Schedule

Watson Kuo

Dual-Rail Superconducting Qubits: Observable Dark States Free from Purcell Loss 

Dual-rail encoding is utilized across quantum computing platforms to convert dominant physical errors into detectable erasures. Recently, dual-rail superconducting qubits have been realized using strongly coupled transmon pairs, where states can be encoded either in individual transmon excitations or within symmetric and antisymmetric collective modes. When both transmons couple symmetrically to a shared readout resonator, the spatial symmetry renders the antisymmetric mode “dark”, effectively decoupling it from the resonator photon field. While conventional circuit quantum electrodynamics(cQED) dictates that stronger qubit-resonator coupling enhances dispersive readout at the cost of increased Purcell decay, we demonstrate that the dark mode circumvents this fundamental trade-off. By incorporating a ZZ interaction between the dark and bright modes, the dark state maintains the zero Purcell loss, while simultaneously exhibiting a dispersive shift virtually identical to that of the bright state. This effect arises from higher-order perturbative contributions involving higher-energy excited states. Our results demonstrate a unique class of quantum states that are fully measurable via dispersive readout yet intrinsically immune to Purcell dissipation in cQED systems.

Neill Lambert

Waveguide QED with open quantum system methods

Waveguide QED is an important tool in quantum information. It can be used to measure, control, and interact with quantum devices.  It also represents an exciting testbed for physical theories in exotic parameter regimes, like ultra-strong coupling between matter and spatially extended light degrees of freedom. I will show how a new type of non-Markovian open quantum theory can be used to study these strong-coupling regimes, and recover spatial dynamic information on how photons are behaving in the waveguide.

Eisuke Abe

Scaling up superconducting quantum circuits with tileable qubit architecture

The development of quantum computers is now in full swing in both atomic and solid-state systems. In the case of superconducting system, the first coherent control of a so-called Cooper-pair box was demonstrated more than a quarter century ago, and consecutive efforts to improve design, materials, control theory since then have led to recent dramatic increases in the number of available qubits (more than a hundred), the qubit coherence (longer than a millisecond), and the control fidelity (better than 99.9% in two-qubit gates). To scale up a superconducting system, one of the key challenges is how to deliver microwave signals to the individual qubits that are just a few hundred microns apart in a two-dimensional chip. To address this issue, we adopt a tileable square-lattice qubit architecture with the coaxial cables addressing the backside of the chip from the vertical direction. In this talk, I will discuss the chip design, three-dimensional integrated wiring and performance of integrated chips of superconducting quantum computers being developed at RIKEN Center for Quantum Computing.

Tsung-Han Liu

Raman Spectroscopic Study on Mixtures of Deep Eutectic Solvent Reline and Water

Deep eutectic solvents (DESs) have attracted growing attention as a promising class of solvents. As a well-known example, a 1:2 molar mixture composed of choline chloride (ChCl) and urea results in a liquid eutectic. The eutectic temperature is 12 °C, much lower than the melting points of ChCl (302 °C) and urea (133 °C). As both ChCl and urea are deliquescent to form hydrogen bonds with water molecules, DESs containing water have been discussed recently. In this study, to understand how water molecules affect conformations in DESs, we systematically investigate the typical DES, ChCl and urea at a 1:2 molar ratio, containing different amount of water via Raman spectroscopy. We focus on three Raman features that characterize molecular conformations: an intense Raman band at 1010 cm −1 of urea; a broad band around 995 cm −1 of urea in DES; and a relatively weak band around 767 cm −1 of ChCl in DES. The 995 cm −1 band strongly depends on the conformation of the urea molecule. The 767 cm −1 band arises from the OCCN + backbone of ChCl and can reflect a conformational change from the gauche to trans form. As water amount increases, there is no observable spectral shift about the ChCl backbone while a downshift for the urea CN bond clearly shows. The current results suggest that upon hydration urea seems to be more sensitive and flexible to change its conformations, and hydrogen bonds between ChCl and urea in DES can be fine-tuned or perturbed by water molecules.

Tomoya Okino

Development of Methodologies for Investigating Multiscale Dynamics of Polyatomic Molecules

To understand the molecular dynamics of polyatomic molecules, it is essential to account for the correlated motion of nuclei and electrons. Conventional methods have faced difficulties in seamlessly measuring both the time regime in which electron correlation is pronounced and that in which nuclear motion dominates. In this presentation, we report the development of a momentum imaging technique for three-dimensional momentum imaging of all fragment ions simultaneously. With a conventional two-dimensional detector, temporal information is mostly limited by the exposure time. In our method, the temporal information carried by the fragment ions is first mapped one-to-one onto polarization information using an electro-optic light modulator and the temporal information is then reconstructed by measuring the polarization angle with a polarization camera. The temporal resolution is determined by the response time of the detection system, which consists of a three-stage microchannel plate assembly and a phosphor screen with a sub-nanosecond fluorescence lifetime. We also report the development of a momentum imaging technique using an event-driven camera compatible with high-repetition-rate light sources.

Yei-Chen Lai

Discriminating the roles of divalent ions in ribozyme catalysis via substrate-mediated spin probing

Self-aminoacylating ribozymes are important models for studying early biochemical evolution and the RNA world hypothesis, particularly the interplay between RNA structure, metal ions, and catalysis. Although divalent metal ions are essential for ribozyme function, their distinct roles in global folding and local catalytic-site organization remain difficult to separate. The related ribozymes S-1A.1-a and S-2.1-a catalyze identical chemistry yet respond differently to Mg2+ and Ca2+, indicating that global folding alone cannot fully explain catalytic activity. To directly probe local catalytic-site dynamics, we developed a substrate-mediated spin-labeling strategy for site-specific electron spin resonance (ESR) spectroscopy. Using the ribozyme’s intrinsic activity, an alkyne-modified substrate was selectively attached at the 2′-hydroxyl reaction site and coupled to an azide-functionalized nitroxide spin label through click chemistry. This rigid triazole linkage provides a specific reporter of local motion and orientational order within the catalytic pocket. Continuous wave ESR (cw-ESR) analyses showed that Mg2+ restricts active-site motion and promotes a defined orientational order required for S-1A.1-a catalysis, whereas Ca2+ produces broader dynamics and a loss of orientational order, explaining its inability to independently support activity. Mixed-ion experiments, cobalt hexammine assays, and Mn–nitroxide DEER distance mapping further distinguished the structural and catalytic contributions of metal ions. These results show that outer-sphere stabilization supports the global architecture of S-1A.1-a, whereas inner-sphere divalent ions define the local dynamics and orientational order required for catalysis. Thus, substrate-mediated spin labeling provides a direct means of quantifying catalytic-site dynamics and reveals that ribozyme activity depends on metal-ion organization near the active site, beyond RNA global folding alone.

Tomoko Inose

Plasmonic nanowire technology for single live-cell interrogation and manipulation

Plasmonic nanowires provide a unique platform for interrogating and manipulating living cells with high spatial precision. Their nanoscale dimensions enable minimally invasive access to a specific intracellular region, while their plasmonic properties allow optical signals and photochemical reactions to be remotely activated through light irradiation at the exposed end of the nanowire. We have developed a series of plasmonic nanowire-based technologies for single-cell analysis, including site-specific intracellular molecular sensing and localized delivery of bioactive molecules. Surface-enhanced Raman scattering enables highly sensitive label-free or molecularly specific detection of intracellular environments and biomolecules at the nanowire tip. In parallel, integrating plasmonic nanowires with light-responsive functional molecules and porous nanomaterials enables light-triggered release of chemical cargo at selected subcellular locations. These approaches combine nanoscale physical access, plasmon-enhanced optical functions, and molecular recognition within a single probe. Plasmonic nanowire technology therefore offers a versatile framework for monitoring dynamic cellular processes, delivering molecular perturbations, and recovering spatially resolved molecular information from individual living cells, with potential applications in single-cell biology, chemical biology, and biomedical research.

I-Chung Lu

Chemical Fingerprinting of Recycled Plastics via IR-ELDI Mass Spectrometry: A Mechanism-Driven Approach to Rapid Classification

Optical sorting is one of the most widely used methods for plastic recycling. However, it often fails on black or dark-colored plastics and on samples with surface contamination or coating, both obscuring the true identity of the underlying material. This talk presents an ambient ionization mass spectrometry platform designed to overcome these limitations. The platform employs an infrared laser to ablate the sample layer by layer, and the exposed polymer then undergoes electrospray-assisted ionization allowing direct surface analysis of recycled plastics. The resulting fragments and oligomer ions reflect the backbone structure of the polymer and its thermal breakdown under laser heating, forming a chemical fingerprint. Surface contaminants such as ink or coatings absorb and desorb differently than the bulk polymer, and the laser strips them away before reaching the polymer, enabling measurement in as little as 1.5 seconds with no extraction, washing, or other preparation. This fingerprint survives even under contamination. A machine learning classifier built on these fingerprints reaches 97% accuracy on clean samples and 94% on unwashed, contaminated ones, demonstrating that the underlying ionization chemistry, not surface appearance, drives robust classification for industrial recycling.

Shuntaro Tani

[to be announced]