Events

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.

Abstract: We take an axiomatic approach to studying multivariate divergences, which are measures of the information content or distinguishability of a tuple of classical or quantum states. Naturally, these divergences cannot increase after applying any physically allowed operation, and they should be additive when the states describe independent systems. These divergences are studied in the context of convertibility of tuples of states: we ask if one tuple of states can be converted into another by a single channel if we have an arbitrarily large number of independent copies of the states, or if we allow the aid of catalyst states. In these settings, convertibility is characterized by the ordering of an axiomatically defined family of divergences. In this thesis, we identify this family of divergences explicitly for two scenarios, one classical and one quantum. In the classical setting, we consider tuples of d≥2 finite probability distributions, and show that the relevant divergences are certain generalizations of the bivariate Rényi divergences. Unlike previous studies, we do not require the distributions to have the same support, yielding interesting new divergences. In the quantum setting, we consider pairs of classical-quantum states with pure component states, and find that majorization is characterized by all α-z relative entropies for α<1. This demonstrates the first operational interpretation of these relative entropies. Our methods utilize real-algebraic techniques involving preordered semirings recently developed by T. Fritz.

Abstract: We propose a novel causal principle that is a genuinely multipartite extension of Reichenbach’s common cause principle, namely, the coordination principle: parties in a network can achieve perfect randomised coordination (i.e. a uniformly random common output) only if they all share a common cause. We prove that quantum information theory satisfies the coordination principle in any network, and derive noise-tolerant Bell-like inequalities that certify the presence of a common cause. We then show that this principle does not follow from the standard no-signaling and independence principles by providing an explicit theory satisfying all these principles while violating the coordination principle. Additionally, we formulate a genuinely quantum coordination task, showing that the preparation of a multipartite GHZ state requires a quantum common cause, which can be certified by experimentally testable Bell-like inequalities. Finally, we discuss the open problem of finding a quantitative, noise-tolerant version of the coordination principle that constrains approximate coordination in any reasonable causal theory.This talk will be based on two upcoming publications:https://arxiv.org/pdf/2605.03120https://arxiv.org/pdf/2605.03132

Abstract: Quantum information is notoriously fragile: interactions with the environment inevitably introduce noise, causing stored information to degrade over time. This raises a fundamental question: Can a noisy quantum memory ever preserve information perfectly, no matter how long we wait?In this talk I will present a complete answer to this question for quantum memories undergoing discrete-time Markovian evolution. We identify the precise dynamical properties that make perfect long-term storage impossible for classical and quantum information, and derive universal upper bounds on the time after which such dynamics inevitably destroy the possibility of perfect retrieval. Conversely, whenever perfect long-term storage is possible, we show that the information must be encoded in the peripheral space of the dynamics. This leads to explicit formulas for the maximum rate at which classical and quantum information can be stored perfectly in the memory. I will also briefly discuss the more realistic setting in which a small probability of decoding error is allowed. This is based on joint work with Satvik Singh and Mizanur Rahaman.

The ninth edition of the Workshop on Quantum Technologies on Small Satellites will take place 19-20 October 2026 in Singapore. The two-day event will focus on (small) satellite technologies and quantum experiments in space – including both space-based and ground architectures, from component through to mission design. Participants are given the opportunity to share ideas, directions, and concerns to advance the state of the field. The workshop is co-hosted by the QTX research forum led by Alexander Ling of NUS and Markus Krutzik of Humboldt-Universität zu Berlin and Ferdinand-Braun-Institut, Leibniz-institut für Höchstfrequenztechnik. The forum met previously in Germany (2018, 2024), UK (2019), United Arab Emirates (2023) and online (2020, 2021).

Abstract: The nitrogen vacancy (NV) center in diamond exhibits spin-dependent fluorescence and long spin coherence times under ambient conditions, enabling applications in quantum information processing and sensing. NV centers near the surface can have strong interactions with external materials and spins, enabling new forms of nanoscale spectroscopy. However, NV spin coherence degrades within 100 nanometers of the surface, suggesting that diamond surfaces are plagued with ubiquitous defects. I will describe our recent efforts to correlate direct materials characterization with single spin measurements to devise methods to stabilize highly coherent NV centers within nanometers of the surface. We deploy these coherent shallow NV centers for a new nanoscale sensing technique, whereby we use covariance measurements of two or more NV centers to measure two-point magnetic field correlators. We demonstrate measurements of correlated applied noise using spin-to-charge readout of two NV centers and implement a spectral reconstruction protocol for disentangling local and nonlocal noise sources. We also demonstrate massively multiplexed magnetometry with high fidelity spin readout of hundreds of NV centers simultaneously. Finally, we develop protocols to use optically unresolved NV center pairs, entangled states of NV center pairs, and nuclear spins as multi-qubit sensors for measuring correlated noise, enabling covariance magnetometry at nanometer length scales. This novel quantum sensing platform will allow us to measure new physical quantities that are otherwise inaccessible with current tools, particularly in condensed matter systems where two-point correlators can be used to characterize charge transport, magnetism, and non-equilibrium dynamics. Our approach for correlating surface spectroscopy techniques with single qubit measurements to realize directed improvements is generally applicable to many systems. Separately, I will describe our recent efforts to tackle noise and microwave losses in superconducting qubits. Building large, useful quantum systems based on transmon qubits will require significant improvements in qubit relaxation and coherence times, which are orders of magnitude shorter than limits imposed by bulk properties of the constituent materials. This indicates that loss likely originates from uncontrolled surfaces, interfaces, and contaminants. Previous efforts to improve qubit lifetimes have focused primarily on designs that minimize contributions from surfaces. However, significant improvements in the lifetime of 2D transmon qubits have remained elusive for several years. We have recently fabricated 2D transmon qubits that have both lifetimes and coherence times exceeding 0.3 milliseconds by using tantalum as the material in the capacitor. Following this discovery, we have parametrized the remaining sources of loss in state-of-the-art devices using systematic measurements of the dependence of loss on temperature, power, and geometry. This parametrization, complemented by direct materials characterization, allows for rational, directed improvement of superconducting qubits. We have used this playbook to tackle the dominant sources of loss and noise to realize 2D transmons with coherence times exceeding 1 millisecond and lifetimes up to 1.68 milliseconds. Because we have improved the underlying material system without alteration to the qubit architecture, these qubits are readily translated to existing control schemes, and we demonstrate single qubit gates with 99.994% fidelity.

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...