Bluefors (Finland)

Pulse tube cryocoolers have been widely used in low temperature superconductors, telescopes, medical devices, helium liquefiers, dry dilution refrigerators and scientific instruments, since their invention in 1964 due to their inherent advantages of low vibration, high reliability, and long mean time between maintenance. 4 K two-stage pulse tube cryocoolers have been used in Cosmic Microwave Background (CMB) Telescopes to increase the sensitivity of instruments and enable low temperature detector technologies. Bluefors Cryocooler Technologies (formerly Cryomech, Inc.) has been continuously improving cooling capacity and energy efficiency of its 4.2 K two-stage pulse tube cryocoolers. The two newest models, the PT425 (2.7 W at 4.2 K) and PT450 (5.0 W at 4.2 K), have been successfully developed and launched in 2021 and 2023, respectively. The PT450 is the world’s largest, commercially available, 4 K pulse tube cryocooler, which provides a minimum cooling performance of 5.0 W at 4.2 K on the 2nd stage with 65 W at 45 K on the 1st stage simultaneously. The cooling performance of a pulse tube cryocooler is tied to the tilt angle of the system relative to the gravity vector, such that the cooling capacity decreases as a function of the tilt angle. The gas gravitational effect on the cooling performance of the PT425 and PT450 has been experimentally investigated. Test results of the tilt angles ranging from 0° (vertical) to 60° are presented in this paper, providing an accurate reference for the tilt angle cryogenic system design in CMB telescopes.

We report a comparative study on microwave control lines for a transmon qubit using (i) flexible stripline transmission lines and (ii) semi-rigid coaxial cables. During each experiment, we performed repeated measurements of the energy relaxation and coherence times of a transmon qubit using one of the wiring configurations. Each measurement run spanned 70–250 h of the measurement time, and four separate cooldowns were performed so that each configuration could be tested twice. From these datasets, we observe that changing the microwave control lines from coaxial cables to flexible stripline transmission lines does not have a measurable effect on coherence compared to thermal cycling the system or random coherence fluctuations. Our results open up the possibility of large-scale integration of qubit control lines with integrated component with planar layouts on flexible substrate.

In the work on superconducting parametric amplifiers, the frequency band below one gigahertz is calling for systematic improvements. Despite a prospect for ultralow added noise, bandwidth limitations have slowed down the integration of such amplifiers into sub-GHz experiments demanding fast ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&lt; 1\, \mu$</tex-math></inline-formula> s) readout speeds. Here, we study the impedance engineering of a flux-driven Josephson parametric amplifier (JPA) at 600 MHz. We propose, simulate and experimentally demonstrate a partially reconfigurable impedance transformer. The transformer enhances the JPA bandwidth to a state-of-the-art value of 10 MHz at 20 dB gain. Our amplifier has immediate applications in the readout of cryogenic sensors and in the reflectometry of quantum dots for spin qubit quantum computing.

Eskola, A. (1988). Our image of man has changed but has our methodology? Nordisk Psykologi, 40, 325–331. Among psychologists, the mechanistic approach has given way to a more modern image of man. More recently, man is regarded as an active being quided by different meanings and rules within a logical framework. However, empirical research methodology lags behind this development. The tendency is towards »deterministic mechanisms«. This article suggests that the so-called »passive role-method« embraces the modern approach to man better than our traditional tools.