Recent & Upcoming Events | Q-Team

14th Trieste–Ljubljana-Zagreb meeting, April 14th 2025, Zagreb

Sun, 06 Apr 2025 00:00:00 +0000

On Monday April 14th 2025, Zagreb will host the 14th Trieste–Ljubljana-Zagreb meeting. This is a regular event attended by researchers from SISSA and ICTP (Italy), FMF UL and JSI (Ljubljana), and Ruđer Boškovič Institute (IRB, Zagreb) for scientists active on quantum many-body physics. The meeting is organized by the QTeam of IRB, but hosted by the neighbouring Institute for Physics (IFS, Bijenička Cesta 46, 10000, Zagreb, Croatia).

Remark: On Tuesday April 15th 2025, on the occasion of the World of Italian Research, the Italian Embassy in Croatia, with the help of IRB’s QTeam, is organizing a symposium on Quantum Technologies, whose program can be downloaded here. Everyone is welcome to attend and participate!

Time
10:30-11:00	Welcoming coffee break
11:00-11:30	Mark Arildsen - SISSA - Symmetry-Resolved Entanglement Entropy in a Non-Abelian Quantum Hall State: Quantum Hall states serve as an excellent platform for exploration of symmetry-resolved entanglement in the (2+1)-dimensional setting. Following on prior investigation of Abelian quantum Hall states [Oblak, Regnault, Estienne, PRB 105, 115131], we now compute the full counting statistics and symmetry-resolved entanglement entropies of the non-Abelian, bosonic Moore-Read quantum Hall state, with the aid of numerical computations from exact matrix product states. We find a form of equipartition of entanglement, up to finite-size corrections. We are also able to perform detailed analysis of the finite-size splittings of the symmetry-resolved entanglement spectrum using conformal field theory, which enables a granular understanding of the role of the finite-size corrections in a range of entanglement measures for these states.
11:30-12:00	Kohei Ogane - JSI -Ergodicity breaking crossover in two dimensions driven by Rydberg blockade: Ergodicity breaking is a phenomenon that isolated quantum systems avoid thermalization and has been studied predominantly in one-dimensional systems under quenched disorder. Two-dimensional ergodicity breaking is much less studied in comparison with that of one dimension. The reason is that numerically simulation of two-dimensional many-body systems is more difficult due to lattice structure. Two-dimensional ergodicity breaking phase is expected to disappear in the thermodynamic limit based on the avalanche scenario. However, the fate of the ergodicity breaking phase in the thermodynamic limit is controversial due to lack of understanding of two-dimensional ergodicity breaking. Inspired by experiments in the Rydberg atoms, I numerically calculated XXZ spin model where spins locate randomly with being subject to the Rydberg blockade. Since the model has no lattice structure, it is possible to test the system size dependence of entanglement entropy and participation entropy by exact diagonalization. I found that the critical disorder strength drifts slowly and robustly with system size and specified the ergodicity breaking crossover in finite system sizes.
12:00-12:30	Hernan Xavier - ICTP - Chiral gravitons on the lattice: Chiral graviton modes are exotic excitations tied to the underlying quantum geometry of fractional quantum Hall states. But do these persist on lattice models where continuum translations is broken and decay channels arise? In this talk, I introduce a field-theoretic framework that captures chiral graviton physics within the bosonic Harper-Hofstadter model. Backed by strong numerical evidence, we fin that these modes remain robust even in the presence of lattice effects, being well captured by our lattice ansatz. I’ll also highlight how geometric quenches offer a practical route to probing chiral gravitons in near-term quantum simulators.
12:30-14:30	Lunch & Discussion
14:30-15:00	Gianpaolo Torre - IRB - Experimental preparation of W-States through topological physics: W-states are important quantum states possessing both bi-partite and multi-partite entanglement and are necessary for several relevant quantum algorithms. We propose a protocol to generate them with an arbitrary number of qubits on a Rydberg atoms platform, by exploiting the principles of {\it topological frustration}. We experimentally achieve fidelities close to 90% (for 11 qubits) and show a promising scaling using accurate numerical simulations, with high fidelities for tens of qubits. In this way, not only do we reach an unparalleled accuracy for the generation of these states compared to the existing approaches, but we also show once more how physics principles can overcome traditional barriers and be exploited toward quantum advantage.
15:00-15:30	Francesco Gentile - SISSA - Entanglement hamiltonian of two disjoint blocks in the harmonic chain: I will talk about the entanglement Hamiltonian of two disjoint blocks in the harmonic chain on the line and in its ground state. In the regime of large mass, the non vanishing terms are only the on-site and the nearest-neighbour ones. Analytic expressions are obtained for their profiles, which are written in terms of piecewise linear functions that can be discontinuous and display sharp transitions as the separation between the blocks changes. In the regime of vanishing mass, where the matrices characterising the entanglement Hamiltonian contain couplings at all distances, we explore the location of the subdominant terms and some combinations of matrix elements that are useful for the continuum limit, comparing the results with the corresponding ones for the free chiral current. The single-particle entanglement spectra of these entanglement Hamiltonians are also investigated.
15:30-16:00	Coffee break
16:00-16:30	Rustem Sharipov - FMF - Ergodic behaviors in reversible 3-state cellular automata: Classical cellular automata represent a class of explicit discrete spacetime lattice models in which complex large-scale phenomena emerge from simple deterministic rules. With the goal to uncover different physically distinct classes of ergodic behavior, we perform a systematic study of three-state cellular automata (with a stable ‘vacuum’ state and ‘particles’ with ± charges). The classification is aided by the automata’s different transformation properties under discrete symmetries: charge conjugation, spatial parity and time reversal. In particular, we propose a simple classification that distinguishes between types and levels of ergodic behavior in such system as quantified by the following observables: the mean return time, the number of conserved quantities, and the scaling of correlation functions. In each of the physically distinct classes, we present examples and discuss some of their phenomenology. This includes chaotic or ergodic dynamics, phase-space fragmentation, Ruelle-Pollicott resonances, existence of quasilocal charges, and anomalous transport with a variety of dynamical exponents.
16:30-17:00	Gianni Aupetit-Diallo - SISSA - Accuracy of time-dependent GGE under weak dissipation: Unitary integrable models typically relax to a stationary Generalized Gibbs Ensemble (GGE), but in experimental realizations dissipation often breaks integrability. In this work, we use the recently introduced time-dependent GGE (t-GGE) approach to describe the open dynamics of a gas of bosons subject to atom losses and gains. We employ tensor network methods to provide numerical evidence of the exactness of the t-GGE in the limit of adiabatic dissipation, and of its accuracy in the regime of weak but finite dissipation. That accuracy is tested for two-point functions via the rapidity distribution, and for more complicated correlations through a non-Gaussianity measure. We combine this description with Generalized Hydrodynamics and we show that it correctly captures transport at the Euler scale. Our results demonstrate that the t-GGE approach is robust in both homogeneous and inhomogeneous settings
17:00-18:30	Poster session
19:00-21:00	Dinner

Useful information

Parking

On the streets or on the neighboring cemetery parking lot.
https://g.co/kgs/uksHwv1
Inside the IRB institute.
https://www.irb.hr/O-IRB-u/Kontaktirajte-nas/Informacije-za-posjetitelje
As you approach the institute, the security staff will raise the barrier to allow you in. Once inside, please proceed to the security desk to collect a temporary badge. We have pre-registered all individuals who entered their names in the spreadsheet.

Meeting location

Institute of Physics (IFS)
http://ifs.hr/
The meeting will be at the main conference all on the first floor of the 3rd wing. A member of our team will be waiting outside the IFS entrance.

Other information

Coffee breaks will take place at the meeting room at IFS
The lunch will be served at IRB.

Local Organizers: Fabio Franchini, Salvatore Marco Giampaolo, Gianpaolo Torre

Italian Research Day in the world, April 15th 2025, Zagreb

Sat, 05 Apr 2025 00:00:00 +0000

On Tuesday April 15th 2025, on the occasion of the World of Italian Research, the Italian Embassy in Croatia, with the help of IRB’s QTeam, is organizing a symposium on Quantum Technologies, whose program can be downloaded here. Everyone is welcome to attend and participate!

Time
10:00	Welcome remarks
	- Mr. Silvio Kutić, CEO of Infobip
	- Mr. Paolo Trichilo, Ambassador of Italy
	- Hon. Furio Radin, Deputy Speaker of the Croatian Parliament
10:15	Introductory remarks
	- Croatian Ministry of Science, Education and Youth
	- Italian Ministry of University and Research
10:30	Opening lecture titled: Quantum Technologies: An overview by Prof. Gioacchino Massimo Palma, Full Professor at the Physics and Chemistry Department of the University of Palermo and President of SISTEQ (Italian Society of Quantum Technologies and Science)
11:00	First Round Table on Quantum Technologies: future perspective or economic reality?
	- Prof. Elisa Ercolessi, Associate Professor at the Department of Physics and Astronomy of the University of Bologna
	- Dr. Ticijana Ban, Assistant Director of the Institute of Physics in Zagreb
	- Dr. Alessandro Zavatta, President and COO of QTI S.R.L. and Head of the Quantum Communications Research Group and Head of Trieste Unit of the CNR-INO (National Research Council-National Institute of Optics)
	- Dr. Peter Jeglič, Head of the Cold Atom Laboratory at the Jožef Stefan Institute in Ljubljana
12:00	Second Round Table on Quantum Technologies: cooperation or competition to the top?
	- Prof. Gioacchino Massimo Palma, Full Professor at the Physics and Chemistry Department of the University of Palermo and President of SISTEQ (Italian Society of Quantum Technologies and Science)
	- Prof. Hrvoje Buljan, Full Professor at the Theoretical Physics Department at the Faculty of Science, University of Zagreb) and Head of QuantixLie Center of Excellence
	- Prof. Francesco Scazza, Associate Professor at the Department of Physics of the University of Trieste and affiliated with ArQuS (Artificial Quantum Systems Laboratory) in Trieste
13:00	Networking lunch offered by the Embassy of Italy in Zagreb

15th Italian Quantum Information Science Conference, 18-22 September 2023, University of Trieste

Mon, 18 Sep 2023 00:00:00 +0000

Abstract

We are at the verge of the Quantum Technology Revolution: quantum mechanics allows for phenomena that have no classical counterparts and which can be harvested for new technologies. An example of the emerging quantum technologies are quantum batteries (QB), i.e. quantum mechanical systems that can store and transfer energy in a coherent way. While the practical implementation of such devices is still far from becoming reality, a serious effort is being devoted to understanding their advantages and limitations, using different platforms and protocols. As it has been recently demonstrated that the introduction of topological frustration in one- dimensional spin-1/2 chains can strongly modify the low energy properties of these systems, we investigate the performance of a quantum battery realized through such frustrated chains and introduce a novel, natural, decoherence mechanism that show their superiority compared to their unfrustrated counterpart. We quantify this superiority using the notion of ergotropy, that is, the amount of energy that can be extracted from a battery with a unitary transformation.

9th Trieste-Ljubljana-Zagreb meeting, Ljubljana, 14 March 2023

Tue, 14 Mar 2023 00:00:00 +0000

Abstract

We are at the verge of the Quantum Technology Revolution: quantum mechanics allows for phenomena that have no classical counterparts and which can be harvested for new technologies. An example of the emerging quantum technologies are quantum batteries (QB), i.e. quantum mechanical systems that can store and transfer energy in a coherent way. While the practical implementation of such devices is still far from becoming reality, a serious effort is being devoted to understanding their advantages and limitations, using different platforms and protocols. As it has been recently demonstrated that the introduction of topological frustration in one-dimensional spin-1/2 chains can strongly modify the low energy properties of these systems, we investigate the performance of a quantum battery realized through such frustrated chains and introduce a novel, natural, decoherence mechanism that show their superiority compared to their unfrustrated counterpart. We quantify this superiority using the notion of ergotropy, that is, the amount of energy that can be extracted from a battery with a unitary transformation.

APS March meeting, Las Vegas, 05-10 March 2023

Sun, 05 Mar 2023 00:00:00 +0000

Abstract

The Frustration of Being Odd

We consider the effects of so-called Frustrated Boundary Conditions (FBC) on quantum spin chains, namely periodic BC with an odd number of sites. In absence of external fields, FBC allow for the direct determination of correlation functions that signal a spontaneous symmetry breaking, such as the spontaneous magnetization. When paired with anti-ferromagnetic interactions, FBC introduce geometrical frustration into the system and the ground state develops properties which differ from those present with other boundary conditions, such as the disappearance of the usual order, possibly replaced by different ones. We argue that FBC introduce a fractionalized excitation that contributes to long-range order in the system, similar to that enjoyed by SPT phases. Our results prove that even the weakest form of geometrical frustration can deeply affect a system’s properties and pave a way for a bottom-up approach to better understand the effects of frustration and their exploitations also for technological purposes.

Complexity of topologically frustrated systems

In my talk, I will present a summary of our main results about the complexity of the ground states of topologically frustrated systems. A topological frustration arises when, in a short-range antiferromagnetic system made of an odd number of spins, periodic boundary conditions are considered. We characterize the increment of the ground state complexity exploiting different approaches as the analysis of the non-stabilizerness (or “magic”) and of the stochastic irreversibility of the entanglement.

Simulating continuous symmetry models with discrete ones

In the past few years it has been demonstrated that the introduction of a frustration of topological origin in one-dimensional spin-1/2 systems can strongly modify their behavior, e.g. by destroying order parameters or by changing the nature of quantum phase transitions. In this work we show that this phenomenon can be exploited for the realization of quantum simulations. In particular, introducing topological frustration in spin chains characterized by a discrete local symmetry, such as a short-range completely anisotropic Heisenberg model or the XY chain, they develop a region in parameter space where their features mimic those of models whose Hamiltonians possess continuous symmetries. This result, together with those of other works in the same field, points towards the conclusion that topologically frustrated systems constitute interesting and efficient platforms for the development of promising quantum technologies.

8th Trieste-Ljubljana-Zagreb meeting, Trieste, 06 December 2022

Tue, 06 Dec 2022 00:00:00 +0000

Abstract

In this talk, I will present recent results on the topic of integrable topologically frustrated quantum spin chains. In particular, I will discuss entanglement properties of frustrated Ising chains with assumed frustrated boundary conditions that imply periodic boundary conditions, an odd number of spins, and antiferromagnetic coupling. The topologically frustrated ground state is a unique example of a state associated with a local and nearest-neighbor coupling Hamiltonian that violates the area-law scaling of entanglement with the subsystem size. Frustrated boundary conditions induce an excess of long-range entanglement that can be analytically described in the thermodynamic limit using the single-particle interpretation. Using an entanglement cooling (disentangling) algorithm, represented by a particular stochastic quantum circuit, we show that the frustration-induced entanglement is robust against the application of local gates. In this process, we additionally demonstrate, how with different choices of local gates the quantum circuit can induce a transition in the entanglement spectrum from the uncorrelated Poissonian distributed eigenvalue spacings to the correlated Wigner-Dyson distribution. Moreover, we ad- vance the characterization of complexity in quantum many-body systems by examining W -state, a well-known state within the quantum information community. Such a state admits an amount of non-stabilizerness or “magic” (measured as the Stabilizer Rényi Entropy – SRE) that grows logarithmic with the number of qubits/spins. We show that topologically frustrated ground states have a value of SRE that is the sum of that of the W-state plus an extensive local con- tribution. Our work reveals that W-states/frustrated ground states display a non-local degree of complexity that can be harvested as a quantum resource and has no counterpart in GHZ states/non-frustrated systems.

[1] J. Odavić et al., arXiv:2209.10541.

[2] J. Odavić et al., arXiv:2210.13495.

Student Workshop on Integrability, Hannover, 27-31 March 2022

Thu, 31 Mar 2022 00:00:00 +0000

Abstract

The presence of a global internal symmetry in a quantum many-body system is reflected in the fact that the entanglement between its subparts is endowed with an internal structure, namely it can be decomposed as sum of contributions associated to each symmetry sector. The study of the symmetry resolution of entanglement measures provides a formidable tool to probe the outof- equilibrium dynamics of quantum systems. As presented in the previous edition of this Workshop by my collaborator Gilles Parez, we initi- ated the study of the time evolution of the symmetry-resolved entanglement entropy after a global quench in the context of free-fermion systems. In this talk, I will present the results of our subse- quent study of the time evolution of its counterpart for non-complementary subsystems, namely the charge-imbalance-resolved negativity, in the same setting. We find that the charge-imbalance- resolved logarithmic negativity shows an effective equipartition in the scaling limit of large times and system size, with a perfect equipartition for early and infinite times. We also derive and conjec- ture a formula for the dynamics of the so-called charged Rényi logarithmic negativities. We argue that our results can be understood in the framework of the quasiparticle picture for the entanglement dynamics, and provide a conjecture that we expect to be valid for generic integrable models.