Magnetic cooling for microkelvin nanoelectronics on a cryofree platform

Abstract

We present a parallel network of 16 demagnetization refrigerators mounted on a cryofree dilution refrigerator aimed to cool nanoelectronic devices to sub-millikelvin temperatures. To measure the refrigerator temperature, the thermal motion of electrons in a Ag wirethermalized by a spot-weld to one of the Cu nuclear refrigerators -is inductively picked-up by a superconducting gradiometer and amplified by a SQUID mounted at 4 K. The noise thermometer as well as other thermometers are used to characterize the performance of the system, finding magnetic field independent heat-leaks of a few nW/mol, cold times of several days below 1 mK, and a lowest temperature of 150 µK of one of the nuclear stages in a final field of 80 mT, close to the intrinsic SQUID noise of about 100 µK. A simple thermal model of the system capturing the nuclear refrigerator, heat leaks, as well as thermal and Korringa links describes the main features very well, including rather high refrigerator efficiencies typically above 80 %.

On-and-off chip cooling of a Coulomb blockade thermometer down to 2.8 mK

“…This is in contrast to the measurements, thus supporting the hypothesis of equilibrated subsystems within the CBT. We also observe that the parasitic heat determined from warm up curves of the Cu plates 25 is similar to that obtained from the CBT model here 40 . This suggests that both the cooling power as well as the parasitic heat leak scale with the volume and area of copper used.…”

“…Each wire is cooled by its own, separate nuclear refrigerator in form of a large Cu plate. However, despite recent progress [18][19][20][21][22][23][24][25] , it remains very challenging to cool nanostructures even below 10 mK. Due to reduced thermal coupling, these samples are extremely susceptible to heat leaks such as vibrations 25 , microwave radiation 26,27 , heat release 17 and electronic noise 20 .…”

“…However, despite recent progress [18][19][20][21][22][23][24][25] , it remains very challenging to cool nanostructures even below 10 mK. Due to reduced thermal coupling, these samples are extremely susceptible to heat leaks such as vibrations 25 , microwave radiation 26,27 , heat release 17 and electronic noise 20 . Metallic Coulomb blockade thermometers (CBTs) have been established as precise and reliable electronic thermometers 18,28,29 , operating down to 10 mK and slightly below 21,22,24,30 .…”

“…The present experiment is performed on a cryo-free platform 25,33 , where each of the 16 leads is equipped with its own nuclear refrigerator (see Fig. 1), consisting of two moles of copper.…”

“…1), consisting of two moles of copper. The system allows for cooling of the Cu pieces down to T Cu = 150 µK 25 , see supplementary for details 34 . To integrate the CBT, it is placed inside a Cu box, see Fig.…”