Szemináriumok

Mire használható a kvantumoptika?

Időpont: 
2021. 02. 19. 16:00
Hely: 
online (youtube)
Előadó: 
Sarkadi Tamás (BME)
A szeminárium részletei: 
https://physics.bme.hu/node/4951
Szeretettel várunk minden érdeklődőt, középiskolás diákokat és bárki mást a BME TTK Science Campus következő online előadására!
 
Február 19. péntek 16:00
 
Sarkadi Tamás (BME TTK Atomfizika Tanszék): 
Mire használható a kvantumoptika?
 
A foton több mint száz éve ismert fogalom a tudósok számára. Az utóbbi  időben viszont a fénykvantum egyre nagyobb szerepet kap a technika, az orvoslás világában, így a mindennapi életünkben is. Az előadásból megtudhatjuk, milyen eszközökkel, módszerekkel dolgoznak a kvantumoptikával foglalkozó kutatók, mérnökök. Megismerkedhetünk a legújabb fejlesztési irányokkal, valamint megtudhatjuk, hogy jelenleg, vagy a közeljövőben hol találkozhatunk kvantumoptikával a hétköznapokban.
 
 
Az előadás a BME TTK Youtube-csatornáján lesz:
Az előadás alatt az előadó élőben válaszol a csetben feltett kérdésekre!
 
 
Kapcsolat: Asbóth János (asboth at phy dot bme dot hu)

NetSquid, a discrete-event simulation platform for quantum networks

Időpont: 
2021. 02. 25. 14:30
Hely: 
online (Teams)
Előadó: 
Tim Coopmans (TU Delft)
A szeminárium részletei: 
https://physics.bme.hu/node/4953
NetSquid is a generic discrete-event based platform for simulating quantum information networks and modular quantum computing systems developed by QuTech (TU Delft / TNO). Its use ranges from the physical layer hardware and the control plane all the way to the application level. NetSquid's main aim is accurate physical simulation, not the least capturing time-dependencies. In this talk, I will introduce NetSquid and discuss several use cases to showcase its power, including long-distance entanglement generation using nitrogen-vacancy centers and atomic-ensemble hardware. NetSquid is freely available for non-commerical use at https://netsquid.org/. The website also contains a 10-minute guide to get started and references to code snippets made by other users.
 
About the speaker: Tim Coopmans is a PhD student in the groups of David Elkouss and Stephanie Wehner (Delft University of Technology), working on the analysis of quantum network protocols. Before that, Tim wrote his master thesis in certification of quantum states under supervision of Jed Kaniewski (then at University of Copenhagen) and Christian Schaffner (University of Amsterdam). His work focuses mostly on long-distance entanglement generation using intermediate nodes known as quantum repeaters. In his spare time, Tim aspires to be a good amateur jazz pianist (with varying success).

Nuclear astrophysics in the era of high precision astrophysics - an experimentalist's view

Időpont: 
2021. 02. 26. 10:15
Hely: 
online (Teams)
Előadó: 
György Gyürki (Atomki)
A szeminárium részletei: 
https://physics.bme.hu/node/4955

Based on the progress of the last almost 100 years, it has become common knowledge that nuclear reactions are responsible for the energy generation of stars as well as for the synthesis of chemical elements building up our universe. Moreover, the nuclear physics background of astrophysical processes is relatively well understood. On the other hand, in the 21th century astrophysical observations and astrophysical models reached unprecedented precision. Consequently, the knowledge of nuclear reactions taking place in various astrophysical events is often not good enough, which represents the highest uncertainty of the models.



Experimental and theoretical study of nuclear reactions of astrophysical relevance is therefore highly needed. In this talk I will use some examples to illustrate the difficulties and methods of experimental nuclear astrophysics in trying to fulfill the needs of high precision astrophysics.

Entanglement transition from continuous quantum measurements

Időpont: 
2021. 03. 01. 14:15
Hely: 
online (Teams)
Előadó: 
Alessandro Romito (Lancaster)
A szeminárium részletei: 
https://physics.bme.hu/node/4943
Quantum measurements can induce an entanglement transition between extensive and sub-extensive scaling of the entanglement entropy. This transition is of great interest since it illuminates the intricate physics of thermalization and control in open interacting quantum systems. Whilst this transition is well established for stroboscopic measurements in random quantum circuits, a crucial link to physical settings is its extension to continuous observations where, for an integrable model, it has been shown that a sub-extensive scaling appears for arbitrarily weak measurements.
 
In this talk, I present results for a one-dimensional quantum circuit evolving under random unitary transformations and generic positive operator-valued measurements of "variable strength". I will show that, for stroboscopic dynamics, there is a phase transition controlled by both the measurement density and the measurement strength. I will further show that the entanglement transition at a finite measurement strength persists for a continuously measured system with randomly non-integrable unitary evolution. I will finally present results for non-interacting models, in which a transition between logarithmic growth and strict localization of entanglement is still possible due to measurement induced dynamics. These results open the possibility to investigate the measurement induced entanglement transition in quantum architectures accessible via continuous measurements. 

Byzantine Fault Tolerance using Entangled Quantum States

Időpont: 
2021. 03. 04. 14:30
Hely: 
online (Teams)
Előadó: 
Andras Palyi (BME)
A szeminárium részletei: 
https://physics.bme.hu/node/4956
Abstract: In distributed computing, a byzantine fault is a condition where some components of a multi-component system fail, but it is unclear which components fail and which ones function properly. A deterministic protocol to reliably broadcast information in such a setting was proposed by Pease et al. [1]. More recent ideas built upon distributed entangled quantum states [2,3,4] are worth considering as they offer a reduced communication cost. In this talk, I will outline recent unpublished results of a Budapest collaboration among researchers of Nokia Bell Labs, BME and the Wigner Research Centre for Physics. I will introduce a family of quantum-aided weak broadcast protocols. I will show our results of a resource optimization procedure, illustrating the engineering aspects of future deployment of such protocols in practice. The protocols I'll discuss rely on a specific 4-qubit entangled resource state. Following earlier work demonstrating the suitability of noisy intermediate-scale quantum (NISQ) devices for the study of quantum networks [5], I will show how to prepare our resource state on publicly available IBM quantum-computer prototypes. Finally, I plan to discuss future research directions toward quantum-aided byzantine fault tolerance.
 
[1] M. Pease et al., J. ACM 27, 228 (1980).
[2] M. Fitzi, N. Gisin, U. Maurer, Phys. Rev. Lett. 87, 217901 (2001).
[3] A. Cabello, Phys. Rev. A 68, 012304 (2003).
[4] S. Gaertner et al., Phys. Rev. Lett. 100, 070504 (2008).
[5] P. Pathumsoot et al., Phys. Rev. A 101, 052301 (2020)
 
About the speaker: Andras Palyi is a theoretical physicist, working as an associate professor at the Department of Theoretical Physics, Budapest University of Technology and Economics. He obtained his PhD in condensed-matter theory at the Eotvos Lorand University in Budapest, and held a postdoc position at the University of Konstanz, in Germany, before moving back to Budapest in 2011. Since his PhD, Andras has been doing research at the interface of condensed-matter physics and quantum information, doing theory work toward the goal of practical, experimental quantum information processing.

Scanning spacetime with patterns of entanglement

Időpont: 
2021. 03. 05. 10:15
Hely: 
online (Teams)
Előadó: 
Bercel Boldis (BME)
A szeminárium részletei: 
https://physics.bme.hu/node/4958
Recently interesting new approaches have appeared dealing with the challenge of representing
inherently quantum phenomena in a classical geometric manner. In particular a connection has been established between the properties of geodesics of an asymptotically anti de-Sitter (AdS) space and the quantum information theoretic quantities of certain regions in a two dimensional Conformal Field Theory (CFT) living on its boundary.
In my presentation I review the static case of the AdS3/CFT2 correspondence. I establish a connection between the geodesics of pure AdS3 space and the boundary quantities characterizing entanglement patterns of the CFT vacuum. I also introduce the space of geodesics, the so-called kinematic space, and explain how the entropic quantities are realized there. Especially working with geodesic N-gons I show that the mutations of their triangulations give rise to a cluster algebraic structure of these polygons [1]. It turns out that this structure can be illustrated as a walk of N-3 particles in the kinematic space.
Finally using the ABHY construction, featuring Dynkin diagrams, I describe and visualize this walk [2].
 
[1] P. Lévay, B. Boldis, Scanning-Spacetime with patterns of entanglement, Physical Review D101,
066021 (2020)
[2] B. Boldis, Entanglement patterns realized as walks in kinematic space, Student Research Societies
(TDK) (2020).

Local Measurements of Interacting Electronic Matter in Magic Angle Graphene

Időpont: 
2021. 03. 08. 14:15
Hely: 
online (Teams)
Előadó: 
Shahal Ilani (Weizmann)
A szeminárium részletei: 
https://physics.bme.hu/node/4957

Abstract in pdf.

 

About the speaker: Prof. Shahal Ilani is a world-leading expert and principal investigator in experimental condensed-matter physics. His lab have developed ultra-clean and highly-controllable carbon-based quantum devices, using those for studying the physics of electrons and nano-mechanics in low dimensions, and as unique scanning probes for visualizing the physics of materials in ways that were previously inaccessible. Shahal has been the recipient of multiple ERC Grants. If you ever wanted to take a virtual 3D tour in a quantum research lab, the Ilani lab provides you with an opportunity: https://www.ilanigroup.com/lab-tour

Fermion Sampling: merging the strengths of Random Circuit Sampling and Boson Sampling

Időpont: 
2021. 03. 12. 10:15
Hely: 
online (Teams)
Előadó: 
Zoltán Zimborás (Wigner/BME)
A szeminárium részletei: 
https://physics.bme.hu/node/4959

In this talk, we present a quantum advantage scheme which is a fermionic analogue of Boson Sampling. This scheme, called Fermion Sampling, uses fermionic linear optical operations together with magic input states. On the one hand side, we provide hardness guarantees for this scheme which is at a comparable level to that of the state-of-the-art hardness guarantees for Random Circuit Sampling, surpassing that of Boson Sampling. On the other hand, we argue that one might perhaps even construct practically useful sampling schemes based on Fermion Sampling similarly to those constructed based Boson Sampling. Finally, we discuss the experimental feasibility of our scheme.

Non-local emergent hydrodynamics in a long-range quantum spin system

Időpont: 
2021. 03. 19. 10:15
Hely: 
online (Teams)
Előadó: 
Izabella Lovas (TU München)
A szeminárium részletei: 
https://physics.bme.hu/node/4960

Generic short-range interacting quantum systems with a conserved quantity exhibit universal diffusive transport at late times. We show how this universality is replaced by a more general superdiffusive transport process in the presence of long-range interactions, decaying algebraically with distance. While diffusive behavior is recovered for a sufficiently fast decay, longer-ranged couplings give rise to an effective classical Levy flight,  a random walk with step sizes following a heavy-tailed distribution. We study this phenomenon in a long-range interacting XY spin chain with conserved total magnetization, at infinite temperature. We investigate the dynamics by employing non-equilibrium quantum field theory and semi-classical phase space simulations. We find that the space-time dependent spin density profiles are self-similar, and show superdiffusive spreading, with scaling functions given by the stable symmetric distributions. We also extract the associated generalized diffusion constant, and demonstrate that it follows the prediction of classical Levy flights; quantum many-body effects manifest themselves in an overall time scale depending only weakly on the precise form of the algebraic long-range interaction. Our findings can be readily verified with current trapped ion experiments.

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