Due to continued dimensional scaling, read sensors in hard disk drives face pressing challenges related to rising electrical resistance and thus impedance mismatch problems. All-metal, or at least low-resistance, magnetic field sensors are thus of high interest to displace current magnetic tunnel junction readers. Spin-accumulation sensors based on metallic nonlocal spin valves (NLSVs) are promising candidates but need further signal optimization, particularly in the ultrathin limit required for applications. Here, we report a wide-ranging study of spin signal optimization in thin $\mathrm{Al}/{\mathrm{Al}\mathrm{O}}_x/\mathrm{Co}$-$\mathrm{Fe}$-based NLSVs, using interfacial resistance-area-product tuning to mitigate spin back-diffusion. The Al-oxidation-controlled resistance-area product is tuned over 8 orders of magnitude, providing a complete picture of the evolution of the interfacial transport mechanism, spin signal, and nonlocal background. Signal improvements up to factors of almost ${10}^3$ are obtained over transparent-interface devices (to about 0.15 Ω, or ∼2 mΩ µ${\mathrm{m}}^2$), and the upper limit of feasible resistance-area product in NLSVs is established. Most significantly, the spin signals in such NLSVs at application-relevant resistances still lie substantially beneath theoretical limits, due to diminished tunneling spin polarization of unknown origin. Connecting tunneling devices to the transparent limit, a universal spin polarization versus interfacial resistance-area product relation is thus uncovered in ${\mathrm{Al}\mathrm{O}}_x$-based devices, highlighting the specific issue limiting technological progress in this area. Potential strategies to achieve further gains are discussed in detail.

In this work, we explore the formation of transmission gaps in wave spectra of a ferrite film covered by a thin vanadium dioxide (${\mathrm{VO}}_2$) stripe with a single groove on its surface. It was found that this waveguide does not manifest noticeable spin-wave reflections, but still demonstrates rejection bands in its transmission characteristic. This is due to a finite drop of spin-wave group velocity in a wide frequency range affected by the conducting ${\mathrm{VO}}_2$ layer with a smooth profile inhomogeneity. The main feature of the proposed waveguides is a short groove length required for the formation of spectral regions with enhanced spin-wave signal rejection. Namely, the utilization of a groove with a length of 66 µm results in a pronounced rejection band with a depth of 10 dB and a width of 19 MHz. To achieve these values in conventional magnonic crystals, several millimeters of a periodic array of reflectors are required. Therefore, we believe that the obtained findings pave a clear way forward for microminiaturizing spin-wave devices, where features of magnonic crystals are exploited.

DNA flexibility is a key determinant of biological function, from nucleosome positioning to transcriptional regulation, motivating a direct measurement of the bend-torque response of individual DNA molecules. In this work, DNA bending is detected with the use of a nanomechanical torque balance formed by the tethering of a ferromagnetic nanoparticle probe by an individual DNA molecule to a diamond magnetic field imager. The torque exerted by the DNA in response to bending caused by an applied magnetic torque is measured by wide-field imaging of quantum defects near the surface of the diamond. Qualitative measurements of differences in DNA biomechanical binding configuration are demonstrated, and as a proof of principle, a quantitative measurement of the bend response is made for individual DNA molecules. This quantum-enabled measurement approach could be applied to characterize the bend response of biophysically relevant short DNA molecules as well as the sequence dependence of DNA bending energy.

Acoustic forces and torques are of immense importance for manipulation of particles, in particular in biomedical applications. While such forces and torques are well understood for small spherical particles with lowest-order monopole and dipole responses, the higher-order effects for larger anisotropic particles have not been properly investigated. Here we examine the acoustic force and torque on an anisotropic (spheroid) particle and reveal two remarkable phenomena. First, we describe the lateral recoil force, orthogonal to the direction of the incident wave and determined by the tilted orientation of the particle. Second, we find conditions for the stable acoustic lift, where the balanced torque and force produce a stable lateral drift of the tilted particle. We argue that these phenomena can bring about new functionalities in acoustic manipulation and sorting of anisotropic particles, including biological objects such as blood cells.

Carbon nanotubes (CNTs), with their unique quasi-one-dimensional structure and robust hexagonal covalent bonding, showcase exceptional carrier mobility and conductivity due to minimal scattering events. Despite this, common defects like voids and impurities in CNTs significantly impact electronic properties by increasing scattering. However, the dynamics may differ fundamentally for CNTs carrying bosons (e.g., phonons). In this letter, we devised a phononic “CNT” for surface acoustic waves (SAWs), utilizing a honeycomb lattice of mechanical resonators on a solid cylinder, mirroring the electronic bands of armchair CNTs—symmetric and gapless. This phononic system, unlike its electronic counterparts, permits the independent excitation of eigenmode. Through mode selection, we achieve symmetry-breaking in its band structure, resulting in two separate chiral SAW bands. This novel chiral anomaly, inherent to the boson system, persists irrespective of excitation. Experimental evidence shows robust antiscattering and defect immunity in SAW transmission. This study broadens the horizon in CNTs, promising advancements in artificial crystals harnessing mechanical and electromagnetic waves. Moreover, the attributes of phononic CNTs—i.e., broadband, robust, efficient, linear dispersion, and high-flux wave transmission—herald new possibilities in phonon-based technologies for information processing, sensing, energy harvesting, and neural networking.

Developing Hamiltonian models for quantum processors with many qubits on the same chip is crucial for advancing quantum computing technologies. Stray couplings between qubits lead to errors in gate operations. This study underscores the importance of incorporating lattice Hamiltonians into quantum circuit design. By comparing many-body effects with two-body stray couplings, we show how adjusting circuit parameters can increase two-qubit-gate fidelity. We find that loosely decoupled qubits result in weaker stray interactions and higher gate fidelity, challenging conventional assumptions. We investigate the scenario where three-body $ZZZ$ interaction surpasses two-body $ZZ$ interactions, highlighting the transformative potential of lattice Hamiltonians for novel multiqubit gates. Moreover, we investigate the cross-resonance gate within the lattice-Hamiltonian framework and examine the impact of microwave pulses on stray coupling. This emphasizes the necessity of developing a comprehensive theoretical framework that includes lattice interactions, which are now critical given the sophistication of contemporary quantum hardware. These insights are vital for developing fault-tolerant quantum computing and next-generation quantum processors.

Fault-tolerant quantum computation requires low physical-qubit gate errors. Many approaches exist to reduce gate errors, including both hardware- and control-optimization strategies. Dynamically corrected gates are designed to cancel specific errors and offer the potential for high-fidelity gates, but they have yet to be implemented in singlet-triplet spin qubits in semiconductor quantum dots, due in part to the stringent control constraints in these systems. In this work, we experimentally implement dynamically corrected gates designed to mitigate hyperfine noise in a singlet-triplet qubit realized in a $\mathrm{Si}$/$\mathrm{Si}\mathrm{Ge}$ double quantum dot. The corrected gates reduce infidelities by about a factor of 3, resulting in gate fidelities above $0.99$ for both identity and Hadamard gates. The gate performances depend sensitively on pulse distortions, and their specific performance reveals an unexpected distortion in our experimental setup.

Piezoelectric microresonators are indispensable in wireless communications, and underpin radio-frequency filtering in mobile phones. These devices are usually analyzed in the quasi(electro)static regime with the magnetic field effectively ignored. On the other hand, at gigahertz frequencies and especially in piezoelectric devices exploiting strong dimensional confinement of acoustic fields, the surface magnetic fields ($B_1$) can be significant. This $B_1$ field, which oscillates at gigahertz frequencies, but is confined to micrometer-scale wavelengths, provides a natural route to efficiently interface with nanoscale spin systems. We show through scaling arguments that $B_1\propto f^2$ for tightly focused acoustic fields at a given operation frequency $f$. We demonstrate the existence of these surface magnetic fields in a proof-of-principle experiment by showing excess power absorption at the focus of a surface acoustic wave (SAW), when a polished yttrium-iron-garnet sphere is positioned in the evanescent field, and the magnon resonance is tuned across the SAW transmission. Finally, we outline the prospects for sensitive spin detection using small-mode-volume piezoelectric microresonators, including the feasibility of electrical detection of single spins at cryogenic temperatures.

Multishape metamaterials exhibit more than one target shape change, e.g., the same metamaterial can have either a positive or negative Poisson’s ratio. So far, multishape metamaterials have mostly been obtained by trial and error. The inverse design of multiple target deformations in such multishape metamaterials remains a largely open problem. Here, we demonstrate that it is possible to design metamaterials with multiple nonlinear deformations of arbitrary complexity. To this end, we introduce a novel sequential nonlinear method to design multiple target modes. We start by iteratively adding local constraints that match a first specific target mode; we then continue from the obtained geometry by iteratively adding local constraints that match a second target mode, and so on. We apply this sequential method to design up to five modes with complex shapes and we show that this method yields at least an 85% success rate. Yet we find that these metamaterials invariably host additional spurious modes, whose number grows with the number of target modes and their complexity, as well as the system size. Our results highlight an inherent tradeoff between design freedom and design constraints and pave the way towards multifunctional materials and devices.

The quantum diamond microscope (QDM) is a recently developed technology for near-field imaging of magnetic fields with micron-scale spatial resolution, under ambient conditions. In the present work, we integrate a QDM with a narrowband measurement protocol and a lock-in camera, and we demonstrate imaging of radio-frequency (rf) magnetic field patterns produced by microcoils, with a spectral resolution of approximately $1\mathrm{Hz}$. This rf QDM provides multifrequency imaging with a central detection frequency that is easily tunable over the megahertz scale, allowing spatial discrimination of both crowded spectral peaks and spectrally well-separated signals. The present instrument has a spatial resolution of approximately $2\text{μ}\mathrm{m}$, a field of view of approximately $300\times 300\text{μ}{\mathrm{m}}^2$, and a per-pixel sensitivity to narrowband fields of about $1\mathrm{nT}{\mathrm{Hz}}^{-1/2}$. Spatial noise can be reduced to the picotesla scale by signal averaging and/or spatial binning. The rf QDM enables simultaneous imaging of the amplitude, frequency, and phase of narrowband magnetic field patterns at the micron scale, with potential applications in real-space NMR imaging, ac susceptibility mapping, impedance tomography, analysis of electronic circuits, and spatial eddy-current-based inspection.

Photonic addressing of superconducting circuits has been proposed to overcome wiring complexity and heat-load challenges. However, such superconducting-photonic links suffer from an efficiency-noise trade-off that limits scalability. This trade-off arises because increasing power conversion efficiency entails reducing optical power, which makes the converted signal susceptible to shot noise. We analyze this trade-off and find that the laser-driven qubit gate infidelity scales inversely with the number of photons used. While methods such as nonlinear detection or squeezed light could mitigate this effect, we consider generating higher-frequency electrical signals, such as millimeter waves (100 GHz), using laser light. At these higher frequencies, circuits have higher operating temperatures and cooling power budgets and alleviate constraints posed by the trade-off. Therefore, we demonstrate an optically driven cryogenic millimeter-wave source with a maximum power efficiency of $8\times {10}^{-5}$ that can generate a maximum of $0.7\text{μ}\mathrm{W}$ of 80 GHz power, with a $1200$-thermal-photon equivalent of added noise at $4\mathrm{K}$. Using this source, we perform frequency-domain spectroscopy of superconducting $\mathrm{Nb}$$\mathrm{Ti}$$\mathrm{N}$ resonators at 80–90 GHz. Our results show a promising approach to lessen the efficiency-noise constraints on superconducting-photonic links, while leveraging the benefits of photonic signal delivery. Further optimization of power efficiency and noise at high frequencies could make scalable photonic control of superconducting qubits viable at temperatures exceeding $1\mathrm{K}$.

Large-scale programmable trapped ion hardware, featuring high gate fidelity and long coherence times, is promising for realizing a practical fault-tolerant quantum computer. However, individual addressing (IA) methods, which are useful for implementing programmable gates in near-term quantum devices, can lead to undesired errors between the target ions and neighboring ions. In this work, we present a low-crosstalk optical addressing system based on multiple optical objectives and acousto-optic deflectors (AODs) with a symmetrical configuration. Two counterpropagating Raman operation beams are both tightly focused, generating an overlapping spot with a waist radius of approximately $1\text{μ}\mathrm{m}$, to address the target ion. As a result, IA crosstalk, characterized by Rabi-rate crosstalk on the spectator ion, is measured to be $1.19(5)\times {10}^{-3}$, with the two ions separated by approximately 5.5 $\text{μ}\mathrm{m}$. This low-crosstalk optical addressing system holds promise for high-fidelity entangling operations, and the symmetrically configured AODs in our method can be readily extended to two dimensions to address a two-dimensional ion crystal.

Optically interfaced solid-state defects are promising candidates for quantum communication technologies. The ideal defect system would feature bright telecom emission, long-lived spin states, and a scalable material platform, simultaneously. Here we use one such system, vanadium (${\mathrm{V}}^{4+}$) in silicon carbide, to establish a potential telecom spin-photon interface within a mature semiconductor host. This demonstration of efficient optical spin polarization and readout facilitates all-optical measurements of temperature-dependent spin relaxation times ($T_1$). By using this technique, and lowering the temperature from approximately 2 K to approximately 100 mK, we observe a remarkable 4-orders-of-magnitude increase in spin $T_1$ across all measured sites, with site-specific values ranging from 57.1 ms to 27.9 s. Furthermore, we identify the underlying relaxation mechanisms, which involve a two-phonon Orbach process, indicating the opportunity for strain tuning to enable qubit operation at higher temperatures. These results position ${\mathrm{V}}^{4+}$ in $\mathrm{Si}\mathrm{C}$ as a prime candidate for scalable quantum nodes in future quantum networks.

Atomic clocks are crucial for science and technology, but their sensitivity is often restricted by the standard quantum limit. To surpass this limit, correlations between particles or interrogation times must be leveraged. Although the sensitivity can be enhanced to the Heisenberg limit using quantum entanglement, it remains unclear whether the scaling of sensitivity with total interrogation time can achieve the Heisenberg scaling. Here, we design an adaptive Bayesian quantum frequency estimation protocol that approaches the Heisenberg scaling and experimentally demonstrate its validity with a cold-atom coherent-population-trapping (CPT) clock. Further, we achieve high-precision closed-loop locking of the cold-atom CPT clock by utilizing our Bayesian quantum frequency estimation protocol. In comparison to the conventional proportional-integral-differential locking, our Bayesian locking scheme not only yields an improvement of 5.1(4) dB in fractional frequency stability, but also exhibits better robustness against technical noises. Our findings not only provide a high-precision approach to lock atomic clocks, but also hold promising applications in various interferometry-based quantum sensors, such as quantum magnetometers and atomic interferometers.

We demonstrate coherent control of a three-electron exchange-only spin qubit with the quantum dots arranged in a close-packed triangular geometry. The device is tuned to confine one electron in each quantum dot, as evidenced by pairwise charge stability diagrams. Time-domain control of the exchange coupling is demonstrated and qubit performance is characterized using blind randomized benchmarking, with an average single-qubit gate fidelity $F=99.84\mathrm{\%}$. The compact triangular device geometry can be readily scaled to larger two-dimensional quantum dot arrays with high connectivity.

Energy-efficient spintronic devices require a large spin-orbit torque (SOT) and low damping to excite magnetic precession. In conventional devices with heavy-metal/ferromagnet bilayers, reducing the ferromagnet thickness to approximately $1$ nm enhances the SOT but dramatically increases damping. Here, we investigate an alternative approach based on a 10-nm-thick single-layer ferromagnet to attain both low damping and a sizable SOT. Instead of relying on a single interface, we continuously break the bulk inversion symmetry with a vertical compositional gradient of two ferromagnetic elements: $\mathrm{Fe}$ with low intrinsic damping and $\mathrm{Ni}$ with sizable spin-orbit coupling. We find low effective damping parameters of ${\alpha }_{\text{eff}}<5\times {10}^{-3}$ in the $\mathrm{Fe}$-$\mathrm{Ni}$ alloy films, despite the steep compositional gradients. Moreover, we reveal a sizable antidamping SOT efficiency of $|{\theta }_{\text{AD}}|\approx 0.05$, even without an intentional compositional gradient. Through depth-resolved x-ray diffraction, we identify a lattice strain gradient as crucial symmetry breaking that underpins the SOT. Our findings provide fresh insights into damping and SOTs in single-layer ferromagnets for power-efficient spintronic devices.

On-demand storage and retrieval of quantum information in coherent light-matter interfaces is a key requirement for future quantum networking and quantum communication applications. Alkali vapor memories offer scalable and robust high-bandwidth storage at high repetition rates, which makes them a natural fit to interface with solid-state single-photon sources. Here, we experimentally realize a room-temperature ladder-type atomic vapor memory that operates on the $\mathrm{Cs}$ D1 line at 895 nm. We provide a detailed experimental characterization and demonstration of on-demand storage and retrieval of weak coherent laser pulses with an average of 0.06(2) photons per pulse at a high signal-to-noise ratio of 830(80). The memory achieves a maximum internal efficiency of ${\eta }_{\text{int}}=15(1)\mathrm{\%}$ and an estimated $1/e$ storage time of ${\tau }_s\approx 32$ ns. Benchmark properties for the storage of single photons from inhomogeneously broadened state-of-the-art solid-state emitters are estimated from the performance of the memory. Together with the immediate availability of high-quality $\mathrm{In}\mathrm{Ga}\mathrm{As}$ quantum dots emitting at 895 nm, these results provide clear prospects for the development of a heterogeneous on-demand quantum light interface.

Sympathetic cooling is a technique often employed to mitigate motional heating in trapped-ion quantum computers. However, choosing system parameters such as number of coolants and cooling duty cycle for optimal gate performance requires evaluating trade-offs between motional errors and other slower errors such as qubit dephasing. The optimal parameters depend on cooling power, heating rate, and ion spacing in a particular system. In this study, we aim to analyze best practices for sympathetic cooling of long chains of trapped ions using analytical and computational methods. We use a case study to show that optimal cooling performance is achieved when coolants are placed at the center of the chain and provide a perturbative upper bound on the cooling limit of a mode given a particular set of cooling parameters. In addition, using computational tools, we analyze the trade-off between the number of coolant ions in a chain and the center-of-mass mode heating rate. We also show that cooling as often as possible when running a circuit is optimal when the qubit coherence time is otherwise long. These results provide a roadmap for how to choose sympathetic cooling parameters to maximize circuit performance in trapped-ion quantum computers using long chains of ions.

In the field of quantum information, hybrid quantum systems comprising magnons and solid-state spins are gaining significant interest. Despite their potential, the scalability of magnon-based quantum devices faces challenges, primarily due to the necessity for close proximity in direct magnon coupling. In this paper, we introduce an approach that enables remote coupling of magnon arrays through microwave photons within a superconducting coplanar waveguide resonator. By applying periodic time-varying magnetic fields, we demonstrate the ability to finely control magnon frequencies, thereby facilitating the adjustment of magnon-magnon hopping dynamics. With appropriate magnetic modulation, the resulting coupled magnon chain emulates a topological reservoir, exemplified by the Su-Schrieffer-Heeger model. When interacting with solid-state spins, such as nitrogen-vacancy centers in diamond, our configuration enables the magnon chain to act as a mediator for tunable and chiral spin-spin interactions. This leads to the generation of significant entanglement between pairs of spins. Our work proposes a scalable quantum device architecture based on magnons and solid-state spins, offering broad possibilities for advances in quantum information processing.

Magnetic Weyl semimetals are promising materials for spintronic applications due to their unique properties in bulk and surface topological states and the rich interplay between band topology and magnetism. While various nontraditional magneto-electrical effects have been studied in magnetic Weyl semimetals, transport properties related to spin-polarized tunneling from these materials remain less explored. In this work, we developed fully epitaxial magnetic tunnel junctions (MTJs) based on a ferromagnetic Weyl semimetal ${\mathrm{Co}}_2\mathrm{Mn}\mathrm{Ga}$. By growing ${\mathrm{Co}}_2\mathrm{Mn}\mathrm{Ga}$ films under different conditions, we fabricated a series of MTJs possessing different degrees of order in the semimetal electrodes and compared their tunneling magnetoresistance (TMR). We find that the TMR becomes enhanced with the improvement of the chemical ordering of ${\mathrm{Co}}_2\mathrm{Mn}\mathrm{Ga}$. Our results reveal the relationship between the spin tunneling in MTJs and the chemical order of the ${\mathrm{Co}}_2\mathrm{Mn}\mathrm{Ga}$ electrode and provide insights on further enhancing TMR via semimetal engineering.