Continuous-variable (CV) entanglement constitutes a powerful approach to deterministic quantum information protocols. Improving the scale of entanglement is of vital importance for enhancing the information capacity of quantum information protocols. Here we demonstrate the deterministic generation of CV entanglement of large-scale Hermite-Gaussian (HG) modes from the four-wave mixing (FWM) process in an atomic vapor. In our experiment, 56 pairs of entangled HG modes are deterministically and simultaneously generated from the FWM process, which increases the number of entangled spatial mode pairs in the CV system. Meanwhile, we experimentally verify the existence of CV entanglement between the evolution process from HG mode to Laguerre-Gaussian mode. Our results shed light on constructing high-capacity CV quantum information protocols and provide a promising platform to study CV entanglement.

We present a method for quantum tomography of multiqubit states. We apply the method to spin-multiphoton states, which we generate using a quantum dot based device. Periodic excitation of a quantum dot confined spin deterministically generates strings of entangled photons in a cluster state, threefold faster than previously demonstrated. Our tomography method uses time-resolved polarization-sensitive multiphoton correlation measurements to measure both the polarization of the confined spin and that of the emitted photons. We develop an edge-sensitive gradient-descent algorithm and apply it to the acquired data to map the periodic physical process that generates the cluster state. We utilize our tomographic method to optimize our quantum dot based device and show that the enhanced generation rate increases the entanglement robustness of the generated multiqubit state.

Optomechanical systems show great potential as quantum transducers and information storage devices for use in future hybrid quantum networks. In this context, optomechanical strong coupling can enable efficient, high-bandwidth, and deterministic transfer of quantum states. While optomechanical strong coupling has been realized at optical frequencies, it has proven difficult to identify a robust optomechanical system that features the low loss and high coupling rates required for more sophisticated control of mechanical motion. In this paper, we demonstrate strong coupling in a Brillouin-based bulk cavity optomechanical system in both the single-mode and the multimode strong-coupling regime, which leads to a useful device both for applications in quantum information and for investigating decoherence phenomena in bulk acoustic wave resonators. Using nontrivial mode hybridizations in the strong-coupling regime, we create hybridized photonic-phononic modes with lifetimes that are significantly longer than those of the uncoupled system. This surprising lifetime enhancement, which results from the interference of decay channels, showcases the use of multimode strong coupling as a general strategy to control extrinsic decoherence mechanisms. Moreover, phonons supported by such bulk-acoustic-wave resonators have a collection of properties, including high frequencies, long coherence times, and robustness against thermal decoherence, that make this optomechanical system particularly enticing for applications such as quantum transduction and memories. Hence, this system provides access to phenomena in a previously unexplored regime of optomechanical interactions and could serve as an important building block for future quantum devices.

One of the main bottlenecks in the pursuit of a large-scale–chip-based quantum computer is the large number of control signals needed to operate qubit systems. As system sizes scale up, the number of terminals required to connect to off-chip control electronics quickly becomes unmanageable. Here, we discuss a quantum-dot spin-qubit architecture that integrates on-chip control electronics, allowing for a significant reduction in the number of signal connections at the chip boundary. By arranging the qubits in a two-dimensional array with about $12\mu \mathrm{m}$ pitch, we create space to implement locally integrated sample-and-hold circuits. This allows us to offset the inhomogeneities in the potential landscape across the array and to globally share the majority of the control signals for qubit operations. We make use of advanced circuit modeling software to go beyond conceptual drawings of the component layout, to assess the feasibility of the scheme through a concrete floor plan, including estimates of footprints for quantum and classical electronics, as well as routing of signal lines across the chip using different interconnect layers. We make use of local demultiplexing circuits to achieve an efficient signal-connection scaling, leading to a Rent’s exponent as low as $p=0.43$. Furthermore, we use available data from state-of-the-art spin qubit and microelectronics technology development, as well as circuit models and simulations, to estimate the operation frequencies and power consumption of a million-qubit array. This work presents a complementary approach to previously proposed architectures, focusing on a feasible scheme to integrating quantum and classical hardware, and identifying remaining challenges for achieving full fault-tolerant quantum computation. It thereby significantly closes the gap towards a fully CMOS-compatible quantum computer implementation.

We report an infrared (IR) imaging study of trilayer graphene (TLG) with both ABA (Bernal) and ABC (rhombohedral) stacking orders using the scattering-type scanning near-field optical microscope (SSNOM). With the SSNOM operating in the mid-IR region, we map in real space the surface plasmon polaritons of ABA TLG and ABC TLG, which are tunable with electrical gating. Through quantitative modeling of plasmonic imaging data, we find that the plasmon wavelength of ABA TLG is significantly larger than that of ABC TLG, resulting in a sizable impedance mismatch and hence a strong plasmon reflection at the ABA/ABC lateral junction. Further analysis indicates that the different plasmonic responses of the two types of TLG are directly linked to their distinct electronic structures and carrier properties. Our work uncovers the physics behind the stacking-dependent plasmonic responses of TLG and sheds light on future applications of TLG and the ABA/ABC junctions in IR plasmonics and planar nano-optics.

Active materials with distinctive nonequilibrium properties have diverse materials science applications. Active systems are common in living matter, such as the filament network in the cell that is activated by molecular motors, and in materials science as exemplified by hydrogels activated by chemical reactions. Here we describe another class of active polymeric filament systems where the filaments are activated by embedded chemically powered nanomotors that have catalytic and noncatalytic parts. Chemical reactions on the catalytic surfaces produce forces that act on the polymeric filaments. By changing the nonequilibrium conditions, these forces can be made to change sign and thereby compress or expand the filaments. The embedded motors provide both the source of activity and the means to control the filament conformational structure. As an example of control, we show that oscillatory variations of the chemical constraints yield gel-like networks that oscillate between expanded or compressed forms, much like those of hydrogels.

The material family of $Y$-type hexaferrites is among the most promising candidates for magnetoelectric memory applications. The magnetoelectric properties in this class of magnets are dominated by a multiferroic phase, termed the FE3 phase, where spin-driven polarization can be switched by a magnetic field, and, conversely, a full magnetic moment can be reversed by an electric field. In this study, we discuss the effect of Cr doping on the stability of competing magnetic and multiferroic phases in the $Y$-type hexaferrites ${\mathrm{Ba}\mathrm{Sr}\mathrm{Co}}_2{\mathrm{Fe}}_{12-x-\delta }{\mathrm{Al}}_x{\mathrm{Cr}}_{\delta }{\mathrm{O}}_{22}$ with $x=0.9$ and $\delta =0.00$, 0.05, and 0.10. We find that Cr doping increases the stability of the multiferroic FE3 phase; while in the Cr-free compound the alternating longitudinal conical (ALC) and proper screw phases are stabilized as zero-field-cooled magnetic phases, the FE3 phase appears besides the ALC phase as a stable zero-field-cooled phase in the $\delta =0.05$ and 0.10 compounds. Moreover, a spin-induced large polarization is observed at and above room temperatures with antisymmetric magnetic field dependence. The magnetoelectric properties, in particular the coupling between polarization and magnetization, are investigated via the measurements in the simultaneous presence of electric and magnetic fields. We find the enhanced stability of the magnetoelectic responses from the multiferroic FE3 phase upon Cr doping, while the coupling between the polarization and magnetization is preserved.

Acoustic waves are ubiquitous in everyday human experience, therefore, precise control over the deformation of acoustic waves is always extremely desirable, which can be used, for example, to transform or hide objects from incident waves. Acoustic illusion devices are generally implemented by transformation acoustics, which can deceive ears or sonar systems. Challenges remain, for example, the complex and extreme material parameters prescribed by coordinate transformation theory make the implementations particularly difficult, even with the help of acoustic metamaterials. Here, the method based on Fabry-Perot resonances offers a feasible solution for achieving three-dimensional (3D) omnidirectional passive acoustic illusion. We theoretically demonstrate 3D acoustic illusion via Mie theory, a reduced version is further designed numerically and implemented experimentally. Our work opens possibilities for the implementation of modern acoustic illusion devices in the future, such as camouflage for antisonar detection.

Current noise levels in physical realizations of qubits and quantum operations limit the applicability of conventional methods to characterize entanglement. In this adverse scenario, we follow a quantum variational approach to estimate the geometric measure of entanglement of multiqubit pure states. The algorithm requires only single-qubit gates and measurements, so it is well suited for noisy intermediate-scale quantum devices. This is demonstrated by successfully implementing the method on IBM Quantum devices for Greenberger-Horne-Zeilinger states of three, four, and five qubits. Numerical simulations with random states show the robustness and accuracy of the method. The scalability of the protocol is numerically demonstrated via matrix-product-state techniques up to $25$ qubits.

We propose here a high-frequency spin-Hall nano-oscillator based on a simple magnetic texture, such as a domain wall, located in an antiferromagnet with an easy-axis anisotropy type. We show that the spin current, polarized along the anisotropy axis, excites a conical precession of the Néel vector in such a domain wall, which allows obtaining a robust ac output signal—contrary to the planar precession in a uniform uniaxial antiferromagnet, where ac output is hard to achieve. The frequency of the auto-oscillations is easily tunable by the applied current up to the terahertz range, and the threshold current vanishes for a pure uniaxial antiferromagnet. By micromagnetic simulations, we demonstrate that the pinning of the domain wall is crucial for the oscillator design, which can be achieved in the nanoconstriction layout of the free layer.

Single-mode high-index-contrast waveguides have been ubiquitously exploited in optical, microwave, and phononic structures for achieving enhanced wave-matter interactions. Although microscale optomechanical and electro-optical devices have been widely studied, optomagnonic devices remain a grand challenge at the microscale. Here, we introduce a planar optomagnonic waveguide platform based on a ferrimagnetic insulator that simultaneously supports single transverse mode of spin waves (magnons) and highly confined optical modes. The colocalization of spin and light waves gives rise to an enhanced inverse Faraday effect, and as a result, magnons are excited by an effective magnetic field generated by interacting optical photons. Moreover, the strongly enhanced optomagnonic interaction allows us to observe such an effect using low-power (milliwatt level) light signals in the continuous-wave form, as opposed to high-intensity (megawatt peak power) light pulses that are typically required in magnetic bulk materials or thin films. The optically driven magnons are detected electrically with preserved phase coherence, showing the feasibility for launching spin waves with low-power continuous optical fields.

The combination of local heating and biasing at the tip-surface junction in temperature-assisted piezoresponse force microscopy (TPFM) opens a pathway for probing local temperature-induced phase transitions in ferroics, exploring the temperature dependence of polarization dynamics in ferroelectrics and potentially discovering coupled phenomena driven by strong temperature and electric field gradients. Here, we analyze the signal-formation mechanism in TPFM and explore the interplay between thermal- and bias-induced switching in model ferroelectric materials. We further explore the contributions of the flexoelectric and thermopolarization effects to the local electromechanical response and demonstrate that the latter can be significant for “soft” ferroelectrics. These results establish a framework for the quantitative interpretation of TPFM observations, predict the emergence of nontrivial switching and relaxation phenomena driven by nonlocal thermal-gradient-induced polarization switching, and open a pathway for exploring the physics of thermopolarization effects in various noncentrosymmetric and centrosymmetric materials.

Single color centers in solid have emerged as promising physical platforms for quantum information science. Creating these centers with excellent quantum properties is a key foundation for further technological developments. In particular, the microscopic understanding of the spin-bath environments is the key to engineer color centers for quantum control. In this work, we propose and demonstrate a distinct high-temperature annealing (HTA) approach for creating high-quality nitrogen vacancy (N-V) centers in implantation-free diamonds. Simultaneously using the created N-V centers as probes for their local environment we verify that no damage is microscopically induced by the HTA. Nearly all single N-V centers created in ultralow-nitrogen-concentration membranes possess stable and Fourier-transform-limited optical spectra. Furthermore, HTA strongly reduces noise sources naturally grown in ensemble samples, and leads to more than threefold improvements of decoherence time and sensitivity. We also verify that the vacancy activation and defect reformation, especially H3 and P1 centers, can explain the reconfiguration between spin baths and color centers. This distinct approach will become a powerful tool in vacancy-based quantum technology.

Recently, there has been growing interest in developing superresolution lenses to focus light beyond the conventional diffraction limit in the far field. Achromatic superresolution is particularly attractive for many practical applications. However, it remains a great challenge to realize an achromatic superresolution focusing lens with both a high numerical aperture and a small depth of focus, which is critical for superresolution imaging with high longitudinal resolution. Here, a method for preparing a multiwavelength achromatic superresolution lens with a high numerical aperture is proposed to control the wave front through a binary-phase zone plate for generating a transverse superresolution focal spot with a small depth of focus. The approach is experimentally verified with an achromatic superresolution lens with a high numerical aperture of 0.95 at six wavelengths in the visible range between 405 and 684 nm. The proposed method is practical for superresolution-related applications, including imaging, microscopy, and data storage.

We investigate quantum repeater protocols that rely on three-qubit repetition codes using nitrogen-vacancy (N-$V$) centers in diamond as quantum memories. N-$V$ centers offer a two-qubit register, corresponding to their electron and nuclear spins, which makes it possible to perform deterministic two-qubit operations within one N-$V$ center. For quantum repeater applications, however, we need to do joint operations on two separate N-$V$ centers. Here, we study two N-$V$-center-based repeater structures that enable such deterministic joint operations. One structure offers less consumption of classical communication, at the cost of more computation overhead, whereas the other relies on a smaller number of physical resources and operations. We assess and compare their performance for the task of secret-key generation under the influence of noise and decoherence with current and near-term experimental parameters. We quantify the regimes of operation where one structure outperforms the other, and find the regions where encoded quantum repeaters offer practical advantages over their nonencoded counterparts.

Quantum sensing is considered to be one of the most promising subfields of quantum information to deliver practical quantum advantages in real-world applications. However, its impressive capabilities, including high sensitivity, are often hindered by the limited quantum resources available. Here, we incorporate the expected information gain (EIG) and techniques such as accelerated computation into Bayesian experimental design (BED) in order to use quantum resources more efficiently. A simulated nitrogen-vacancy center in diamond is used to demonstrate real-time operation of the BED. Instead of heuristics, the EIG is used to choose optimal control parameters in real time. Moreover, combining the BED with accelerated computation and asynchronous operations, we find that up to a tenfold speedup in absolute time cost can be achieved in sensing multiple surrounding ${}^{13}\mathrm{C}$ nuclear spins. Our work explores the possibilities of applying the EIG to BED-based quantum-sensing tasks and provides techniques useful to integrate BED into more generalized quantum sensing systems.

Exciton-polaritons are hybrid light-matter states that arise from strong coupling between an exciton resonance and a photonic cavity mode. As bosonic excitations, they can undergo a phase transition to a condensed state that can emit coherent light without a population inversion. This aspect makes them good candidates for thresholdless lasers, yet short exciton-polariton lifetime has made it difficult to achieve condensation at very low power densities. In this sense, long-lived symmetry-protected states are excellent candidates to overcome the limitations that arise from the finite mirror reflectivity of monolithic microcavities. In this work we use a photonic symmetry-protected bound state in the continuum coupled to an excitonic resonance to achieve state-of-the-art polariton condensation threshold in a $\mathrm{Ga}\mathrm{As}$/($\mathrm{Al},\mathrm{Ga}$)$\mathrm{As}$ waveguide. Most important, we show the influence of fabrication control and how surface passivation via atomic layer deposition provides a way to reduce exciton quenching at the grating sidewalls.