On-and-off chip magnetic cooling for nanoelectronics below 1 mK

Mohammad Samani1*, Christian P. Scheller1*, Nikolai Yurttagül2

Omid Sharifi Sedeh1, Grigoras Kestutis2, Alex T. Jones3,Jonathan Prance3, Richard P. Haley3, Mika Prunnila2, Dominik Zumbühl1

* Equally contributed to this work
1 Department of Physics, University of Basel
2 VTT Technical ResearchCentre of Finland Ltd, QTF Centre of Excellence
3 Department of Physics, Lancaster University

Why go below 1 mK?

Fragile fractional quantum Hall states
Pan W. et al., Physical Review B 91, 041301(R) (2015)

Helical nuclear spin systems
Scheller C. P. et al., Physical Review Letters 112, 066801 (2014)
S. Chesi et al., Physical Review Letters 101,146803 (2008)

Metallic states of disordered superconductors
Tamir I. et al., Science Advances 5, 3 (2019)
C. Bøttcher et al., Nature Physics 14, 1138 (2018)

Long coherence times of semi- and superconducting qubits
Devoret M., Schoelkopf R., Science 339, 1169 (2013)
J. Clarke, F. Wilhelm, Nature 453, 1031 (2008)

Adiabatic Nuclear Demagnetization

Established method since 1960s

Cools nuclei spin in bulk copper to $\approx$100 pK
Knuuttila T. A. et al., Journal of Low Temperature Physics 123, 65-102 (2001)

In an adiabatic process of demagnetization $$S\left(\frac{B_i}{T_i}\right) = S\left(\frac{B_f}{T_f}\right)$$ $$\boxed{\frac{T_f}{B_f} = \frac{T_i}{B_i}}$$

Experimental Components

Palma M. et al., Rev. Sci. Instr. 88, 043902 (2017)
Scheller C. P. et al. APL 104, 211106 (2014)

Coulomb Blockade Thermometer

$$ \frac{g(V)}{g_T} = 1-\frac{E_c}{k_B T} f\left(\frac{eV}{N k_B T}\right) \textrm{,} f(x) = \frac{x \sinh(x) - 4\sinh^2(x/2)}{8 \sinh^4(x/2)} $$
$$ \frac{\Delta g}{g_T} \approx \frac{u}{6}-\frac{u^2}{60}+... \textrm{,} u = E_c/k_B T$$
Meschke M. et al., Journal of Low Temperature Physics 134, 1119-1143 (2004)

Calibration

Manuscript in preparation for publication

1. Precooling

3. Warm up


2. Demagnetization

Manuscript in preparation for publication

A Low-Temperature Trace

Manuscript in preparation for publication

Summary

Direct measurement of electronic temperatures below 250 µK in cryo-free dilution fridge
Coulomb Blockade Thermometer with high gate capacitance suitable for measurements below $E_c$
European Microkelvin Platform provides user access to microkelvin apparatus.
Contact: Mohammad Samani m.samani@unibas.ch