Classical computing uses electronic charge to transfer and manipulate information. However, electrons carry quantum properties that are not harnessed in electronics. Quantum spintronics investigates the use of quantum spin instead of, or in conjunction with, electronic charge. By doing more with less, the aim is to revolutionize the speed, capacity, stability and energy efficiency of computation.
Manipulating spins typically requires magnets and large currents. Anyone who's held a charging electronic device knows currents lead to heating. Cooling then translates to a considerable energy cost. For example, high performance computers (HPC) are cooled with up to 17,000 litres of water per second, and an estimated 3% of Europe's energy consumption goes towards HPC and data centres. Current densities for spin manipulation can be up to ten thousand times greater than what fire safety regulations allow in domestic wiring.
To mitigate the heating effect, we can use superconductors. These are relatively common materials in which electrons can flow without heating when cooled to cryogenic temperatures. There can be great energy benefit in cooling superconductors to achieve high currents, e.g. as used in MRI scanners. Superconductivity is caused by a special relationship between the spins of electron pairs. In the emerging field of superconducting spintronics, that spin is harnessed for computing, while reaping the cooling benefit. However, magnets destroy superconductivity quickly, limiting the range of application. By designing the system to regroup spins into new pairs called "triplets", the superconductivity becomes unaffected by magnetic fields.
This project aims to show how triplets can be generated and controlled in novel systems, advancing cool spintronic computing to new classes of application. By challenging the traditional paradigm of how devices are built and effects are mediated, we will develop the theory to show triplets as a powerful and versatile tool for computation.
In the first year of the project, we have published a proof of principle calculation showing how superconductors and ferromagnets can interact via light, meaning we can study this interaction without their properties destroying each other. We have expanded this investigation by developing the quantum mechanical descriptions of the interaction, and expect to send these results for peer review towards the end of the year. Moreover, we have shown that geometric curvature can be used to generate and control triplets in materials that are robust against impurities. This opens a pathway for new spintronic device design, as well as new targets for fundamental research into geometric effects. We have identified several new, promising directions, which will form the basis of a future funding proposal. We have discussed our findings and our group?s goals with a wide variety of audiences, from undergraduate physics students to the public at large via YouTube, and from high school students in Australia to theatre producers in England.
The rapidly developing field of spintronics, where quantum spins are used as information carriers in place of or in conjunction with electrons in conventional electronics, has the potential to revolutionize the speed, capacity and energy efficiency of computation. Spintronic nanostructures can be incorporated into existing semiconductor systems, and are therefore also strong candidates for scalable quantum computing, which utilizes the quantum state to provide unprecedented computational capacity.
The primary challenge in spintronics is to limit the excessive heating that occurs due to the large current magnitudes typically required to induce magnetization/spin dynamics. Investigations into the superconducting proximity effect, where properties of adjacent materials “leak” across interfacial barriers in multi-layered nanostructures, have indicated that it will be possible to solve this problem by harnessing superconductive dissipationless currents. The correlations carrying conventional superconductivity have zero net spin (singlets). These are not compatible with magnetic spintronic structures due to their rapid decay. However, it is possible to polarize the pairs to carry net spin (triplets), which extends their range significantly, to the extent that they can be used as information carriers in superconducting spintronics.
This project will provide the theoretical foundation for generating and controlling triplet superconducting correlations in three novel systems: non-equilibrium nanowires with curvature, spatially separated hybridization with magnetic excitations in a microwave cavity, and triplet/qutrit entanglement in superconductor-ferromagnet thin-films. This will present new design applications, a pathway for union with quantum optics and long-range signal transfer, and decoherence-robust entanglement. The results will have a significant impact on the future of high-efficiency, low-dissipation spin transport in spintronics and quantum computing.