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Quantum Sounds Symposium Brought Together Music and Quantum Physics

The Quantum Sounds Symposium took place from June 6 to 8, 2023, offering the public and the ICFO community an opportunity to explore the intersection between quantum physics and music composition, data sonification, interactive sound design, and audio software development.

The three-day event featured a series of talks, lecture-recitals, and Quantum Random Number Generator jam sessions, blending science, art, and performance. Invitees also visited ICFO laboratories and led themed group discussions with registered participants.

On June 6 and 7, sessions were held at ICFO in Castelldefels, while on June 8, activities moved to La Salle-Ramón Llull University and Hangar.org in Barcelona.

The symposium welcomed leading figures from academia, industry, and the arts. Highlights included:

  • Eduardo Reck Miranda, Paulo Itaboraí, and Cephas Teom (University of Plymouth), who presented the lecture-concert Tensorial Ripples.

  • Eli Fieldsteel (University of Illinois), who introduced LightMatrix, a light-sensitive musical control interface.

  • James Weaver and Brian Ingmanson (IBM), who demonstrated Hilbert Space Deep House, exploring electronic dance music composed with quantum states.

  • Rodney DuPlessis (Worcester Polytechnic Institute), with a performance on composing with classical and quantum harmonic oscillators.

  • Spencer Topel (Physical Synthesis) and Florian Carle (Yale Quantum Institute), who explored superconducting qubits in Reflections of the Quantum Realm.

  • Angel Faraldo and Carlos Abellan (QUSIDE), who presented Looped in the Sound of Photon.

  • Bob Coecke (Quantinuum), who gave a talk-demonstration on quantum compositionality for musical creation.

  • James Harley (University of Guelph) and Marcin Halat, who revisited Iannis Xenakis’ ideas in Random Walks in Sound and Music.

The event also featured panel discussions with international experts, including Mónica Bello (Arts-CERN), Anna Sanpera (UAB), Leticia Tarruell (ICFO), and Maciej Lewenstein (ICFO), covering themes such as quantum sounds, photons and vibrations, music and quantum computing, and the future of quantum arts and creativity.

The symposium was organized by Dr. Reiko Yamada and Prof. Dr. Maciej Lewenstein of ICFO, in collaboration with Dr. Osvaldo Jiménez Farías (La Salle-URL) and Dr. Jose Manuel Berenguer (University of Barcelona, Hangar.org).

The project received funding from the European Research Council (ERC) under the EU Horizon 2020 research and innovation programmes (NOQIA grant agreement No. 833801) and (OPTOlogic grant agreement No 899794).

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Exciton fission – one photon in, two electrons out

Exciton fission one photon in two electrons out
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OPTOLOGIC meets at Benasque for the CGA meeting

OPTOlogic CGA Meeting

The European OPTOlogic project held its first in-person CGA meeting in Benasque, Huesca, at the “Pedro Pascual” Science Center on March 9th and 10th, 2023. Notably, ICREA Professor of ICFO Dr. Jens Biegert and project manager Judith Salvador from ICFO organized the successful meeting to unite the entire project consortium. The primary objectives of the meeting were threefold: first, to share updates on each work unit’s current status and progress; second, to present and learn about the diverse results and latest advancements; and finally, to foster discussions to exchange ideas and find solutions to complex challenges in the project’s final stages.

Furthermore, this CGA meeting marked a significant milestone as the consortium’s first in-person gathering since the project began in September 2020. The productive two-day event provided a valuable platform for consortium members to engage in discussions and collaboratively address potential theoretical and experimental changes. Consequently, these in-depth conversations and collaborative efforts were crucial for ensuring the project’s continued success and advancement towards its ultimate goals. Moreover, the meeting fostered a sense of community and renewed motivation among the participants, who departed with a clearer vision for the project’s remaining tasks. In addition, the picturesque setting of Benasque further enhanced the collaborative atmosphere, providing a serene environment for focused discussions and the exchange of innovative ideas.

 

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Jens Biegert – Optica Board of Directors

Jens Biegert joins Optica Board of Directors
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Generation of many-body Bell correlated states in optical lattices

Many-body Bell correlated states in optical lattices

OPTOlogic researchers from ICFO, in collaboration with the University of Warsaw and the Institute of Physics, Polish Academy of Sciences, show how to generate many-body Bell correlated states using ultracold quantum gases in optical lattices. 

Quantum Correlations and Their Significance

Quantum correlations are a fundamental aspect of quantum mechanics. They refer to the correlations between the outcomes of measurements performed on two or more particles in a quantum system. These correlations can exhibit strange and counterintuitive behaviors not present in classical systems.

Entanglement and Bell Correlations

The phenomenon of entanglement exemplifies quantum correlations. It describes the correlation between two or more particles, a property that classical physics cannot explain. For example, if two particles entangle, the outcome of the measurement performed on one particle can predict the state of the other, even if the particles are separated by large distances. Bell correlations offer another example, referring to correlations between the outcomes of measurements performed on two or more particles that any local hidden variable theory cannot explain. These correlations often demonstrate the non-classical nature of quantum mechanics and the limitations of classical theories.

Quantum Correlations in Quantum Technologies

Quantum correlations play a key role in developing quantum technologies that exploit the unique properties of quantum systems to perform tasks not possible using classical technologies, including quantum teleportation, quantum cryptography, and quantum computing. However, the generation of many-body Bell correlated states, especially those implemented during the One-Axis Twisting protocol (OAT) procedure, posed an open question for science until now.

Breakthrough in Generating Many-Body Bell Correlated States

In an international study published in Physical Review Letters, ICFO researchers Dr. Marcin Płodzień (also NAWA Bekker 2020 Fellow) and ICREA Prof. Maciej Lewenstein, in collaboration with Prof.Jan Chwedeńczuk from the University of Warsaw and Prof. Emilia Witkowska from the Institute of Physics, Polish Academy of Sciences, have shown that massively correlated quantum many-body states could be generated through current ultracold bosons in optical lattices experiments, using the One-Axis Twisting protocol (OAT) known for generating spin squeezed states.

Spin squeezing states

While entanglement shows how correlated particles can be, spin squeezing is a phenomenon that occurs in a system of particles with a shared quantum state, such as a group of atoms or ions. It involves decreasing as much as possible the uncertainty in the measurement of one of the observables, or “spin” variables, at the expense of increasing the uncertainty in the measurement of the other variables involved.

One-Axis Twisting Protocol (OAT) for Spin Squeezed States

One of the most well-known methods for generating squeezed entangled states is the one-axis twisting protocol (OAT). It can be implemented using various ultra-cold systems interacting through collisions or atom-light interactions and it was well understood that it creates many-body entangled states and two-body Bell correlations.

Novel Insights from the Research

Researchers showed that the one-axis twisting also serves as a viable resource for powerful many-body Bell correlations. They presented a systematic analytical study of creating many-body Bell-correlated states during one-axis twisting dynamics in two-component bosonic systems. They provided the critical time at which the many-body Bell correlations emerge together with a simple yet powerful formula for characterizing the depth of the Bell correlations and entanglement, then applied these findings to classify the generation of many-body Bell correlations in systems of two-component bosons loaded into a one-dimensional optical lattice.

Practical Implications of the Study

The results of this study show that current technology can create such correlations. This holds great importance for potential applications, as Bell correlations can boost the precision of quantum sensors or improve the security of quantum cryptography protocols. Creating such ultra-non-classical many-body states holds fundamental relevance, especially in light of the recent Nobel prize awarded for pioneering studies of such phenomena.

 

Cited article: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.129.250402

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Misha Ivanov invited to ICFO to give a talk about Attosecond control of electron dynamics in simple and strongly correlated materials

As part of the Light for Graphene (L4G) seminars on December 12th, 2022, ICFO welcomed Mikhail Ivanov, who delved into processes associated with electron dynamics in correlated materials. Professors Maciej Lewenstein and Jens Biegert graciously hosted the session. Below, you’ll find details encompassing the abstract of the discussion alongside Dr. Ivanov’s professional trajectory.

Abstract:

Attosecond spectroscopy and strong light fields boldly embarked into solid-state physics about a decade ago.

Throughout this decade, we have come to appreciate that strong light fields drive electrons in solids not solely on the time-scale of the pulse envelope but also on the sub-cycle time scale. This control over light oscillations and polarization at the sub-cycle level presents intriguing opportunities to manipulate electronic responses on a sub-femtosecond time scale. Furthermore, I will exemplify these opportunities with a series of cases, ranging from PHz valleytronics in graphene to attosecond spectroscopy of the 2D Hubbard model.

Should time permit for the preparation of new slides, I intend to shift the focus entirely towards discussing our latest findings. These findings delve into resolving the mystery of insanely fast 1 fsec dephasing times in strongly driven solids and probing the enigmatic behavior of not-so-massless, massless Fermions in Weyl semimetals.

Biography:

Education and Early Career

Mikhail Ivanov heads the Theory Department at Max Born Institute and also holds a Professor position in the Department of Physics at Humboldt University.

Born in the USSR and educated at Moscow State University, Misha left Moscow within a year after the USSR ceased to exist.

International Work Experience

Since then, he has worked extensively in Canada, Poland, the UK, and Germany. Currently, he leads the Department of Theory at the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy in Berlin, alongside his professorship at Humboldt University Berlin.

Current Positions and Affiliations

Despite his global journey, Misha maintains his professorial role at Imperial College London due to his fondness for the city. Additionally, he holds a visiting professor appointment at the Technion in Haifa, Israel, reflecting his deep affection for the country.

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High Harmonic spectroscopy unveils the phase transitions of high-temperature superconductors

Researchers from ICFO, ICMAB-CSIC and Guangdong Technion-Israel Institute of Technology have developed a new methodology to investigate and measure the quantum phase transitions of a high-temperature superconductor by using High Harmonic spectroscopy.

Exploring Superconductors

Superconductors are materials that exhibit the ability to conduct electricity without any resistance. This phenomenon occurs in materials when they cool below the so-called superconductor transition temperature, often at very low temperatures (a few degrees above absolute zero). Among these materials are the so-called high-temperature superconductors, which function as superconductors at temperatures above 77K (the boiling point of liquid nitrogen). Researchers have found these materials to be crucial in developing new electronic and information processing devices, as well as optical quantum computers, and even in improving the efficiency of electrical transmission lines.

Challenges in Understanding High-Temperature Superconductivity

However, scientists have observed that high-temperature superconductivity closely relates to controlling their microscopic dynamics. So far, detecting the various microscopic quantum phases in these complex materials has proven quite challenging. Not only do these dynamic states have incomplete physical processes due to their wide array of quantum states, but the current methods used to explore their dynamics at microscopic scales lack sensitivity. Therefore, researchers need new tools to better understand the dynamic evolution of these types of superconductors.

Now, in an international study, ICFO researchers Utso Bhattacharya, Ugaitz Elu, Tobias Grass, Piotr T. Grochowski, Themistoklis Sidiropoulos, Tobias Steinle, and Igor Tyulnev, led by ICREA Professors Jens Biegert and Maciej Lewenstein, in collaboration with ICMAB-CSIC researchers Jordi Alcalà and Anna Palau, and Marcelo Ciappina, from the Guangdong Technion-Israel Institute of Technology, proposed a new methodology based on the use of High Harmonic spectroscopy (HHS) to investigate the transitions between the different phases of  YBCO, a copper oxide cuprate material which is a well-known high-temperature superconductor. This study represents a major scientific breakthrough since it is the first time that highly non-linear and non-perturbative diagnostics/detection methodology is used to understand the behavior of strongly correlated materials.

Experimental and Theoretical Innovations

In light of the experimental results, the researchers surpassed expectations and presented a new theoretical model to identify the connection between the measured optical spectra and the transition between the different quantum states of YBCO: strange metal, pseudogap, and superconductor. The study, recently published in the journal PNAS, showcases their findings.

In their experiment, the researchers used 100nm thick films of YBCO mounted on a micro-refrigerator. They first characterized the superconducting properties of the YBCO films and confirmed their quality. Then, using ultra-short infrared laser pulses, they induced high harmonics generation in the material samples, which they placed inside a vacuum chamber and cooled to a temperature of 77K.

High Harmonics are the high-energy photons emitted by the electrons of a system when it experiences a strong laser field. These emitted photons have a frequency many times that of the driving laser field.

Upon hitting the surface, they recorded the reflected radiation with a spectrograph to study the harmonic spectrum. This spectrum contains the imprints of this nonlinear optical response and has a connection with the phase transitions.

Theoretical Modeling

Observing these experimental results in the lab and the absence of a theory that could explain what they were observing, the researchers developed a new strong-field quasi-Hubbard model to shed light on the connections between the measured high harmonics and the formation of Cooper pairs, that is, the paired electrons responsible for the superconducting phase.

When applying this new theoretical model, the theoretical calculations of the high harmonic spectra obtained matched the experimental data. “The model faithfully reproduces the functional form of the measurement data over the entire temperature range and for several orders of magnitude of harmonic amplitude,” the authors highlighted. This new approach, as they noted, has allowed a theoretical connection between the measurements and the underlying microscope dynamics, providing a “powerful new methodology to study the quantum phase transitions” in correlated materials.

Finally, the team emphasizes that their work offers a “first striking example” of how High Harmonic Spectroscopy can distinguish correlated phases of matter. They also believe that it paves the way for a “refined understanding of the physical processes occurring inside high-temperature superconductors”.

Acknowledgements

We thank V. Kunets from MMR Technologies and X. Menino at Institut de Ciencies Fotoniques for technical support and Dr. K. Dewhurst and Dr. S. Sharma for help with the ELK code. J.B., U.E., T.P.H.S., T.S., and I.T. acknowledge financial support from the European Research Council (ERC) for ERC Advanced Grant “TRANSFORMER” (grant 788218) and ERC Proof of Concept Grant “miniX” (grant 840010). J.B. and group acknowledge support from FET -OPEN “PETACom” (grant 829153), FET-OPEN “OPTOlogic” (grant 899794), EIC-2021-PATHFINDEROPEN “TwistedNano” (grant 101046424), Laserlab-Europe (grant 654148), Marie Sklodowska-Curie ITN “smart-X” (grant 860553), Plan Nacional PID-PID2020-112664GB-I00-210901, AGAUR for 2017 SGR 1639, “Severo Ochoa” (grant SEV-2015-0522), Fundació Cellex Barcelona, the CERCA Programme/Generalitat de Catalunya, and the Alexander von Humboldt Foundation for the Friedrich Wilhelm Bessel Prize. U.B., T.G., P.T.G., and M.L. acknowledge funding from the ERC for ERC Advanced Grant NOQIA; Agencia Estatal de Investigación (R&D project CEX2019-000910-S, funded by MCIN/AEI/10.13039/501100011033, Plan National FIDEUA PID2019-106901GB-I00, FPI, QUANTERA MAQS PCI2019-111828-2, Proyectos de I+D+I “Retos Colaboración” RTC2019-007196-7); Fundació Cellex; Fundació Mir-Puig; Generalitat de Catalunya through the CERCA program; AGAUR grant 2017 SGR 134; QuantumCAT U16-011424, cofunded by ERDF Operational Program of Catalonia grant 2014-2020; EU Horizon 2020 FET-OPEN OPTOLogic (grant 899794); National Science Centre, Poland (Symfonia grant 2016/20/W/ST4/00314); Marie Skłodowska-Curie grant STREDCH 101029393; “La Caixa” Junior Leaders fellowships (ID100010434); and EU Horizon 2020 under Marie Skłodowska-Curie grant agreement 847648 (LCF/BQ/PI19/11690013, LCF/BQ/PI20/11760031, LCF/BQ/PR20/11770012, and LCF/BQ/PR21/11840013). P.T.G. acknowledges the Polish National Science Center grants 2018/31/N/ST2/01429 and 2020/36/T/ST2/00065 and is supported by the Foundation for Polish Science. Center for Theoretical Physics of the Polish Academy of Sciences is a member of the National Laboratory of Atomic, Molecular and Optical Physics. A.P. and J.A. acknowledge support from the Spanish Ministry of Economy and Competitiveness through the “Severo Ochoa” Programme for Centres of Excellence in R&D (grant SEV-2015-0496), SuMaTe project (RTI2018-095853-B-C21) cofinanced by the European Regional Development Fund, and the Catalan Government grant 2017-SGR-1519. Supported by EU COST action NANOCOHYBRI CA16218. M.C. acknowledges financial support from the Guangdong Province Science and Technology Major Project (Future functional materials under extreme conditions – 2021B0301030005).
We also acknowledge the Scientific Services at Institut de Ciència de Materials de Barcelona and ICN2.
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Entanglement reveals itself to Attosecond physics

Entanglement

Researchers from ICFO and Aarhus University report in Nature Communications a novel technique that uses orbital angular momentum to detect entanglement in the attosecond regime.

The Significance of Entanglement in Quantum Physics and Attosecond Physics

Entanglement is one of the sweet words we listen to lately when referring to quantum physics. It has provided staggering results in quantum simulations and computing, proving to optimize time in calculations, or even enhance imaging processes. In addition, attosecond physics is the field of physics that studies processes that occur in matter on the scale of attoseconds, i.e. 10-18s the time it takes for electrons to move through atoms and molecules. The combination of entanglement techniques and attoscience has led to a new field where attosecond imaging methods exploit quantum phenomena like interference, however, the role of entanglement remains unclear/unexplored.

Recent Advances in Studying Entanglement in Attoscience

Now, the potential for entanglement to optimize or improve attosecond imaging has been unexplored so far because, among other things, scientists never assumed that it would have such a leading role in the process. However, in recent years, there has been a growing interest in entanglement in attoscience, with the main focus on the entanglement between electrons and ions, revealing a connection between them that allows better understanding of coherence. Most of the focus has been on the connection between electrons and ions, but studies on the entanglement between two ionized electrons have received less attention. And those few studies that have tackled the issue have based their work on the entanglement of continuous quantities, which are challenging to compute and interpret, and often impossible to measure.

Demonstrating Entanglement through Electron Vortex States

In a recent study published in Nature Communications, ICFO researchers Andrew S. Maxwell, who then transferred to Aarhus carrying this study, and ICREA Prof. at ICFO Maciej Lewenstein, in collaboration with Lars Madsen from Aarhus University, have shown that the production and measurement of electron vortex states, which are free electrons with helical wavefront that may carry orbital angular momentum (OAM), offer a solution to the above problems.

Quantifying Entanglement and Developing Detection Methods

In their study, they exploit the discrete degree of freedom, the OAM—inherent to all free particles, to clearly demonstrate the manifestation of entanglement in non-sequential double ionization (NSDI), a highly correlated two-electron ionization process. Through known conservation laws and the superposition of intermediate excited states, they demonstrate that the OAM of the two ionized electrons in NSDI is in fact entangled.

They then use the logarithmic negativity as a way to quantify the entanglement for a wide range of targets and parameters. They construct an entanglement witness, which provides a novel way for detecting the entanglement in an experiment in a much simpler way, avoiding full tomographic measurements. The interplay of intermediate excited states allows the photoelectrons to approach maximally entangled states. Furthermore, the entanglement is robust as it survives incoherent averaging over the focal volume of the laser.

Implications of OAM Entanglement for Attosecond Imaging

The use of this new technique involving OAM in attosecond processes provides a new pathway for improving imaging techniques and learning how to control matter on ultrafast times scales. Furthermore, the OAM entanglement of the photoelectrons demonstrates the fundamental non-classical nature of NSDI.

Schematic illustration of the non-sequential double ionization (NSDI) phenomenon involving the highly correlated two-electron ionization process.

(a) NSDI process depicted for the EI and RESI mechanisms. Interaction via the field (e.g. tunnel ionization) is depicted by a dashed line, excitation in the singly charged ion is denoted by dotted lines, while the recollision and OAM sharing is denoted by the yellow spark. The two-electron states are defined in the paper (b) The excitation pathways in RESI, which lead to different final OAM states and an entangled superposition.

 

Links

Link to paper

Link to the research group led by ICREA Prof. at ICFO Maciej Lewenstein

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Probing the properties of matter with high harmonic generation spectroscopy

Probing the properties of matter

High Harmonic Generation and Attosecond Spectroscopy

Observing how molecules bend, stretch, break, or transform requires sub-atomic spatial and few-femtoseconds temporal resolution. The emergence of High Harmonic Generation (HHG) not only enabled the development of attosecond table-top technology but also opened a new route towards attosecond spectroscopy which carries angstrom-scale spatial resolution, making high harmonic generation spectroscopy one of the most prominent tools to understand details about the structure and dynamics of composite, quantum, organic materials.

Light-Matter Interaction at Low and Hight Intensity

When light interacts with matter, it allows us to observe, probe and understand how matter behaves and works. If the intensity of the light that interacts with matter is low, three main things can happen: the matter absorbs the light, affecting the electrons of the atoms that compose the material, it transmits it or it reflects it. In any of these interactions with light, the electrons within the atoms that form the matter are only slightly perturbed by this light, undergoing quantum transitions from one energy level to another.

But what happens if the light becomes more and more intense? The conventional picture of light-matter interactions changes completely. When intense light interacts with matter, it reshapes the properties of the material,  modifying its electronic and optical properties to a point where it can dramatically change the band structure of a crystal.

In a recent study published in Nature Photonics, researchers Álvaro Jimenez-Galan, Olga Smirnova and Misha Ivanov from Max-Born-Institut in Berlin, in collaboration with researchers from Weizmann Institute in Israel, Stanford University, and the Instituto de Ciencias de Materiales de Madrid (ICMM), demonstrate the link between nonlinear matter interactions in strongly driven crystals and the sub-cycle modifications in their effective band structures.

Findings from Two-Colour HHG Spectroscopy

In their study, the team of scientists was able to use two-colour HHG spectroscopy to show that sub-femto-second variations of the electric field of the incident light-wave can generate a rapidly changing voltage that leads to sub-cycle modifications of the band structure of the material, which can drive changes in its macroscopic properties such as transmittance and conductance.

Their theoretical and numerical results carried out with HHG spectroscopy are capable of identifying the dynamical transitions between the conduction bands of the material as well as probing their structural dependence (in this case materials with large bandgaps, such as MgO). This opens a new window for the observation of new electronic phenomena in novel materials.

Link to the paper

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Abelian-Higgs mechanism in 1+1 dimension

A team of researchers has uncovered hidden gems lurking behind the Abelian-Higgs model in one spatial dimension and time.

The Promise of Quantum Simulators

While universal fault-tolerant quantum computing with error correction remains elusive, special-purpose quantum computers, i.e. quantum simulators, hold the future. Although the physics community strongly believes that quantum simulators have already led to quantum advantage, especially in studies of quantum dynamics and quantum disordered systems, there are no rigorous proofs yet. Moreover, most of the applications of quantum simulators have concerned models of condensed matter physics. However, this paradigm is beginning to change. Increasingly, impressive applications to quantum chemistry and optimization problems are emerging. In physics, the current focus is on quantum simulation of fundamental models of high energy physics: Lattice Gauge Theories and Quantum Field Theories.

The Higgs mechanism is an essential ingredient of the Standard Model of particle physics that explains the ‘mass generation’ of gauge bosons. While its seemingly simple one-dimensional lattice version may serve as an interesting novel quantum simulator, until now, researchers had not explored it.

New Insights from Recent Research

In a recent study published in Physical Review Letters, Titas Chanda with Jakub Zakrzewski from Jagiellonian University in Cracow, Luca Tagliacozzo from the Institute of Fundamental Physics IFF-CSIC and ICREA professor Maciej Lewenstein from ICFO took up the challenge to fill this gap. Unlike the system in the continuum, researchers identified two distinct regions in the lattice version. Specifically, they found the confined and Higgs regions. Moreover, these two regions are separated by a line of first-order phase transitions that ends in a second-order critical point. Furthermore, above this critical point, the regions are smoothly connected by a crossover. Additionally, the presence of a second-order critical point allows researchers to construct an unorthodox continuum limit of the theory described by a conformal field theory (CFT). This work strongly motivates current prospects of quantum simulations of quantum gauge theories and opens a path toward observing the Higgs mechanism in experiments with cold atomic setups.

Cited article: Titas Chanda, Maciej Lewenstein, Jakub Zakrzewski, and Luca Tagliacozzo. Phase Diagram of 1+1D Abelian-Higgs Model and Its Critical Point. Phys. Rev. Lett. 128, 090601

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