EMP User Meeting - Program

Program

All times below are listed for CET time zone.

10:00 – 10:10 Welcome session (Peter Skyba)

Morning session
Chair: Silke Bühler-Paschen
10:10 – 10:30 Alexey Fedorchenko (B.I. Verkin Institute, NASU, Kharkiv, Ukraine): Magnetic behaviour of cobalt(II)-containing layered double hydroxides
10:30 – 10:50 Daniel Staško (Charles University, Prague, Czech Republic): Low temperature investigation of the CeCuAl3 intermetallic compound at extreme   pressures
10:50 – 11:10 Loredana Gastaldo (Heidelberg University, Heidelberg, Germany): Study of the electron capture process in Be-7 with metallic magnetic calorimeters

Short break 11:10 – 11:20

Chair: Dominik Zumbühl
11:20 – 11:40 Sergey Kubatkin (Chalmers University, Sweden): Use of microkelvin platform: from quantum computation to novel phases in 2D material
11:40 – 12:00 Dominic Lennon (Oxford University, UK): Machine learning enables automatic tuning of quantum devices faster than human experts
12:00 – 12:20 Asser Elsayed (IMEC Belgium): Mobility limiting factors in Si-MOSFETs fabricated with a full CMOS process
12:20 – 12:40 General discussion, comments and questions

Break for lunch 12:40 – 14:00

Afternoon session
Chair: John Saunders
14:00 – 14:20 Femke Bangma (Nijmegen High Field lab/Radboud University, Netherland): Hyperfine interactions at ultra-low temperatures: their role in PrOs4Sb12
14:20 – 14:40 Manuel Brando (MPI for Chemical Physics of Solids, Dresden, Germany): Electrical transport measurements to investigate unconventional superconductivity in YbRh2Si2
14:40 – 15:00 Romain Danneau (Karlsruhe Institute of Technology, Karlsruhe, Germany): Critical current fluctuations in graphene Josephson Junctions

Short break 15:00 – 15:10

Chair: Richard Haley
15:10 – 15:30 Carlos Uriarte (Universidad Rey Juan Carlos, Madrid, Spain): Design of a levitation experiment in superfluid 3He
15:30 – 15:50 Erwin Schuberth (TU Munich, Germany): Magnetic susceptibility measurements on YbRh2Si2 at ultralow temperatures: a status report
15:50 – 16:10 Eddy Collin (CNRS, Grenoble, France): A macroscopic object in its quantum ground state of motion
16:10 – 17:00 General discussion, comments and questions

17:00 – 18:00 EMP General Assembly (Partner’s representatives only)

Abstracts

Andrew Armour (Group Leader, Nottingham, UK), Mika Sillanpää (Aalto, Finland), Xin Zhou (IEMN, France) and Eddy Collin (CNRS, Grenoble, France)

Recent advances in observing and exploiting macroscopic mechanical motion at the quantum limit brought opto-mechanical experiments down to always lower temperatures and smaller sizes, boosting a new research area were (more compatible) low energy photons are employed: microwave opto-mechanics.

Superconducting microwave circuits are in use and bridge opto-mechanics with quantum electronics, which positions the former as a new resource for quantum information processing. But microwave opto-mechanical platforms provide also unique capabilities for testing quantum mechanics at the most basic level: if one thinks about these devices in terms of quantum-limited detectors, the focus is on the thermodynamic baths that continuously interact with the mechanical degree of freedom. The fundamental questions that are addressed are then quantum thermodynamics, the boundary between
classical and quantum mechanics defined by wavefunction collapse, and ultra-low temperature materials properties.

In order to perform such experiments at the frontier of modern physics, we created a unique micro-wave/micro-Kelvin opto-mechanical platform. We demonstrate for the first time the passive cooling of a 15 MHz aluminium drumhead mechanical device down to 500 micro-K, reaching a population for the fundamental mode of 0.3 quanta on average; all higher modes being empty to a very high probability. Using microwave opto-mechanics as a non-invasive detector, we report on the in equilibrium thermal properties of this lowest frequency mode, challenging theory in an unprecedented experimental area.

Carlos Uriarte (Universidad Rey Juan Carlos, Madrid, Spain)

Motivated by recent experiments with a goalpost wire moving in superfluid 3He at supercritical velocities without breaking up the superfluid state, we are designing an experiment with a sphere levitating in superfluid 3He. Moving the sphere will help understand the mechanism behind the supercritical dissipationless flow. Our goal is to move the sphere through the superfluid by levitating it using magnetic fields. While Earnshaw’s theorem prevents levitation of a charge or a paramagnetic object using a static magnetic field, levitation can be achieved using superconductors.

Here we report a finite element study developed to model the experimental set-up for a superconducting type I indium sphere. The parameters required to produce levitation are optimized introducing variations in the model. Our analysis has produced experimentally realistic parameters of the coils and currents needed. The final design will be implemented in the actual experiment.

Manuel Brando (Max Planck Institute for Chemical Physics of Solids, Dresden, Germany)

In my talk I will summarize the work done by three institutions (MPI-CPfS Dresden, Goethe-University Frankfurt and RHUL London) within the EMP collaboration. The aim and at the same time the challenge of our project was to measure electrical transport of the unconventional superconductor YbRh2Si2 (Tc = 2mK [1]) down to 0.5mK. This requires very sensitive low dissipation techniques. We did it using SQUID-based electrical transport technique developed at Royal Holloway. We have also performed measurements in magnetic field to study the anisotropy of the T-B phase diagram which is rather complex due to the interplay between nuclear-electronic magnetism and superconductivity.

[1] Schubert et al. Science 351, 6272 (2016)

Femke Bangma1 , Lev Levitin2, Marijn Lucas2, Andrew Casey2, Jan Nyeki2, John Saunders2  and Alix McCollam1
1 High Field Magnet Laboratory (EMFL-HFML), Radboud University, Nijmegen, The Netherlands
2 London Low Temperature Laboratory, Royal Holloway, University of London, Egham, Surrey, TW20 0EX, United Kingdom

PrOs4Sb12 exhibits antiferroquadrupolar (AFQ) order at temperatures below ~1K and magnetic fields between ~5 and 14 T. The AFQ phase boundary terminates in quantum critical points at 0 K. Previous experiments showed unexpected temperature dependence of the size of the Fermi surface within
the AFQ phase, below about ~250 mK [1]. This effect was tentatively attributed to the influence of hyperfine levels, creating a composite nuclear-electronic order at the lowest temperatures. To further investigate this unusual order and its effect on the AFQ quantum critical point, we have
carried out ultra-low temperature magnetic susceptibility measurements of PrOs4Sb12 , in magnetic fields of up to 5.4 T, at the EMP facility at Royal Holloway. In my talk, I will present the results of these experiments, which allowed us to track the AFQ phase boundary and evolution of the Fermi
surface down to 1 mK. The low field quantum critical point is clearly shifted by the hyperfine interaction, and the continued development of the Fermi surface into the low mK range suggests that the nuclear and quadrupole states are indeed mixed at low temperature.

[1] A. McCollam et al., Physical Review B 88, 075102 (2013).

Daniel Staško (Charles University, Prague, Czech republic)

CeCuAl3 is a representative of CeTX3 intermetallic compounds (T = d-element and X = p-element) crystallizing in the tetragonal non-centrosymmetric BaNiSn3-type structure. This structure has attracted much attention due to the pressure induced superconductivity in a lattice without inversion symmetry
observed in CeRhSi3 [1] or CeIrSi3 [2]. CeCuAl3, revealing a so-called vibron state [3], that is, a strong interaction between orbital and lattice degrees of freedom leading to a new quasi-bound state, was studied from the viewpoint of possible superconductivity as well. The low-temperature high-pressure
investigation of CeCuAl3 was motivated by strikingly similar structural and bulk properties of these analogues. The study targeted two issues: (i) a potential so-far-unreported superconductivity, and (ii) the impact of applied pressure on the vibron state, or more generally magnetic excitations in CeCuAl3. Extreme conditions were applied employing Bridgman anvil cells with a pressure limit of up to 12 GPa and a dry refrigerator allowing to reach 10 mK temperature.

[1] N. Kimura, et al., Phys. Rev. Lett. 95, 247004 (2005)
[2] I. Sugitani, et al., J. Phys. Soc. Japan 75, 043703 (2006)
[3] D. T. Adroja, et al., Phys. Rev. Lett. 108, 216402 (2012)

Dominic Lennon (Oxford University, UK)

Bringing a spin qubit into operation requires a large parameter space to be explored. This process is intractable for humans as the complexity of circuits grows. We developed a statistical machine learning algorithm that navigates the entire parameter space. We demonstrate fully automated tuning of double quantum dot devices in 70 minutes and under; faster than human experts. We also demonstrate that the algorithm can be adapted to tune a wide range of devices architectures and material systems. We also show that the algorithm is capable of providing a quantitative measure of device variability. These are key demonstrations of quantum device tuning and characterisation with an approach general enough to be readily applicable to different types of quantum devices.

Alexey Fedorchenko (B. Verkin Institute for Low Temperature Physics and Engineering, NASU, Kharkiv, Ukraine)

Layered double hydroxides (LDHs) consist of the alternating positively-charged mixed metal M2+ – M3+ hydroxide layers with the interlayers occupied by charge-compensating anions and water molecules. In the hydroxide layers, the metal cations are coordinated by 6 hydroxyl ions in such a way that O-H bonds are perpendicular to the plane of the layers. LDHs are natural examples of immensely flexible chemical structure, in which the cations ratio M2+ /M3+ can vary, thereby providing a possibility to alter their magnetic properties in the case when at least one of M2+ and M3+ is magnetic ion.

Here we report on the low-temperature glassy magnetic behaviour of Co2+(n)Al3+ LDHs with the fixed cobalt-to-aluminum cations ratio (n = 2 and 3) and intercalated with NO3 anion. Static magnetization was measured in zero-field-cooled (ZFC) and field-cooled (FC) modes in low magnetic field of 100 Oe. Dynamic susceptibility was taken at different frequencies (up to 1 kHz). In addition, low temperature and magnetic field-dependent heat capacity has been investigated. It was found the Shottky-like anomalies which reproduce magnetic susceptibility anomalies discovered in the same temperature range. Under magnetic field action, the heat capacity anomalies become broader and fully suppressed at the field value around 50 kOe.

A Elsayed1T N Camenzind2, F A Mohiyaddin1, J Jussot1, S Kubicek1, B Govoreanu1, D M Zumbühl2 and I Radu1
1 IMEC, Kapeldreef 75, Leuven 3001, Belgium
2 Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland

We investigate the transport properties of different gate stacks  deposited on 300-mm Si wafers in an industrial fab. Hall-bar  transistors with a sub 10 nm oxide are fabricated using a  co-integrated optical and e-beam lithography process. A peak  mobility of 17500 cm2/(V.s) and a critical density for conduction down  to 0.95×1011 cm−2 are measured at a temperature of 0.1 K. We present  experimental values of transport  [cid:image005.png@01D71B59.E6E89340]  and quantum  [cid:image006.png@01D71B59.E6E89340]  scattering lifetimes with  respect to both temperature and sheet density. We show that large  angle scattering is the main mobility limiting factor in our  samples. We further show experimental difference in mobility for  different metal gates due to strain and oxygen scavenging effects.

Loredana Gastaldo1, Peter Rubovic2, Fedor Simkovic3 and Ivan Stekl3
1 Kirchhoff Institute for Physics, Heidelberg University, Heidelberg, Germany
2 National Radiation Protection Institute (SURO), Prague, Czech Republic
3 Institute of Experimental and Applied Physics, Czech Technical University in Prague, Prague, Czech Republic

The analysis of the calorimetric measurement of the spectrum derived from electron capture in Be-7 enclosed in low temperature metallic magnetic calorimeters (MMCs) can be used for a precise characterization of the decay process. In fact, MMCs are characterized by a very good energy resolution of a few eV FWHM in detectors optimized for soft x-ray spectroscopy and they feature a well understood detector response. Be-7 ions will be enclosed in the absorber of a MMC array via ion-implantation. This method has been already proved not to generate damages in the detector or modification in the detector response within the ECHo experiment, for which Ho-163 was implanted in MMC absorber. The first goal of our project is the characterization of the L/K capture ratio. As a second investigation we will derive information on the energy distribution for the nuclear recoil of the daughter Li-7 atom. We will summarize the present status of the project and present the plan to perform this measurement in 2022.

Sergey Kubatkin (Chalmers University, Sweden)

I plan to describe two projects, planned for the facilities at Royal Holloway University of London, UK and Aalto University, Finland. Two projects are very different, but both of them are based on the state-of-the-art achievements of our research group at Chalmers. Enabling experiments, performed together with British and Finnish researchers, have a significance on their own.

The first project will answer the question: ‘Is it possible to create a solid-state-environment to the qubit, which is similar to the vacuum that is available to atomic-physics scientists.’ – We plan to check experimentally if a scalable superconducting qubit technology, suffering at the moment from the noise and decoherence of solid-state environment, can reach the level of coherence, achieved in atomic-physics-based experiments with just a few ‘cold atoms’ and ‘ion-based’ qubits. For this purpose, we plan to use tunable field-resilient superconducting resonators, developed at Chalmers. In the preliminary experiments we have already learned a lot about spurious Two-Level Systems (TLS), limiting coherence in solid state devices. In brief, we aim here at freezing the spectral diffusion of TLS at ultralow temperatures.

The second project is dealing with exploring the properties of novel graphene-based two-dimensional materials, developed at Chalmers. Extremely uniform doping of graphene, comparable to the best results obtained with hBN-encapsulated flakes, is now available at the wafer-scale, enabling us to study physics of graphene at the Dirac point, which is not obscured by the sample-specific mesoscopic fluctuations, inherent to microscopic samples. Intercalation of graphene with heavy metal, like Au, provides a promising route to induce Spin-Orbit Interaction in graphene. We plan to study the effects of this interaction on charge transport in this novel material. The basic science experiments, described in this part, may also lead to practical applications of novel 2D materials, leading, e.g., to quantum-limited radiation sensors.

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