Low Temperature Physics

Group Members

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Research Activity

We perform experiments on superfluids and other materials with applications in areas such as nanoelectronics, cosmology and turbulence.

The group has a strong international reputation for performing state-of-the-art experiments at the lowest achievable temperatures. Our custom made dilution refrigerators, built in-house, achieve world-record low temperatures. We have pioneered several innovative approaches, including:

  • 'Lancaster-style' demagnetisation stages to cool superfluid helium-3 to record low temperatures
  • 'heat-flush' procedures to produce highly purified helium-4
  • ion transport measurement methods for quantum fluids
  • novel NMR systems
  • various mechanical oscillator techniques which provide extremely sensitive thermometry and bolometry at microkelvin temperatures

We are well known for providing these sub-millikelvin low temperature environments with advanced in-house cryogenic engineering, and for our accompanying expertise in ultra-sensitive measurement techniques and the development of specialised instrumentation.

Creating, controlling and exploiting the ultra-low temperature environment has proven crucial for the research and development of quantum-enhanced devices. Our platform technology provides the extreme cold and isolation necessary to probe the subtle quantum behaviours that are otherwise hidden by thermal fluctuations or external disturbance.

We have a broad research portfolio in low temperature physics and specialise in quantum fluids and solids research. We have performed ground-breaking analysis on numerous topics, including

  • superfluid analogues of cosmological processes
  • ion and vortex ring dynamics
  • ballistic quasiparticle beams
  • exotic superfluid spin phenomena
  • superfluid phase nucleation
  • phase boundary dynamics
  • wave turbulence
  • quantum turbulence

Key Research

  • Cooling and sensitive measurement techniques
  • Quantum fluids and solids
  • Superfluid 3He
  • Superfluid 4He
  • Properties of materials at ultra-low temperatures
  • MEMS and NEMS devices at low temperatures
  • Extremely cold devices and associated quantum technologies
  • Development of sensitive measurement techniques

PhD Opportunities

  • Cooling nano-electromechanical systems to low temperatures

    Supervisor

    Dr Sergey Kafanov

    In this project, the PhD student will work within the ULT group to investigate the behaviour of Micro-Electro-Mechanical (MEM) and Nano-Electro-Mechanical (NEM) resonators in the vacuum and superfluid 3He at world-record low temperatures. There is a growing demand for cooling micro and nano-electromechanical oscillators down to submillikelvin temperatures, and existing research indicates that 3He superfluid is the best available coolant to achieve this. The goals of the project are to understand and overcome existing cooling restrictions and to reach submillikelvin temperatures. Furthermore, MEM and NEM beams could be used to probe superfluid 3He at various sub-gap frequencies and length scales comparable to the coherence length of the condensate. This would have very far-reaching scientific and technological impacts. 

  • Superfluid 3He far from equilibrium

    In this project, the PhD student will work within the ULT group to study non-equilibrium phenomena in a well-known system with an established theoretical framework - superfluid 3He. Coherent condensates (or at least those to which we have experimental access) are fragile objects that only exist at the extremes of very low temperatures. We can study condensates over a wide range of conditions from the virtually zero-entropy zero-temperature quiescent state through to the regime where we have the destruction of coherence. 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 above the accepted Landau critical value. This was quite unexpected. Using for the first time the powerful combination of nuclear magnetic resonance with steady superflow in 3He at ultralow temperatures we aim to investigate several emergent phenomena such as quantum critical phase transitions between different superfluid phases.

  • Quantum turbulence and vortex pinning in superfluid 4He

    Turbulence, we all know, is ubiquitous, impinging forcefully, not only on human activity but also overall nature on scales from the nuclear to the cosmological. That said, it is almost embarrassing that we still have no adequate theory of turbulence. This is where studies of quantum turbulence, the version of turbulence only occurring in superfluids, can play a part. Quantum turbulence is very different as there is no viscous dissipation since pure condensates do not support viscous forces. Nevertheless, the most fundamental difference arises from the phase coherence in the condensate that ensures that any vortices are singly quantised and thus identical. In consequence, we can regard such an ensemble as providing an ideal “atomic theory” of turbulence.

    In this project, the student will work within the ULT group to study quantum turbulence and vortex pinning in superfluid 4He using torsional oscillator techniques. All earlier experiments on the generation of quantum turbulence by oscillating structures have used objects with convex surfaces; the flow around them is classically unstable at a low velocity, and the two expected transitions to turbulence are not distinguishable. In contrast, in this project the helium will be inside a pill-box that oscillates about its axis, thus eliminating all flow over convex surfaces. The two transitions should then be well separated and identifiable as characteristic increases in damping. The fundamental properties of the remanent vortices themselves will be studied, by investigating their pinning to microscopic protuberances. 

  • Visualisation of Quantum Turbulence via Andreev Reflection in superfluid 3He

    Turbulence, we all know, is ubiquitous, impinging forcefully, not only on human activity but also overall nature on scales from the nuclear to the cosmological. That said, it is almost embarrassing that we still have no adequate theory of turbulence. This is where studies of the quantum turbulence, the version of turbulence only occurring in superfluids, can play a part. Quantum turbulence is very different as there is no viscous dissipation since pure condensates do not support viscous forces. Nevertheless, the most fundamental difference arises from the phase coherence in the condensate that ensures that any vortices are singly quantised and thus identical. In consequence, we can regard such an ensemble as providing an ideal “atomic theory” of turbulence.

    In this project, the student will work within the ULT group to study numerically and experimentally visualization of quantum turbulence in superfluid 3He. We have pioneered the non-invasive detection of vortices by a surprisingly simple method which uses the Andreev reflection of quasiparticle excitations from the flow field circling each vortex. Our advanced vortex-detection techniques using mechanical oscillators provide knowledge of the turbulent behaviour that is simply not accessible in other systems. The measurements will be contrasted with computer simulations of moderately dense, three-dimensional, quasiclassical vortex tangles and the Andreev reflection of thermal quasiparticle excitations by these tangles. The research project will also address the question of how the Andreev reflectivities can distinguish quasiclassical and ultraquantum regimes of quantum turbulence, revealing their nature and signature properties

  • Miniature atomic clock based on endohedral fullerenes

    Atomic clocks are among the most precise scientific instruments ever made and are key to advanced navigation, communication, and radar technologies. We are pursuing a new approach to create a clock that will fit on a chip. Instead of atomic vapours, we will use electron and nuclear spins in endohedral fullerene molecules – nature’s atom traps - whose energy levels offer an exquisitely stable frequency reference. To make this novel approach work, we must overcome a range of physics and engineering challenges, including detecting spin resonance from a small number of spins, identifying the energy levels involved, and miniaturizing the control electronics and magnet. The reward will be a completely new technology with a wide range of civilian and military uses. We are looking for a candidate who has a strong interest in applying quantum physics in new technology and is motivated to develop the new and demanding electronic measurement techniques that will be necessary.

    References

    • “Keeping Perfect Time with Caged Atoms”, K. Porfyrakis and E.A. Laird, IEEE Spectrum (Dec 2017, p34)
    • “The spin resonance clock transition of the endohedral fullerene 15N@C60”, R.T. Harding et al. Phys Rev Lett. 119 140801 (2017)

    Supervisor

    • Edward Laird

     

  • Studying quantum motion using a vibrating carbon nanotube

    To predict the behaviour of a small particle, for example, an electron moving through a molecule, it is essential to use the concept of quantum superposition – the particle may traverse a superposition of multiple paths simultaneously. Such superposition states have been beautifully demonstrated for photons, atoms, and molecules, but it is an exciting open question of why larger objects do not show this behaviour.

    We can address this question experimentally by studying the motion of mesoscopic objects containing millions of atoms. This project will make and measure vibrating carbon nanotubes, whose resonant frequencies are high enough that they can be cooled to their quantum ground state. We recently showed theoretically how to use an analogue of a grating interferometer to measure interference between different paths of motion. This project will use advanced cryogenic and nanofabrication technology at Lancaster to experiment.

    References

    • “Displacemon electromechanics: how to detect quantum interference in a nanomechanical resonator”. K.E. Khosla at al. Physical Review X 8 21052 (2018)
    • “Resonant optomechanics with a vibrating carbon nanotube and a radio-frequency cavity”, N. Ares et al. Phys Rev Lett. 117 170801 (2016)

    Supervisor

    • Edward Laird
  • The coldest liquid in the Universe

    Supervisor

    Dr Dmitry Zmeev

    Description

    We will attempt to achieve the lowest temperature for any liquid. The project is concentrated around developing and demonstrating a new technique for cooling superfluid Helium-3. By utilising the nuclei of solid Helium-3 adsorbed on the surface of aerogel as a refrigerant in the adiabatic demagnetisation process, we will try and cool the superfluid to well below 100 microkelvins. Measuring such low temperatures is an arduous task. We will develop a method based on creating a Bose-Einstein Condensate of magnons within the superfluid and measurement its decay due to the very few thermal excitations remaining in the liquid. If successful, we will seek to apply the developed technique to cooling other systems, such as electrons in quantum devices, where lower temperature means longer coherence times.

     

     

     

  • SQUID noise thermometry for nanodevices at submillikelvin temperatures

    Supervisor

    Dr Viktor Tsepelin, Dr Jonathan Prance

    Description

    In this project, the PhD student will work within the Ultra Low Temperature group to design, build and investigate Superconducting Quantum Interference Device (SQUID) based noise thermometry for nanodevices. There is a huge demand for cooling micro and nano-sized samples down to submillikelvin temperatures and ULT currently holds world record on cooling electrons in nano samples. Cooling is accomplished either by submerging nano samples in liquid helium-3 or by the direct adiabatic demagnetization of nano samples. The outstanding challenge is to measure temperature accurately, reliably and fast. Unprecedented SQUID sensitivity will permit us developing a non-contact thermometer measuring magnetic noise raising from the oscillations of the electrons in the metallic nano samples. The amount of noise is temperature-dependent and can be calculated from the first principles, which allows the thermometer to be self-calibrated. We aim to use cross-correlation between SQUID two-channels to eliminate any noise from the SQUID amplifier thus making it operational down to submillikelvin temperatures (~50 microkelvins).

Postgraduate Training

We run training sessions for postgraduate students throughout the year, covering both specific low temperature technology and more general research skills.

You can also attend a series of lectures jointly organised with the University of Manchester. These will allow you to meet students from other institutions, as well as being taught new material that may be of use to you in future years.

The nature of the training is dependent on your project requirements and the skills you will need to make progress in your work. You will engage in a continual discussion with us to ensure that we provide the most relevant and practical training. The Faculty of Science and Technology, ISS, and the Library offer additional training.

You will receive training in a wide range of formats on topics of interest to your project:

  • North West England Solid State lectures organised by Manchester and Lancaster universities
  • Physics of superfluids and superconductors
  • Essential cryogenic safety and safe handling of cryogenic liquids
  • Operation of sophisticated low temperature refrigeration equipment
  • Fabrication of NEMs and MEMs devices
  • Experimental instrumentation design and construction
  • Innovative measurement techniques
  • Data acquisition techniques
  • Data analysis and computer-based simulation techniques
  • Preparation of manuscripts, posters and oral presentations

You could attend a variety of scientific conferences, allowing you to present your work. If necessary, you will receive additional support and advice on the preparation of posters and oral presentations. You also have the chance to develop their presentation skills via participation in the Department’s public understanding of physics outreach programme.

New tutorials, workshops and conferences include: