Advancing the frontiers of quantum science and engineering

Abstract: A near-term quantum error correction (QEC) circuit will be based on imperfect components. To ensure that the information after faulty QEC operations remains reliable, we need QEC circuits to work in a fault-tolerant regime, where the rate of logical errors produced by a QEC operation is driven lower than the physical fault rates. For quantum Low-density Parity Check (qLDPC) codes, a widely used fault-tolerant QEC circuit repeats the stabilizer measurement circuits > d times, where d is the code distance. To minimize this depth, so-called “single-shot” QEC schemes with additional redundancies to protect against measurement errors have been studied. These methods, while successful, often leave gaps between theory and experimental viability since additional redundancies in a code make its repetition-based QEC circuit non-trivial, in general. Our work focuses on finding viable alternative circuits that could have single-shot properties while being fault-tolerant at the same time. We propose two methods and analyze their effectiveness. We hypothesize that, and give intuitions as to why, these strategies may lead to good circuit solutions within the topological code family.

Abstract: We analyze qubit-qubit entanglement from an energetic perspective. Our findings reveal an energetic trade-off between quantum coherence and entanglement rooted in energy conservation. For each qubit, we define the coherent (incoherent) energy as the modulus square of its mean dipole (its fluctuations). The coherent energies are maximal when the qubits are in a product state. They decrease as entanglement builds up under energy conserving processes, yielding coherent energy deficits. If the joint qubit-qubit state is pure, these deficits are equal and exactly amount to the square negativity of entanglement, a well-known measure of entanglement. If the joint qubit-qubit state is a mixture of pure states, each deficit splits into two components, one of quantum origin corresponding to the average square negativity of the pure states, and a classical one reflecting the mixedness of the joint state. Minimizing the quantum deficits over the possible decompositions in pure states yields the square negativity of the mixture.

Abstract: What are the gaps between Academia, Industry, and Entrepreneurship? In 2026, QAI Ventures is going to support quantum-related entrepreneurship in Singapore with two full-time programs: the QAI Quantum Venture Builder and the QAI Accelerator. Starting in March and in July 2026 respectively, these programs are built for prospective founders and early-stage start-ups to gain all the skills-, structure, and network needed to build strong ventures and acquire skills- that aren't the focus of academia. This talk will be a chance for attendees to learn about the programs, discuss the (evolving) notion of a quantum ecosystem, and decide whether and how to take the next steps towards entrepreneurial ambitions.Applications for both the Venture Builder as well as the Accelerator are currently open. You are welcome to reach out to the QAI Team (singapore@qai-ventures.com), schedule a meeting, or read up more here: https://qai-ventures.com/accelerator-singapore .

Abstract: We show that encrypted cloning of unknownquantum states is possible. Any number of encrypted clones of a qubit can becreated through a unitary transformation, and each of the encrypted clones canbe decrypted through a unitary transformation. The decryption of an encryptedclone consumes the decryption key, i.e., only one decryption is possible, inagreement with the no-cloning theorem. Encrypted cloning represents a newparadigm that provides a form of redundancy, parallelism or scalability wheredirect duplication is forbidden by the no-cloning theorem. For example, apossible application of encrypted cloning is to enable encrypted quantummulti-cloud storage.

Abstract: The design of a high optical access cryogenic system for Rydberg atom arrays is discussed. Technical challenges around thermal/acoustic isolation and vacuum are also presented. The trap lifetime is measured to be 3000s and the Rydberg coherence is characterized. Next, a quantum many-body simulator employing a cavity-coupled BEC is presented. Interactions between atoms are mediated by scattering into the cavity mode which leads to a quantum phase transition at zero temperature. Steps to engineer atom-atom interactions that are fully tuneable in range, shape, and sign are then presented along with a proof of concept test in one dimension.

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.