Ryuji Takagi

Recovery of the second law in fully quantum thermodynamics Quantum thermodynamics investigates how robust the second law of thermodynamics serves as the unique fundamental law in the small quantum world. To tackle this problem, the quantum coherence constitut...

Posted a joint work with Naoto Shiraishi on quantum thermodynamics. We managed to characterize the state transformability (for general coherent states!) with a correlated catalyst by the single free energy ordering. arxiv.org/abs/2510.05642

Quantum Resources workshop 2026 The workshop "Quantum Resources 2026" will take place in Tokyo, Japan in March. Submissions welcome!

The next quantum resources workshop happens in Tokyo! Looking forward to seeing many of you there!

2026.quantumresources.science

Submission deadline: 31 October 2025
Workshop: 16–20 March 2026

Quantum algorithms for Uhlmann transformation Uhlmann's theorem is a central result in quantum information theory, associating the closeness of two quantum states with that of their purifications. This theorem well characterizes the fundamental t...

Posted our work on Uhlmann transformation, where we provided its algorithmic implementation. As an application, we improved on the prior state-of-the-art cost for fidelity estimation in purified access model. Joint work with Takeru Utsumi, Yoshifumi Nakata, and Qisheng Wang. arxiv.org/abs/2509.03619

Our paper (w/ Marek, @ryujitakagi.bsky.social, @nellynghy.bsky.social ) on Quantum Dynamic Programming has recently been published in PRL: journals.aps.org/prl/abstract...

Xin Yi from CQT wrote a great highlight article for this paper: www.cqt.sg/highlight/20...

Our work on quantum thermodynamics has been published in PRL. We showed that Gibbs-preserving operations may incur infinite costs to implement, prompting us to reconsider the physical justification of their use. Joint work with Hiroyasu Tajima. journals.aps.org/prl/abstract...

Thanks Henrik for the heads-up on your interesting work! We will definitely have a close look at this!

Universal work extraction in quantum thermodynamics Evaluating the maximum amount of work extractable from a nanoscale quantum system is one of the central problems in quantum thermodynamics. Previous works identified the free energy of the input state...

Posted a preprint with @kaitowatanabe.bsky.social on quantum thermo. We introduced a "universal work extractor", which is designed independently of the input state but still extracts the optimal work from every input state given in the iid form.
arxiv.org/abs/2504.12373

Kaito Watanabe "Black box work extraction and composite hypothesis testing" #QuantumResources2025

Glad to learn about these results. I'll likely adapt my talk for Thursday a bit based on what I learned.