A modular approach to multi-component molecular assemblies

The idea that technologically advanced devices could be made by chemistry is appealing because chemistry is generally less demanding in use of energy than more conventional nanofabrication approaches. This work falls into this general area. The aim of the work is to design the molecular components that could be assembled, in the long term, into useful devices. The major difficulties are to understand the influence of one component on another in detail, and to this end we will make and study assemblies starting with assemblies where there are two components - a qubit (the quantum equivalent of the bit used in conventional computing) and a switchable molecule; our aim is to understand what happens to the qubit when the switch is on and off, and hence we can chose which switches are suitable for use with qubits. From the assemblies with two components we will move to more complicated assemblies, containing two distinct qubits and two distinct switches.
The materials will be studied using electron paramagnetic resonance (EPR) spectroscopy, which is extremely sensitive to the behaviour of single electron spins. Single electron spins can, at the simplest level, be regarded as magnets and the EPR experiment involves using microwaves to flip the electron from having its local magnetic moment aligned with an external field to aligned opposed to the external field. We can use the results to find out if single electrons are communicating with other electrons, and with sophisticated experiments can make specific electrons adopt specific orientations.

Quantum information processing has immense potential impact, and there is recent evidence that devices based on quantum physics will be used in the medium term. An American company, D-wave, has recently sold a "quantum computer" that performs calculations by quantum annealing (a). The approach uses electron spins within solid-state qubits, and was very controversial when the first claims were made. There is still no agreement it is a "quantum computer" because the approach falls outside the conventional bounds defined by the quantum computing community. The consortium that has bought D-wave's device includes NASA and Google, and has paid $ 15 million for one device.

A USA group has reported a quantum simulator(b), created by trapping three hundred Be+ ions in a 2D- crystalline array in a large magnetic field; this is reaching a level where significant computations can be performed. Groups at IBM are studying small arrays (ca. eight iron atoms) as information storage and possible spintronic devices (c). Colleagues at Grenoble have reported prototype molecular spin valves and transistors (d). This is an immensely exciting time in the area, with a huge range of approaches being explored; all these routes are justified because this is genuinely transformational science and we must continue to explore every possible avenue until success is achieved.

Some of this work involves molecular chemistry (d), other nanofabrication by microscopy (c). The best methods for making specific quantum devices remain to be discovered. Some approaches have a lead, but they tend to be highly energy inefficient. Studying chemistry as an approach is pursued in Europe and Japan. The UK team involved in this proposal are among the world leaders in the field, and their work already has huge academic impact. If the long term goals of the work were met - to construct useful quantum devices from molecular chemistry - it would transform how we perform certain calculations and would allow computation to solve some problems that are impossible to solve using classical computers. The challenges are enormous, but the potential rewards are much greater.

a. Nature 2011, 473, 194; b. Nature 2012, 484, 489 ; c. Science 2012, 335, 2012;
d. Nature 2012, 488, 357.