of kilowatts of electrical power. The consumer market potential was obviously very slim. In the late 1960s, this changed completely: with the rise of integrated semiconductor micro-chips, new standards were set in cost-effectiveness, number of transistors within a processor, energy consumption, and reliability, thus paving the way for the digital technology of the last decades. The latest trend across all major producers (AMD, Apple, Intel, Qualcomm, Samsung) is to integrate processor and memory modules on the same monolithic System-on-Chip, which minimises the effects of noise and signal loss.
A vision for the future of quantum technologies
According to Dr Florian Kaiser, group leader of the Quantum Materials team at the Luxembourg Institute of Science and Technologies (LIST), recent advances in quantum technology have proven that it is now feasible to develop a scalable platform based on monolithic quantum System-on-Chips.
At the core of this technology are qubits based on optically-active spins in a semiconductor crystal – so-called ‘colour centres’. Colour centres are based on atomically small defects or impurities within their otherwise perfect host crystal, which results in systems with single-atom-like quantum properties. Photons emitted by colour centres can serve as a photonic communication bus, e.g. to transfer quantum information between multiple colour centres, or to route information within a quantum internet. The electron spin of colour centres can serve as an excellent bus for quantum processing and memories: via precise control of the electron spin, it becomes possible to manipulate dozens of highly coherent nuclear spin qubits in the vicinity of a colour centre, and these nuclear spins belong to today’s best quantum processing and memory systems.
In the last two decades, spectacular experiments were made with colour centres in diamond, however, scalability has been challenged by the limited availability of diamond, and the absence of large-scale diamond fabrication facilities. Thus, recent work has focused on replacing diamond by more industry-compatible materials.
Silicon carbide: A promising semiconductor platform for quantum technology
About ten years ago, researchers started to investigate colour centres in silicon carbide, which is the industry’s leading high-power semiconductor. Several studies showed that small-scale quantum processors and quantum memories based on silicon carbide colour centres can directly compete with their diamond counterparts. Further, the first attempts towards micro-integration into photonic quantum chips were promising.
The next natural step for research in the years to come is to maximise the reproducibility of both high-performance quantum colour centres and the design of the integrated photonic quantum chips.
“To improve the reproducibility of colour centres, we must optimise every single step along the fabrication line,” said Dr Kaiser. “In a nutshell, this requires us to minimise undesired crystal damage when creating colour centres into the material, or when etching the required photonic nanostructures in the cleanroom.”
To accelerate this research, the team has recently set up a high-throughput quantum colour centre characterisation platform, which maximises the parameter space that they can study within a reasonable time horizon.
The vision for highly reproducible photonic quantum chips should leverage professional nanofabrication at established semiconductor foundries, which will require a tighter interaction between academic and industrial partners, potentially mediated by real-time operating systems (RTOs).
The team of Dr Kaiser is set to tackle both these challenges, including several significant project fundings from the Luxembourg government (estimated €4.5m), and the European Research Council (estimated €3m).
Dr Kaiser added: “What makes silicon carbide unique amongst other promising quantum technology platforms is that it is an established industrial semiconductor. This has allowed us to use standard electronic devices through which charge noise around colour centres can be suppressed, which has turned out to be the key towards maximising coherence times. Additionally, many silicon carbide foundries exist already today, meaning that large-scale, cost-effective fabrication of quantum chips can be implemented as soon as the tipping point is reached.”
Practical applications in the upcoming years
A natural development of implementing quantum technology based on colour centres in silicon carbide will be the quantum internet. The excellent quantum memories associated with silicon carbide colour centres can be used to set up quantum repeater nodes, which are the only known approach towards a long-distance fully secure quantum communication network.
Please note, this article will also appear in the 22nd edition of our quarterly publication.
