Conferences
 

School and Workshop on
Quantum Information and Quantum Gravity

 School of Physics, IPM
28 Mordad - 1 Shahrivar 1402 (19-23 August 2023)
 
School's Speakers

- Mohammad Sadegh Khazali, University of Tehran
Title: Implementation of Quantum Information: A Comprehensive Overview of Different Platforms

Abstract: Quantum information has revolutionized the field of computing and communication. However, implementation of quantum information in different platforms is still a challenging task. In this session, we will provide a comprehensive overview of the implementation of quantum information in different platforms, including neutral atoms, ion traps, photonic, and superconducting qubits. The session will cover the fundamental principles and practical aspects of quantum information implementation. Participants will gain an understanding of the strengths and limitations of different platforms. This summer school session is ideal for graduate students, researchers, and professionals who are interested in quantum information and its implementation.
- Mohammad Reza Mohammadi Mozaffar, University of Guilan

Title: Introduction to Holographic Entanglement
 Abstract: This is a pedagogical introduction to the holographic entanglement entropy and related topics. Starting with the conceptual basis of the gauge/gravity dualities, the subject is developed emphasizing some concrete topics, which are discussed in detail. A very brief introduction to AdS/CFT correspondence is provided, containing the minimal ingredients to understand the origin of the holographic proposals for computing the entanglement entropy and other correlation measures both in static and dynamical setups. Other topics covered are the quantum extremal surface, geometry from entanglement, island formula and replica wormholes.
- Ali Mollabashi, YITP

Title: A Brief Introduction to Entanglement in Quantum Field Theories
 Abstract: These two lectures are introductory to Euclidean and Lorentzian approaches to studying the entanglement properties in QFTs. Most of the focus will be on introducing appropriate tools to study entanglement measures in free and holographic conformal field theories. I will try to go through the technical details of explicit examples.

Note                    Audio File
- Ali Hamed Moosavian

Title: A brief introduction to quantum algorithms.

Abstract: In this informative introductory talk, we explore the intriguing world of quantum algorithms and their components. We take a closer look at the fundamental elements that form the basis of these algorithms and examine their implementation in complex computational processes. Through illustrative examples, we observe how these building blocks come together to harness the potential of quantum computing, potentially transforming our problem-solving methods.
- Mohammad Hassan Vahidinia, IASBS

Title: An Introduction to black hole thermodynamics and information problem
 Abstract: These lectures are intended to be a pedagogical introduction to some key concepts in black hole physics and their relevance to quantum information theory. We start by exploring the physics of an accelerated observer and the equivalence principle, then turn our attention to the causal structure of space-time, with an emphasis on the idea of the horizon. We then demonstrate how the quantum entanglement of vacuum in the presence of a horizon results in Unruh temperature and Hawking radiation. This enables us to associate temperature and entropy with the black hole horizon, allowing us to examine a black hole as a thermodynamic system. Next, we’ll explore how the entropy of black holes supports the holographic principle in gravitational systems and the Bekenstein entropy bound in non-gravitational systems. We’ll also provide a brief overview of Casini’s approach to formulating and proving the Bekenstein bound. Finally, we take a brief look at the black hole information problem from Page’s perspective.
- Saleh Rahimi, IPM

Title: Quantum sampling problems with linear optics

Abstract: As universal fault-tolerant quantum computers are still not available, there is keen interest in intermediate models of quantum computation. It is believed that these models can demonstrate quantum-computational speedups using simpler physical systems and algorithms. A class of these intermediate models consists of quantum sampling problems, which aim to generate samples from the output probability distribution of a quantum circuit. In the first lecture, I will review basic quantum-optical elements for describing the quantum-optical sampling and discuss their classical hardness. In the second, I will delve into various versions of boson-sampling problems and discuss recent results on the demonstration of quantum speedups through boson-sampling experiments.

- Fatemeh Tarighi Tabesh, IPM

Title: Theory of Open Quantum Systems and Its Applications

Abstract: All quantum systems undoubtedly interact with their surroundings which generally results in the loss of typical quantum properties such as coherence or entanglement as well as energy dissipation. The performance of quantum technologies is highly limited by the effects of decoherence due to their interaction with some environments. In the school, we will address the foundation theory of open quantum systems such as completely positive maps and quantum channels, Kraus representation, quantum channels for qubits, Lindblad master equation, Heisenberg-Langevin equation, damped simple harmonic oscillator, decoherence and the emergence of the classical world. In addition, we will introduce the Markovian and non-Markovian dynamics that the latter implies the presence of memory effects. We will also discuss spin dephasing and coherence times of nitrogen vacancy (NV) color centers in diamond as well as the role of memory effects on energy and ergotropy of quantum batteries in the framework of open system dynamic.
Workshop's Speakers

- Mohsen Alishahiha, IPM

Title: On universal behavior of Complexity

Abstract: We introduce a general framework to study complexity as a probe for quantum chaos. We shall explore universal behavior the complexity may exhibit as a function of time and in what extend it may be considered as a probe for quantum chaos.

- Zahra Baghali Khanian, Technical University of Munich

Title: Rate distortion theory for mixed states 

Abstract: We consider the compression of asymptotically many copies of ensembles of mixed quantum states where the encoder has access to a side information system. The figure of merit is per-copy or local error criterion. Rate-distortion theory studies the trade-off between the compression rate and the per-copy error. The optimal trade-off can be characterized by the rate-distortion function, which is the best rate given a certain distortion. We derive the rate-distortion function of mixed-state compression. The rate-distortion functions in the entanglement-assisted and unassisted scenarios are in terms of a single-letter mutual information quantity and the regularized entanglement of purification, respectively. Our compression scheme covers both blind and visible compression models (and other models in between) depending on the structure of the side information system.

- Amin Faraji, Sharif University of Technology

Title: Path Integral Optimization and Quantum Complexity

Abstract: In this talk, I will discuss some aspects of quantum complexity with emphasis on path integral optimization. In particular, I will argue how this optimization leads to a new understanding of the structure of spacetime.

- Reza Fareghbal, Shahid Beheshti University

Title: A novel connection between holographic dual of BMSFT spacelike and CFT timelike entanglement entropies.

Abstract: BMS-invariant field theories (BMSFT) are  proposed as the holographic dual of asymptotically flat spacetimes. It is expected that holographic dual of all quantities in BMSFTs are given by taking the flat-space limit from the corresponding quantities in the AdS/CFT correspondence. However, such a limit from the spacelike entanglement entropy of a CFT and its dual extremal curve in the bulk AdS geometry is not well-defined.  In this talk we discuss that in order to find the BMSFT entanglement entropy holographically, one needs to start from a timelike subsystem in AdS/CFT.

- Saeed Mehraban, Tufts University

Title: Approximate unitary t-designs by short-depth quantum circuits and applications 

Abstract: The uniform distribution over unitary operations, a.k.a. the Haar measure, is a central resource in quantum information science; it is also a plausible toy-model for chaotic quantum dynamics. While preparing the Haar measure requires exponential time, many applications and features of the Haar measure only rely on a few moments of this distribution. As a result, approximate unitary t-designs which reliably approximate up to the first t moments of the Haar measure are of prime importance. Polynomial-size random quantum circuits, on the other hand, capture polynomial-size quantum circuits and are quantum analogs of the Brownian motion. A well known result of Brandao, Harrow and Horodecki implies that random quantum circuits are approximate unitary t-designs. The depth at which a random quantum circuit becomes approximate t-design models the time-scale at which local quantum dynamics becomes chaotic. In this talk I will explain recent findings about this time-scale for random quantum circuits with different geometries. I will explain applications to speed of scrambling quantum information near black holes and hardness of sampling from random quantum circuits. 

The talk is based on joint works with Aram Harrow, Linghang Kong, Zi-Wen Liu and Peter Shor (arXiv: 1809.06957, 1906.02219)

- Klaus Mølmer, Niels Bohr Institute, University of Copenhage


Title: Flying qubits

Abstract: Wave packets of radiation can act as “flying qubits” and transmit quantum states and quantum gate operations in quantum optics and quantum information technologies. A theoretical description of how a wave packet of quantum radiation interacts with a local material quantum system is, hence, crucial and necessary, but no textbook provides a general description of this elementary process!
In the talk, I will review a few quantum computing proposals that employ radiation, and I will present a physically motivated derivation of a (simple) density matrix theory for the excitation of a general quantum system by incident quantum pulses of radiation. This theory differs significantly from the treatment of interactions between, e.g., an atom and a single optical mode in cavity QED. In particular, the theory acknowledges the multi-mode character of the final state of the field while it permits evaluation of the quantum state of any specified outgoing wave packet mode. We present applications of the theory to recent experiments with atomic and superconducting systems that interact with pulses of optical, microwave and acoustic radiation.

- Mohsen Razavi, University of Leed
 Title: Quantum Communications Networks: Opportunities and Challenges

- Farzin Salek, Technical University of Munich

Title: Multipartite Entanglement and Conference Key in Quantum Networks

Abstract: Multipartite entanglement theory is a fascinating research topic within the field of quantum information theory. It explores the complex relationships and correlations that can exist among multiple quantum systems. Understanding multipartite entanglement is crucial for advancing our knowledge of quantum computing, communication, and fundamental principles of quantum mechanics. During this presentation, we start by providing an overview of entanglement theory and interconversion between various classical and quantum resources. We will then present novel discoveries concerning two interconnected problems involving the extraction of correlations from a given mixed quantum state: the first is the distillation of a conference key when the state is shared between a number of players and inaccessible environment; the environment, apart from starting off with this quantum side information, also observes the public communication between the players. The second is the distillation of Greenberger-Horne- Zeilinger (GHZ) states by means of LOCC from the given mixed state. These problem settings extend our previous paper  [FS & AW, IEEE Trans. Inf. Theory 68(2):976-988, 2022], and we generalise its results: using a quantum version of the task of communication for omniscience, we derive a novel lower bound on the distillable conference key from any multipartite quantum state by means of a so-called non-interacting communication protocol. Secondly, by making the conference key distillation protocol coherent, we derive novel lower bounds on the distillation rate of GHZ states.

- Ala Shayeghi

Title: Lower bounds on the space overhead of quantum error correction

Abstract: The feasibility of quantum computing relies heavily on finding efficient quantum error correction schemes. Current techniques generally induce large overheads. I will discuss two lower bounds on the space overhead necessary for protecting quantum information from noise. For the first bound, I will focus on a circuit model allowing very general quantum operations assisted with error-free classical computation. For the second bound, I will restrict quantum operations to be geometrically local and discuss how locality increases the necessary overhead for achieving a desired logical error rate.

Based on joint works with Nouédyn Baspin, Omar Fawzi, and Alexander Müller-Hermes, available at https://arxiv.org/abs/2202.00119 and https://arxiv.org/abs/2302.04317.

- Mohammad Mehdi Sheikh-Jabbari, IPM

Title:  Approaches to Quantum Gravity

Abstract: Gravity is the only interaction which appears among all existing objects and in our current physics it is formulated through Einstein theory of General Relativity (GR). Although it has many theoretical appealing features and successes with the current experiments and observations, GR suffers from theoretical shortcomings. It is thought that  these shortcomings can be addressed within a theory of quantum gravity (QGr). Despite of many efforts and trying various approaches, a consistently quantized gravity (or quantum GR) has remained elusive. In this talk after reviewing these shortcomings, discuss three different schools of thought on the issue of QGr and briefly mention different approaches within these schools of thought to GR theoretical shortcomings and/or formulation of QGr.

Note                      Audio File

- Armin Tavakoli, Lund University

Title: Efficient entanglement detection in high dimension

Abstract: High-dimensional entanglement is a present frontier in quantum information. For a pair of particles, I discuss how to construct entanglement witnesses that can detect genuine high-dimensional entanglement using a small number of projections. These ideas are then taken further to the regime of multipartite and high-dimensional entanglement. Finally, we raise the question of what happens to standard entanglement witness methods once tiny systematic errors are permitted in the measurement devices.
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