quantum – Progress in Research

Towards more sustainable superconductor applications

Posted on 11/12/202306/08/2024 by Erik Franco

A significant step forward in superconductivity research has recently been made. The discovery could pave the way for sustainable technologies and contribute to a more environmentally friendly future.

The study just published in Nature Communications by researchers from Politecnico di Milano, Chalmers University of Technology in Göteborg and Sapienza Università di Roma sheds light on one of the many mysteries of high-critical-temperature copper-based superconductors. Even at temperatures above the critical temperature, they are special, behaving like “strange” metals. This means that their electrical resistance changes with temperature differently than that of normal metals.

This is the result of more than five years of work. We used a technique, called RIXS, largely developed by us at the Politecnico di Milano. Thanks to numerous measurement campaigns and to new data analysis methods, we were able to prove the existence of the quantum critical point.
Giacomo Ghiringhelli, Professor at the Department of Physics and coordinator of the research

The research hints at the existence of a quantum critical point connected to the phase called “strange metal”. A quantum critical point identifies specific conditions where a material undergoes a sudden change in its properties due solely to quantum effects. Just like ice melts and becomes liquid at zero degrees Celsius due to microscopic temperature effects, cuprates turn into a ‘strange’ metal because of quantum charge fluctuations.

The research is based on X-ray scattering experiments conducted at the European Synchrotron ESRF and at the British synchrotron DLS. They reveal the existence of charge density fluctuations affecting the electrical resistance of cuprates in such a way as to make them “strange”. The systematic measurement of how the energy of these fluctuations varies allowed identifying the value of the charge carrier density at which this energy is minimum: the quantum critical point.

The discovery represents an important advancement in understanding not only the anomalous properties of the metallic state of cuprates, but also the still obscure mechanisms underlying high-temperature superconductivity.

A better understanding of cuprates will guide the design of even better materials, with higher critical temperatures, and therefore easier to exploit in tomorrow’s technologies.

Arpaia, R., Martinelli, L., Sala, M.M. et al.
Signature of quantum criticality in cuprates by charge density fluctuations.
Nat Commun 14, 7198 (2023)

Read the study online

Quantum tunnelling of electrons in bidimensional materials

Posted on 26/07/202306/08/2024 by Erik Franco

Sustainable optical computers based on photonic logic gates with low power consumption, but also nano-scaled (one billionth of a metre) optical chips and novel sensors with high sensitivity: the research carried out by an international team opens those new intriguing perspectives for the near future. The team is coordinated by Politecnico di Milano – Department of Physics in collaboration with University of Sheffield (UK); researchers from University of Manchester and Exeter (UK) collaborated too.

The researchers observed that the effect of quantum tunnelling of electrons between two adjacent layers of atomically thin semiconductors drastically modifies their transparency, after being illuminated by laser light.

The work has been recently published on the prestigious journal Nature Communications.

More in details, the research team explored the effects of this bidirectional “transport” of electrons between a layer of an atomically thin material to another one, the so-called quantum tunnelling.

Because of this transfer, the electrons are delocalized among the layers and they compete with the electrons localized in only one layer to occupy the same energetic state. This phenomenon follows the so-called Pauli exclusion principle, which also hinders the light absorption if the states are already occupied by the electrons. This process can strongly modify the optical properties of the employed materials, increasing their transparency after the illumination with laser light.

In summary, the competition between electrons generates a drastic decrease of the light absorption in such materials, increasing their laser-induced transparency.

The observation of such properties paves the way for new research horizons in the field of photonics and materials science, for future applications in optical and quantum computing.

The work was partially funded by the European Union in the framework of the Graphene Flagship (project “GrapheneCore3” lead by Prof. Giulio Cerullo) and the Marie Curie Individual Fellowship project “Enosis” lead by Dr. Armando Genco.

The paper on Nature Communications

Launch of QUID, the Italian quantum communication network

Posted on 23/06/202306/08/2024 by Erik Franco

The QUID (Quantum Italy Deployment) project is the Italian implementation of the European Quantum Communication Infrastructure (EuroQCI), promoted by the European Commission with the aim of creating a European infrastructure for quantum communication.

In the course of the project, existing communication infrastructures, whether fibre-optic or airborne, will be integrated and equipped with quantum key distribution (QKD) systems, which will cover a large part of the national territory; at the same time, QUID promotes the development of Italian companies that produce systems and services for quantum communication to different categories of users.

The main purpose of QUID is the development of nodes in quantum metropolitan area networks (QMANs), interconnected through the Italian Quantum Backbone, an infrastructure that covers the Italian territory and distributes, with unprecedented stability and accuracy, time and sampling frequency signals using commercial optical fibres. In each QMAN, quantum key exchanges will take place between nodes using discrete variable QKD systems; distances greater than metropolitan will be covered using ‘trusted’ nodes or innovative Twin-Field QKD techniques (with ‘untrusted’ nodes).

QUID will also unite important sites for the connection between fibre-optic communication and the space segment of the European QCI.

Alongside these infrastructural activities, QUID places great emphasis on the development of methods for the optimal delivery of quantum communication services.

Finally, QUID leaves room for the development of innovative QKD techniques, for increasing the transmission frequency, for the use of new types of optical fibres and for free-space transmission.

The QUID consortium brings together leading Italian companies in the sector, leading research institutes involved in quantum communication, for both the terrestrial and space segment, and universities engaged in innovation and education.

The involvement of companies that produce QKD devices, operate telecommunications networks and terrestrial and space services, and that offer integrated IT security solutions, will enable the easy connection of QKD systems in communication networks across the country.

New ways of creating chemical bonds for increasingly complex molecules

Posted on 10/11/202206/08/2024 by Erik Franco

A study published recently in Nature Chemistry that combines experimental measurements and theoretical simulations has highlighted a new class of chemical reactions whose speed is controlled by quantum phenomena. Study participants included researchers from the Politecnico di Milano and also from the Universty of Perugia, the Scuola Normale Superiore in Pisa and the University of Bologna.

The discovery can be explained by these images:

If we imagine a chemical reaction as a pathway that must be travelled in order to go from reactants to products (figure 1), it is reasonable to expect that the reaction will occur if the reactants have sufficient energy to overcome the energy bottleneck (barrier) separating the reactants and the products (top), and that it won’t occur if the energy is insufficient (bottom).

Through the reaction mechanism discovered in this study, we can bypass the barrier even when the reactant’s energy is low, by means of a quantum leap onto a parallel reactive pathway with a lower barrier. The mechanism that enables this reaction is of a quantum nature and is known as spin inversion (figure 2).

The class of reactions studied, known as spin-forbidden, is difficult to approach because it requires the use of advanced calculation methods.

Evidence of the existence of this new reactive pathway, significant around and below room temperature, will allow us both to identify certain active reaction pathways in astrochemical and biological environments that have hitherto been difficult to understand, and to design new chemical synthesis pathways.

In fact, the proposed reactive pathway allows us to conceive new methods for creating chemical bonds between different reactants and can thus be added to the chemist’s toolbox for constructing increasingly complex molecules.

Using new theoretical and computational tools developed by teams in Milan, Pisa and Bologna, we were able to reproduce the experimental data measured by our colleagues in Perugia, demonstrating for the first time that, for a particular reactant system, the addition of oxygen to nitrogen compounds, the proposed mechanism is active.
Carlo Cavallotti, professor at the Politecnico di Milano and author of the study

Photons to create an artificial quantum neuron

Posted on 13/04/202206/08/2024 by Erik Franco

A group of researchers of the Department of Physics at the Politecnico di Milano, the National Research Council (CNR) and the University of Vienna, have developed a device, called a quantum memristor, which could combine artificial intelligence and quantum computing.

This is an advance that can open up as yet unseen potential, allowing to employ the very high computational power guaranteed by quantum technologies in the fields of application of artificial intelligence, which already range from automatic speech interpretation to face recognition, from medical diagnostics to autonomous driving.

Artificial intelligence algorithms are based on mathematical models called neural networks, inspired by the biological structure of the human brain, which is made up of interconnected nodes (neurons). One of the fundamental components of neural networks is the memristor (or memory-resistor), a component that changes its electrical resistance based on a memory of the current that passed through it, in a way that is surprisingly similar to that of neural synapses, i.e. the connections between neurons in the brain.

The group of experimental physicists led by Roberto Osellame (CNR) has shown that it is possible to engineer an optical device with the same functional characteristics as the memristor, capable of operating on quantum states of light and thus encoding and transmitting quantum information: a quantum memristor.

We also simulated an entire optical network made up of quantum memristors, showing that it could be used to learn both classical and quantum tasks.
Andrea Crespi, professor of Experimental Physics at the Politecnico di Milano

This result seems to suggest that the quantum memristor may be the missing link between artificial intelligence and quantum computing, unleashing the potential of quantum resources within artificial intelligence applications.

The study received the cover of the April issue of Nature Photonics magazine.

The study on Nature Photonics

© photo: Equinox Graphics

Italian Quantum Weeks – Milano

Posted on 05/04/202206/08/2024 by Erik Franco

On the occasion of the first World Quantum Day, Politecnico di Milano, together with Università degli Studi di Milano and CNR IFN of Milan, will participate to the Italian Quantum Weeks, a national event dedicated to quantum mechanics and quantum technologies that will take place in 17 Italian cities.

In Milan the program includes guided tours to the research laboratories of Politecnico di Milano, Università degli Studi di Milano and CNR IFN, seminars on quantum mechanics and the exhibition “Saying the unspeakable: quantum superposition”.

Full program and registration form

Super fast quantum battery

Posted on 19/01/202206/08/2024 by Erik Franco

Researchers from the Physics Department of the Politecnico di Milano and the Institute of Photonics and Nanotechnologies of the Cnr have built a battery which, following the laws of quantum physics, has a recharge time that is inversely related to the battery capacity.

Tersilla Virgili (Institute of Photonics and Nanotechnologies of the National Research Council Cnr-Ifn) and Giulio Cerullo (Physics Department of the Politecnico di Milano) have shown that it is possible to manufacture a type of quantum battery where the charging power increases faster by increasing the battery capacity.

The fabricated device is a microcavity in which the active material consists of organic molecules dispersed in an inert matrix.

Each molecule represents a unit that can exist in a quantum superposition state of two energy levels (fundamental and excited), similar to the way a qubit, the basic unit of quantum information, can be both 0 and 1 simultaneously in quantum computers. By constructing the quantum battery in a way that units can exist in superposition, the total system can behave collectively. This behaviour, known as quantum coherence, allows the units to act cooperatively, giving rise to a hyper-fast charge that depends on the number of molecule-units.
Prof. Giulio Cerullo

This new technology could find possible applications in devices such as wireless chargers, solar cells and cameras.

Superabsorption in an organic microcavity: towards a quantum battery.