May 2024 - ITP-quantumseminare - lists.phys.ethz.ch

QIT seminars this week
by Ladina Hausmann 27 May '24

27 May '24

Hi all, This week we have planned two QIT seminars: On Tuesday Daan Janssen will tell us about his recent paper on “Quantum reference frames, measurement schemes and the type of local algebras in quantum field theory”. The talk will take place at 15:00 in HIT F12 and on zoom https://ethz.zoom.us/j/362994444. On Thursday Maurice Hanisch will tell us about his master thesis on “Soft Information Decoding: Are we overlooking measurement details in quantum error correction?”. The talk will take place at 14:00 in HIT E41.1. See below for the abstracts. Best, Ladina Title: Quantum reference frames, measurement schemes and the type of local algebras in quantum field theory Abstract: We develop an operational framework, combining relativistic quantum measurement theory with quantum reference frames (QRFs), in which local measurements of a quantum field on a background with symmetries are performed relative to a QRF. This yields a joint algebra of quantum-field and reference-frame observables that is invariant under the natural action of the group of spacetime isometries. For the appropriate class of quantum reference frames, this algebra is parameterised in terms of crossed products. Provided that the quantum field has good thermal properties (expressed by the existence of a KMS state at some nonzero temperature), one can use modular theory to show that the invariant algebra admits a semifinite trace. If furthermore the quantum reference frame has good thermal behaviour (expressed in terms of the properties of a KMS weight) at the same temperature, this trace is finite. We give precise conditions for the invariant algebra of physical observables to be a type II_1 factor. Our results build upon recent work of Chandrasekaran, Longo, Penington and Witten [JHEP 2023, 82 (2023)], providing both a significant mathematical generalisation of these findings and a refined operational understanding of their model. **** Title: Soft Information Decoding: Are we overlooking measurement details in quantum error correction? Abstract: Quantum computers can provide asymptotically faster computation times than their classical counterparts in specific applications. However, to outperform the classical computers we have today, we need large-scale, fault-tolerant devices. Quantum error correction (QEC) is considered one of the most promising ways of achieving this milestone. However, much work is still needed to improve both the QEC methods and the quantum hardware on which they run. This talk will explore improving the performance of quantum error correction through a more refined approach to evaluating the measurement data we use for error detection. By integrating soft information—analog data that provides probabilistic insights rather than binary results—we can significantly improve the performance of QEC protocols. Initially, I will introduce quantum error correction and a widely used decoding strategy. Then, I will share results from my current master’s thesis on how soft information can more efficiently protect against quantum noise. This talk aims to demonstrate that soft information QEC can contribute meaningfully toward more reliable quantum computing.

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QIT seminar on Thursday at 14:00 in E41.1
by Ladina Hausmann 21 May '24

21 May '24

Hi all, this week Petia Arabadjieva will tell us about her master thesis "Towards more practical proofs of quantum computational advantage through knowledge assumptions", see below for the abstract. The talk will take place on Thursday at 14:00 in HIT E41.1. Best, Ladina **** Title: Towards more practical proofs of quantum computational advantage through knowledge assumptions Abstract: Demonstrating quantum advantage, the point where a quantum computer can solve a problem that no existing classical computer can, is both a theoretical and technological challenge. It requires a problem that is plausibly intractable for classical algorithms and which admits an efficient quantum algorithm, ideally one that can be performed with noisy intermediate-scale quantum (NISQ) devices. Additionally, the problem's solution should be efficiently verifiable by a classical computer. Existing single-round protocols (like asking the quantum computer to factor a large number) require large quantum circuits, whereas multi-round ones use smaller circuits but require experimentally challenging mid-circuit measurements. As such, current proofs of quantum advantage are out of reach for near-term devices. In this talk, I will provide an overview of the main paradigms for demonstrating quantum computational advantage, highlighting their respective strengths and weaknesses, with an emphasis on interactive (i.e. multi-round) proofs of quantumness. The main focus will be an exposition of the two-round BCMVV18 protocol. Finally, I will briefly outline the main result of my thesis: how we modified the BCMVV18 protocol into a single-round proof of quantumness through the use of a knowledge assumption.

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No seminar this week
by Ladina Hausmann 13 May '24

13 May '24

Hi all, this week there is no seminar planned. As already advertised in his talk last week Gilles Brassard is giving the ITS Colloquium talk on Thursday. For details see: https://eth-its.ethz.ch/activities/its-science-colloquium/Gilles-Brassard.h…. Best, Ladina

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This weeks QIT seminars
by Ladina Hausmann 06 May '24

06 May '24

Hi all, Despite the holiday on Thursday, we have two talks scheduled this week: On Wednesday Lefteris Tselentis will tell us about "The Möbius games and other Bell tests for relativity”. The talk will take place at 14:00 in HIT F12. On Friday Gilles Brassard will tell us about "Probability and consequences of living inside a computer simulation”. The talk will take place at 14:00 in HIT F12. See below for the abstracts. Best, Ladina ************** Title: The Möbius games and other Bell tests for relativity Abstract: We derive multiparty games that, if the winning chance exceeds a certain limit, prove the incompatibility of the parties' causal relations with any partial order. This, in turn, means that the parties exert a back-action on the causal relations; the causal relations are dynamical. For example, a general-relativistic violation of that inequality certifies change of curvature, in the same sense as a quantum-mechanical violation of a Bell inequality certifies a source of entanglement. We discuss these games as device-independent tests of spacetime's dynamical nature in general relativity. To do so, we design a relativistic setting where, in the Minkowski spacetime, the winning chance is bound to the limits. While we do not show the violation of these inequalities within the framework of general relativity, we find otherwise tame processes with classical control of causal order that win the games deterministically. These suggest a violation of the bounds in gravitational implementations. We obtain these games by uncovering a "pairwise central symmetry" of the correlations in question. This symmetry allows us to recycle the facets of the acyclic subgraph polytope studied by Grötschel, Jünger, and Reinelt in the mid-80s for combinatorial optimization. This abstract is based on the following work: https://arxiv.org/abs/2309.15752 ************** Title: Probability and consequences of living inside a computer simulation Abstract: The question of whether or not we are living inside a computer simulation has inspired a large amount of fiction (notably the novel Simulacron-3 and the movie The Matrix), but, unsurprisingly, not much serious research. Among the more reasonable and quantitative attempts, let us mention Nick Bostrom’s simulation argument: if societies do not tend to self-destruct before acquiring a technology sufficiently advanced to create simulations that are indistinguishable from reality, in which countless simulated beings strive, our probability of living inside such a simulation approaches unity. Elon Musk even declared in 2016 that "the odds we’re in base reality is one in billions". Was he right? Through a refinement of Bostrom's argument and the introduction of an equation reminiscent of the one Drake postulated to estimate the number of extraterrestrial civilisations in the universe, we come to the opposite conclusion: the probability that we live in base reality is rather high. Nevertheless, it is legitimate to wonder if we could use quantum cryptography to preserve our privacy against our overlords should we actually live in a computer simulation.

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