# Seminars & Events

**October 25, 2019 at 11:15 **

**Seminar given by Andreas Hartmann**

Institute for Theoretical Physics, University of Innsbruck

Title: **Shortcuts to adiabaticity in many-body quantum heat engines**

Abstract:

Quantum thermodynamics concerns the realisation thermodynamic cycles in quantum many-body systems. Due to the requirement of adiabaticity, a major challenge is to yield a non-vanishing power output or cooling power at finte times, respectively. One possibility available for coherent quantum strokes is to implement shortcuts to adiabaticity (STAs) to speed-up such, otherwise infinitely-long, cycles. Here we investigate the applicability of local approximate counter-diabatic protocols on many-body quantum heat engines (QHEs) where the working medium of our QHE is a many-body spin system. The counter-diabatically driven Otto cycle in this work shows a considerable increase in efficiency and power output compared to the adiabatic Otto cycle.

Place: Institute of Theoretical Physics and Astrophysics (IFTiA), Faculty of Mathematics, Physics and Informatics UG, Wita Stwosza 57, Gdansk, third floor, seminar room no. 361

**October 23, 2019 at 11:15 **

**Seminar given by Markus Grassl**

Title: **Symmetries of Weyl-Heisenberg SIC-POVMs**

Abstract:

SIC-POVMs are generalised quantum measurements which are of particular interest in the context of quantum state tomography and quantum key distribution. Alternatively, they can be described by d^2

normalised vectors in the d-dimensional complex vector space such that the inner product between any pair of vectors has constant modulus. It has been conjectured that SIC-POVMs exist for all dimensions and that they can be constructed as orbits of a so-called fiducial vector under the Weyl-Heisenberg group. Despite a lot of effort, exact fiducial vectors are known for only a few dimensions, and numerical ones up to around dimension 150, together with some solutions in larger dimensions. Recently, exact and numerical solutions in record-dimensions 323 and 844, respectively, have been found as part of conjectured families obeying additional symmetries.

The talk will present the symmetries for this putative family together with generalisations. Links to number-theoretic conjectures in this context will be presented as well. This allows to convert numerical solutions of moderate precision into exact solutions, including dimension 844 mentioned above as well as the new record dimension 1299.

Place: International Centre for Theory of Quantum Technologies, Wita Stwosza 63, Gdansk (Chemistry Department), third floor, seminar room no. F305

**October 21, 2019 at 12:15 **

**Seminar given by Arieh Ben-Naim**

The Hebrew University of Jerusalem, Israel

Title: **Entropy and the Second Law based on Information Theory**

Place: Institute of Theoretical Physics and Astrophysics (IFTiA), Faculty of Mathematics, Physics and Informatics UG, Wita Stwosza 57, Gdansk, third floor, seminar room no. 361

**October 18, 2019 at 12:15 **

**Seminar given by Borhan Ahmadi**

University of Kurdistan Hewler (UKH), Irak

Title: **Quantum thermodynamic force and flow**

Abstract:

Why do quantum evolutions occur and why do they stop at certain points? In classical thermodynamics, affinity was introduced to predict in which direction an irreversible process proceeds. In this paper, the quantum mechanical counterpart of the classical affinity is found. It is shown that the quantum version of affinity can predict in which direction a process evolves. A new version of the second law of thermodynamics is derived through quantum affinity for energy-incoherent state interconversion under thermal operations. we will also see that the quantum affinity can be a good candidate to be responsible, as a force, for driving the flow and backflow of information in Markovian and non-Markovian evolutions. Finally, we show that the rate of quantum coherence can be interpreted as the pure quantum mechanical contribution of the total thermodynamic force and flow. Thus it is seen that, from a thermodynamic point of view, any interaction from the outside with the system or any measurement on the system may be represented by a quantum affinity.

Place: Institute of Theoretical Physics and Astrophysics (IFTiA), Faculty of Mathematics, Physics and Informatics UG, Wita Stwosza 57, Gdansk, third floor, seminar room no. 361

**October 11, 2019 at 12:15 **

**Seminar given by Anubhav Chaturvedi**

National Quantum Information Centre (KCIK), University of Gdansk

Title: **Unifying quantum theory’s ontological (hidden variable) incompatibility**

Abstract:

The ontological (hidden variable) framework provides for a vital ground for notions of classicality such as Bell’s local causality, Kochen-Specker’s non-contextuality, and Spekken’s non-contextuality. These notions of classicality formulated as principles, yield operational consequences that contradict predictions of quantum theory, thereby systematically discarding substantial classes of ontological models of quantum theory. Crucially, these notions highlight the different ways in which quantum theory departs from classical theories.

In this seminar, I shall facilitate a unifying insight into these seemingly distinct, yet related notions of classicality. Subsequently, I will present a new notion of classicality as the (hopefully natural) next piece in the puzzle. We refer to this notion as “bounded ontological distinctness”, quantum violation of which implies “quantum preparations, measurements, and transformations are more distinct than they are distinguishable”. This notion not only addresses many of the shortcomings of the other well-known notions of classicality but also unifies them such that violations of the other notions imply the violation of bounded ontological distinctness.

Place: Institute of Theoretical Physics and Astrophysics (IFTiA), Faculty of Mathematics, Physics and Informatics UG, Wita Stwosza 57, Gdansk, third floor, seminar room no. 361

**October 3, 2019 at 11:30 a.m. **

**Seminar given by Tim Evans**

University of Sydney

Title: **Scalable Bayesian learning of local Hamiltonians and Lindbladians**

Abstract:

As the size of quantum devices continues to grow, the development of scalable methods to characterise and diagnose noisy devices is becoming an increasingly important problem. Recent results demonstrate how a local Hamiltonians and Lindbladians can be reconstructed from a single, arbitrary steady state with a number of measurements that scales efficiently in the size of the system. These methods, however, can only characterise the system up to scalar factor and lack sufficient robustness to noise, both of which are imperative to be of practical use. In this talk I will present a Bayesian method that addresses both of these issues by making use of any, or all, of the following: experimental control of Hamiltonian couplings, the preparation of multiple states and the availability of any prior information we may already have for the Hamiltonian couplings. Moreover we provide an adaptive measurement protocol that can be performed online, updating estimates and their corresponding uncertainties as experimental data becomes available.

Place: International Centre for Theory of Quantum Technologies, Wita Stwosza 63, Gdansk (Chemistry Department), seminar room no. F16