2026.04.13. Gakuhen-B "Quantum Energy Innovation" Seminar Series (Philip Taranto)

As part of our area’s seminar series, a seminar by Philip Taranto from The University of Manchester will be held on Monday, April 13, 2026, at Kyushu University’s Ito Campus.

Details are as follows:

Speaker: Philip Taranto (The University of Manchester)
Date: Monday, April 13, 2026, 14:45–
Place: Room 826, West Building 2, Ito Campus, Kyushu University

Title: Higher-Order Quantum Operations
Abstract:
Quantum operations form a fundamental pillar of quantum theory and play a central role in quantum technology. Traditionally, quantum operations were regarded solely as devices for transforming quantum states, such as quantum communication channels between distant parties or quantum gate elements in a quantum circuit. However, quantum operations themselves can also undergo transformations and thus be considered inputs to higher-order quantum operations (HOQOs). From a broad perspective, HOQOs are arbitrary transformations between quantum objects, beyond states and operations: For instance, transformations between unitary gates, quantum channels, measurements, quantum circuits, multi-time processes, and others.
The HOQOs approach has led to powerful mathematical methods and a solid framework for analysing quantum circuits and addressing questions such as estimating, discriminating, and learning quantum operations and quantum measurements, analysing and formalising non-Markovian processes and quantum memory. Beyond its practical applications, HOQOs also provide a framework for addressing foundational questions in quantum theory. Quantum operations exhibit a richer structure than quantum states, particularly due to their functional nature, which involves a clear distinction between input and output. Consequently, when considering transformations between two or more operations, questions regarding causality naturally arise. This opens the possibility for quantum processes with indefinite causality and raises fundamental questions about how causality should be understood in quantum theory.
This talk will provide a guide to HOQOs, covering the mathematical requirements and central concepts and definitions. The methods are followed by various examples that aid in the comprehension of core ideas and illustrate their pivotal role in various applications. After an initial pedagogical part, this work illustrates the power and versatility of the HOQO approach by presenting known applications to multiple branches of quantum theory, ranging from applications to foundations.