Author: francesco
The meaning of "Quantum Quia"
December 8, 2021 December 9, 2021 francescoLeave a comment
I take the opportunity of the 700th anniversary of Dante's death to explain the meaning of this blog's name.
Illustration by Gustave Doré.
In Dante's Purgatorio, Canto III, Virgil warns Dante about the limits of human intellect, which is able to understand and describe relations between events (the quia, Latin for "because/for"), but not the events' "true reality".
Fast forward to the 21st century, I believe that this viewpoint is close in spirit to the idea, which I'm very fond of at present, that the deepest laws of physics tell us more about our "learning mechanisms" than they do about "reality" (whatever that means).
Here is the excerpt from Dante's Purgatorio, Canto III, verses 37-45:
"State contenti, umana gente, al quia,
che se possuto aveste vedere tutto
mestier non era parturir Maria;
e disiar vedeste sanza frutto
tai che sarebbe lor disio quetato,
ch'etternalmente è dato lor per lutto:
io dico d'Aristotile e di Plato
e di molt'altri"; e qui chinò la fronte,
e più non disse, e rimase turbato.
The same excerpt in English:
"Mortals, remain contented at the quia;
For if ye had been able to see all,
No need there were for Mary to give birth;
And ye have seen desiring without fruit,
Those whose desire would have been quieted,
Which evermore is given them for a grief.
I speak of Aristotle and of Plato,
And many others;" and here bowed his head,
And more he said not, and remained disturbed.
Some publicity
November 30, 2021 francescoLeave a comment
This #AVSQuantumScience paper shares a new approach to statistical mechanics that replaces reverse processes with consistent inference, clarifying the 2nd Law's meaning and revealing new possibilities, classical and quantum alike. @quantumlah @AVS_Members https://t.co/ziG6JjmHAJ
— AIP Publishing (@AIP_Publishing) November 20, 2021
Postdoc position available
October 18, 2021 October 19, 2021 francescoLeave a comment
Position title and duration: postdoc or research assistant professor, depending on the candidate's qualifications. The appointment is offered initially for a one-year period, with the possibility of further extensions up to three years of total duration.
Description: this position is offered by the Quantum Information Theory Group within the collaboration "Extreme Universe", headed by Prof. Tadashi Takayanagi (YITP, Kyoto University). This collaboration brings together Japan-based world-renowned researchers in quantum information theory, quantum gravity, cosmology, and condensed matter physics, with the aim of creating new and exciting bridges between these very active areas of research. The successful candidate will work in close contact with Prof. Francesco Buscemi (Nagoya University), but is expected to interact also with the rest of the collaboration group and to participate in various interdisciplinary meetings within the project. The successful candidate is expected to commence their appointment on April 2022 or as soon as possible after that.
Requirements: applicants are expected to hold a PhD degree in a theoretical field related to quantum information sciences by the time they begin their appointment. Ideally, they will be familiar with recent ideas and techniques in quantum information theory and have at the same time strong interests in fundamental questions in theoretical physics.
Submission procedure: interested candidates should provide
a cover letter;
an up-to-date curriculum vitae;
a research statement;
an up-to-date list of research achievements (including published papers, preprints, talks, posters, etc.);
contact information of three references able to provide recommendation letters upon request.
The application can be done by sending the above documents directly to buscemi@nagoya-u.jp or through the project's webpage at https://academicjobsonline.org/ajo/jobs/19880 (where also other openings are advertised)
Submission deadline: 30 November 2021
For further inquiries, please contact me at buscemi@nagoya-u.jp
No Hamiltonian? No time-reversal. Only retrodiction.
October 8, 2021 October 8, 2021 francescoLeave a comment
Is there an observer-independent time-reversal in physics? Only for Hamiltonian dynamics, we argue. Otherwise there's only retrodiction, which of course depends on the retrodictor's (prior) believes. The paper (co-authored with Clive C. Aw and Valerio Scarani) is freely available from AVS Quantum Science website, where it is highlighted as a Featured Article. Below is a talk I recently gave on these ideas.
Overview on the Petz transpose map
September 24, 2021 francescoLeave a comment
I was recently invited to give an overview talk on Petz's "transpose" or "recovery" map at the workshop Workshop on Quantum Information and Quantum Black Holes, organized by Norihiro Iizuka (Osaka) and Tomonori Ugajin (Kyoto). I've put together what I came to learn about the properties of Petz's transpose map, its uses is various areas of information theory and physics, and (most importantly!) its conceptual meaning. Slides are available here. Mark Wilde's textbook contains a chapter entirely devoted to the technical aspects of Petz's map and the theory of approximate recoverability.
Fugue in D Minor for four voices (subject by Gedalge)
August 29, 2021 January 11, 2022 francescoLeave a comment
I wrote this while preparing for the Eighth Year Exam of Classical Composition at the Conservatory of Milan, in 1999 (or perhaps 2000?). The subject (the first four bars) is one of Gedalge's classical treatise's exercises (it's the number 4). I remember it was really a pleasure to see a fugue getting together nicely, and this is one of the best I wrote. (My countersubject, in particular, functions very well…)
I am jealously preserving all my handwritten scores, but recently I also found a transcription I made in Finale (I believe that was the 1998 version; a real pain to use) and here is its MIDI rendition: enjoy! 🙂
Lisa, in this house we obey the laws of thermodynamics!
June 15, 2021 francescoLeave a comment
About the logical foundations of the second law of thermodynamics
May 20, 2021 francesco1 Comment
"The law that entropy always increases holds, I think, the supreme position among the laws of Nature. If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equations – then so much the worse for Maxwell's equations. If it is found to be contradicted by observation—well, these experimentalists do bungle things sometimes. But if your theory is found to be against the Second Law of Thermodynamics I can give you no hope; there is nothing for it to collapse in deepest humiliation."
― Arthur Eddington, The Nature of the Physical World, Chap. 4
But why is that so? Why is the Second Law so "special" among the other laws of physics?
Simply because—as we argue in a paper recently published on Physical Review E and freely available on the arXiv—the Second Law is not so much about physics, as it is about logic and consistent reasoning. More precisely, we argue that the Second Law can be seen as the shadow of a deeper asymmetry that exists in statistical inference between prediction and retrodiction, and ultimately imposed by the consistency of the Bayes–Laplace Rule.
A little bit of background. In the past two decades, thermodynamics has undergone unprecedented progresses. These can be traced back to the developments of stochastic thermodynamics, on the one hand, and the theory of nonequilibrium fluctuations, on the other. The latter, in particular, has shown that the Second Law emerges from a more fundamental "balance relation" between a physical process and its reverse. According to such a balance relation, for example, scrambled eggs are not forbidden to unscramble spontaneously—instead, the probability of such a process is just extremely tiny, compared with that of its more familiar reverse. In turn, entropy—i.e. the thing that "no one knows what it really is", according to the apocryphal exchange between Shannon and von Neumann—precisely is a measure of such a disparity.
In this paper we go one step further and show that the existence of a disparity is not due to some kind of "physical propensity" that irreversible processes have for unfolding in one direction more likely than in the opposite direction—an explanation that would lead to a circular argument—, but to the intrinsic asymmetry that exists between prediction and retrodiction in inferential logic. We thus conclude that the foundations of the Second Law are not to be found within physics, but one step below, at the level of logic.
A nice little piece written by CQT/NUS outreach is also available here.
Colloquium on Bayesian retrodiction in statistical physics
February 10, 2021 February 10, 2021 francescoLeave a comment
One month ago I gave a colloquium at the 13th Annual Symposium of the Centre for Quantum Technologies (CQT) in Singapore. I decided to speak about my recent work on the role of Bayesian retrodiction in statistical mechanics — more precisely, in the conceptual foundations underlying fluctuation relations and the second law of thermodynamics.
Occasional references to the yin, the yang, and baseball bats, all point to the previous colloquium by Ruth Kastner (also available on Youtube).
The preprint is available on the arXiv: https://arxiv.org/abs/2009.02849
Invited talk at AQIS 2020
December 23, 2020 February 10, 2021 francescoLeave a comment
Given at the Asian Quantum Information Science Conference 2020 (link).