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(001) Si spin qubits are being intensively studied because they have structures similar to that of CMOS devices currently being produced, and thus have the advantage of utilizing state-of-the-art miniaturization, integration, and variation-reduction-technologies. However, there are still issues, such as further improvement of relaxation and decoherence time, stabilization of valley-splitting control, and reduction of the variation caused by the roughness of the interface. In this study, new measures are proposed to address these three issues. Instead of confining an electron to the minimum energy point $X_0$ of the conduction band along the band structure $\Gamma-\Delta-X$ in (001) Si crystals, we propose confining an electron to the L point along $\Gamma-\Lambda-L$ in (111) Si crystals. At the $X_0$ point, the symmetry causes spin-orbit interaction to act on the electron, and the sixfold degeneracy is lifted into a fourfold and a twofold, and the valley-splitting of the twofold conflicts with the two-level system. In the symmetry of the $L$ point, substantial spin polarization disappears, facilitating the reduction of the spin-orbit interaction, and the fourfold degeneracy is lifted to threefold and single, and the single becomes ground state. The need to increase the magnitude of the valley-splitting is exempt, allowing the electron to be controlled away from the interface, which is expected to reduce the variation caused by the roughness of the interface. Data on the confinement of an electron to the $L$ point and the control of fourfold degeneracy are needed, and it is hoped that prototype silicon spin qubits constructed on (111) Si crystals will be developed and that the proposed device structure will help implement quantum computers based on Si devices., Comment: 10 pages, 14 figures

Current fault-tolerant quantum computer (FTQC) architectures utilize several encoding techniques to enable reliable logical operations with restricted qubit connectivity. However, such logical operations demand additional memory overhead to ensure fault tolerance. Since the main obstacle to practical quantum computing is the limited qubit count, our primary mission is to design floorplans that can reduce memory overhead without compromising computational capability. Despite extensive efforts to explore FTQC architectures, even the current state-of-the-art floorplan strategy devotes 50% of memory space to this overhead, not to data storage, to ensure unit-time random access to all logical qubits. In this paper, we propose an FTQC architecture based on a novel floorplan strategy, Load/Store Quantum Computer Architecture (LSQCA), which can achieve almost 100% memory density. The idea behind our architecture is to separate all memory regions into small computational space called Computational Registers (CR) and space-efficient memory space called Scan-Access Memory (SAM). We define an instruction set for these abstract structures and provide concrete designs named point-SAM and line-SAM architectures. With this design, we can improve the memory density by allowing variable-latency memory access while concealing the latency with other bottlenecks. We also propose optimization techniques to exploit properties of quantum programs observed in our static analysis, such as access locality in memory reference timestamps. Our numerical results indicate that LSQCA successfully leverages this idea. In a resource-restricted situation, a specific benchmark shows that we can achieve about 90% memory density with 5% increase in the execution time compared to a conventional floorplan, which achieves at most 50% memory density for unit-time random access. Our design ensures broad quantum applicability., Comment: 17 pages, 15 figures, accepted to HPCA2025

Unconventional superconductivity is often accompanied by non-Fermi liquid (NFL) behavior, which emerges near a quantum critical point (QCP) - a point where an electronic ordered phase is terminated at absolute zero under non-thermal parameters. While nematic orders, characterized by broken rotational symmetry, are sometimes found in unconventional superconductors, the role of nematic fluctuations in driving NFL transport behavior remains unclear. Here, we investigated electrical and thermoelectric transport properties in FeSe$_x$Te$_{1-x}$ thin films and observed hallmark NFL behavior: temperature-linear resistivity and logarithmic divergence of thermoelectricity at low temperatures. Notably, the thermoelectricity peaks sharply at the nematic QCP ($x$ = 0.45), highlighting the dominant role of nematic fluctuations in the NFL transport. Furthermore, we found that the pair-breaking mechanisms in the superconducting phase crosses over from orbital- to Pauli-limited effects, indicating the mass enhancement near the nematic critical regime. These findings reveal the profound impact of nematic fluctuations on both normal-state transport and superconducting properties., Comment: 20 pages, 4 figures, and supplemental material

WordNet provides a carefully constructed repository of semantic relations, created by specialists. But there is another source of information on semantic relations, the intuition of language users. We present the first systematic study of the degree to which these two sources are aligned. Investigating the cases of misalignment could make proper use of WordNet and facilitate its improvement. Our analysis which uses templates to elicit responses from human participants, reveals a general misalignment of semantic relation knowledge between WordNet and human intuition. Further analyses find a systematic pattern of mismatch among synonymy and taxonomic relations~(hypernymy and hyponymy), together with the fact that WordNet path length does not serve as a reliable indicator of human intuition regarding hypernymy or hyponymy relations.

Recently, much work has concerned itself with the enigma of what exactly PLMs (pretrained language models) learn about different aspects of language, and how they learn it. One stream of this type of research investigates the knowledge that PLMs have about semantic relations. However, many aspects of semantic relations were left unexplored. Only one relation was considered, namely hypernymy. Furthermore, previous work did not measure humans' performance on the same task as that solved by the PLMs. This means that at this point in time, there is only an incomplete view of models' semantic relation knowledge. To address this gap, we introduce a comprehensive evaluation framework covering five relations beyond hypernymy, namely hyponymy, holonymy, meronymy, antonymy, and synonymy. We use six metrics (two newly introduced here) for recently untreated aspects of semantic relation knowledge, namely soundness, completeness, symmetry, asymmetry, prototypicality, and distinguishability and fairly compare humans and models on the same task. Our extensive experiments involve 16 PLMs, eight masked and eight causal language models. Up to now only masked language models had been tested although causal and masked language models treat context differently. Our results reveal a significant knowledge gap between humans and models for almost all semantic relations. Antonymy is the outlier relation where all models perform reasonably well. In general, masked language models perform significantly better than causal language models. Nonetheless, both masked and causal language models are likely to confuse non-antonymy relations with antonymy.

Continuous-variable (CV) quantum computing is a promising candidate for quantum computation because it can, even with one mode, utilize infinite-dimensional Hilbert spaces and can efficiently handle continuous values. Although photonic platforms have been considered as a leading platform for CV computation, hybrid systems that use both qubits and bosonic modes, e.g., superconducting hardware, have shown significant advances because they can prepare non-Gaussian states by utilizing the nonlinear interaction between the qubits and the bosonic modes. However, the size of hybrid hardware is currently restricted. Moreover, the fidelity of the non-Gaussian state is also restricted. This work extends the projective squeezing method to establish a formalism for projecting quantum states onto the states that are unitary-transformed from the squeezed vacuum at the expense of the sampling cost. Based on this formalism, we propose methods for simulating larger quantum devices and projecting states onto the cubic phase state, a typical non-Gaussian state, with a higher squeezing level and higher nonlinearity. To make implementation practical, we can, by leveraging the interactions in hybrid systems of qubits and bosonic modes, apply the smeared projector by using either the linear-combination-of-unitaries or virtual quantum error detection algorithms. We numerically verify the performance of our methods and show that projection can suppress the effect of photon-loss errors., Comment: 14 pages and 9 figures

Emergent phenomena arising from nontrivial band structures based on topology and symmetry have been attracting keen interest in contemporary condensed-matter physics. Materials such as SnTe and PbTe are one such example, which demonstrate a topological phase transition while showing ferroelectric instability derived from their rock-salt structure. The ferroelectricity can lift the valley degeneracy, enabling the emergence of the Z2 topological insulator phase, although its observation in transport phenomena remains elusive. Here, we report magnetotransport properties of ferroelectric (Sn,Pb)Te thin films with finely-controlled Fermi levels via In doping. We identified the ferroelectric topological insulator phase from the observations of the quantum Hall states with filling factors of $\nu$ = 1, 2 and 3 with both spin- and valley-degeneracy lifting. The electronic states are two-dimensional, indicating the ferroelectricity-induced topological surface states with a single Dirac cone. The finding of the new topological state with ferroelectricity will further expand the field of topological physics and advance the development of functional properties, such as topological nonlinear photonics and nonreciprocal transport with memory effect., Comment: 21 pages, 4 figures

Distributed quantum computation (DQC) is a promising approach for scalable quantum computing, where high-fidelity non-local operations among remote devices are required for universal quantum computation. These operations are typically implemented through state and gate teleportation with the consumption of high-fidelity entanglement prepared via entanglement purification. However, noisy local operations and classical communication (LOCC) limit the fidelity of purified entanglement, thereby degrading the quality of non-local operations. Meanwhile, circuit knitting and cutting, which simulate non-local operations by preparing separable states along with LOCC, has been considered for DQC as an alternative. Although this approach needs no entanglement among remote devices, it requires excessive circuit runs. Here, we present a protocol utilizing virtual operations that purifies noisy entanglement at the level of expectation values. Our protocol offers the following advantages over conventional methods: surpasses the fidelity limit of entanglement purification in the presence of noise in LOCC, requires fewer sampling shots than circuit knitting, and exhibits robustness against infidelity fluctuations in shared noisy Bell states, unlike probabilistic error cancellation. Our protocol bridges the gap between the entanglement-based and circuit-knitting DQC methods, offering a flexible approach to achieve further scalability despite hardware limitations., Comment: 8+13 pages, 2+8 figures, minor corrections, references added

We report the re-measurement of the $a$-axis spin susceptibility component in an early-stage sample of the spin-triplet superconductor UTe$_2$ with the transition temperature of $T_{\rm SC}$ = 1.6 K. Using Knight-shift measurements along the $b$ axis and at a 10-degree tilt from the $b$ axis towards the $a$ axis, we accurately determined the $a$-axis component without directly measuring the $a$-axis Knight shift. Our results reveal a decrease of approximately 3\% in the $a$-axis spin susceptibility in the superconducting state under $a$-axis magnetic field $\mu_0 H_a \sim 0.1$ T, indicating that the spin susceptibility decreases similarly in both early-stage and ultraclean samples with $T_{\rm SC}$ = 2.1 K. The previously reported absence of the reduction in Knight shift is attributed to the missing of signal from the superconducting region and to the detection of residual signals from the non-superconducting region instead. We also found that the decrease in the $a$-axis spin susceptibility is immediately suppressed with increasing the $a$-axis magnetic field and is estimated to be completely suppressed at around 1.5 T due to superconducting spin rotation., Comment: 5 pages, 3 figures

The edge-device environment imposes severe resource limitations, encompassing computation costs, hardware resource usage, and energy consumption for deploying deep neural network models. Ultra-low-bit quantization and hardware accelerators have been explored as promising approaches to address these challenges. Ultra-low-bit quantization significantly reduces the model size and the computational cost. Despite progress so far, many competitive ultra-low-bit models still partially rely on float or non-ultra-low-bit quantized computation such as the input and output layer. We introduce Efficiera Residual Networks (ERNs), a model optimized for low-resource edge devices. ERNs achieve full ultra-low-bit quantization, with all weights, including the initial and output layers, being binary, and activations set at 2 bits. We introduce the shared constant scaling factor technique to enable integer-valued computation in residual connections, allowing our model to operate without float values until the final convolution layer. Demonstrating competitiveness, ERNs achieve an ImageNet top-1 accuracy of 72.5pt with a ResNet50-compatible architecture and 63.6pt with a model size less than 1MB. Moreover, ERNs exhibit impressive inference times, reaching 300FPS with the smallest model and 60FPS with the largest model on a cost-efficient FPGA device., Comment: 11pages, 2 figures, the model implementation is available at https://github.com/LeapMind/ERN

Japan faces many challenges related to its aging society, including increasing rates of cognitive decline in the population and a shortage of caregivers. Efforts have begun to explore solutions using artificial intelligence (AI), especially socially embodied intelligent agents and robots that can communicate with people. Yet, there has been little research on the compatibility of these agents with older adults in various everyday situations. To this end, we conducted a user study to evaluate a robot that functions as a facilitator for a group conversation protocol designed to prevent cognitive decline. We modified the robot to use backchannelling, a natural human way of speaking, to increase receptiveness of the robot and enjoyment of the group conversation experience. We conducted a cross-generational study with young adults and older adults. Qualitative analyses indicated that younger adults perceived the backchannelling version of the robot as kinder, more trustworthy, and more acceptable than the non-backchannelling robot. Finally, we found that the robot's backchannelling elicited nonverbal backchanneling in older participants., Comment: Published at Proceedings of the 2023 32nd IEEE International Conference on Robot and Human Interactive Communication (RO-MAN 2023)

We study the embedded topology of certain conic-line arrangements of degree 7. Two new examples of Zariski pairs are given. Furthermore, we determine the number of connected components of the conic-line arrangements. We also calculate the fundamental groups using SageMath and the package Sirocco in the appendix., Comment: 35 pages, 14 figures

We describe the new design and current performance of the Mid-InfraRed Spectrometer and Imager (MIRSI) on the NASA Infrared Telescope Facility (IRTF). The system has been converted from a liquid nitrogen/liquid helium cryogen system to one that uses a closed-cycle cooler, which allows it to be kept on the telescope at operating temperature and available for observing on short notice, requiring less effort by the telescope operators and day crew to maintain operating temperature. Several other enhancements have been completed, including new detector readout electronics, an IRTF-style standard instrument user interface, new stepper motor driver electronics, and an optical camera that views the same field as the mid-IR instrument using a cold dichroic mirror, allowing for guiding and/or simultaneous optical imaging. The instrument performance is presented, both with an engineering-grade array used from 2021-2023, and a science-grade array installed in the fall of 2023. Some sample astronomical results are also shown. The upgraded MIRSI is a facility instrument at the IRTF available to all users., Comment: 15 pages, 17 figures, accepted to PASP

By quantizing network weights and activations to low bitwidth, we can obtain hardware-friendly and energy-efficient networks. However, existing quantization techniques utilizing the straight-through estimator and piecewise constant functions face the issue of how to represent originally high-bit input data with low-bit values. To fully quantize deep neural networks, we propose pixel embedding, which replaces each float-valued input pixel with a vector of quantized values by using a lookup table. The lookup table or low-bit representation of pixels is differentiable and trainable by backpropagation. Such replacement of inputs with vectors is similar to word embedding in the natural language processing field. Experiments on ImageNet and CIFAR-100 show that pixel embedding reduces the top-5 error gap caused by quantizing the floating points at the first layer to only 1% for the ImageNet dataset, and the top-1 error gap caused by quantizing first and last layers to slightly over 1% for the CIFAR-100 dataset. The usefulness of pixel embedding is further demonstrated by inference time measurements, which demonstrate over 1.7 times speedup compared to floating point precision first layer.

Honeycomb-lattice antiferromagnets have attracted wide attention for exploration of exotic heat transport and their interplay with magnetic excitations. In this work, we have revealed a contrasting behavior in the magneto-thermal conductivity (MTC) between two Co-based honeycomb-lattice magnets Co4M2O9 (M = Nb, Ta), despite their identical lattice structures and quite similar magnetism. Co4Ta2O9 exhibits enhanced MTC of about 550% at 9 T of an in-plane magnetic field, comparable to other honeycomb-magnets, while MTC for Co4Nb2O9 reaches only ~30%. This marked difference is ascribed to distinct features in the field-induced evolution of magnetic excitations that resonantly scatter phonons. This finding sheds light on implicit impacts of non-magnetic ions on thermal transport, and hints at the potential for broad heat-transport tunability while preserving magnetism and lattice structures., Comment: 7 pages, 4 figures, doi.org/10.1103/PhysRevB.110.L041116

We have developed an innovative lighting system that changes specific target colors while keeping the lights appearing naturally white. By precisely controlling the spectral power distribution (SPD) of illumination and harnessing the unique phenomenon of metamerism, our system achieves unique color variations in ways you've never seen before. Our system calculates the optimal SPDs of illumination for given materials to intensively induce metamerism, and then synthesizes the illumination using various colors of LEDs. We successfully demonstrated the system's implementation at Paris Fashion Week 2024. As models step onto the stage, their dresses initiate a captivating transformation. Our system altering the colors of the dresses, showcasing an impressive transition from one stunning color to another.

We report low-temperature powder X-ray and neutron diffraction studies on breathing pyrochlore magnets Cu$M$Cr$_{4}$S$_{8}$ ($M$ = Al, Ga), which undergo a magnetic transition at $T_{\rm N} \approx$ 21 and 31 K for {$M$ = Al and Ga, respectively. X-ray diffraction reveals that the magnetic transition accompanies a structural transition from cubic $F{\overline 4}3m$ to polar orthorhombic $Imm2$ symmetry for both the compounds, with larger distortion observed for $M$ = Ga at low temperatures. Neutron diffraction reveals incommensurate magnetic modulation ${\mathbf Q} = (q_{\rm IC}, 0.5, 0)$ in the orthorhombic setting, where $q_{\rm IC} \approx$ 0.39 and 0.31 for $M$ = Al and Ga, respectively. Our magnetic-structure analysis suggests cycloid-type magnetic order but not proper-screw type for both the compounds. We find strong correlation between the local spin configuration and Cr-Cr bond lengths, indicating that the spin-lattice coupling as well as the magnetic frustration play an important role in determining the ground state. Cu$M$Cr$_{4}$S$_{8}$ potentially offers a platform to explore magnetoelectric effects arising from the helimagnet driven electric polarity., Comment: 8 pages, 6 figures, 5 tables

We prove that no concavity properties are preserved by the Dirichlet heat flow in a totally convex domain of a Riemannian manifold unless the sectional curvature vanishes everywhere on the domain., Comment: 18 pages. Comments welcome!

We have developed a circularly polarized dielectric rutile (TiO$_2$) cavity with a high quality-factor that can generate circularly polarized microwaves from two orthogonal linearly polarized microwaves with a phase difference of $\pm \pi/2$ using a hybrid coupler. Using this cavity, we have established a new methodology to measure the microwave Hall conductivity of a small single crystal of metal in the skin-depth region. Based on the cavity perturbation technique, we have shown that all components of the surface impedance tensor can be extracted under the application of a magnetic field by comparing the right- and left-handed circularly polarized modes. To verify the validity of the developed method, we performed test measurements on tiny Bi single crystals at low temperatures. As a result, we have successfully obtained the surface impedance tensor components and confirmed that the characteristic field dependence of the ac Hall angle in the microwave region is consistent with the expectation from the dc transport measurements. These results demonstrate a significant improvement in sensitivity compared to previous methods. Thus, our developed technique allows more accurate microwave Hall measurements, opening the way for new approaches to explore novel topological quantum phenomena, such as time-reversal symmetry breaking in superconductors., Comment: 11 pages, 7 figures

Topological semimetals are intriguing targets for exploring unconventional physical properties of massless fermions. Among them, nodal line or nodal ring semimetals have attracted attention for their unique one-dimensional band contact in momentum space and resulting nontrivial quantum phenomena. By field angular resolved magnetotransport measurements and theoretical calculations, we show that pressurized black phosphorus (BP) is an ideal nodal ring semimetal with weak spin-orbit coupling, which has a sole and carrier density-tunable nodal ring isolated from other trivial bands. We also revealed that the large magnetoresistance effect and its field-angular dependence in semimetallic BP are due to highly anisotropic relaxation time. Our results establish pressurized BP as an elemental model material for exploring nontrivial quantum properties unique to the topological nodal ring.

The thermoelectric Nernst effect of solids converts heat flow to beneficial electronic voltages. Here, using a correlated topological semimetal with high carrier mobility $\mu$ in presence of magnetic fluctuations, we demonstrate an enhancement of the Nernst effect close to a magnetic phase transition. A magnetic instability in NdAlSi modifies the carrier relaxation time on 'hotspots' in momentum space, causing a strong band filling dependence of $\mu$. We quantitatively derive electronic band parameters from a novel two-band analysis of the Nernst effect $S_{xy}$, in good agreement with quantum oscillation measurements and band calculations. While the Nernst response of NdAlSi behaves much like conventional semimetals at high temperatures, an additional contribution $\Delta S_{xy}$ from electronic correlations appears just above the magnetic transition. Our work demonstrates the engineering of the relaxation time, or the momentum-dependent self energy, to generate a large Nernst response independent of a material's carrier density, i.e. for metals, semimetals, and semiconductors with large $\mu$.

The design of translation symmetric bosonic codes, e.g., Gottesmann-Kitaev-Preskill and squeezed cat codes, is robust against photon loss, but the computation accuracy is limited by the available squeezing level. Here, we introduce the \textit{projective squeezing} (PS) method for computing outcomes for a higher squeezing level by revealing that a linear combination of displacement operators with periodic displacement values constitutes the smeared projector onto the better code space; we also show the analytical relationship between the increased squeezing level and the projection probability. We introduce concrete implementation methods for PS based on linear-combination-of-unitaries and virtual quantum error detection. We also numerically verify our analytical arguments and show that our protocol can mitigate the effect of photon loss.

We propose a scheme for generating a high-purity single photon on the basis of cavity quantum electrodynamics (QED). This scheme employs a four-level system including two excited states, two ground states, and two driving lasers; this structure allows the suppression of the re-excitation process due to the atomic decay, which is known to significantly degrade the single-photon purity in state-of-the-art photon sources using a three-level system. Our analysis shows that the re-excitation probability arbitrarily approaches zero without sacrificing the photon generation probability when increasing the power of the driving laser between the excited states. This advantage is achievable by using current cavity-QED technologies. Our scheme can contribute to developing distributed quantum computation or quantum communication with high accuracy., Comment: Main text: 5 pages, 2 figures, Appendix: 10 pages

The normal-conducting state of the superconductor UTe$_2$ is studied by entropy analysis for magnetic fields along the $b$-axis, obtained from magnetization using the relation $(\partial M/\partial T)_B=(\partial S/\partial B)_T$. We observe a strong increase in entropy with magnetic field due to metamagnetic fluctuations (spatially uniform, $Q=0$). The field dependence is well described by the Hertz-Millis-Moriya theory for quantum criticality of itinerant metamagnetism. Notably, the lower bound of the quantum-critical region coincides well with the position of the minimum in the superconducting transition temperature $T_c(B)$. Hence, our results suggest that $Q=0$ fluctuations reinforce the superconductivity., Comment: accepted as a Letter in Phys. Rev. B

We performed high-magnetic-field magnetization, polarization, and ultrasonic measurements in Ba$_2$CuGe$_2$O$_7$ to investigate field-induced multiferroic properties arising from a cross-correlation between electric dipoles and electric quadrupoles in addition to cross-correlation between magnetic dipoles and electric dipoles. Magnetization $M$ shows saturation behavior above 20 T for several magnetic field directions, however, electric polarization $P_c$ exhibits an increase, and elastic constants show a softening above 20 T. Based on quantum states with a crystalline electric field for the $D_{2d}$ point group and $d$-$p$ hybridization between Cu-$3d$ and O-$2p$ electrons, we confirmed that the matrix of an electric dipole $P_z$ was proportional to that of an electric quadrupole $O_{xy}$. Furthermore, considering the spin-orbit coupling of $3d$ electrons and the Zeeman effect, we showed that $P_z$ and $O_{xy}$ simultaneously exhibited field-induced responses. These findings indicate that the orbital degrees of freedom, in addition to the spin degrees of freedom, contribute to the high-field multiferroicity in Ba$_2$CuGe$_2$O$_7$., Comment: 28 pages, 13 figures, accepted in Phys. Rev. B (20 Feb. 2024)

In this study, we performed high-magnetic-field magnetization, dielectric, and ultrasound measurements on an organic salt showing a ferroelectric spin-Peierls (FSP) state, which is in close proximity to a quantum critical point. In contrast to the sparsely distributed gas-like spin solitons typically observed in conventional spin-Peierls (SP) states, the FSP state exhibits dense liquid-like spin solitons resulting from strong quantum fluctuations, even at low fields. Nevertheless, akin to conventional SP systems, a magnetic-field-induced transition is observed in the FSP state. In conventional high-field SP states, an emergent wave vector results in the formation of a spin-soliton lattice. However, in the present high-field FSP state, the strong quantum fluctuations preclude the formation of such a soliton lattice, causing the dense solitons to remain in a quantum-mechanically melted state. This observation implies the realization of a quantum liquid--liquid transition of topological particles carrying spin and charge in a ferroelectric insulator.