Aalto University: The First Bluefors Systems Still Cooling

The first two Bluefors systems were built for the Aalto University Department of Applied Physics in 2006 – and these systems remain operational to this day, serving as a steadfast and dependable platform for research conducted at millikelvin temperatures.

Over the years, several generations of PhD students and post-docs have relied on these pioneering systems to conduct their innovative research. Read on to learn how the first systems were born, what kind of experiments have been performed on them, and how the collaboration between Aalto University and Bluefors has grown during the years.

The Emergence of Dry Dilution Refrigerators

Jukka Pekola, a professor in the Department of Applied Physics at Aalto University and the Centre of Excellence in Quantum Technology, QTF, boasts over 30 years of experience in quantum technology research. His research domain encompasses quantum thermodynamics, with a special focus on refrigeration and thermometry applications. Leading a dedicated research group, Jukka’s team primarily investigates quantum phenomena and devices, centering their efforts on understanding the charge transport and thermal properties of metallic, superconducting, and hybrid nanostructures.

Jukka’s passion lies in gaining a comprehensive understanding of natural phenomena, not confined to theoretical realms but also through rigorous experimentation. His research group’s experiments are conducted exclusively at low temperatures, predominantly utilizing superconducting quantum structures housed within dilution refrigerators.

Until 2007, the group mainly used wet dilution refrigerators. While functional for low noise DC transport measurements, these setups proved inadequate for modern RF experiments on quantum circuits that need large space to house amplifiers and circulators.

Jukka underscores the significant insight gained from extensive discussions with Rob Blaauwgeers, Bluefors’ co-founder and Chief Strategy Officer. At the time, Rob was employed at the Low Temperature Laboratory of TKK (now Aalto University). These discussions illuminated the fantastic opportunities presented by emerging dry dilution refrigerators. Among their advantages are a spacious working environment, powerful cooling capabilities, sturdy construction, and dependable operation – all without the logistical challenges associated with helium transfers and deliveries.

As a result, the first two Bluefors systems, one of them named after Jukka’s Pico-group as “Pico-Dry,” emerged. These were prototypes developed by Rob with Pieter Vorselman in 2006, shortly before the company’s official launch.

Still Cool After All These Years

“Pico-Dry has been a reliable workhorse”, Jukka says, and underscores how it has again-and-again provided a stable platform for experiments in the 20 mK temperature range.

While the dilution refrigerator has now been operating reliably for almost 20 years, there was one point when Jukka and his team thought the time had come for Pico-Dry to retire, as it had suffered mechanical damage. “We reached out to Bluefors and experienced remarkable customer service: there might be some emotional attachment to this fridge on both sides!” Jukka remarks.

He explains that a Bluefors service technician quickly evaluated the situation, disappeared, and returned in two weeks with custom-made parts to replace the malfunctioning pumping line and damaged support structures. “After inserting these new parts, the fridge operated as if brand new!” Jukka declares.

There are now four Bluefors dilution refrigerators in Jukka’s research group, and many more in other groups at Aalto.

Increasing Research Potential with Bluefors Systems

Jukka’s research team focuses on thermodynamics in quantum systems, necessitating precise temperature control ranging from about 10 mK up to almost 1 K in their experiments. “This can be reliably achieved in these fridges,” Jukka confirms.

When asked how the Bluefors systems have enhanced the research at Aalto University Jukka emphasizes that the Bluefors fridges offer stable operating conditions, ample space for experiments at 10 mK, the capability for multiple simultaneous experiments, and substantial cooling power. Furthermore, Jukka highlights how Bluefors fridges have broadened the scope of experiments, particularly for microwave-frequency projects utilizing superconducting quantum circuits.

“There have been numerous experiments conducted by multiple generations of PhD students and post-docs on PicoDry,” Jukka mentions. “To name just a few, we have developed fast non-invasive thermometry on nanostructures, measured fundamental temperature fluctuations in small metallic calorimeters, observed the intriguing dynamics of quasiparticles (unpaired electrons in superconductors) over extended periods of time, and developed a thermal detector of Landau-Zener transitions in superconducting qubits.”

Navigating Future Frontiers in Quantum Technology

At the core of successful research lies longevity: models are formulated, experiments are conducted, and results drive further discussion, development, and experimentation. Equipment reliability is paramount as it needs to endure the rigors of scientific inquiry.

Bluefors, with its origins in academia, continues to support scientific advancement, enriching our comprehension of the world. Regarding future collaborative efforts between Bluefors and Aalto University, Jukka sees value in increased collaboration in the joint development of measurement techniques and devices. “Such discussions have already been initiated, and one possibility would be to have joint PhD student projects and an exchange of post doc level researchers,” Jukka continues.

The intensive development towards quantum computing has been pivotal for both the academic community and Bluefors. However, he underscores that quantum computing is not the sole application of quantum technologies: “Quantum technologies encompass other spearheads as well.” Jukka states that, for instance, sensors based on quantum and nanostructures have also been central areas of interest over the years. “Quantum sensors are thus a natural common denominator for Bluefors, Aalto, and VTT in the future as well.”

Fostering Research Excellence

The enduring performance of the first Bluefors dilution refrigerators stands as a testament to their reliability and longevity. Over time, these refrigerators have facilitated invaluable research endeavors, providing a stable platform for scientific exploration.

Bluefors provides solutions for scientists so that they can do pioneering work on new discoveries. Aalto University plays a significant role in quantum research through its innovative ecosystem, state-of-the-art facilities, and collaborative partnerships, contributing to global efforts to realize the potential of quantum technologies.

Together, Aalto University and Bluefors foster research excellence, push the boundaries of scientific discovery, driving progress forward.

Learn more about our current dilution refrigerators or contact our sales engineers for more information.