Superfluid 3He Far from Equilibrium

This fellowship proposal answers the EPSRC's call to tackle outstanding grand challenges in the areas of physics of systems far from equilibrium and physics of emergent phenomena. My vision is to approach these challenges by studying non-equilibrium phenomena in a well-known system with an established theoretical framework - superfluid 3He.
Coherent condensates (or superfluids) are the simplest "complex" systems that we have, in that the condensate is governed by just one global wave function describing the whole macroscopic ensemble. This simplicity makes them ideal playgrounds for studying and testing ideas that cover a vast range of apparently unrelated physical systems from the subnuclear to the cosmological. Of interest here, superfluids are absolutely ideal for studying systems far from equilibrium and also host an abundance of emergent phenomena. Coherent condensates (or at least those to which we have experimental access) are fragile objects only existing at very low temperatures. Almost uniquely that means that we can study them over the whole range of conditions from the virtually zero-entropy zero-temperature quiescent state all the way through to the regime where we have the complete destruction of the coherence. Producing and studying the simplest forms of states far from equilibrium is essential for creating falsifiable theories and reliable numerical models. By understanding the simplest states we can progress to the understanding of more complex phenomena, adjusting the theoretical models with the firm knowledge that they do work in simpler situations.
That said, in this application I propose several experiments which take our model condensate, superfluid 3He, to the limit. The main interest here is that although perceived wisdom suggests that the destruction of coherence is pretty well understood, in reality that is very far from the truth. It is "common knowledge" that when we move a scatterer through a superfluid, then at some critical velocity the superfluidity should catastrophically break down and return the system to the normal state. Recently, we have shown at Lancaster that this does not happen in superfluid 3He up to velocities well in excess of the accepted Landau value. This was quite unexpected. In the proposed experimental programme I will aim to find the reason for the existence of supercritical supercurrents which flow around the scatterer and also find the domain of their stability. To this end I will utilise a combination of nuclear magnetic resonance to probe the condensate's wave function with a device capable of uniform motion through the condensate - a recently pioneered addition to the arsenal of the superfluid research techniques.
Using for the first time the powerful combination of nuclear magnetic resonance with steady superflow in 3He at ultralow temperatures will also enable us to investigate several emergent phenomena. For example, the superfluid 3He system is an ideal medium for the study of quantum critical phase transitions between different superfluid phases which can be accessed by changing the pressure of the superfluid near the absolute zero of temperature.

The proposed research is of fundamental kind, driven by the desire to improve knowledge and understanding of nature under extreme conditions and far from equilibrium. As such, it has a potential to impact many walks of life.
My research will affect the publishing industry, physics students and lecturers. I will try to explain a completely new phenomenon - the supercritical supercurrent - which was thought impossible by many. Every textbook touching on aspects of superfluidity and superconductivity makes reference to the Landau criterion for superfluidity, implying that superfluidity must be destroyed above a certain critical velocity of the flow - the Landau velocity. These texts now need to be updated to take into account the observation of the supercritical superflow resulting from my research.
Majorana fermions, the quasiparticles I will try to identify in superfluid 3He, are also predicted to exist in many other topological condensed matter systems. Theoretical schemes suggest that Majorana particles may find a use in quantum computing. Since they are unaffected by small perturbations, a Majorana-based quantum computer will require a lower level of error correction than a 'conventional' quantum computer where errors occur owing to particle decoherence.
The staff trained on this project will provide a valuable resource. Today over 250 (1000) low temperature research groups (researchers) in Europe make use of sub-Kelvin temperatures. Ten major companies and 15 SMEs have cryoengineering groups. Their total turnover is about 1 000 000 000 euros and 50 000 000 euros, respectively. This activity generates a European need for more than 100 low temperature scientists and cryoengineers per year (estimate from the European MICROKELVIN network, http://www.microkelvin.eu/). Staff working on this project will develop a broad range of skills required in designing, building and day-to-day running of the experiments. They include transferrable skills in vacuum technology, cryogenics, precise measurements, developing novel instrumentation and techniques, data analysis, preparing results for publication in high-impact journals and for presentation in front of various audiences, all very saleable skills in this expanding field.
The experience gained from the intensive programme planned for this Fellowship will contribute to shaping me into an efficient group leader.