Journal Club on Condendensed Matter Theory
Physikalisches Institut, Universität Bonn
We are now in the second year of the Journal Club. Details about talks from the previous season can be found here.
Season 1: WiSe22-SoSe23
Season 2: WiSe23
Season 3: SoSe24
Season 4: SoSe25
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Talks This Season:
| Speaker | Date | Title |
|---|---|---|
| 1. Dr. Franco Lisandrini (AG Kollath) | May 08, 2024 (Wednesday) | Finite-temperature Simulations with Stochastic Matrix Product States |
| [Slides],[Abstract] | ||
| 2. Julien Breiher (AG Luitz) | May 15, 2024 (Wednesday) | Transversal Injection: Using the Surface Code to Prepare Non-Pauli Eigenstates |
| [Slides],[Abstract] | ||
| 3. Sagnik Ghosh (AG Luitz) | June 5, 2024 (Wednesday) | Discrete time-crystals in linear potentials |
| [Slides],[Abstract] | ||
| 4. Dr. Maxime Debertolis (AG Luitz) | June 19, 2024 (Wednesday) | Computational supremacy in quantum simulation |
| [Slides],[Abstract] | ||
| 8. Dr. Simon Balthasar Jäger (AG Kollath) | October 30, 2024 (Wednesday) | Atom-only descriptions of atom-cavity systems |
| [Slides],[Abstract] | ||
| 9. Sagnik Ghosh (AG Luitz) | November 06 , 2024 (Wednesday) | Replica Trick, Symmetry and Breaking in context of Measurement Induced Phase Transitions: A very brief intro |
| [Slides],[Abstract] |
Details of Talks:
1. May 08, 2024 (Wednesday)
Title: Finite-temperature Simulations with Stochastic Matrix Product States
Speaker: Dr. Franco Lisandrini (AG Kollath)
In this JC talk I will present Stochastic MPS, a method for simulating finite-temperate (quasi-)one-dimensional systems proposed in a preprint from last December (https://arxiv.org/abs/2312.04420). Before that, I will briefly introduce other finite-temperature methods commonly used with MPS (Purification and METTS).
Reference: https://arxiv.org/abs/2312.04420
2. May 15, 2024 (Wednesday)
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Title: Transversal Injection: Using the Surface Code to Prepare Non-Pauli Eigenstates
Speaker: Julien Breiher (AG Luitz)
In order to perform large scale Quantum Computing, one would need qubits with error rates on the order of 1e-20. Although Quantum Error Correction can help mitigate the error rate problem for the memory part of the computation, the implementation of gates and the initialization of states stays a big problem to solve with several explored avenues. In this Journal Club we will look at a classical algorithm developed using `Transversal Injection' to prepare the logical system in non Pauli eigenstates in the hopes of attaining Universal Quantum Computation. We will demonstrate this idea on the simple example of the surface code.
Reference: https://arxiv.org/pdf/2404.01301
3. June 5, 2024 (Wednesday)
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Title: Discrete time-crystals in linear potentials
Speaker: Sagnik Ghosh (AG Luitz)
Discrete time crystalline (DTC) phases require a seemingly impossible combination of non-adiabatic driving and a finite-entropy long-time state, which is, however, possible in non-ergodic systems. Previous works have often relied on disorder for the required non-ergodicity; here, we describe the construction of a DTC phase in non-disordered, non-integrable Ising-type systems. After discussing the conditions for interacting and periodically driven systems to display such phases in general, we propose a concrete model and then provide approximate analytical arguments and direct numerical evidence that it satisfies the conditions and displays a DTC phase robust to local periodic perturbations.
Reference: https://arxiv.org/abs/2403.01912
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Title: Computational supremacy in quantum simulation
Speaker: Dr. Maxime Debertolis (AG Luitz)
Quantum computers hold the promise of solving certain problems that lie beyond the reach of conventional computers. Establishing this capability, especially for impactful and meaningful prob- lems, remains a central challenge. One such problem is the simulation of nonequilibrium dynamics of a magnetic spin system quenched through a quantum phase transition. State-of-the-art classi- cal simulations demand resources that grow exponentially with system size. Here we show that superconducting quantum annealing processors can rapidly generate samples in close agreement with solutions of the Schr¨odinger equation. We demonstrate area-law scaling of entanglement in the model quench in two-, three- and infinite-dimensional spin glasses, supporting the observed stretched-exponential scaling of effort for classical approaches. We assess approximate methods based on tensor networks and neural networks and conclude that no known approach can achieve the same accuracy as the quantum annealer within a reasonable timeframe. Thus quantum annealers can answer questions of practical importance that classical computers cannot.
Reference: https://arxiv.org/abs/2403.00910
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Title: Atom-only descriptions of atom-cavity systems
Speaker: Dr. Simon Balthasar Jäger (AG Kollath)
We present a general approach to derive Lindblad master equations for a subsystem whose dynamics is coupled to dissipative bosonic modes. The derivation relies on a Schrieffer-Wolff transformation which allows to eliminate the bosonic degrees of freedom after self-consistently determining their state as a function of the coupled quantum system. We apply this formalism to the dissipative Dicke model and derive a Lindblad master equation for the atomic spins, which includes the coherent and dissipative interactions mediated by the bosonic mode. In addition, we also provide an overview of more complex systems where this method can be applied to including the description of ground-state cavity cooling of interacting spins and interaction and dissipation engineering of spins interacting with an array of cavities.
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Title: Replica Trick, Symmetry and Breaking in context of Measurement Induced Phase Transitions: A very brief intro
Speaker: Sagnik Ghosh (AG Luitz)
I decided to do this talk cause somehow, I got asked about replica tricks by four different people in last two months and seems like there is a renewed interest in our group with the replica trick. In this talk I will briefly formulate the replica trick, why it works and in what situations its useful, and what are the correct limits in which situation. We would carry out an example of applications of the replica trick in the context of Sherrington-Kirkpatrick model and develop the notion of Replica symmetry, its breaking and set up the recovery of correct results with the Parisi scheme. Then we would turn to Replicas in the Measurement Induced Phase Transition Problem and discuss why the relevant replica limits here are different than for system with quenched disorder. Most of the materials I cover are due to Georgio Parisi et. al. and Adam Nahum et. al.