April 2025 - ITP-quantumseminare

No QIT seminar this week
by Ladina Hausmann 28 Apr '25

28 Apr '25

Hi all, There is no QIT seminar planned for this week. Best, Ladina

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No QIT seminar this week
by Ladina Hausmann 22 Apr '25

22 Apr '25

Hi all, There is no QIT seminar planned for this week. Best, Ladina

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Thursday's QIT seminar in HIT E41.1 at 11:00
by Ladina Hausmann 15 Apr '25

15 Apr '25

Hi all, this week our visitor Álvaro Yángëuz will tell us about “Quantum pseudoresources imply cryptography”, see below for the abstract. The talk will take place on Thursday at 11:00 in HIT E 41.1. Best, Ladina *** Title: Quantum pseudoresources imply cryptography Abstract: While one-way functions (OWFs) serve as the minimal assumption for computational cryptography in the classical setting, in quantum cryptography, we have even weaker cryptographic assumptions such as pseudo-random states, and EFI pairs, among others. Moreover, the minimal assumption for computational quantum cryptography remains an open question. Recently, it has been shown that pseudoentanglement is necessary for the existence of quantum cryptography (Goulão and Elkouss 2024), but no cryptographic construction has been built from it. In this work, we study the cryptographic usefulness of quantum pseudoresources —a pair of families of quantum states that exhibit a gap in their resource content yet remain computationally indistinguishable. We show that quantum pseudoresources imply a variant of EFI pairs, which we call EPFI pairs, and that these are equivalent to quantum commitments and thus EFI pairs. Our results suggest that, just as randomness is fundamental to classical cryptography, quantum resources may play a similarly crucial role in the quantum setting. Finally, we focus on the specific case of entanglement, analyzing different definitions of pseudoentanglement and their implications for constructing EPFI pairs. Moreover, we propose a new cryptographic functionality that is intrinsically dependent on entanglement as a resource.

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Summer School on Quantum Foundations, 16-20 June 2025 in Zurich
by Lidia del Rio 08 Apr '25

08 Apr '25

Dear physics and foundations enthusiasts, It is a pleasure to announce the fourth edition of our summer school Solstice of Foundations! It will take place at the University of Zurich, 16-20 June 2025. We encourage you to send your PhD and Masters students to the school - they will return with a consolidated understanding of quantum foundations and an academic network of peers interested in the same topics. This year's edition will focus on the importance of *agents, relativity and correlations* in the foundations of quantum mechanics.This includes quantum reference frames, modelling observers as explicit physical systems, the motility of the Heisenberg cut, multi-agent paradoxes, and the role of the observer and boundaries in novel approaches to relativity and quantum gravity. More on the programme below. --------------------------------------------------------------------------------------------------- *Information and registration:* http://foundations.squids.ch <http://foundations.squids.ch> *15th May*: Deadline for student support applications 20th May: Notification for student support applications *31st May*: Registration deadline for in-person participants *Format:* Hybrid. Both in-person and online participation are possible; in-person participation is encouraged. *Registration fee: *CHF 150 for Masters students, 200 for PhD students, 250 non-students. Online attendance is free for students, but registration is mandatory. Students based in Zurich may volunteer to help with the school and have the fee waived. *Required background: *The school is aimed at participants familiar with basics of quantum mechanics, and ideally introductory courses on quantum information theory. --------------------------------------------------------------------------------------------------- The school is structured in three thematic blocks: 1. Foundations of quantum physics Introduction to foundations of quantum physics; different approaches to quantum foundations; Bell non-locality; contextuality. These lectures will take place on Monday-Tuesday. Lecturers: * *Robert Spekkens*, Perimeter Institute for Theoretical Physics, Canada * *David Schmid*, Perimeter Institute for Theoretical Physics, Canada 2. Agents and paradoxes in physical theories How to model observers as physical systems, in quantum theory and beyond; Wigner-friend scenarios; paradoxes that emerge when trying to combine the viewpoints of different observers; relation to contextuality; systems as subjective concepts. These lectures will take place on Tuesday-Wednesday. Lecturers: * *Renato Renner*, ETH Zurich, Switzerland * *Yìlè Yīng*, Perimeter Institute for Theoretical Physics, Canada 2. From quantum reference frames to quantum gravity Modelling quantum reference frames; physical objects as imperfect reference frames; frame transformations; the equivalence principle; spacial superpositions of masses and gravitational fields; introduction to quantum gravity; the role of boundaries and observers in quantum gravity. These lectures will take place on Thursday-Friday. Lecturers: * *Anne-Catherine de la Hamette*, IQOQI, Austria * *Flaminia Giacomi*, ETH Zurich, Switzerland * *Daniele Oriti*, Complutense University of Madrid --------------------------------------------------------------------------------------------------- May your well-being be strongly correlated with the wonderful Spring weather in Switzerland, Lídia and Nuriya PS: For questions, please contact Nuriya at foundations(a)squids.ch or her academic address in CC; Lídia is mostly non-signalling for the rest of the year. ......... Dr. Lídia del Rio Essentia Foundation Research Fellow for Quantum Information Theory Institute of Physics, University of Zurich I am on partial sick leave for the next few months, with limited working hours and access to email. For urgent queries, please contact my colleagues.

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Thursday's QIT seminar at 11:00 in HIT E41.1
by Ladina Hausmann 07 Apr '25

07 Apr '25

Hi all, This week Giuseppe Calabrese will tell us about “Limits of noisy quantum metrology with correlated qubits”, see below for the abstract. The talk will take place at 11:00 in HIT E41.1. Best, Ladina ************** Title: Limits of noisy quantum metrology with correlated qubits Abstract: Quantum metrology aims to estimate unknown parameters with the highest possible precision. By leveraging quantum resources as probes, measurement accuracy can achieve the Heisenberg Limit (HL), where the estimation error scales as 1/n with the number of spatial or temporal resources, offering a quadratic improvement over the Standard Limit (SL) of 1/\sqrt{n}. However, noise fundamentally limits this advantage. For uncorrelated noise models, optimal performance typically requires costly resources such as real-time measurements and feed-forward QEC, noiseless ancillae or long-range entangled multi-probe states, making experimental implementations challenging. In this thesis, we investigate classically correlated noise models with restricted - specifically unitary - controls, and derive upper and lower bounds on the estimation precision, quantified by the Quantum Fisher Information (QFI). Our results show that correlations enhance metrological performance: perfect correlations allow the HL to be reached even without control operations, while in cases where only the SL is achievable, correlations still improve precision by increasing the QFI scaling constant. Finally, we present protocols that attain the optimal QFI scaling in different noise scenarios.

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Thursday's QIT seminar at 11:00 in HIT F 13
by Ladina Hausmann 01 Apr '25

01 Apr '25

Hi all, This week, Simon Fuchs will tell us about “A Generalisation of Reflected Entropy”, see below for the abstract. The talk will take place on Thursday at 11:00 in HIT F 13. Best, Ladina ******** Title: A Generalisation of Reflected Entropy Abstract: Holographic theories are quantum field theories for which there exists a dictionary that translates quantum observables into geometrical quantities. This allows us to assign geometrical meaning to correlation measures, in analogy to the black hole entropy. In this context, reflected entropy was introduced and a geometric dual was conjectured. This is enticing as reflected entropy is a witness of non-bipartite correlations, allowing for a geometric indicator of an otherwise elusive phenomenon. Despite its early success, reflected entropy was found to be non-monotonic: it can increase after tracing out a subsystem. Thus, it cannot make quantitative measurements of correlation, motivating the search for an alternative. In my semester project, we analyse such a candidate: twofold replica entropy. Based on the replica trick—a technique used in some quantum gravity approaches—it generalises the definition of reflected entropy. Whether this alternative can save the principle of reflected entropy remains uncertain. We find that the version of twofold replica entropy that limits itself to replicas with pure composite state reproduces the main flaw of reflected entropy: non-monotonicity. While many properties of general twofold replica entropy remain unknown due to its more complex definition, we can show that it differs from its pure counterpart.

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