Characterization of two-level system noise for microwave kinetic inductance detector comprising niobium film on silicon substrate

A microwave kinetic inductance detector (MKID) is a cutting-edge superconducting detector. It comprises a resonator circuit constructed with a superconducting film on a dielectric substrate. To expand its field of application, it is important to establish a method to suppress the two-level system (TLS) noise that is caused by the electric fluctuations between the two energy states at the surface of the substrate. The electric field density can be decreased by expanding the strip width (S) and gap width from the ground plane (W) in the MKID circuit, allowing the suppression of TLS noise. However, this effect has not yet been confirmed for MKIDs made with niobium films on silicon substrates. In this study, we demonstrate its effectiveness for such MKIDs. We expanded the dimension of the circuit from (S, W) = (3.00 μm, 4.00 μm) to (S, W) = (5.00 μm, 23.7 μm), and achieved an increased suppression of 5.5 dB in TLS noise

Search for Dark Photon Dark Matter in the Mass Range 41--74 μeV\mu\mathrm{eV} using Millimeter-Wave Receiver and Radioshielding Box

Dark photons have been considered potential candidates for dark matter. The dark photon dark matter (DPDM) has a mass and interacts with electromagnetic fields via kinetic mixing with a coupling constant of $\chi$. Thus, DPDMs are converted into ordinary photons at metal surfaces. Using a millimeter-wave receiver set in a radioshielding box, we performed experiments to detect the conversion photons from the DPDM in the frequency range 10--18 GHz, which corresponds to a mass range 41--74 $\mu\mathrm{eV}$. We found no conversion photon signal in this range and set the upper limits to $\chi < (0.5\text{--}3.9) \times 10^{-10}$ at a 95% confidence level.Comment: 8 pages, 14 figure

Search for Dark Photon Dark Matter in the Mass Range 74-110 μeV with a Cryogenic Millimeter-Wave Receiver

ミリ波を用いたダークマター探索手法を確立. 京都大学プレスリリース. 2023-03-07.Thinking big and dark by starting small and light: Millimeter-wave technologies assist in examining 'light' dark matter. 京都大学プレスリリース. 2023-03-23.We search for the dark photon dark matter (DPDM) using a cryogenic millimeter-wave receiver. DPDM has a kinetic coupling with electromagnetic fields with a coupling constant of χ and is converted into ordinary photons at the surface of a metal plate. We search for signal of this conversion in the frequency range 18-26.5 GHz, which corresponds to the mass range 74-110 μeV/c². We observed no significant signal excess, allowing us to set an upper bound of χ<(0.3-2.0)×10⁻¹⁰ at 95% confidence level. This is the most stringent constraint to date and tighter than cosmological constraints. Improvements from previous studies are obtained by employing a cryogenic optical path and a fast spectrometer

Pointing calibration of GroundBIRD telescope using Moon observation data

Understanding telescope pointing (i.e., line of sight) is important for observing the cosmic microwave background (CMB) and astronomical objects. The Moon is a candidate astronomical source for pointing calibration. Although the visible size of the Moon (\ang{;30}) is larger than that of the planets, we can frequently observe the Moon once a month with a high signal-to-noise ratio. We developed a method for performing pointing calibration using observational data from the Moon. We considered the tilts of the telescope axes as well as the encoder and collimation offsets for pointing calibration. In addition, we evaluated the effects of the nonuniformity of the brightness temperature of the Moon, which is a dominant systematic error. As a result, we successfully achieved a pointing accuracy of \ang{;3.3}. This is one order of magnitude smaller than an angular resolution of \ang{;36}. This level of accuracy competes with past achievements in other ground-based CMB experiments using observational data from the planets.Comment: 18 pages, 17 figures, 3 table

High temperature structural and thermoelastic behaviour of mantle orthopyroxene: an in situ neutron powder diffraction study

The temperature induced structural evolution and thermoelastic behaviour of a natural (Pbca) orthopyroxene (Opx), with chemical formula M2(Mg0.856Ca0.025Fe2+ 0.119) M1(Mg0.957Fe2+ 0.011Fe3+ 0.016 Cr0.011Al0.005)Al0.032Si1.968O6, from a suite of high pressure ultramafic nodules of mantle origin, have been investigated by in-situ neutron powder diffraction at several temperatures starting from 1,200C down to 150C. Unit-cell parameter variations as a function of T show no phase transition within this temperature range. The volume thermal expansion coefficient, a = V\u20131(dV/dT)P0, varies linearly with T. The axial thermal expansion coefficients, aj = lj \u20131(dlj/dT)P0, increase non-linearly with T. The principal Lagrangian unit-strain coefficients (e//a, e//b, e//c), increase continuously with T. However, the orientation of the unit-strain ellipsoid appears to change with T. With decreasing T, the values of the unit-strain coefficients along the b and c axes tend to converge. The orientation at DeltaT = 1,080 C is maintained down to the lowest temperature (150 C). The two non-equivalent tetrahedral chains, TAnOA3n and TBnOB3n, are kinked differently. At room-T, the TBnOB3n chain is more strongly kinked by about 23\ub0 than the TAnOA3n chain. With increasing T, the difference decreases by 3\ub0 for the TBnOB3n chain. The intersite cation exchange reaction between M1 and M2 (Mg2+ and Fe2+) shows a slight residual order at 1,200 C followed by reordering with decreasing temperature although seemingly not with a definite progressive trend. At the lowest temperature reached (150 C), reordering has occurred with the same value of partitioning coefficient KD as that before heating. The absence of the expected phase transition is most likely due to the presence of minor amounts of Fe3+, Al, Ca and Cr which must play a crucial role on the thermoelastic behaviour and phase stability fields in natural Opx, with consequent important petrologic and geological implications