Journal of Low Temperature Physics最新文献

Electrons trapped on the surface of liquid helium is an extremely clean system which holds promise for a scalable qubit platform. However, the superfluid surface is not free from fluctuations which might cause the decay and dephasing of the electron’s quantized states. Understanding and mitigating these fluctuations is essential for the advancement of electrons-on-helium qubit technology. Some work has been recently done to investigate surface oscillations due to the mechanical vibration of the cryostat using a superconducting coplanar waveguide resonator. In the present work, we focus on a sub-hertz frequency range and observe a strong effect of surface oscillations on the temporal dynamics of the Rydberg transition of electrons confined in a microchannel trapping device. We suggest possible origin of such oscillations and find a reasonable agreement between the corresponding estimation of the oscillation frequency and the observed result.

The MIllimeter Sardinia radio Telescope Receiver based on Array of Lumped elements (MISTRAL) KIDs is a millimeter camera operating at 90GHz that was recently installed on the Sardinia Radio Telescope (SRT) as part of the SRT-HighFreq program, which aims to expand the capabilities of the radio telescope up to the W-band. After technical and scientific commissioning (2023–2024), MISTRAL will be open to proposals from scientists as a facility instrument. MISTRAL provides a wide 4’ field of view, sampled at a resolution of 12” with approximately 400 kinetic inductance detectors. The sky in the W-band is well explored by CMB experiments; however, their resolution is limited to about 1’. Using large single-dish radio telescopes like SRT or the Green Bank Telescope allows to probe angular scales down to 10–12”, allowing scientists to obtain new data and complementary information in multiple scientific cases. In this contribution, we will review observational perspectives and performance forecasts of MISTRAL, based on laboratory measurements of the noise properties, for selected scientific cases such as galactic science and high-resolution measurements of the Sunyaev–Zel’Dovich effect in galaxy clusters and in the cosmic web.

In this study, we investigate the behavior of non-relativistic quantum particles interacting with a modified Pöschl-Teller potential in the backdrop of a topological defect created by global monopoles. We derive the radial equation of the Schrödinger wave equation through a wave function ansatz and obtain an approximate (ell ne 0)-state eigenvalue solution by employing the Nikiforov-Uvarov method. Our analysis demonstrates that the presence of a global monopole affects both the energy eigenvalue and the wave functions of non-relativistic quantum particles, deviating from the behavior observed in flat space with this potential. Furthermore, we calculate the Shannon entropy for this quantum system and evaluate how the existence of the topological defect and potential influences it.

In this work an overview is given on experiments with surface electrons above the quantum solids hydrogen and neon. While two-dimensional ensembles of surface electrons on the quantum liquid superfluid helium have been studied already in great detail, investigations of electrons on quantum solids are rather sparse. Since recently electron-on-neon qubits have been shown to exhibit very long coherence times, there is a demand for understanding the conditions for a successful growth of thin solid neon films as a qubit substrate. Therefore, in this review also the triple point wetting phenomenon of the hydrogen isotopes and neon is discussed, which dominates the growth of solid films of these materials.

The influence of nonstoichiometry on the structural and magnetic properties of (hbox {Sr}_2hbox {FeMoO}_6) (SFMO) has been investigated by varying the ratio of Fe in polycrystalline samples. We demonstrate that changes in the Fe/Mo ratio can elevate the Curie temperature ((T_textrm{C})) in SFMO, even though the total magnetic moment is reduced at the same time. The discoveries of the stoichiometric imbalance between the cations Fe and Mo are discussed in the context of first-principles calculations on the electronic and magnetic structures of SFMO using the GGA+U method. Our theoretical results reveal that Fe deficiency reduces the (T_textrm{C}) due to the antiparallel alignment of Fe moments in Mo positions, which is consistent with experimental observations. In contrast, accurate (T_textrm{C}) trends for Fe excess are reproduced only by considering spin disorder, with both parallel and antiparallel Fe moment orientations. These insights provide a detailed understanding of the magnetic interactions in SFMO. Our findings lay the groundwork for developing innovative SFMO-based materials and emphasize the significance of stoichiometry control in optimizing SFMO properties.

Liquid helium cryogenic system is crucial for achieving low-temperature superconductivity in particle accelerator and controllable nuclear fusion devices. However, the heat conductivity of copper in the 4K region is 400–800 W m⁻¹ K⁻¹, which limits the performance of superconductivity system. The application of helium-based oscillating heat pipe (OHP) promotes this deficiency mitigation, with a maximum effective thermal conductivity (ETC) ranging from 4000 to 16,000 W m⁻¹ K⁻¹. Although numerous scholars have experimentally observed the maximum efficiency point of OHP, but its underlying mechanism remains unclear. In this study, a test rig for measuring the heat transfer performance and dynamic parameters of helium-based OHP in the 4K region was constructed. A numerical simulation method for the gas–liquid two-phase unsteady flow process in the OHP was established. The amplitude and period distribution of dynamic pressure fluctuations in OHP were analyzed. The correlation between its pressure fluctuations and heat transfer process was explored. Finally, the mechanism of the maximum efficiency point was revealed with the oscillating characteristics for helium-based OHP in the 4K region.

In this article, a novel DC-biased interface for multi-channel superconducting computers was designed, fabricated, and tested. Conventional interfaces for Josephson-CMOS memory rely on Josephson latching drivers (JLDs) or SQUID (Superconducting Quantum Interference Device) stacks to convert weak signals. However, SQUID stacks achieve high frequencies (tens of GHz) but produce only a few millivolts of output and occupy large areas, while JLDs provide higher output voltages (tens of millivolts) but require AC bias. To address these limitations, an interface based on SiGe BiCMOS (Silicon-Germanium Bipolar CMOS) technology was proposed, integrating the functions of JLDs and CMOS amplifiers into a single chip. Fabricated using a 130 nm SiGe BiCMOS process, the interface converts 200 µV to 1.2 V with a power consumption of only 386 µW per channel at 4.2 K. Low-frequency measurements demonstrated 21-channel signal conversion without the need for clock synchronization or additional amplifiers, significantly simplifying the cryogenic system. The proposed interface features key advantages, including DC bias, high gain, and asynchronous operation, making it a practical solution for superconductor–semiconductor signal conversion. While its maximum speed is currently limited, this interface represents a promising step toward scalable, energy-efficient multi-channel superconducting computers.

We observed surface X-ray diffraction from ⁴He submonolayers adsorbed on a single-surface graphite using synchrotron X-rays. Time evolutions of scattering intensities along the crystal truncation rod (CTR) were observed even after reaching the base low temperature in a selected condition of sample preparation. Our simulations for CTR scatterings based on the random double-layer model, in which helium atoms are distributed randomly in the first and second layers with a certain occupancy ratio, can consistently explain the observed intensity changes. These results support the scenario that He atoms are stratified initially as a nonequilibrium state and then relaxed into a uniform monolayer by surface diffusion, where the relaxation process was observed as a decrease in CTR scattering intensity. The observed time constant was, however, much longer than those estimated from quantum and thermal surface diffusions. This implies homogeneous processes in surface diffusions were strongly suppressed by local potentials in such as atomic steps or microcrystalline boundaries.

We used the method of electron spin resonance (ESR) to investigate the temperature-dependent recombination rate of H atoms in solid molecular hydrogen deuteride (HD). A 1.5 (mu)m thick solid molecular HD film was deposited at a rate of 2 monolayer/s, onto a gold surface maintained at T=1.5 K. H and D atoms were accumulated in the film by maintaining radio-frequency electric discharge above the film for 19 days. After further storage of the sample for 48 h, at T < 1 K, the D atom signal vanished. The concentration of H atoms was monitored as the sample was warmed stepwise from 1.1 K to 2.8 K. The recombination rate of H atoms in solid HD was found to be proportional to temperature in this range.

We have performed numerical calculations of the structure of the single-quantum vortex in superfluid (^3)He-A. The GPU-accelerated large-scale numerical simulation is performed in the Ginzburg-Landau model and resolves length scales of both coherence-length-sized hard core and dipolar-length-sized soft core of the vortex. The calculations support previously suggested qualitative structure of the vortex, recently named as eccentric fractional skyrmion, and provide numerical values for the vortex energy, sizes and locations of the hard and soft cores and highly-asymmetric flow profile of the vortex.