Lecture

Lectures on Quantum Measurement Theory: IV

June 30 (Tue) 15:30 - 17:00, 2026

Masanao Ozawa (Professor Emeritus, Nagoya University)

Lecture IV: Instruments in classical mechanics, quantum field theory, and cognitive science In algebraic quantum field theory, measurements describable by interactions between the field and the measuring apparatus are characterized by the class of completely positive instruments that satisfy the condition called the normal extension property (NEP) (Okamura-Ozawa 2016). In classical mechanics, traditionally only non-invasive measurements—those with trivial interaction—were considered admissible, for the observability of the trajectory of motion. Here, however, the full class of measurements realizable by classical-mechanical interactions is characterized in terms of instruments with NEP for the basis of the study of invasive measurements of classical systems. Cognitive processes are also represented by completely positive instruments, along with the long-standing paradigm provided by von Helmholtz, who described a sensation-perception process as a sort of measuring interaction and referred to it as an unconscious inference. This framework is used to show the compatibility of the question order effect and the response replicability effect (Ozawa-Khrennikov 2019), which failed to be explained in an earlier approach using only projective measurement models. It is shown that there exists an instrument model, realizing both the question order effect and the response replicability effect, that is also capable of almost faithfully reproducing public-opinion survey data such as the well-known Clinton-Gore survey by Gallup in 1997 (Ozawa-Khrennikov 2021).

Venue: Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

Lectures on Quantum Measurement Theory: III

June 23 (Tue) 15:30 - 17:00, 2026

Masanao Ozawa (Professor Emeritus, Nagoya University)

Lecture III: Measurement error, disturbance, the universally valid reformulation of Heisenberg’s uncertainty principle, and a quantitative generalization of the Wigner–Araki–Yanase theorem Definitions of measurement error and disturbance are introduced (Ozawa 2002, 2019) and it is shown that there exists a solvable model for a physically realizable measurement that serves as a counterexample both to Heisenberg’s uncertainty principle in the conventional formulation and to the SQL (Ozawa 1988, 1989, 2002). Thus, those limits are no more considered as universal limits. In fact, the above counter example to SQL was found in 1988 using the idea of contractive state measurements by Yuen (1983) and the LIGO was started in 1994 to succeed in the gravitational wave detection in 2015 as announced in 2016. New formulations are then proved for the uncertainty principle concerning the errors in the approximate simultaneous measurement of two physical quantities, called the "joint error relation" (Ozawa 2003b, 2004), and for the uncertainty principle concerning the error and disturbance associated with the measurement of a single physical quantity, called the "error-disturbance relation" (Ozawa 2003a). From the error-disturbance relation, a quantitative relation for measurement error under an additive conservation law is proved (Ozawa 2002a, 2003b), generalizing the "Wigner–Araki–Yanase theorem" (Wigner 1952, Araki-Yanase 1960), which states that a physical quantity not commuting with a conserved quantity cannot be measured accurately by a measurement interaction satisfying an additive conservation law. The above relation also derives limits for realizing quantum computing and operations under conservation laws (Ozawa 2002b), the results later developed as the resource theory of asymmetry.

Venue: Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

Lectures on Quantum Measurement Theory: II

June 16 (Tue) 15:30 - 17:00, 2026

Masanao Ozawa (Professor Emeritus, Nagoya University)

Lecture II: Modern approach: Quantum instruments, POVMs, measuring processes, intersubjectivity, and value reproducibility The modern approach to quantum measurement theory is based on the "realizability theorem" stating that a measurement is physically realizable if and only if its statistical properties are represented by a completely positive instrument, and this is also equivalent to saying that the measurement can be described by an interaction with a measuring apparatus (Ozawa 1984, 2004). The conventional analysis of a measuring process determines the post-measurement object state by applying the "projection postulate" to the meter measurement in the post-measurement state that "entangles" the object and the apparatus, but the above result has been established without assuming the projection postulate altogether; rather we use only the classical Bayesian probability update rule (Ozawa 1984). We introduce the "intersubjectivity theorem" that states that, when multiple observers simultaneously and statistically correctly measure the same physical quantity, they obtain the same measurement value and the "value reproducibility theorem" that states that a statistically correct measurement correctly reproduces the value of the physical quantity immediately before the measurement (Ozawa 2025). The above three theorems essentially solves the so-called measurement problem, since we eliminate the collapse of the wave function and we establish the reality of the the pre-measurement value of the measured observable to be copied to the meter value and to be recorded by the observer.

Venue: Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

Lectures on Quantum Measurement Theory: I

June 2 (Tue) 15:30 - 17:00, 2026

Masanao Ozawa (Professor Emeritus, Nagoya University)

Lecture I: Conventional approach: Repeatability, Heisenberg’s original uncertainty principle, and the SQL for gravitational-wave detection The conventional approach to quantum measurement theory taken by von Neumann (1932), Dirac (1958), and Schrödinger (1935) assumes the "repeatability hypothesis" stating that if a physical quantity is measured twice in succession, then the same value is obtained each time, which is often quantitatively generalized to the "approximately repeatable hypothesis" stating that after a measurement of a physical quantity with error ε, the post-measurement deviation around the measured value is no larger than ε; this is equivalent to saying that the state after obtaining a measurement result with error ε becomes an ε-approximate eigenstate corresponding to that measurement result. From the approximate repeatability hypothesis, one can derive "Heisenberg’s original formulation of the uncertainty principle," namely, that when position and momentum are approximately measured simultaneously, the product of their respective errors is at least ℏ/2 (Heisenberg 1927, Kennard 1927, Ozawa 2015), as well as the "standard quantum limit (SQL) for monitoring the free-mass position", which states that when the position of a free mass m is measured at a time interval τ, the result of the second measurement cannot be predicted with uncertainty smaller than (ℏτ/ m)^{1/2} (Caves 1985). The last result leads to a sensitivity limit for interferometric gravitational-wave detectors, and in the early 1980s it was therefore argued that gravitational waves of the expected strength could not be observed using interferometric detectors (Braginsky et al. 1980, Caves et al. 1980).

Venue: Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

Quantum Simulation of Non-Abelian Gauge Theories: Correcting Common Misconceptions (3/3)

April 7 (Tue) 18:00 - 19:30, 2026

Masanori Hanada (Reader, School of Mathematical Sciences, Queen Mary University of London, UK)

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: Japanese

Quantum Simulation of Non-Abelian Gauge Theories: Correcting Common Misconceptions (2/3)

March 31 (Tue) 18:00 - 19:00, 2026

Masanori Hanada (Reader, School of Mathematical Sciences, Queen Mary University of London, UK)

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: Japanese

Quantum Simulation of Non-Abelian Gauge Theories: Correcting Common Misconceptions (1/3)

March 24 (Tue) 18:00 - 19:00, 2026

Masanori Hanada (Reader, School of Mathematical Sciences, Queen Mary University of London, UK)

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: Japanese

9th QGG Intensive Lectures – Correlation Effects in Quantum Many-Body Systems: Some Prototypical Examples in Condensed Matter Physics

November 19 (Wed) - 20 (Thu) 2025

Norio Kawakami (Deputy Director, Fundamental Quantum Science Program, TRIP Headquarters, RIKEN)

The ninth installment of the Intensive Lecture Series, organized by the Quantum Gravity Gatherings (QGG) study group at RIKEN iTHEMS, will feature Prof. Norio Kawakami from the Fundamental Quantum Science Program (FQSP) under RIKEN's Transformative Research Innovative Platform (TRIP). Over the course of two days, Prof. Kawakami will deliver a lecture series on quantum many-body systems. In recent years, insights from quantum many-body physics have become central to research in quantum gravity, where correlation effects induced by gravity play nontrivial roles. By bridging perspectives from gravitational physics and quantum many-body dynamics, one hopes to understand how macroscopic spacetime and its geometric properties emerge from the collective behavior of quantum constituents at microscopic scales. In this lecture series, Prof. Kawakami will introduce the fundamental properties of correlation effects through representative examples in condensed matter physics. A distinctive aspect of this event is its joint organization with the Fundamental Quantum Science Program (FQSP) at RIKEN. The goal is to further strengthen connections between the quantum gravity, condensed matter, and quantum information communities. The lectures will be delivered in a blackboard-style format (in English), designed to foster interaction, active participation, and in-depth Q&A discussions. In addition, short talk sessions will be held, giving participants the opportunity to present briefly on topics of their choice. Through this informal and dynamic setting, we hope to spark active interactions among participants and create an environment where ideas can be shared openly and enthusiastically. Abstract: Some examples of theoretical methods to treat strongly correlated systems in condensed matter physics are explained. We start with the Kondo effect, which is one of the most fundamental quantum many-body problems and has been intensively studied to date in a wide variety of topics such as dilute magnetic alloys, heavy fermion systems, quantum dot systems, etc. Dynamical mean-field theory (DMFT) is then introduced, which enables us to systematically treat strongly correlated materials such as a Mott insulator. It is shown that the essence of DMFT is closely related to the Kondo effect. Furthermore, we explain how to apply conformal field theory (CFT) to treat correlation effects in one-dimensional electron systems.

Venue: #435-437, 4F, Main Research Building

Event Official Language: English

Lectures on Neutron Star Structure IV

October 28 (Tue) 15:30 - 17:00, 2025

Mark Alford (Professor, Washington University in St. Louis, USA)

This is a lecture series by Prof. Mark Alford (Washington University in St. Louis) on the structure of neutron stars. Oct. 7 (Tues), 15:30-17:00 Lecture I : Quark matter: the high-density frontier The densest predicted state of matter is color-superconducting quark matter, which has some affinities to electrical superconductors, but a much richer phase structure because quarks come in many varieties. This form of matter may well exist in the core of compact stars, and the search for signatures of its presence is currently proceeding. I will review the nature of color-superconducting quark matter, and discuss some ideas for finding it in nature. Oct. 14 (Tues), 15:30-17:00 Lecture II: Solid quark matter I will review three ways in which quark matter can occur in a solid phase, where translational invariance is broken by some sort of crystalline structure. These include a color superconductor of the Fulde-Ferrell-Larkin-Ovchinnikov type, mixed phases that can arise at a nuclear/quark matter interface, and the strangelet crystal crust of a strange star. Oct. 21 (Tues), 15:30-17:00 Lecture III: Dissipation in neutron star mergers In a neutron star merger, nuclear matter experiences dramatic changes in temperature and density that happen in milliseconds. Mergers therefore probe dynamical properties that may help us uncover the phase structure of ultra-dense matter. I will describe some of the relevant material properties, focusing on flavor equilibration and its consequences such as bulk viscosity and damping of oscillations. Oct. 28 (Tues), 15:30-17:00 Lecture IV: Neutrinos in dense matter: beyond modified Urca Neutrino absorption and emission (the "Urca process") is an essential aspect of the formation and cooling of neutron stars and of the dynamics of neutron star mergers. In this talk I will describe the traditional way of calculating Urca rates, explain its shortfalls, and propose an alternative approach, the nucleon width approximation.

Venue: Seminar Room #359, Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

Lectures on Neutron Star Structure III

October 21 (Tue) 15:30 - 17:00, 2025

Mark Alford (Professor, Washington University in St. Louis, USA)

This is a lecture series by Prof. Mark Alford (Washington University in St. Louis) on the structure of neutron stars. Oct. 7 (Tues), 15:30-17:00 Lecture I : Quark matter: the high-density frontier The densest predicted state of matter is color-superconducting quark matter, which has some affinities to electrical superconductors, but a much richer phase structure because quarks come in many varieties. This form of matter may well exist in the core of compact stars, and the search for signatures of its presence is currently proceeding. I will review the nature of color-superconducting quark matter, and discuss some ideas for finding it in nature. Oct. 14 (Tues), 15:30-17:00 Lecture II: Solid quark matter I will review three ways in which quark matter can occur in a solid phase, where translational invariance is broken by some sort of crystalline structure. These include a color superconductor of the Fulde-Ferrell-Larkin-Ovchinnikov type, mixed phases that can arise at a nuclear/quark matter interface, and the strangelet crystal crust of a strange star. Oct. 21 (Tues), 15:30-17:00 Lecture III: Dissipation in neutron star mergers In a neutron star merger, nuclear matter experiences dramatic changes in temperature and density that happen in milliseconds. Mergers therefore probe dynamical properties that may help us uncover the phase structure of ultra-dense matter. I will describe some of the relevant material properties, focusing on flavor equilibration and its consequences such as bulk viscosity and damping of oscillations. Oct. 28 (Tues), 15:30-17:00 Lecture IV: Neutrinos in dense matter: beyond modified Urca Neutrino absorption and emission (the "Urca process") is an essential aspect of the formation and cooling of neutron stars and of the dynamics of neutron star mergers. In this talk I will describe the traditional way of calculating Urca rates, explain its shortfalls, and propose an alternative approach, the nucleon width approximation.

Venue: Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

Lectures on Neutron Star Structure II

October 14 (Tue) 15:30 - 17:00, 2025

Mark Alford (Professor, Washington University in St. Louis, USA)

This is a lecture series by Prof. Mark Alford (Washington University in St. Louis) on the structure of neutron stars. Oct. 7 (Tues), 15:30-17:00 Lecture I: Quark matter: the high-density frontier The densest predicted state of matter is color-superconducting quark matter, which has some affinities to electrical superconductors, but a much richer phase structure because quarks come in many varieties. This form of matter may well exist in the core of compact stars, and the search for signatures of its presence is currently proceeding. I will review the nature of color-superconducting quark matter, and discuss some ideas for finding it in nature. Oct. 14 (Tues), 15:30-17:00 Lecture II: Solid quark matter I will review three ways in which quark matter can occur in a solid phase, where translational invariance is broken by some sort of crystalline structure. These include a color superconductor of the Fulde-Ferrell-Larkin-Ovchinnikov type, mixed phases that can arise at a nuclear/quark matter interface, and the strangelet crystal crust of a strange star. Oct. 21 (Tues), 15:30-17:00 Lecture III: Dissipation in neutron star mergers In a neutron star merger, nuclear matter experiences dramatic changes in temperature and density that happen in milliseconds. Mergers therefore probe dynamical properties that may help us uncover the phase structure of ultra-dense matter. I will describe some of the relevant material properties, focusing on flavor equilibration and its consequences such as bulk viscosity and damping of oscillations. Oct. 28 (Tues), 15:30-17:00 Lecture IV: Neutrinos in dense matter: beyond modified Urca Neutrino absorption and emission (the "Urca process") is an essential aspect of the formation and cooling of neutron stars and of the dynamics of neutron star mergers. In this talk I will describe the traditional way of calculating Urca rates, explain its shortfalls, and propose an alternative approach, the nucleon width approximation.

Venue: Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

Lectures on Neutron Star Structure I

October 7 (Tue) 15:30 - 17:00, 2025

Mark Alford (Professor, Washington University in St. Louis, USA)

This is a lecture series by Prof. Mark Alford (Washington University in St. Louis) on the structure of neutron stars. Oct. 7 (Tues), 15:30-17:00 Lecture I: Quark matter: the high-density frontier The densest predicted state of matter is color-superconducting quark matter, which has some affinities to electrical superconductors, but a much richer phase structure because quarks come in many varieties. This form of matter may well exist in the core of compact stars, and the search for signatures of its presence is currently proceeding. I will review the nature of color-superconducting quark matter, and discuss some ideas for finding it in nature. Oct. 14 (Tues), 15:30-17:00 Lecture II: Solid quark matter I will review three ways in which quark matter can occur in a solid phase, where translational invariance is broken by some sort of crystalline structure. These include a color superconductor of the Fulde-Ferrell-Larkin-Ovchinnikov type, mixed phases that can arise at a nuclear/quark matter interface, and the strangelet crystal crust of a strange star. Oct. 21 (Tues), 15:30-17:00 Lecture III: Dissipation in neutron star mergers In a neutron star merger, nuclear matter experiences dramatic changes in temperature and density that happen in milliseconds. Mergers therefore probe dynamical properties that may help us uncover the phase structure of ultra-dense matter. I will describe some of the relevant material properties, focusing on flavor equilibration and its consequences such as bulk viscosity and damping of oscillations. Oct. 28 (Tues), 15:30-17:00 Lecture IV: Neutrinos in dense matter: beyond modified Urca Neutrino absorption and emission (the "Urca process") is an essential aspect of the formation and cooling of neutron stars and of the dynamics of neutron star mergers. In this talk I will describe the traditional way of calculating Urca rates, explain its shortfalls, and propose an alternative approach, the nucleon width approximation.

Venue: Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

Lectures on General Probabilistic Theories: From Introduction to Research Participation

October 6 (Mon) - 9 (Thu) 2025

Hayato Arai (JSPS Research Fellow, Graduate School of Arts and Sciences, The University of Tokyo)

(The deadline of the registration is on Sep 30.) 100 years have passed since quantum mechanics was born. The mathematical model has been describing the physical world remarkably well. However, the foundations of this model still remain unclear. A comprehensive understanding of quantum theory, including its foundations, is becoming even more important in an era where the demands of realizing quantum information technologies pose significant theoretical and experimental challenges. The framework of General Probabilistic Theories (GPTs) is a modern approach to the foundations of quantum theory. It deals with mathematical generalizations of both classical and quantum theories and has attracted increasing attention in recent years. Roughly speaking, research on GPTs has three major objectives: characterizing the models of classical and quantum theories, investigating the fundamental limits of physical and information-theoretic properties arising from operational requirements, and deepening our understanding of the mathematical structures underlying classical and quantum theories. The studies of GPTs have provided many new perspectives on these topics. However, at the same time, there remain many important open problems in the field. For this reason, more researchers are encouraged to enter and contribute to research on GPTs. This intensive three-day lecture series is designed to provide researchers and graduate students with the essential knowledge necessary for research on GPTs, starting from an introduction to the subject. The lectures will cover the mathematical foundations, physical and information-theoretic concepts, and both the established results and future directions of GPT research. The 1st day will present the necessary mathematical structures, including convex geometry, positive cones, and the operational formulation of probabilistic models. The 2nd day will explore composite systems, information-theoretic quantities, symmetries, and Euclidean Jordan algebras. The 3rd day will survey key results on discrimination and communication tasks, the characterization of classical and quantum theories, and open problems that connect GPTs to quantum information science and beyond. Note: The content of each lecture may extend into the next slot or be covered earlier, depending on the pace of discussion and participant questions. The 1st day (6th Oct.): Mathematical Introduction to GPTs Venue: Large Meeting Room, 2F, Wako Welfare & Conference Building 10:30-12:00 Lecture 1 (Introduction and Mathematics on Positive Cones) 12:00-13:30 Lunch time 13:30-15:00 Lecture 2 (Mathematics on Positive Cones) 15:00-15:30 Coffee break 15:30-17:00 Lecture 3 (Introduction to General Models and Relation between Operational Probability Theories) The 2nd day (7th Oct.): Physical and Information Theoretical Concepts in GPTs Venue: Large Meeting Room, 2F, Wako Welfare & Conference Building 10:30-12:00 Lecture 4 (Composite Systems in GPTs) 12:00-13:30 Lunch time 13:30-15:00 Lecture 5 (Information Quantities) 15:00-15:30 Coffee break 15:30-17:00 Lecture 6 (Dynamics, Symmetry, and Euclidean Jordan Algebras) The 3rd day (8th Oct): Previous and Future Studies in GPTs Venue: Meeting Room 435-437, 4F, Wako Main Research Building 10:30-12:00 Lecture 7 (Discrimination and Communication Tasks) 12:00-13:30 Lunch time 13:30-15:00 Lecture 8 (Characterization of Classical and Quantum Theories) 15:00-15:30 Coffee break 15:30-17:00 Lecture 9 (Other Topics, Open Problems, and Future Directions) 18:00- Dinner The day of no lecture (9th Oct): Open Discussion and Q&A Research discussions will take place between the lecturer and participants in areas such as the hallways on the 3rd and 4th floors of the Main Research Bldg, RIKEN Wako Campus.

Venue: Welfare and Conference Bldg. 2F Meeting Room, RIKEN Wako Campus / #435-437, Main Research Building

Event Official Language: English

8th QGG Intensive Lecture: Quantum reference frames and their applications in high-energy physics

September 24 (Wed) - 26 (Fri) 2025

Philipp Höhn (Assistant Professor, Qubits and Spacetime Unit, Okinawa Institute of Science and Technology Graduate University (OIST))

Quantum reference frames (QRFs) are a universal tool for dealing with symmetries in quantum systems. Roughly speaking, they are internal subsystems that transform in some non-trivial way under the symmetry group of interest and constitute the means for describing quantum systems from the inside in purely relational terms. QRFs are thus crucial for describing and extracting physics whenever no external reference frame for the symmetry group is available. This is in particular the case when the symmetries are gauge, as in gauge theory and gravity, where QRFs arise whenever building physical observables. The choice of internal QRF is typically non-unique, giving rise to a novel quantum form of covariance of physical properties under QRF transformations. This lecture series will explore this novel perspective in detail with a specific emphasis on applications in high-energy physics and gravity. I will begin by introducing QRFs in mechanical setups and explain how they give rise to quantum structures of covariance that mimic those underlying special relativity. I will explain how this leads to subsystem relativity, the insight that different QRF decompose the total system in different ways into gauge-invariant subsystems, and how this leads to the QRF dependence of correlations, entropies, and thermal properties. We will then explore how relational dynamics in Hamiltonian constrained systems and the infamous "problem of time" can be addressed with clocks identified as temporal QRFs. In transitioning to the field theory setting, we will first consider hybrid scenarios, where QRFs are quantum mechanical, but the remaining degrees of freedom are quantum fields including gravitons. I will explain how this encompasses the recent discussion of "observers", generalized entropies, and gravitational von Neumann algebras by Witten et al. and how subsystem relativity leads to the conclusion that gravitational entanglement entropies are observer dependent. We will then discuss the classical analog of QRFs in gauge theory and gravity and how they can be used to build gauge-invariant relational observables and to describe local subsystems. This will connect with discussions on edge and soft modes in the literature, the former of which turn out to be QRFs as well. This has bearing on entanglement entropies in gauge theories, which I will describe on the lattice, providing a novel relational construction that overcomes the challenges faced by previous constructions, which yielded non-distillable contributions to the entropy and can be recovered as the intersection of "all QRF perspectives". Finally, I will describe how the classical discussion of dynamical reference frames can be used to build a manifestly gauge-invariant path integral formulation that opens up novel relational perspectives on effective actions and the renormalization group in gravitational contexts, which is typically plagued by a lack of manifest diffeomorphism-invariance. I will conclude with open questions and challenges in the field. Program: September 24 10:15 - 10:30 Registration and reception with coffee 10:30 - 12:00 Lecture 1 12:00 - 13:30 Lunch 13:30 - 15:00 Lecture 2 15:00 - 16:00 Coffee break 16:00 - 17:00 Lecture 3 17:10 - 18:10 Short talk session 18:20 - 21.00 Banquet September 25 10:15 - 10:30 Morning discussion with coffee 10:30 - 12:00 Lecture 4 12:00 - 13:30 Lunch 13:30 - 15:00 Lecture 5 15:00 - 16:00 Coffee break 16:00 - 17:00 Lecture 6 17:10 - 18:10 Short talk session September 26 10:15 - 10:30 Morning discussion with coffee 10:30 - 12:00 Lecture 7 12:00 - 13:30 Lunch 13:30 - 15:00 Lecture 8 15:00 - 16:00 Coffee break 16:00 - 17:00 Lecture 9 & Closing

Venue: #435-437, 4F, Main Research Building

Event Official Language: English