Quasiparticle Imaging and Superfluid Flow Experiments at Ultralow Temperatures

Lead Research Organisation: Lancaster University
Department Name: Physics

Abstract

Our group has pioneered novel techniques to cool superfluid 3He to ultra-low temperatures where thermal quasiparticle excitations are highly ballistic, having intrinsic mean-free-paths which approach kilometre length scales. Superfluid 3He displays a wide range of exotic spin, orbital and mass superfluid behaviour, providing an ideal system to study and to gain a better understanding of quantum systems in general. We have developed techniques to generate beams of ballistic quasiparticles and scatter them from various obstacles formed in the superfluid. Superfluid structures such as vortices, textures and phase boundaries have a large cross-section for Andreev reflection (a form of near-perfect retro-reflection of excitations unique to superfluids and superconductors), so are readily probed by excitation beams. We aim to further develop the techniques to build a quasiparticle camera to directly image superfluid structures providing time and spatial resolution to study their dynamics.We will first apply the technique to image the beam of excitations which is emitted by a vibrating wire above some critical velocity. The excitations are created by the wire as it breaks apart the `paired-atom' superfluid condensate. Quantum vortices (line defects in the superfluid with a well-defined circulating flow) are also produced above this critical velocity. The two processes appear to be closely linked, but the mechanism is not understood. The images will allow us to simultaneously observe the pair-breaking beam and vortices, which will provide detailed information about the generation processes.At higher velocity amplitudes, vibrating wires produce quantum turbulence, a complex tangle of vortex lines. Despite its overwhelming importance to a wide range of science and technology, turbulence in general is poorly understood. Quantum turbulence is conceptually much simpler than classical turbulence and is far more amenable to computer simulation. The study of superfluid turbulence may thus eventually provide a better understanding of turbulence in general. There are several interesting unanswered questions to be addressed in quantum turbulence, such as how it develops and decays in the absence of viscous forces at low temperatures. We aim to use the new imaging techniques to directly image quantum turbulence to provide detailed dynamical information for direct comparison with theory.We will also develop a new technique to allow very precise controlled motion of an object in the superfluid to study various flow related properties. In particular, it will allow a comprehensive study of the pair-breaking mechanism over a wide frequency range, including near-uniform (zero frequency) flow. This is interesting since the mechanism is thought to involve the population of bound surface states (including so-called Majorana states which have received a great deal of recent theoretical interest) and there may be analogies with quantum Hawking radiation.The flow device will also allow us to measure extremely low velocities. This will enable us to explore possible supersolid behaviour in solid 4He at low temperatures by measuring the slow motion of a wire through the solid. Supersolidity is a very exotic phenomenon, predicted by some theories, where a quantum solid can exhibit frictionless flow. There is widespread speculation that supersolidity has been observed in 4He at low temperatures, but the observations might also be explained by defects in the solid with superfluid cores. This topic remains highly controversial and has received a great deal of interest. The current device will be very sensitive to both defects and supersolid flow, thus providing key information to resolve this issue.We will also investigate new avenues for research in exotic superfluid phases, spin superfluidity and high frequency/small length scale phenomena. The new techniques developed will be very versatile with a wide range of future applications.

Planned Impact

Superfluids are ideal systems to study a wide range of fundamental physics, with close analogies with superconductivity, particle physics and cosmology. So the academic beneficiaries of this research reach far wider than the immediate field of quantum fluids and solids. We have a good track record for exploiting these analogies, and we expect to continue this in the current proposal. A few recent examples of projects spanning wider fields, which have arose as a direct result of our research are: (1) The European MICROKELVIN collaboration (2009), a 4.2Meuro FP7 project to widen access to ultralow temperatures for nano-science, condensed matter physics, cosmology and instrumentation (our group is one of three core access-providing partners with 12 partners in total including a commercial cryogenic business); (2) The ESF COSLAB Network (2001-2006), a 350keuro multidisciplinary initiative to exploit analogies between cosmology and condensed-matter systems. This network was founded on our pioneering work investigating vortex production in rapid phase transitions and analogies with cosmic string creation in the early Universe. This work led to a 300k(ECU) EC-HCM Network Phase transitions in the early Universe (1995-8), followed by a FF516k ESF Network Topological Defects in Particle Physics, Condensed Matter and Cosmology (1997-2000) and then to COSLAB; (3) ULTIMA (2005), a 300keuro dark matter detector project. Our invention and development of `black-body radiator' devices inspired the 2001 MACHe3 project in Grenoble to explore their potential use in making a full-scale dark-matter detection facility, which then led to ULTIMA. The techniques developed in this proposal will have various impacts. The ability to image structures with quasiparticles will be a major step in further developing low temperature technologies, allowing far more detailed studies of a wide range of quantum phenomena. The development of custom tuning forks with our industrial collaborator, Statek, may also lead to wider impacts. To optimise the tuning forks for low temperature applications, we will need to further minimize intrinsic losses in order to maximize sensitivity at the lowest temperatures. Potentially this could lead to improved designs for more conventional uses of tuning forks (e.g. they are widely used in timing devices such as wrist watches) which would then have wider impacts in manufacturing and commerce. The proposed research will also contribute towards a better understanding of quantum systems (superfluids and superconductors) and of turbulence. This could have a very significant impact in the long term, since quantum systems are likely to play an increasingly central role in future electronics industries, and a better understanding of turbulence would have far reaching impacts in, e.g., transport and energy production industries. We are very successful at disseminating our research to a wide audience. We regularly: publish in high impact journals; give invited talks at major conferences (note we will host the main Quantum Fluids and Solids conference in 2012); give research seminars at other institutions; and visit other leading research groups. Our department has a full-time industrial liaisons officer who will help us to better disseminate our work to industry and to exploit any new opportunities for collaborative work. We also disseminate our research to the wider public by our web pages and various outreach activities. We have good contacts with local schools and we regularly give talks, lab tours and demonstrations for school visits, prospective students and their parents. We will continue to develop all of these activities. Our group is well known internationally for developing new techniques and for performing novel experiments at the lowest temperatures. Our leading role in this field, impacts on the overall profile of UK research and its reputation for pushing the boundaries of what is technically possible.

Publications

10 25 50
 
Description Numerical simulations were conducted on Andreev reflection from realistic 3D quantum tangles and directly compared to measurements of quantum turbulence in superfluid 3He-B. Our results show that Andreev reflection is strongly correlated to the vortex line density and validates visualization of quantum turbulence using Andreev reflection in 3He-B.

Research on quantum turbulence in 3He-B at temperatures down to 150 µK was carried out using measurements of Andreev reflection noise spectra and showed creation and development of turbulent tangle from independent ballistic vortex rings.

Two dimensional quasiparticle camera has been build and was used to measure beam profile of the black body radiator in superfluid 3He-B. The same camera will be used to visualise quantum turbulence creation by a vibrating wire in pure superfluid.

We have demonstrated that the damping of oscillating objects in superfluid 4He is governed by acoustic emission at high frequencies, and that the onset velocity of nucleation in quantum turbulence has a square-root frequency dependence for frequencies up to 100 kHz.

Damping experienced by a low frequency vibrating wire was measured and showed self-shielding, by creation of quantum turbulence. The same vibrating wire was used to study Landau critical velocity in the limit of constant speed, and contrast the results with dissipation observed during oscillatory motion.
Exploitation Route Our results on Andreev reflection in He3 validates visualization of superfluid quantum turbulence in pure quantum limit using ambient thermal excitations. So far it is the only method to visualize turbulence at lowest temperatures and studies on nucleation of turbulence and formation of a tangle will help to improve understanding of turbulence in general with has very wide implications.

Developed quasiparticle camera will help to understand propagation of ballistic excitation, their interaction with surfaces and reflection from surrounding surfaces. Such studies of thermal excitations in Helium-3 might help to understand and detect Majorana particles that are currently actively investigated in other systems.

The knowledge of acoustic emission of vibrating objects in helium can be used to improve cooling of nanoelectromechanical structures NEMS down towards very low temperatures and to achieve ground state in NEMS devices. The attainability of the ground state is essential for for quantum computing.
Sectors Aerospace, Defence and Marine,Education,Electronics,Manufacturing, including Industrial Biotechology,Security and Diplomacy

 
Description The UK has a significant high-technology industry with many contributing companies whose specialisation is a cryogenic equipment for use at millikelvin temperatures. The world-leading millikelvin and microkelvin research in the UK provides ideas and manpower to the commercial sector. It also provides a reputational underpinning since international customers have a high regard for UK research in this area. We have a direct impact on the development of commercial instrumentation and equipment, through consulting and advising commercial entities throughout Europe. We have a steady stream of interested parties coming to examine our cryostats and components. We put this activity on a more regular basis with the creation of a spin-out company, Lancaster Cryogenics Limited in 2011. This provides a channel for us to exploit the cryogenic expertise and specialist knowledge gained by our research activity. Our work on widening access to microkelvin temperatures for other users may produce significant impacts in the medium term. For instance, it may provide essential support for the development of new quantum technologies which have potential for revolutionary impacts in science and subsequent commercial activity. We work directly with Oxford Instruments plc on an InnovateUK/EPSRC award for commercialising the applications of quantum technology. Several of our graduate students have gone on to work for high-tech companies. Examples include large companies such as Oxford Instruments, Leiden Cryogenics and Rolls Royce, as well as a range of SMEs throughout the UK and Europe. Our state-of-the-art laboratory is a focus for public and school visits to view world-class research. We provide demonstrations and tours for 1000+ visitors each year. We provide work experience programs and give talks at local schools and public lectures. These outreach activities are embedded in the way we carry out our work. Our department has an outreach fellow, a former physics teacher at a local school, with whom we work to develop new initiatives such as physics enrichment days for pupils and support for physics teachers in the local community. We engage with the public media wherever possible. For example in 2006 we gave superfluid demonstrations filmed for the BBC and PBS for the "Absolute Zero" documentary, broadcast in the UK and America; our 2008 work on analogue cosmological branes was featured by The Daily Telegraph, becoming the most read article on their website at that time; our 2008 work on rogue waves was reported on Fox News; we recreated early superconductivity experiments for the 2011 BBC4 Jim Al-Khalili documentary "Shock and Awe: The Story of Electricity"; in 2012 our laboratory featured on BBC and ITN national news programmes, highlighting potential hazards of liquid nitrogen use in restaurants and bars.
Sector Aerospace, Defence and Marine,Education,Electronics,Manufacturing, including Industrial Biotechology
Impact Types Cultural,Economic

 
Description EPSRC
Amount £994,241 (GBP)
Funding ID EP/L000016/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 07/2013 
End 06/2017
 
Description Flow Instabilities in Superfluid Helium due to Oscillating Structures
Amount € 3,440 (EUR)
Organisation European Commission 
Sector Public
Country European Union (EU)
Start 04/2015 
End 07/2015
 
Description Microscopic dynamics of quantized vortices in turbulent superfluid in the T=0 limit
Amount £693,939 (GBP)
Funding ID EP/P025625/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 04/2017 
End 03/2021
 
Description Flow Instabilities in Superfluid Helium due to Oscillating Structures (Charles University in Prague) 
Organisation Charles University
Department Faculty of Mathematics and Physics
Country Czech Republic 
Sector Academic/University 
PI Contribution We have developed small quartz piezo-electric forks, which were used to create flow instabilities in superfluid 4He. Our team has carried out measurements of force-velocity characteristics of the tuning forks down to very low temperatures.
Collaborator Contribution Our partners provided infrastructure to measure onset of turbulence using second sound and allowed to contrast different measurements techniques.
Impact We have published several papers as the result of this collaboration (Journal of Low Temperature Physics, and Physical Review B).
Start Year 2015
 
Description Turbulence visualization with Newcastle University 
Organisation Newcastle University
Department School of Mathematics and Statistics
Country United Kingdom 
Sector Academic/University 
PI Contribution We have directly compared experimental measurements and numerical simulations of quantum turbulence in superfluid 3He. Our team has done the experimental measurements in the vicinity of absolute zero of temperature. We have developed a code for faster calculations of Andreev reflection of thermal quasiparticles from tangles.
Collaborator Contribution Our partners have developed state-of-the-art numerical simulations of realistic 3D tangles of quantum turbulence. They have calculated Andreev reflection from vortex ring and vortex lines. Furthermore, analytical framework for Andreev reflections from vortices was developed.
Impact We have published several papers in Physical Review Letters and Physical Review B as a result of collaboration.
Start Year 2014