Events

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)].

Abstract: Photonic quantum technologies leverage low-noise transmission and high-bandwidth capabilities of light, making them an appealing platform for scalable quantum information processing. Realizing this potential requires integrated architectures that combine high-fidelity single-photon generation with strong photon-photon nonlinearities. In this talk, I will present coherent solid-state emitter-waveguide interfaces that enable deterministic light-matter interactions in integrated photonic circuits, providing a scalable route toward quantum photonic networks. I will discuss deterministic photonic-state generation [1,3], the interplay of decoherence mechanisms [2], and low-loss, CMOS-compatible photonic circuits for encoding and manipulating single photons [4] .I will then show how emitter-waveguide-mediated photon-photon nonlinearities can enable deterministic KLM-type quantum operations and nonlinear quantum photonic circuits [5,6]. Finally, I will outline future directions based on heterogeneous integration [7] and programmable systems of interacting with radiative dipoles [8,9]. Ref: * equally contributed first-author. # corresponding author [1] R. Uppu, F. T. Pedersen, Y. Wang, et al., Science Advances 6, eabc8268(2020). [2] Y. Wang, et al., (submit). [3] A. Tiranov, et al, Science 379, 389 (2023).   [4] Y. Wang, et al., npj Quantum Information 9 (1), 94 (2023). [5] K. H. Nielsen*, Y. Wang*#, Nature Communications 16,11397(2025). [6]  K. H. Nielsen, et al., Y. Wang#, S. Paesani#, arXiv:2604.21758. [7] H.  Salamon#, Y. Wang#, et al., Nano Letters 25 (46), 16366(2025). [8] C. Qvotrup*, Y. Wang*#, et al., Physical Review Applied 24(5), 054016(2025). [9] Y. Wang*#, C. Qvotrup*, et al., arXiv:2503.01012.

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

Abstract: Coherently-driven Kerr-nonlinear systems offer an invaluable engineering flexibility for the generation of quantum states of visible light, at the cost of remaining confined within the set of Gaussian states. In a series of experimental and theoretical work performed in discrete modes Kerr-nonlinear microresonators, we show that by manipulating the intracavity mean-field and the quantum fluctuations components separately, we can create surprisingly deep and diverse quantum photonic resources, beyond squeezed and heralded states.

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...