Journal of Low Temperature Physics最新文献

The LUCE (LUtetium sCintillation Experiment) project will search for the (^{176})Lu electron capture based on a milli-Kelvin calorimetric approach. This decay is of special interest in the fields of nuclear structure, rare event searches, and measurements of nuclear matrix elements of long-lived isotopes. The experiment is primarily searching for a mono-energetic peak from the (7^- rightarrow 2^+) forbidden transition. The current status and design of a novel cryogenic module for the measurements of the electron capture in (^{176})Lu are reported on. Details of future measurement plans are presented.

We describe a testbed to characterize the optical response of compact superconducting on-chip spectrometers in development for the EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) mission. EXCLAIM is a balloon-borne far-infrared experiment to probe the CO and CII emission lines in galaxies from redshift 3.5 to the present. The spectrometer, called µ-Spec, comprises a diffraction grating on a silicon chip coupled to kinetic inductance detectors (KIDs) read out via a single microwave feedline. We use a prototype spectrometer for EXCLAIM to demonstrate our ability to characterize the spectrometer’s spectral response using a photomixer source. We utilize an on-chip reference detector to remove the spectral structure introduced by the off-chip optics and a silicon etalon to calibrate the absolute frequency.

In recent years, global investment in magnetic resonance imaging (MRI) has surged, with 3 T MRI technology overtaking 1.5 T as the standard in hospitals gradually. A combination of linear programming, genetic algorithms, and nonlinear programming was employed to design an actively shielded 3 T superconducting MRI magnet system. This magnet consists of seven main coils and two shielding coils, achieving a magnetic field with a peak-to-peak inhomogeneity of 10 ppm within a 50-cm-diameter spherical volume (DSV). To address the risk of quench in superconducting magnets, which can lead to damage due to excessive temperature, voltage, and stress, a quench protection system is crucial. The designed system segments the coils for protection, using diode pairs and shunt resistors to manage the quench. Initial simulations indicated that temperature rises and voltages were within safe limits, but some coils were slow to quench or did not quench at all, risking burnout. To mitigate this, quench propagation heating plates were added to increase the quench speed. Updated simulations showed rapid quench across all coils and a significant reduction in hot spot temperatures and peak voltages.

The fractional electron capture probabilities of ⁵⁹Ni were measured using metallic magnetic calorimeters (MMCs). ⁵⁹Ni was one of the radionuclides chosen as a part of the European Metrology Research (EMPIR) project MetroMMC. The measurement was performed by using the decay energy spectroscopy (DES) technique, where the radionuclide is embedded in the absorber to have a 4π geometry. Two different source preparation techniques adapted for the measurement are also discussed: electroplating on gold foil and micro-drop-dispensing on gold nanofoam. The total energy spectra obtained from both sources are compared with each other, and the measured fractional electron capture probabilities are compared with those available in the literature and from the BetaShape code.

Superconducting quantum interference device (SQUID) has been widely used in various metrological and high-precision-demanding applications, owing to its excellent magnetic flux resolution. Nevertheless, the SQUID with nonlinear flux-to-voltage characteristics makes the stable and accurate readout circuit crucial for applications. In this paper, we design a self-feedback differential low-noise amplifier (SDLA) which relies on the flux-loop lock (FLL) to construct the direct readout circuit. This weakens the feedback current and maintains the balance between two-terminals SQUID, thus minimizing the influence of wire resistors. The SDLA is composed of matched transistors and two amplifiers that maintain stable amplification performance and low noise performance through current feedback. In a series of experiments, the feedback current is reduced to the pA level, minimizing wire resistor influences. And, the white input voltage noise of the readout circuit is around 0.65 nV/Hz^1/2.

Several proposed space-based X-ray observatories apply TES-based micro-calorimeters as energy-dispersive imaging detector. The number of independently readout pixels is an important figure of merit for the scientific yield of such instruments. Design studies have shown that the power consumption of the SQUID readout is one of the driving design parameters which limits the maximum number of pixels which can be accommodated. Different multiplexing schemes, each with different properties and multiplexing factors have been proposed and demonstrated for the readout of the TES-based detectors. In an effort to estimate how the different readout multiplexing schemes differ in scalability for future space-based applications, we have made a comparison of the reported power consumption of the main multiplexing schemes currently under consideration for different space-based telescopes, i.e. time-domain multiplexing, frequency-domain multiplexing, and microwave SQUID multiplexing. It was found that, despite the different architectures and multiplexing factors, the power consumption per pixel at cryogenic temperatures is rather similar. We will analyze the origin of this phenomenon, and discuss directions of development to further improve on this number.

Considering both interspecies and intraspecies quantum fluctuations in quasi-one dimensional ultracold Bose–Bose mixtures, we show that new LHY-like effects lead to generalized stability conditions against collapse and phase separation. Moreover, we demonstrate that the stability of self-bound droplets is enhanced by interspecies correlations. The contribution to the energy of the quadratic fluctuations is shown to have negligible effects in the Bogoliubov approximation.

In recent years, as two-dimensional (2D) materials have been widely used in electronic devices, searching for 2D high superconducting transition temperature ((T_{c})) superconductors has also attracted great attentions. In this work, based on first-principles calculations and Eliashberg equation, the electronic structure, electron-phonon coupling (EPC) and possible superconductivity of alkali metal-deposited monolayer BC: MBC (M = Na, K) are studied. The results show that MBC (M = Na, K) are metallic and potential superconductors. The calculated EPC constants of MBC (M = Na, K) are 0.97 and 1.48, respectively. The strong coupling of MBC (M = Na, K) mainly origins from the coupling between electrons with the in-plane vibration modes of C and B atoms. The (T_{c}) of MBC (M = Na, K) are 34.1 K and 41.7 K, respectively, and the (T_{c}) of NaBC can be increased to 45.6 K under 2% biaxial tensile strain, and the (T_{c}) of KBC can be boosted to 53.8 K under 1% biaxial tensile strain. It is anticipated that the predicted monolayer MBC (M = Na, K) and its strained cases can be realized in future experiments.

In this study, we investigate the thermal properties of the relativistic Klein-Gordon oscillator with non-minimal coupling in one, two, and three dimensions within the framework of superstatistics theory. We focus on three distinct distributions: Gamma, Log-Normal, and F-distributions, each described by a specific probability density function (f(beta )). To compute the partition function, we apply the Euler-MacLaurin formula, incorporating the low-energy asymptotics approximation of superstatistics and accounting for the remainder term (R_{i}). Our study involves a detailed analysis of how entropy (S) and specific heat (C_{v}) vary with temperature (1/beta) and the universal parameter (q), based on the derived partition functions. The variations in these thermodynamic quantities are explored across different dimensionalities and statistical frameworks, providing insights into the interplay between statistical distributions and the thermal dynamics of the system. This approach allows us to understand the influence of non-equilibrium conditions and fluctuating temperature fields on the behavior of relativistic quantum systems. By extending the analysis to multiple dimensions and distribution types, we aim to offer a comprehensive view of how superstatistical distributions affect the thermodynamic properties of the Klein-Gordon oscillator, thus contributing to the broader understanding of thermal dynamics in relativistic systems.

Several experiments are currently carried out to measure the magnitude of the B mode polarization of the cosmic microwave background (CMB). It is a strong indicator of the presence of gravitational waves from the early universe inflationary epoch. As the average variations of the B mode components of the CMB are expected to be of the order of a few tens of nK or below, the detection of these polarized signals requires an ultrasensitive system. This article is focused on CMB detection at frequencies around the 150 GHz band of the electromagnetic spectrum, near the peak of the CMB 2.7K blackbody band of the EM spectrum. We propose a readout system for CMB cryogenic detection based on a software-defined radio (SDR) that uses frequency division multiplexing (FDM), a Goertzel channelizer and a radio frequency microwave SQUID multiplexer ((mu)MUX) working at the cryogenic temperatures of (approx) 320mK. These interfaces can be used to read an array of 1024 magnetic microbolometers (MMBs) as detectors that are photon-limited for CMB detection in the band of interest. As part of the requirements for these measurements, we introduce a design of the detection and read out chain and show its expected performance and potential implementation. The proposed system can read the desired number of detectors from an array in a modular way, which allows future expansions, and its frequency division multiplexing system improves the cooling capacity of the cryostat by minimizing the amount of active cryogenic electronics. In this article, we first describe this proposed FDM readout chain and then present noise measurements of a test implementation.