Superfluid 3He Far from Equilibrium

Lead Research Organisation: Lancaster University
Department Name: Physics

Abstract

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.

Planned Impact

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.

Publications

10 25 50
 
Title The World's Coolest LEGO Set! An educational film made by Joshua Chawner. 
Description A world leading team of ultra-low temperature physicists at Lancaster University decided to place a LEGO figure and four LEGO blocks inside their record-breaking dilution refrigerator. This machine - specially made at the University - is the most effective refrigerator in the world, capable of reaching 1.6 millidegrees above absolute zero (minus 273.15 Centigrade), which is about 200,000 times colder than room temperature and 2,000 times colder than deep space. The film has subtitles in 8 languages. 
Type Of Art Film/Video/Animation 
Year Produced 2019 
Impact The excerpts of the film were shown by CNN with a reach of 380 million households and featured by several hundred other news outlets around the world. The film was viewed more than 230 thousand times on traceable outlets (>100,000 views on YouTube alone). The film educates the public about the field of low-temperature physics and the absolute scale of temperatures. 
URL https://www.youtube.com/watch?v=zaIFZsBOeZc
 
Description The ground state of a fermionic superfluid condensate is well protected against perturbations in the presence of an isotropic gap. Regions of gap suppression, surfaces and vortex cores which host Andreev-bound states, seemingly lift that strict protection. We have shown that the role of bound states is more subtle: when a macroscopic object moves in superfluid 3He at velocities exceeding the Landau critical velocity, little to no bulk pair breaking takes place, while the damping observed originates from the bound states covering the moving object. We identified two separate timescales that govern the bound state dynamics, one of them much longer than theoretically anticipated, and showed that the bound states do not interact with bulk excitations.
Exploitation Route For instance, speculations on neutron star superfluidity may benefit from the knowledge that the Landau velocity can be neglected in certain scenarios.
Sectors Other

 
Description We have made a YouTube film about our research. The film itself was viewed more than 100k times over 2 months https://www.youtube.com/watch?v=zaIFZsBOeZc Moreover, excerpts from the film were shown on CNN, reaching hundreds of millions of households worldwide. The research, on which the film is based, has been highlighted by the world press in 31 languages and 60 countries.
First Year Of Impact 2019
Impact Types Cultural,Societal

 
Description Fellowship for Samuli Autti
Amount € 47,000 (EUR)
Organisation Jenny and Antti Wihuri Foundation 
Sector Charity/Non Profit
Country Finland
Start 01/2018 
End 12/2018
 
Description Fellowship for Samuli Autti
Amount € 47,000 (EUR)
Organisation Jenny and Antti Wihuri Foundation 
Sector Charity/Non Profit
Country Finland
Start 01/2019 
End 12/2019
 
Title Helium isotope separation facility 
Description Helium isotope separation facility separates 3He and 4He atoms using chromatography at 4.2 K. We have improved the previous design (https://link.springer.com/article/10.1007%2Fs10909-005-2318-8) and obtained a significant increase in the performance of the apparatus. 
Type Of Material Improvements to research infrastructure 
Year Produced 2018 
Provided To Others? Yes  
Impact We were able to recover 100 litres of pure 3He (>99.99%) from contaminated (1% 4He) 3He. The market cost of this amount of 3He is ~£200,000. 
 
Description Kapitza Institute 
Organisation Russian Academy of Sciences
Department P.L. Kapitza Institute for Physical Problems
Country Russian Federation 
Sector Public 
PI Contribution 2018. We ran an experiment together with a visiting PhD student (Arkady Soldatov), having significantly extended his area of expertise over the 2 months of visit time. 2019. I have visited Kapitza Institute in May 2018 to discuss the progress of our experiment and their experiments.
Collaborator Contribution 2018. Our partners have provided valuable information based on their experience and shared samples of porous material nafen which we will use in our future experiments. 2019. We have successfully built and tested our experimental setup with a sample of nafen provided by Kapitza Institute. Their advice on handling the samples was invaluable.
Impact 2018. A paper is being written and a new type of helium isotope separation facility is being developed. 2019 We are now writing 2 papers on previous experiments, the isotope separation facility has proven to perform extremely well. 2020. One paper is submitted and is available on the arXiv https://arxiv.org/abs/2002.10865
Start Year 2017
 
Description Universidad Rey Juan Carlos 
Organisation King Juan Carlos University
Country Spain 
Sector Academic/University 
PI Contribution We hosted Dr Manuel Arrayas for 10 days and discussed current and further experiments in this project.
Collaborator Contribution Dr Arrayas and his colleague Dr José L. Trueba agreed to start modelling a levitating actuator based upon a system of coils and superconductor.
Impact Dr Arrayas and his colleague Dr José L. Trueba agreed to start modelling a levitating actuator based upon a system of coils and superconductor.
Start Year 2020
 
Description Demonstration of properties of materials at low temperature to members of public 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Schools
Results and Impact We demonstrate properties of materials at low temperatures to prospective Lancaster physics students and their parents. We also give tours of our laboratories. Approximately 400 prospective students and as many parents/accompanying persons have watched the demonstrations and took part in the tours. I have also gave a lecture on low temperature physics as a part of a masterclass to ~10 school pupils in May 2018 and to the 25 school students in the "East Lancashire Scholars Programme". The demonstrations always get positive reviews in the feedback forms.
Year(s) Of Engagement Activity 2018,2019
 
Description Low temperature physics demonstrations 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact About 20 parents/accompanying persons of prospective students are shown around the low temperature laboratory. We also stage a demonstration of low-temperature physics experiments. The participants ask questions about the experiments and the research-centred teaching. ~10-15 visits takes place over the year.
Year(s) Of Engagement Activity 2017,2018