SCHEDULe
Abstract: Here we review that it is possible to study steady-state properties like transport between two baths using finite-size quantum systems. In particular, we show that for times that scale algebraically with the size of the setup, one can observe the same currents that would emerge with infinite baths. The emerging current is in fact independent on the microscopic details of the preparation of the setup, but only on the macroscopic properties. Furthermore, the current fluctuations, both from different preparations of the setup, or on the time evolution, decrease exponentially with the size of the setup. We will conclude describing the experimental realizations with a superconducting qubits processor of these ideas, and how this can be use to engineer finite-size baths.
Abstract: At present, the main obstacle to realizing fault-tolerant quantum computation is the large number of qubits required for quantum error correction. Using quantum error correction codes with higher encoding rates, particularly quantum low-density parity-check (qLDPC) codes, is a promising approach to reducing this overhead. Such codes can enable fault-tolerant quantum computation with constant qubit overhead. However, the complex structure of high-rate codes often leads to logical operations with time complexity higher than the surface code. This increased time overhead can negate their advantages when considering total spacetime cost. In this talk, I will present a collection of techniques for achieving time-efficient, low-overhead fault-tolerant quantum computation on high-rate qLDPC codes. Within the framework of qLDPC code surgery, we first show how algebraic and graph-theoretic methods can be used to appropriately deform the code, enabling parallel logical operations and magic-state injection on multiple logical qubits within a single code block. These methods are generic and allow one to achieve the maximum parallelism compatible with commutation constraints. Next, we introduce a scheme for multi-block architectures that further reduce spacetime overhead through cross-block parallel operations and leveraging local testability.
Abstract: Nonstabilizerness or ‘magic’ characterizes the amount of non-Clifford operations needed for quantum computing and is a necessary condition for quantum advantage.
Recent developments enabled the study of magic on quantum computers and many-body states. We reveal the fundamental limits of testing magic and its connection with entanglement.
Further, we study the magic in critical many-body systems, and uncover its universal behavior in dynamical systems. Finally, we discuss how to combine Clifford circuits and matrix product states to efficiently simulate systems with both volume-law entanglement and magic. We demonstrate magic as a powerful tool to probe the computational complexity of quantum many-body systems.
Abstract: Photon-mediated interactions in ensembles of highly-excited emitters can give rise to Dicke
superradiance, in which radiative decay is collectively enhanced. While this effect can be
harnessed for applications ranging from precision sensing to novel light sources, it can also be
detrimental, leading to enhanced collective decoherence. This raises a fundamental and
unresolved question: what are the fundamental limits to collective decay in many-body
systems?
Here, we prove that Dicke superradiance is not physically observable in an ordered emitter
array with only nearest-neighbor interactions, in any spatial dimension [1]. Instead, collective
enhancement of decay requires the inclusion of at least next-nearest-neighbor interactions.
Building on this insight, we develop a general theory of correlated decay applicable to a broad
class of many-body systems, from which we derive universal scaling laws for the maximal decay
rate as a function of system size [2]. For atomic lattices, these scalings depend solely on the
array dimensionality and are remarkably insensitive to microscopic short-range details.
These results set fundamental bounds on collective decay for all quantum states, provide new
insights on the behavior of generic driven-dissipative systems, and may ultimately constrain the
scalability of quantum processors and simulators based on atom arrays.
[1] Mok, Asenjo-Garcia, Sum, and Kwek. Phys. Rev. Lett. 130, 213605 (2023)
[2] Mok*, Poddar*, Sierra, Rusconi, Preskill, and Asenjo-Garcia. arXiv:2406.00722 (2024)
Abstract: Real-time quantum Krylov diagonalisation provides a systematic, low-memory, open-loop approach to quantum simulation. We extend unitary, real-time quantum Krylov methods to non-Hermitian, non-Normal operators, such as Liouvillians. We show that beyond more stringent requirements for simulation (longer circuits, doubling the number of qubits), the resulting classical problem is more challenging as a result of non-Normality.
We demonstrate the method with an application to a driven-dissipative quantum system: the Kerr Cat qubit.
Abstract: At first sight, the group SU(2) appears to be one of the simplest structures in quantum mechanics
yet it hides a surprisingly rich topological landscape. SU(2) governs the unitary evolution of a
two-level quantum system and underlies essentially all quantum algorithms, as learned from
quantum signal processsing[1]. Geometrically equivalent to the three-sphere S
3, SU(2) seems innocuous—until one considers the space of unitary loops, where complex structures closely
related to mathematical knots naturally emerge.
Knots, understood as embeddings of a circle in three-dimensional space [2], have a long history
from Gauss’s early work on linking to modern developments in topology and quantum field
theory[3,4]. Far from being purely abstract, knot theory plays a role in diverse physical systems,
including fluid dynamics, protein folding, and polymer physics [5].
In this talk, I show that simple qubit Hamiltonian dynamics can generate non-trivial knots
embedded in SU(2), revealing that even basic questions such as the classification of periodic
unitary operators become highly nontrivial once topology is taken into account. I conclude by
discussing connections to quantum signal processing and quantum control.
[1] J. M. Martyn, Z. M. Rossi, A. K. Tan, and I. L. Chuang, A Grand Unification of Quantum
Algorithms, PRX Quantum 2, 040203 (2021).
[2] D. Rolfsen, Knots and Links (AMS Chelsea Publishing, Providence, RI, 2003).
[3] E. Witten, Quantum field theory and the Jones polynomial, Commun. Math. Phys. 121, 351
(1989).
[4] M. Atiyah, Quantum physics and the topology of knots, Rev. Mod. Phys. 67, 977 (1995).
[5] L. H. Kauffman, Knots and Physics (World Scientific, Singapore, 1991; 4th ed. 2012).
Abstract: Quantum computing holds the potential to revolutionise fields such as scientific discovery, materials research, and chemistry. Realising this potential, however, requires a transition from isolated experimental milestones to a robust computational paradigm that is simultaneously useful, reliable, and certifiable. In this talk, I present a research programme organised around these three pillars. I first address utility by discussing the development of near-term quantum algorithms for practical problems, with an emphasis on extracting concrete computational benefits while respecting realistic hardware constraints. I then turn to reliability, describing contributions aimed at making quantum error correction a practical reality through fault-tolerant protocols that protect fragile quantum information from noise and enable reliable quantum computation at scale. Finally, I focus on trust through the lens of quantum certification, presenting protocols for verification and self-testing that provide rigorous guarantees of computational integrity. These certification protocols address the fundamental challenge of ensuring that a device is genuinely quantum and performing correctly, even when the hardware is accessed remotely via the cloud or treated as an untrusted black box. By unifying these three pillars, this body of work establishes a coherent pathway for moving beyond proof-of-principle experiments towards a useful, reliable, and certifiable quantum advantage.
Abstract: Neutral atoms trapped in optical tweezers have rapidly emerged as a leading platform for both gate-based (digital) quantum computing and programmable analog quantum simulation. In this talk, I will review QuEra’s progress toward scalable neutral-atom quantum processors and highlight recent experimental and theoretical advances that bring this architecture closer to fault-tolerant operation.
I will begin with several quantum simulation experiments performed on Aquila, QuEra’s cloud-accessible analog neutral-atom device, demonstrating how programmable simulators can function as shared scientific instruments—enabling broad, community-driven exploration of many-body quantum phenomena. I will then turn to QuEra’s efforts in digital quantum computing with the reconfigurable neutral-atom architecture, including a recent demonstration of logical magic state distillation. Building on these results, I will discuss ongoing experimental architecture developments and advances in quantum error correction (QEC) aimed at realizing scalable, universal, error-corrected computation with neutral-atom systems. Many of the foundational ideas and early demonstrations underlying this technology were developed at Harvard in the Lukin group.
Finally, in the spirit of celebrating Professor Kwek’s 65th birthday, I will share a few personal reflections on how my journey in quantum science began with his mentorship and training—those formative experiences during my undergraduate research that helped shape the direction and values of my career in quantum.
Abstract: This talk will highlight my research programme on nonlinear dynamics at CQT. I will begin by introducing a simple classical model of stable nonlinear oscillations, widely known as the Stuart-Landau oscillator. This model can be quantised easily by a Lindblad-form generator of time evolution, and I will use the quantised Stuart-Landau oscillator as the basis for discussing my interests in quantum nonlinear dynamics:
1) Noise-induced transitions as defined by Horsthemke and Lefever. Classically, these are bifurcations induced by multiplicative noise in the system. Such transitions are analogous to phase transitions in many-body systems, but are exclusively a consequence of noise in the (single-body) system. How can we model multiplicative quantum noise and can we formulate a theory of quantum noise-induced transitions?
2) The Stuart-Landau oscillator is the weakly-nonlinear limit of more general oscillator models, such as the van der Pol oscillator. General oscillator models can attain strong nonlinearities, and thus exhibit different sorts of behaviour. Can we formulate a quantum oscillator model that permits arbitrary nonlinearities and have the quantum Stuart-Landau oscillator emerge as a special case?
3) Nonlinear oscillations play an important role in dynamical systems, but they are only a subset of nonlinear dynamics. Can we quantise more general systems defined by a pair of differential equations dx/dt = f(x,y) and dy/dt=g(x,y) in phase space?
Abstract: In recent years, driven by the rapid development of integrated quantum
photonic chip technology, quantum computing and its practical applications have
achieved breakthrough progress. Silicon photonics-based platforms offer a novel
pathway toward practical miniaturized quantum systems due to their outstanding
scalability, room-temperature stability, and advantages in large-scale manufacturing
cost. In this talk, I will systematically present our research team’s latest research in
implementing optical quantum neural networks on integrated photonic architectures.
Specifically, I will discuss quantum generative neural networks, Gaussian boson
sampling-assisted unsupervised learning, and their applications in graph data
processing and molecular simulation.
NUSS Kent Ridge Guild House
The Scholar Chinese Restaurant
Level 1 9 Kent Ridge Dr,
Singapore 119241
Abstract: Several architectures have a biased noise profile which can be exploited to achieve higher code performance. Floquet codes, meanwhile, can be particularly suitable to setups with low connectivity or native two-qubit entangling measurements, but adapting such codes to biased noise regimes has not been investigated previously. In this talk, I will introduce the X3Z3 Floquet code, a dynamical code with improved performance under biased noise compared to other Floquet codes. The enhanced performance is attributed to a simplified decoding problem resulting from a persistent stabiliser-product symmetry, which surprisingly exists in a code without constant stabilisers. Even if such a symmetry is allowed, we prove that general dynamical codes with two-qubit parity measurements cannot admit one-dimensional decoding graphs, a key feature responsible for the high performance of bias-tailored stabiliser codes. Despite this, our comprehensive simulations show that the symmetry of the X3Z3 Floquet code renders its performance under biased noise far better than several leading Floquet codes. To maintain high-performance implementation in hardware without native two-qubit parity measurements, we introduce ancilla-assisted bias-preserving parity measurement circuits. Our work establishes the X3Z3 code as a prime quantum error-correcting code, particularly for devices with reduced connectivity, such as the honeycomb and heavy-hexagonal architectures.
Abstract: As an alumni of the early CQT, I will present activities around my recent research interests in quantum metrology in atomic systems.
Frequency is a quantity where human beings have established the highest measurement capabilities, boasting up to 16 digits of significant figures today, and up to 19 in the near future. At the heart of frequency metrology, a key notion related to the quantum world is the definition of the second, the SI system of time (interval), defined using an atomic transition since 1967, and measured using atomic clocks.
Even though the performance of the clock keeps improving, we face today a significant obstacle towards meaningfully demonstrating the quantum projection noise for frequency metrology, due the indisposition of a electromagnetic radiation source with sufficient spectral purity.
Standard ultra frequency stable oscillators employ high-finesse Fabry-Perot cavity as references, achieving a few $10^{-16}$ fractional frequency instabilities at room temperature, and limited by thermodynamics. Going back to atomic systems, my team and I explore the fundamental limits of spectroscopy based frequency stabilization techniques, by using long-lived, optically pumping spectral hole structures in $\mathrm{Eu}^{3+}:\mathrm{Y}_2 \mathrm{SiO}_5$ at cryogenic down to dilution temperatures as inaccurate but potentially extremely stable frequency references. In particular, I will show that both the sensing noise and the systematic effects can be made compatible with $10^{-18}$ at 1 s, thereby paving the way towards quantum limited clocks for timing applications and beyond.
Abstract: Optical pumping is a fundamental technique in quantum optics lying at the core of the operation of lasers, masers and optical cooling, amongst many other applications. It combines a coherent and an incoherent exchange of energy to transfer population from a lower to a higher energy level in finite dimensional quantum systems and it essentially limited by temperature and the separation of these energy levels. From a quantum thermodynamics perspective, a finite dimensional system can be seen as a quantum battery and optical pumping as a charging technique aiming at storing energy in the system that can later be used as a quantum fluid in a thermal machine or as a purifying technique aiming at reducing the entropy of the system and increasing its purity. When dealing with quantum batteries one relevant question concerns the differences and eventual advantages over their classical counterparts, whether in the efficiency of the energy transference, input power, total stored energy, or other relevant physical quantities. Here, we show how a modified optical pumping scheme exploits a purely quantum effect related to the vacuum of the electromagnetic field to enhance the charging and purify a two-level quantum battery. These results display a genuine quantum thermodynamical effect that can help both the optimization of quantum batteries and the resetting of qubits.
Abstract: In quantum information processing, the development of fast and robust control schemes remains a central challenge. Although quantum adiabatic evolution is inherently robust against control errors, it typically demands long evolution times. In this talk, we present a scheme to achieve rapid adiabatic evolution, in which nonadiabatic transitions induced by fast changes in the system Hamiltonian are mitigated by flipping the nonadiabatic transition matrix using π pulses. This enables a faster realization of adiabatic evolution while preserving its robustness. We demonstrate the effectiveness of our scheme in both two-level and three-level systems. Numerical simulations show that, for the same evolution duration, our scheme achieves higher fidelity and significantly suppresses nonadiabatic transitions compared to the traditional STIRAP protocol.
Abstract: Photon-atom coupling plays a central role in quantum optics. However, specific energy levels and optical transitions in natural or artificial atoms limit the exploration of novel quantum phenomena in light-matter interactions. In this talk, I will discuss topological superatoms which consist of topology-protected collective quantum states. These superatoms have tunable properties, such as energy structure and quantum coherence. The interaction between light and topological superatoms shows collectively enhanced optical properties, and produces hybrid quasi-bound state in the continuum. Topological superatoms also nontrivially modify single-atom dynamics, and provide a way to study open quantum systems.
Abstract: Kwek is the primary reason I ended up in Singapore. This was the beginning of an unexpected and unplanned adventure—a captivating journey that was both personal and professional. I’ll share some memories of our collaborative work, projects, and the times we spent discussing life, the universe, and everything in between.
Entangled celebrations
and quantum odyssey
Date
4 to 6 February 2026
Venue
NUS Shaw Foundation Alumni House
11 Kent Ridge Dr, Singapore 119244