The Silicon Vacancy in Silicon Carbide: a promising qubit in a technological material

How small can one shrink an electronic memory? The ultimate limit in storage can be reached by encoding information in a single particle, for example a single electron or a single atomic nucleus. There are several ways to encode a bit of information into an electron. For example, one could label "1" the presence of the particle, and "0" its absence. Or, one could use an intrinsic property of quantum objects called "spin", which makes the particle behave as a tiny magnet. In this case, "1" would be encoded, for example, as spin pointing to the North Pole and "0" as spin pointing to the South Pole of the single particle magnet.
Using single particles to encode information can give advantages that go beyond miniaturization. Electron spins obeys the laws of quantum mechanics. In quantum physics, the spin of an electron is not required to point either "North" or "South", like a magnetic needle, but it can be "North" AND "South" at the same time. Or, while a bit in a computing device is either in the "0" or "1" state, a quantum bit can be both at the same time. This is much more than a bizarre curiosity: in the last few decades, we have learnt that the laws of quantum mechanics can be exploited to perform tasks impossible for classical physics, such as secure communication, faster computing or precise sensing.

The goal of this project is to measure and control single spins in silicon carbide, a material consisting of a lattice of silicon and carbon atoms. A silicon atom missing in this lattice creates a defect which hosts a single electronic spin that can be measured and manipulated by laser and radiofrequency pulses. Basically, this system behaves as a single atom trapped in silicon carbide. Why silicon carbide? In addition to hosting spins with great properties, silicon carbide is a technological material routinely used by the semiconductor industry to manufacture transistors and other microelectronic components. The availability of established recipes for growth, doping and nano-fabrication can lead to practical quantum devices.
Control of single spins in silicon carbide is still in its infancy. We learned only recently how electrons are arranged in these defects. Only in the past year, control of a single spin in silicon carbide was demonstrated. There is plenty of information missing, and we can improve the efficiency of our control tools by learning more about the structure of these defects.
This project will characterize the electronic structure of these defects by studying how they absorb and emit light. By operating at very low temperatures, the noise related to atomic vibrations which would mask the optical signal will be frozen out. The knowledge about light emission and absorption, and its relation to the spin trapped in the defect, will enable us to realizing exciting schemes that use single spins to encode and decode information for future technologies.

Due to a combination of outstanding spin properties, large-scale commercial availability of high-purity wafers and established fabrication techniques, silicon carbide offers a great opportunity for real-world quantum devices. Using this platform, the vision of an integrated chip, comprising optically-active spins in nanophotonic structures and electronic circuitry for charge control and spin manipulation can become a reality. While this project deals with the basic physics of spin qubits in SiC, this is the first step required to develop this vision and to generate impact.

Economic and Commercial Impact
In the short term, Norstel AB, a leading supplier of high-purity SiC wafers and industrial partner of this project, will gain the valuable benefits. The material they provide will be characterized using state-of-the-art single defect spectroscopy techniques, applied for the first time to SiC only in 2015.
In the medium term, this research will generate knowledge on SiC defects, which will have impact on the semiconductor community. SiC plays a critical role in several industrial sectors, including aerospace, electronics, industrial furnaces and wear-resistant mechanical parts. In electronics, SiC is the material of choice for sensors operating in harsh environments (aerospace, oil and gas, and geothermal exploration). In the UK, several companies are active on SiC power electronics, for example Dynex Semiconductors, Rolls Royce, BAE Systems. Moreover, Raytheon recently opened a SiC foundry in Glenrothes (Scotland). My research output can positively affect international industries active both in material growth and in device processing, among others Cree Inc, United Silicon Carbide Inc, Infineon, ROHM, Norstel, Dow Corning, NovaSiC. I will make sure that knowledge is transferred to the engineering community and to the semiconductor industry sector through the strategies outlined in "Pathways to Impact".

Societal Impact
In the longer term (>10 years), quantum technology with a technologically mature material such as SiC can pave the way to real-world quantum devices. In particular, I envision SiC quantum devices embedding integrated microcavities for efficient spin-photon interfacing as nodes for quantum communication networks. Highly coherent spins will function as a long-term quantum memory and near-infrared photons will distribute quantum information among the nodes.
A second application is in the field of sensing. Single spins are the smallest possible magnetic field sensors, providing high measurement sensitivity at the ultimate limits of spatial resolution. Nanoscale magnetic field sensors could benefit the information technology sector, allowing mapping of currents in microelectronic circuits or magnetic storage devices and enabling non-invasive high-resolution probing of failures. Or they could have a great impact on biomedical and pharmaceutical research and development, by offering a tool for nanoscale magnetic resonance imaging of molecules.
Finally PhD students and post-docs working on the project will acquire skills in areas like laser physics, optics, electron spin resonance, high-speed electronics, cryogenics, programming and data analysis, which can be employed in academia and high-tech industries.

The public and policy-makers
Through the activities outlined in "Pathways to Impact", the public will gain awareness of the latest results in quantum physics, the promises of quantum technology and the impact of my own work. This will set them in a position to make conscious informed choices regarding why these activities are worth the taxpayer support.