Can a gas of spin-up and spin-down fermions become ferromagnetic because of repulsive interactions? We addressed this question, for which there is not yet a definitive theoretical answer, in an ...experiment with an ultracold two-component Fermi gas. The observation of nonmonotonic behavior of lifetime, kinetic energy, and size for increasing repulsive interactions provides strong evidence for a phase transition to a ferromagnetic state. Our observations imply that itinerant ferromagnetism of delocalized fermions is possible without lattice and band structure, and our data validate the most basic model for ferromagnetism introduced by Stoner.
The efficient delivery of light energy is a prerequisite for the non-invasive imaging and stimulating of target objects embedded deep within a scattering medium. However, the injected waves ...experience random diffusion by multiple light scattering, and only a small fraction reaches the target object. Here, we present a method to counteract wave diffusion and to focus multiple-scattered waves at the deeply embedded target. To realize this, we experimentally inject light into the reflection eigenchannels of a specific flight time to preferably enhance the intensity of those multiple-scattered waves that have interacted with the target object. For targets that are too deep to be visible by optical imaging, we demonstrate a more than tenfold enhancement in light energy delivery in comparison with ordinary wave diffusion cases. This work will lay a foundation to enhance the working depth of imaging, sensing and light stimulation.
Imaging an object embedded within a scattering medium requires the correction of complex sample-induced wave distortions. Existing approaches have been designed to resolve them by optimizing signal ...waves recorded in each 2D image. Here, we present a volumetric image reconstruction framework that merges two fundamental degrees of freedom, the wavelength and propagation angles of light waves, based on the object momentum conservation principle. On this basis, we propose methods for exploiting the correlation of signal waves from volumetric images to better cope with multiple scattering. By constructing experimental systems scanning both wavelength and illumination angle of the light source, we demonstrated a 32-fold increase in the use of signal waves compared with that of existing 2D-based approaches and achieved ultrahigh volumetric resolution (lateral resolution: 0.41 Formula: see text, axial resolution: 0.60 Formula: see text) even within complex scattering medium owing to the optimal coherent use of the broad spectral bandwidth (225 nm).
In many complex physical phenomena such as wave propagation in scattering media, the process of interest often cannot be easily distinguished from other processes because only the total combined ...process is accessible. This makes it difficult to extract the precise knowledge of each subprocess. Here, we derive an analytic expression describing the way the eigenchannel coupling of the total process distributes its energy to the individual subprocesses, with only partial information on each subprocess such as the average eigenvalue 〈τ〉 and enhancement factor η. We found that the ratio of (η - 1)〈τ〉 between two subprocesses is a critical parameter determining the preferable subprocess in the energy coupling. This work provides a new analytic framework for understanding the effect of wavefront shaping in the control of wave propagation in disordered media.
In complex media, light waves are diffused both in space and time due to multiple light scattering, and its intensity is attenuated with the increase of propagation depth. In this paper, we propose ...an iterative wavefront shaping method for enhancing time-gated reflection intensity, which leads to efficient light energy delivery to a target object embedded in a highly scattering medium. We achieved an over 10 times enhancement of reflectance at the specific flight time and demonstrated the focusing of light energy to the target object. Since the proposed method does not require reflection matrix measurement, it will be highly suited to samples in mechanically dynamic conditions.
Light waves propagating through complex biological tissues are spatially spread by multiple light scattering, and this spread limits the working depth in optical bioimaging, phototherapy, and ...optogenetics. Here, we propose the iterative phase conjugation of time-gated backscattered waves for enhancing the light energy delivered to a target object embedded in a scattering medium. We demonstrate the enhancement of light energy delivered to a target object hidden behind a 200-µm-thick mouse skull by more than ten times in comparison with the initial random input. The maximum enhancement was reached in only 10 iterations, more than a hundred times smaller than existing methods based on either a time-gated reflection matrix or iterative feedback optimization of the time-gated reflection intensity. Consequently, the proposed method is less sensitive to sample perturbations. Furthermore, the number of images required for optimization remained almost unchanged with an increase in the illumination area, unlike existing methods, where the convergence time scales with the illumination area. The proposed method provides high operation speed over a wide illumination area, which can facilitate the use of wavefront shaping in practical applications.
Cav1.3 has been suggested to mediate hippocampal neurogenesis of adult mice and contribute to hippocampal-dependent learning and memory processes. However, the mechanism of Cav1.3 contribution in ...these processes is unclear. Here, roles of Cav1.3 of mouse dorsal hippocampus during newborn cell development were examined. We find that knock-out (KO) of Cav1.3 resulted in the reduction of survival of newborn neurons at 28 days old after mitosis. The retroviral eGFP expression showed that both dendritic complexity and the number and length of mossy fiber bouton (MFB) filopodia of newborn neurons at ≥ 14 days old were significantly reduced in KO mice. Both contextual fear conditioning (CFC) and object-location recognition tasks were impaired in recent (1 day) memory test while passive avoidance task was impaired only in remote (≥ 20 days) memory in KO mice. Results using adeno-associated virus (AAV)-mediated Cav1.3 knock-down (KD) or retrovirus-mediated KD in dorsal hippocampal DG area showed that the recent memory of CFC was impaired in both KD mice but the remote memory was impaired only in AAV KD mice, suggesting that Cav1.3 of mature neurons play important roles in both recent and remote CFC memory while Cav1.3 in newborn neurons is selectively involved in the recent CFC memory process. Meanwhile, AAV KD of Cav1.3 in ventral hippocampal area has no effect on the recent CFC memory. In conclusion, the results suggest that Cav1.3 in newborn neurons of dorsal hippocampus is involved in the survival of newborn neurons while mediating developments of dendritic and axonal processes of newborn cells and plays a role in the memory process differentially depending on the stage of maturation and the type of learning task.
Shaping the wavefront of an incident wave to a complex scattering medium has demonstrated interesting possibilities, such as sub-diffraction wave focusing and light energy delivery enhancement. ...However, wavefront shaping has mainly been based on the control of transmitted waves that are inaccessible in most realistic applications. Here, we investigate the effect of maximizing the backscattered waves at a specific flight time on wave propagation dynamics and energy transport. We find both experimentally and numerically that the maximization at a short flight time focuses waves on the particles constituting the scattering medium, leading to the attenuation of the wave transport. On the contrary, maximization at a long flight time induces constructive wave interference inside the medium and thus enhances wave transport. We provide a theoretical model that explains this interesting transition behavior based on wave correlation. Our study provides a fundamental understanding of the effect of wave control on wave dynamics inside scattering medium.
Compensation of sample-induced optical aberrations is crucial for visualizing microscopic structures deep within biological tissues. However, strong multiple scattering poses a fundamental limitation ...for identifying and correcting the tissue-induced aberrations. Here, we introduce a label-free deep-tissue imaging technique termed dimensionality reduction adaptive-optical microscopy (DReAM) to selectively attenuate multiple scattering. We established a theoretical framework in which dimensionality reduction of a time-gated reflection matrix can attenuate uncorrelated multiple scattering while retaining a single-scattering signal with a strong wave correlation, irrespective of sample-induced aberrations. We performed mouse brain imaging in vivo through the intact skull with the probe beam at visible wavelengths. Despite the strong scattering and aberrations, DReAM offered a 17-fold enhancement of single scattering–to–multiple scattering ratio and provided high-contrast images of neural fibers in the brain cortex with the diffraction-limited spatial resolution of 412 nanometers and a 33-fold enhanced Strehl ratio.
Deep imaging based on wave correlation is used to attenuate multiple scattering and visualize mice brains through intact skulls.
Optical imaging of objects embedded within scattering media such as biological tissues suffers from the loss of resolving power. In our previous work, we proposed an approach called collective ...accumulation of single scattering (CASS) microscopy that attenuates this detrimental effect of multiple light scattering by combining the time-gated detection and spatial input-output correlation. In the present work, we perform a rigorous theoretical analysis on the effect of multiple light scattering to the optical transfer function of CASS microscopy. In particular, the spatial frequency-dependent signal to noise ratio (SNR) is derived depending on the intensity ratio of the single- and multiple-scattered waves. This allows us to determine the depth-dependent resolving power. We conducted experiments using a Siemens star-like target having various spatial frequency components and supported the theoretical derived SNR spectra. Our study provides a theoretical framework for understanding the effect of multiple light scattering in high-resolution and deep-tissue optical imaging.
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