Timescales for thermalization and many-body quantum chaos

• Lea Santos (University of Connecticut)

Room: Aula Renzo Leonardi In this talk, we review the connection between thermalization in isolated many-body quantum systems and the emergence of quantum chaos. This relationship is explored to address the timescales for isolated many-body quantum systems to reach thermal equilibrium after a dynamical quench, which remains an important open question. We examine how the equilibration process depends on the models, observables, energy of the initial state, and system size, revealing distinct dynamical behaviors across different timescales. Special attention is given to the dynamical manifestations of many-body quantum chaos and methods for detecting them in experimental setups, such as cold atoms, ion traps, and NMR systems. We show that coupling the system to a dephasing environment can reduce dynamical fluctuations that might otherwise obscure these manifestations.

Frequency-bin based photonic quantum information processing

• Noemi Tagliavacche (Università di Pavia)

Room: Aula Renzo Leonardi Quantum technologies play a crucial role in both scientific and technological advancement, leveraging the unique properties of quantum mechanics - such as superposition and entanglement - to enhance the performance of classical systems and enable new device functionalities. Light-based quantum technologies utilize photons as fundamental carriers of information, taking advantage of their long coherence times, fast propagation speeds and ease of manipulation. Well-explored degrees of freedom for encoding quantum information include polarization, orbital angular momentum, path, and time of arrival. Less investigated is frequency-bin encoding, in which quantum information is encoded in discrete frequency (energy) bands. This approach has great potential because it inherently supports high-dimensional encoding, is compatible with existing fiber-optic infrastructure, and allows for easy manipulation of the quantum states using standard telecommunication fiber components. Frequency-bin entangled states can be efficiently generated in integrated photonics by exploiting spontaneous parametric processes in microring resonators. On-chip integration enables both the engineering of the generated quantum states and the scalability of the frequency-bin approach. In this talk, we will explore the potential of frequency-bin encoding in quantum information processing, from the generation of non-classical states of light to their applications in quantum communication and computation.

Photon technology Italy SRL - Superconducting Nanowire Single Photon Detectors: From Research to Industry

• chengjun Zhang (University of Naples, Photon technology Italy)

Room: Aula Renzo Leonardi Superconducting nanowire single photon detectors (SNSPDs) are advanced devices renowned for their high system efficiency up to 98% at infrared wavelengths, low dark count rate less than 0.02 cps, and fast count rate, making them ideal for single photon detection applications such as quantum communication, photonic quantum computing, imaging, and LIDAR. Today, I will share the advanced SNSPD technologies developed by our group and discuss our efforts to transition these innovations from research to industry and scientific applications.

High-dimensional quantum key distribution rates for multiple measurement bases

• Giovanni Chesi (University of Pavia)

Room: Aula Renzo Leonardi High-dimensional quantum key distribution rates for multiple measurement bases Quantum key distribution (QKD) protocols take at least two advantages from high-dimensional (HD) systems: the secret key rate scaling as the dimension and the opportunity of exploiting more than two mutually- unbiased bases (MUBs). Indeed, if the dimension d of the system is a prime power, then d + 1 MUBs exist. Here, we retrieve analytic key rates for a BBM92-like protocol where the dimension of the Hilbert space is generic and different numbers m of MUBs are considered. A similar task has been addressed in Ref. [1], where the authors optimized the key rate for generic dimension and m = 3. We extend their analysis by considering every allowed number of MUBs and identify the optimal number of MUBs providing the larger secure key rate. In the limit of infinite number of rounds, we find the analytic expression for the asymptotic key rate with m = d + 1 MUBs and provide a numeric evaluation for m <d +1. We show that, as one may expect, both the key rate and the maximum tolerable error rate increase as m increases. In the finite-key scenario, we retrieve upper bounds on the key rate in the presence of collective and coherent attacks. In particular, we compare the rates obtained by using a specific entropic uncertainty relation (EUR) with the ones obtained from the asymptotic equipartition property (AEP). The EUR al- lows to achieve a tighter bound for small numbers of rounds (< 106), but can be exploited just for m = 2, while the AEP can be used for every choice of m, up to m = d + 1. This is shown in Fig. 1, where we set d = 5 and plotted the key rates as a function of the number of rounds N. Here, we also compare the rates obtained from different choices of m. Surprisingly, we find that for N < 106 the highest key rate is obtained by exploiting just three MUBs.

Quantum computing and Art: reinterpreting classical masterpieces

• Arianna Crippa (CQTA, DESY)

Room: Aula Renzo Leonardi In this presentation I will talk about an application of quantum computing to compose artworks. The main idea of this project is to revisit three paintings of different styles and historical periods: “Narciso”, by Michelangelo Merisi (Caravaggio), “Les fils de l’homme”, by René Magritte and “192 Farben”, by Gerard Richter. We utilize the output of a quantum computation to change the composition in the paintings, leading to a series titled “Quantum Transformation I, II, III ”. In particular, the figures are discretized into square lattices and the order of the pieces is changed according to the result of the quantum simulation. Besides experimenting with hardware runs and circuit noise, our goal is to reproduce these works as physical oil paintings on wooden panels. With this process, we complete a full circle between classical and quantum techniques and contribute to rethinking Art practice in the era of quantum computing technologies.

Tensor network for quantum simulations

• simone montangero (Padova university)

Room: Aula Renzo Leonardi We review some recent results on developing efficient tree tensor network algorithms and their application to quantum simulation benchmarking and theoretical interpretations. In particular, we present results on two- and three-dimensional systems in and out of equilibrium and on the computation of entanglement of formation in critical quantum many-body systems at finite temperature. Finally, we present the application of tensor-network methods for the solution of hard classical combinatorial problems via mapping to many-body quantum Hamiltonians.

QuantumToolbox.jl: An efficient Julia framework for simulating open quantum systems

• Alberto Mercurio (École Polytechnique Fédéral de Lausanne (EPFL))

Room: Aula Renzo Leonardi Quantum simulations are essential for exploring open quantum systems. However, balancing ease of use with high computational performance remains a challenging task. In this talk, I present QuantumToolbox.jl, an open-source Julia package for simulating open quantum dynamics. Designed with a syntax familiar to users of QuTiP (Quantum Toolbox in Python), QuantumToolbox.jl leverages Julia’s high-performance computing capabilities to provide efficient and scalable simulations. The package supports GPU acceleration and distributed computing without requiring significant code changes. Additionally, QuantumToolbox.jl integrates automatic differentiation tools, facilitating gradient-based optimization tasks such as quantum optimal control. Benchmark comparisons highlight substantial performance improvements, demonstrating QuantumToolbox.jl’s potential as a powerful tool for quantum research.

Quantum reservoir computing

• Viktor Svensson (University of Oslo)

Room: Aula Renzo Leonardi A universal quantum computer has to execute a long series of high-fidelity gates to be useful, which is very difficult to achieve experimentally. However, universal computing is only one approach to computation. There are other forms which sacrifice universality for fewer requirements on the physical system, such as analog simulation, annealing or variational approaches. This talk is about reservoir computing - a minimal computational model which shows how even a random system could be used to process information. Quantum reservoir computing may provide a practical way to utilize the noisy systems of the near future, but is there a quantum advantage?

Unraveling the emergence of quantum state designs in systems with symmetry

• Naga Dileep Varikuti (Pitaevskii BEC Center, CNR-INO and Department of Physics, University of Trento)

Room: Aula Renzo Leonardi Quantum state designs enable efficient sampling of random quantum states, with applications ranging from circuit design to black hole physics. While symmetries are known to reduce randomness, their role in generating state designs remains unclear. The projected ensemble framework [2, 3], which uses local projective measurements and many-body quantum chaos, has recently been introduced to generate efficient approximate state t-designs. In this framework, projective measurements are applied to the larger subsystem (bath) of a single bipartite state undergoing quantum chaotic evolution. This process generates a set of pure states on the smaller subsystem. These states, along with the Born probabilities, form the projected ensembles. Remarkably, when the measured subsystem is sufficiently large, the projected ensembles converge to state designs. This phenomenon, known as emergent state designs, is closely related to a stringent generalization of the well-studied eigenstate thermalization hypothesis. In our work 1, we probe how symmetries influence the emergence of state designs from random generator states. Our main findings involve identifying a sufficient condition on the measurement bases when the generator states are eigenstates of an arbitrary symmetry operator. Failing to satisfy this condition can lead to the localization of projected states in the Hilbert space, as illustrated in Fig. 1. By considering the translation symmetric generator states, we derive this condition and identify bases that fail to generate the designs when the condition is violated. To solidify our results, we study the emergence of designs from a generator state evolving under the dynamics of a chaotic tilted field Ising chain with translation symmetry with the Hamiltonian: \begin{equation} H=\sum_{j}\sigma^{x}{j}\sigma^x{j+1}+h_x\sum_{j}\sigma^{x}{j}+h_y\sum{j}\sigma^{y}_{j} \end{equation} We find faster convergence towards designs compared to when translation symmetry is broken. We extend these findings to other symmetries, offering insights into deep thermalization and equilibration in quantum many-body systems. Due to the generality of our formalism, we extend the results to other symmetry classes,s including Z2 and reflection symmetries. We further obtain the moments of the projected ensembles under the symmetry constraints.

Error mitigation with post-selection in symmetry-constrained Quantum Simulations: an application to lattice gauge theories

• Edoardo Ballini (Università di Trento)

Room: Aula Renzo Leonardi In physics, symmetries are ubiquitous. Quantum simulation of symmetry-constrained systems represent an outstanding challenge in the rapidly evolving field of quantum technology and information. A key prerequisite is the protection of the symmetry sector we want to study against errors that, if unchecked, would lead to unwanted symmetry-breaking results. In this framework, post-selection is one of the simplest yet effective methods for mitigating errors in simulations of symmetry-constrained theories. However, applying it to systems affected by non-Abelian symmetries becomes non-trivial, as the symmetry generators typically do not commute with each other. In this seminar, I will review the fundamental post-selection techniques for error mitigation of symmetry-breaking errors in quantum simulations of symmetry-constrained systems. In particular, I will show possible post-selection applications to lattice gauge theories (LGTs), that underlie our understanding of fundamental forces of modern physics, and that are characterized by multiple local symmetries. I will discuss differences in the application of those post-selection methods between Abelian and non-Abelian LGTs.

Voltage-controlled synthesis of higher harmonics and 4e supercurrent in hybrid Josephson junction circuits

• Luca Banszerus (University of Vienna)

Room: Aula Renzo Leonardi Epitaxial semiconductor-superconductor hybrid materials provide a novel highly-tunable platform to study exotic emergent quantum phenomena, taking advantage of gate-controlled density, ballistic transport, and non-sinusoidal current-phase relations. In my talk, I will introduce the hybrid Josephson rhombus, a highly tunable superconducting circuit element containing four semiconductor-superconductor hybrid Josephson junctions embedded in a loop. Combining magnetic frustration with gate-voltage-controlled tuning of individual Josephson couplings provides deterministic control of the harmonic content of the rhombus CPR. For balanced Josephson couplings at full frustration, the hybrid rhombus displays a pi-periodic Josephson potential, indicating coherent charge-4e transport. Tuning away from the balanced configuration, the device displays superconducting diode effect with efficiency exceeding 25%. These results showcase the potential of hybrid Josephson rhombi as fundamental building blocks for noise-resilient qubits and quantum devices with custom transport properties.

Poor man's Majorana modes in interacting hybrid superconductor-semiconductor devices

• Michele Burrello (Università di Pisa)

Room: Aula Renzo Leonardi Recent experiments in hybrid semiconductor-superconductor devices demonstrated the possibility of realizing the so called "Poor man's Majorana modes" (PMMs). These are zero-energy modes that fulfill most of the properties of standard Majorana modes in topological superconductors, despite not being topologically protected. PMMs are indeed realized in fine-tuned devices composed by quantum dots and superconducting elements, which mimic minimal Kitaev chains with two sites only. The exquisite control granted by these hybrid systems, however, allow for tuning the cotunneling and Andreev processes between quantum dots, thus enabling a remarkable control over the emerging PMMs. In this talk, I will introduce the platforms used to realize PMMs and present the design of devices with floating superconducting islands which combine PMMs with electrostatic interactions. These devices enable the integration of PMMs with transmons and other superconducting systems, they can be integrated with state-of-the-art sensors for charge and fermionic parity, and allow for the design of two-state systems for the exploration of exotic Kondo problems, including the topological Kondo effect which is considered a hallmark for the non-locality of Majorana modes.

Connecting XX Spin Chain to Kinetically Constrained PXP Model via Lattice Gauge Theory: anomalous transport and fluctuations

• Devendra Singh Bhakuni (Abdus Salam International Centre for Theoretical Physics (ICTP))

Room: Aula Renzo Leonardi I will present a mapping that transforms the kinetically constrained PXP model into a constrained XX model with non-local constraints. The constraint can be tuned to interpolate between the free fermionic XX model at one end and the PXP model at the other. This transformation reveals additional conservation laws that help explain some of the unusual properties of the model. Finally, I will also present some results about the impact of disorder in such constrained systems and, in particular, how the constraints influence localization.

Quantinuum - Transformative Value of Quantum and AI: Bringing Meaningful insights for Critical Applications Today

• Elvira Shishenina

Room: Aula Renzo Leonardi The ability to solve classically intractable problems defines the transformative value of quantum computing, offering new tools to address complex humanity challenges and redefine industries. Quantinuum’s hardware is leading the way in early fault-tolerance. By integrating quantum technology with AI and high-performance computing, we are building systems designed to address real-world problems with efficiency, precision and scale. This approach empowers critical applications from hydrogen fuel cells and carbon capture to precision medicine, food security, and cybersecurity, providing meaningful insights at a commercial level today.

Quantum Computational Fluid Dynamics

• Dieter Jaksch (University of Hamburg)

Room: Aula Renzo Leonardi Variational quantum algorithms are particularly promising early applications of quantum computers since they are comparatively noise tolerant and aim to achieve a quantum advantage with only a few hundred qubits. They are applicable to a wide range of optimization problems arising throughout the natural sciences and industry. To demonstrate the possibilities for the aeroscience community, we describe how variational quantum algorithms can be utilized in computational fluid dynamics. We discuss how classical fluid dynamics problems are translated into quantum variational algorithms by using matrix product operators as a programming paradigm. The intricate multi-scale nature, describing the coupling between different-sized eddies in space and time, allows us to design an efficient structure-resolving tensor network based description of turbulent flows and compute their dynamics. We show how boundary conditions can be incorporated. We provide estimates for how the runtimes of the resulting quantum algorithms scale with problem size and show that only a logarithmically small number of qubits are required. We then discuss several fundamental examples demonstrating the power of these quantum algorithms. In addition, we discuss how current practical limitations in size and also imperfections of quantum hardware affect the performance of variational algorithms and determine quantum hardware requirements that might allow gaining a quantum advantage over standard classical approaches to fluid dynamics problems. Finally, we demonstrate the power of tensor network based classical algorithms for computational fluid dynamics that arise as an intermediate step in the translation to fully quantum algorithms.

Vortex Dynamics in Strongly Interacting Superfluid

• Lorenzo Maffi (University of Padua, INFN Padova Section,)

Room: Aula Renzo Leonardi Interactions can play a determinant role in low dimensions for topological and chiral states of matter by giving rise to interesting emergent phenomena such as quasiparticle fractionalization and quantum phase transitions. Recent experimental evidence from Floquet engineered ultracold atomic systems [1], have provided a starting point for observing correlated vortex structures of the Laughlin bosonic Hall effect. Motivated by these experimental advances, we have investigated the quantum dynamics of large vortices in strongly interacting superfluids. For one quantum of flux and close to half-filling, the change in sign of the Hall conductivity [2] suggests an abrupt change in vortex response and dynamics, due to effective strong quantum fluctuations. In this contribution we will present some preliminary results on vortex dynamics in the presence of strong correlations for different filling factors, giving rise to chiral vortex motion and non-trivial trajectories near to half-filling. We provide a mapping to a dual effective free theory explaining our observations. These results motivate novel transport measurements to delve into the phenomenology of single and multi-vortex dynamics in state-of-the-art bosonic platforms.

Dynamical Mean-Field Theory for Open Many-Body Quantum Systems

• Matteo Seclì (EPFL)

Room: Aula Renzo Leonardi Understanding and simulating the complexities of quantum many-body systems out of equilibrium is still a major challenge in quantum physics. In this talk, I will introduce Dynamical Mean-Field Theory (DMFT) as a powerful approach to tackle this problem, with a focus on bosonic, driven-dissipative lattices. Starting from the basic intuition behind DMFT, I will discuss its extension to open, bosonic quantum systems (OpenBDMFT) and highlight recent insights — such as the emergence of the steady-state quantum Zeno effect — that showcase the method's reach and versatility. I will also discuss numerical strategies — including Krylov subspaces and polynomial expansions — that allow OpenBDMFT to scale beyond the limits of full exact diagonalization.

Calculation of Green’s Functions using quantum computers for small superfluid systems

• Samuel Aychet-Claisse (CEA Saclay)

Room: Aula Renzo Leonardi Quantum many-body problems, such as the study of nuclear structure, are difficult to treat with classical computers due to exponential complexity. One way to overcome this limitation would be to use quantum computers, which allow to reduce computational cost. In this context, it is important to test quantum algorithms on simple, yet nontrivial models, with the goal of assessing their efficiency and benchmarking them. Focusing on the pairing Hamiltonian, this work addresses the computation of odd systems and Green’s functions. Hybrid quantum-classical computations are compared to exact results and standard BCS techniques.

Constrained dynamics in the 2D quantum Ising model

• Luka Pavesic (University of Padova)

Room: Aula Renzo Leonardi The quantum Ising model on a square lattice exhibits an emergent dynamical constraint: in the ordered phase, the dynamics approximately conserve the total length of the domain walls. We numerically investigate the dynamics in the crossover from the constrained to the diffusive regime on lattices of up to 16×16 spins. The dynamical constraint, and the subsequent fragmentation of the Hilbert space lead to anomalously long thermalization times. Within the prethermal regime, we find confined elementary excitations, slow growth of entanglement, and suppression of the light-cone correlation spread. We probe the dynamics of interfaces through sudden quenches of product states with domains of opposite magnetization. This allows us to identify and understand dominant microscopic processes; resonant edge modes which originate at the corners and freely propagate along flat interfaces. Given that it occurs in a very general setup, the discussed phenomena plays an important role in various fields of research, from the physics of confinement, quantum coarsening and roughening transitions, to the nucleation of false vacuum bubbles.

Dissipative and dispersive cavity optomechanics with a suspended frequency-dependent mirror

• Juliette Monsel (Chalmers University of Technology)

Room: Aula Renzo Leonardi An optomechanical microcavity can considerably enhance the interaction between light and mechanical motion by confining light to a subwavelength volume. However, this comes at the cost of an increased optical loss rate. A pathway to reduce optical losses is to use a strongly frequency-dependent mirror, such as a photonic crystal mirror. In this talk, I will present the quantum-coupled-mode description we formulated for such a system [1], including both the standard dispersive optomechanical coupling as well as dissipative coupling, and show how it matches our experimental measurements of a free-space on-chip optomechanical microcavity [2]. Finally, I will outline strategies to achieve ground-state cooling in such a device [1], including using a coherent feedback scheme [3]. [1] J. Monsel, A. Ciers, S. K. Manjeshwar, W. Wieczorek, and J. Splettstoesser, Phys. Rev. A 109, 043532 (2024). [2] S. Kini Manjeshwar, A. Ciers, J. Monsel, H. Pfeifer, C. Peralle, S. M. Wang, P. Tassin, and W. Wieczorek, Opt. Express 31, 30212 (2023). [3] L. Du, J. Monsel, W. Wieczorek, and J. Splettstoesser, arXiv:2405.13624.

Nanodiamonds with Group IV color centers with tunable emission for Quantum applications

• Roy KONNOTH ANCEL (University of Technology Troyes)

Room: Aula Renzo Leonardi Color centers have become a hot topic in recent times for their potential applications in quantum technologies particularly in the context of realizing quantum networks. Employing a scheme that relies on the coupling between single photons and atom-like transitions among spin states in a diamond colour center, it is possible to exploit both the strong coherence properties of photons and the easy control of spin states within the colour centers. In this work, we seek to ascertain the feasibility of using single photons from germanium vacancy (GeV) and Silicon vacancy (SiV) centers located within nanodiamonds, as the basis for a quantum network. The advantage of using nanodiamond-based GeV centers lies in the ease of photon extraction along with the ability to control the colour center more easily through external fields without sacrificing spectral purity. The superior conversion rate of GeV and SiV centres compared to nitrogen vacancy centres is also a strong point, as well as the larger splitting of the spin levels compared to silicon vacancy centres, which makes control of the spin qubit easier. The project will involve selection of ideal nanodiamonds through the characterization of optical properties such as photoluminescence and second order correlation. We will examine the scope of a novel wavelength tuning strategy involving piezoelectric ZnO coatings. We are also part of a few collaborations; Single photons from Silicon vacancies or Quantum dots will be used to develop quantum memristors with colleagues from University of Trento, Time tagging data from single photon sources will be used to assess randomness of photon arrival times with a collaborator at Dublin city university, the effect of a magnetic ion on Nitrogen vacancy centers in bulk diamond will also be studied and other collaborations within L2n are also ongoing.

Janas - Estimating molecular ground-state energies with Rydberg arrays

• Giovanni Varutti (University of Trieste, eXact lab S.r.l.)

Room: Aula Renzo Leonardi Janas is a startup that uses quantum computing technologies and techniques to solve today's industrial problems. In the NISQ settings, we think that only a hybrid approach with the right mix of conventional high performance computing (the specialty of our parent company eXact lab), machine learning and quantum processing can provide an edge in the near term. We further claim that quantum simulation provides a more reliable platform until error corrected digital quantum computing will become available. We show the computation of the ground state energy of small molecules on neutral-atom quantum computing platforms, comparing the digital and analog paradigms. The smart arrangement of the register makes the analog drive competitive with digital quantum computing. We acknowledge funding from the EU's NextGenEU programme through ICSC Spoke 8 project JANAS-QMLMS.

The road to early fault-tolerance

• Thomas O'Brien (Google Quantum AI)

Room: Aula Renzo Leonardi For the last five years, quantum computing has been in the era colloquially known as 'NISQ' - where computation is limited by error rates instead of qubit count. The next steps on quantum computing roadmaps push us into the early-fault tolerant era. Here, limited amounts of error correction will be available, but achieving beyond-classical quantum computation will require robust algorithm design, and error mitigation. I will cover the learnings that we have made over the last 5 years, explain how early-fault tolerant algorithms differ from the circuits we have used thus far, and suggest means to future-proof research in near-term quantum computing from becoming redundant.

Classification of qubit cellular automata on hypercubic lattices

• Andrea Pizzamiglio

Room: Aula Renzo Leonardi In this talk, I will provide an introduction to Quantum Cellular Automata (QCAs) and to the problem of their classification. Then I will present a thorough classification in the case of translation-invariant qubit systems on hypercubic lattices with nearest neighbor scheme --- a foundational framework for both many-body quantum physics and quantum computation. Our classification encompasses all admissible local rules for these qubit QCAs, along with their implementation as finite-depth quantum circuits. Furthermore, we define a multidimensional-index that measures the information flow generated by these QCAs, generalizing those one-dimensional indices as GNVW index, Kitaev flow or winding number, and the associated classification. Our results offer valuable insights into the ongoing challenge of classifying QCAs and topological phases in $D\geq 2$ spatial dimensions, potentially advancing both theoretical understanding and practical applications in quantum simulation. We simulate various families of these QCAs to relate their entanglement generation capabilities to the parameters of the quantum gates implementing them, showcasing the potential wealth of applications of our classification. This talk is based on joint work with Paolo Perinotti and Alessandro Bisio arXiv:2408.04493.

A negative-index Josephson metamaterial: wave mixing and beyond

• Giulio Cappelli (CNRS Institut Néel)

Room: Aula Renzo Leonardi Since their initial proposal, materials with a negative refractive index, also dubbed as left-handed, have attracted significant interest because of their unusual electromagnetic properties and promising technological applications. Recently, they have gained renewed attention in the field of circuit quantum electrodynamics as potential platforms for achieving near-quantum-limited parametric amplification. I will discuss the first realization of a negative-index Josephson metamaterial that supports propagating waves. The Josephson junctions nonlinearity, together with the left-handed dispersion, where phase and group velocity have opposite signs, enables various parametric processes, ranging from self-phase-matched broadband amplification to both frequency conversion and amplification of counter-propagating waves. Beyond these nonlinear optical effects, negative-index Josephson metamaterials also offer opportunities to explore new phenomena in quantum optics. I will describe a recent experiment in which we observed the generation of entangled photons propagating in opposite directions within such a metamaterial.

Design of an analog quantum simulators with superconducting transmon qubit

• Alessandro Cattaneo (Università Milano-Bicocca)

Room: Aula Renzo Leonardi Analog quantum computing is emerging as a powerful approach for addressing computationally intractable problems in quantum many-body physics. Classical computers struggle to simulate these systems due to the exponential growth in computational resources required as system size increases. Unlike digital quantum computers, which rely on discrete qubits and gate-based operations, analog quantum computers use continuous variables to directly model quantum dynamics. This allows for a more natural representation of quantum systems, minimizing the need for error-prone digital decompositions. However, this advantage comes at a cost: analog quantum computing requires specialized hardware architectures tailored to specific problems, sacrificing the flexibility of digital approaches. In this direction, the Quantum Architecture for Theory & Technology (QUART&T) project aims to develop a quantum device composed of multiple coupled superconducting qubits and resonators, designed for efficient quantum simulations of many-body interactions, including (p, d), (p, ³H), and (p, ³He) scattering processes and possibly real time-evolution of models mimicking lattice models with gauge degrees of freedom. The project focuses on key technological advancements, such as implementing all-to-all coupling through tunable couplers, integrating high-coherence superconducting qubits, and exploring higher-dimensional quantum systems (qudits) to enhance computational capabilities. As an initial step for this project, we are conducting an in-depth study on tunable couplers due to their significant advantages in building analog quantum simulators. Notably, these couplers allow for parametrically controlled communication between qubits, which enables real-time regulation of how each quantum element contributes to the system’s time evolution by simply adjusting an external parameter. Moreover, tunable couplers can enhance communication between quantum elements, effectively creating a fully configurable network up to all-to-all connectivity configuration. These couplers leverage on tunable elements, such as a Direct Current Superconducting QUantum Interference Device (DC-SQUID) that can be tuned with an external magnetic flux. In this presentation, we will outline the general aim of the project, the preliminary simulation results for the Hamiltonian that governs the desired evolution, and the first simulated design that will implement it. **Acknowledgements** This work is supported by QUART&T, a project funded by the Italian Institute of Nuclear Physics (INFN) within the Technological and Interdisciplinary Research Commission (CSN5) and Theoretical Physics Commission (CSN4) and by the PNRR MUR Projects PE0000023-NQSTI and CN00000013-ICSC.

Quantum Simulation Algorithms for Many Fermion Systems in First Quantization

• Luca Spagnoli (University of Trento)

Room: Aula Renzo Leonardi In this work, we compare the quantum simulation of a pionless effective field theory using the first and second quantization frameworks, as well as evaluate the performance of various algorithms within the first quantization framework. We demonstrate that using the first quantization formalism can yield an exponential advantage over second quantization as the lattice size increases. However, this advantage comes with a trade-off of polynomially worse scaling in the number of particles. Consequently, we show that for scattering processes and simulations that require being "far" from the boundaries, the first quantization framework is likely the more suitable choice. We show that this is the case when considering a simple Hamiltonian with two and three-body contact interaction.

Speeding up early fault-tolerant quantum simulations of chemistry with modern signal processing tools

• Davide Castaldo (ETH - Zurich, Department of Chemistry and Applied Biosciences)

Room: Aula Renzo Leonardi Quantum phase estimation (QPE) is a flagship algorithm for quantum simulation on fault-tolerant quantum computers. However, recent resource stimates[1] suggest that surpassing classical simulation techniques requires millions of gates and hundreds of logical qubits. Consequently, significant effort is being devoted to developing QPE-like algorithms that could demonstrate practical quantum advantage on early fault-tolerant quantum computers—i.e., devices with error correction but a limited number of qubits[2]. A promising approach to reducing QPE’s computational cost lies in recognizing that it estimates molecular energies by sampling the autocorrelation function in the time domain and performing a Fourier transform. This connection to signal recovery has recently inspired several methods for computing eigenvalues of quantum Hamiltonians using shallower QPE-like circuits[3,4,5]. Speeding up computation requires minimizing three key factors: (i) the total number of sampled points, (ii) the number of measurements per sampled point of the autocorrelation function, and (iii) the total length of the acquired signal. We adapt recent results from the field of compressed sensing[6,7] to design a quantum algorithm that simultaneously estimates ground and excited state energies while drastically reducing the total number of circuit executions[8]. At the same time, it demonstrates robustness to shot noise. We perform a numerical analysis in both weak and strong correlation regimes, providing evidence that the algorithm achieves optimal (Heisenberg) scaling. Finally, we explore how the quality of the initial input state affects the accuracy of the estimates, suggesting that these improvements could lead to a practical quantum advantage. [1] A. M. Dalzell, S. McArdle, M. Berta, P. Bienias, C.-F. Chen, A. Gily´en, C. T. Hann, M. J. Kastoryano, E. T. Khabiboulline, A. Kubica, et al., arXiv preprint arXiv:2310.03011 (2023). [2] A. Katabarwa, K. Gratsea, A. Caesura, and P. D. Johnson, PRX quantum 5, 020101 (2024). [3] C. Yi, C. Zhou, and J. Takahashi, Quantum 8, 1579 (2024). [4] Z. Ding, H. Li, L. Lin, H. Ni, L. Ying, and R. Zhang, Quantum 8, 1487 (2024). [5] H. Li, H. Ni, and L. Ying, Physical Review A 108, 062408 (2023). [6] G. Tang, B. N. Bhaskar, P. Shah, and B. Recht, IEEE transactions on information theory 59, 7465 (2013). [7] Y. Wang and Z. Tian, IEEE Signal Processing Letters 25, 1715 (2018). [8] D. Castaldo and S. Corni, In preparation, (2025).

Hybrid Quantum-Classical Strategy for Spectra Computation

• Alessandro Santini (CPHT, Ecole Polytechnique)

Room: Aula Renzo Leonardi We introduce a hybrid classical–quantum algorithm designed to efficiently compute molecular spectra. Our approach combines classical methods with sample‐based quantum diagonalization, using snapshots of the quantum system’s evolution at selected times we construct a tailored subspace. By integrating these classical techniques with a post-evolution sampling strategy, we effectively capture the dominant dynamical features of molecular excitations. This strategy enables the accurate estimation of spectral quantities with limited resource demands and enhanced robustness against quantum noise, paving the way for scalable simulations of complex molecular systems.

Structure Characteristics of Light Nuclei Calculated within the Variational Approach

• Borys Hryniuk (Bogolyubov Institute for Theoretical Physics of the National Academy of Sciences of Ukraine)

Room: Aula Renzo Leonardi A method is developed to solve the few-body problem for systems of quantum particles in the bound states. In the framework of the variational method in the Gaussian representation, the structure characteristics of light nuclei 6Li, 6He, 10Be, 10C, 14C, 14N, 14O are studied within three-, four-, and five-cluster models (α-clusters plus two extra nucleons). Specific properties of the charge density distributions, formfactors, pair correlation functions, and the momentum distributions of these nuclei are analyzed. Within the same approach, formfactors and density distributions of 12C, 16O, and 20Ne nuclei are calculated in the framework of the α-cluster model.

IQM - Quantum error correction with star architecture QPU

• Florian Vigneau

Room: Aula Renzo Leonardi The architecture of a QPU affects the performance of quantum error correction. The Star-configuration offers higher connectivity than the square-grid topology and thus enables more hardware efficient implementation of some error correction codes. We demonstrate error detection using a four-qubit code on a star-topology QPU. Our QPU features six superconducting transmon qubits coupled to a central resonator via tunable couplers. We apply two-qubit gates between pairs via the central resonator with a specific protocol based on qubit-resonator interaction. On this hardware, we characterize the lifetime, coherence time, and perform state tomography of the logical states.

QKD in Denmark

• Michael Galili (Technical University of Denmark)

Room: Aula Renzo Leonardi In this talk I will discuss a selection of recent and current QKD activities in Denmark including research results and field demonstrations as well as the status and plans for the Danish Quantum Communication Infrastructure - QCI.DK

A quantum photonic integrated SWAP test circuit for entanglement witness

• Sebastiano Guaraldo

Room: Aula Renzo Leonardi The detection and quantification of quantum entanglement poses significant challenges, especially as the size of quantum systems increases. Conventional methods such as quantum state tomography become impractical for large systems due to their exponential complexity. In this context, the SWAP test circuit, known for calculating the overlap between two quantum states, can be adapted as a tool for entanglement witnessing. The talk will present an integrated photonic circuit designed to implement the SWAP test algorithm and show how it can be used for entanglement detection. The circuit relies solely on linear optical components and operates at room temperature.

Fusion-based quantum computing with deterministic entanglement sources

• Ming Lai Chan (Sparrow Quantum/ Niels Bohr Institute)

Room: Aula Renzo Leonardi Fusion-based quantum computing (FBQC) is a promising model for realizing photonic quantum computers. Compared to measurement-based quantum computing (MBQC), FBQC does not require the generation of a full photonic cluster state prior to measurements. Instead, the cluster state is generated and simultaneously measured by fusions between smaller entangled states. The current approach to generate these states, as mainly pursued by big companies like PsiQuantum, uses probabilistic linear optics which might not be scalable in the long run due to low success rates. In this talk, I will discuss our recent efforts in creating these small entangled states with solid-state quantum dots. An electron spin trapped in the quantum dot can be periodically excited to emit multi-photon entangled states in demand, which might significantly boost the success rate and reduce resource cost. I will then show how these deterministic entangled-photon sources can be integrated into a bigger picture to realize FBQC and describe the architectural blueprint.

Directional emission of a giant atom super-strongly coupled to a Coupled Cavity Array

• Enrico Di Benedetto (Università degli Studi di Palermo)

Room: Aula Renzo Leonardi The introduction of high kinetic platforms in circuit QED allow for realization of coupled cavity array with low disorder, small footprint and large inter-site couplings [1]. This enables the study of challenging regimes of light-matter interaction within the paradigm of waveguide QED [2] e.g., giant qubits coupled non-locally to the waveguide. In this work, we conduct an experiment using a giant atom super-strongly coupled to a 1D bath reproducing the photonic analogue of the Su-Schrieffer-Heeger model [3]. Remarkably, on top of standard atom-photon bound states, the qubit induces mode localization in the waveguide, somehow similar to the formation of a Bound-In-Continuum state [4], when the qubit is tuned in the bandgap of the system. This localization phenomenon can be harnessed to induce directional spontaneous emission of the qubit. We explain the emergence of this qubit-induced localization with a Green-function-based argument [5] and propose a setup in which the qubit is manipulated by exploiting the atom-photon bound state in the bandgap and then the information stored in it is sent out directionally through these localized bath modes. These findings open new direction to manipulate nonclassical excitation in waveguide QED e.g., for routing or state transfer applications. References: [1] V. Jouanny et al, Band engineering and study of disorder using topology in compact high kinetic inductance cavity arrays (2024), arXiv:2403.18150 [2] F. Ciccarello et al, Waveguide Quantum Electrodynamics, Optics & Photonics News, OPN 35, 34 (2024) [3] Asboth et al, Lecture Notes in Physics, 919 (2016) [4] S. Longhi, Eur. Phys. J. B 57, 45-51 (2007) [5] L. Leonforte et al, Quantum Sci. Technol. 10 015057 (2024)

Erbium atoms in optical tweezers

• Arina Tashchilina

Room: Aula Renzo Leonardi Laser-cooled neutral atom arrays in optical tweezers are rapidly advancing as a scalable platform for quantum computing. Alkaline-earth metals and lanthanides provide unique advantages in atomic manipulation due to their rich spectra, enabling new possibilities in quantum science. We have built a novel system for quantum computation based on erbium atoms [1]. In my talk, I will explore the possibility of using different optical transitions for cooling, single-atom operation, and imaging and investigate the Rydberg excitation spectrum. We performed a detailed study of the dynamics of erbium atoms on the narrow intercombinational transition both experimentally and theoretically. We developed a Monte Carlo algorithm, validated it in experiments, and used it to identify conditions for efficient in-trap Doppler cooling. Allowing us to have continuous nondestructive imaging on intercombinational transition. As a preliminary investigation of erbium atoms excited to Rydberg states, we performed spectroscopy for the 47s and 48d states in tweezers, confirming earlier results obtained with a hot erbium beam [2]. Additionally, we demonstrated the excitation of single atoms to the Rydberg state, marking the first step toward two-atom entanglement in erbium atoms.