Magnetic detection under high pressures using designed silicon vacancy centres in silicon carbide.

Pressure-induced magnetic phase transitions are attracting interest as a means to detect superconducting behaviour at high pressures in diamond anvil cells, but determining the local magnetic properties of samples is a challenge due to the small volumes of sample chambers. Optically detected magnetic resonance of nitrogen vacancy centres in diamond has recently been used for the in situ detection of pressure-induced phase transitions. However, owing to their four orientation axes and temperature-dependent zero-field splitting, interpreting these optically detected magnetic resonance spectra remains challenging. Here we study the optical and spin properties of implanted silicon vacancy defects in 4H-silicon carbide that exhibit single-axis and temperature-independent zero-field splitting. Using this technique, we observe the magnetic phase transition of Nd2Fe14B at about 7 GPa and map the critical temperature-pressure phase diagram of the superconductor YBa2Cu3O6.6. These results highlight the potential of silicon vacancy-based quantum sensors for in situ magnetic detection at high pressures.

Collective Microwave Response for Multiple Gate-Defined Double Quantum Dots.

We fabricate and characterize a hybrid quantum device that consists of five gate-defined double quantum dots (DQDs) and a high-impedance NbTiN transmission resonator. The controllable interactions between DQDs and the resonator are spectroscopically explored by measuring the microwave transmission through the resonator in the detuning parameter space. Utilizing the high tunability of the system parameters and the high cooperativity (Ctotal > 17.6) interaction between the qubit ensemble and the resonator, we tune the charge-photon coupling and observe the collective microwave response changing from linear to nonlinear. Our results present the maximum number of DQDs coupled to a resonator and manifest a potential platform for scaling up qubits and studying collective quantum effects in semiconductor-superconductor hybrid cavity quantum electrodynamics systems.

Ultrafast and Electrically Tunable Rabi Frequency in a Germanium Hut Wire Hole Spin Qubit.

Hole spin qubits based on germanium (Ge) have strong tunable spin-orbit interaction (SOI) and ultrafast qubit operation speed. Here we report that the Rabi frequency (fRabi) of a hole spin qubit in a Ge hut wire (HW) double quantum dot (DQD) is electrically tuned through the detuning energy (ϵ) and middle gate voltage (VM). fRabi gradually decreases with increasing ϵ; on the contrary, fRabi is positively correlated with VM. We attribute our results to the change of electric field on SOI and the contribution of the excited state in quantum dots to fRabi. We further demonstrate an ultrafast fRabi exceeding 1.2 GHz, which indicates the strong SOI in our device. The discovery of an ultrafast and electrically tunable fRabi in a hole spin qubit has potential applications in semiconductor quantum computing.

Probing Two Driven Double Quantum Dots Strongly Coupled to a Cavity.

We experimentally and theoretically study a driven hybrid circuit quantum electrodynamics (cQED) system beyond the dispersive coupling regime. Treating the cavity as part of the driven system, we develop a theory applicable to such strongly coupled and to multiqubit systems. The fringes measured for a single driven double quantum dot (DQD)-cavity setting and the enlarged splittings of the hybrid Floquet states in the presence of a second DQD are well reproduced with our model. This opens a path to study Floquet states of multiqubit systems with arbitrarily strong coupling and reveals a new perspective for understanding strongly driven hybrid systems.

Coherent phonon dynamics in spatially separated graphene mechanical resonators.

Vibrational modes in mechanical resonators provide a promising candidate to interface and manipulate classical and quantum information. The observation of coherent dynamics between distant mechanical resonators can be a key step toward scalable phonon-based applications. Here we report tunable coherent phonon dynamics with an architecture comprising three graphene mechanical resonators coupled in series, where all resonators can be manipulated by electrical signals on control gates. We demonstrate coherent Rabi oscillations between spatially separated resonators indirectly coupled via an intermediate resonator serving as a phonon cavity. The Rabi frequency fits well with the microwave burst power on the control gate. We also observe Ramsey interference, where the oscillation frequency corresponds to the indirect coupling strength between these resonators. Such coherent processes indicate that information encoded in vibrational modes can be transferred and stored between spatially separated resonators, which can open the venue of on-demand phonon-based information processing.

Coherent Control and Magnetic Detection of Divacancy Spins in Silicon Carbide at High Pressures.

Spin defects in silicon carbide appear to be a promising tool for various quantum technologies, especially for quantum sensing. However, this technique has been used only at ambient pressure until now. Here, by combining this technique with diamond anvil cell, we systematically study the optical and spin properties of divacancy defects created at the surface of SiC at pressures up to 40 GPa. The zero-field-splitting of the divacancy spins increases linearly with pressure with a slope of 25.1 MHz/GPa, which is almost two-times larger than that of nitrogen-vacancy centers in diamond. The corresponding pressure sensing sensitivity is about 0.28 MPa/Hz-1/2. The coherent control of divacancy demonstrates that coherence time decreases as pressure increases. Based on these, the pressure-induced magnetic phase transition of Nd2Fe14B sample at high pressures was detected. These experiments pave the way to use divacancy in quantum technologies such as pressure sensing and magnetic detection at high pressures.

YUCCA2 (YUC2)-Mediated 3-Indoleacetic Acid (IAA) Biosynthesis Regulates Chloroplast RNA Editing by Relieving the Auxin Response Factor 1 (ARF1)-Dependent Inhibition of Editing Factors in Arabidopsis thaliana.

Although recent research progress on the abundant C-to-U RNA editing events in plant chloroplasts and mitochondria has uncovered many recognition factors and their molecular mechanisms, the intrinsic regulation of RNA editing within plants remains largely unknown. This study aimed to establish a regulatory relationship in Arabidopsis between the plant hormone auxin and chloroplast RNA editing. We first analyzed auxin response elements (AuxREs) present within promoters of chloroplast editing factors reported to date. We found that each has more than one AuxRE, suggesting a potential regulatory role of auxin in their expression. Further investigation unveiled that the depletion of auxin synthesis gene YUC2 reduces the expression of several editing factors. However, in yuc2 mutants, only the expression of CRR4, DYW1, ISE2, and ECD1 editing factors and the editing efficiency of their corresponding editing sites, ndhD-2 and rps14-149, were simultaneously suppressed. In addition, exogenous IAA and the overexpression of YUC2 enhanced the expression of these editing factors and the editing efficiency at the ndhD-2 and rps14-149 sites. These results suggested a direct effect of auxin upon the editing of the ndhD-2 and rps14-149 sites through the modulation of the expression of the editing factors. We further demonstrated that ARF1, a downstream transcription factor in the auxin-signaling pathway, could directly bind to and inactivate the promoters of CRR4, DYW1, and ISE2 in a dual-luciferase reporter system, thereby inhibiting their expression. Moreover, the overexpression of ARF1 in Arabidopsis significantly reduced the expression of the three editing factors and the editing efficiency at the ndhD-2 and rps14-149 sites. These data suggest that YUC2-mediated auxin biosynthesis governs the RNA-editing process through the ARF1-dependent signal transduction pathway.

Anisotropic g-Factor and Spin-Orbit Field in a Germanium Hut Wire Double Quantum Dot.

Holes in nanowires have drawn significant attention in recent years because of the strong spin-orbit interaction, which plays an important role in constructing Majorana zero modes and manipulating spin-orbit qubits. Here, from the strongly anisotropic leakage current in the spin blockade regime for a double dot, we extract the full g-tensor and find that the spin-orbit field is in plane with an azimuthal angle of 59° to the axis of the nanowire. The direction of the spin-orbit field indicates a strong spin-orbit interaction along the nanowire, which may have originated from the interface inversion asymmetry in Ge hut wires. We also demonstrate two different spin relaxation mechanisms for the holes in the Ge hut wire double dot: spin-flip co-tunneling to the leads, and spin-orbit interaction within the double dot. These results help establish feasibility of a Ge-based quantum processor.

Tunable parametric amplification of a graphene nanomechanical resonator in the nonlinear regime.

Parametric amplification is widely used in nanoelectro-mechanical systems to enhance the transduced mechanical signals. Although parametric amplification has been studied in different mechanical resonator systems, the nonlinear dynamics involved receives less attention. Taking advantage of the excellent electrical and mechanical properties of graphene, we demonstrate electrical tunable parametric amplification using a doubly clamped graphene nanomechanical resonator. By applying external microwave pumping with twice the resonant frequency, we investigate parametric amplification in the nonlinear regime. We experimentally show that the extracted coefficient of the nonlinear Duffing force α and the nonlinear damping coefficient η vary as a function of external pumping power, indicating the influence of higher-order nonlinearity beyond the Duffing (∼x 3) and van der Pol (∼[Formula: see text]) types in our device. Even when the higher-order nonlinearity is involved, parametric amplification still can be achieved in the nonlinear regime. The parametric gain increases and shows a tendency of saturation with increasing external pumping power. Further, the parametric gain can be electrically tuned by the gate voltage with a maximum gain of 10.2 dB achieved at the gate voltage of 19 V. Our results will benefit studies on nonlinear dynamics, especially nonlinear damping in graphene nanomechanical resonators that has been debated in the community over past decade.

Narrow-band asymmetric transmission based on the dark mode of Fano resonance on symmetric trimeric metasurfaces.

Asymmetric transmission (AT) is useful for polarization manipulation. We report narrowband AT that utilizes a triple-layered symmetric trimeric metasurface with near-field coupling of the dark mode of the Fano resonance. The coupling strength of the dark mode was tuned by using a mid-layer to break the dim AT between two slit layers. The peak transmission of linearly polarized waves and percentage bandwidth reached 0.7719 and 1.26% (numerical simulations) and 0.49 and 1.9% (experiments), respectively. Coupled-mode theory and field patterns are utilized to explain the underlying physical mechanisms of the mid-layer assisted field coupling. These results are useful for Fano-resonance-based devices.

Identification of NEO1 as a prognostic biomarker and its effects on the progression of colorectal cancer.

BACKGROUND: Due to the high morbidity and poor clinical outcomes, early predictive and prognostic biomarker identification is desiderated in colorectal cancer (CRC). As a homologue of the Deleted in Colorectal Cancer (DCC) gene, the role of Neogenin-1 (NEO1) in CRC remained unveiled. This study was designed to probe into the effects and potential function of NEO1 in CRC. METHODS: Online databases, Gene Set Enrichment Analysis (GSEA), quantitative real-time PCR and western blotting were used to evaluate NEO1 expression in colorectal cancer tissues. Survival analysis was performed to predict the prognosis of CRC patients based on NEO1 expression level. Then, cell proliferation was detected by colony formation and Cell Counting Kit 8 (CCK-8) assays. CRC cell migration and invasion were examined by transwell assays. Finally, we utilized the Gene Set Variation Analysis (GSVA) and GSEA to dig the potential mechanisms of NEO1 in CRC. RESULTS: Oncomine database and The Cancer Genome Atlas (TCGA) database showed that NEO1 was down-regulated in CRC. Further results validated that NEO1 mRNA and protein expression were both significantly lower in CRC tumor tissues than in the adjacent tissues in our clinical samples. NEO1 expression was decreased with the progression of CRC. Survival and other clinical characteristic analyses exhibited that low NEO1 expression was related with poor prognosis. A gain-of-function study showed that overexpression of NEO1 restrained proliferation, migration and invasion of CRC cells while a loss-of-function showed the opposite effects. Finally, functional pathway enrichment analysis revealed that NEO1 low expression samples were enriched in inflammation-related signaling pathways, EMT and angiogenesis. CONCLUSION: A tumor suppressor gene NEO1 was identified and verified to be correlated with the prognosis and progression of CRC, which could serve as a prognostic biomarker for CRC patients.

Giant Anisotropy of Spin Relaxation and Spin-Valley Mixing in a Silicon Quantum Dot.

In silicon quantum dots (QDs), at a certain magnetic field commonly referred to as the "hot spot," the electron spin relaxation rate (T_{1}^{-1}) can be drastically enhanced due to strong spin-valley mixing. Here, we experimentally find that with a valley splitting of 78.2±1.6 µeV, this hot spot in spin relaxation can be suppressed by more than 2 orders of magnitude when the in-plane magnetic field is oriented at an optimal angle, about 9° from the [100] sample plane. This directional anisotropy exhibits a sinusoidal modulation with a 180° periodicity. We explain the magnitude and phase of this modulation using a model that accounts for both spin-valley mixing and intravalley spin-orbit mixing. The generality of this phenomenon is also confirmed by tuning the electric field and the valley splitting up to 268.5±0.7 µeV.

Coupling a Germanium Hut Wire Hole Quantum Dot to a Superconducting Microwave Resonator.

Realizing a strong coupling between spin and resonator is an important issue for scalable quantum computation in semiconductor systems. Benefiting from the advantages of a strong spin-orbit coupling strength and long coherence time, the Ge hut wire, which is proposed to be site-controlled grown for scalability, is considered to be a promising candidate to achieve this goal. Here we present a hybrid architecture in which an on-chip superconducting microwave resonator is coupled to the holes in a Ge quantum dot. The charge stability diagram can be obtained from the amplitude and phase responses of the resonator independently from the DC transport measurement. Furthermore, we estimate the hole-resonator coupling rate of gc/2π = 148 MHz in the single quantum dot-resonator system and estimate the spin-resonator coupling rate gs/2π to be in the range 2-4 MHz. We anticipate that strong coupling between hole spins and microwave photons in a Ge hut wire is feasible with optimized schemes in the future.

Coherent Phonon Rabi Oscillations with a High-Frequency Carbon Nanotube Phonon Cavity.

Phonon-cavity electromechanics allows the manipulation of mechanical oscillations similar to photon-cavity systems. Many advances on this subject have been achieved in various materials. In addition, the coherent phonon transfer (phonon Rabi oscillations) between the phonon cavity mode and another oscillation mode has attracted many interest in nanoscience. Here, we demonstrate coherent phonon transfer in a carbon nanotube phonon-cavity system with two mechanical modes exhibiting strong dynamical coupling. The gate-tunable phonon oscillation modes are manipulated and detected by extending the red-detuned pump idea of photonic cavity electromechanics. The first- and second-order coherent phonon transfers are observed with Rabi frequencies 591 and 125 kHz, respectively. The frequency quality factor product fQm ∼ 2 × 1012 Hz achieved here is larger than kBTbase/h, which may enable the future realization of Rabi oscillations in the quantum regime.

Strongly Coupled Nanotube Electromechanical Resonators.

Coupling an electromechanical resonator with carbon-nanotube quantum dots is a significant method to control both the electronic charge and the spin quantum states. By exploiting a novel microtransfer technique, we fabricate two separate strongly coupled and electrically tunable mechanical resonators for the first time. The frequency of the two resonators can be individually tuned by the bottom gates, and in each resonator, the electron transport through the quantum dot can be strongly affected by the phonon mode and vice versa. Furthermore, the conductance of either resonator can be nonlocally modulated by the other resonator through phonon-phonon interaction between the two resonators. Strong coupling is observed between the phonon modes of the two resonators, where the coupling strength larger than 200 kHz can be reached. This strongly coupled nanotube electromechanical resonator array provides an experimental platform for future studies of the coherent electron-phonon interaction, the phonon-mediated long-distance electron interaction, and entanglement state generation.

Improving the luminescence enhancement of hybrid Au nanoparticle-monolayer MoS2 by focusing radially-polarized beams.

Monolayer transition-metal dichalcogenides (TMDs) have grown as fantastic building blocks for optoelectronic applications, owing to their direct band gap, transparency, and mechanical flexibility. Since the luminescence of monolayer TMDs suffers from low light absorption and emission, surface plasmons, which confine light at subwavelength and enhance the local electric field, are utilized to boost both excitation and emission fields of TMDs, enabling strong light-matter interaction at the nano-scale. Meanwhile, radially-polarized beams (RPBs) as new and attractive excitation source have found many applications in surface plasmon polaritons, optical tweezer and so on. Here, by using RPBs, we demonstrate the photoluminescence (PL) enhancement of monolayer molybdenum disulfide (MoS2) hybridized with 210 nm-diameter gold nanoparticle (AuNP) is improved by about 1.37-fold compared with linearly-polarized beams (LPBs). Besides, the PL enhancement with RPBs depends on the size of AuNP as well. With 210nm-diameter AuNP, the PL enhancement is more than 1.5-fold higher than that with 60nm-diameter AuNP. This study highlights that RPBs are superior to LPBs for tuning the near-field system response and shows that RPBs drive a valuable avenue to further study the emerging two-dimentional materials.

Tunable Hybrid Qubit in a GaAs Double Quantum Dot.

We experimentally demonstrate a tunable hybrid qubit in a five-electron GaAs double quantum dot. The qubit is encoded in the (1,4) charge regime of the double dot and can be manipulated completely electrically. More importantly, dot anharmonicity leads to quasiparallel energy levels and a new anticrossing, which help preserve quantum coherence of the qubit and yield a useful working point. We have performed Larmor precession and Ramsey fringe experiments near the new working point and find that the qubit decoherence time is significantly improved over a charge qubit. This work shows a new way to encode a semiconductor qubit that is controllable and coherent.

Tunable capacitive coupling between two semiconductor charge qubits.

Strong coupling between two qubits is one of the main requirements for high fidelity two-qubit logic operations. Here we experimentally investigate the capacitive coupling between two double quantum dots. A pair of open slot confinement gates is used to enhance the coupling. We find that the coupling energy J can be conveniently tuned in a broad range. Through numerical simulations, we study the effect of J on two-qubit operations. The analysis shows that our experimentally obtained J is adequate to achieve high fidelity two-qubit entanglement and logic gates.

Coupling Two Distant Double Quantum Dots with a Microwave Resonator.

We fabricated a hybrid device with two distant graphene double quantum dots (DQDs) and a microwave resonator. A nonlinear response is observed in the resonator reflection amplitude when the two DQDs are jointly tuned to the vicinity of the degeneracy points. This observation can be well fitted by the Tavis-Cummings (T-C) model which describes two two-level systems coupling with one photonic field. Furthermore, the correlation between the DC currents in the two DQDs is studied. A nonzero cross-current correlation is observed which has been theoretically predicted to be an important sign of nonlocal coupling between two distant systems. Our results explore T-C physics in electronic transport and also contribute to the study of nonlocal transport and future implementations of remote electronic entanglement.

Ultra-wideband surface plasmonic Y-splitter.

We present an ultra-wideband Y-splitter based on planar THz plasmonic metamaterials, which consists of a straight waveguide with composite H-shaped structure and two branch waveguides with H-shaped structure. The spoof surface plasmonic polaritons (SSPPs) supported by the straight waveguide occupy the similar dispersion relation and mode characteristic to the ones confined by the branch waveguides. Attributing to these features, the two branch waveguides can equally separate the SSPPs wave propagating along the straight plasmonic waveguide to form a 3dB power divider in an ultra-wideband frequency range. To verify the functionality and performance of the proposed Y-splitter, we scaled down the working frequency to microwave and implemented microwave experiments. The tested device performances have clearly validated the functionality of our designs. It is believed to be applicable for future plasmonic circuit in microwave and THz ranges.