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We study the sampling complexity of a probability distribution associated with an ensemble of identical noninteracting bosons undergoing a quantum random walk on a one-dimensional lattice. With uniform nearest-neighbor hopping we show that one can efficiently sample the distribution for times logarithmic in the size of the system, while for longer times there is no known efficient sampling algorithm. With time-dependent hopping and optimal control, we design the time evolution to approximate an arbitrary Haar-random unitary map analogous to that designed for photons in a linear optical network. This approach highlights a route to generating quantum complexity by optimal control only of a single-body unitary matrix. We study this in the context of two potential experimental realizations: a spinor optical lattice of ultracold atoms and a quantum gas microscope.

We demonstrate site-resolved imaging of individual bosonic atoms in a Hubbard-regime two-dimensional optical lattice with a short lattice constant of 266 nm. To suppress the heating by probe light with the 1S0-1P1 transition of the wavelength λ = 399 nm for high-resolution imaging and preserve atoms at the same lattice sites during the fluorescence imaging, we simultaneously cool atoms by additionally applying narrow-line optical molasses with the 1S0-3P1 transition of the wavelength λ = 556 nm. We achieve a low temperature of , corresponding to a mean oscillation quantum number along the horizontal axes of 0.22(4) during the imaging process. We detect, on average, 200 fluorescence photons from a single atom within a 400 ms exposure time, and estimate a detection fidelity of 87(2)%. The realization of a quantum gas microscope with enough fidelity for Yb atoms in a Hubbard-regime optical lattice opens up the possibilities for studying various kinds of quantum many-body systems such as Bose and Fermi gases, and their mixtures, and also long-range-interacting systems such as Rydberg states.

Quantum-gas microscopes are used to study ultracold atoms in optical lattices at the single-particle level. In these systems atoms are localised on lattice sites with separations close to or below the diffraction limit. To determine the lattice occupation with high fidelity, a deconvolution of the images is often required. We compare three different techniques, a local iterative deconvolution algorithm, Wiener deconvolution and the Lucy–Richardson algorithm, using simulated microscope images. We investigate how the reconstruction fidelity scales with varying signal-to-noise ratio, lattice filling fraction, varying fluorescence levels per atom, and imaging resolution. The results of this study identify the limits of singe-atom detection and provide quantitative fidelities which are applicable for different atomic species and quantum-gas microscope setups.

We demonstrate single-site-resolved fluorescence imaging of ultracold 87Rb atoms in a triangular optical lattice by employing Raman sideband cooling. Combining a Raman transition at the D1 line and a photon scattering through an optical pumping of the D2 line, we obtain images with low background noise. The Bayesian optimisation of 11 experimental parameters for fluorescence imaging with Raman sideband cooling enables us to achieve single-atom detection with a high fidelity of (96.3 ± 1.3)%. Single-atom and single-site resolved detection in a triangular optical lattice paves the way for the direct observation of spin correlations or entanglement in geometrically frustrated systems.

We propose a quantum gas microscope for ultracold atoms that enables nondestructive atom detection, thus evading higher-band excitation and change of the internal degrees of freedom. We show that photon absorption of a probe beam cannot be ignored even in dispersive detection to obtain a signal-to-noise ratio greater than unity because of the shot noise of the probe beam under a standard measurement condition. The first scheme we consider for the nondestructive detection, applicable to an atom that has an electronic ground state without spin degrees of freedom, is to utilize a magic-wavelength condition of the optical lattice for the transition for probing. The second is based on the dispersive Faraday effect and squeezed quantum noise and is applicable to an atom with spins in the ground state. In this second scheme, a scanning microscope is adopted to exploit the squeezed state and reduce the effective losses. Application to ultracold ytterbium atoms is discussed.

Quantum gas microscopes, which image the atomic occupations in an optical lattice, have opened a new avenue to the exploration of many-body lattice systems. Imaging trapped systems after freezing the density distribution by ramping up a pinning lattice leads, however, to a distortion of the original density distribution, especially when its structures are on the scale of the pinning lattice spacing. We show that this dynamics can be described by a filter, which we call in analogy to classical optics a quantum point spread function. Using a machine learning approach, we demonstrate via several experimentally relevant setups that a suitable deconvolution allows for the reconstruction of the original density distribution. These findings are both of fundamental interest for the theory of imaging and of immediate importance for current quantum gas experiments.

The site-resolved detection of ultracold atoms in optical lattice potentials is a powerful technique to study lattice models of correlated quantum matter. In their recent paper, Yamamoto et al (2016 New J. Phys. 18 023016) demonstrate a quantum gas microscope for ultracold ytterbium atoms. By simultaneously cooling these atoms on two optical transitions, they show that fluorescent images of the lattice gas can be obtained while keeping the atoms pinned to their lattice sites even for a lattice spacing as small as 266 nm. This promises to be a powerful enabling tool for studies of metrology and quantum magnetism with quantum degenerate gases of ytterbium.

A particular strength of ultracold quantum gases is the range of versatile detection methods that are available. As they are based on atom–light interactions, the whole quantum optics toolbox can be used to tailor the detection process to the specific scientific question to be explored in the experiment. Common methods include time-of-flight measurements to access the momentum distribution of the gas, the use of cavities to monitor global properties of the quantum gas with minimal disturbance, and phase-contrast or high-intensity absorption imaging to obtain local real-space information in high-density settings. Even the ultimate limit of detecting each and every atom locally has been realized in two dimensions using so-called quantum gas microscopes. In fact, these microscopes have not only revolutionized detection—they have also revolutionized the control of lattice gases. Here, we provide a short overview of quantum gas microscopy, highlighting the new observables it can access as well as key experiments that have been enabled by its development.Ultracold gases provide a platform for idealized realizations of many-body systems. Thanks to recent advances in quantum gas microscopy, collective quantum phenomena can be probed with single-site resolution.

Amid global efforts toward carbon neutrality, nanoconfined catalysis has emerged as a transformative strategy to address energy transition challenges through precise regulation of catalytic microenvironments. This review systematically examines recent advancements in nanoconfined catalytic systems for carbon-based energy conversion (CO2, CH4, etc.), highlighting their unique capability to modulate electronic structures and reaction pathways via quantum confinement and interfacial effects. By categorizing their architectures into dimension-oriented frameworks (1D nanotube channels, 2D layered interfaces, 3D core-shell structures, and heterointerfaces), we reveal how geometric constraints synergize with mass/electron transfer dynamics to enhance selectivity and stability. Critical optimization strategies—including heteroatom doping to optimize active site coordination, defect engineering to lower energy barriers, and surface modification to tailor local microenvironments—are analyzed to elucidate their roles in stabilizing metastable intermediates and suppressing catalyst deactivation. We further emphasize the integration of machine learning, in situ characterization, and modular design as essential pathways to establish structure–activity correlations and accelerate industrial implementation. This work provides a multidimensional perspective bridging fundamental mechanisms with practical applications to advance carbon-neutral energy systems.

The colorful reactive dyes are toxic, carcinogenic to living organisms and pollute the water environment. We, for the first time, have studied the lab-scale synthesis of novel and eco-friendly carbon quantum dots (CQDs) from Spirulina platensis by microwave-assisted technology. Fluorescence, absorbance, emission, and excitation spectra of biosynthesized CQDs were recorded by UV transilluminator, UV, and photoluminescence spectrophotometer. Elemental analysis of CQDs were carried out by using energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Morphological properties of CQDs were studied by using transmission electron microscope (TEM), scanning electron microscope (SEM), and particle size analyzer. Up to 95.5% of Reactive Red M8B was degraded by CQDs within 6 h under sunlight. Dye degradation was facilitated by optimized parameters such as concentration of dyes, catalyst, and pH. Photocatalytic activity of CQDs were studied by gas chromatography mass spectrometry (GC/MS). It proved that the complex molecules were degraded to simpler and easily degradable molecules. Dye degradation reaction follows first-order kinetics, and the synthesized CQDs contain 89% of scavenging activity. MTT assay proved that the treated water was toxic free and charcoal was used to remove the CQDs from treated water in order to standardize the permitted level of physico-chemical parameters such as biological oxygen demand (BOD), chemical oxygen demand (COD), total organic carbon (TOC), and total inorganic carbon (TIC); chemical, metal, and toxic-free dye treated water was suitable to recycle for algae cultivation. Graphical Abstract