Advancing the frontiers of quantum science and engineering

Abstract: Quantum error correction (QEC) is central to scalable quantum computing in silicon device. We pursue a QEC approach that is hardware efficient and co-designed with the native device Hamiltonian, available control degrees of freedom, and realistic noise processes. In this talk, we introduce bosonic encodings in hybrid systems combining superconductors and semiconductors. While superconducting resonators in these systems are typically used for readout and mediating long range interactions between semiconductor spin qubits, we instead store quantum information in the bosonic modes of the resonator and use a semiconductor spin as an ancilla. We analyze the resonator–spin Hamiltonian to identify terms limiting to fidelity of state preparation, and determine how operating point selection and pulse design suppress detrimental contributions. We then quantify the resonator quality factor and the resonator–spin coupling required for bosonic state preparation with high fidelity. Building on this foundation, we will develop hardware efficient QEC primitives in hybrid devices, including stabilized logical storage via reservoir engineering, and protected two mode gates potentially mediated by silicon spin qubits with long T1. As a longer term complement, we will explore high spin qudits as truncated oscillator spaces for codes adapted to hardware.

Abstract: Wave-like dark matter candidates produce extremely weak, narrowband electromagnetic signatures, so improving the scan rate at a fixed sensitivity is central to their detection. In this talk I will present a quantum-enhanced protocol for detecting wave-like dark matter using an array of N entangled superconducting cavities initialized in an m-photon Fock state. By distributing and recollecting the quantum state with entanglement operation, the scan rate scales as N²(m+1) when thermal excitation is the dominant background, which can significantly outperform classical approaches under matched conditions. I will then describe our experimental effort on the hardware and control elements required to realize this idea, including high-Q niobium cavities that support large Fock-state preparation and long integration times, high-fidelity microwave beamsplitter operations enabled by tunable couplers, and filtered, low-loss quantum interconnects. Together these elements not only make the sensing protocol experimentally feasible, but also provide the foundation for a modular SRF-cavity quantum processor for broader quantum information tasks.

Abstract: Photonic interconnects facilitated with integrated optical cavities are the building blocks for large-scale ion trap quantum computing. We have designed and fabricated a monolithic miniature linear ion trap using selective laser etching of glass that can accommodate a fiber-based micro-cavity. Cavity mirrors with desired shapes and quality are produced on optical fibre tips robustly using an adaptive CO2 laser shooting algorithm. Currently we are working on combining these two vital components, the miniature ion trap and micro-cavity, in a vacuum chamber to demonstrate the coupling of anion to the cavity. In parallel, we also work on technologies that would enable the scaling of the cavit-based photonic interconnects, such as MEMS-based cavity mirrors and conductive mirror coatings.

Abstract: Superconducting circuits with long-lived microwave cavitiesare able to leverage the dynamics of light and matter for bosonic quantuminformation processing. The dynamics can be greatly extended by employingfrequency-tunable transmons biased with magnetic flux, whereby the interactionswith the microwave cavity can be modified on demand. However, adding a fluxsource to the circuit reduces the cavity photon lifetimes from the ms range totens of µs, compromising the ability of the bosonic mode to store andmanipulate many-photon states. This thesis demonstrates how to enhance the fluxcontrol of microwave cavities without compromising protection. Several hardwaresolutions were explored, including off-plane remote flux sources routed by amagnetic hose, and lithographically printed on-chip lines equipped withmultiple stages of filtering. I experimentally demonstrate the application ofthese developments for operational primitives of interest for quantuminformation processing, such as the calibration of nonlinearities to differentinteraction regimes, the activation of parametric resonances with adjustablecoupling strength, and the use of number-selective transmon-cavity sidebandsfor the control of a cavity qudit. These results provide a stepping stone forthe exploration of more complex synthetic light-matter systems leveragingalternative nonlinear circuits and driven-dissipative dynamics. 

Abstract: The intersection of quantum computation and machine learning represents a new frontier in science and technology. In this talk, I will first present how generative models for quantum states, enriched with symmetries and physics principles, opens up novel avenues for addressing the challenges posed by high-dimensional simulation of quantum systems. It offers  new opportunities to the study of high energy physics, quantum materials, quantum information and computation. Meanwhile, I will discuss recent explorations for developing machine learning and robotics methods powered by physics and quantum theories. This includes the development of a family of generative models grounded in various physical processes, the creation of efficient neural network solvers for generic PDEs inspired by quantum principles, and the optimization of multi-legged robots' locomotion through many-body physics theory.

Abstract: Bosonic cQED systems are a promising platform for hardware-efficient and error-correctable quantum information processing due to the infinite Hilbert space of superconducting cavities. To achieve universal control, multiple cavity modes are typically coupled to an auxiliary qubit, whose discrete transitions are used to enact logical gates. This ultimately limits the quality of the gates performed on the bosonic mode, due to the shorter qubit coherence times. Here, we present the latest results and updates of a CZ gate for different rotationally-symmetric codes that relies only on the non-linearity provided by the Josephson junction, without actively populating the excited energy levels of the qubit. Such a gate can also be applied to detect for photon loss in a fault-tolerant manner.

Abstract: The nitrogen vacancy (NV) center in diamond exhibits spin-dependent fluorescence and long spin coherence times under ambient conditions, enabling applications in quantum information processing and sensing. NV centers near the surface can have strong interactions with external materials and spins, enabling new forms of nanoscale spectroscopy. However, NV spin coherence degrades within 100 nanometers of the surface, suggesting that diamond surfaces are plagued with ubiquitous defects. I will describe our recent efforts to correlate direct materials characterization with single spin measurements to devise methods to stabilize highly coherent NV centers within nanometers of the surface. We deploy these coherent shallow NV centers for a new nanoscale sensing technique, whereby we use covariance measurements of two or more NV centers to measure two-point magnetic field correlators. We demonstrate measurements of correlated applied noise using spin-to-charge readout of two NV centers and implement a spectral reconstruction protocol for disentangling local and nonlocal noise sources. We also demonstrate massively multiplexed magnetometry with high fidelity spin readout of hundreds of NV centers simultaneously. Finally, we develop protocols to use optically unresolved NV center pairs, entangled states of NV center pairs, and nuclear spins as multi-qubit sensors for measuring correlated noise, enabling covariance magnetometry at nanometer length scales. This novel quantum sensing platform will allow us to measure new physical quantities that are otherwise inaccessible with current tools, particularly in condensed matter systems where two-point correlators can be used to characterize charge transport, magnetism, and non-equilibrium dynamics.Our approach for correlating surface spectroscopy techniques with single qubit measurements to realize directed improvements is generally applicable to many systems. Separately, I will describe our recent efforts to tackle noise and microwave losses in superconducting qubits. Building large, useful quantum systems based on transmon qubits will require significant improvements in qubit relaxation and coherence times, which are orders of magnitude shorter than limits imposed by bulk properties of the constituent materials. This indicates that loss likely originates from uncontrolled surfaces, interfaces, and contaminants. Previous efforts to improve qubit lifetimes have focused primarily on designs that minimize contributions from surfaces. However, significant improvements in the lifetime of 2D transmon qubits have remained elusive for several years. We have recently fabricated 2D transmon qubits that have both lifetimes and coherence times exceeding 0.3 milliseconds by using tantalum as the material in the capacitor. Following this discovery, we have parametrized the remaining sources of loss in state-of-the-art devices using systematic measurements of the dependence of loss on temperature, power, and geometry. This parametrization, complemented by direct materials characterization, allows for rational, directed improvement of superconducting qubits. We have used this playbook to tackle the dominant sources of loss and noise to realize 2D transmons with coherence times exceeding 1 millisecond and lifetimes up to 1.68 milliseconds. Because we have improved the underlying material system without alteration to the qubit architecture, these qubits are readily translated to existing control schemes, and we demonstrate single qubit gates with 99.994% fidelity.

Abstract: Quantum error correction offers a path to practical quantum computing by combining multiple physical qubits into a single logical qubit. The central promise of this approach relies on the "threshold theorem": if physical error rates can be reduced below a critical threshold value, increasing the number of physical qubits (the code distance) should result in an exponential suppression of the logical error rate. In this talk, I will describe the first experimental demonstration of this foundational principle using Willow, a new generation of superconducting quantum processors from Google Quantum AI. As we scale the surface code from distance 3 to 7, the logical error rate is exponentially suppressed, culminating in a logical memory that persists longer than the coherence time of all constituent physical qubits. I will also discuss the engineering challenges required to achieve this performance. More information about this work can be found in Nature 638, 920–926 (2025).

ACTI will bring together the growing community of ion-trappers from Asia and across the globe. As an inaugural conference, this year will highlight various scientific fields covered by trapped ion research within Asia and facilitate meaningful exchange between junior and senior members of the different groups.

The goal of this workshop is to bring the active research community together to discuss the progress, challenges and new possible directions for quantum repeaters and networks. We invite researchers working on key enabling technologies and system integration, protocols for connecting repeaters across network links with high fidelity, architectures for large-scale networks, and applications of distributed quantum entanglement. The WQRN has been and continues to be a limited-attendance, few-day workshop, in which participants are given the opportunity to share ideas, directions, and concerns to advance the state of the field. Talks are by invitation only and catered to broadly cover the applications, theory, components, and worldwide directions in quantum repeaters and networks. These talks frame group discussion sessions for which all participants are welcome to contribute; participants are also welcome to contribute to a poster session.