Open quantum systems

The term open quantum system is used to describe any quantum mechanical system in contact with an uncontrollable and non-negligible environment, and the study of such systems requires a set of tools beyond that of standard quantum mechanics. In reality, almost everything interacts with its surroundings on a microscopic level. Hence, there are no truly isolated systems.

Modern quantum technologies, which rely on quantum effects beyond those described by equilibrium chemistry and condensed matter theory, are increasingly reaching the point where they cannot avoid significant interactions with their environments. In order to control these interactions, and even potentially harness them, it is important that we have a firm theoretical understanding of the way in which they can affect the behaviour of an open system.

We are interested in how different kinds of environments affect the quantum behaviour of systems ranging from artificial, nanoscale devices to complex, biological molecules. In particular, we are working on characterizing how the transfer of energy within these kinds of systems is assisted by their surroundings. This ties in to our interests in thermodynamics, and some of the predictions of our models are in reach of cutting-edge experiments which we hope to perform.

Coherent Energy transport

New Journal of Physics 15, 075018 (2013) and arXiv:1111.1646

NetworkProcesses whereby energy – in the form of electronic excitations – is transferred across a network are ubiquitous in both condensed matter physics and biochemistry. In regular lattices, purely coherent transport, whilst impossible to realise in most physical settings, is the fastest and most efficient way to transfer excitations between sites. However, systems of interest are often highly disordered – they lack symmetry – and it has been suggested that unavoidable environmental noise, which destroys quantum coherence, could improve the speed and efficiency of the transport process.

By using sophisticated mathematical techniques (see for example the two papers above), we aim to model the effect of the environment more accurately and thus deduce which of its properties influence the energy transport dynamics and in what way. The understanding gained in this way can be used to analyse the importance of quantum coherence in certain biological molecules, such as the well-studied Fenna-Matthews-Olsen and electron transport chains in mitochondria, as well as to inspire the design of useful artificial devices.

Latest paper: Olfaction

arXiv:1403.6483

NoseWhilst olfaction (smelling) is believed to principally rely on the detection of molecules by their shape, via a ‘lock-and-key’ mechanism, a secondary mechanism has been proposed whereby electrons in olfactory receptors are caused to tunnel by the presence of certain vibrational frequencies in their environment. Molecules each have their own vibrational spectrum, therefore the detection of a particular set of frequencies indicates a specific chemical species.

In our most recent paper on open quantum systems (above), we provide a full quantum mechanical analysis of the proposed olfactory model. We show how, in contrast to the results of earlier semiclassical treatments, structure in the environment of the olfactory receptor can affect its ability to distinguish different vibrational frequencies. In the future this research could influence the construction of artificial, nanoscale molecular sensors.

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