Advancing the frontiers of quantum science and engineering

Abstract: Entanglement is one of the most puzzling features of quantum theory and is of great importance for the emerging field of quantum information. Bound entanglement is a peculiar form of entanglement that emerges in certain mixed quantum states. It is not distillable by local operations and classical communication, and bound-entangled states differ from both free entangled (distillable) states and separable states. First, I present the experimental demonstration and characterization of the entanglement properties of a four-qubit polarization bound-entangled state, the so-called Smolin state. We realized the entanglement-unlocking protocol for this state and identified states within the set of bound-entangled states that experimentally violate the CHSH inequality while still having a positive partial transpose. Second, I present the observation of three-qubit bound-entanglement activation and the superadditivity of distillable entanglement, in which two individually non-distillable states become distillable when combined.

Abstract: Discrete-event simulation (DES) engines like NetSquid are essential tools for designing and optimizing quantum communication networks, allowing protocol feasibility studies and requirement assessments without expensive hardware deployment. However, as network scale and physical parameter set grow, these simulators hit hard computational limits. Here, we introduce NetSquid's design and show how it bridges device-level parameters to network-level protocol metrics using a comparison of BB84 and MDI-QKD as a running example. We demonstrate what makes it powerful - and confront its fundamental scaling bottleneck. A modest parameter sweep over a physically realistic metropolitan network of 100 nodes on a modern high-end consumer device can require full CPU utilisation for periods of the order of one week or more. This is a scaling issue core to any DES engine. Quantum memories, entanglement swapping and other quantum-native effects introduce more complex interdependencies resistant to parallelisation. We close by posing the open question of what this means for the trajectory of quantum network modelling: whether to optimise existing DES frameworks, or to design bespoke for specific network architectures as the field reaches application scale.

Abstract: As quantum key distribution (QKD) matures, the next phase of deployment will see complex QKD networks operating alongside classical network infrastructure, with different technologies supporting different network segments. At the Technology Innovation Institute (TII) in Abu Dhabi, our strategy is guided by this vision of heterogeneous, multi-modality quantum networks. In this talk, I will present an overview of QKD solutions, including an entanglement-based multi-user system, a short-range cost-optimized "last mile" solution, and an optical ground-station, built and tested for satellite QKD connectivity. Together, this portfolio has the potential to unlock sophisticated QKD networks that extend the promise of quantum-backed security to an ever-wider range of use cases and applications.

Abstract: Many questions in seismology, from characterising the dynamics of natural hazards and estimating earthquake ground motion in cities to monitoring subsurface changes, require us to record the seismic wavefield at metre-scale resolution across tens of kilometres. Achieving this with conventional seismic instruments remains difficult because sufficiently dense networks are expensive to deploy and maintain.  Distributed acoustic sensing (DAS) offers a new way to bridge this observational gap. DAS commonly uses phase-sensitive optical time-domain reflectometry (ϕ-OTDR) to measure changes in the phase of Rayleigh-backscattered light along an optical fibre, providing a distributed measurement of dynamic strain or strain rate. By turning optical-fibre cables into dense arrays of vibration sensors, DAS can provide thousands of measurements at metre-scale spacing over tens of kilometres. It can also repurpose existing telecommunications fibres, allowing us to make seismic observations in previously-inaccessible regions including noisy cities and offshore environments.   In this talk, I will introduce DAS and share examples from our DAS experiments in Australia and New Zealand. I will show how we use these observations to study fault structures that spans multiple length scales and to monitor environmental processes. I will also discuss the practical side of conducting DAS experiments, including working with dark fibre, characterizing DAS arrays, making sense of complex seismic wavefields, managing very large datasets, and lastly, moving towards open DAS datasets.

Abstract: We derive simple and unified closed-form expressions for projections with respect to fidelity (equivalently, the Bures and purified distances) onto several sets of interest. These include projections of bipartite positive semidefinite (PSD) matrices onto the set of PSD matrices with a given marginal, and projections of ensembles of PSD matrices onto the set of PSD decompositions of a given matrix, with important special cases corresponding to projections onto the set of quantum channels (via the Choi isomorphism) and onto the set of measurements. We introduce prior-channel decompositions of completely positive (CP) maps, which uniquely decompose any CP map into a prior PSD matrix and a quantum channel. This decomposition generalizes the Choi-Jamiolkowski isomorphism by establishing a bijective correspondence between arbitrary bipartite PSD matrices and channel-state pairs, and we show that it arises naturally from the fidelity projections developed here. As applications, we show that the pretty good measurement - associated with a weighted ensemble - is the fidelity projection of the ensemble onto the set of measurements, and that the Petz recovery map - associated with a reference state and forward channel - is the projection of a CP map (constructed from the channel-state pair) onto the set of reverse quantum channels, thereby recasting the well-known identification of the Petz map with quantum Bayes' rule in information-geometric terms. Our results also provide an information-geometric underpinning of the Leifer-Spekkens quantum state over time formalism [Leifer and Spekkens, Phys. Rev. A 88, 052130 (2013)].

As frontier technologies scale, the computational infrastructure on which they run must be secure, verifiable, and energy-efficient by design. We give a hardware-aware route to scalable quantum learning that addresses these requirements on photonic platforms. The construction rests on three recent results, set out here as one pipeline. The first is a photonic quantum convolutional neural network (PQCNN) with adaptive state injection [1]. It uses the natural particle-number symmetry of linear optics to avoid the training pathologies of generic variational circuits and runs on existing programmable photonic hardware. The second is a Verifiable Blind Observable Estimation (VBOE) protocol [2] that gives the first composable cryptographic certificate on the expectation values estimated by near-term quantum classical hybrid algorithms, with no extra qubit cost. The third is a recent experimental multi-client verifiable blind quantum computation on a Qline architecture [3] that extends the same trust model to distributed multi-tenant settings, certifying server honesty under untrusted state preparation. We work the synthesis on a workload already realized in the laboratory, the binary image classification of [1] on programmable photonic hardware, and discuss how the construction extends to other near-term observable-estimation workloads. [1] L. Monbroussou et al., and F. Sciarrino, “Photonic quantum convolutional neural networks with adaptive state injection,” Advanced Photonics (2025); arXiv:2504.20989. [2] B. Yang, E. Kashefi, H. Ollivier, “Verifiable blind observable estimation,” arXiv:2510.08548 (2025). [3] B. Polacchi, D. Leichtle, G. Carvacho, G. Milani, N. Spagnolo, M. Kaplan, E. Kashefi, F. Sciarrino, “Experimental Verifiable Multiclient Blind Quantum Computing on a Qline Architecture,” Physical Review Letters (2025); arXiv:2407.09310.

Venue: CQT Level 5 Seminar Room, S15-05-14

The Quantum Information Processing Conference (QIP) is the largest quantum information processing technology conference, which annually gathers the world’s brightest researchers and industry leaders for a week long program to present and discuss the latest achievements in quantum computing, cryptography, information theory, mathematics and physics. Recent editions have drawn nearly 1000 participants. In 2027, CQT will host the 30th edition of this conference in Singapore. QIP2027 will take place 20-26 February 2027.

The International Conference on Women in Physics (ICWIP) of the International Union of Pure and Applied Physics (IUPAP) will take place in the National University Singapore (NUS) during 7-11 June 2027, hosted by the Physics Department, NUS and the Centre for Quantum Technologies, Singapore. The ICWIP2027 is the 9th in a series of triennial conferences by IUPAP since 2002 that brings together practitioners from all over the world in order to deliberate on both topics in physics and processes within physics practice, with the goal of transforming physics into a welcoming inclusive enterprise for everyone. The conference will feature inspiring keynote talks by eminent women scholars, sessions where participants can present their own research in physics and on equity and inclusion in physics, interactive workshops to engage with the barriers to equity and inclusion in physics, call-to-action sessions on recommendations for the profession and more...