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Physical Review Applied

High-Performance Cryogen-Free Platform for Microkelvin-Range Refrigeration

Ján Nyéki, Marijn Lucas, Petra Knappová, L. V. Levitin, Andrew J. Casey, J. Saunders, Harriet van der Vliet, A.J. Matthews

Published Oct 24, 2022• 8 citations
Publisher

Abstract

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.

DOI
10.1103/physrevapplied.18.l041002

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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 \ensuremathμ\ensuremath{\mu}\ensuremathμK, 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.
The superconducting quantum computer with strong data storage capability and fast execution speed has attracted a lot of attention in recent years and is finding practical applications in fields such as finance, military, biomedicine, and artificial intelligence. To suppress the thermal noise and to achieve high coherence, the quantum chips require millikelvin temperature, which poses a significant challenge for the suitable cryogenic system. The dilution refrigerator (DR) with ultra-low vibration and electromagnetic interference becomes an appropriate candidate for this purpose. To achieve the aimed millikelvin temperature, a cryogen-free DR composed of a Gifford-McMahon type pulse tube refrigerator (GM-type PTR), Joule-Thompson refrigerator (JTR), and dilution unit is investigated. This article presents the structural design of the DR and the coupling system with superconducting quantum chips. The cooling performance of the designed DR is estimated based on the developed cryogenic system. The minimum deduced temperature of 0.76 K in the still is achieved and the next steps to obtain the final temperature of 5 mK are underway.
We present the design and performance of a compact, fully cryogen-free cooling platform as a technology demonstrator for quantum hardware applications. The system leverages a four-stage continuous adiabatic demagnetization refrigerator (cADR) to achieve continuous cooling below 30 mK without the use of helium-3. Integrated mechanical and superconducting heat switches enable efficient thermal cycling, while high-density radio frequency (RF) wiring provides the infrastructure required for control and readout of a five-qubit superconducting quantum processor. Housed in a single rack with a spacious, accessible sample stage, the platform demonstrates that cADR technology can be realized in a compact form factor and provides a basis for future quantum hardware platforms operating under stringent space and infrastructure constraints.
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.
Cryogen-free dilution refrigerators generally simplify low temperature research but some types of samples, including superconducting qubits and other nanoelectronic devices, are affected by environmental heat sources such as stray photons or residual helium. We present the design and performance of a hermetic cell installed on the mixing chamber plate of a cryogen-free dilution refrigerator. The performance was quantified by measuring the dependence of the resonance frequency of a mechanical oscillator installed inside the cell on the mixing chamber temperature down to 10 mK. We found the expected logarithmic temperature dependence of the resonance frequency down to the lowest temperatures, demonstrating that the efficiency of the hermetic shield is significantly better than that of a simpler shield with no visible gaps.
Rapid thermal cycling is a central bottleneck in the development of superconducting quantum devices: conventional dilution refrigerators require cooldowns of a day or more and substantial cryogenic infrastructure, which throttles the fabricate-measure-redesign loop. We present an ultracompact dilution refrigerator (3 kg in mass and 100 mm in diameter) that completes a full cooldown-warm-up cycle to a base temperature of 70 mK in 1.2 hours when unloaded, and in 2.1 hours when fully equipped with the microwave wiring required for qubit measurements, while delivering 20 microW of cooling power at 100 mK. We validate the platform through a complete characterization of a two-fluxonium device: we extract the full circuit Hamiltonian by two-tone spectroscopy, measure energy-relaxation and coherence times, and benchmark single-qubit control. Although the relaxation time is limited by the base temperature of the system, we reach a single-qubit gate fidelity of up to 99%, at the coherence limit set by our operating temperature. These results demonstrate that compact, fast-cycling dilution refrigeration can support state-of-the-art quantum-device characterization without sacrificing measurement quality, offering a practical route to high-throughput quantum-hardware development.
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$\pm777μK,remainingbelow300K, remaining below 300K,remainingbelow300μKfor27hours,thusprovidingsufficienttimeformeasurements.Finally,wegiveanoutlookforcoolingbelow50K for 27 hours, thus providing sufficient time for measurements. Finally, we give an outlook for cooling below 50Kfor27hours,thusprovidingsufficienttimeformeasurements.Finally,wegiveanoutlookforcoolingbelow50μ$K for a new generation of microkelvin transport experiments.