Observation of magnetic amplification using dark spins.

Quantum amplification enables the enhancement of weak signals and is of great importance for precision measurements, such as biomedical science and tests of fundamental symmetries. Here, we observe a previously unexplored magnetic amplification using dark noble-gas nuclear spins in the absence of pump light. Such dark spins exhibit remarkable coherence lasting up to 6 min and the resilience against the perturbations caused by overlapping alkali-metal gas. We demonstrate that the observed phenomenon, referred to as "dark spin amplification," significantly magnifies magnetic field signals by at least three orders of magnitude. As an immediate application, we showcase an ultrasensitive magnetometer capable of measuring subfemtotesla fields in a single 500-s measurement. Our approach is generic and can be applied to a wide range of noble-gas isotopes, and we discuss promising optimizations that could further improve the current signal amplification up to [Formula: see text] with [Formula: see text]Ne, [Formula: see text] with [Formula: see text]Xe, and [Formula: see text] with [Formula: see text]He. This work unlocks opportunities in precision measurements, including searches for ultralight dark matter with sensitivity well beyond the supernova-observation constraints.

Neural specialization with generalizable representations underlies children's cognitive development of attention.

From childhood to adulthood, the human brain develops highly specialized yet interacting neural modules that give rise to nuanced attention and other cognitive functions. Each module can specialize over development to support specific functions, yet also coexist in multiple neurobiological modes to support distinct processes. Advances in cognitive neuroscience have conceptualized human attention as a set of cognitive processes anchored in highly specialized yet interacting neural systems. The underlying mechanisms of how these systems interplay to support children's cognitive development of multiple attention processes remain unknown. Leveraging developmental functional magnetic resonance imaging with attention network test paradigm, we demonstrate differential neurocognitive development of three core attentional processes from childhood to adulthood, with alerting reaching adult-like level earlier, followed by orienting and executive attention with more protracted development throughout middle and late childhood. Relative to adults, young children exhibit immature specialization with less pronounced dissociation of neural systems specific to each attentional process. Children manifest adult-like distributed representations in the ventral attention and cingulo-opercular networks, but less stable and weaker generalizable representations across multiple processes in the dorsal attention network. Our findings provide insights into the functional specialization and generalization of neural representations scaffolding cognitive development of core attentional processes from childhood to adulthood. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Atypical child-parent neural synchrony is linked to negative family emotional climate and children's psychopathological symptoms.

[Correction Notice: An Erratum for this article was reported in Vol 79(2) of American Psychologist (see record 2024-62662-005). In the article "Atypical Child-Parent Neural Synchrony Is Linked to Negative Family Emotional Climate and Children's Psychopathological Symptoms," by Haowen Su, Christina B. Young, Zhuo Rachel Han, Jianjie Xu, Bingsen Xiong, Zisen Zhou, Jingyi Wang, Lei Hao, Zhi Yang, Gang Chen, and Shaozheng Qin (American Psychologist, 2024, Vol. 79, No. 2, pp. 210-224, https://doi.org/10.1037/amp0001173), Figure 2 and its caption were corrected to fix a mismatch between the r coefficients and scatterplots. The caption was changed from "(c) Child-parent hippocampal activity concordance was significantly higher for boundary than nonboundary event time series (Z = 2.30, p = .01). (d) Child-parent vmPFC activity concordance was marginally significantly higher for boundary than nonboundary time series (Z = -1.39, p = .08)" to "(c) Child-parent vmPFC activity concordance was marginally significantly lower for boundary than nonboundary time series (Z = -1.39, p = .08). (d) Child- parent hippocampal activity concordance was significantly higher for boundary than nonboundary event time series (Z = 2.30, p = .01)." In addition, in the second sentence of the second paragraph of the "Reduced Child-Parent vmPFC Connectivity With the Hippocampus Links to Negative Family Emotional Climate and Children's Internalizing Symptoms" section, "anxious/depressed" and "internalizing" were switched. All versions of this article have been corrected.] Family emotional climate is fundamental to children's well-being and mental health. Family environments filled with negative emotions may lead to increased psychopathological symptoms in the child through dysfunctional child-parent interactions. Single-brain paradigms have uncovered changes in brain systems and networks related to negative family environments, but how the neurobiological reciprocity between child and parent brains is associated with children's psychopathological symptoms remains unknown. Here, we first investigated the relation between family emotional climate and children's psychopathological symptoms in 395 child-parent dyads. Using a naturalistic movie-watching functional magnetic resonance imaging technique in a subsample of 50 child-parent dyads, we further investigated the neurobiological underpinnings of how family emotional climates are associated with children's psychopathological symptoms through child-parent neural synchrony. Children from negative family emotional climate experienced significantly more severe psychopathological symptoms. In comparison to child-stranger dyads, child-parent dyads exhibited higher intersubject correlations in the dorsal and ventral portions of the medial prefrontal cortex (mPFC), and greater concordance of activity with widespread regions critical for socioemotional skills. Critically, negative family emotional climate was associated with decreased intersubject functional correlation between the ventral-mPFC and the hippocampus during movie watching in child-parent dyads, which further accounted for higher children's internalizing symptoms. Together, our findings provide insights into the neurobiological mechanisms that negative family environments can cause and maintain psychopathological symptoms in children through atypical child-parent neural synchrony. This has important implications for a better understanding of how child-parent connections may mediate the relation between environmental risks and developmental outcomes. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Room-temperature wavelike exciton transport in a van der Waals superatomic semiconductor.

The transport of energy and information in semiconductors is limited by scattering between electronic carriers and lattice phonons, resulting in diffusive and lossy transport that curtails all semiconductor technologies. Using Re6Se8Cl2, a van der Waals (vdW) superatomic semiconductor, we demonstrate the formation of acoustic exciton-polarons, an electronic quasiparticle shielded from phonon scattering. We directly imaged polaron transport in Re6Se8Cl2 at room temperature, revealing quasi-ballistic, wavelike propagation sustained for a nanosecond and several micrometers. Shielded polaron transport leads to electronic energy propagation lengths orders of magnitude greater than in other vdW semiconductors, exceeding even silicon over a nanosecond. We propose that, counterintuitively, quasi-flat electronic bands and strong exciton-acoustic phonon coupling are together responsible for the transport properties of Re6Se8Cl2, establishing a path to ballistic room-temperature semiconductors.

Optical Imaging of Ultrafast Phonon-Polariton Propagation through an Excitonic Sensor.

Hexagonal boron nitride (hBN) hosts phonon polaritons (PhP), hybrid light-matter states that facilitate electromagnetic field confinement and exhibit long-range ballistic transport. Extracting the spatiotemporal dynamics of PhPs usually requires "tour de force" experimental methods such as ultrafast near-field infrared microscopy. Here, we leverage the remarkable environmental sensitivity of excitons in two-dimensional transition metal dichalcogenides to image PhP propagation in adjacent hBN slabs. Using ultrafast optical microscopy on monolayer WSe2/hBN heterostructures, we image propagating PhPs from 3.5 K to room temperature with subpicosecond and few-nanometer precision. Excitons in WSe2 act as transducers between visible light pulses and infrared PhPs, enabling visible-light imaging of PhP transport with far-field microscopy. We also report evidence of excitons in WSe2 copropagating with hBN PhPs over several micrometers. Our results provide new avenues for imaging polar excitations over a large frequency range with extreme spatiotemporal precision and new mechanisms to realize ballistic exciton transport at room temperature.

Ultrafast imaging of polariton propagation and interactions.

Semiconductor excitations can hybridize with cavity photons to form exciton-polaritons (EPs) with remarkable properties, including light-like energy flow combined with matter-like interactions. To fully harness these properties, EPs must retain ballistic, coherent transport despite matter-mediated interactions with lattice phonons. Here we develop a nonlinear momentum-resolved optical approach that directly images EPs in real space on femtosecond scales in a range of polaritonic architectures. We focus our analysis on EP propagation in layered halide perovskite microcavities. We reveal that EP-phonon interactions lead to a large renormalization of EP velocities at high excitonic fractions at room temperature. Despite these strong EP-phonon interactions, ballistic transport is maintained for up to half-exciton EPs, in agreement with quantum simulations of dynamic disorder shielding through light-matter hybridization. Above 50% excitonic character, rapid decoherence leads to diffusive transport. Our work provides a general framework to precisely balance EP coherence, velocity, and nonlinear interactions.

Search for exotic parity-violation interactions with quantum spin amplifiers.

Quantum sensing provides sensitive tabletop tools to search for exotic spin-dependent interactions beyond the standard model, which have attracted great attention in theories and experiments. Here, we develop a technique based on Spin Amplifier for Particle PHysIcs REsearch (SAPPHIRE) to resonantly search for exotic interactions, specifically parity-odd spin-spin interactions. The present technique effectively amplifies exotic interaction fields by a factor of about 200 while being insensitive to spurious magnetic fields. Our studies, using such a quantum amplification technique, explore the parity-violation interactions mediated by a new vector boson in the challenging parameter space (force range between 3 mm and 1 km) and set the most stringent constraints on axial-vector electron-neutron couplings, substantially improving previous limits by five orders of magnitude. Moreover, our constraints on axial-vector couplings between nucleons reach into a hitherto unexplored parameter space. The present constraints complement the existing astrophysical and laboratory studies on potential standard model extensions.

Limits on Axions and Axionlike Particles within the Axion Window Using a Spin-Based Amplifier.

Searches for the axion and axionlike particles may hold the key to unlocking some of the deepest puzzles about our Universe, such as dark matter and dark energy. Here, we use the recently demonstrated spin-based amplifier to constrain such hypothetical particles within the well-motivated "axion window" (10 µeV-1 meV) through searching for an exotic dipole-dipole interaction between polarized electron and neutron spins. The key ingredient is the use of hyperpolarized long-lived ^{129}Xe nuclear spins as an amplifier for the pseudomagnetic field generated by the exotic interaction. Using such a spin sensor, we obtain a direct upper bound on the product of coupling constants g_{p}^{e}g_{p}^{n}. The spin-based amplifier technique can be extended to searches for a wide variety of hypothetical particles beyond the standard model.

Floquet Spin Amplification.

Detection of weak electromagnetic waves and hypothetical particles aided by quantum amplification is important for fundamental physics and applications. However, demonstrations of quantum amplification are still limited; in particular, the physics of quantum amplification is not fully explored in periodically driven (Floquet) systems, which are generally defined by time-periodic Hamiltonians and enable observation of many exotic quantum phenomena such as time crystals. Here we investigate the magnetic-field signal amplification by periodically driven ^{129}Xe spins and observe signal amplification at frequencies of transitions between Floquet spin states. This "Floquet amplification" allows us to simultaneously enhance and measure multiple magnetic fields with at least one order of magnitude improvement, offering the capability of femtotesla-level measurements. Our findings extend the physics of quantum amplification to Floquet spin systems and can be generalized to a wide variety of existing amplifiers, enabling a previously unexplored class of "Floquet spin amplifiers".

Dark-Exciton Driven Energy Funneling into Dielectric Inhomogeneities in Two-Dimensional Semiconductors.

The optoelectronic and transport properties of two-dimensional transition metal dichalcogenide semiconductors (2D TMDs) are highly susceptible to external perturbation, enabling precise tailoring of material function through postsynthetic modifications. Here, we show that nanoscale inhomogeneities known as nanobubbles can be used for both strain and, less invasively, dielectric tuning of exciton transport in bilayer tungsten diselenide (WSe2). We use ultrasensitive spatiotemporally resolved optical scattering microscopy to directly image exciton transport, revealing that dielectric nanobubbles are surprisingly efficient at funneling and trapping excitons at room temperature, even though the energies of the bright excitons are negligibly affected. Our observations suggest that exciton funneling in dielectric inhomogeneities is driven by momentum-indirect (dark) excitons whose energies are more sensitive to dielectric perturbations than bright excitons. These results reveal a new pathway to control exciton transport in 2D semiconductors with exceptional spatial and energetic precision using dielectric engineering of dark state energetic landscapes.

Search for exotic spin-dependent interactions with a spin-based amplifier.

Development of new techniques to search for particles beyond the standard model is crucial for understanding the ultraviolet completion of particle physics. Several hypothetical particles are predicted to mediate exotic spin-dependent interactions between standard-model particles that may be accessible to laboratory experiments. However, laboratory searches are mostly conducted for static spin-dependent interactions, with a few experiments addressing spin- and velocity-dependent interactions. Here, we demonstrate a search for these interactions with a spin-based amplifier. Our technique uses hyperpolarized nuclear spins as an amplifier for pseudo-magnetic fields produced by exotic interactions by a factor of more than 100. Using this technique, we establish constraints on the spin- and velocity-dependent interactions between polarized neutrons and unpolarized nucleons for the force range of 0.03 to 100 meters, improving previous constraints by at least two orders of magnitude in partial force range. This technique can be further extended to investigate other exotic spin-dependent interactions.

Floquet maser.

The invention of the maser stimulated revolutionary technologies such as lasers and atomic clocks. Yet, realizations of masers are still limited; in particular, the physics of masers remains unexplored in periodically driven (Floquet) systems, which are generally defined by time-periodic Hamiltonians and enable observation of many exotic phenomena such as time crystals. Here, we investigate the Floquet system of periodically driven 129Xe gas under damping feedback and unexpectedly observe a multimode maser that oscillates at frequencies of transitions between Floquet states. Our findings extend maser techniques to Floquet systems and open avenues to probe Floquet phenomena unaffected by decoherence, enabling a previously unexplored class of maser sensors. As a first application, our maser offers the capability of measuring low-frequency (1 to 100 mHz) magnetic fields with subpicotesla-level sensitivity, which is substantially better than state-of-the-art magnetometers and can be applied to, for example, ultralight dark matter searches.