09:00  10:20

Student talks


Wael Elkamhawy
(TU Darmstadt)
Description of 31Ne in Halo EFT
Previous investigations of 31Ne via 1nremoval reactions on C and Pb targets revealed that it is a deformed nucleus with a significant pwave halo component. We construct a pwave halo effective field theory for 31Ne in order to provide an appropriate framework for its description. Within this framework, we establish correlations between different observables, which enables us to make theoretical predictions for the properties of 31Ne.


Fabian Hildenbrand
(TU Darmstadt)
Effective field theory for threebody hypernuclei
We construct a shortrange effective field theory with contact interactions for threebody hypernuclei in the strangeness $S=1$ sector. An asymptotic analysis is performed in the $I=0$ and $I=1$ isospin channels and the corresponding effective Lagrangians are constructed. It turns out that a $\Lambda$NN threebody force is required for consistent renormalisation in both channels. We present universal correlations between observables and discuss the possibility of a $\Lambda$nn bound state in this effective theory.


Marcel Schmidt
(TU Darmstadt)
Halo effective field theory for nuclear reactions
Direct reaction measurements serve as powerful tools to study halo nuclei. As an archetype example of such an exotic nucleus, Beryllium11 consists of a tightlybound core and a weaklybound valence neutron in the two halo states $1/2^+$ and $1/2^$.
In this talk, we propose an effective field theory for the transfer reaction Be10(d,p)Be11 which exploits the remarkable energy scale separation of the halo system. The theory contains nonrelativistic fields for the valence neutron, the proton as well as the core. In contrast, the deuteron and both Beryllium11 states are generated dynamically in the respective twobody systems. They are treated using auxiliary fields.
We diagrammatically construct the full nonperturbative scattering amplitude in the strong sector including optical potentials for highmomentum loss channels. In contrast, longrange Coulomb interactions are treated perturbatively. Finally, we present calculations for the differential reaction cross section and compare it with experimental results.


Lucas Souza
(Technnological Institute of Aeronautics)
Reactions and structure of threefragment weakly bound nuclei
Light halo nuclei form part of the neutronrich drip line.
We investigate how structure effects of twoneutron halo nuclei like $^{20}$C and $^{22}$C appears from some reactions.
We discuss two kind of reactions being: the twoneutron halo breakup reaction on a heavy target and also, we consider the possibility of finding Efimov excited states on $^{20}$C in a proton collision.
Twofragment nuclei when scatter from a target may undergo a fragmentation process where one of the fragment is observed while the other fragment and the target are not. The inclusive breakup processes are important as the singles spectra can supply important information about the unobserved twobody subsystem.
The extention these threebody theories to
derive an expression for the fragment yield in the reaction $A(a,b)X$, was done in Ref.[1], where the projectile is $a=x_1+x_2+b$. Borromean, twonucleon, halo nuclei are examples of unstable threefragments projectiles.
Here we use a model from [1] to treat inclusive nonelastic break up reactions involving weakly bound threecluster nuclei.
The inclusive breakup cross section is the sum of a generalized fourbody form of the elastic breakup cross section plus the inclusive nonelastic breakup cross section that involves the ``reaction'' cross section, of the participant fragments, $x_1$ and $x_2$. This latter one, objective of our studies in principle, contains the incomplete fusion of the threefragment projectile.
We also focus to describe the elastic scattering of a proton reaction on a neutronneutroncore halo nuclei.
The first excited state of the $^{20}$C is obtained from neutron colision leading to a Efimov polarization potential.
Was computed the transition form factor of the momentum transfer by the proton to the halo nuclei.
\newline
\newline
[1] B.V. Carlson, T. Frederico, M.S. Hussein; Phys. Lett. B, {\bf 767}, (2017) 53.

10:20  10:50

Break

10:50  12:30

Student talks


Olga Klimenko
(Joint Institute for Nuclear Research)
Helium trimer via Faddeev differential equation


Christiane Schmickler
(TU Darmstadt)
Tetramer bound states in heteronuclear systems
We calculate the universal spectrum of trimer and tetramer states
in heteronuclear mixtures of ultracold atoms with different masses in
the vicinity of the heavylight dimer threshold. To extract the energies, we
solve the three and fourbody problem for simple two and
threebody potentials tuned to the universal region
using the Gaussian expansion method.
We focus on the case of one light particle of mass $m$ and two or three
heavy bosons of mass $M$ with resonant heavylight interactions.
We find that trimer and tetramer cross into the heavylight dimer threshold
at almost the same point and that as the mass ratio $M/m$ decreases,
the distance between the
thresholds for trimer and tetramer states becomes smaller.
We also comment on the possibility of observing exotic
threebody states consisting of a dimer and two atoms in this
region and compare with previous work.


Elkjaer Rasmussen Stig
(Aarhus University)
Window for Efimov physics for fewbody systems with finiterange interactions
We investigate the two lowestlying weakly bound states of $N\leq 8$ bosons as functions of the strength of twobody Gaussian interactions. We observe the limit for validity of Efimov physics. We calculate energies and second radial moments as functions of scattering length. For identical bosons we find that two $(N − 1)$body states appear before the $N$body ground states become bound. This pattern ceases to exist for $N\geq 7$ where the size of the ground state becomes smaller than the range of the twobody potential. All meansquareradii for $N \geq 4$ remain finite at the threshold of zero binding, where they vary as $(N − 1)^p$ with $p = −3/2, −3$ for ground and excited states, respectively. Decreasing the mass of one particle we find stronger binding and smaller radii. The identical particles
form a symmetric system, while the lighter particle is further away in the ground states. In the excited states we find the identical bosons either surrounded or surrounding the light particle for few or many bosons, respectively. We demonstrate that the first excited states for all strengths resemble twobody halos of one particle weakly bound to a dense $N$body system for $N = 3, 4$. This structure
ceases to exist for $N \geq 5$.


Thomas Secker
(Eindhoven University of Technology)
Finiterange Efimov physics in the unitary Bose gas
The recent experimental exploration of the unitary Bose gas opens up new directions in the study of stronglycorrelated quantum manybody physics. This strongly interacting Bose system is deeply affected by threebody phenomena such as the universal Efimov effect. Experiments with atomic gases revealed that the longrange part of the twobody interaction is crucial in this context. Therefore, we study finite range effects of three stronglyinteracting particles via the offshell twobody Toperator in momentum space. We investigate this operator both for simple square well and for full coupled channel interactions close to Feshbach resonances, which we then expand in separable terms to efficiently solve the three body Faddeev equations in momentum space.


Artem Korobitsin
(Joint Institute for Nuclear Research)
Theoretical study of the neon clusters
Small clusters of rare gas atoms are of a great interest in the recent years. They belong to a large class of molecules interacting via potentials of vanderWaals type and have unique quantum properties. One of these properties is the Efimov effect [1]. This effect reflects the difference in the properties of the twobody and the three  body systems. When there are at least two subsystems of zero binding energy, the three  body system has an infinite number of weakly bound states  this is the essence of the Efimov effect. Calculations of ultracold three  body clusters require methods suitable for solving three  body bound state and scattering problems in configuration space [2]. One of the effective methods for studying three  particle systems is based on using the differential Faddeev equations in the total angular momentum representation [3].
$\quad$ This work is aimed at a theoretical investigation of the neon atomic clusters. We developed a numerical algorithm for solving differential Faddeev equations in the total angular momentum representation [3]. This algorithm has been realized in the programming language C++. The developed numerically effective computational scheme, especially in combination with an option of using multiple processors, makes it possible to calculate wide range of three  body problems. For the calculations of the spectrum of neon trimer we use finitedifference approximation and cubic polynomial splines for solving the differential Faddeev equations with the zero asymptotic boundary conditions. To increase the speed of calculation a template library Eigen [4] for linear algebra is used. We have applied developed numerical algorithm for solving the above mentioned equations for the $^{20}$Ne three  atomic system. To describe the interatomic interaction the realistic potentials HFDB [5] and TT [6] were used. The calculated results of binding energies of the ground and the first excited states for neon trimer are in a good agreement with the results obtained using different methods by other authors.
\noindent{\textbf{References}}\\
$[1]$ V.N. Efimov, Phys. Atom. Nucl. \textbf{12}, 1080 (1970); Phys. Lett. B \textbf{33}, 563 (1970)\\
$[2]$ E.A. Kolganova, A.K. Motovilov and W. Sandhas
FewBody Syst. \textbf{51}, 249257 (2011)\\
$[3]$ V.V. Kostrykin, A.A. Kvitsinsky and S.P. Merkuriev, FewBody Syst. \textbf{6}, 97 (1989); \\ A.A. Kvitsinsky and C.Y. Hu, FewBody Syst. \textbf{12}, 7 (1992); V.A. Roudnev, S.L. Yakovlev and\\ S.A. Sofianos,
FewBody Syst. \textbf{37} 179 (2005)\\
$[4]$ \url{http://eigen.tuxfamily.org}
$[5]$ R.A. Aziz and M.J. Slaman, J.Chem.Phys. \textbf{130}, 187 (1989)\\
$[6]$ K.T. Tang and J.P. Toennies, J.Chem.Phys. \textbf{118}, 49764983 (2003)\\

12:30  13:50

Lunch and discussion

13:50  15:50

Student talks


John Hadder Sandoval Quesada
(Sao Paulo State University)
From 3D to 1D: squeezing the Efimov effect
We present a method to study the continuous dimensional transition of the quantum mechanical threebody problem. The theoretical development presented here can be extended to any asymmetric threebody systems with particles interacting by a shortrange potential . We considered an AAB system formed by two identical bosons, A, and a different particle, B. We calculate the energy spectrum and show how it changes when we move from three to two and one spatial dimension.


Derick Rosa
(São Paulo State University)
Bound states of a light atom and two heavy dipoles in two dimensions
We study a threebody system, formed by a light particle and two identical heavy dipoles, in two dimensions in the BornOppenheimer approximation. We present the analytic lightparticle wave function resulting from an attractive zerorange potential between the light and each of the heavy particles. It expresses the largedistance universal properties which must be reproduced by all realistic shortrange interactions. We calculate the threebody spectrum for zero heavyheavy interaction as function of light to heavy mass ratio. We discuss
the relatively small deviations from Coulomb estimates and the degeneracies related to radial nodes and angular momentum quantum numbers. We include a repulsive dipoledipole interaction and investigate the threebody solutions as functions of strength and dipole direction. Avoided crossings occur between levels localized in the emerging small and largedistance minima, respectively. The characteristic exchange of properties like mean square radii are calculated. Simulation of quantum information transfer is suggested. For large heavyheavy
particle repulsion all bound states have disappeared into the continuum. The corresponding critical strength is inversely proportional to the square of the mass ratio, far from the linear dependence from the Landau criterion


Rafael Barfknecht
(Aarhus University)
Dynamical realization of magnetic states in a strongly interacting Bose mixture
We describe the dynamical preparation of magnetic states in a strongly interacting twocomponent Bose gas in a harmonic trap. By mapping this system to an effective spin chain model, we obtain the dynamical spin densities and the fidelities for a fewbody system. We show that the spatial profiles transit between ferromagnetic and antiferromagnetic states as the intraspecies interaction parameter is slowly increased.


Oleksandr Marchukov
(Tel Aviv University)
Phase fluctuation in fragmented BECs
When describing interacting Bose gases with a finite number of particles confined in 1D traps, the meanfield approach appears to not reproduce phase fluctuations accurately. In order to improve this description the Bose gas should be considered fragmented, i.e. contain several states into which the gas could condense. More formally, following Penrose and Onsager, it means that there are more than one macroscopically occupied singleparticle states, in contrast to the "simple" BEC. Then the beyondmeanfield manybody methods are required.
In this work we consider a mesoscopic number of weaklyinteracting bosons trapped in a 1D harmonic potential using multiconfigurational timedependent Hartree method for indistinguishable particles (MCTDHX). We calculate the fragmented ground state of the system for different interaction strengths. Using the singleparticle density matrix of the gas we calculate quantum phase fluctuations and find that they may serve as a definite signature of a fragmentation in a condensate. Additionally, the discrepancies between the meanfield and selfconsistent manybody results may be used as a benchmark for the MCTDHX method, which is to the best of our knowledge still lacking in cold atomic gases. Moreover, for a twoboson system we demonstrate a very satisfactory agreement between the MCTDHX, Monte Carlo (for hardcore bosons) and analytical results.


Usui Ayaka
(Okinawa Institute of Science and Technology Graduate University)
Dynamical phase transition of a TonksGirardeau gas
We investigate Dynamical Phase Transitions (DPTs) in a strongly correlated quantum gas in one dimension, which is TonksGirardeau Gas (TG gas), after a quench. We consider situations that DPTs are created by suddenly turning on a lattice potential in an infinite well potential, which is also called as pinning phase transition. The momentum distribution of TG gas can be described with just singleparticle states, owing to strong repulsive interaction. This makes it much faster to compute momentum distribution. As a result, it is found that the peak of momentum distribution tells us DPTs, as the peak drops when the number $N_lat$ of wells in the lattice corresponds to the particle number $N_p$ like the Mottinsulator phase. Also, when the number $N_lat$ corresponds to divisors of particle number $N_p$, that is $N_p / N_lat = n$ with integer $n$, the peak of momentum distribution gets depressed as the lattice is deep enough. TG gas is a realistic system for experiments, so it is expected that our results are confirmed.


Andreas Bock Michelsen
(Aarhus University)
A new method for constructing spin chains from spectral data
A 1D few body system of aligned spins with a single oppositely alig
ned spin (a spin chain) is a system showing great promise in quantum
informatics. Many of the desired applications of such a system can be ex
pressed through the specication of a certain spectrum of eigenvalues and
eigenvectors. This project seeks to develop a method for systematically
predicting which symmetric trapping potential would yield a specic type
of spectrum, using recently published code, machine learning and local
density approximations to make the process as automatic as possible.
Researchers will be able to use this to explore the feasibility of realizing
any such system with a specic spectrum, ultimately resulting in an
immediate blueprint for experimental implementation. This will make it
easy to explore new systems for quantum state transfer, robust informa
tion storage, or something else entirely. The poster presents the various
observations and tools used in the process, as well as the promising rst
results of its implementation, exploring new implementations of quantum
communication spin chains resilient to disruption by external coupling.

15:50  16:20

Coffee break

16:20  18:00

Student talks


Evgenii Mardyban
(Joint Institute for Nuclear Research)
Description of alternating parity bands in heavy nuclei using supersymmetric quantum mechanics


Andre Chaves
(University of Minho)
Optical properties of excitons in 2D materials
We present a unified description of the excitonic properties of four monolayer transitionmetal dichalcogenides (TMDC's)
using an equation of motion method for deriving the BetheSalpeter equation in momentum space.
Our method is able to cope with both continuous and tightbinding Hamiltonians, and is less computational demanding than the traditional firstprinciples approach.
We show that the role of the exchange energy is essential to
obtain a good description of the binding energy of the excitons.
The exchange energy at the $\Gamma$point is also essential to obtain the correct position of the Cexciton peak.
Using our model we obtain a good agreement between the Rydberg series measured for WS$_2$.
We discuss how the absorption and the Rydberg series depend on the doping.
Choosing the interaction parameter and the doping we obtain a good qualitative agreement between the experimental absorption and
our calculations for WS$_2$.


Anoop Divakaran
(Malaviya National Institute of Technology)
Surface oxidation in Bi2Te3 and its effect on TI surface states
Bismuth telluride is a wellknown topological insulator having a large number of applications in the field of quantum computing and spintronics. Topologically protected surface states in these materials resemble two dimensions confinements, which can host quantum transport phenomena such as quantum Hall effect. Oxidation of exposed TI materials plays a major role in deteriorating the surface state properties by adding impurity charge carriers on the surface. We have investigated the process of surface oxidation in chemically synthesised Bismuth telluride(BT) nanostructures. Different spectroscopic techniques like Raman, soft Xray absorption, and Xray photoemission spectroscopy was used and confirmed the formation of individual oxides. We could observe two additional modes corresponding to $\alpha $ Bi${_2} $O${_3}$) and TeO${_2}$) in Raman spectra of BT nanostructures. Considerable increase in the quantity of Bi${_2} $Te${_3}$ in nanostructures than in single crystals, confirmed by XPS studies indicate the dependence of oxidation on the surface to volume ratio. Surface encapsulation of these materials has resulted in a reduction of surface oxidation to a great extent without affecting other physical properties. This study is imperative to perceive the generic trend in the surface oxidation, its dimensionality dependence which is well correlated with the oxidation behaviour of single crystals. Sound understanding of bond formation in oxides help us to predict the carrier dynamics of surface states after exposure. This information can be used to model real world TI systems
and to extract pure surface state properties to better explore them.


Jorge Henrique de Alvarenga Nogueira
(Università degli Studi di Roma La Sapienza)
Threebody bound states with zerorange interaction in the BetheSalpeter approach
The Bethe–Salpeter equation for three bosons with zerorange interaction is solved for the first time. For comparison the lightfront equation is also solved. The input is the twobody scattering length and the outputs are the threebody binding energies, Bethe–Salpeter amplitudes and lightfront wave functions. Three different regimes are analyzed: (i) For weak enough twobody interaction the threebody system is unbound. (ii) For stronger twobody interaction a threebody bound state appears. It provides an interesting example of a deeply bound Borromean system. (iii) For even stronger twobody interaction this state becomes unphysical with a negative mass squared. However, another physical (excited) state appears, found previously in lightfront calculations. The Bethe–Salpeter approach implicitly incorporates threebody forces of relativistic origin, which are attractive and increase the binding energy.
