Floquet Engineering to Overcome No-Go Theorem of Noisy Quantum Metrology.

Permitting a more precise measurement to physical quantities than the classical limit by using quantum resources, quantum metrology holds a promise in developing many revolutionary technologies. However, the noise-induced decoherence forces its superiority to disappear, which is called no-go theorem of noisy quantum metrology and constrains its application. We propose a scheme to overcome the no-go theorem by Floquet engineering. It is found that, by applying a periodic driving on the atoms of the Ramsey spectroscopy, the ultimate sensitivity to measure their frequency characterized by quantum Fisher information returns to the ideal t^{2} scaling with the encoding time whenever a Floquet bound state is formed by the system consisting of each driven atom and its local noise. Combining with the optimal control, this mechanism also allows us to retrieve the ideal Heisenberg-limit scaling with the atom number N. Our result gives an efficient way to avoid the no-go theorem of noisy quantum metrology and to realize high-precision measurements.

The Value of the Alvarado Score for the Diagnosis of Acute Appendicitis in Children: A Systematic Review and Meta-Analysis.

BACKGROUND: Relevant guidelines recommend the use of the Alvarado score (AS) to assist in the diagnosis of acute appendicitis (AA) in children. To provide reference evidence for the clinical application of AS, we performed a meta-analysis of studies related to the diagnostic accuracy of AS in children with AA. METHODS: We searched the relevant literature from databases including CNKI, WanFangdata, VIP, CBM, the Cochrane Library, PubMed, Embase, and Web of Science databases from the date of database creation to April 30, 2022, and screened them according to nadir criteria, followed by data extraction and then combined effect sizes to assess the accuracy of AS for diagnosis in children. RESULTS: Twenty-six studies involving 2579 cases were finally included, including 19 studies with Alvarado score and 8 studies with modified Alvarado Score (1 study included both Alvarado Score and modified Alvarado Score). The combined sensitivity (SE) of AS for diagnosing AA in children was 76.0% (95% CI 74.0-78.0%; I2 = 95.1%); combined specificity (SP) was 71.0% (95% CI 68.0-74.0%; I2 = 86.4%); combined positive likelihood ratio (LR+) was 2.43 (95% CI 1.92- 3.07; I2 = 78.7%); combined negative likelihood ratio (LR-) was 0.28 (95% CI 0.20-0.41; I2 = 94.2%); combined AUC = 0.8092, Q∗ = 0.7439; combined diagnostic ratio (DOR) was 8.96 (95% CI 5.65 -14.21; I2 = 76.2%). The combined effect size I2 was greater than 50% for all children with a modified AS diagnosis of AA, so all analyses used a random-effects model, which showed a combined SE of 87.0% (95% CI 85.0 - 88.0%; I2 = 85.5%); the combined SP was 47.0% (95% CI 43.0 - 51.0%. I2 = 88.7%); combined LR+ was 1.68 (95% CI 1.31-2.17; I2 = 85.9%); combined LR-was 0.28 (95% CI 0.20-0.39; I2 = 74.3%); combined AUC = 0.8672 and Q∗ = 0.7978. The combined DOR was 6.43 (95% CI 3.38-12.26; I2 = 80.0%). CONCLUSION: The results of this meta-analysis suggest that the accuracy of AS in diagnosing AA in children is moderate, and AS can be an auxiliary tool for the diagnosis of AA in children, relying on AS alone for the diagnosis of AA is not recommended; AS can be further improved scientifically to increase its diagnostic value.

Generating Stable Spin Squeezing by Squeezed-Reservoir Engineering.

As a genuine many-body entanglement, spin squeezing (SS) can be used to realize the highly precise measurement beyond the limit constrained by classical physics. Its generation has attracted much attention recently. It was reported that N two-level systems (TLSs) located near a one-dimensional waveguide can generate SS by using the mediation effect of the waveguide. However, a coherent driving on each TLS is used to stabilize the SS, which raises a high requirement for experiments. We here propose a scheme to generate stable SS resorting to neither the spin-spin coupling nor the coherent driving on the TLSs. Incorporating the mediation role of the common waveguide and the technique of squeezed-reservoir engineering, our scheme exhibits the advantages over previous ones in the scaling relation of the SS parameter with the number of the TLSs. The long-range correlation feature of the generated SS along the waveguide in our scheme may endow it with certain superiority in quantum sensing, e.g., improving the sensing efficiency of spatially unidentified weak magnetic fields.