A physically unclonable function (PUF) is an embedded hardware security measure that provides protection against counterfeiting. Here we present our work on using an array of randomly-magnetized micron-sized ferromagnetic bars (micromagnets) as a PUF. We employ a 4 $\mu$m thick surface layer of nitrogen-vacancy (NV) centers in diamond to image the magnetic fields from each micromagnet in the array, after which we extract the magnetic polarity of each micromagnet using image analysis techniques. After evaluating the randomness of the micromagnet array PUF and the sensitivity of the NV readout, we conclude by discussing the possible future enhancements for improved security and magnetic readout.

Metamaterials comprising assemblies of dielectric resonators have attracted much attention due to their low intrinsic loss and isotropic optical response. In particular, metasurfaces made from silicon dielectric resonators have shown desirable behaviors such as efficient nonlinear optical conversion, spectral filtering and advanced wave-front engineering. To further explore the potential of dielectric metamaterials, we present all-dielectric metamaterials fabricated from epitaxially grown III-V semiconductors that can exploit the high second-order optical susceptibilities of III-V semiconductors, as well as the ease of monolithically integrating active/gain media. Specifically, we create GaAs nano-resonators using a selective wet oxidation process that forms a low refractive index AlGaO (n~1.6) under layer similar to silicon dielectric resonators formed using silicon-on-insulator wafers. We further use the same fabrication processes to demonstrate multilayer III-V dielectric resonator arrays that provide us with new degrees of freedom in device engineering. For these arrays, we experimentally measure ~100% reflectivity over a broad spectral range. We envision that all-dielectric III-V semiconductor metamaterials will open up new avenues for passive, active and nonlinear all dielectric metamaterials

We investigate the anisotropic effect of magnetization plateaus in the antiferromagnetic Heisenberg model on a kagome strip chain. The kagome strip chain Heisenberg model, composed of a hexagonal net of triangles forming five-site unit cells, exhibits four magnetization plateaus in the presence of an applied magnetic field. Using numerical density matrix renormalization group method, we find that the magnetization plateaus are stable against anisotropic interactions in the same direction of the applied magnetic field, but the plateaus become much smaller with anisotropic interactions in other directions. We further show the anisotropic effect of the magnon excitations of the 0.6 plateau state using linear spin wave theory. The magnon bandwidth remains small when tuning the anisotropic interactions along the field where the magnetization plateau is stable, while the band becomes more dispersive with anisotropic interactions perpendicular to the field. In addition, upon tuning down the interaction strength for the two lower legs below a critical value, the Hamiltonian of the kagome strip chain is dominated by two separate spin chains. This can be used to determine the effective lattice structure in materials with strong distortions. Our results enhance the theoretical understanding of the anisotropic effect and the nature of magnetization plateaus in kagome strip chain materials, which can contribute to the design and manipulation of kagome materials with tailored properties.

As one of the most intriguing states of matter, the chiral spin liquid (CSL) has attracted much scientific interest while its existence and mechanism in crystalline strongly correlated systems remain hotly debated. On the other hand, strong correlation driven emergent phenomena can be realized in twisted transition metal dichalcogenide bilayers with a tremendously tunable large length scale providing a new platform for the emergence of CSLs. We focus on a strongly correlated model relevant to heterobilayer $\textrm{WSe}_{2}/\textrm{MoSe}_{2}$ and investigate the Mott insulating phase at half filling under an out-of-plane magnetic field. Considering both its orbital and spin Zeeman effects we identify three conventionally ordered phases including a $120^{\circ}$ Néel phase, a stripe phase, and an up-up-down phase. For intermediate fields an emergent quantum spin liquid phase is identified with partial spin polarization. We further characterize its topological nature as the $\nu$ = 1/2 Laughlin CSL through the topological entanglement spectrum and quantized spin pumping under spin flux insertion. In addition, we map out the quantum phase diagram for different twisted angles in an experimentally accessible parameter regime.

Quantum information communication, sensing, and computation often require complex and expensive instrumentation resulting in a large entry barrier. The Quantum Instrumentation Control Kit (QICK) overcomes this barrier for superconducting qubits with a collection of software and firmware for state-of-the-art radio frequency system on chip (RFSoC's) field programmable gate architecture (FPGA) chips. Here we present a software and firmware extension to QICK, the Quantum Instrumentation Control Kit - Defect Arbitrary Waveform Generator (QICK-DAWG), which is an open-source software and firmware package that supports full quantum control and measurement of nitrogen-vacancy defects in diamond and other quantum defects using RFSoC FPGAs. QICKDAWG extends QICK to the characterization of nitrogen-vacancy defects and other diamond quantum defects by implementing DC-1 GHz readout, AOM or gated laser control, and analog or photon counting readout options. QICK-DAWG also adds pulse sequence programs and data analysis scripts to collect and characterize photoluminescence (PL) intensity, optically detected magnetic resonance (ODMR) spectra, PL readout windows, Rabi oscillations, Ramsay interference spectra, Hahn echo spin-spin relaxation times T$_2$, and spin-lattice relaxation times T$_1$. We demonstrate that QICK-DAWG is a powerful new paradigm of open source quantum hardware that significantly lowers the entry barrier and cost for quantum sensing using quantum defects.

Recently, a single atom transistor was deterministically fabricated using phosphorus in Si by H-desorption lithography with a scanning tunneling microscope (STM). This milestone in precision, achieved by operating the STM in the conventional tunneling mode, typically utilizes very slow ($\sim\!10^2~\mathrm{nm^2/s}$) patterning speeds. By contrast, using the STM in a high voltage ($>10~\mathrm{V}$) field emission mode, patterning speeds can be increased by orders of magnitude to $\gtrsim\!10^4~\mathrm{nm^2/s}$. We show that the rapid patterning negligibly affects the functionality of relatively large micron-sized features, which act as contacting pads on these devices. For nanoscale structures, we show that the resulting transport is consistent with the donor incorporation chemistry enhancing the device definition to a scale of $10~\mathrm{nm}$ even though the pattering spot size is $40~\mathrm{nm}$.

Deterministic control over the location and number of donors is crucial to donor spin quantum bits (qubits) in semiconductor based quantum computing. In this work, a focused ion beam is used to implant antimony donors close to quantum dots. Ion detectors are integrated next to the quantum dots to sense the implants. The numbers of donors implanted can be counted to a precision of a single ion. In low-temperature transport measurements, regular coulomb blockade is observed from the quantum dots. Charge offsets indicative of donor ionization are also observed in devices with counted donor implants.

In the last decade, symmetry-protected bound states in the continuum (BICs) have proven to be an important design principle for creating and enhancing devices reliant upon states with high quality (Q) factors, such as sensors, lasers, and those for harmonic generation. However, as we show, current implementations of symmetry-protected BICs in photonic crystal slabs can only be found at the center of the Brillouin zone and below the Bragg-diffraction limit, which fundamentally restricts their use to single-frequency applications. By 3D-micro printing a photonic crystal structure using two-photon polymerization, we demonstrate that this limitation can be overcome by altering the radiative environment surrounding the slab to be a three-dimensional photonic crystal. This allows for the protection of a line of BICs by embedding it in a symmetry bandgap of the crystal. Moreover, we experimentally verify that just a single layer of this photonic crystal environment is sufficient. This concept significantly expands the design freedom available for developing next-generation devices with high-Q states.

Designing material properties on demand has important implications to potential future technological applications. While theoretically it is always possible to tune various intrinsic energy scales, there are fundamental limitations to this approach in experiment. In recent years, ultrafast spectroscopy has evolved as a promising tool to use light to dynamically induce non-trivial electronic states of matter. Here we theoretically investigate light pulse driven dynamics in a Kondo system close to quantum criticality. We show, that light can dehybridize the local Kondo screening and induce magnetic order out of a previously paramagnetic state. We demonstrate that, depending on the laser pulse field parameters, it is possible to deconfine the Kondo singlet and thereby induce second order phase transition to a dynamically ordered state, as well as a dynamic Lifshitz transition that changes the Fermi surface topology from hole- to electron-like.

We design a quantum molecular dynamics method for strongly correlated electron metals. The strong electronic correlation effects are treated within a real-space version of the Gutzwiller variational approximation (GA), which is suitable for the inhomogeneity inherent in the process of quantum molecular dynamics (MD) simulation. We also propose an efficient algorithm based on the second-moment approximation to the electronic density of states for the search of the optimal variation parameters, from which the effective renormalized interatomic MD potentials are fully determined. By considering a minimal one-correlated-orbital Anderson many-particle model based on tight-binding hopping integrals, this fast GA-MD method is benchmarked with that using exact diagonalization to solve the GA variational parameters. In the infinite damping limit, the efficiency and accuracy are illustrated. This novel method will open up an unprecedented opportunity enabling large-scale quantum MD simulations of strongly correlated electronic materials.

We report ultrafast x-ray scattering experiments of the quasi-1D charge density wave (CDW) material (TaSe$_4$)$_2$I following photoexcitation with femtosecond infrared laser pulses. From the time-dependent diffraction signal at the CDW sidebands we identify an amplitude mode derived primarily from the transverse acoustic component of the CDW static distortion. The dynamics of this acoustic amplitude mode are described well by a model of a displacive excitation, which we interpret as mediated through a coupling to the optical phonon component associated with the tetramerization of the Ta chains.

The nitrogen-vacancy (NV) color center in diamond has demonstrated great promise in a wide range of quantum sensing. Recently, there have been a series of proposals and experiments using NV centers to detect spin noise of quantum materials near the diamond surface. This is a rich complex area of study with novel nano-magnetism and electronic behavior, that the NV center would be ideal for sensing. However, due to the electronic properties of the NV itself and its host material, getting high quality NV centers within nanometers of such systems is challenging. Band bending caused by space charges formed at the metal-semiconductor interface force the NV center into its insensitive charge states. Here, we investigate optimizing this interface by depositing thin metal films and thin insulating layers on a series of NV ensembles at different depths to characterize the impact of metal films on different ensemble depths. We find an improvement of coherence and dephasing times we attribute to ionization of other paramagnetic defects. The insulating layer of alumina between the metal and diamond provide improved photoluminescence and higher sensitivity in all modes of sensing as compared to direct contact with the metal, providing as much as a factor of 2 increase in sensitivity, decrease of integration time by a factor of 4, for NV $T_1$ relaxometry measurements.