June 2021 - ITP-quantumseminare - lists.phys.ethz.ch

Tomorrow's QIT Seminar
by Joe Renes 28 Jun '21

28 Jun '21

Hi all, Tomorrow Severin Tschui will present his master's thesis with Zhikuan Zhao from the computer science department, entitled "Supervised Classification with Quantum Embeddings", and Arman Pour Tak Dost will present his semester project with Mischa, entitled "Quasi-Ideal clocks and their environments". See below for their abstracts. We'll start at 2pm on zoom: https://ethz.zoom.us/j/362994444. Best, Joe %%%%%%%%% Speaker: Severin Tschui Title: Supervised Classification with Quantum Embeddings Abstract: The theory of supervised classification using quantum algorithms is reviewed, focusing on the similarity between classical kernel machines and a quantum classifier model. The model is based on identifying the encoding of classical data in a quantum Hilbert space as a feature map, termed quantum embedding. An ansatz is defined on how to realise such an embedding using quantum circuits, and a code framework is provided which handles the implementation and simulation. We apply the model to classify four different data sets, finding that it reaches high training accuracy in all cases but failing to generalise on two data sets with greater dimension. We present a novel idea for assessing quantum embedding quality and carry out a simulation to investigate its merits. The experiment did not deliver statistically significant results to confirm or refute if the method is viable. Speaker: Arman Pour Tak Dost Title: Quasi-Ideal clocks and their environments Abstract: In this presentation, we motivate the axioms that clocks should satisfy. They were already known but motivated from a different point of view. It turns out that quantum clocks are more precise than classical clocks. We want to investigate the physicality of this result and present different approaches. We find a collision model that could potentially realize the clock experimentally. Yet, there is a rescaling procedure involved, the physicality of which remains for further investigations.

1 0

tomorrow's QIT Seminar
by Joe Renes 21 Jun '21

21 Jun '21

Hi all, Tomorrow we have two master students finishing up, Julian Schuhmacher, who was at IBM with Ivano Tavernelli, and Yanglin Hu, who was working with Mischa. See below for their titles and abstracts. We'll start at 2pm on zoom: https://ethz.zoom.us/j/362994444 Best, Joe Speaker: Julian Schuhmacher Title: Towards large scale simulations with quantum computers and machine learning potentials Abstract:The simulation of materials with molecular dynamics (MD) simulations is an important tool to understand and predict the properties of materials. Historically, accurate MD simulations were driven by computationally costly, yet still approximated, first-principles electronic structures calculations like Density Functional Theory (DFT), and therefore were limited to small system sizes and short simulation times. In the last few years, the application of machine learning potentials, trained on DFT or post-Hartree Fock data, allowed to run MD simulations at the accuracy of ab initio methods, but at a fraction of the computational cost. Speaker: Yanglin Hu Title: Feasibility of Experimental Realizations of Quantum Effects in Gravitational Time Dilation Abstract: A potentially detectable quantum discrepancy to time dilation in delocalized clocks was derived previously. However, no experiment was put forward to experimentally test it. In this work, we investigate the possibility to conduct a real experiment. The expectation value and the variance of the quantum discrepancy are derived with the Lindblad equation and second-order perturbation theory. Two experimental protocols based on Strontium and Magnesium optical lattice clocks are proposed. Numerical results show that it would be possible to detect the quantum discrepancy with next-generation Magnesium optical lattice clocks. We also investigate the effect of decoherence mechanisms on clock's accuracy. Upper bounds on decoherence rates in order to detect the quantum discrepancy are also given.

1 0

Tomorrow's QIT Seminar
by Joe Renes 14 Jun '21

14 Jun '21

Hi all, Tomorrow our new postdoc Vilasini will tell us about "Causality and its compatibility with space-time structure". See below for the abstract. We start at 2pm on zoom: https://ethz.zoom.us/j/362994444. Best, Joe Abstract: We often do not distinguish between the directions of causation and (space-)time, even though causality can be defined operationally and independent of a space-time structure. Separating the concepts of causality and space-time and characterising how they fit together would give crucial insights into the different notions of causality such as operational causality, relativistic causality and logical consistency. Motivated by this, we develop a causal modelling framework for operationally characterising causation in the presence of cyclic, fine-tuned and non-classical causal influences. In the process, we distinguish between two kinds of causal loops that can arise in our framework, depending on operational detectability. We then define how this general class of causal models can be embedded “compatibly” in a space-time structure i.e., without leading to signalling outside the future. We derive necessary and sufficient conditions for a causal model to be compatible with an embedding in a space-time structure, and to rule out certain kinds of causal loops in the model. In particular, this provides an operational framework for analysing causality in the post-quantum “jamming” theories proposed in [1,2], and generalises their results from Bell-type scenarios to arbitrary causal structures. Furthermore, we show that post-quantum jamming can lead to superluminal signalling, contrary to the claims of [1,2], we identify missing assumptions in these claims as well as new features of post-quantum theories that admit jamming non-local correlations. Joint work with Roger Colbeck. [1] Grunhaus, J., Popescu, S., Rohrlich, D. Phys. Rev. A53, 3781–3784 (1996). [2] Horodecki, P. , Ramanathan, R. Nat. Comms. 10, 1701 (2019).

1 0

Tomorrow's QIT Seminar
by Joe Renes 07 Jun '21

07 Jun '21

Hi all, Tomorrow we will hear from two speakers, Martina Niggli and Aaron Leu, on their master thesis and semester project, respectively. See below for the titles and abstracts. We start at the usual time, 2pm on zoom: https://ethz.zoom.us/j/362994444. Best, Joe Speaker: Martina Niggli Title: Quantum State Discrimination: Global Measurements vs. One-way LOCC Abstract: The task of quantum state discrimination is considered in two different setups: First, we analyze the setup where one party is provided with a quantum system that was prepared in one of two states at random. We review the optimal measurement to distinguish between the two states, the Helstrom measurement, and we provide a theorem that characterizes the set of all optimal measurements. Second, we look at the setup where each of two spatially separated parties is provided with one part of a composite system, which was prepared in one of two possible states. The two parties are restricted to one-way LOCC strategies in order to determine the state of their shared system. We review a known optimal strategy for pure states, and we provide a new strategy that can be applied for arbitrary states. The success probability of this new strategy is compared to that of a global Helstrom measurement for different types of states, and we characterize conditions under which the new strategy performs optimally. Speaker: Aaron Leu Title: Information-to-work conversion Abstract: As stated in the formulation of the second law of thermodynamics by Kelvin and Plank, it is impossible to convert heat directly into work. However, it has been known for more than 50 years that one can use information to extract work out of a heat reservoir, but it has only been implemented experimentally a few years ago. In most of the experiments they were able to measure or calculate the extracted work, but they did not describe information flows at all. The characterisation of the information was hardly possible, because feedback control was required. In order to describe the whole system with all its energy and information flows, we need a closed autonomous quantum system. A broad variety of Quantum technologies provide us with a lot of different tools, advantages and disadvantages. Our goal is to find a platform to implement an information-to-work protocol, which fulfills our requirements and is experimentally feasible. We restrict ourselves to quantum technologies that are available at the ETH, such that we can start a collaboration for an experimental realization in the future.

1 0