Our visiting researcher Maksym Teslyk is presenting work which is part of his Ph.D. dissertation. It relates to both classical and quantum physical information theory and to general relativity. The picture is Kip Thorne’s black hole visualization from the movie Interstellar.
Abstract:
A spherical system of mass M is represented as a set of Unruh horizons. The approach allows to estimate the total entropy of Unruh radiation from the set and calculate its ratio to the Bekenstein-Hawking entropy. The contribution of mass and spin s of the emitted particles is taken into account. For large values of M, the ratio exhibits susceptibility to the intrinsic degrees of freedom and varies from 0% (s = 0) to 19% (s = 5/2).
Time and place: Thursday Nov. 16th, room PS439 in Pilestredet 35.
Typically, atoms and molecules exposed to strong laser field, which, incidentally, was the topic of this year’s Nobel prize in physics, are described theoretically and computationally without considering magnetic interactions. However, with strong enough fields and low/high enough photon energies, this approach breaks down – rendering the problem much tougher.
This was one of several topics for discussion.
Morten and I also had the pleasure to learn about ongoing activities within quantum information technology at the University of Warsaw – both theoretically and experimentally. We were quite impressed by their various labs – and their efficient setups.
Impressive was also a relevant word for describing the city. Well worth a visit!
Something to stretch towards: Julia Derlikiewicz (left) and Marie Skłodowska Curie (right).
We thank our hosts, Katarzyna, Julia, Deeksha, Jurek, and Mihai, so much for their overwhelming hospitality and hope that we can return the favor at some point.
Tuesday Nov. 17th we have the pleasure of hearing Noah Oldfield, from Simula Research Lab, presenting results and research question related to his ongoing project. It involves software testing on actual quantum computers. See the abstract below for more details.
Quantum program outputs enable the development of unique quality assurance techniques. Our research focuses on efficiently distinguishing a specialized ideal state vector from the sampled state vector of a program using inference techniques.
To accomplish this, we utilized a hill climbing algorithm for stochastic searches between basis transformations, circumventing the exponential scaling of brute force searches with increased qubit numbers. We conducted tests on a suite of automatically generated faulty programs.
For those programs with state vectors representable in the Hadamard basis, we observed improved testing runtimes and enhanced phase gate fault detection.
We are pleased to see that the Kode24, and online magazine for developers, has taken an interest for quantum computing – again. Under the heading “Hva er greia med …” [What’s the deal with …], this interview, conducted by journalist Kurt Lekanger, introduces a few of the basics.
As a part of our contributions to this year’s Forskningsdagene, the OsloMet Quantum Hub had the pleasure of contributing to OsloMet’s actitiveis at Holmlia. The Makerspace at our faculty was responsible for making Ungforsk happen – with an very interesting program put together to spur the curiosity of youth school pupils. Indeed an impressive job planning, announcing and implementing. Kudos to Notto Thelle, Kersti Fosse Blålid – and all other colleges and voluenteers involved. Read more about what went on at Ungforsk here:
Slightly younger pupils were invited to a mini-Forskningstorg where one of the stands was dedicated to introducing them to quantum technology. Thanks, Aleksandar Davidov, Bendik Dalen and Kristian Wold, for your efforts!
The events took place 20th and 21st of September. A total of 400 pupils got a glimpse of quantum technology – first and foremost through playing Quantum Moves – a game developed at Aarhus University addressing quantum control and adiabatic quantum computing. Actually, the game is surprisingly addictive …
Olav-Johan Øye has, under the heading student stories, written a nice piece about Maryam and her work at Ruter – the public company that organizes public transport in the Oslo region.
Her work involves both quantum and AI technology. Read all about it here:
A while ago, in an episode of the popular Scandinavian talk show Skavlan, the founder of Norwegian Air Shuttle, Bjørn Kjos, met with famous mathematician and Fields medalist Cedric Villani. Kjos was talking about how he had been trying to solve the Schrödinger equation – seemingly impressing Villani quite a bit. “Wow, you are brave!” he exclaimed. However, I suppose he would have been even more impressed if Kjos had taken on the Dirac equation.
You may have learned that when material things start approaching the speed of light, the absolute speed limit of nature, our world starts looking strange. According to Einstein’s theory of relativity, things become shorter and time evolves more slowly.
Perhaps you have also heard that no-one has succeeded in formulating a theory comprising both quantum physics and relativity. Luckily, this is only partly true. More specifically, it is true when it comes to Einstein’s theory of general relativity, which deals with gravitation and is essential to our understanding of how the universe came about and evolves.
General theory’s predecessor, special relativity, however, is happily united by quantum physics. This union is entitled the Dirac equation, which the Brit Paul Dirac introduced in 1928 – only a couple of years after Erwin Schrödinger published his famous equation. Dirac and Schrödinger shared a Nobel price for that only a few years later.
Paul Dirac in 1933 – the year when he shared a Nobel price in physics with Erwin Schrödinger.
The Dirac equation includes the Schrödinger equation as a special case – except that it also encompasses the strange notion of electron spin. This is, however, not the strangest thing that emerges from Dirac’s equation.
The equation is plagued with several issues which makes it hard to solve – also numerically. One of these issues is that it features solutions of negative energy – in addition to the expected ones. The meaning of these odd solutions remained a mystery for a while – even to Paul Dirac himself. In an interesting interview conducted by Friedrich Hund in 1982 – well worth seeing – he talks about how he spent a year or so pondering on how to deal with them. His solution, eventually, was to postulate a sea of occupied states – a sea from which particles could be promoted leaving behind a hole. Somewhat exotic, you may think.
These notions are, as it turns out, related to the existence of anti-matter. For every particle there is an odd twin with much of the same properties – except that most of them have opposite sign. Not a very intuitive conclusion; you cannot blame anyone – including Dirac – for being puzzled by this notion. I guess this is one of the many concepts emerging from quantum physics which merits the exclamation “who ordered that?!”. (The quote originates from Isodor Rabi, the father of the MR technique, when he heard about the discovery of the muon particle, one of the electron’s heavier siblings.)
Nonetheless, anti-matter exists; we have seen it. Moreover, we have seen that pairs of particle and anti-particle may be created – they may emerge out of nothing, so to speak. Needless to say, this complicates life for anyone who may want to describe quantum physics close to the speed of light theoretically or computationally. We cannot even say for sure how many particles we are dealing with!
Luckily for us, there is a window between the point where classical, classical in the meaning non-relativistic, breaks down and the point at which pair creation needs to be considered. For instance, with the strongest of lasers, electrons may be accelerated to a certain fraction of the speed of light – thus necessitating a relativistic treatment. Even in cases where these laser fields are not strong enough to start producing particle anti-particle pairs, the numerical description is still hard enough. Thus, we were thrilled to see that relativistic effects could, to a large extent, be treated by introducing the concept of relativistic mass into the Schrödinger equation. In effect, the electron becomes a bit heavier as it becomes faster. This, in turn, contributes to enhance the effect of atomic stabilization – the notion that an atom becomes less likely to be torn apart by a laser field as you increase the strength of the laser. In other words: Yet another non-intuitive feature of quantum physics – perhaps a topic for a future blog post.
Friday 8th of september, Diedrik Leijenaar Oksens finished his master project entitled Constructing Quantum Gates Using Optimization Techniques.
In his work Diedrik started out with a model with two interacting qubits in the form of spin 1/2-particles exposed to the same, dynamic magnetic field. The first aim was to tailor this field so that we could construct specific quantum gates. The next part, the harder one, was to introduce noise and see if we could mitigate this noise by adjusting the magnetic field. The answer to this question was, unfortunately, nah.
Diedrik’s project included the development of a rather advanced MATLAB implementation. Not only did he solve a complex and highly non-convex optimization problem, he also did so by for cost landscapes for which each point required the repeated solution of dynamical equations. Here is one illustration of such a landscape:
This, in turn, involved both the “traditional” Schrödinger equation and the more involved Lindblad equation, the latter for introducing non-reversible noise mechanisms.
The fact that this implementation, in the end, is quite generic – and relies on rather abstract theoretical concepts, renders his work even more impressive.
As I am sure this very text reflects, we, his advisors, are quite proud of Diedrik’s acheivements.
For the next one, we’ll have to see if we can find other ways of mitigating decoherence …
At JavaZone last week, according to themselves the biggest European community-driven conference for modern developers, Andreas Ahlgren – among others – gave a thrilling presentation on quantum computing and its possibilities. Andreas, our hub’s “partner in quantum”, one of the international leaders of Sopra Steria’s quantum initiative (among other things). In his presentation he got to demonstrate his impressive skills when it comes to “thinking outside the box”, unhindered by limitations of imagination.
Sobolev space formulation of density-functional theory: Solving the v-representability problem.
14th September 13:00, room PS340, building P35.
Density-functional theory is one of the principal methods in physics, chemistry and materials science used for calculating properties of many-body systems based on their electronic structure. It rests on a reformulation of the explicit energy expression in terms of the full quantum state into an implicit energy functional defined for a reduced quantity, the one-particle density. While considerably reducing the computational complexity, if corresponding approximations are available, this reformulation introduces certain mathematical problems. Most notably, it is not explicitly known which set of densities actually stems from solutions to the quantum many-body problem, i.e., the lowest-eigenvalue solution to the time-independent Schrödinger equation. In this talk a recently found resolution to this so-called “v-representability problem” is presented in the reduced setting of a 1-dim ring system with densities from a Sobolev space.
