Attaining millikelvin (mK) temperatures is often a prerequisite for the study of quantum phenomena and the operation of quantum devices. Adiabatic demagnetization refrigeration (ADR) is an effective, easy, and sustainable alternative to evaporation or dilution cooling with the rare and superexpensive ${}^3\text{He}$. Paramagnetic salts, traditionally used for mK ADR, suffer from chemical instability related to water of crystallization. We report synthesis, characterization, as well as low-temperature magnetization and specific heat measurements of two alternative UHV-compatible candidate materials ${\text{NaYbP}}_2{\text{O}}_7$ and ${\text{KYbP}}_2{\text{O}}_7$. Utilizing the physical property measurement system at 2 K, the ADR of sintered pellets with Ag powder admixture starting at 5 T yields base temperatures (warm-up times) of 45 mK (55 min) and 37 mK (35 min) for ${\text{NaYbP}}_2{\text{O}}_7$ and ${\text{KYbP}}_2{\text{O}}_7$, respectively, slightly advantageous to $\text{KBaYb}({\text{BO}}_3{)}_2$ (45 mK and 40 min) studied under similar conditions.

We show that one-dimensional Floquet trimer arrays with periodically oscillating waveguides support two different and co-existing types of topological Floquet edge states in two different topological gaps in the Floquet spectrum. In these systems nontrivial topology is introduced by longitudinal periodic oscillations of the waveguide centers, leading to the formation of Floquet edge states in a certain range of oscillation amplitudes despite the fact that the structure spends half of the period in “instantaneously” nontopological phase, and only during the other half-period it is “instantaneously” topological. Two co-existing Floquet edge states are characterized by different phase relations between bright spots in the unit cell—in one mode these spots are in phase, while in the other mode they are out of phase. We show that in focusing nonlinear medium topological Floquet edge solitons, representing exactly periodic nonlinear localized Floquet states, can bifurcate from both these types of linear edge states. Both types of Floquet edge solitons can be stable and can be created dynamically using two-site excitations.

We propose a composite acoustic metamaterial consisting of Mie resonators and a Helmholtz resonator array. Such a design achieves a broadband acoustic attenuation in the low-frequency regime. This wideband soundproofing effect may be explained using the transfer-matrix method and the lumped-element model. Transmission loss and transmittance are robust and tested both numerically as well as experimentally. Through the composite design, using a deep-subwavelength structure, we successfully achieve a broadband low-frequency acoustic attenuation that blocks over 90% of incident acoustic energy within a frequency range of 1250 Hz. Our work offers a design paradigm by which to realize extraordinary airborne acoustic silencing in low-frequency regimes.

Measuring the orbital-angular-momentum (OAM) complex spectrum of light is very important in OAM-based applications. In this paper, we propose and experimentally demonstrate a simple scheme to measure the OAM complex spectrum of light with the fast Fourier transform (FFT). The light with input OAM modes coaxially interferes with a Gaussian light beam that is generated locally to achieve the intensity distribution of the interference. By subtracting the intensity distribution of the input OAM light from this interference intensity distribution, the OAM complex spectrum can be extracted by employing the FFT transform on the result of the subtraction. In addition, we also present an approach to enlarge the range of detectable OAM modes (from 1 to 50) and analyze the effects of optical alignment and the number of superimposed OAM modes on the measurement results. The proposed scheme is demonstrated in a proof-of-principle experiment, where six superimposed OAM modes can be measured without error, with their average deviation of amplitude and phase being 0.07 and 0.308, respectively. The proposed scheme can exploit applications in some advanced domains, including OAM sensing, OAM imaging, optical communication decoding, and various other OAM-based systems.

A variety of magnetic resonance relaxometry methods have been developed to determine pore size in porous rocks. Uncertainties in pore-size estimates may occur due to uncertainty in the relaxation-diffusion regime. We have developed a direct and rapid one-dimensional method based on Brownstein-Tarr theory to help remedy this problem. The correlation between magnetic resonance relaxation behavior and the temperature-dependent self-diffusion coefficient of pore fluids was employed to estimate the pore size and surface relaxivity of a series of reservoir rocks. Relaxation is anticipated to depend on diffusion in the intermediate regime of Brownstein-Tarr theory. Water-saturated glass-bead packs were employed in initial Carr-Purcell-Meiboom-Gill experiments at variable temperature. The calculated pore size matches the estimated geometric pore size. The proposed method was applied to determine the pore size of Berea, Buff Berea, and Nugget sandstones. The pore sizes determined with the three pore geometries are in good agreement with scanning electron microscopy and micro-computed-tomography measurements. The experimentally observed changes in relaxation times and their corresponding intensities indicate an intermediate Brownstein-Tarr regime for all systems examined in this work.

We show that, in the x-ray magnetic resonant scattering (XRMS) of a two-dimensional array of submicron magnets, the collected intensity at each Bragg reflection is correlated to the reflected light from locations of the magnets that have the same angle of curvature. This converts XRMS in a kind of magnetic microscope capable of spatially resolving the magnetization of the small-size magnets, averaged over the magnets illuminated by the x rays. This result is used to study the magnetization of trilayer submicron disk-shaped magnets consisting of two magnetostatically coupled ferromagnetic layers, about 15 nm thick, separated by a nonmagnetic spacer. These kinds of systems are less known than the single-layer ones, despite having potentially more interesting functionalities for device applications, mainly due to the difficulty to distinguish the magnetization of each of the layers within the magnets. This problem is overcome by XRMS thanks to its chemical sensitivity and its relatively large depth probe. XRMS is also a photon-in photon-out technique that allows measuring under external magnetic fields. This permits the extraction of the local hysteresis loops at different locations of the disks. The technique demonstrates to be very sensitive to the magnetization distribution across each of the layers at any field intensity, with an estimated lateral resolution below 200 nm. This serves to detect, and also explain, chiral asymmetries in the magnetic circulation of the vortex in each of the layers.

We study gain without inversion due to coherence effects in a Doppler-broadened degenerate three-level system of a rubidium-hydrogen mixture in a miniaturized micron-scale custom vapor cell. The cell miniaturization gives rise to collisions of atoms with the walls of the cell. This, combined with the high collision rate with the hydrogen buffer gas, allows us to observe gain in the absorption spectra. Furthermore, we analyze the role of cell miniaturization in the evolution of the gain profile. In addition to fundamental interest, the observation of gain without inversion in our miniaturized cells paves the way for applications such as miniaturized lasers without inversion.

We show, theoretically and experimentally, how the absolute orientation and polarization state of radio-frequency (rf) magnetic fields in a transverse two-dimensional (2D) plane can be uniquely determined using two optically pumped atomic magnetometers. In addition, the output signals from these quantum sensors can be readily expressed as a magnetic Jones vector. This composite device can complement electric field detection in finding rf directions or it can be used in applications where the electric field is negligible. The latter is found in a myriad of applications where the source can be modeled as radiating magnetic dipoles in the near-field limit. This tool could be used to characterize the response of a material to rf excitation or to distinguish signal from noise.

Doubly parametric quantum transducers (DPTs), such as electro-optomechanical devices, show promise as quantum interconnects between the optical and microwave domains, thereby enabling long-distance quantum networks between superconducting qubit systems. However, any transducer will inevitably introduce loss and noise that will degrade the performance of a quantum network. We explore how DPTs can be used to construct a network capable of distributing remote two-mode microwave entanglement over an optical link by comparing 14 different network topologies. The 14 topologies we analyze consist of combinations of different transducer operations, entangled resources, and entanglement-swapping measurements. For each topology, we derive a necessary and sufficient analytic threshold on DPT parameters that must be exceeded in order to distribute microwave-microwave entanglement. We find that the thresholds are dependent on the given network topology, along with the available entanglement resources and measurement capabilities. In the high-optical-loss limit, which is relevant to realistic networks, we find that down-conversion of each half of an optical two-mode squeezed vacuum state is the most robust topology. Finally, using currently achievable experimental capabilities, we find the encouraging result that several of these topologies could produce microwave-microwave entanglement. However, most of these topologies cannot work given current transducer performance, which demonstrates the importance of thoroughly analyzing all possible networks.

Cascaded dynamic metasurfaces with multiple control points promise augmented capabilities but have received little attention to date owing to complexity in design. The inclusion of multiple control knobs within a single surface offers more degrees of freedom, which can be optimized—jointly with the static geometry—to provide added functionality. We study a cascaded system with two dynamic layers, each possessing patchlike elements that can be tuned with a varactor diode. A resistor is additionally included to add asymmetry in the resonance loss provided by each layer. With this architecture we study the reflection properties of the surface and demonstrate the ability to independently tune the magnitude and the phase from the single, electrically thin surface. Tuning the magnitude and phase separately is a widely sought-after behavior and is used herein to demonstrate multiple communications modulation methods including phase-shift keying and 16-point quadrature amplitude modulation.

We present and theoretically analyze the performance of a nonlocal superconducting single-photon detector. The device operates due to the energy-to-phase conversion mechanism, where the energy of the absorbed single photon is transformed in a variation of the superconducting phase. Within this scope, the detector is designed in the form of a double-loop superconductor–normal-metal–superconductor ($S$-$N$-$S$) Josephson interferometer, where the detection occurs in a long $S$-$N$-$S$ junction and the readout is operated by a short $S$-$N$-$S$ junction. The variation of the superconducting phase across the readout junction is measured by recording the quasiparticle current flowing through a tunnel-coupled superconducting probe. By exploiting realistic geometry and materials, the detector is able to reveal single photons of frequency down to 10 GHz when operated at 10 mK. Furthermore, the device provides a value of the signal-to-noise ratio of up ${10}^4$ in the range from 10 GHz to 10 THz by selection of the magnetic flux and the bias voltage. This device will hopefully find direct application as a single-photon detector in both basic science and quantum technology, while the energy-to-phase conversion mechanism could be the basis of nonlocal readout and memory architectures for superconducting qubits.

Surface acoustic waves (SAWs) have significant potential for energy-efficient control of magnetic domain walls (DWs) owing to the magnetoelastic coupling effect. However, the dissipation of radio-frequency (rf) power in a SAW device can result in heating, which can also affect the DW motion. In this work, the heating of a SAW device consisting of a $\mathrm{Pt}$/$\mathrm{Co}$/$\mathrm{Ta}$ thin film with perpendicular magnetic anisotropy in between two interdigitated transducers is measured in situ with use of an on-chip $\mathrm{Pt}$ film as a thermometer within the SAW beam path. The application of SAWs at a center frequency of 48 MHz and a total rf power of 21 dBm results in a temperature increase of approximately 10 K within the SAW beam path owing to rf-power dissipation. DW velocity in a $\mathrm{Pt}$/$\mathrm{Co}$/$\mathrm{Ta}$ thin film is evaluated separately with use of Kerr microscopy at various temperatures or in the presence of SAWs. With a 10-K increase in temperature only, the DW velocity is found to increase from $33\pm 3\text{μ}\mathrm{m}/\mathrm{s}$ (at room temperature) to $104\pm 8\text{μ}\mathrm{m}/\mathrm{s}$ under an external magnetic field of 65 Oe. Traveling-SAW-assisted DW velocity ($116\pm 3\text{μ}\mathrm{m}/\mathrm{s}$) is slightly higher than that with a 10-K temperature increase alone, suggesting that the heating plays the major role in promoting DW motion, whereas the DW motion is significantly enhanced ($418\pm 8\text{μ}\mathrm{m}/\mathrm{s}$) in the presence of standing SAWs, indicating that magnetoelastic coupling is more important than heating in this scenario.

Permalloy, despite being a widely used soft magnetic material, still requires optimization in terms of magnetic softness and magnetostriction for its use in magnetoresistive-sensor applications. Conventional annealing methods are often insufficient to locally achieve the desired properties for a narrow parameter range. In this study, we report a significant improvement in the magnetic softness and magnetostriction in a 30-nm permalloy film after ${\mathrm{He}}^{+}$ irradiation. The irradiation treatment reduces the induced anisotropy by a factor of 10 and the hard-axis coercivity by a factor of 5 compared with the values in the as-deposited state. In addition, the effective magnetostriction of the film is significantly reduced by a factor ten (below $1\times {10}^{-7}$) after irradiation. All the above-mentioned effects can be attributed to the isotropic crystallite growth of the ${\mathrm{Ni}}_{81}$${\mathrm{Fe}}_{19}$ alloy and to the intermixing at the magnetic layer interfaces under light-ion irradiation. We support our findings with X-ray-diffraction analysis of the textured ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$ alloy. Importantly, the sizable magnetoresistance is preserved after the irradiation. Our results show that compared with traditional annealing methods, the use of ${\mathrm{He}}^{+}$ irradiation leads to significant improvements in the magnetic softness and reduces strain cross-sensitivity in permalloy films required for 3D positioning and compass applications. These improvements, in combination with the local nature of the irradiation process, make our findings valuable for the optimization of monolithic integrated sensors, where classic annealing methods cannot be applied due to complex interplay within the components in the device.

Magnetic ultrathin films grown on heavy metal substrates often exhibit rich spin structures due to the competition between various magnetic interactions such as Heisenberg exchange, Dzyaloshinskii-Moriya interaction and higher-order spin interactions. Here we employ spin-polarized scanning tunneling microscopy to study magnetic nanoskyrmion phase in $\mathrm{Fe}$ monolayer grown on $\mathrm{Ir}(111)$ substrate. Our observations show that the formation of nanoskyrmion lattice in the $\mathrm{Fe}/\mathrm{Ir}(111)$ system depends sensitively on the growth conditions and various nonskyrmion spin states can be formed. Remarkably, the application of voltage pulses between the tip and the sample can trigger a nonskyrmion-to-skyrmion phase transition. Such a phase transition is determined by the total injected energy during the voltage pulse suggesting that there exists a potential barrier between a metastable nonskyrmion spin state and a true skyrmion ground state. The creation of a skyrmion lattice at the nanoscale will be useful to design skyrmion-based spintronic devices.

Ultrasound-directed self-assembly (DSA) enables organizing and orienting particles dispersed in a fluid medium into specific patterns, thus agglomerating them into pattern features with different packing density than when first dispersed in the fluid medium. In this paper, we theoretically derive and experimentally validate a three-dimensional model of the ultrasound DSA process to simulate and quantify the local packing density of spherical microparticles when assembled into pattern features. We study the packing density as a function of process parameters, including particle volume fraction, particle size, and medium viscosity. The results show that the local particle packing density increases with increasing particle volume fraction and reaches a maximum of 45% independent of medium viscosity. Also, the local particle packing density increases with decreasing particle size for constant particle volume fraction. The results shed light on the relationship between the process parameters and the local particle packing density within pattern features resulting from ultrasound DSA. This knowledge is useful in the context of using ultrasound DSA to manufacture engineered composite materials that require high particle packing density, or packing density gradients, e.g., to increase mechanical or electrical properties, or to tailor combustion of energetic particles, among other applications.

Simulating quantum many-body systems is a highly demanding task since the required resources grow exponentially with the dimension of the system. In the case of fermionic systems, this is even harder since nonlocal interactions emerge due to the antisymmetric character of the fermionic wave function. Here, we introduce a digital-analog quantum algorithm to simulate a wide class of fermionic Hamiltonians including the paradigmatic one-dimensional Fermi-Hubbard model. These digital-analog methods allow quantum algorithms to run beyond digital versions via an efficient use of coherence time. Furthermore, we exemplify our techniques with a low-connected architecture for realistic digital-analog implementations of specific fermionic models.

The development of fast magnonic information-processing devices requires operating with short spin-wave pulses, but, the shorter the pulses, the more affected they are by information loss due to broadening and dispersion. The capability of engineering spin-wave pulses and controlling their propagation could solve this problem. Here, we provide a method to generate linear spin-wave pulses with a desired spatial-temporal profile in magnonic waveguides based on inverse design. As relevant examples, we theoretically predict that both rectangular and self-compressing spin-wave pulses can be generated in state-of-the-art waveguides with fidelities $\gtrsim 96\mathrm{\%}$ using narrow stripline antennas. The method requires minimal computational overhead and is universal, i.e., it applies to arbitrary targeted pulse shapes, type of waves (exchange or dipolar), waveguide materials, and waveguide geometries. It can also be extended to more complex magnonic structures. Our results could lead to the utilization of large-scale magnonic circuits for classical and quantum information processing.

We measure electron- and nuclear-spin transition frequencies in the ground state of nitrogen-vacancy (N-$V$) centers in diamond for two nitrogen isotopes (${}^{14}\mathrm{N}$-$V$ and ${}^{15}\mathrm{N}$-$V$) over temperatures ranging from 77 to 400 K. Measurements are performed using Ramsey interferometry and direct optical readout of the nuclear and electron spins. We extract coupling parameters $Q$ (for ${}^{14}\mathrm{N}$-$V$), $D$, $A_{\parallel }$, $A_{\perp }$, and ${\gamma }_e/{\gamma }_n$, and their temperature dependences for both isotopes. The temperature dependences of the nuclear-spin transitions within the $m_s=0$ spin manifold near room temperature are found to be 0.52(1) ppm/K for ${}^{14}\mathrm{N}$-$V$ ($|m_I=-1⟩\leftrightarrow |m_I=+1⟩$) and $-1.1(1)$ ppm/K for ${}^{15}\mathrm{N}$-$V$ ($|m_I=-1/2⟩\leftrightarrow |m_I=+1/2⟩$). An isotopic shift in the zero-field splitting parameter $D$ between ${}^{14}\mathrm{N}$-$V$ and ${}^{15}\mathrm{N}$-$V$ is measured to be $\sim 120$ kHz. Residual transverse magnetic fields are observed to shift the nuclear-spin transition frequencies, especially for ${}^{15}\mathrm{N}$-$V$. We have precisely determined the set of parameters relevant for the development of nuclear-spin-based diamond quantum sensors with greatly reduced sensitivity to environmental factors.