Journal of Low Temperature Physics最新文献

We propose a novel scheme of a directional quantum splitter using two two-level quantum dots (QDs), infinite and semi-infinite plasmonic waveguides, and theoretically illustrate the directional controllable routing properties, such as reflection and transfer spectra, in proposed model via real space approach when single photons are of entrance into the semi-infinite waveguide. We consider the reflection and transfer properties on controlling the impact of several parameters, such as inter-particle distance, coupling strength, detuning and so on. The characteristics of our investigation is that when the frequency of the incoming single photon are nearly similar to one of eigenfrequencies of an additional QD, our proposed the system acts as a directional quantum splitter with a high transfer ratio toward the specific path. That is, the incident single photons could be come out of only one side of infinite waveguide with the transfer rate of over 0.5 because the additional QD absorbs the energy of single photons through the coherent interaction. These properties could be unlocked new opportunities to realize the quantum communication networks and quantum computation systems based on practical single-photon switch or quantum logic gates.

The Simons Observatory (SO) is a cosmic microwave background (CMB) experiment located in the Atacama Desert in Chile that will make precise temperature and polarization measurements over six spectral bands ranging from 27 to 285 GHz. Three small aperture telescopes (SATs) and one large aperture telescope (LAT) will house (sim)60,000 detectors and cover angular scales between one arcminute and tens of degrees. We present the performance of the dichroic, low-frequency (LF) lenslet-coupled sinuous antenna transition-edge sensor (TES) bolometer arrays with bands centered at 27 and 39 GHz. The LF focal plane will primarily characterize Galactic synchrotron emission as a critical part of foreground subtraction from CMB data. We will discuss the design, optimization, and current testing status of these pixels.

We describe a pathfinder experiment named DEEPDISH (dark matter extended energy probe: dielectric infrared superconducting haloscope) to search unexplored regions of dark matter (DM) parameter space: first for dark photon DM and later for axion DM with the application of a magnetic field. The DM would convert to photons within an optical stack and subsequently be detected by a microwave kinetic inductance detector (MKID) array.

Achieving high spectral and spatial resolution of wide astrophysical objects in the X-ray band will be the main focus of the future X-ray space telescopes. We explore a new technological solution based on high impedance NbSi TES detectors ((sim )2 M(Omega )) enabling the transfer of the pre-amplification stage to higher temperatures (4 K) and the use of a 50 mK CMOS time-division multiplexer to reduce power dissipation at 50 mK. We present the design and first tests, down to 200 mK, of this CMOS ASIC eventually able to work down to 50 mK and multiplexing 16 high impedance NbSi TES detectors to one 4 K amplifier with a total power budget under 2 (mu )W. In parallel of this development we fabricated 4-by-4 NbSi pixel matrices to build a complete demonstrator (comprising the detector array, presented in another paper to be published, the multiplexing ASIC and the 4 K amplification stage). We aim at a multiplexing frame time of 48 (mu )s leaving 3 (mu )s for reading-out each high impedance pixel. The multiplexing ASIC embeds parasitic capacity compensation techniques.

The BeEST experiment is a precision laboratory search for physics beyond the standard model that measures the electron capture decay of (^7)Be implanted into superconducting tunnel junction (STJ) detectors. For Phase-III of the experiment, we constructed a continuously sampling data acquisition system to extract pulse shape and timing information from 16 STJ pixels offline. Four additional pixels are read out with a fast list-mode digitizer, and one with a nuclear MCA already used in the earlier limit-setting phases of the experiment. We present the performance of the data acquisition system and discuss the relative advantages of the different digitizers.

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.