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2024 Vol. 54, No. 7

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Physics
Freestanding oxide membranes: synthesis, tunable physical properties, and functional devices
Ao Wang, Jinfeng Zhang, Lingfei Wang
2024, 54(7): 0701. doi: 10.52396/JUSTC-2023-0103
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Abstract:
The study of oxide heteroepitaxy has been hindered by the issues of misfit strain and substrate clamping, which impede both the optimization of performance and the acquisition of a fundamental understanding of oxide systems. Recently, however, the development of freestanding oxide membranes has provided a plausible solution to these substrate limitations. Single-crystalline functional oxide films can be released from their substrates without incurring significant damage and can subsequently be transferred to any substrate of choice. This paper discusses recent advancements in the fabrication, adjustable physical properties, and various applications of freestanding oxide perovskite films. First, we present the primary strategies employed for the synthesis and transfer of these freestanding perovskite thin films. Second, we explore the main functionalities observed in freestanding perovskite oxide thin films, with special attention tothe tunable functionalities and physical properties of these freestanding perovskite membranes under varying strain states. Next, we encapsulate three representative devices based on freestanding oxide films. Overall, this review highlights the potential of freestanding oxide films for the study of novel functionalities and flexible electronics.
Balancing the minimum error rate and minimum copy consumption in quantum state discrimination
Boxuan Tian, Zhibo Hou, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo
2024, 54(7): 0704. doi: 10.52396/JUSTC-2023-0155
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Abstract:
Extracting more information and saving quantum resources are two main aims for quantum measurements. However, the optimization of strategies for these two objectives varies when discriminating between quantum states $ |\psi_0\rangle$ and $|\psi_1\rangle $ through multiple measurements. In this study, we introduce a novel state discrimination model that reveals the intricate relationship between the average error rate and average copy consumption. By integrating these two crucial metrics and minimizing their weighted sum for any given weight value, our research underscores the infeasibility of simultaneously minimizing these metrics through local measurements with one-way communication. Our findings present a compelling trade-off curve, highlighting the advantages of achieving a balance between error rate and copy consumption in quantum discrimination tasks, offering valuable insights into the optimization of quantum resources while ensuring the accuracy of quantum state discrimination.
On capped Higgs positivity cone
Dong-Yu Hong, Zhuo-Hui Wang, Shuang-Yong Zhou
2024, 54(7): 0705. doi: 10.52396/JUSTC-2023-0159
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Abstract:
The Wilson coefficients of the standard model effective field theory are subject to a series of positivity bounds. It has been shown that while the positivity part of the Ultraviolet (UV) partial wave unitarity leads to the Wilson coefficients living in a convex cone, further including the nonpositivity part caps the cone from above. For Higgs scattering, a capped positivity cone was obtained using a simplified, linear unitarity condition without utilizing the full internal symmetries of Higgs scattering. Here, we further implement stronger nonlinear unitarity conditions from the UV, which generically gives rise to better bounds. We show that, for the Higgs case in particular, while the nonlinear unitarity conditions per se do not enhance the bounds, the fuller use of the internal symmetries do shrink the capped positivity cone significantly.
Astronomy
On joint analysing XMM-NuSTAR spectra of active galactic nuclei
Jia-Lai Kang, Jun-Xian Wang
2024, 54(7): 0702. doi: 10.52396/JUSTC-2023-0160
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Abstract:
A recently released XMM-Newton note revealed a significant calibration issue between nuclear spectroscopic telescope array (NuSTAR) and XMM-Newton European Photon Imaging Camera (EPIC) and provided an empirical correction to the EPIC effective area. To quantify the bias caused by the calibration issue in the joint analysis of XMM-NuSTAR spectra and verify the effectiveness of the correction, in this work, we perform joint-fitting of the NuSTAR and EPIC-pn spectra for a large sample of 104 observation pairs of 44 X-ray bright active galactic nuclei (AGN). The spectra were extracted after requiring perfect simultaneity between the XMM-Newton and NuSTAR exposures (merging Good Time Intervals, GTIs from two missions) to avoid bias due to the rapid spectral variability of the AGN. Before the correction, the EPIC-pn spectra are systematically harder than the corresponding NuSTAR spectra by $\Delta \varGamma \sim 0.1 $, subsequently yielding significantly underestimated cutoff energy Ecut and the strength of reflection component R when performing joint-fitting. We confirm that the correction is highly effective and can commendably erase the discrepancy in best-fit Γ, Ecut, and R. We thus urge the community to apply the correction when joint-fitting XMM-NuSTAR spectra, but note that the correction is limited to 3–12 keV and therefore not applicable when the soft X-ray band data are included. Besides, we show that as merging GTIs from two missions would cause severe loss of NuSTAR net exposure time, in many cases, joint-fitting yields no advantage compared with utilizing NuSTAR data alone. We finally present a technical note on filtering periods of high background flares for XMM-Newton EPIC-pn exposures in the Small Window mode.
How is a black hole created from nothing?
Zhongchao Wu
2024, 54(7): 0703. doi: 10.52396/JUSTC-2024-0010
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Abstract:
Using the synchronous coordinates, the creation of a Schwarzschild black hole immersed in a de Sitter spacetime can be viewed as a coherent creation of a collection of timelike geodesics. The previously supposed conical singularities do not exist at the horizons of the constrained instanton. Instead, the unavoidable irregularity is presented as a non-vanishing second fundamental form elsewhere at the quantum transition 3-surface. The same arguments can be applied to charged, topological or higher dimensional black hole cases.
Engineering & Materials
Higher-order mode analysis for SOLEIL-type superconducting cavity
Xiyuan Chai, Qin Li, Yunpeng Xu, Yungai Tang, Mingsheng Tan, Cong-Feng Wu
2024, 54(7): 0706. doi: 10.52396/JUSTC-2023-0150
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Abstract:
A 499.8 MHz SOLEIL-type superconducting cavity was simulated and designed for the first time in this paper. The higher-order mode (HOM) properties of the cavity were investigated. Two kinds of coaxial HOM couplers were designed. Using 4 L-type and 4 T-type HOM couplers, the longitudinal impedance was suppressed to 3 kΩ, and the transverse impedance below 30 kΩ/m. The HOM damping requirements of Hefei Advanced Light Facility (HALF) were satisfied. This paper conducts an in-depth study on the radio frequency (RF) design, multipacting optimization, and thermal analysis of these coaxial couplers. Simulation results indicated that under operating acceleration voltage, the optimized couplers does not exhibit multiplicating or thermal breakdown phenomena. The cavity has the potential to reach a higher acceleration gradient.

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