Szemináriumok

Solving Nonlinear Differential Equations with Differentiable Quantum Circuits

Időpont: 
2021. 09. 28. 14:15
Hely: 
online (Teams)
Előadó: 
Vincent Elfving (Qu & Co)

Abstract & Reference: https://journals.aps.org/pra/abstract/10.1103/PhysRevA.103.052416 

 

About the speaker: Vincent is a quantum-physicist with a doctorate from the University of Copenhagen where his research focused on quantum-computational chemistry and theoretical quantum-optics at the Niels Bohr Institute under supervision of professor Anders Sørensen. Previously he completed his Masters at the University of Tokyo and Bachelors at Delft University of Technology. Vincent also worked as a researcher at Google, in the quantum-hardware team of John Martinis, where he focused on implementing quantum-computational chemistry simulations and quantum optimization strategies on current-day quantum-processors with three different superconducting qubit architectures. In his role as CTO of Qu & Co, Vincent leads the company's quantum-algorithm development activities and our implementations of such algorithms on the quantum-processors of hardware partners.

A renormalization group approach to (artificial) intelligence

Időpont: 
2021. 10. 01. 10:15
Hely: 
online (Teams)
Előadó: 
Antal Jakovác (Wigner)

The functioning of the renormalization group, in particular how it interpolates between different fixed points, is very similar to the understanding process of an intelligent actor (be it artificial or a natural one). Exploiting this analogy, we try to give a mathematical model of intelligence and understanding. We show how these thoughts work in scientific exploration, in image recognition, and we try to point out what is the main difference between the two. We also give some applications to demonstrate how these ideas can work in reality.

Spectral Properties of Coupled Two-Level Emitters

Időpont: 
2021. 10. 05. 14:15
Hely: 
online (Teams)
Előadó: 
Elnaz Darsheshdar (U of Kurdistan)

Spectral filtering allows us to manipulate the collected light statistics and the resonances induced by dipole-dipole interactions give rise to specific correlations, where the time symmetry of the correlations is broken. Based on the collective dressed states, we will explain that the study encompasses both the case of real processes, where the photons are associated with specific resonances and classical correlations between each other, and virtual processes, where pairs of photons are emitted with non- classical correlations. On the other hand, the dipole-dipole interactions give rise to new sidebands in the fluorescence spectrum due to specific couplings among the collective dressed levels which in turn depends on the spatial configuration of atoms. These couplings are the main responsible for the frequencies and variety of sidebands. We will explain the general method for finding the dressed energy levels for a system of any number of strongly coupled atoms and we solve this problem for two different spatial configurations of three coupled two-level emitters. We show that the coupling among dressed levels and consequently energies and number of sidebands in the fluorescence spectrum are different for each configuration. Thus, the fluorescence spectrum of strongly interacting atoms contains information about the number and configuration of atoms.

Electronic transport in designer van der Waals materials

Időpont: 
2021. 10. 12. 14:30
Hely: 
BME building F, 2nd floor, lecture hall 13
Előadó: 
Péter Makk (BME)
First talk of the 2021 Fall series of the BME Szilárd Leó Colloquium: https://physics.bme.hu/kollokvium
 
In recent years the study of 2D materials has become one of the most important topics in solid state physics. Novel 2D materials include insulators, semiconductors, Dirac and Weyl semimetals, superconductors, topological insulators, and very recently even magnetic materials have been found. These materials can be combined using the van der Waals stacking method, similarly to putting bricks of LEGO together. Moreover, by controlling the twist angle between the materials moiré superlattices can be formed leading to the modification of graphene’s band structures. Surprisingly, at special, “magic” angles, flat bands form with gate tunable superconducting, Mott insulating and other interesting correlated phases. In this talk I will give a glimpse into this rapidly evolving field.

Microwave to optical transducer via a Bose-Einstein condensate of atoms

Időpont: 
2021. 10. 15. 10:15
Hely: 
online (Teams)
Előadó: 
Kurkó Árpád (Wigner, ELTE)
A quantum network consists of a set of quantum processing and storage nodes distributed at different locations and connected by optical fibers that transmit quantum information with photons. There are several candidates for the implementation of the nodes, perhaps the most promising is the one which is based on superconducting electronic circuits. This platform operates in the microwave regime, and quantum-coherent microwave-to-optical converters will play the key role for the realization of a quantum network with the superconducting circuit nodes. Stimulated Raman scattering of atoms with Λ-configuration of levels is a promising tool for transducing microwave photons to optical photons. We consider [1] an atomic Bose-Einstein condensate whose large phase-space density highly amplifies the coupling to the microwave field. We determine the optimal conditions for the emitted optical photons to be collected into the guided modes of optical fibers.
 
 
[1]: Árpád Kurkó, Péter Domokos, David Petrosyan, András Vukics: arXiv:2108.13719 [quant-ph]

Duality and Form Factors in the Thermally Deformed Two-Dimensional Tricritical Ising Model

Időpont: 
2021. 10. 22. 10:15
Hely: 
online (Teams)
Előadó: 
Máté Lencsés (BME)
We consider [1] a simple generalization of the well-known Ising model allowing for vacancies i.e. spins to be absent. In two dimensions this model has a tricritical point which is described by the tricritical Ising model. The thermal deformation of the tricritical point can be described by an integrable field theory in the scaling limit. It is called the $E_7$ model and has seven stable particles with known scattering amplitudes. The model possesses a low-temperature/high-temperature duality, reminiscent of the Kramers--Wannier duality in the Ising model. However, there are two distinct order operators with the corresponding disorder ones. Using bootstrap principles and exploiting the duality, we construct the matrix elements (form factors) of the order/disorder operators between the ground state and one- and two-particle states. Utilizing Hamiltonian truncation methods and the so-called $Delta$-theorem we verify the validity of the construction. Using the form factors, we calculate one- and two-particle contributions to the dynamical structure factors of the theory, which might be accessible for experimental study.
 
 
[1]: A. Cortés Cubero, R. M. Konik, M. Lencsés, G. Mussardo, G. Takács: arXiv:2109.09767

Mozog-e a Föld? - ScienceCampus előadás

Időpont: 
2021. 10. 22. 16:00
Hely: 
BME TTK F épület, III. lépcsőház, F3213-as terem
Előadó: 
Bokor Nándor (BME)
Mit nevezhetünk fizikailag releváns értelemben 'mozgásnak'? Mozog-e ilyen értelemben a Föld? Létezik-e gravitációs erő? Az ilyen kérdéseken való töprengéssel eljuthatunk az általános relativitáselmélet alapgondolatához.
 
További információ és megközelítés:
 
Az előadássorozat FB oldalát:
 
Az előadásokkal elsősorban a természettudományok iránt érdeklődő középiskolás korosztályt célozzuk meg, de természetesen minden érdeklődőt szeretettel
várunk!

Tailoring the band structure of twisted double bilayer graphene with pressure

Időpont: 
2021. 10. 29. 10:15
Hely: 
BME building F, seminar room of the Dept. of Theoretical Physics
Előadó: 
Bálint Szentpéteri (BME)
Twisted two-dimensional structures open new possibilities in band structure engineering. In twisted graphene heterostructures, the small relative rotation of two graphene layers changes their band structure drastically. In twisted bilayer graphene at magic twist angles, flat bands emerge, which give a new drive to the field of strongly correlated physics [1]. The twisted double bilayer graphene is also an interesting system with correlated and topologically non-trivial phases. In this system the dual gating allows changing of the Fermi level, hence the electron density, and allows tuning the interlayer potential, giving further control over band gaps [2,3,4]. In this talk, I show that by applying hydrostatic pressure, additional control of the band structure becomes possible due to the tunability of tunnel couplings between the layers [5]. The band structure can be drastically changed by pressure, in good agreement with our simulations. Furthermore, our measurements suggest that the pressure can decrease the correlation effects.
 
[1] Cao, Y.; Fatemi, V.; Fang, S.; Watanabe, K.; Taniguchi, T.; Kaxiras, E.; Jarillo-Herrero, P. Unconventional superconductivity in magic-angle graphene superlattices. Nature 2018, 556, 43-50.
 
[2] Cao, Y.; Rodan-Legrain, D.; Rubies-Bigorda, O.; Park, J. M.; Watanabe, K.; Taniguchi, T.; Jarillo-Herrero, P. Tunable correlated states and spin-polarized phases in twisted bilayer-bilayer graphene. Nature 2020, 583, 215-220.
 
[3] He, M.; Li, Y.; Cai, J.; Liu, Y.; Watanabe, K.; Taniguchi, T.; Xu, X.; Yankowitz, M. Symmetry breaking in twisted double bilayer graphene. Nature Physics 2020, 17, 26-30.
 
[4] Liu, X.; Hao, Z.; Khalaf, E.; Lee, J. Y.; Ronen, Y.; Yoo, H.; Najafabadi, D. H.; Watanabe, K.; Taniguchi, T.; Vishwanath, A.; Kim, P. Tunable spin-polarized correlated states in twisted double bilayer graphene. Nature 2020, 583, 221-225.
 
[5] Szentpéteri, B.; Rickhaus, P.; de Vries, F. K.; Márffy, A.; Fülöp, B.; Tóvári, E.; Watanabe, K.; Taniguchi, T.; Kormányos, A.; Csonka, Sz.; Makk, P. Tailoring the band structure of twisted double bilayer graphene with pressure. Nano Letters 2021.

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