Quantum Foundation Seminar
12 events
-
SeminarIntroduction to quantum resource theories (3)
May 15 (Fri) 9:00 - 17:00, 2026
Ryuji Takagi (Associate Professor, Graduate School of Arts and Sciences, The University of Tokyo)
One of the central goals of quantum information theory is to quantitatively clarify the relationship between the performance of quantum information processing and the valuable quantum features that underlie it. In this lecture, we will discuss quantum resource theories, a framework that provides a useful approach to this question. By presenting concrete examples—starting with entanglement theory, the most representative resource theory—as well as recent research results, we will see how perspectives and tools from information theory enable the quantification of quantum resources and the characterization of their convertibility. Beyond entanglement theory, we plan to discuss other key settings such as quantum thermodynamics, resource theory of asymmetry, and quantum magic—relevant resource in fault-tolerant quantum compuation. The overall aim of this lecture is to provide new analytical viewpoints that can be applied to a wide range of systems and quantum information processing tasks. While we do not plan to change the overall start and end times for each day, the detailed lecture schedule is subject to change. The intensive course will be held over three days. Please register for the course using the form. The registration deadline is May 7 (Thu). Please note that the registration form is the same for all three days, so you only need to register once. The 3rd day: May 15 (Fri) 9:00–10:30 Lecture 7 10:30–11:00 Coffee break 11:00–12:30 Lecture 8 12:30-13:30 Lunch time 13:30-15:00 Free discussion/Summary of the lectures 15:00-15:30 Coffee break 15:30-17:00 Lecture 9/Seminar This event is in-person only.
Venue: #435-437, 4F, Main Research Building
Event Official Language: English
-
Seminar
From Birkhoff's Polytope to Petz Recovery: Unistochastic Matrices, Quantum Channels, and Approximate Markov Chains
May 13 (Wed) 13:30 - 15:00, 2026
Claude Gravel (Assistant Professor, Department of Computer Science, Toronto Metropolitan University, Canada)
A doubly stochastic matrix is unistochastic if its entries correspond to the squared moduli of a unitary matrix. Determining which n × n doubly stochastic matrices admit such a representation remains an open problem at the intersection of convex geometry, combinatorics, and quantum information. For 3 × 3 matrices, elegant triangle inequalities provide a complete characterization: the unistochastic set occupies approximately 75% of the Birkhoff polytope and exhibits deltoid cross-sections. For n ≥ 4, the characterization problem remains unresolved and is influenced in unexpected ways by the prime factorization of n via the defect of the Fourier matrix. This presentation surveys these results and then establishes a connection to a second, seemingly unrelated question: given a tripartite quantum state with small conditional mutual information, to what extent can one subsystem be recovered from the others? The Petz recovery map and its rotated variants offer a universal solution. These two topics are linked through coherification, which concerns when a classical stochastic process can be elevated to coherent quantum dynamics, and through the conditional mutual information as a continuous measure of non-unistochasticity. The talk concludes with open problems at this interface, including the star-shapedness conjecture for n = 4 and the pursuit of tighter recovery bounds.
Venue: #359, Seminar Room #359
Event Official Language: English
-
Seminar
Introduction to quantum resource theories (2)
May 12 (Tue) 9:00 - 17:00, 2026
Ryuji Takagi (Associate Professor, Graduate School of Arts and Sciences, The University of Tokyo)
One of the central goals of quantum information theory is to quantitatively clarify the relationship between the performance of quantum information processing and the valuable quantum features that underlie it. In this lecture, we will discuss quantum resource theories, a framework that provides a useful approach to this question. By presenting concrete examples—starting with entanglement theory, the most representative resource theory—as well as recent research results, we will see how perspectives and tools from information theory enable the quantification of quantum resources and the characterization of their convertibility. Beyond entanglement theory, we plan to discuss other key settings such as quantum thermodynamics, resource theory of asymmetry, and quantum magic—relevant resource in fault-tolerant quantum compuation. The overall aim of this lecture is to provide new analytical viewpoints that can be applied to a wide range of systems and quantum information processing tasks. While we do not plan to change the overall start and end times for each day, the detailed lecture schedule is subject to change. The intensive course will be held over three days. Please register for the course using the form. The registration deadline is May 7 (Thu). Please note that the registration form is the same for all three days, so you only need to register once. The 2nd day: May 12 (Tue) 9:00–10:30 Lecture 3 10:30–11:00 Coffee break 11:00–12:30 Lecture 4 12:30-13:30 Lunch time 13:30-15:00 Lecture 5 15:00-15:30 Coffee break 15:30-17:00 Lecture 6 This event is in-person only.
Venue: #435-437, 4F, Main Research Building
Event Official Language: English
-
Seminar
Introduction to quantum resource theories (1)
May 11 (Mon) 13:30 - 17:00, 2026
Ryuji Takagi (Associate Professor, Graduate School of Arts and Sciences, The University of Tokyo)
One of the central goals of quantum information theory is to quantitatively clarify the relationship between the performance of quantum information processing and the valuable quantum features that underlie it. In this lecture, we will discuss quantum resource theories, a framework that provides a useful approach to this question. By presenting concrete examples—starting with entanglement theory, the most representative resource theory—as well as recent research results, we will see how perspectives and tools from information theory enable the quantification of quantum resources and the characterization of their convertibility. Beyond entanglement theory, we plan to discuss other key settings such as quantum thermodynamics, resource theory of asymmetry, and quantum magic—relevant resource in fault-tolerant quantum compuation. The overall aim of this lecture is to provide new analytical viewpoints that can be applied to a wide range of systems and quantum information processing tasks. While we do not plan to change the overall start and end times for each day, the detailed lecture schedule is subject to change. The intensive course will be held over three days. Please register for the course using the form. The registration deadline is May 7 (Thu). Please note that the registration form is the same for all three days, so you only need to register once. The 1st day: May 11 (Mon) 13:30-15:00 Lecture 1 15:00-15:30 Coffee break 15:30-17:00 Lecture 2 This event is in-person only.
Venue: #435-437, 4F, Main Research Building
Event Official Language: English
-
Seminar
From Classical Definiteness to Geometric Predictability: Complementarity, Coherence, and Thermodynamic Triality
April 10 (Fri) 15:30 - 17:00, 2026
Ezra Acalapati Madani (Ph.D. Student, Laboratoire de Physique de l'École Normale Supérieure, France)
Wave–particle complementarity is one of the central principles of quantum mechanics, traditionally quantified through the Englert–Greenberger–Yasin relation between which-way information and interference visibility. In higher-dimensional and resource-theoretic settings, however, visibility is no longer unique, and it becomes natural to reformulate complementarity in terms of basis-dependent predictability, coherence, and mixedness. In this talk, I present two related works along this line. First, I discuss an exact complementarity relation between classical definiteness and quantumness, where definiteness is defined operationally through the resilience of a quantum state under nonselective dichotomic yes/no measurements, while the complementary quantum contribution is quantified using a Kirkwood–Dirac-based notion of coherence/interference motivated by recent KD-based coherence measures. Second, I introduce a geometric predictability defined by the Bures distance between the dephased state and the maximally mixed state. This predictability depends only on the observed measurement statistics and admits a closed form in terms of the Bhattacharyya overlap. For pure states, it satisfies an exact complementarity relation with nonclassical Kirkwood–Dirac coherence; for mixed states, this motivates a convex-roof extension whose operational meaning is the classically irreducible part of measurement randomness, with implications for guessing probability and min-entropy. Finally, motivated by the decomposition of entropy production into population and coherence contributions in quantum thermodynamics, and by standard wave–particle–mixedness triality relations, I show how the usual predictability–coherence duality can be promoted into a triality relation involving predictability, coherence, and mixedness. Altogether, the talk connects wave–particle duality, coherence resource theories, operational guessing tasks, and thermodynamic balance relations within a unified framework.
Venue: #359, Seminar Room #359
Event Official Language: English
-
Seminar
Quantum States Over Time: From Foundations To Applications
March 24 (Tue) 15:30 - 17:00, 2026
Minjeong Song (Research Fellow, Centre for Quantum Technologies, National University of Singapore, Singapore)
In this talk, I will introduce quantum states over time (QSOT), a formalism for describing quantum systems over space-time. I will begin by reviewing how QSOT has emerged in the literature. While conventional density operator formalism has been effective across many areas of quantum information theory, QSOT was developed to meet more specialized research needs— most notably, as a key ingredient to develop a quantum version of Bayes’ theorem. I will end the first part of my talk by comparing various QSOT that have been proposed. In the second part, I will discuss the causal compatibility problem as an application of QSOT. I will focus on the temporal compatibility problem, which asks the following: from correlations in measurement outcomes alone, can two otherwise isolated parties establish whether such correlations are atemporal (i.e., temporally incompatible)? That is, can they rule out that they have been given the same system at two different times? I will first explain how characterizing measurement statistics in a causal agnostic scenario is equivalent to characterizing a specific type of QSOT, known as pseudo-density operators. I will then present our recent findings obtained by analyzing pseudo-density operators; In particular, we demonstrate that atemporality is distinct from entanglement, though they appear to be equivalent at first glance. Specifically, we show atemporality implies entanglement, but not vice versa, thus revealing that atemporality is a strictly stronger form of quantum correlations than entanglement. Nevertheless, we also find that sufficiently strong entanglement does imply atemporality.
Venue: #359, Seminar Room #359
Event Official Language: English
-
Seminar
Spectral 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
-
Seminar
Recent 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
-
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
-
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
-
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
-
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
12 events