Seminar: Non-stationary quantum many-body dynamics
Posted December 4, 2020 by Dermot Green
Wednesday 9 December 4pm
Location: MS Teams
Speaker: Dr Berislav Buca (Clarendon Lab, University of Oxford)
The assumption that quantum systems relax to a stationary (time-independent) state in the long-time limit underpins statistical physics and much of our intuitive understanding of scientific phenomena. For isolated systems this follows from the eigenstate thermalization hypothesis. When an environment is present the expectation is that all of phase space is explored, eventually leading to stationarity. However, real-world phenomena, from life to weather patterns are persistently non-stationary. I will discuss simple algebraic conditions that prevent a quantum many-body system from ever reaching a stationary state, not even a non-equilibrium one. I call these algebraic conditions dynamical symmetries. This unusual state of matter, characterized by persistent oscillations, has been recently called a time crystal. I show that its existence can be even, counter-intuitively, induced through the dissipation itself. I give several physically relevant examples in both closed and open quantum many-body systems, including an isolated XXZ spin chain that for which the frequency of the persistent oscillations is fractal function of the interaction strength, a quasi-1D magnet with attractor-like dynamics, a spin-dephased Fermi-Hubbard model, and a two-component BEC in a lossy optical cavity which was recently experimentally studied. Finally, I briefly discuss ongoing work about emergence of discrete time translation symmetry in a random collision model.
B Buca, J Tindall, D Jaksch. Nat. Comms. 10 (1), 1730 (2019)
M Medenjak, B Buca, D Jaksch. arXiv:1905.08266 (2019)
B Buca, D Jaksch. Phys. Rev. Lett. 123, 260401 (2019)
J Tindall, B Buca, J R Coulthard, D Jaksch. Phys. Rev. Lett. 123, 030603 (2019)
J Tindall, C Sanchez Munoz, B Buca, D Jaksch. New J. Phys. 22 013026 (2020)
C Booker, B Buca, D Jaksch. arXiv:2005.05062 (2020)
B Buca et al. arXiv:2008.11166 (2020)
Dogra, et al. Science, 366, 1496 (2019)
Seminar: Bayesian inference for quantum sensors and open quantum systems
Posted November 16, 2020 by Dermot Green
Wednesday 25 November 4pm
Location: MS Teams
Speaker: Dr Ricardo Puebla, CTAMOP, Queen’s University Belfast
Inference techniques built on the Bayes’ theorem provide powerful tools for hypothesis testing and/or parameter estimation. In spite of other inference techniques, Bayesian inference deals with a probabilistic description of the key quantities to be determined. This is done by updating any prior information or knowledge according to the likelihood between the given set of observations and the proposed model to explain them. Such Bayesian techniques are routinely employed in many branches of science, and have been proven very useful in situations with a reduced number of observations and/or complex underlying models.
In this seminar I will review the main ingredients of Bayesian analysis and how to apply these techniques to quantum mechanical systems. In particular, I will discuss two illustrative and practical examples to showcase the suitability of Bayesian inference in quantum systems, namely, (i) an atomic-size quantum sensor aiming at detecting electromagnetic fields, and (ii) the inference of the environment properties of an open quantum system.
James Walters Remembered (part 3)
Posted September 28, 2020 by Andrew Brown
James Walters Remembered (part 2)
Posted by Andrew Brown
Some of James’ colleagues and collaborators have sent messages of condolence since his passing. We record them here to remember James.
I only met James a few of times but he was very helpful and friendly towards Barry and me.
Dr Mark Law (Aberdeen)
James was a wonderful scientist and a very generous friend.
Professor Mike Charlton (Swansea)
A few months ago I had a message from him, as PRA editor, saying he could not referee a manuscript because of illness, but had no idea it was so serious.
Professor Ugo Ancarani (Metz)
James has been such a big part of the UK positron community and of the wider antimatter and atomic collisions communities. A very sad news indeed!
Professor Gaetana (Nella) Laricchia (UCL)
Although I did not know James closely, I met him several times when visiting Queen’s, and his work on positron and Ps collisions inspired me a lot in my studies of Ps collisions. He was really a master in this field!
Professor Ilya Fabrikant (Lincoln, Nebraska)
It’s always sad to learn of the death of someone you knew. James was a stalwart in positron atomic physics to say the least. My impression from the outside is that he helped a number of young people too.
Professor Cliff Surko (San Diego, California)
James was the person next door to my office in the very old premises of the Department in University Row (?) when I first visited Queen’s as a postdoc with Phil in 1971: he warmly welcomed me and introduced me to all the others. He never lost his kindness and his desire to teach the young.
Professor Franco Gianturco (Rome/Innsbruck)
It was my special privilege to work with James Walters for over thirty years. James was a gentle, kind, modest man whose wonderful wit and good humor charmed everyone who met him. His self-effacing manner endeared him to his students and friends. His PhD students venerated him; his colleagues admired and respected him. I will miss him.
Professor Colm Whelan (Old Dominion University, Norfolk, Virginia)
James was a wonderful colleague, very reliable and supportive of his colleagues, and a wonderful mentor for students and younger colleagues alike. He was an excellent teacher and a highly respected researcher.
Professor Alan Hibbert (Queen’s University Belfast)
James Walters Remembered (part 1)
Posted by Andrew Brown
Following the death of CTAMOP stalwart, James Walters we remember our colleague and friend this week with several pieces from those who knew him best.
James’ Cousin, Rosemary, gave the eulogy at his funeral, and has kindly provided us with a copy for those who weren’t able to attend.
I’m Rosemary, one of James’s first cousins and I am both honored and humbled to give this tribute. I don’t know how it is your families but as cousins we tended to meet up at family weddings and funerals, promising each other “we must meet up again in other circumstances” and then life moves on. Not having spent more time with James in adult years is a regret we all share, and I have learnt so much about James in the last week. As my cousin Anne said, James was married to the university and his colleagues and students were his family. I am very grateful to friends and especially to his colleagues who have filled in many gaps and I unashamedly confess to plagiarizing some of their comments.
This week I have received so many e mails or phone calls about James and all talk about James as a quiet modest man, with a ready wit and good humour and whose formidable intellect was always present, but not always apparent.
My fun memories are of our childhood summers, spent mostly at Pickie pool or Ballyholme beach, with our cousins. It seemed the summers were long and sunny, picnics on the beach, while we played, scrambled over the rocks to Pickie pool, dived from great heights in competition with each other. Although I have a vague memory that perhaps James was not a fan of the diving. James was particularly close to his older cousin Robert, who sadly passed away almost exactly one year ago.
There were the childhood scientific experiments my father took us out on, measuring the depth of water from the wee rowing boats at Bangor to the seabed. I also remember James sitting at our dining room table with my brother James and my father, solving complicated algebraic equations and discussing matter, ions and black holes. I was about 10 at the time, trying earnestly to be clever and scientific, and failing miserably. There were long, very long games of chess with James and my brother, another skill I never learnt.
James attended Sullivan Upper prep department, where his school reports describe him as a quiet hardworking, studious boy. He then attended Sullivan upper grammar school, one school report writing “excellent” after a maths exam scored 100%. To encourage the rest of us mere mortals another described his algebraic exam result as “disappointing”. The mark was 80 something! His interests in the latter years included the debating society, the French circle, and somewhat surprisingly the boys hockey team. I’m told he was once picked for the rugby team, but felt cheated of a Saturday morning he could have spent studying maths. He was house captain and in his final year a prefect.
He then won a scholarship to study at Trinity college Cambridge. His parents were rightly proud but sadly, while James was only 18, just two weeks into his first semester, his mother died.
As with most Cambridge scholars James enjoyed life there, making life-long friends with whom he kept in touch and it was there he developed his passion for cinema. His tastes were conservative, Hollywood musicals and epics such as Ben Hur and Spartacus. He jested that one of his ambitions at Cambridge was to have an “all -flick week”, i.e. visit the cinema every day for a week. At that stage he was completing his PhD and we doubt if this cinema week ever occurred! However, even in later years James would describe a good day as one that ended re-watching an old movie!
Having completed his PhD at Cambridge, James moved home to N Ireland as a lecturer at Queens University Belfast. He advanced through his academic career and was appointed Professor of theoretical physics early in the 1990’s. He taught both undergraduate and postgraduate courses, his students describing him as one of the best lecturers ever and again that caring attribute showing, as he took his students out for coffee or lunch, visiting some when ill, attending their family weddings and fulfilling, as I said earlier, being part of the family at Queens.
He supervised many Phd students; among them Ann Kernoghan, Jenny Blackwood, Sharon Gilmore, Tony Yu, Charlie Starrett, Martin Mc Govern and Professor Mary Mc Alinden CMath FIMA at Nottingham Trent University, with whom he did collaborative work.
He published at least 200 research papers spanning 50 years from 1970 until his last, co-authored with Colm Whelan in July 2020.
He also published three books.
He was acknowledged as a “giant in his field”. Measurements of atomic collisions were performed all over the world to test his predictions that were invariably correct.
He was a appointed a member of the prestigious Royal Irish Academy in 2003 and in 2005 he was elected Fellow of the American Physical Society for many significant contributions to atomic collision theory, a rare honour for a non American scientist.
Although retired, James continued giving lectures and publishing papers his last only a few months ago I July of this year.
A very fitting short tribute to James was posted by his department:
“Professor James Walters, a fellow of the Institute of Physics and a member of the Royal Irish Academy has played a key role in in the CTAMOP and the school for nearly 5 decades, contributing significantly to the building up of Queens as a Centre of Excellence for theoretical and computational Atomic Physics, and the training of generations of researchers active in this field.”
What a legacy, to inspire the next generations and indeed beyond, one of whom recently had work experience with James. Donal, the son of Francesca Shearer who was a colleague and good friend of James is with us today is now in his second year studying mathematics at Queens!
But beyond this legacy, James has left a rich network of friends and colleagues who will miss him dearly, to some he was like a fixed star in the universe, a constant in their life, to some he was like a brother and those involved in the study of atomic collisions, they have lost their brightest star.
As a family we have had great comfort knowing his life was so rich in friendships.
Professor H R J Walters PhD CPhys MRIA FInstP
Posted September 7, 2020 by Andrew Brown
It is with great sadness that we announce that long-time CTAMOP member, Professor H R James Walters passed away on 6th September 2020.
Professor Walters, a Fellow of the Institute of Physics and a Member of the Royal Irish Academy, has played a key role in the CTAMOP and the School more generally for nearly 5 decades, contributing significantly to the building up of Queen’s reputation as a centre of excellence for Theoretical and Computational Atomic Physics, and the training of generations of researchers active in this field.
Quantum Clocks in Nature Communications
Posted June 1, 2020 by Andrew Brown
A team of physicists led by Professor Caslav Brukner from the University of Vienna and the Institute for Quantum Optics and Quantum Information (IQOQI) Vienna explored the temporal localisability of events when quantum systems influence space-time according to Einstein’s general relativity. Dr Alessio Belenchia, from Queen’s University Belfast, is among the authors of this new work.
The study develops a framework to define events and their localisation with respect to a quantum clock reference frame, also in the presence of gravitating quantum systems. The major results are that the time localisability of events becomes relative, depending on the reference frame, and that for each event there exists always a (quantum) clock according to which that event occurs at a sharp, precise time. This is useful because, using this clock as a reference, the time evolution of quantum systems can be described as it is in ordinary situations where all events are localised in time.
Postgraduate research position: applications open
Posted November 21, 2019 by Andrew Brown
A PhD position is available immediately to work at the Quantum Technology Group at Queen’s with Prof M Paternostro on non-equilibrium quantum thermodynamics enhanced by machine learning. The position will be funded by the Royal Society Wolfson Research Fellowship recently awarded to Prof Paternostro.
Applications through the portal will be accepted until 13 December 2020. All applicants will be interviewed and the successful candidate is expected to start in early 2020.
Computer time allocation on worlds fastest supercomputer
Posted November 5, 2019 by Andrew Brown
Congratulations to Connor Ballance, who has been awarded a large tranche of resource on the world’s fastest supercomputer, Summit.
Connor is part of the “High-Performance Computation for Fusion Energy Wall Erosion Diagnostics” project– headed by Auburn University researcher, Stuart Loch– which has been awarded around 9 million CPU hours on the machine to investigate atomic physics problems relevant for the operation of nuclear fusion reactors.
The research team will use Summit to produce accurate tungsten erosion and redeposition diagnostics for fusion tokamak experiments such as the DIII-D tokamak in California. The project is also of relevance for world-wide efforts on fusion energy, such as the ITER experiment under construction in France.
Job opportunity in CTAMOP
Posted October 21, 2019 by Andrew Brown
A new Research Fellow position has been created in the Quantum Technology group for research into Quantum Thermodynamics.
The deadline for applications is 3 January, 2020.
Full details and application form can be found here.
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