Poster Sessions

Further info on the poster session venue can be found here.

Posters may be printed with maximum A0 dimensions and vertical layout.

Presenters are listed below in alphabetical order.

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1. Crossing the Superfluid Sopersolid quantum transition of an elongated dipolar condensate

Aitor Alaña (UPV/EHU, Bilbao)

We provide a theoretical characterization of the dynamical crossing of the superfluid-supersolid phase transition for a dipolar condensate confined in an elongated trap, as observed in the recent experiment by G. Biagioni et al. [Phys. Rev. X 12, 021019 (2022)]. By means of the extended Gross-Pitaevskii theory, which includes the Lee-Huang-Yang quantum fluctuation correction, we first analyze the ground state configurations of the system as a function of the interparticle scattering length, for both trap configurations employed in the experiment. Then, we discuss the effects of the ramp velocity, by which the scattering length is tuned across the transition, on the collective. excitations of the system in both the superfluid and supersolid phases. We. find that, when the transverse confinement is sufficiently strong and the transition has a smooth (continuous) character, the system essentially displays a (quasi) 1D behavior, its excitation dynamics being dominated by the axial breathing modes. Instead, for shallower transverse trapping, when the transition becomes discontinuous, the collective excitations of the supersolid display a coupling with the transverse modes, signalling the onset of a dimensional crossover.

2. Dynamical structure factor of an attractive 2D Hubbard model of dilute fermions via analytic continuation

Christian Apostoli (University of Milano)

Searching for the Higgs mode of superconductors, we simulate by Quantum Monte Carlo techniques an attractive 2D Hubbard model of fermions at low density. For different values of the interaction strength, we compute its density-density and spin-spin correlations in imaginary time. Then we perform analytic continuation to retrieve the dynamical structure factor in both the density and the spin channel, using two techniques: Genetic Inversion by Falsification of Theories (GIFT) and Differential Evolution for Analytic Continuation (DEAC). Finally, we compare the resulting spectra with those yielded by the free electron gas and the generalized random phase approximation (GRPA).

3. Superfluidity and Bose-Einstein condensation in a Bose gas with disorder

Gregory Astrakharchik (UPC & UB, Barcelona)

We investigate the phenomenon of Bose-Einstein condensation and superfluidity in a Bose gas at zero temperature with the disorder. By using the diffusion Monte Carlo method, we calculate the superfluid and the condensate fraction of the system as a function of density and strength of disorder. In the regime of weak disorder, we find agreement with the analytical results obtained within the Bogoliubov model. For strong disorder, the system enters an unusual regime where the superfluid fraction is smaller than the condensate fraction.

4. Impurity Physics with Bose-Einstein Condensates

Søren Balling (University of Aarhus)

This scientific work revolves around the experimental realization of so-called Bose-Einstein condensates. These macroscopic quantum mechanical objects serve as a medium for quantum simulation. Currently, the Bose-Einstein condensates of potassium are used to simulate impurities in solids. In particular, the quasi-particles Bose polaron and Bose bi-polaron are investigated with respect to their spectroscopic and dynamical properties. 

5. Artificial atoms from cold bosons in one dimension

Fabian Brauneis (TU Darmstadt)

We study an analogue of an atom realized by a one-dimensional Bose gas. Repelling bosons (“electrons”) are attracted to an impurity, the “nucleus”. The interplay between the attractive impurity-boson and repulsive boson-boson interaction leads to a crossover between different states of the system when the parameters are varied. We discuss the three resulting states of the system – bound, transition and scattering – within the mean-field approximation. In particular, we calculate the critical particle number supporting a bound state. To validate our mean-field results, we use the flow equation approach also known as in-medium similarity renormalization group method (IM-SRG).

6. Exploring imbalanced Fermi gases in 2D

Cesar Cabrera Cordova (University of Hamburg)

Ultracold Fermi gases with tunable interactions have enabled the realization of the famous BEC-BCS crossover from a Bose-Einstein condensate (BEC) of molecules to a Bardeen-Cooper-Schrieffer (BCS) superfluid of weakly bound Cooper pairs. In my poster, I will present how by using Bragg spectroscopy, we measure the full momentum-resolved low-energy excitation spectrum of strongly interacting Fermi gases and directly observe the smooth transformation from a bosonic to a fermionic superfluid that takes place in the BEC-BCS crossover. I will introduce the rich physics of imbalanced Fermi gases and our latest results towards the study of these systems in 2D.

7. Dynamics of massive vortices in a superfluid rotating annulus

Matteo Caldara (SISSA, Trieste)

We analyze an immiscible binary mixture of Bose-Einstein condensates loaded in a planar rotating annulus where two-dimensional point vortices in one species host the atoms of the other species, that play the role of a massive core. The fully analytical massive point-vortex model shows that the uniform precession of a single massless vortex becomes unstable in the presence of a sufficiently large filled core, while a small core mass can lead to small radial oscillations as a consequence of inertial effects. These results are confirmed by the numerical solution of coupled two-component GP equations. The analysis is then extended to a symmetric N-vortices necklace (N>1) inside the planar annulus.

8. Optimization Methods for a Fermionic Quantum Processor

Cristina Cicali (Forschungszentrum Jülich)

We investigate the precise control of quantum optical elements in neutral-atom quantum processors. Optimization methods are critical to avoid decoherence effects in order to produce high-fidelity operations. In the FermiQP project, we are working with the group of Christian Groß (Tübigen) to optimize the atom transport between distant optical lattice sites in a fermionic-based quantum processor. We present the first version of a transport optimization which aims to balance between decoherence and excitations. 

9. High-fidelity ground state preparation for quantum simulations of the two-dimensional Z2 lattice gauge theory

Jesús Cobos Jiménez (UPV/EHU, Bilbao)

A new variational method for the ground state preparation of the Z2 gauge theory in digital quantum computers is proposed. It is based on the well-known QAOA, but the variational ansatz includes a non-unitary operation acting over the reference state. The introduction of this non-unitary operation induces an improvement in the fidelity of the ground state approximation with respect to the traditional QAOA. It is shown that the implementation of the non-unitary operation on a quantum computer does not introduce a disproportionate computational overhead, enabling this method to be used in future quantum simulations of the Z2 gauge theory.

10. Quantum Monte Carlo study of repulsive two-dimensional Bose-Fermi mixtures

Jacopo D’Alberto (University of Milano)

In the present work, a Quantum Monte Carlo study is conducted in the mass-balanced case for a repulsive two-dimensional Bose-Fermi mixture. In particular, Variational Monte Carlo and Fixed-Node Diffusion Monte Carlo are used, for two representative bosonic concentrations, to evaluate the zero-temperature equation of state and the effective fermionic mass. The results are then compared with the perturbative theory showing a good agreement for weak interactions. Additionally, a phase separation of the bosonic component is observed for strong Bose-Fermi repulsions.

11. Static and dynamic properties of self-bound droplets of light in hot vapours

Heitor Da Silva (CNRS – INPHYNI, Nice & UFRN, Natal)

The propagation of light in a non-linear medium is described, within the paraxial approximation, by a 2D nonlinear Schrödinger equation. Due to its similarity with the Gross-Pitaevskii equation, which describes the dynamics of a BEC, many theoretical and experimental investigations of phenomena which have already been studied and realized in BECs have been recently analysed in alternative experimental platforms such as hot atomic vapours. In this work, we characterize self-bound states of light in hot vapours, in analogy to droplet states in binary mixtures of BECs and dipolar systems.

12. Hole-induced anomaly in the thermodynamic behavior of a one-dimensional Bose gas

Giulia De Rosi (UPC, Barcelona)

We reveal an intriguing anomaly in the temperature dependence of the specific heat of a one-dimensional Bose gas. The observed peak holds for arbitrary interaction and remembers a superfluid-to-normal phase transition in higher dimensions, but phase transitions are not allowed in one dimension. The presence of the anomaly signals a region of unpopulated states which behaves as an energy gap and is located below the hole branch in the excitation spectrum. The anomaly temperature is found to be of the same order as the energy of the maximum of the hole branch. We rely on the Bethe Ansatz to obtain the specific heat exactly and provide interpretations of the analytically tractable limits. The dynamic structure factor is computed with the Path Integral Monte Carlo method for the first time. We notice that at temperatures similar to the anomaly threshold, the energy of the thermal fluctuations becomes comparable with the maximal hole energy, leading to a qualitative change in the structure of excitations. This excitation pattern experiences the breakdown of the quasi-particle description for any value of the interaction strength at the anomaly, similarly to any superfluid phase transition at the critical temperature. We provide indications for future observations and how the hole anomaly can be employed for in-situ thermometry, identifying different collisional regimes and understanding other anomalies in atomic, solid-state, electronic, spin-chain and ladder systems.

13. Spin squeezing in the two-component Bose-Hubbard model with long-range interactions

Marlena Dziurawiec (Wrocław University of Science and Technology)

We study a dynamical generation of spin-squeezing with ultra-cold atoms in two internal states loaded in a one-dimensional optical lattice with unit filling. We describe the system by the two-component Bose-Hubbard model taking into account short and long-range interactions. The atoms are initially in the spin coherent state in the superfluid phase, delocalized over the entire lattice. In the absence of dipolar interaction, the quantum dynamics of the system are well captured by the one-axis twisting model. In the general case, the zero-momentum part of the system Hamiltonian leads to the non-isotropic two-axis counter-twisting model. We study the scaling of the best squeezing and the best squeezing time with the number of atoms from the resulting model and show that Heisenberg-limited squeezing is possible in a wide range of anisotropy.

14. Controlling the rotational dynamics of molecules by external fields

Juan Manuel García Garrido (University of Granada)

We present a theoretical study of the rotational and vibrational dynamics of a diatomic molecule in the electric field produced by an optical centrifuge. A significant population from the initial wave packet is transferred to other vibrational bands, making the rigid rotor approximation no longer valid for this laser field regime. Molecule dissociation is also possible.  Our results were compared with those obtained from a similar pulse with constant intensity. For this pulse, a similar set of vibrational bands, but with a different weight, are populated. However, the population transferred to the continuum band is even larger for the same peak intensity, due to the centrifuge pulse transferring less energy. 

15. A new programmable quantum simulator with two-electron Rydberg atoms in optical tweezer arrays

Veronica Giardini (University of Firenze)

In the last twenty years, a lot of different platforms for quantum simulation have been constructed using a variety of quantum architectures. This novel platform is based on individual Rydberg Sr atoms trapped in a scalable array of optical tweezers, with fully programmable geometry and zero confrontational entropy, where many-body states can be engineered with high control over their individual constituents. This platform allows for the creation of a very robust entangled state that can be exploited to implement state-of-the-art quantum simulation schemes.

16. Ultradilute quantum liquid of dipolar atoms in a bilayer

Grecia Guijarro (UPC, Barcelona & University of Saarlandes)

Quantum liquids are self-bound fluids which exhibit quantum mechanical effects at the macroscopic level. We show that ultradilute quantum liquids can be formed with ultracold bosonic dipolar atoms in a bilayer geometry. Contrary to previous realizations of ultradilute liquids, there is no need of stabilizing the system with an additional repulsive short-range potential. The advantage of the proposed system is that dipolar interactions on their own are sufficient for the creation of a self-bound state and no additional short-range potential is needed for the stabilization. We perform quantum Monte Carlo simulations and find a rich ground state phase diagram that contains quantum phase transitions between liquid, solid, atomic gas, and molecular gas phases. The stabilization mechanism of the liquid phase is consistent with the microscopic scenario in which the effective dimer-dimer attraction is balanced by an effective three-dimer repulsion. The equilibrium density of the liquid, which is extremely small, can be controlled by the interlayer distance. From the equation of state, we extract the spinodal density, below which the homogeneous system breaks into droplets. Our results offer a new example of a two-dimensional interacting dipolar liquid in a clean and highly controllable setup.

17. Relativistic scattering for bosonic and fermionic particles: Klein paradox and pair creation

Xabier Gutiérrez de la Cal (UPV/EHU, Bilbao)

We analyse the dynamics across a supercritical barrier for Klein-Gordon and Dirac particles. We use a multiple reflection scattering (MRS) approach and, with it, we are able to construct divergent and convergent series associated with different solutions. We show that for bosons the divergent series is related to causal solutions, while the convergent series is acausal. This creation of particle-antiparticle pairs, in which charge is created at the barrier boundaries but the total charge is conserved, is related to the Klein paradox. In the case of fermions, the convergent series is causal, and there is no charge creation. 

18. Towards coupling an atom array with an optical cavity

Giacomo Riccardo Hvaring (Atominstitut, TU Wien)

A central challenge in the field of quantum computation and information processing is to scale up the system size while retaining full connectivity between the individual qubits of the device. In our research group at TU Wien, led by Prof. Julian Léonard, the goal is to establish a new quantum processor architecture based on neutral atoms, that are trapped in a tweezer array and placed inside a fibre cavity.

For the first time, fibre cavities make it feasible to combine the extensive toolkit of ultracold atom experiments with non-local interactions mediated by photons. Via these interactions, we will be able to introduce entangling gates between any two atoms independent of their distance in the cavity. We are currently setting up experiments to demonstrate the working principle of the novel approach.

19. Ultracold fermions in optical superlattices

Valentin Jonas (University of Bonn)

We study the physics of fermionic potassium atoms in three-dimensional optical lattices, where different dimensions are realizable with appropriate confinement. A bichromatic, in-plane superlattice along one direction allows for the realization of the Su-Schrieffer-Heger model and the interacting Rice-Mele model in one dimension, which are expected to give access to topologically protected states. By implementing a dynamic control over the superlattice phase we aim to investigate Floquet-driven systems, where the tunnelling can be tuned using periodic phase modulation.

20. Effect of an optical dipole trap on resonant atom-light interactions

Teresa Karanikolaou (ICFO, Barcelona)

The optical properties of a fixed atom are exquisitely well-known and investigated. For example, one important phenomenon is that the atom can have an extraordinarily strong response to a resonant photon, as characterized by a resonant elastic scattering cross section given by the wavelength of the transition itself, 〖σ_sc∼λ〗^2. The case of a tightly trapped ion, where the ground and excited states are equally trapped, is also well-known. Then, the elastic cross section is reduced by a fraction corresponding to the square of the “Lamb-Dicke parameter”, while this same parameter also dictates the probability of inelastic scattering that gives rise to motional heating.  In contrast, there are many emerging quantum optics setups involving neutral atoms in tight optical dipole traps, such as coupled to nanophotonic waveguides and cavities or in atomic arrays, where the goal is to utilize efficient atom-light interactions on resonance. Often, while the ground state is trapped, the excited state may in fact be untrapped or even anti-trapped. Here, we systematically analyze the consequences that this unequal trapping has on reducing the elastic scattering cross section, and increasing the motional heating rate. This analysis may be useful to optimize the performance of quantum optics platforms where equal trapping cannot be readily realized.

21. Dark solitons in dipolar Bose gases and Bose-Bose mixtures

Jakub Kopyciński (Center for Theoretical Physics PAS, Warsaw)

We look into dark solitons in both dipolar Bose gas and Bose-Bose mixtures. We present solitonic solutions of one-dimensional Gross-Pitaevskii-like equations accounting for beyond mean-field effects. The results show there are certain critical values of the interactions, for which the widths of motionless solitons diverge. Moreover, there are peculiar solutions of motionless solitons with a non-zero density minimum. We also present the energy spectrum of these solitons with additional excitation subbranches appearing. Finally, we perform a series of numerical experiments revealing the coexistence of a dark soliton inside a quantum droplet.

22. Dynamical phase transitions in collective systems 

Ángel López Corps (IEM, CSIC, Madrid)

We study dynamical phase transitions in collective quantum systems. Such systems are characterized by infinite-range interactions and exhibit a rich variety of phase transitions, including ground-state and excited-state quantum phase transitions. By taking an initial state out of equilibrium and monitoring the dynamics of relevant observables, we uncover a strong relationship between dynamical phase transitions and the static non-analyticities in the high-lying eigenstates. We also propose a microcanonical ensemble describing asymptotic equilibrium states in the phases demarcated by the dynamical phase transition. Also, the return probability can show non-analytical points only in one of the two phases. 

23. Emergence of hydrodynamics in a 2D few fermion system

Philipp Lunt (University of Heidelberg)

A striking manifestation of the collective behaviour of many particles is the emergence of hydrodynamics, the effective description of a system as a fluid. The fundamental requirements for hydrodynamic behaviour in the mesoscopic particle number limit are however still unclear [1].  Here, we use deterministically prepared closed shell configurations of a few fermionic 6Li in an elliptical two-dimensional harmonic trap to investigate the effect of atom number and interaction strength on the hydrodynamic behaviour. Our spin and single-atom resolved imaging technique [2] allows us to study single-particle resolved correlations of any order between the atoms. Two different matter-wave magnification techniques provide access to momentum and real space at different times during the expansion, such that we can directly observe the inversion of the aspect ratio, as well as the formation of pairs over time.  

[1] B. Schenke, “The smallest fluid on Earth”, Rep. Prog. Phys. 84,082301 (2021)

[2] M. Holten et al. “Observation of Cooper pairs in a mesoscopic two-dimensional Fermi gas”, Nature 606, 287–291 (2022)

24. Quantum droplets in quasi-1D Bose gas with non-local interactions

Maciej Marciniak (Center for Theoretical Physics PAS, Warsaw)

The ultracold quantum gases interacting by non-local forces have been a subject of great interest recently. Under certain conditions, the interplay between short-range repulsion and long-range attraction leads to the formation of self-bound structures such as quantum droplets. Although these objects were originally observed for atoms trapped in a harmonic potential, they may also be found in quasi-1D optical lattices. In this project, we have investigated the droplet behavior after a sudden quench from a regime of strongly repulsive contact interaction to the attractive one. This analysis is an extension of the phenomenon known as super-Tonks-Girardeau gas.

25. Impurity with a resonance in the vicinity of the Fermi energy

Mikhail Maslov (ISTA, Wien)

We study an impurity with a resonance level that coincides with the Fermi energy of the surrounding Fermi gas. Such an impurity causes a rapid variation of the scattering phase shift for fermions at the Fermi surface, introducing a new characteristic length scale into the problem. We investigate manifestations of this length scale in the self-energy of the impurity and in the many-body density function of the bath. Our calculations reveal a model-independent deformation of the density of the Fermi gas. Overall, our results are relevant for studies that involve quasiparticle interference methods or fermion-mediated RKKY-type interactions in Bose-Fermi mixtures.

26. Electronic structure of triatomic ultra-long Rydberg molecules

David Mellado-Alcedo (University of Granada)

Triatomic ultra-long Rydberg molecules are formed by a Rydberg atom and a polar molecule. They present strong permanent dipole moment, sensitivity to small external electric fields, and applications in ultracold chemical reactions or quantum simulations. In this work, the electronic structure of the molecules Rb-RbCs and Cs-RbCs is studied. The system is described beyond the Born-Oppenheimer approximation and the rovibrational-coupled Schrödinger equation is solved by including the kinetic coupling terms of two close-energy electronic adiabatic potential curves. The study of the weights of the Rydberg-atom partial wave and the Franck-Condon factors guides the required experimental conditions to create these molecules. 

27. Towards the realization of an ion crystal rotor immersed in an ultracold gas of Lithium atoms

Naoto Mizukami (INRiM, LENS & Politecnico di Torino)

Trapped ions are an excellent platform for exploring mesoscopic systems. When confined in an isotropic plane, trapped ions undergo a phase transition to a charged rotor in which the particles are delocalized in the angular direction. This transition has been studied theoretically but never explored in detail. Here, we experimentally investigate this transition in a two-dimensional crystal of Barium ions. We compare the results with a Monte Carlo simulation and we find an excellent agreement. Furthermore, we plan to introduce an ultracold Lithium buffer gas to reduce the ions’ temperature and witness the emergence of quantum fluctuations.

28. Scalable Qubit Arrays for Quantum Computation and Simulation (SQuAre)

Boyko Nikolov (University of Strathclyde)

The SQuAre project at the University of Strathclyde aims to deliver a useful platform for digital quantum computation and analogue quantum simulation based on hundreds of individually trapped Cs atoms confined with tightly-focused light. We present progress towards this goal by demonstrating high-fidelity single qubit MW operations and Bell state generation using highly-excited Rydberg states performed on large numbers of atoms in both red- and blue-detuned holographic optical dipole traps, which can be re-arranged in deterministic patterns using a moveable tweezer trap. With this hardware platform, we aim to explore novel multi-qubit gate operations and tackle real-world quantum optimisation problems.

29. Thermal Separation in Repulsive two-component Bose Mixtures

Gerard Pascual (UPC, Barcelona)

We study repulsive two-component Bose mixtures in a finite-size box through Path-Integral Monte Carlo simulations. For different values of the s-wave scattering length of the interspecies potential, we calculate, among other physical properties, the polarization of the system at different temperatures. We find two different behaviors: for phase separated states at T=0, temperature induces a diffusion effect but, for miscible states at T=0, a maximum in the polarization appears at a certain temperature lower than the critical one. We relate this thermal separation to the bunching effect that clusters particles of the same species.

30. Itinerant ferromagnetism in dilute SU(N) Fermi gases

Jordi Pera (UPC, Barcelona)

We present exact analytic results for the energy of a SU(N) repulsive Fermi gas as a function of the spin-channel occupation at second order in the gas parameter. This is an extension of previous results that now incorporates the degree of polarization of the system. Therefore, the magnetic properties of the gas can be obtained, free from numerical uncertainties. For spin 1/2 we find that second-order corrections change the itinerant ferromagnetic transition from continuous to first-order. Instead, for spin larger than 1/2 the phase transition is always of first-order type. The transition critical density reduces when the spin increases, making the phase transition more accessible to experiments with ultracold dilute Fermi gases. Estimations for Fermi gases of Yb and Sr with spin 5/2 and 9/2, respectively, are reported.

31. Beam shaping and aberration correction using a spatial light modulator

Ana Perez Barrera (ICFO, Barcelona)

Creating arbitrary potentials and correcting optical aberrations are important requirements in ultracold atom experiments. In this work, we manipulate the wavefront of an incoming beam using a spatial light modulator to create arbitrary intensity patterns and correct optical aberrations. We explore simple wavefront manipulations, such as the generation of Laguerre-Gaussian beams, and we use iterative Fourier transform algorithms to create arbitrary intensity patterns.  In one approach, we correct aberrations using Laguerre-Gaussian beams and an iterative algorithm. In another approach,  we measure the aberrated wavefront by mimicking the working principle of a Shack-Hartmann wavefront sensor.

32. One-axis twisting as a method of generating many-body Bell correlations

Marcin Plodzien (ICFO, Barcelona)

We demonstrate that the one-axis twisting is a powerful source of many-body Bell correlations. We develop a fully analytical and universal treatment of the process, which allows for identifying the critical time at which the Bell correlations emerge, and predicting the depth of Bell correlations at all subsequent times. Our findings are illustrated with a highly non-trivial example of the OAT dynamics generated using the two-component Bose-Hubbard model realized in a system composed of a few ultracold atoms trapped in a one-dimensional optical lattice.

33. A single-photon source based on Rydberg atoms

Jan Reuter (Forschungszentrum Jülich)

The leading effects of a single-photon source based on Rydberg atoms are the strong van-der-Waals interaction between the atoms as well as the collective decay of the atom ensemble. To ensure robustness, we investigated the behavior of moving Rydberg atoms and optimized the laser pulse sequence. For that, we simulated the transitions of Rubidium atoms from the ground state over the Rydberg state up to the singly-excited states. We can show that the collective decay of the single excitations leads to a fast and directed photon emission, while double excitations will behave like two separated, none interacting atoms.

34. Few distinguishable fermions in a one-dimensional harmonic trap

Abel Rojo-Francàs (UB, Barcelona)

We study systems of a few particles trapped in a harmonic oscillator potential with short-range interactions, modelled by a delta potential. There are recent experimental and theoretical studies with these conditions. We provide a method to improve the results when one uses the exact diagonalization method, compared with exact results for the SU(N) symmetric case. In addition, we deal with systems without symmetric interactions, paying special attention to an impurity configuration.

35. Advances in the Quantum Technology Laboratory at Cinvestav Unidad Queretaro

César Jesús Ruíz Loredo (Cinvestav del IPN, Mexico City)

The Quantum Technology Laboratory at Cinvestav develops experiments on ultra-cold atoms, atomic BEC, and photonic systems to realise quantum simulation and next-generation technologies such as high-precision sensors and communication systems integrating atom-based memories.