Quantum Foundation Seminar
7 events
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SeminarSpectral Codes : A Geometric Formalism for QEC
February 19 (Thu) 15:00 - 16:30, 2026
Satoshi Kanno (Researcher, Research Institute of Advanced Technology, SoftBank Corp.)
In this talk, I will introduce a novel geometric framework for quantum error correction based on spectral triples in noncommutative geometry. In this formulation, quantum error-correcting codes are described as spectral projections onto the low-energy eigenspaces of Dirac-type operators, where the separation between logical information and local errors is captured geometrically. This approach provides a unified spectral and geometric understanding of key properties such as code distance and error thresholds. Moreover, it accommodates various existing codes, including classical linear codes, stabilizer codes, GKP codes, and topological codes. This geometric perspective also suggests intriguing connections to deformation quantization and holographic quantum error correction, offering promising directions for future research.
Venue: #359, Seminar Room #359
Event Official Language: English
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Seminar
Quantum geometric tensor determines the i.i.d. conversion rate in the resource theory of asymmetry for any compact Lie group
February 13 (Fri) 10:00 - 11:30, 2026
Koji Yamaguchi (Academic Researcher, Faculty of Information Science and Electrical Engineering, Kyushu University)
If you are not affiliated with RIKEN, please register using the registration form. Registration deadline: 12nd Feb. (Thu), 2026 Quantifying physical concepts in terms of the ultimate performance of a given task has been central to theoretical progress, as illustrated by thermodynamic entropy and entanglement entropy, which respectively quantify irreversibility and quantum correlations. Symmetry breaking is equally universal, yet lacks such an operational quantification. While an operational characterization of symmetry breaking through asymptotic state-conversion efficiency is a central goal of the resource theory of asymmetry (RTA), such a characterization has so far been completed only for the group among continuous symmetries. Here, we identify the complete measure of symmetry breaking for a general continuous symmetry described by any compact Lie group. Specifically, we show that the asymptotic conversion rate between many copies of pure states in RTA is determined by the quantum geometric tensor, thereby establishing it as the complete measure of symmetry breaking. As an immediate consequence of our conversion rate formula, we also resolve the Marvian-Spekkens conjecture on conditions for reversible conversion in RTA, which has remained unproven for over a decade. By applying our analysis to a standard setup in quantum thermodynamics, we show that asymptotic state conversion under thermal operations generally requires macroscopic coherence in the thermodynamic limit.
Venue: #359, Seminar Room #359
Event Official Language: English
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Seminar TomorrowRecent progress in the resource theory of asymmetry and its applications
February 12 (Thu) 13:30 - 15:00, 2026
Hiroyasu Tajima (Associate Professor, Department of Informatics, Faculty of Information Science and Electrical Engineering, Kyushu University)
If you are not affiliated with RIKEN, please register using the registration form. Registration deadline: 12nd Feb. (Thu), 2026 Symmetry and symmetry breaking are among the central themes in physics and have attracted the interest of many physicists. Recently, the resource theory of asymmetry (RTA) [1-4], which approaches these issues from the perspective of resource theories, has been actively studied. In the past few years, several foundational advances have been made in this framework. In particular, the iid-complete monotone that plays a role analogous to entanglement entropy has been identified for arbitrary compact Lie groups [2] as well as for arbitrary finite groups [3]. The resolution for compact Lie groups includes, as a corollary, a solution to the Marvian–Spekkens conjecture [4]. Building on this theoretical foundation, several developments related to the Wigner–Araki–Yanase (WAY) theorem [5-7] have also been obtained. These include extensions of the WAY theorem to the implementation of arbitrary unitary gates [8], and a unification of the WAY-type theorems, i.e. the WAY theorem, the Eastin–Knill theorem (a fundamental limitation on error correction under symmetry) [9], and the above unitary-gate results. The unification is formulated a universal trade-off inequality relating symmetry, irreversibility, and quantumness for arbitrary quantum dynamics [10]. Using this tradeoff relation, the WAY-type limitations can now be applied, for example, to quantum thermodynamics[11] and black hole evaporation [10] etc. If time permits, I will also briefly touch upon some other recent developments, such as extensions of the above tradeoff and the WAY theorem to general resource theory beyond symmetry [12].
Venue: #359, Seminar Room #359
Event Official Language: English
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Seminar
A one-world interpretation of quantum mechanics
January 16 (Fri) 14:00 - 16:00, 2026
Isaac Layton (Postdoctoral Researcher, Department of Physics, Graduate School of Science, The University of Tokyo)
The measurement problem arises in trying to explain how the objective classical world emerges from a quantum one. In this talk I’ll advocate for an alternative approach, in which the existence of a classical system is assumed a priori. By asking that the standard rules of probability theory apply to it when it interacts with a system linearly evolving in Hilbert space, I’ll show that with a few additional assumptions one can recover the unitary dynamics, collapse and Born rule postulates from quantum theory. This gives an interpretation of quantum mechanics in which classically definite outcomes are always assigned probabilities, rather than superpositions, giving one-world instead of many. The main technical tool used is a change of measure on the space of classical paths, the functional form of which characterises the quantum dynamics and Born rules of a class of quantum-like theories. Time allowing, I will also discuss how these results clarify which additional assumptions must be accepted if one wishes to seriously consider classical alternatives to quantum gravity.
Venue: #445-447, 4F, Main Research Building / via Zoom
Event Official Language: English
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Seminar
Algebraic structures in QFT in the presence of a quantum reference frame
October 9 (Thu) 14:00 - 15:00, 2025
Kasia Rejzner (Professor, Department of Mathematics, University of York, UK)
In this talk I will show how operational description of measurement with the use of quantum reference frames (QRF) affects the algebraic structure of quantum field theory (QFT). I will focus on the example of a quantum clock coupled to a QFT on de Sitter spacetime, previously discussed by Chandrasekaran, Longo, Pennington and Witten. This talk is based on my recent work with Chris Fewster, Daan Janssen, Leon Loveridge and James Waldron.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English
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Seminar
Detectability of post-Newtonian classical and quantum gravity via quantum clock interferometry
July 22 (Tue) 14:00 - 15:00, 2025
Eyuri Wakakuwa (Associate Professor, Department of Mathematical Informatics, Graduate School of Informatics, Nagoya University)
Understanding physical phenomena at the intersection of quantum mechanics and general relativity remains a major challenge in modern physics. While various experimental approaches have been proposed to probe quantum systems in curved spacetime, most focus on the Newtonian regime, leaving post-Newtonian effects such as frame dragging largely unexplored. In this study, we propose and theoretically analyze an experimental scheme to investigate how post-Newtonian gravity affects quantum systems. We consider two setups: (i) a quantum clock interferometry configuration designed to detect the gravitational field of a rotating mass, and (ii) a scheme exploring whether such effects could mediate entanglement between quantum systems. Due to the symmetry of the configuration, the proposed setup is insensitive to Newtonian gravitational contributions but remains sensitive to the frame-dragging effect. Assuming the validity of the quantum equivalence principle, this approach may provide insights not only into the quantum nature of gravity but also into whether spacetime itself exhibits quantum properties. However, our analysis reveals that, within realistic experimental parameters, the expected effects are too small to be detected. We discuss possible interpretations of this undetectability, and its implications for tests of quantum gravity.
Venue: #445--447, 4F, Main Research Building (Main Venue) / via Zoom
Event Official Language: English
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Seminar
A review of incompatibility in quantum information science (Topical Review Meeting #1)
May 26 (Mon) 16:00 - 17:30, 2025
Haruki Emori (Ph.D. Student, Graduate School of Information Science and Technology, Hokkaido University)
As the first activity of the Quantum Foundation Study Group, we will hold a Topical Review Meeting. In quantum mechanics and quantum information science, the exploration of “quantumness” is of fundamental importance. One key concept that captures quantumness is “incompatibility”. In this meeting, I will give a review on incompatibility. If time permits, I would also like to introduce some of my recent research on this topic and engage in discussions with the participants.
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English
7 events