Graphene based quantum information technologies

Moore's law states that the computer processing power roughly doubles every 18 months, however this will not hold any longer when transistors reach the size of individual atoms. At this microscopic scale, quantum-mechanical phenomena play a central role and are no longer a simple support in improving the building blocks as is the case in most current information technologies (IT). Rather than viewing the quantum-mechanical behaviour as a problem, modern quantum information technology (QIT) uses quantum mechanics for novel schemes of storing, processing and exchanging information according to the fundamental laws of quantum physics. This additional freedom will enable future QIT to perform tasks which are not possible in standard IT. Clearly, this makes a strong case for future economic development as demonstrated for example by the Microsoft investment in creating Station-Q, which is a dedicated research centre in QIT.

One of the major challenges in QIT is the "loss of information" in a relatively short time, a problem known as short quantum coherence time in semiconductor and superconducting quantum bits. Here we propose to overcome these limitations by exploiting the potential of graphene in QIT-devices. This is a deceptively simple material -one carbon atom thick- with high electrical conductivity. The relativistic charge carriers in graphene are expected to have an extraordinarily long coherence time which will allow the manipulation and transfer of information over macroscopic distances in a circuit even at room temperature. This is a property which is not found in any other known material. A prominent feature of these relativistic charge carriers is a novel charge conversion mechanism at the interface with superconductors, which spontaneously delivers spatially separated quantum-entangled pairs of electrons travelling on specularly symmetric trajectories. Pairs of entangled particles, so-called EPR pairs, play a special role and have been used as toy objects for fundamental studies. They form the core of Einstein's "spooky interaction at a distance", but also provide the basis of future applications like secure encoding, teleportation, quantum information technology and quantum computation. A solid state entangler device of electrons/holes has never been demonstrated before and its realization exploiting the unique properties of graphene is at the core of this proposal.

Quantum information technology (QIT) holds the promise of a significant impact on society. However, the short quantum coherence time found in standard semiconductor or superconductor-based quantum bits constitutes a serious limitation. Graphene is an ideal candidate for such technologies, as it is a sheet of carbon just one atom thick, with an expected spectacularly long quantum coherence time. This project is directed specifically at tuning the electronic properties of graphene so as to allow the full potential of this material to be exploited in novel QIT devices. The outputs of the project, the development of graphene-based solid state entangler devices, will be fundamental to the commercial and the economic development of QITs. The ability to embed graphene-based solid state entanglers into future computers would improve national security, as the transmitted information by these novel devices would be protected by the fundamental laws of quantum mechanics. Graphene-QITs have the potential to improve social welfare by replacing the currently used encoding of information with a quantum mechanically protected system which cannot be cracked. These devices would be of great relevance for commercial and military applications, and will also facilitate faster interactions and exchanges between individuals and communities. Furthermore, graphene makes transistors more than 100 times faster than the silicon-based transistors used in today's electronics and therefore it could lead to electronic devices that are smaller, faster, and less power hungry than those made out of standard semiconductors. The use of graphene in these devices opens up an entirely new avenue towards the development of QIT-devices, thus fostering the economic competitiveness of the United Kingdom. Apart from their expense, today`s QIT-devices, based on carbon nanotubes or nanowires can create major recycling problems, and they may also be carcinogenic if they become airborne and are inhaled. The chances that graphene could be inhaled are very low since this material is a two-dimensional sheet which can be fabricated in large areas (100cmx100cm). Thus, by incorporating graphene in devices, the components of the future will not have negative effects on our health, will be much easier to recycle, and thereby will be environmentally more attractive. Even though only 5 years have passed since graphene has been experimentally accessed, the demonstration of a Josephson supercurrent in graphene/superconductor hybrid structures [H. B. Heersche et al., Nature 446, 56-59 (2007)] clearly shows that the next few years can be regarded as realistic timescale for many of the benefits of the above described devices to be realised. The interdisciplinary nature of the proposed project provides excellent educational and outreach opportunities for the staff and students working on the project. For example, the undergraduate and graduate students involved in the project will be exposed to the state-of-the-art tools of modern semiconductor and superconductor research. The skills learned by the students in this project are highly marketable and will serve as a valuable asset for employment in industrial, governmental or academic institutions. Our dissemination plan: hosting workshops, conferences, general public demonstrations and presentations, attending conferences and publication in peer-reviewed high-impact journals, will ensure that our work will enhance the knowledge of public as well as the public engagement with research.