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Wydział Fizyki UW > Badania > Seminaria i konwersatoria > Exact Results in Quantum Theory
2019-06-14 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
Jacek Wojtkiewicz (KMMF)

Rieman zeta function, distribution of the prime numbers, Riemann hypothesis, part II

Ogólne fakty o funkcjach dzeta and Xi Riemanna będą zapodane, \i jak to przez Riemanna do wyprowadzenia wzoru na rokład primesów zostało wykorzystane, \i jak mimochodem hipoteza Riemanna się pojawia, \jako wzmianka — ale po pół wieku już własnym życiem żyła; \Riemanna ciąg myśli przedstawić zamiaruję, \do czego książke Edwardsa nagminie wykorzystuję, \abyście w klimaty problemu za 1.000.000 wprowadzeni zostali, \i trochę nad tą zagadką — Szanowni Słuchacze — podumali. \
2019-05-31 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
prof. Jarosław Piasecki (IFT UW)

Bose Gas Within the Hartree-Fock Approximation

Main results derived in a recent study of an interacting Bose gas within the Hartree–Fock approximation will be discussed. The Kac scaling of the pair potential is used to show that• Bose–Einstein condensation can be destroyed by sufficiently long-range weak repulsive interactions• Bose–Einstein condensation occurs when the range of the binary potential is not too large• For a given potential there exists a critical temperature beyond which BE condensation is not possibleAt the end of the seminar, some challenging open problems will be presented.
2019-05-24 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
Andrzej Dragan (IFT UW)

Unruh massive particles cannot be observed

2019-05-17 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
Magdalena Stobińska (IFT UW)

Quantum interference enables constant-time quantum information processing

It is an open question of how fast information processing can be performed and whether quantum effects can speed up the best existing solutions. Signal extraction, analysis, and compression in diagnostics, astronomy, chemistry, and broadcasting build on the discrete Fourier transform. It is implemented with the Fast Fourier Transform (FFT) algorithm that assumes a periodic input of specific lengths, which rarely holds true. A less-known transform, the Kravchuk-Fourier (KT), allows one to operate on finite strings of arbitrary length. It is of high demand in digital image processing and computer vision but features a prohibitive runtime. Here, we report a one-step computation of a fractional quantum KT. A quantum d-nary (qudit) architecture we use comprises only one gate and offers processing time independent of the input size. The gate may employ a multiphoton Hong-Ou-Mandel effect. Existing quantum technologies may scale it up towards diverse applications.
2019-04-26 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
prof. dr hab. Robert Alicki (Uniwersytet Gdański)

Quantum features of macroscopic fields. Entropy and dynamics

Macroscopic fields like electromagnetic, MHD, acoustic or gravitational waves are usually described by classical wave equations with possible additional damping terms. The aim of this paper is to develop a complete macroscopic formalism including random/thermal sources, dissipation and random scattering of waves by the environment. The proposed reduced state of field (RDF) combines averaged field with the two-point correlation function called single-particle density matrix. The evolution equations for RDF is obtained by reduction of the generalized quasi-free dynamical semigroups describing irreversible evolution of bosonic quantum field and the definition of RDF's entropy follows from the von Neumann entropy of quantum field states. The presented formalism can be applied, for example, to superradiance phenomena and allows to unify the Mueller and Jones calculi in polarization optics.
2019-04-12 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
Marcin Napiórkowski (KMMF)

A variational approach to the interacting Bose gas

I will discuss an effective, variational model that describes the homogeneous Bose gas in the thermodynamic limit. In particular, I will address the question of how the presence of interactions changes the critical temperature of a Bose-Einstein condensate. I will present results obtained both in 2 and 3 dimensions.
2019-04-05 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
Jacek Wojtkiewicz (KMMF)

Funkcja dzeta Riemanna, dystrybucja liczb pierwszych, hipoteza Riemanna

Rieman zeta function, prime number distribution, Riemann hypothesis

Ogólne fakty o funkcjach dzeta and Xi Riemanna będą zapodane,i jak to przez Riemanna do wyprowadzenia wzoru na rokład primesów zostało wykorzystane,i jak mimochodem hipoteza Riemanna się pojawia,jako wzmianka -- ale po pół wieku już własnym życiem żyła;Riemanna ciąg myśli przedstawić zamiaruję,do czego książke Edwardsa nagminie wykorzystuję,abyście w klimaty problemu za 1.000.000 wprowadzeni zostali,i trochę nad tą zagadką -- Szanowni Słuchacze -- podumali.

Introduction to Riemann zeta function and its relation with the distribution of prime numbers.
2019-03-29 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
Michał Siłkowski (IFT UW)

Long-range asymptotics of exchange energy in the hydrogen molecule

Studies on exchange energy in the hydrogen molecule reach back to the early days of quantum mechanics. Although the non-relativistic system itself and the formulation of the problem appear relatively simple, its long-range asymptotics still raises controversy, primarily due to cumbersome electron correlation effects and near singular wavefunction in the proximity of internuclear axis. I will present and discuss high-precision variational calculations of energy splitting between the lowest singlet and triplet states in the hydrogen molecule. Owing to explicitly correlated exponential basis employed in the calculations, we claim that due to its correct asymptotic behaviour our numerical results resolve the controversy of functional asymptotic form of exchange energy in H2.
2019-03-15 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
Mikołaj Misiak (IFT UW)

Perturbative calculations in QFT and the Laporta algorithm

In searches for new phenomena in particle physics, we are often interested in observing tiny deviations from the Standard Model (SM) predictions. In consequence, the SM predictions must be known very precisely. This is often a challenge even in situations when purely perturbative calculations are sufficient. At present, the most powerful methods amount to expressing the observables of interest in terms of so-called Master Integrals (MIs). The MIs are not being evaluated directly but rather via solving systems of differential equations. In the process of finding the MIs via the Laporta algorithm, large numbers (often billions) of linear equations need to be generated and solved, with simplifications of complicated rational functions at each step. In consequence, even the most powerful present-day computer clusters are sometimes insufficient. The situation could radically improve is a clever mathematical solution of the considered algebraic problem could be found in general.
2019-03-08 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
Nguyen Viet Dang (Université Claude Bernard Lyon)

Renormalization, Gaussian Free Fields and a conjecture of Quillen on determinant lines

I will discuss the quantization of quadratic Lagrangians in an external potential focusing on the example of some massive Gaussian Free Field with position-dependent mass viewed as some external potential.We show how to make sense of the effective action by a renormalization obtained by subtracting only local counterterms and we will give some geometrical applications. Then we shall relate our results to some unpublished conjecture from Quillen (30th april 1989) on determinant line bundles.
2019-03-01 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
Radek Adamczak (MIMUW)

Uncertainty principles for random matrices

I will present uncertainty principles for several measurements (on a finite dimensional system) defined by independent random (Haar distributed) unitary matrices. Emphasis will be put on relations expressed in terms of the Shannon entropy (obtained with R. Latała, Z. Puchała, K. Życzkowski) and in terms of the total variation or Hellinger distances. If time permits I will discuss connections with high dimensional probability as well as applications to information locking and quantum data hiding.
2019-01-25 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
Mikołaj Korzyński (CFT PAN)

Probing the spacetime curvature using geometric optics

In general relativity light propagation is affected by gravity, leading to the well-known effects of light bending, Shapiro delays and gravitational redshift. On top of that, the results of observation of light by an observer are also affected by the special relativistic phenomena like the aberration or time dilation. All these effects influence the measurements of shape, parallax, redshift and position drift (proper motion) of distant objects. We show that all results of those measurements can be understood as functions of the curvature along the line of sight, as well as kinematic variables describing the momentary motions of the observer and the sources, measured with respect to their local inertial frames. This opens up the possibility to probe the spacetime curvature directly using optical observations. All results are very general and their potential applications include cosmology, astrophysics and numerical relativity.
2019-01-18 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
Jan Derezinski (KMMF)

From the conformal group to symmetries of hypergeometric type equations. IV

This is the last part of the series. I will speak about symmetries of the heat equation, which are known under the name of the Schroedinger Lie algebra/group. I will show how they lead to the symmetries of the confluent and Hermite equation. References [1] Jan Derezinski, Hypergeometric type functions and their symmetries, Annales Henri Poincare 15 (2014), 1569–1653. [2] Jan Derezinski, Przemysaw Majewski, From conformal group to symmetries of hypergeometric type equations, SIGMA 12 (2016).
2019-01-11 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
Kamil Serafin (IFT UW)

Off-shell Coulomb potential from QED

I will present a derivation of the Schrodinger equation for twocharged particles from Quantum Electrodynamics (QED).First I compute renormalized Hamiltonian of QED, whichacts in whole Fock space. Then I reduce it using Wilsonianrenormalization group procedure to the sector with onlytwo charged particles and obtain the Schrodinger equation."Off-shell" means that energy in the interaction is notconserved, which is contrasted with the textbook procedurethat is based on energy-conserving scattering. Moreover,renormalized particles have a nonzero size, hence, the off-shellpotential differs slightly from the classical Coulomb potential.
2018-12-21 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
Jaroslaw Wawrzycki (IFJ PAN)

Solution of the Adiabatic Limit Problem. QED Without Infinities

In this seminar, we present a positive solution to the adiabatic limit problem in causal perturbative QED, as well as give a contribution to the solution of the convergence problem for the perturbative series in QED, by using white noise construction of free fields. The method is general enough to be applicable to more general causal perturbative QFT, such as Standard Model with the Higgs field.
2018-12-14 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
Andriy Panasyuk (Uniwersytet Warmińsko-Mazurski)

On linear-quadratic Poisson pencils on gl(3)

In a recent paper Vladimir Sokolov introduces a three-parametric family of quadratic Poisson structures on gl(3) each of which is compatible with the canonical linear Poisson bracket. The complete involutive family of polynomial functions related to these bi-Poisson structures contains the Hamiltonian of the so-called elliptic Calogero-Moser system, the quantum version of which is also discussed in the same paper.We show that there exists a 10-parametric family of quadratic Poisson structures on gl(3) compatible with the canonical linear Poisson bracket and containing the Sokolov family. The quantization matters will be also touched in this talk. (The joint work with Ihor Mykytyuk.)
2018-12-07 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
Hélder Larraguível (IFT UW)

Matrix integrals as exact results

In this talk I will show the various appearances of matrix integrals in physics, from chaotic quantum systems to classical and quantum 1-D integrable systems, from 2-D CFT to 4-D SUSY theories, from 0-D gauge theories to 3-D topological QFT. Moreover, I will also discuss the topological recursion, an algorithm compute all order asymptotics of certain class of matrix integrals integrals and many other systems.
2018-11-30 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
Adrian Lewandowski (AEC, ITP, University of Bern)

LSZ-reduction for fields with mixing

The Dyson formula for the scattering operator usually gives ambiguous results for diagrams with corrections to external lines. The well-known solution to this problem is based on the Lehmann–Symanzik–Zimmermann (LSZ) formalism. In this talk, after reviewing the problem and its solution, I will give a simple prescription for LSZ-reduction in the case of mixing between an arbitrary number of fields.
2018-11-23 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
Gioele Botta (IFT UW)

Quantum reduced loop gravity effective hamiltonians from a statistical regularization scheme

We introduce a new regularization scheme for quantum cosmology in Loop Quantum Gravity using the tools of Quantum Reduced Loop Gravity. In particular we show how the two regularization schemes adopted in Loop Quantum Cosmology can be seen as particular case of our new scheme. Within this new scheme a new corrected effective Hamiltonian for a FRLW (k=0) universe is presented and we show how the corrections with respect to Loop Quantum Cosmology lead to a strong departure from the time symmetric bounce scenario, which is replaced by the so called emergent-bouncing universe. The extension of this scheme for the anisotropic case will be discussed.
2018-11-16 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
Jeremy Faupin (Université de Lorraine)

Hamiltonian models of the Fermi theory of weak interactions with cut-offs

In this talk, we will consider mathematical models describing the processes of the Fermi theory of weak interactions. The formal QFT Hamiltonian arising from the Standard Model of particle physics in ill-defined. To obtain a self-adjoint operator on a tensor product of Fock spaces, spatial and high-energy cut-offs are introduced into the interaction term. We will review some results concerning the spectral and scattering theories of such models. First, we will consider models describing the weak decay of massive vector bosons into the full family of leptons. Neutrinos may be treated as massive or massless particles. Next, we will study abstract effective models of interacting fermion fields describing processes such as the decay of a muon into an electron, a muon neutrino, and an electron antineutrino. This talk is based on joint works with B. Alvarez and J.-C. Guillot.
2018-11-09 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
Grzegorz Łach (IFT UW)

Tarcie Casimira

Casimir Friction

The Casimir Effect — force acting on surfaces imposing boundary conditions on quantum or classical fields. When the surfaces are in relative motion what possible appears is a dissipative velocity dependent force commonly called the Casimir friction. I will describe the recent theoretical results with special emphasis on atom-surface interactions.
2018-10-26 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
Jan Derezinski (KMMF)

From the conformal group to symmetries of hypergeometric type equations. Part III

Properties of hypergeometric type equations become quite transparent if they are derived from appropriate 2nd order partial differential equations with constant coefficients. In particular, symmetries of the hypergeometric and Gegenbauer equation follow from conformal symmetries of the 4- and 3-dimensional Laplace equation. The symmetries of the confluent and Hermite equation follow from the so-called Schroedinger symmetries of the heat equation in 2 and 1 dimension. Finally, the properties of the Bessel equation follow from the Helmholtz equation in 2 dimensions. The lectures are based on [1, 2]. References:[1] Jan Derezinski, Hypergeometric type functions and their symmetries, Annales Henri Poincare 15 (2014), 1569– 1653. [2] Jan Derezinski, Przemysław Majewski, From conformal group to symmetries of hypergeometric type equations, SIGMA 12 (2016).
2018-10-19 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
Romuald Janik (UJ)

Towards holography for quantum mechanics – a toy model for AdS/CFT

(the initial talk of the stringtheory.pl/2018 conference, conference program: https://stringtheory.pl/stringtheory-pl-2018/)
2018-10-12 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
Jan Derezinski (KMMF)

From the conformal group to symmetries of hypergeometric type equations. Part II

Properties of hypergeometric type equations become quite transparent if they are derived from appropriate 2nd order partial differential equations with constant coefficients. In particular, symmetries of the hypergeometric and Gegenbauer equation follow from conformal symmetries of the 4- and 3-dimensional Laplace equation. The symmetries of the confluent and Hermite equation follow from the so-called Schroedinger symmetries of the heat equation in 2 and 1 dimension. Finally, the properties of the Bessel equation follow from the Helmholtz equation in 2 dimensions. The lectures are based on [1, 2]. References:[1] Jan Derezinski, Hypergeometric type functions and their symmetries, Annales Henri Poincare 15 (2014), 1569– 1653. [2] Jan Derezinski, Przemysław Majewski, From conformal group to symmetries of hypergeometric type equations, SIGMA 12 (2016).
2018-10-05 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 14:15  Calendar icon
Jan Derezinski (KMMF)

From the conformal group to symmetries of hypergeometric type equations. Part I

Properties of hypergeometric type equations become quite transparent if they are derived from appropriate 2nd order partial differential equations with constant coefficients. In particular, symmetries of the hypergeometric and Gegenbauer equation follow from conformal symmetries of the 4- and 3-dimensional Laplace equation. The symmetries of the confluent and Hermite equation follow from the so-called Schroedinger symmetries of the heat equation in 2 and 1 dimension. Finally, the properties of the Bessel equation follow from the Helmholtz equation in 2 dimensions. The lectures are based on [1, 2]. References:[1] Jan Derezinski, Hypergeometric type functions and their symmetries, Annales Henri Poincare 15 (2014), 1569– 1653. [2] Jan Derezinski, Przemysław Majewski, From conformal group to symmetries of hypergeometric type equations, SIGMA 12 (2016).
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