Below you will find a list of seminars organised by ICTQT. For comprehensive list of quantum events in other institutions please see the KCIK website.
Speaker: Adamantia Zampeli (Universidad Nacional Autónoma de México)
Abstract
In this talk, I will introduce the main elements and ideas of the general boundary formulation [R. Oeckl. A local and operational framework for the foundations of physics. Advances in Theoretical and Mathematical Physics, 23(2):437–592, 2019. arXiv: 1610.09052.]. This is a formalism inspired by quantum gravity approaches and quantum information theoretic ideas and it generalises quantum field theory in such a way to deal with local measurements in local spacetime regions. It can therefore serve as a framework for reconciling quantum field theory with quantum information theory and describe measurement set-ups more general that the scattering (S-matrix) picture of particle physics. This is known to be non-trivial because the naïve application on quantum fields of mathematical objects representing measurements in the non-relativistic theory can lead to violations of locality and causality. This has been indicated by the Reeh-Schlieder theorem, as well as the more recent analysis by Sorkin [R. D. Sorkin. Impossible measurements on quantum fields. In B. L. Hu and T. A. Jacobson, editors, Directions in General Relativity: Papers in Honor of Dieter Brill, Volume 2, volume 2, page 293, January 1993.]. Here, I will focus on the composition of measurements (and observables) in relativistic quantum field theory and discuss how we deal with this problem in the context of the general boundary formulation.
Speaker: Robert Spekkens (Perimeter Institute for Theoretical Physics)
Abstract
Can the effectiveness of a medical treatment be determined without the expense of a randomized controlled trial? Can the impact of a new policy be disentangled from other factors that happen to vary at the same time? Questions such as these are the purview of the field of causal inference, a general-purpose science of cause and effect, applicable in domains ranging from epidemiology to economics. Researchers in this field seek in particular to find techniques for extracting causal conclusions from statistical data. Meanwhile, one of the most significant results in the foundations of quantum theory—Bell’s theorem—can also be understood as an attempt to disentangle correlation and causation. Recently, it has been recognized that Bell’s 1964 result is an early foray into the field of causal inference and that the insights derived from almost 60 years of research on his theorem can supplement and improve upon state-of-the-art causal inference techniques. In the other direction, the conceptual framework developed by causal inference researchers provides a fruitful new perspective on what could possibly count as a satisfactory causal explanation of the quantum correlations observed in Bell experiments. Efforts to elaborate upon these connections have led to an exciting flow of techniques and insights across the disciplinary divide. This talk will explore what is happening at the intersection of these two fields.Speaker: Dorota Maria Grabowska
Abstract
Constrained Hamiltonians are ubiquitous in fundamental physics, as any gauge theory – general relativity, electromagnetism, Yang–Mills, string theory – all result in such Hamiltonians. Unfortunately, implementing these Hamiltonians on digital quantum computers poses a number of difficulties, both theoretical and practical. In this talk, I will discuss our recent work on implementing 2+1 dimensional U(1) gauge theories onto quantum hardware. While this theory is not phenomenologically relevent to Standard Model physics, it is a fantastic toy model for non-Abelian gauge theories in higher dimensions. In particular, I will discuss the ways this theory demonstrates the many pitfalls of carrying out simulations of gauge theories in a resource-efficent manner.Speaker: Dominik Šafránek (Institute for Basic Science, South Korea)
Abstract
I will introduce a protocol which allows to unitarily extract work out of sources of quantum states characterized only by a single type of coarse measurement. This defines a new notion of extractable work, which we call observational ergotropy, because it is directly related to observational entropy.
Speaker: Pedro Dieguez (ICTQT)
Abstract
Wheeler’s delayed-choice experiment, a scenario wherein a classical apparatus, typically an interferometer, is settled only after the quantum system has entered it, has corroborated the complementarity principle. However, the quantum version of Wheeler’s delayed-choice experiment has challenged the robustness of this principle. Based on the visibility at the output of a quantum-controlled interferometer, a conceptual framework has been put forward which detaches the notions of wave and particle from the quantum state.
In this talk, I will present our results concerning a quantum-controlled reality experiment, a slightly modified setup that is based on exchanging the causal order between the two main operations of the quantum Wheeler’s delayed-choice arrangement. We employed an operational criterion of physical realism to reveal a different state of affairs concerning the wave-and-particle behavior in this new setup.
An experimental proof-of-principle will be presented for a two-spin-1/2 system in an interferometric setup implemented in a nuclear magnetic resonance platform. Finally, it will be discussed how our results validate the complementarity principle.
Speaker: Eric Aurell (KTH Royal Institute of Technology)
Abstract
Speaker: Giovanni Scala (ICTQT, UG)
Abstract
We introduce a family of positive linear maps in the algebra of 3 x3 complex matrices, which generalizes the seminal positive non-decomposable map originally proposed by Choi.
Necessary and sufficient conditions for decomposability are derived and demonstrated. The proposed maps offer a new method for the analysis of bound entangled states of two qutrits.
Based on: https://arxiv.org/abs/2212.03807
Speaker: Satoshi Yoshida (University of Tokyo)
Abstract
In this work, we report a deterministic and exact algorithm to reverse any unknown qubit-encoding isometry operation. We present the semidefinite programming (SDP) to search the Choi matrix representing a quantum circuit reversing any unitary operation. We derive a quantum circuit transforming four calls of any qubit-unitary operation into its inverse operation by imposing the SU(2)×SU(2) symmetry on the Choi matrix. This algorithm only applies only for qubit-unitary operations, but we extend this algorithm to any qubit-encoding isometry operations. For that, we derive a subroutine to transform a unitary inversion algorithm to an isometry inversion algorithm by constructing a quantum circuit transforming finite sequential calls of any isometry operation into random unitary operations.
Speaker: Adam Sawicki (Centre for Theoretical Physics, Polish Academy of Sciences, Warsaw)
Abstract
Speaker: M.Hopjan (J. Stefan Institute, Ljubljana)
Abstract
Recently it was shown, in the three-dimensional Anderson model [1] and the avalanche model of ergodicity breaking transitions [2], that the spectral form factor and the Thouless time extracted from the spectral form factor are scale invariant quantities at eigenstate transition. Thus they represent useful measures for characterisation of eigenstate transition. In the literature, an alternative definition of the Thouless time was given in terms of survival probability [3,4] which measure the stability of an initial state. Motivated by this fact, we investigate the survival probability measure and possible connections to the spectral form factor measure.
We focus on differences in behavior of the survival probability across the eigenstate transitions. Remarkably, we observe scaling invariant power-law decay of the survival probability at the transition in three physically relevant models: the three-dimensional Anderson model, one-dimensional Aubry-Andre model, and the avalanche model of ergodicity breaking transitions. We discuss connections of this universality to the universality of the spectral form factor measure. Our study [5] demonstrate that both quantities, the survival probability and the spectral form factor, are useful tool for detection of the eigenstate transitions.
[1] J. Šuntajs, T. Prosen and L. Vidmar, Annals of Physics 435, 168469 (2021)
[2] J. Šuntajs and L. Vidmar, Phys. Rev. Lett. 129, 060602 (2022)
[3] M. Schiulaz, E. J. Torres-Herrera, and L. F. Santos, Phys. Rev. B 99, 174313 (2019)
[4] T. L. M. Lezama, E. J. Torres-Herrera, F. Pérez-Bernal, Y. Bar Lev, and L. F. Santos, Phys. Rev. B 104, 085117 (2021)
[5] M. Hopjan and L. Vidmar, ArXiv:2212.13888