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Recent experimental advance in creating dissipative couplings provides a new route for engineering exotic lattice systems and exploring topological dissipation. Using the spatial lattice of atomic spinwaves in a vacuum vapor cell, where purely dissipative couplings arise from diffusion of atoms, we experimentally realize a dissipative version of the Su-Schrieffer-Heeger (SSH) model. We construct the dissipation spectrum of the topological or trivial lattices via electromagnetically-induced-transparency (EIT) spectroscopy. The topological dissipation spectrum is found to exhibit edge modes within a dissipative gap. We validate chiral symmetry of the dissipative SSH couplings, and also probe topological features of the generalized dissipative SSH model. This work paves the way for realizing non-Hermitian topological quantum optics via dissipative couplings., 6 pages, 4 figures

Different categories of social calls may be used in a variety of behavioral contexts and may have different functions. Here, we show that Great Himalayan leaf-nosed bats emit two types of calls: bent upward frequency modulated (bUFM) calls emitted during agonistic interactions between two bats that have perched close to each other and stepped upward frequency modulated (sUFM) calls emitted by a roosting individual when a free-flying bat approached. There were significant differences in acoustic parameters between bUFM calls and sUFM calls. Moreover, we tested different choices of Hipposideros armiger to playback of bUFM calls and sUFM calls. The bats avoided the location of bUFM call playbacks independent of the simultaneous playback of echolocation pulses, silence, or sUFM calls. The bats also avoided approaching the side of the flight room where sUFM calls were broadcast when also presented with playbacks of echolocation pulses, but not when simultaneously presented with silence. The results suggest that bUFM calls may serve the function of territorial defense, while sUFM calls may convey warning information. Our results, therefore, imply that the two types of calls have different functions depending on behavioral context. These differences in function suggest that bats can detect context-dependent modifications of acoustic cues across the two types of social calls.

We introduce a procedure to generate supersinglets, the multipartite generalization of angular momentum singlet states. A supersinglet is defined as a total spin zero state consisting of $ N $ spin-$ j $ particles. They are highly entangled and have zero spin variance in any direction, and as such are potentially useful for quantum metrology. Our scheme is based on projective measurements that measure the collective spin of the whole spin ensemble. A local unitary rotation is applied conditionally on the measurement outcome, such as to maximize the probability of obtaining spin zero on the subsequent measurement. The sequence is repeated in the $ z $- and $ x $-basis until convergence is obtained towards the supersinglet state. Our sequence works regardless of the initial state, and no postselection is required. Due to the use of strong projective measurements, very fast convergence towards zero spin variance is obtained. We discuss an example implementation using quantum nondemolition measurements in atomic ensembles, and perform numerical simulations to demonstrate the procedure.

Background In genus Rhinolophus, species in the Rhinolophus philippinensis and R. macrotis groups are unique because the horseshoe bats in these group have relatively low echolocation frequencies and flight speeds compared with other horseshoe bats with similar body size. The different characteristics among bat species suggest particular evolutionary processes may have occurred in this genus. To study the adaptive evidence in the mitochondrial genomes (mitogenomes) of rhinolophids, especially the mitogenomes of the species with low echolocation frequencies, we sequenced eight mitogenomes and used them for comparative studies of molecular phylogeny and adaptive evolution. Results Phylogenetic analysis using whole mitogenome sequences produced robust results and provided phylogenetic signals that were better than those obtained using single genes. The results supported the recent establishment of the separate macrotis group. The signals of adaptive evolution discovered in the Rhinolophus species were tested for some of the codons in two genes (ND2 and ND6) that encode NADH dehydrogenases in oxidative phosphorylation system complex I. These genes have a background of widespread purifying selection. Signals of relaxed purifying selection and positive selection were found in ND2 and ND6, respectively, based on codon models and physicochemical profiles of amino acid replacements. However, no pronounced overlap was found for non-synonymous sites in the mitogenomes of all the species with low echolocation frequencies. A signal of positive selection for ND5 was found in the branch-site model when R. philippinensis was set as the foreground branch. Conclusions The mitogenomes provided robust phylogenetic signals that were much more informative than the signals obtained using single mitochondrial genes. Two mitochondrial genes that encoding proteins in the oxidative phosphorylation system showed some evidence of adaptive evolution in genus Rhinolophus and the positive selection signals were tested for ND5 in R. philippinensis. These results indicate that mitochondrial protein-coding genes were targets of adaptive evolution during the evolution of Rhinolophus species, which might have contributed to a diverse range of acoustic adaptations in this genus.

In Drosophila ovary, niche is composed of somatic cells, including terminal filament cells (TFCs), cap cells (CCs) and escort cells (ECs), which provide extrinsic signals to maintain stem cell renewal or initiate cell differentiation. Niche establishment begins in larval stages when terminal filaments (TFs) are formed, but the underlying mechanism for the development of TFs remains largely unknown. Here we report that transcription factor longitudinals lacking (Lola) is essential for ovary morphogenesis. We showed that Lola protein was expressed abundantly in TFCs and CCs, although also in other cells, and lola was required for the establishment of niche during larval stage. Importantly, we found that knockdown expression of lola induced apoptosis in adult ovary, and that lola affected adult ovary morphogenesis by suppressing expression of Regulator of cullins 1b (Roc1b), an apoptosis-related gene that regulates caspase activation during spermatogenesis. These findings significantly expand our understanding of the mechanisms controlling niche establishment and adult oogenesis in Drosophila.

This study was performed to investigate the biocompatibility (BC), magnetothermal effect, and DNA binding biological characteristics of manganese zinc ferrite nanoparticles (Mn0.6Zn0.4Fe2O4-NPs (MZF-NPs)) coated with pegylated manganese (PEG-MZF-NPs). Their functions as gene transfer carrier for gene therapy and magnetic medium for tumor hyperthermia were also explored. The manganese zinc ferrite nanoparticles were synthesized through high temperature cracking, and their characterizations were discovered. Hemolysis test and MTT assay were performed to evaluate biocompatibility, and their self-heating effects in the alternating magnetic field were investigated. PEG-MZF-NPs with different concentrations were measured by using 7.0 T Micro-MR scanner (MRI) to calculate the T2 value and r2 relaxation rate of each sample. The CD44-shRNA plasmids were constructed, and their ability to bind PEG-MZF-NPs were examined. The DNA release from PEG-MZF-NP/DNA complex and protection of DNA from nuclease digestion were also detected. After CD44-shRNA-EGFP were transfected into the ovarian cancer SK-OV-3 cells by using PEG-MZF-NPs as carriers, the transfection efficiency was detected by a flow cytometer and expression of CD44 mRNA and protein in cells was detected using RT-PCR and Western blot, respectively. We successfully prepared PEG-MZF-NPs with favorable dispersity, magnetic responsiveness, and BC. Typically, the excellent magnetothermal effect can be used for a tumor magnetothermal therapeutic study. In vitro MRI showed the application potential for being magnetic resonance T2 relaxation contrast agents and the possibility to achieve goal of integration of targeting diagnosis and treatment. The CD44-shRNA plasmids have been successfully constructed and concluded that PEG-MZF-NPs may serve as gene transfer carriers for gene therapy.

The objective of this work was to investigate the effect of boletus polysaccharide (BPS) on diabetic hepatopathy in streptozotocin (STZ)–induced type 2 diabetes mellitus (T2DM) rats for the first time. The rats were fed with high-fat diet (HFD) for 4 weeks and induced with STZ by a single intraperitoneal injection to develop T2DM model. The HFD was given continually for another 4 weeks after diabetes induction, following the drugs of BPS (400 mg/kg bw/day) infused to stomach of rats once a day. After the administration, blood was drawn from the posterior orbital venous plexus of the inner canthus and the rats were then sacrificed. The blood glucose and lipid, alanine transaminase (ALT) and aspartate transaminase (AST) were detected immediately. Besides, their livers were dissected for biochemical and histopathological assays. And the levels of malonaldehyde, glutathione and antioxidant enzymes in liver were detected. In addition, histopathological examinations of liver were performed to verify the liver injury. The expressions of NF-κB, TNF-α, SREBP1c, and CYP7A1 were test to trace out the mechanistic pathways. Compared with T2DM model group, the blood glucose, TC, TG, ALT, AST, and MDA and so on were significantly reduced, and CAT, SOD, GSH, GPx were significantly increased in the rats treated with BPS. The histopathological examination showed the liver injury in BPS treated rats was alleviated. The expressions of SREBP1c, NF-κB and TNF-α were significantly decreased, and the expressions of CYP7A1 was significantly increased. All these experimental findings demonstrate that BPS exhibited antidiabetic effects rats possibly through its inhibition of oxidative stress and inflammation, supporting that BPS has a promising therapeutic effect in the treatment of diabetic hepatopathy in rats.

We experimentally demonstrate tunable non-Hermitian coupling in an atomic-vapor cell where atomic coherences in different optical channels are dissipatively coupled through atomic motion. Introducing a far-detuned light wall in the reservoir between the optical channels, we decorate the inter-channel coupling term so that it can be switched from dissipative to coherent. The tunable non-Hermiticity is then confirmed through measurements of the inter-channel light transport where the light-wall-induced phase shift is directly probed. Based on the tunable non-Hermiticity, we further discuss an exemplary scheme in which our setup can serve as a building block for the experimental study of exotic non-Hermitian criticality.

If one has access to information about a quantum system both before and after a measurement, the usual remit of Heisenberg uncertainty relation (HUR) does not apply. Here, we theoretically and experimentally demonstrate that, in such a scenario, one can retrodict position and momentum measurements without being limited by HUR. The experiment uses a large ensemble of 10^11 atoms in a macroscopic vapor cell, and the results may be applicable for quantum state estimation and sensing, especially for sensitive magnetometers equally capable of measuring the amplitude and phase of an RF magnetic field both below the standard quantum limit.

In quantum mechanics, the Heisenberg uncertainty relation presents an ultimate limit to the precision by which one can predict the outcome of position and momentum measurements on a particle. Heisenberg explicitly stated this relation for the prediction of “hypothetical future measurements”, and it does not describe the situation where knowledge is available about the system both earlier and later than the time of the measurement. Here, we study what happens under such circumstances with an atomic ensemble containing 1011 rubidium atoms, initiated nearly in the ground state in the presence of a magnetic field. The collective spin observables of the atoms are then well described by canonical position and momentum observables, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\hat{x}}_{\text{A}}$$\end{document}x^A and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\hat{p}}_{\text{A}}$$\end{document}p^A that satisfy \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$[{\hat{x}}_{\text{A}},{\hat{p}}_{\text{A}}]=i\hslash$$\end{document}[x^A,p^A]=iℏ. Quantum non-demolition measurements of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\hat{p}}_{\text{A}}$$\end{document}p^A before and of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\hat{x}}_{\text{A}}$$\end{document}x^A after time t allow precise estimates of both observables at time t. By means of the past quantum state formalism, we demonstrate that outcomes of measurements of both the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\hat{x}}_{\text{A}}$$\end{document}x^A and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\hat{p}}_{A}$$\end{document}p^A observables can be inferred with errors below the standard quantum limit. The capability of assigning precise values to multiple observables and to observe their variation during physical processes may have implications in quantum state estimation and sensing., If we have access to information about a quantum system both before and after a measurement, we are not in the usual remit of the Heisenberg uncertainty principle anymore. Here, the authors demonstrate that, in such a scenario, one can retrodict position and momentum measurements without being limited by HUR.

It has been evidenced that liver cancer stem cells (LCSCs) are to blame hepatocellular carcinoma (HCC) occurrence, development, metastasis, and recurrence. Using iron-platinum nanoparticles (FePt-NPs) as a carrier and CD133 antigen as a target, a new strategy to targetly kill LCSCs by integrating HSV-TK suicide gene, 131I nuclide irradiation, and magnetic fluid hyperthermia (MFH) together was designed and investigated in the present study. The results showed that FePt-NPs modified with PEI (PEI-FePt-NPs) could bind with DNA, and the best binding ratio was 1 : 40 (mass ratio). Moreover, DNA binding to PEI-FePt-NPs could refrain from Dnase1 enzyme digestion and could release under certain conditions. LCSCs (CD133+ Huh-7 cells) were transfected with pHRE-Egr1-HSV-TK by PEI-FePt-NPs, and the transfection efficiency was 53.65±3.40%. These data showed a good potential of PEI-FePt-NPs as a gene transfer carrier.131I was labeled with anti-CD133McAb in order to facilitate therapy targeting. The combined intervention of pHRE-Egr1-HSV-TK/anti-CD133McAb-131I/MFH mediated by PEI-FePt-NPs could greatly inhibit LCSCs’ growth and induce cell apoptosis in vitro, significantly higher than any of the individual interventions (p<0.05). This study offers a practicable idea for LCSC treatment, and PEI-FePt-NPs may act as novel nonviral gene vectors and a magnetic induction medium.

Nature | Vol 581 | 14 May 2020 | 159ArticleSpin squeezing of 1011 atoms by prediction and retrodiction measurementsHan Bao1, Junlei Duan1, Shenchao Jin1, Xingda Lu1, Pengxiong Li1, Weizhi Qu1, Mingfeng Wang1,2, Irina Novikova3, Eugeniy E. Mikhailov3, Kai-Feng Zhao4, Klaus Mølmer5 ✉, Heng Shen6,7 ✉ & Yanhong Xiao1,6 ✉The measurement sensitivity of quantum probes using N uncorrelated particles is restricted by the standard quantum limit1, which is proportional to N1/. This limit, however, can be overcome by exploiting quantum entangled states, such as spin-squeezed states2. Here we report the measurement-based generation of a quantum state that exceeds the standard quantum limit for probing the collective spin of 1011 rubidium atoms contained in a macroscopic vapour cell. The state is prepared and verified by sequences of stroboscopic quantum non-demolition (QND) measurements. We then apply the theory of past quantum states3,4 to obtain spin state information from the outcomes of both earlier and later QND measurements. Rather than establishing a physically squeezed state in the laboratory, the past quantum state represents the combined system information from these prediction and retrodiction measurements. This information is equivalent to a noise reduction of 5.6 decibels and a metrologically relevant squeezing of 4.5 decibels relative to the coherent spin state. The past quantum state yields tighter constraints on the spin component than those obtained by conventional QND measurements. Our measurement uses 1,000 times more atoms than previous squeezing experiments5–10, with a corresponding angular variance of the squeezed collective spin of 4.6 × 10−13 radians squared. Although this work is rooted in the foundational theory of quantum measurements, it may find practical use in quantum metrology and quantum parameter estimation, as we demonstrate by applying our protocol to quantum enhanced atomic magnetometry.

Spin-squeezed state is a many-body entangled state of great interest for precision measurements. Although the absolute sensitivity at the standard quantum limit is better for a larger atom number, the greater dominance of classical noises over atom projection noise makes it harder to achieve spin squeezing. Here, we show both theoretically and experimentally that adiabatic pulse control of the pump field in state preparation is indispensable to sufficient noise suppression, which is the prerequisite for spin squeezing. This technique is generally applicable to spin-squeezing experiments involving a large ensemble and is thus of significance for quantum metrology applications.

An atomic magnetometer detects atomic responses to the magnetic field, and its sensitivity is ultimately limited by quantum noise fluctuations. For magnetometers based on nonlinear magneto-optical rotation (NMOR), the possible concurrent generation of light squeezing due to polarization self-rotation complicates the optimization for magnetometer sensitivity. Here, we study NMOR magnetometers with frequency-modulated light in a paraffin coated 87Rb vapor cell in the low and high power regimes corresponding to situations with and without light squeezing, respectively, with detection observables being different Stokes components reflecting the magnetic-field-induced atomic circular dichroism or birefringence. We found that the overall best sensitivity is achieved in the low power regime when there is no light squeezing and for circular dichroism measurement. We provide a general insight on parameter optimization and the choice of detection observables, from the delicate trade-off between the atomic responses and the noises including the technical and quantum optical noises. Our results could have practical significance in optical atomic magnetometry.

Spatially splitting nonclassical light beams is in principle prohibited due to noise contamination during beam splitting. We propose a platform based on thermal motion of atoms to realize spatial multiplexing of squeezed light. Light channels of separate spatial modes in an anti-relaxation coated vapor cell share the same long-lived atomic coherence jointly created by all channels through the coherent diffusion of atoms which in turn enhances individual channel's nonlinear process responsible for light squeezing. Consequently, it behaves as squeezed light in one optical channel transferring to other distant channels even with laser powers below the threshold for squeezed light generation. An array of squeezed light beams was created with low laser power $\sim\text{mW}$. This approach holds great promise for applications in multi-node quantum network and quantum enhanced technologies such as quantum imaging and sensing., 5 pages, 5 figures

Animal vocalizations experience pressures from ecological conditions, but their diversification may be constrained by morphology and evolutionary history. To date, the relative contribution of these factors to acoustic diversity is unclear in most vertebrate groups. Bats constitute one of the most speciose and diverse mammal groups, and most bat species rely on vocalizations for orientation, foraging, and communication. Here, we examine echolocation calls of 207 bat species across 17 families to weigh the relative role of phylogenetic inertia, natural selection, and morphological constraints in shaping echolocation call diversity in bats. Using the large dataset, we confirm that foraging guilds, phylogenetic relationships, and forearm length account for the majority of the variation in call parameters among bats. Foraging guilds play a major role in influencing call parameters in low duty cycle bats. At the family level, the variation in call parameters is primarily explained by differences in body size and phylogenetic relationships. Path analyses indicate that phylogeny determines call output not only by their direct effect on call parameters but also by having an indirect effect via foraging guilds and body size. These results demonstrate that natural selection, phylogenetic constraint, and morphological constraint shape echolocation call divergence in bats. Our findings underscore the importance of both adaptive and non-adaptive mechanisms underlying the evolution of echolocation calls in bats. Ecology, morphology, and evolutionary history are tightly coupled; therefore, disentangling the relative strength of these components underlying acoustic diversity is a big challenge. Using a large dataset of bats, we assess the influence of phylogeny, ecology, and body size on echolocation call parameters. We conclude that ecological selection, phylogenetic constraint, and morphological constraint play a crucial role in shaping echolocation call divergence among bats. This study expands our knowledge of the relative contribution of adaptive and maladaptive mechanisms to echolocation call diversity at different taxonomic levels in bats.

Recent advances in non-Hermitian physical systems have led to numerous novel optical phenomena and applications. Such systems typically involve gain and loss associated with dissipative coupling to the environment, hence interesting quantum phenomena are often washed out, rendering most realizations classical. Here, in contrast, we propose to employ dissipative coupling to enable quantum correlations. In particular, two distant optical channels are judiciously designed to couple to and exchange information with a common reservoir environment, under an anti-parity-time-symmetric setting of hot but coherent atoms. We realize a non-Hermitian nonlinear phase sensitive parametric process, where atomic motion leads to quantum correlations between two distant light beams in the symmetry-unbroken phase. This Letter starts a new route to exploring the non-Hermitian quantum phenomena by bridging the fields of atomic physics, non-Hermitian optics, quantum information, and reservoir engineering. Potential applications include novel quantum light sources, quantum information processing and sensing, and generalization to correlated many-body systems.

For analysis of vocal syntax, accurate classification of call sequence structures in different behavioural contexts is essential. However, an effective, intelligent program for classifying call sequences from numerous recorded sound files is still lacking. Here, we employed three machine learning algorithms (logistic regression, support vector machine and decision trees) to classify call sequences of social vocalizations of greater horseshoe bats (Rhinolophus ferrumequinum) in aggressive and distress contexts. The three machine learning algorithms obtained highly accurate classification rates (logistic regression 98%, support vector machine 97% and decision trees 96%). The algorithms also extracted three of the most important features for the classification: the transition between two adjacent syllables, the probability of occurrences of syllables in each position of a sequence, and the characteristics of a sequence. The results of statistical analysis also supported the classification of the algorithms. The study provides the first efficient method for data mining of call sequences and the possibility of linguistic parameters in animal communication. It suggests the presence of song-like syntax in the social vocalizations emitted within a non-breeding context in a bat species.

The measurement sensitivity of quantum probes using N uncorrelated particles is restricted by the standard quantum limit

Why some species are widespread across continents while others are confined geographically remains an open question in ecology and biogeography. Previous research has attempted to explain interspecific variation in geographic range size based on differences in dispersal ability. However, the relationship between dispersal ability and geographic range size remains uncertain, particularly in mammals. The goal of this study is to test whether geographic range size can be predicted by dispersal capacity among vespertilionid bats within a phylogenetic comparative framework. We integrated a large dataset on range area, longitudinal extent, wing morphology (a proxy for dispersal ability), migratory habit, and biogeographic realm across 126 vespertilionid bat species. We used phylogenetic regressions to disentangle the associations between these predictor factors and species range size while controlling for the effects of migration and biogeographic realm. Our analyses revealed that bat species with higher wing loading exhibit larger distribution ranges than those with lower wing loading, and that the size of geographic ranges was associated with wing aspect ratio in bats. These results highlight the relationship between wing morphology and range size in flying mammals, and suggest a role of dispersal capacity in shaping species’ geographic distributions.

Spin squeezing can improve atomic precision measurements beyond the standard quantum limit (SQL), and unitary spin squeezing is essential for improving atomic clocks. We report substantial and nearly unitary spin squeezing in ^{171}Yb, an optical lattice clock atom. The collective nuclear spin of ∼10^{3} atoms is squeezed by cavity feedback, using light detuned from the system's resonances to attain unitarity. The observed precision gain over the SQL is limited by state readout to 6.5(4) dB, while the generated states offer a gain of 12.9(6) dB, limited by the curvature of the Bloch sphere. Using a squeezed state within 30% of unitarity, we demonstrate an interferometer that improves the averaging time over the SQL by a factor of 3.7(2). In the future, the squeezing can be simply transferred onto the optical-clock transition of ^{171}Yb.

Species delimitation and evolutionary reconstruction remain challenging for non-model species that have experienced reticulate evolution and exhibit conflicting patterns of differentiation among multiple lines of evidence, such as mitochondrial and nuclear data and phenotypes. Here, we applied an integrative taxonomic approach to a case study of Rhinolophus macrotis complex, whose taxonomic status remains controversial, to provide insight into the systematics and evolutionary history of these species. By integrating traditional genetic markers with different modes of inheritance, genome-wide SNPs as well as phenotypic characteristics, we clarified the presence of three closely related species, R. episcopus, R. siamensis, and R. osgoodi, within this complex, and proposed a new taxonomic treatment for R. osgoodi. Our results suggested that hybridization and introgression are the main causes of low mtDNA divergence in these species. Combined with the demographic inference, we deduced that glacial-interglacial cycles drove geographic isolation and secondary contacts of these species, then promoted hybridization and lineage fusion among them, finally resulting in a reticulate evolutionary pattern. Overall, our study highlights the importance of combining multiple types of data to delimit species, especially those with conserved morphology, and to reveal the sophisticated processes of speciation.

Weak measurement (WM) with state pre- and post-selection can amplify otherwise undetectable small signals and thus promise great potentials in precision measurements. Although frequency measurements offer the hitherto highest precision owing to stable narrow atomic transitions, it remains a long-standing interest to develop new schemes to further escalate their performance. Here, we propose and demonstrate a WM-enhanced spectroscopy technique which is capable of narrowing the resonance to 0.1 Hz in a room-temperature atomic vapor cell. Potential of this technique for precision measurement is demonstrated through weak magnetic field sensing. By judiciously pre- and post-selecting frequency-modulated input and output optical states in a nearly-orthogonal manner, a sensitivity of $\text{7 fT/}\sqrt{\text{Hz}}$ near DC is achieved, using only one laser beam of $\text{7 }\text{\mu W}$ power. Additionally, our results extend the WM framework to a non-Hermitian Hamiltonian, and shed new light in metrology and bio-magnetic field sensing applications., Comment: 11 pages, 5 figures