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Acquisition of a Dilution Refrigerator to Center for Quantum Devices

The experimental tasks in my upcoming EU project requires me to operate and develop sensitive nanoscale hybrid quantum devices at 20 mK and in high magnetic fields. Establishing and controlling such conditions, as well as sharing techniques and samples between the involved PIs, are a prerequisite for experimental success in establishing the proposed quantum effects in electrical measurements of nanostructured devices.

The experimental tasks in my upcoming EU project requires me to operate and develop sensitive nanoscale hybrid quantum devices at 20 mK and in high magnetic fields. Establishing and controlling such conditions, as well as sharing techniques and samples between the involved PIs, are a prerequisite for experimental success in establishing the proposed quantum effects in electrical measurements of nanostructured devices. Over the last few years, we have successfully developed Bluefors XLD dilution refrigerators and their sample-insert capabilities (used by activities supported by Microsoft Research that are related to my EU project) to allow the type of electrical measurement and manipulation experiments at temperatures below 20 mK and in high magnetic fields that are needed for my project.

European Research Council(ERC) — Synergy grant called Nonlocal. Grant agreement number: 856526 Nonlocal ER-2019-SYG.

A cryostat is required that allows automatic loading of sample inserts (identical with existing sample inserts to be used on related projects) into a dilution refrigerator that can produce high magnetic fields (up to 6 Tesla) and low temperatures (below 100 mK).

Due to room-temperature decay of samples a fast initial cooldown to below 100 Kelvin is essential. The degradation of freshly fabricated samples (‘aging’) is partially due to exposure to atmosphere (exposure to oxygen and moisture) and partially due to thermally activated microscopic changes in the sample. An automatic loader alleviates these problems, by applying vacuum right away and by quickly cooling the sample within a pre-cooled cryostat. This process cannot be achieved by dilution refrigerators without sample-loader functionalities, due to the large thermal mass associated with superconducting vector magnets and their slow cooling rate when cooling down from room temperature. Without an automated vacuum loader, our EU project (which involves various sensitive materials systems) would be constraint to non-aging samples, which may not exist and may therefore prevent successful completion of our project.

For the work flow in our EU project to be successful, it is essential that the system is compatible with the sample inserts of several other Bluefors XLD cryostats that are already installed in the laboratory and that are successfully used by Microsoft Research in our center for complementing research projects. Changing samples between dissimilar sample inserts would come with a high risk of electrostatic-discharge damage of the devices, and would further require expensive development of high-frequency sample boards, sample-board mounting hardware, and cryogenic sample-board high-frequency wiring.

Also, due to laboratory space constraints this cryostat will replace an existing Bluefors cryostat, and Bluefors is the only manufacturer that can readily make a cryostat with identical foot print and infrastructure requirements (pulse tube cooling, ceiling hangars, electricity requirements).

Non-automatic bottom loaders would require two persons to physically operate the loader (meaning samples cannot be loaded outside working hours and only by breaking Covid distancing rules), and the different geometry of the sample insert and cold finger make is impossible to shield the measurement loom. Shielding is important to prevent quasi-particle poisoning, which is known to be highly detrimental to hybrid devices as those proposed in our EU project.

Internet address: https://bluefors.com

Internet address: www.KLFU.dk