Xianjing Zhou

Electrons trapped on solid neon surfaces serve as low-noise charge qubits with long coherence times and high operational fidelities. Such charge qubits offer full electrical control and compact device footprints, convenient for scaling up with quantum circuits. Realizing two-qubit gates on this platform is a critical step towards practical quantum information processing. In this work, we report the first experimental demonstration of coherent manipulation of multiple interacting electron-on-solid-neon (eNe) charge qubits. By exploiting the electrons naturally confined in close proximity by the surface structures of solid neon, we have achieved a direct qubit-qubit coupling strength of up to 62.5 MHz, as well as implemented cross-resonance (CR) and bSWAP two-qubit gates using global microwave drives. The natural electron confinement by solid neon mitigates the high-density-wiring challenge, simplifies the multi-qubit control, and establishes a unique path to scale up the eNe qubit platform.

Cryogenic solid neon has recently emerged as a pristine solid host for single electron qubits. At ~10 mK temperatures, electron-on-solid-neon (eNe) charge qubits have exhibited exceptionally long coherence times and high operation fidelities. To advance this platform towards a scalable quantum information architecture, systematic characterization of its noise feature is imperative. Here, we show the remarkable resilience of solid neon against charge and thermal noises when eNe qubits are operated away from the charge-insensitive sweet-spot and at elevated temperatures. Without optimizing neon growth, the measured charge (voltage) noise on solid neon is already orders of magnitude lower than that in most stringently grown semiconductors, rivaling the best records to date. Up to 400 mK, the eNe charge qubits operated at ~5 GHz can maintain their echo coherence times over 1 microsecond. These observations highlight solid neon as an ideal host for quantum information processing at higher temperatures and larger scales.

In this review, we introduce a developing qubit platform: floating-electron-based qubits. Electrons floating in a vacuum above the surface of liquid helium or solid neon emerge as promising candidates for qubits, especially due to their expected long coherence times. Despite being in the early stages, a variety of recent experiments from different groups have shown substantial potential in this role. We survey a range of theoretical proposals and recent experiments, primarily focusing on the use of the spin state as the qubit state, wherein the spin and charge states are hybridized. Throughout these proposals and experiments, the charge state is coupled to an LC resonator, which facilitates both the control and readout mechanisms for the spin state via an artificially introduced spin–charge coupling.

What causes Cooper pairs to form in unconventional superconductors is often elusive because experimental signatures that connect to a specific pairing mechanism are rare. Here, we observe distinct dependences of the superconducting transition temperature T_c on carrier density n_2D for electron gases formed at KTaO₃ (111), (001) and (110) interfaces. For the (111) interface, a remarkable linear dependence of T_c on n_2D is observed over a range of nearly one order of magnitude. Further, our study of the dependence of superconductivity on gate electric fields reveals the role of the interface in mediating superconductivity. We find that the extreme sensitivity of superconductivity to crystallographic orientation can be explained by pairing via inter-orbital interactions induced by an inversion-breaking transverse optical phonon and quantum confinement. This mechanism is also consistent with the dependence of T_c on n_2D. Our study may shed light on the pairing mechanism in other superconducting quantum paraelectrics.

The spatiotemporal aspects of early signaling events during interactions between cells and their environment dictate multiple downstream outcomes. While advances in nanopatterning techniques have allowed the isolation of these signaling events, a major limitation of conventional nanopatterning methods is its dependence on gold (Au) or related materials that plasmonically quench fluorescence and, thus, are incompatible with super-resolution fluorescence microscopy. Here we describe a novel method that integrates nanopatterning with single-molecule resolution fluorescence imaging, thus enabling mechanistic dissection of molecular-scale signaling events in conjunction with nanoscale geometry manipulation. Our method exploits nanofabricated titanium (Ti) whose oxide (TiO₂) is a dielectric material with no plasmonic effects. We describe the surface chemistry for decorating specific ligands such as cyclo-RGD (arginine, glycine and aspartate: a ligand for fibronectin-binding integrins) on TiO₂ nanoline and nanodot substrates, and demonstrate the ability to perform dual-color super-resolution imaging on these patterns. Ti nanofabrication is similar to other metallic materials like Au, while the functionalization of TiO₂ is relatively fast, safe, economical, easy to set up with commonly available reagents, and robust against environmental parameters such as humidity. Fabrication of nanopatterns takes ~2–3 d, preparation for functionalization ~1.5–2 d, and functionalization 3 h, after which cell culture and imaging experiments can be performed. We suggest that this method may facilitate the interrogation of nanoscale geometry and force at single-molecule resolution, and should find ready applications in early detection and interpretation of physiochemical signaling events at the cell membrane in the fields of cell biology, immunology, regenerative medicine, and related fields.

Progress towards the realization of quantum computers requires persistent advances in their constituent building blocks—qubits. Novel qubit platforms that simultaneously embody long coherence, fast operation and large scalability offer compelling advantages in the construction of quantum computers and many other quantum information systems^1,2,3. Electrons, ubiquitous elementary particles of non-zero charge, spin and mass, have commonly been perceived as paradigmatic local quantum information carriers. Despite superior controllability and configurability, their practical performance as qubits through either motional or spin states depends critically on their material environment^3,4,5. Here we report our experimental realization of a qubit platform based on isolated single electrons trapped on an ultraclean solid neon surface in vacuum^{6,7,8,9,10,11,12,13}. By integrating an electron trap in a circuit quantum electrodynamics architecture^{14,15,16,17,18,19,20}, we achieve strong coupling between the motional states of a single electron and a single microwave photon in an on-chip superconducting resonator. Qubit gate operations and dispersive readout are implemented to measure the energy relaxation time T₁ of 15 μs and phase coherence time T₂ over 200 ns. These results indicate that the electron-on-solid-neon qubit already performs near the state of the art for a charge qubit²¹.

The hybridization of magnons and phonons is playing a critical role in the emerging field of hybrid magnonics because it combines the high tunability of magnetism with the long lifetime of mechanics for comprehensive coherent information processing. Recently there has been increasing interest in thin-film bulk acoustic waves because of their long lifetimes at high frequencies. However, the unique multimode nature of such phonon modes has not been exploited as an important resource for coherent information processing. In this Letter we study the simultaneous hybridization of multiple high-overtone bulk acoustic resonances with a magnon and a microwave mode. The demonstrated multimode hybridization allows us to observe coherent pulse echoes, opening opportunities for both fundamental studies and practical applications of hybrid magnonics.

A superconducting interface: Interfaces between materials can harbor quantum states that belong to neither of the materials. A classic example is the superconducting interface between two insulating oxides, LaAlO ₃ and SrTiO ₃ , with a critical temperature of around 200 millikelvin. Liu et al. observed superconductivity at a different interface—formed between KTaO ₃ as a substrate and an overlayer of either EuO or LaAlO ₃ —at a considerably higher temperature of about 2 kelvin. Transport measurements displayed anisotropy, which may indicate an unusual superconducting state. Science , this issue p. 716