All posts by ruiunai

Antonio Manesco

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Antonio Manesco

Quantum Tinkerer group, Delft University of Technology

 

Identifying biases of the Majorana scattering invariant

When: 12:00-13:00 CET, May 8th (Thursday), 2025

Where: Sala de Seminarios (182), ICMM-CSIC, Campus de Cantoblanco, Madrid

The easily accessible experimental signatures of Majorana modes are ambiguous and only probe topology indirectly: for example, quasi-Majorana states mimic most properties of Majoranas. Establishing a correspondence between an experiment and a theoretical model known to be topological resolves this ambiguity. Here we demonstrate that, already theoretically, determining whether a finite system is topological is by itself ambiguous. In particular, we show that the scattering topological invariant –a probe of topology most closely related to transport signatures of Majoranas–has multiple biases in finite systems. For example, we identify that quasi-Majorana states also mimic the scattering invariant of Majorana zero modes in intermediate-sized systems. We expect that the bias due to finite size effects is universal, and advocate that the analysis of topology in finite systems should be accompanied by a comparison with the thermodynamic limit. Our results are directly relevant to the applications of the topological gap protocol.

 

Jan Marcus Dahlström

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Jan Marcus Dahlström

Department of Physics, Lund University

 

Ultrafast-and-ultrastrong coupling at ultraviolet wavelengths

When: 12:00-13:00 CET, April 9th (Wednesday), 2025

Where: Sala de Seminarios (182), ICMM-CSIC, Campus de Cantoblanco, Madrid

Recent advances in free-electron laser (FEL) technology have intensified interest in light-matter interactions in the XUV regime. Our group has been at the forefront of theoretical developments in this field and working closely with experimentalists, c.f. [1] and [2]. While previous studies have focused on traditional strong-coupling processes, enforcing energy conservation via the rotating-wave approximation, we explore now a distinct regime that challenges traditional approximations, namely a regime for ultrastrong coupling on ultrafast timescales, which leads to giant counter-rotating oscillations on the attosecond timescale. Additionally, the use of time symmetries in strong-coupling will be introduced to control quantum entanglement in photoionization [3].

[1] Nandi, S., et al. Observation of Rabi dynamics with a short-wavelength free-electron laser. Nature 608, 488–493 (2022).
[2] Nandi, S., et al. Generation of entanglement using a short-wavelength seeded free-electron laser. Sci. Adv.10, eado0668 (2024).
[3] Stenquist, A. and Dahlström, J. M. . Harnessing time symmetry to fundamentally alter entanglement in photoionization. Phys. Rev. Research 7, 013270 (2025).

David Ayuso

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David Ayuso

Department of Chemistry, Molecular Sciences Research Hub,  Imperial College London, W12 0BZ London, UK

 

Ultrafast chirality: shaping light in 3D to twist electrons on a sub-femtosecond timescale

When: 11:00-12:00 CET, April 9th (Wednesday), 2025

Where: Sala de Seminarios (182), ICMM-CSIC, Campus de Cantoblanco, Madrid

Chirality—the property of an object that cannot be superimposed on its mirror image—is ubiquitous in nature. Like our hands, opposite versions of the same chiral molecule (R and S enantiomers) behave identically unless they interact with another chiral object. Molecular chirality is rapidly becoming essential in nanotechnology [1], e.g. for developing molecular motors and spintronic devices. The unbalance between R and S biomolecules on Earth (amino acids, sugars, DNA, etc.) supports life. This homochirality gives different biological activities to opposite versions of a chiral drug or pesticide, with profound implications for pharmaceuticals and agriculture. Moreover, abnormal enantiomeric ratios of chiral biomarkers have recently been linked to cancer, Alzheimer’s, diabetes, and other diseases [2].

Having efficient tools for rapid chiral discrimination is therefore vital. However, current optical methods are inefficient because they rely on the (chiral) helix that circularly polarised light draws in space. The pitch of this helix—determined by light’s wavelength—is ~10,000 times larger than the molecules. Consequently, the molecules perceive the helix as a flat circle, hardly feeling its chirality. This results in weak chiral sensitivity, typically <0.1%, which presents major limitations [3]. We can overcome these limitations by creating synthetic chiral light [4-6], where the tip of the electric-field vector traces a 3D chiral trajectory in time. This new type of chiral light can drive ultrafast chiral currents inside the molecules, which interact with the chiral molecular skeleton in a highly enantiosensitive manner, leading to 100% chiral sensitivity.

In this presentation, I will show how we can shape light’s polarisation in 3D to achieve highly efficient chiral sensing [4-10] and manipulation [11], together with theoretical and computational results that support the feasibility of our approaches. Current optical instrumentation enables several strategies for 3D shaping, such as using several laser beams that propagate non-collinearly [4-6,11], only one beam but tightly focused [7,8], vortex beams to create topological chiral light [9], or ultrafast TACOS [10]. I will discuss how we can bring these ideas to free-electron lasers (FEL), taking advantage of important developments in FEL science and technology that enable the generation of phase-locked two-colour radiation.

[1] J. Brandt et al, Nature Reviews Chemistry 1, 0045 (2017)
[2] Y. Liu et al, Nature Reviews Chemistry 7, 355 (2023)
[3] D. Ayuso et al, Phys Chem Chem Phys 24, 26962 (2022)
[4] D. Ayuso et al, Nature Photonics 13, 866 (2019)
[5] D. Ayuso et al, Nature Communications 12, 3951 (2021)
[6] J. Vogwell et al, Science Advances 9, eadj1429 (2023)
[7] D. Ayuso et al, Optica 8, 1243 (2021)
[8] L. Rego et al, Nanophotonics 12, 14, 2873 (2023)
[9] N. Mayer et al, Nature Photonics 18, 1155 (2024)
[10] J. Terentjevas et al, ArXiv:2406.14258v1 (2024)
[11] A. Ordóñez et al, ArXiv:2309.02392 (2023)

Juan Torres Luna

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Juan Torres Luna

TU Delft – Quantum Tinkerer group

 

Understanding the fate of the poor man’s Majorana in the long-chain limit

When: 12:00-13:00 CET, February 18th (Tuesday), 2025

Where: Sala de Seminarios (182), ICMM-CSIC, Campus de Cantoblanco, Madrid

The quality of topological qubits based on Majorana bound states (MBS) depends uniquely on two properties: the size of the topological gap and the MBS localization length. While the Kitaev model features perfectly localized MBS and a maximal gap, realistic systems exhibit finite localization length and the gap is limited by proximity effect, which raises the question of what platform can realise the best MBS. In this work, we study the quality of MBS in two platforms: the Lutchyn-Oreg (LO) model and the quantum dot chain model.
For the quantum dot chain, we find a trade-off between weak coupling—where the gap is small and the localization length is small—and the strong coupling regime—where the gap is large and the localization length is large. For the LO model, we find that the interplay between spin-orbit coupling and momentum yields a gap and localization length that cannot be simultaneously optimized. In order to find the best MBS that each model can achieve, we use multi-objective optimization to find the set of optimal localization lengths and gaps. We demonstrate that quantum dot chains can achieve MBS quality comparable to nanowire models, with extra tunability of the gap and localization. Our results highlight quantum dot chains as a versatile platform for high-quality MBS and topological quantum computing.

 

Amir Rahamni

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Amir Rahamni

Instytut Fizyki PAN, Warsaw, Poland

 

Quantum Many-Body Interactions and Light-Matter Coupling: Expanding the Frontier of Reservoir Computing and Machine Learning

When: 12:00-13:00 CET, December 2nd (Tuesday), 2024

Where: Sala de Juntas, ICMM-CSIC, Campus de Cantoblanco, Madrid

Quantum reservoir computing (QRC) has emerged as a powerful paradigm for tackling machine-learning tasks by using the rich dynamics of quantum systems. At its core, QRC relies on effective control drives to encode input data and nonlinear mappings to transform these inputs into output features. Photonic platforms are likely candidates for QRC. However, they often lack sufficient nonlinearity for optimal performance. To overcome this limitation, a hybrid optoelectronic approach can be used, combining the speed of optical processing with the inherent nonlinearity of electronics. In this seminar, we present a method to enhance nonlinearity by employing wavefunction engineering within the regime of light-matter coupling. We explore various structures, including GaAs and TMD materials in cavities and waveguides. Through some examples, we demonstrate improvements in the accuracy of some quantum tasks, highlighting the potential of QRC in advancing machine learning.

Andrea Maiani (26/11/24)

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Andrea Maiani

WINQ Postdoctoral fellow, Nordita.

 

Impurity States in Altermagnetic Superconductors

When: 12:00-13:00 CET, November 26th (Tuesday), 2024

Where: Sala de Seminarios (182), ICMM-CSIC, Campus de Cantoblanco, Madrid

 

Altermagnets are a novel class of magnetic materials distinct from ferromagnets and antiferromagnets, characterized by vanishing net magnetization and unique spin-split band structures – appealing features for exotic quantum phenomena and spintronics applications. This talk explores the interplay between altermagnetism and superconductivity, focusing on how impurities can serve as local probes of altermagnetic superconductors. I will briefly introduce altermagnetic materials, their interplay with superconductivity, and review the basic theory of impurity states in superconductors. I will then present our original theoretical work on the role of impurities in altermagnetic superconductors, predicting the emergence of spin-polarized subgap states that extend along the crystal axes. These states form degenerate doublets, which can be split by crystal symmetry breaking or a magnetic field aligned with the Néel vector. Their unique spatial and spin properties provide measurable signatures via scanning tunneling microscopy, serving as a hallmark for altermagnetic superconductivity. Finally, I will discuss the interaction between impurities, revealing a position-dependent, spin-selective coupling that enables in-situ control of devices crucial for quantum information processing and topological superconductivity.

Natalia Berloff (07/11/24)

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Natalia Berloff

Department of Applied Mathematics and Theoretical Physic, University of Cambridge, UK

Non-Hermitian Gain-Based Computing with Coupled Light-Matter Systems 

When: 12:00-13:00 CET, November 7th (Thursday), 2024

Where: Sala de Seminarios (182), ICMM-CSIC, Campus de Cantoblanco, Madrid

Gain-based computing utilizing non-Hermitian dynamics in light-matter interactions presents a novel approach to physics-based hardware and physics-inspired algorithms. By encoding complex optimization problems into the gain and loss rates of driven-dissipative systems, we leverage non-Hermiticity to destabilize non-optimal states and guide the system toward the global minimum. The incorporation of prior knowledge about ground state energies into the complex part of the energy enhances the system’s ability to navigate complex energy landscapes.
In this paradigm, the system undergoes symmetry-breaking transitions on a dynamically changing loss landscape, selecting modes that minimise losses and manifesting the optimal solutions to the original problems. This approach enables solving significant combinatorial optimization problems via mapping to Ising, XY, and k-local Hamiltonians, applicable across various physical platforms, including photonic, electronic, and atomic systems.
 Despite advancements, critical questions remain regarding scalability, the impact of phase space structures on system performance, and the identification of problems best suited for these unconventional computing architectures. I will address these challenges in my talk by understanding the dynamic behaviour during symmetry-breaking transitions, optimizing trajectories toward global minima, quantifying error probabilities, and using dissipation and nonlinearities to correct errors.

 

 

 

Valeria Ferrari (31/10/2024)

Sin categoría

 

 

Valeria Ferrari

Departamento de Física de la Materia Condensada, Comisión Nacional de Energía Atómica (CNEA). Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Instituto de Nanociencia y Nanotecnologia (CNEA-CONICET)

Radiation Effects at Oxide-Water Interfaces: Current Insights and Future steps 

When: 12:00-13:00 CET, October 31th (Thursday), 2024

Where: Seminar Room (182), ICMM-CSIC, Campus de Cantoblanco, Madrid

 

The interaction between ionizing radiation and oxide-water interfaces is a key topic in material science research in the quest for materials with technological applications, such as nuclear waste management, metal corrosion in aqueous environments, and biological systems exposed to radiation. This talk will explore atomic-level processes occurring at these interfaces, with particular emphasis on hydrogen generation in oxides such as zirconia and copper oxide, both of which are used in nuclear facilities.

The current challenges in understanding the mechanisms behind these processes through electronic structure methodologies will be discussed, including density functional theory (DFT) and many-body perturbation theory (MBPT) approaches, such as the GW approximation and the Bethe-Salpeter equation (BSE). Our preliminary results in these materials, focusing on excitonic properties and radiation-induced processes, will also be presented.

This work is part of the Horizon project titled “Materials Radiation: From Basics to Applications” (MAMBA), which aims to deepen the understanding of material responses to irradiation and apply this knowledge to tailor and control the properties of materials exposed—either intentionally or unintentionally—to intense radiation environments. Finally, the talk will outline the future steps in this research, including modeling different oxide facets, analyzing excitonic wave functions, and using machine learning to describe the corresponding oxide-water interfaces.

 

Manhong Yung (17/10/2024)

Sin categoría

 

 

Manhong Yung

Southern University of Science and Technology, China

From quantum inspired to quantum speedup

When: 12:00-13:00 CET, October 17th (Thursday), 2024

Where: Seminar Room (182), ICMM-CSIC, Campus de Cantoblanco, Madrid

Quantum computing has reached a critical moment. On the one hand, quantum hardware are continuously advancing. On the other hand, quantum computational advantage over classical computing has not yet been available for practical problems. Moreover, the road to universal quantum computing is still long. The highly anticipated quantum variational algorithm is still constrained by a small number of qubits and shallow circuits. Some scholars even think that “NISQ is dead”. In this talk, based on the applications of quantum-inspired algorithms, we introduce the concept of quantum acceleration algorithms and discuss how NISQ quantum hardware can act as an accelerator and add to the value of quantum computing through the mixture with classical computing.

Fernando Martín (10/10/2024)

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Fernando Martín

Departamento de Química, Universidad Autónoma de Madrid, 28049 Madrid, Spain

Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nano), 28049 Madrid, Spain

 

Attochemistry: chemistry at the attosecond time scale

When: 12:00-13:00 CET, October 10th (Thursday), 2024

Where: Salón de Actos, ICMM-CSIC, Campus de Cantoblanco, Madrid

With the advent of attosecond light pulses at the dawn of the twenty first century, access to the time scale of electronic motion, i.e., the ultimate time scale responsible for chemical transformations, was finally at our reach. Since the first attosecond pump-probe experiments performed in molecules [1,2], the field has grown exponentially, leading to a discipline that we call attochemistry [3]. As a result, it is nowadays possible to follow in real time the motion of the “fast” electronic motion in molecules, mostly in the gas phase, and understand how this motion affects the “slower” motion of atomic nuclei and vice versa. There are, however, new scenarios [4] that will allow one to extend the range of applications to more complex molecular systems, including the condensed phase, and to overcome some of the limitations of current attosecond technologies [5-9], such as the low intensity of attosecond pulses produced by high harmonic generation, the impossibility to generate such pulses in the visible and UV spectral regions to avoid molecular ionization, or the difficulties to combine them with truly imaging methods as those used in condensed matter physics for direct time-resolved observations of the electron density without the need for reconstruction from measured photoelectron, photoion or transient absorption spectra.

In this talk, I will describe current experimental and theoretical efforts aiming at overcoming the above-mentioned limitations, thus giving attochemistry the necessary push to investigate problems of real chemical interest.

References:
[1]  G. Sansone, F. Kelkensberg, J. F. Pérez-Torres, F. Morales, M. F. Kling, W. Siu, O. Ghafur, P. Johnsson, M. Swoboda, E. Benedetti, F. Ferrari, F. Lépine, J. L. Sanz-Vicario, S. Zherebtsov, I. Znakovskaya, A. L’Huillier, M. Yu. Ivanov, M. Nisoli, F. Martín, and M. J. J. Vrakking, Nature 465 763 (2010).

[2] F. Calegari, D. Ayuso, A. Trabattoni, L. Belshaw, S. De Camillis, S. Anumula, F. Frassetto, L. Poletto, A. Palacios, P. Decleva, J. B. Greenwood, F. Martín, and M. Nisoli, Science 346, 336 (2014).

[3] M. Nisoli, P. Decleva, F. Callegari, A. Palacios, and F. Martín, Chem. Rev. 117, 10760 (2017).

[4] F. Calegari and F. Martín, Commun. Chem. 6, 184 (2023).

[5] A. Palacios and F. Martín, WIREs Comput. Mol. Sci. e1430 (2020).

[6] G. Grell, Z. Guo, T. Driver, P. Decleva, E. Plésiat, A. Picón, J. González-Vázquez, P. Walter, J. P. Marangos, J. P. Cryan, A. Marinelli, A. Palacios, and F. Martín, Phys. Rev. Res. 5, 023092 (2023).

[7] M. Galli et al, Optics Letters 44, 1308 (2019).

[8] M. Reduzzi et al, Optics Express 31, 26854 (2023).

[9] M. Garg, A. Martín-Jiménez, M. Pisarra, Y. Luo, F. Martín and K. Kern, Nature Photonics 16, 196 (2022).

[10]  F. Vismarra, F. Fernández-Villoria, D. Mocci, J. González-Vázquez, Y. Wu, L. Colaizzi, F. Holzmeier, J. Delgado, J. Santos, L. Bañares, L. Carlini, M. Castrovilli, P. Bolognesi, R. Richter, L. Avaldi, A. Palacios, M. Lucchini, M. Reduzzi, R. Borrego- Varillas, N. Martín, F. Martín, and M. Nisoli, Nature Chemistry in press.