Events

Abstract: Quantum memory based on ensembles of two-level systems is a promising platform for scalable quantum information processing and communication. However, achieving high efficiency requires operating in the regime of high collective cooperativity, which can also lead to increased noise in the output state due to amplified spontaneous emission. Recently, experiments have observed that the use of chirped pulses, which are widely employed for high-fidelity adiabatic population inversion, can significantly suppress this noise.   In this work, we develop a clean theoretical model of photon-echo-based quantum memory protocols using chirped pulses, focusing in particular on the revival of silenced echo (ROSE) protocol and the rephased amplified spontaneous emission (RASE) protocol. By taking into account both inhomogeneous broadening and inhomogeneity in the coupling strengths, we provide a complete explanation of the observed noise suppression. Our theoretical modelling clarifies the dynamics of these protocols and provides guidance for the design of future protocols.

Abstract: Privacy amplification aims to transform a partially secret key for which an adversary has side information into a uniform key independent of the adversary’s side information. It is used in cryptographic protocols such as QKD to extract the randomness of Alice and Bob’s raw keys which may be partially known to Eve. Obtaining tighter bounds on the distance between the output distribution and the uniform distribution allows for extracting more randomness from the imperfect key and therefore improving the key rate. In this talk, we will introduce a new quantity that generalizes recent results by Bartosz Regula and Marco Tomamichel based on measured Rényi collision entropy. We will study its properties and derive corresponding bound for privacy amplification. Finally, we will talk about a new setting in which the seed is accessed via its purification and investigate the security challenges.

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).

Abstract: Honeywell is advancing quantum technologies across quantum computing and quantum-secure communications, with growing relevance for academic research partnerships. In this seminar, Stefan Lespezeanu will provide an overview of Honeywell’s quantum business, with a focus on quantum communications—particularly space-based Quantum Key Distribution (QKD), secure ground infrastructure, and system-level architectures for quantum-safe networking. The talk will highlight how these industry efforts intersect with academic research, and outline opportunities for collaboration in validation, integration, and future quantum-enabled networks.

Abstract: We explore the generation of verifiably secure randomness via quantum phenomena using modern information theory tools. We analyse classes of protocols which are implementable in near term quantum devices, but with applications that are relevant beyond the NISQ era. In the first half, we focus on quantum key distribution, a cryptographic primitive that allows two parties to privately agree on a secret key in the presence of an eavesdropper and even with untrusted devices —an impossibility without leveraging quantum phenomena--- which rely solely on the monogamy of entanglement property of multi-partite quantum states. In the second half, we turn to the class of quantum randomness expansion protocols known as “certified randomness”, which are of practical interest as they can be implemented on near term quantum devices via the process of random circuit sampling, which requires measurement on a circuit randomly chosen from a suitable ensemble.

Abstract: Many quantum technology applications demand properties that are impossible to realize within a single physical platform. Hybrid quantum systems offer a powerful solution: by combining complementary components, their strengths can be pooled and their weaknesses mutually compensated. In this talk, I will explore hybrid platforms connecting flying qubits (photons) and stationary qubits (spins), focusing on spin ensembles coupled to microwave photons in superconducting circuits.Starting from the first demonstration of strong coupling between nitrogen-vacancy (NV) spin ensembles in diamond and superconducting microwave cavities, I will show how this platform enables rich quantum optical phenomena — from protecting collective spin states against decoherence, to spectral hole burning for coherence engineering in microwave photonics, to understanding the fundamental spin lifetime limits set by phononic vacuum modes. Collective coupling also gives rise to superradiance, and I will briefly discuss our journey from the first observation of superradiant emission in NV ensembles to the recent discovery of self-induced superradiant masing, driven by many-body spin-spin interactions.As an outlook, I will present a radical new platform: atomic impurities embedded in noble gas quantum solids grown directly on superconducting cavities. Recent experiments demonstrate strong coupling of sodium atoms in a neon crystal to a superconducting circuit, opening a path toward coherent coupling of a single spin defect to a superconducting resonator.Research was supported by the Center of Excellence: QuantA, the Austrian Science Fund (FWF)projects I3765 (MICROSENS), P34314 (Spins in Quantum Solids), and by the and the ERC-AdG Emergence in Quantum Physcs (EmQ)

Abstract: In this talk, we present a quantum-inspired tensor-network approach for computing the discrete Laplace transform, or z-transform, on classical hardware. The method combines a non-unitary damping transform with a Quantum Fourier Transform (QFT) in a compressed tensor-network form, allowing large transforms to be handled efficiently. We will describe how the algorithm is  constructed using a QFT-inspired gate structure and discuss its runtime scaling in comparison with standard methods.

Venue: Level 3 Seminar Room, S15-03-15

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.

Abstract: A many-body system, whether in contact with a large environment or evolving under complex dynamics, can typically be modeled as occupying the thermal state singled out by Jaynes' maximum entropy principle. Here, we find analogous fundamental principles identifying a noisy quantum channel T to model the system's dynamics, going beyond the study of its final equilibrium state. Our maximum channel entropy principle states that T should maximize the channel's entropy, suitably defined, subject to any available macroscopic constraints. These may correlate input and outputs, and may lead to restricted or partial thermalizing dynamics including thermalization with average energy conservation. This principle is reinforced by an independent extension of the microcanonical derivation of the thermal state to channels, which leads to the same T. Our technical contributions include a derivation of the general mathematical structure of T, a custom postselection theorem relating an arbitrary permutation-invariant channel to nearby i.i.d. channels, as well as novel typicality results for quantum channels for noncommuting constraints and arbitrary input states. We propose a learning algorithm for quantum channels based on the maximum channel entropy principle, demonstrating the broader relevance of T beyond thermodynamics and complex many-body systems. (Based on the works [arXiv:2508.03993] and [arXiv:2508.03994].)

Abstract: Organised by Singapore’s Centre for Quantum Technologies (CQT), the hackamonth is an innovative approach to hackathons: a month-long, collaborative experience where participants work on quantum computing for meaningful problems. Typical hackathons are short and competitive, ending with prizes. With our hackamonth, we want to have real scientific impact.