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arXiv:2110.06293

Microkelvin electronics on a pulse-tube cryostat with a gate Coulomb blockade thermometer

Samani, Mohammad, C. P. Scheller, Nikolai Yurttagül, Kestutis Grigoras, David Gunnarsson, Omid Sharifi Sedeh, Alexander Thomas Jones, Jonathan R. Prance, R. P. Haley, Mika Prunnila, Dominik M. Zumbühl

Published Oct 12, 2021• 0 citations
arXivHTMLPDF

Abstract

Access to lower temperatures has consistently enabled scientific breakthroughs. Pushing the limits of \emph{on-chip} temperatures deep into the microkelvin regime would open the door to unprecedented quantum coherence, novel quantum states of matter, and also the discovery of unexpected phenomena. Adiabatic demagnetization is the workhorse of microkelvin cooling, requiring a dilution refrigerator precooling stage. Pulse-tube dilution refrigerators have grown enormously in popularity due to their vast experimental space and independence of helium, but their unavoidable vibrations are making microkelvin cooling very difficult. On-chip thermometry in this unexplored territory is also not a trivial task due to extreme sensitivity to noise. Here, we present a pulse-tube compatible microkelvin sample holder with on-board cooling and microwave filtering and introduce a new type of temperature sensor, the gate Coulomb blockade thermometer (gCBT), working deep into the microkelvin regime. Using on- and off-chip cooling, we demonstrate electronic temperatures as low as 224$\pm$7$μ$K, remaining below 300$μ$K for 27 hours, thus providing sufficient time for measurements. Finally, we give an outlook for cooling below 50$μ$K for a new generation of microkelvin transport experiments.

DOI
10.48550/arxiv.2110.06293

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Access to lower temperatures has consistently enabled scientific breakthroughs. Pushing the limits of \emph{on-chip} temperatures deep into the microkelvin regime would open the door to unprecedented quantum coherence, novel quantum states of matter, and also the discovery of unexpected phenomena. Adiabatic demagnetization is the workhorse of microkelvin cooling, requiring a dilution refrigerator precooling stage. Pulse-tube dilution refrigerators have grown enormously in popularity due to their vast experimental space and independence of helium, but their unavoidable vibrations are making microkelvin cooling very difficult. On-chip thermometry in this unexplored territory is also not a trivial task due to extreme sensitivity to noise. Here, we present a pulse-tube compatible microkelvin sample holder with on-board cooling and microwave filtering and introduce a new type of temperature sensor, the gate Coulomb blockade thermometer (gCBT), working deep into the microkelvin regime. Using on- and off-chip cooling, we demonstrate electronic temperatures as low as 224±\pm±7μμμK, remaining below 300μμμK for 27 hours, thus providing sufficient time for measurements. Finally, we give an outlook for cooling below 50μμμK for a new generation of microkelvin transport experiments.
Temperatures below 1 mK on-chip hold great potential for quantum physics but present a great challenge due to the lack of suitable thermometry and the detrimental pulse-tube vibrations of cryogen-free refrigerators. Here, we solve the pulse-tube problem using a rigidly wired metallic sample holder, which provides a microkelvin environment with low heat leaks despite the vibrations. Further, we demonstrate an improved type of temperature sensor, the gate Coulomb blockade thermometer (gCBT), employing a gate metallization covering the entire device. This immunizes against nanofabrication imperfections and uncontrollable offset charges, and extends the range to lower temperatures compared to a junction CBT with the same island capacitance, here down to $\ensuremath{\approx}$160 $\ensuremath{\mu}$K for a 10% accuracy. Using on- and off-chip cooling, we demonstrate electronic temperatures as low as 224 $\ifmmode\pm\else\textpm\fi{}$ 7 $\ensuremath{\mu}$K, remaining below 300 $\ensuremath{\mu}$K for 27 hours, thus providing time for experiments. Finally, we give an outlook for cooling below 50 $\ensuremath{\mu}$K for a future generation of microkelvin transport experiments.
Abstract Fragile quantum effects such as single electron charging in quantum dots or macroscopic coherent tunneling in superconducting junctions are the basis of modern quantum technologies. These phenomena can only be observed in devices where the characteristic spacing between energy levels exceeds the thermal energy, kBT, demanding effective refrigeration techniques for nanoscale electronic devices. Commercially available dilution refrigerators have enabled typical electron temperatures in the 10 to 100 mK regime, however indirect cooling of nanodevices becomes inefficient due to stray radiofrequency heating and weak thermal coupling of electrons to the device substrate. Here, we report on passing the millikelvin barrier for a nanoelectronic device. Using a combination of on-chip and off-chip nuclear refrigeration, we reach an ultimate electron temperature of Te = 421 ± 35 μK and a hold time exceeding 85 h below 700 μK measured by a self-calibrated Coulomb-blockade thermometer.
Accessibility to the microkelvin temperature regime is important for quantum technology research. Cryogen-free dilution refrigerators opened up the millikelvin temperature range, but the perception is that ultralow temperatures are difficult to reach and require specialist infrastructure. The authors report the design of a microkelvin platform based on a nuclear-demagnetization stage, engineered and optimized for operation on a cryogen-free dilution refrigerator. The study demonstrates temperatures as low as 395 $\ensuremath{\mu}$K, and a protocol that enables experiments operated below 1 mK for 95% of the time, providing an efficient cryogen-free microkelvin environment for a wide range of applications.
Abstract We report recent progress toward the realization of a sub-mK, low-vibration environment at the bottom stage of a dry dilution refrigerator for use in mechanical tests of quantum mechanics. Using adiabatic nuclear demagnetization, we have cooled a silicon cantilever force sensor to T≈1T\approx 1T≈1 T ≈ 1 mK. The temperature of the tip holder of the cantilever chip was determined via a primary magnetic flux noise thermometer. The quality factor of the cantilever continues to increase with decreasing temperature, reaching Q≈4⋅104Q\approx 4\cdot 10^4Q≈4⋅104 Q ≈ 4 · 10 4 at 2 mK. To demonstrate that the vibration isolation is not compromised, we report the detection of the thermal motion of the cantilever down to T≈20T \approx 20T≈20 T ≈ 20 mK, only limited by the coupling to the SQUID readout circuit. We discuss feasible improvements that will allow us to probe unexplored regions of the parameter space of continuous spontaneous localization models.
The performance and accuracy of quantum electronics is substantially degraded when the temperature of the electrons in the devices is too high. The electron temperature can be reduced with appropriate thermal anchoring and by filtering both the low frequency and radio frequency noise. Ultimately, for high performance filters the electron temperature can approach the phonon temperature (as measured by resistive thermometers) in a dilution refrigerator. In this application note, the method for measuring the electron temperature in a typical quantum electronics device using Coulomb blockade thermometry is described. This technique is applied to find the readily achievable electron temperature in the device when using the QFilter provided by QDevil. With our thermometry measurements, using a single GaAs/AlGaAs quantum dot in an optimized experimental setup, we determined an electron temperature of 28 ±\pm± 2 mK for a dilution refrigerator base temperature of 18 mK.
When operated in a dilution cryostat, a MHz-frequency nanomechanical device relies on active cooling to reach its quantum ground state. However, a proper understanding of its environmental interactions and mechanical quantum decoherence would require in-equilibrium cooling, with the thermal bath reaching sub-mK temperatures. This is very demanding and requires cooling via adiabatic nuclear demagnetization. The authors successfully demonstrate the technique, with a scheme to measure the temperature on-chip to verify equilibrium with the cryostat. An unexpected instability of unknown origin is observed at very low temperatures, presenting a strong limitation to progress in this field.