Research Fellows Directory
Dr Mark Buitelaar
University College London
The elementary unit of quantum information is the quantum bit or qubit. Like the classical bit, the qubit is a two-level system but with the intriguing ability to exist in a superposition of states. This means it can be in the on and off state at the same time which has profound implications if we consider quantum systems of more than one qubit. Instead of each qubit carrying any well-defined information of its own, the information is encoded in their joint properties. In quantum mechanics, the qubits are described as being entangled. The challenge is to find ways to harness quantum phenomena such as superposition and entanglement to construct a quantum computer that is able to perform computational tasks that are unattainable in a classical context.
A very natural quantum two-level system, and the subject of my research, is the electron spin. In my research I am using carbon materials for which spin coherence times - the time during which coupled qubits remain entangled and are allowed to evolve according to the laws of quantum mechanics - are expected to be exceptionally long. More precisely, spin qubits are studied in carbon nanotubes and graphene; nanomaterials that consist of single layers of graphite in a one and two-dimensional form, respectively. During the first year of the Fellowship I have shown how to detect spin states in these materials by converting the spin degree of freedom to a much easier measurable charge state or electrical current. In particular I have developed a technique for which this can be done on very short timescales by sending microwaves towards the devices and by probing the reflected signal. In the next few years I will build on these techniques to experimentally determine the spin coherence times and demonstrate quantum entanglement in spin qubits.