Molecular quantum devices

Whenever a fundamental new principle of science is discovered, the chances are that sooner or later a way will be found to use it for a new technology. The quantum mechanical principles of superposition and entanglement, identified back in the 1930s, are now understood to offer spectacular potential for technological applications. Superposition describes how an object can be in two states at once, as it were 'here' and 'there' at the same time. Two or more objects in superposition states can be entangled, so that measurements on each of them are correlated in a way that goes beyond anything we would expect from everyday intuition. Exploiting these effects in practical devices would provide new capabilities for fields such as molecular light harvesting and for molecular quantum technologies such as sensors, simulators, and quantum computers.

Successful laboratory experiments have shown that molecules of various kinds can exhibit these crucial quantum properties. Molecules are composed of electrons and atomic cores or 'nuclei'. Both electrons and nuclei can have a property called spin associated with them that makes them behave like tiny bar magnets. We have confirmed that electron and nuclear spins can be put into superpositions or entangled, and they can last for a long time in that condition. Most of the experiments so far have been in small test tubes. The crucial step now is to implement the same effects in nanometre scale electrical devices, such as single electron transistors consisting of single sheets of carbon rolled up as nanotubes or flat as sheets of graphene. By making hybrid technologies that combine molecules with nanoelectronics, we will lay the foundation for scaling up to more complex systems.

At this very small size, different atoms or molecules in different places affect the behaviour of the device. A breakthrough in the past few years enables us to see the positions of individual atoms in the materials which we want to use in our devices. The technique is aberration-corrected electron microscopy, and provided the electrons are not too energetic it is possible to look at the structures which we have made without damaging them. In this way we shall be able to relate the device performance to the atomic resolution microscopy of the component materials.

To take this quantum nanotechnology from engineering to application is extremely challenging, and lies at the limit of what is realistically feasible. It needs a team with a remarkable combination of expertise, who know how to collaborate across scientific fields. We must:
1. design the devices which we shall build, based on a deep understanding of how to control their quantum states;
2. produce the materials which we need, such as molecules with suitable spin states with carbon nanotubes and graphene for electrical substrates;
3. make nanoscale devices and examine them in a microscope to see where the individual atoms and molecules are;
4. perform the experiments to develop the quantum control and measurement for the effects which we aim to exploit;
5. undertake theoretical modelling to understand the electron behaviour and to design new materials systems for improved performance.

We are fortunate in having the right people and facilities to do this. The platform grant will sustain a team which brings together all the relevant skills. Together we shall make progress towards the emerging quantum technologies that will implement the deep resources of quantum mechanics in working solid state devices.

Our underlying motivation in the research to be supported by this Platform Grant is that it should contribute to practical technologies which exploit the quantum resources of superposition and entanglement. If and when such technologies become available there will be simultaneous societal benefits, to users, and commercial benefits, to manufacturers.

The EPSRC Physics Grand Challenges include 'Quantum Physics for New Quantum Technologies' as one of four themes to be pursued, recognizing that they should not be addressed exclusively by physics. The societal and economic impacts of quantum technologies are well summarized in the full report, "Progress in this Grand Challenge could have huge economic benefit through leading to the development of new high value, high tech industries. Companies may manufacture devices or use quantum technology to simulate complex systems in areas such as metrology, sensing, cryptography, drug discovery, or energy. The societal impact also has the potential to be large as information and information technology is such a pervasive part of modern life. Quantum technology may help us solve major global challenges and will most certainly change the technology people use everyday."

We foresee three classes of technology from our research:

1. New technologies which use the deeper quantum phenomena of superposition and entanglement. The first of these may be sensors for small changes in magnetic field, with entanglement enhanced sensitivity and nanoscale size. A second application may lie in using synthetic molecular structures as simulators for studying other quantum processes that lie beyond modeling techniques such as mean field theories. Ultimately there is the exciting prospect of quantum computing, which has driven so much of the development of quantum information processing, and to which our research may contribute some building blocks.

2. Existing technologies which will benefit from the enhanced quantum properties which we shall develop such as long coherence times. Electron spin resonance is an established technique for determining distances in biology, and the availability of molecules with longer coherence times will increase accuracy and make it possible to measure larger separations. Suitable biocompatible molecules may also contribute to the application of ESR imaging for certain niche problems in medicine.

3. Technological spin-offs which do not use coherence or entanglement, but which can benefit from the materials and techniques which we develop in pursuit of the quantum goals. Fullerene molecules serve as an excellent acceptor in nanocomposite photovoltaic structures, and what we learn through functionalizing fullerenes may offer new routes to tailoring their electrical and chemical properties. Anything that we learn about carbon materials and their properties in devices has the potential to contribute to the current pursuit of carbon-based electronics.

We also find that our work can be explained in such as way as to excite the imagination of some of the best and brightest school students, and thus motivate them to choose to study mathematical and physical science subjects at A level and beyond, thus helping to sustain a future supply of qualified people for a wide range of professions and industrial careers.