Hybrid Rotaxanes as Scaleable Two Qubit-Gates for Quantum Information Processing

Modern computers work by storing and processing information in "bits". Within a bit the information is stored either as a 0 or 1. The huge computing power we now possess has some limitations. For example, computers are very fast at multiplying numbers together - 2 x 3 x 3 x 5 x 7 x 11 x 17 x 23 x 41 = 111094830. The reverse operation is slow on a modern computer, i.e. if you are given 111094830 a computer would find it difficult working out the factors multiplied together. This operation - factoring large numbers into primes - looks like a mathematical oddity, but is the basis of how information is encrypted in the modern world.
An alternative computer - based on quantum information processing (QIP) - would operate in a very different way, using the strange principles of quantum mechanics. The information would be stored in a "qubit". In contrast to a bit, a qubit stores information as 0, 1 and the superposition of all numbers between 0 and 1. As an analogy: if a bit is like a light switch - either on or off - a qubit is like a dimmer switch, but one which is set at all positions simultaneously. In most cases a quantum computer would have few advantages over a normal computer, however in some cases - and factorising large numbers into primes is one example - then a quantum computer can perform a calculation quickly that is impossibly slow classically.
Some examples have been reported where simple calculations have been performed, but no quantum computer has been reported that could carry out a complex computation. Our proposal is develop molecules that can act as qubits, link then together to form the fundamental units for a computer - a two-qubit gate - and then develop further chemistry that would allow us to prepare devices with these molecular qubits.

The potential impact of a functioning quantum computer is enormous. As evidence we can cite the Canadian company - D-Wave Systems Inc - which is now marketing a device which is claims is some form of a quantum computer, and it is being priced at $10 M per computer. Despite this price, and strong doubts in some areas that D-Wave Systems' claims are correct, Lockheed Martin has already invested in the company.
If successful, the existing algorithms written for quantum computing would lead to some calculations - e.g. searching unsorted directories, factorising large numbers into primes - becoming much faster than using a conventional computer. This would have an impact across industry and society, e.g. factorising numbers into primes is the basis of the encoding used to safeguard much information in the digital world. Proposals dating back to Feynman suggest that we will only make significant progress in simulating quantum systems if we can use quantum computers. A quantum computing capable of performing complex algorithms would change the world.

The work we are doing lies at the boundary between supramolecular chemistry and molecular magnetism. Performing even simple algorithms using a supramolecular approach would have a significant academic impact, and would immediately impact on peripheral fields. For example, we have interest from Bruker, who manufacture EPR spectrometers, who believe successful implementation of simple codes using their pulsed EPR spectrometers would impact on their sales.

Longer term, if we could show that supramolecular chemistry can contribute to construction of devices for information processing we will hugely influence future research. The huge energy and environmental costs of current means for fabricating microelectronic devices will be difficult to sustain, and technical issues imposed by lithographic techniques also suggest we should be looking seriously at other approaches. Therefore any steps we take towards a functioning devices will impact on the possibility of microelectronics companies looking more seriously at molecular approaches to device construction.

In the Pathways to Impact document we list the routes we will take to maximise impact. We are involved with an instrument manufacturer (Bruker) and an SME (Synthetic Nanomachines Ltd) already. We also have plans for public engagement, including writing articles for popular science magazines, mounting exhibits and science festivals, and hosting "internships" for sixth-year school pupils.