Advancing the frontiers of quantum science and engineering

Abstract: Like many traditional electronic structure methods, the recently proposed antisymmetrized product of 2D-block geminals (AP2D-BG) approach [1,2] faces exponential computational scaling with respect to the dimension of the one-electron, “spin-orbital”, Hilbert space, limiting its applicability on classical hardware. Adapting the method to quantum computers could eliminate these constraints without increasing computational overhead. However, the fundamental differences between classical and quantum architectures prevent a direct transfer. To address this, the method has been reformulated within a unitary coupled-cluster (UCC) framework. The new approach called the “2D-Block pair Unitary Coupled Cluster” (2D-BpUCC) method, leverages localized orbital pairs and unitary transformations to reduce the complexity of quantum circuits while preserving accuracy. Compared with previously proposed UCC methods, it offers several advantages to harness the power of near-term quantum devices. In particular, we will show that Trotterization can be completely avoided [3].[1] A P. Cassam-Chena ̈ı, Thomas Perez, Davide Accomasso, J. Chem. Phys 158, 074106 (2023)[2] P. Cassam-Chena ̈ı, L. Jourdan, J. Chem. Phys 163, 174111 (2025).[3] L. Jourdan and P. Cassam-Chena ̈ı, A Remarkable Application of Zassenhaus Formula to Quantum Physics and Chemistry, https://hal.science/hal-05220683, arXiv:2510.24364Please register at: https://nus-sg.zoom.us/meeting/register/lUY6oQmUQJm0yTQCXJUOIg

Quantum communications and quantum sensing promise fundamentally new performance limits in security, precision, and resilience—but only if they can be engineered into robust, scalable systems. This session introduces ST Engineering’s Advanced Networks and Sensors domain and our emerging Quantum Communications and Sensors programme, highlighting how academic quantum research intersects with system engineering, integration, and deployment. Wewill discuss key technology directions, open research problems, and how graduate‑level quantum expertise translates into impactful engineering careers. The session will also highlight career pathways and research‑to‑engineering opportunities for students interested in working at the forefront of engineering quantum technology.

Abstract: Bosonic circuit QED leverages the high-dimensional Hilbert space of the harmonic oscillator mode in a cavity, providing a hardware-efficient platform for quantum information processing, as well as an accessible testbed for exploring light-matter interaction. Recent developments in flux-tunable architectures offer real-time control of distinct interaction regimes between cavity and transmon. Additionally, flux tunability provides a clear path for engineering losses, allowing the preparation of quantum states on the verge of a phase transition. In this talk, we discuss the implementation of a single-atom laser by parametrically controlling the state of a flux-tunable transmon coupled to a high-Q cavity. This configuration allows dynamic tuning of the coupling parameters approaching the thermodynamic limit, where we can investigate first-order phase transitions. The photon blockade effect is mitigated by coupling our qubit to an auxiliary low-Q mode, also used for readout. Our setup enables tomography of the light field to study some of the distinctive features of single-atom lasing, such as sub-Poissonian photon statistics and the bistability of the Wigner function. These results are relevant to the study of dissipative systems and find potential use cases in metrology and sensing.

Abstract: From correlations in measurement outcomes alone, can two otherwise isolated parties establish whether such correlations are atemporal? That is, can they rule out that they have been given the same system at two different times? Classical statistics says no, yet quantum theory disagrees. In this talk, we introduce a measure of when such quantum correlations can be identified as atemporal, using semidefinite programming. With this computable measure of atemporality, we demonstrate the asymmetry of atemporality under time reversal, and reveal it to be a measure of spatial quantum correlation distinct from entanglement. Our results indicate that certain quantum correlations possess an intrinsic arrow of time, and enable classification of general quantum correlations across space-time based on their (in)compatibility with various underlying causal structures.

Abstract: Classical cryptography, which often involves pre-shared secret keys, is vulnerable to malicious parties who employ various methodologies to gain unauthorized access to the keys, underlying the safety of our network. Quantum cryptography, such as Quantum Key Distribution (QKD), leverages the no-cloning property of quantum mechanics to improve the security level without the need for pre-distributed secret keys. Extending beyond secret keys sharing, special relativity can also be incorporated to authenticate the geographical location of the node within the network, a method called Quantum Position Verification (QPV). In this talk, I focus on the development of hardware platforms specifically designed for free-space photon-polarization realization of QPV at Harvey Mudd College. Our objective is to provide a proof-of-concept demonstration of a QPV network operating over a kilometer range. The proposed demonstration includes two verifier nodes and one prover node, the position of which is verified using QPV. We utilize a free-space polarization photonic qubit link, accompanied with wavelength-multiplexed classical communication pathways, to perform BB84-type transactions. In addition, we employ the Xilinx Zynq FPGA platform to control and maintain the timing of these transactions to verify the prover node’s position relative to each verifier node. Our photon source has demonstrated a qubit polarization basis transition in under 20 ns, while the classical communication link has achieved a bit-error-rate below one-in-a-million at 10 MHz over a 10-meter separation. We are currently working on refining the polarization qubit generation and measurement methodologies to obtain a higher fidelity BB84-type qubit. At the same time, we are extending the range of our classical link moving closer to the kilometer range while examining potential higher data transmission speeds up to 25 MHz.

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.