Periodic Reporting for period 4 - QUENOCOBA (Quantum Emitters in non-conventional baths)
Reporting period: 2022-03-01 to 2023-02-28
The field of Quantum Optics investigates the interaction between light and matter at the fundamental level. There, emitters (typically atoms) absorb and emit light (photons), giving rise to many phenomena that we observe in our lives. Furthermore, this simple process is at the basis of many devices, ranging from lasers to the most sophisticated medical tools. It also plays a crucial role in the development of new applications, like quantum computers, quantum communication devices, or quantum sensors.
In very recent years, technological advances have allowed us to trespass microscopic frontiers and enter a new dimension in the interaction of light and matter. Now it is possible to put atoms close to some dieletric materials (isolators), where they behave in a completely different way to what it has been observed so far. In particular, if one is able to write some microscopic structures on that material (yielding, what is called, a photonic crystal) atoms absorb and emit photons in a very different way as in free space. For instance, one atom (emitter) can emit and reabsorb a photon many times before it finally reaches out, or several of them can interchange one photon, giving rise to effective atom-atom interactions. One speaks of a “structured” bath for the emitter, in the sense that the density of states, that defines how photons move in the photonic crystal, has unconventional properties. In fact, we know neither what new phenomena can occur in this situation, nor how to describe them theoretically.
The problem addressed in QUENCOBA is precisely to investigate this QUantum Emitters in NOn-COnventinal BAths and to extend the theory of Quantum Optics to this new and complex scenario. It also aimed at developing the theoretical and computational tools to address the difficult problems that arise in the description of those experiments, as well as to harness those new phenomena to build better quantum devices. Although this project dealt with basic science, as it aimed at understanding fundamental processes that occur under special situations, it also developed the theoretical and computational techniques that are required to build such devices.
The overall objectives of the project were: (i) to develop the theoretical tools required to investigate this new area of research; (ii) to explore and characterize novel phenomena and to develop the analytical and computational techniques required for that; and (iii) propose and analyze other physical setups where those phenomena can be observed and exploited (in the context of quantum information and simulation). The research involveed the development of innovative techniques to describe new scenarios in quantum optics and many-body physics, as well as research on atoms interacting with photonic crystals, in optical lattices, and quantum dots interacting with surface acoustic waves.
In conclusion, we have investigated how atoms interacting with engineered baths give rise to novel phenomena, like the absence of emission of photons or the emission in very peculiar patterns. These phenomena can be observed experimentally, and could be harnessed in different ways, for instance to obtain better quantum photon emitters, or to address difficult problems in chemistry. Along the way, we have introduced new methodologies to deal with complex situations and developed a variety of computational methods that may be used in other contexts, like condensed matter or high energy physics.
In very recent years, technological advances have allowed us to trespass microscopic frontiers and enter a new dimension in the interaction of light and matter. Now it is possible to put atoms close to some dieletric materials (isolators), where they behave in a completely different way to what it has been observed so far. In particular, if one is able to write some microscopic structures on that material (yielding, what is called, a photonic crystal) atoms absorb and emit photons in a very different way as in free space. For instance, one atom (emitter) can emit and reabsorb a photon many times before it finally reaches out, or several of them can interchange one photon, giving rise to effective atom-atom interactions. One speaks of a “structured” bath for the emitter, in the sense that the density of states, that defines how photons move in the photonic crystal, has unconventional properties. In fact, we know neither what new phenomena can occur in this situation, nor how to describe them theoretically.
The problem addressed in QUENCOBA is precisely to investigate this QUantum Emitters in NOn-COnventinal BAths and to extend the theory of Quantum Optics to this new and complex scenario. It also aimed at developing the theoretical and computational tools to address the difficult problems that arise in the description of those experiments, as well as to harness those new phenomena to build better quantum devices. Although this project dealt with basic science, as it aimed at understanding fundamental processes that occur under special situations, it also developed the theoretical and computational techniques that are required to build such devices.
The overall objectives of the project were: (i) to develop the theoretical tools required to investigate this new area of research; (ii) to explore and characterize novel phenomena and to develop the analytical and computational techniques required for that; and (iii) propose and analyze other physical setups where those phenomena can be observed and exploited (in the context of quantum information and simulation). The research involveed the development of innovative techniques to describe new scenarios in quantum optics and many-body physics, as well as research on atoms interacting with photonic crystals, in optical lattices, and quantum dots interacting with surface acoustic waves.
In conclusion, we have investigated how atoms interacting with engineered baths give rise to novel phenomena, like the absence of emission of photons or the emission in very peculiar patterns. These phenomena can be observed experimentally, and could be harnessed in different ways, for instance to obtain better quantum photon emitters, or to address difficult problems in chemistry. Along the way, we have introduced new methodologies to deal with complex situations and developed a variety of computational methods that may be used in other contexts, like condensed matter or high energy physics.
The main results of the project are:
• The analysis of one and few quantum emitters coupled to structured baths modelled by tight-binding models in one (linear), two (square), and three (cubic and other configurations) dimensional lattices. Derivation of non-conventional long-range models.
• In a honey-comb lattice in two dimensions, the effective model has true long-range interactions decaying inversely proportional to the distance without an exponential overall correction.
• In a topological bath (defined by the so-called SSH model) in one dimension, chiral bound sates appear, and mediate a very non-conventional spin model with, eg, a double Neel phase.
• In a fermionic bath (i.e.. similar to the Kondo model), the dynamics can be understood as a renormalization group flow.
• In a waveguide, one can efficiently generate multi-photon Fock states which can be used in metrology applications.
• Proposals for experimental observation of the emerging phenomena with atoms close to photonic crystals, cold atoms in optical lattices, Rydberg atoms in Bose-Einstein condensates, or electrons in magnetic traps.
• A proposal for quantum simulation of chemistry compounds with cold atoms in optical lattices.
• A new technique to measure Renyi entropies in many-body systems.
• A computational variational method for many body system based on Gaussian and non-Gaussian states.
• A computational method to analyze quantum emitters interacting with two dimensional many-body reservoirs or disordered systems based on tensor networks.
• A computational method for quantum problems combining tensor networks and Monte Carlo techniques.
• A computational method for quantum problems combining machine learning and tensor network techniques.
• The introduction of Field Tensor Network states, i.e. Tensor networks in the continuum.
• The proposal for the creation of highly entangled photonic states using Rydberg atoms, atoms close to dielectric, and superconducting devices.
• The analytical result describing super-radiance in the thermodynamic limit, a text-book problem for which only certain approximations existed.
• The experimental simulation of quantum chemistry using quantum dots.
• The extension of methods used to find many-body ground states to finite temperature and its application to systems in lattices.
The results give a quite complete picture of the physical phenomena that occur when atoms interact with a structured bath, including non-Markovian, individual and collective behavior. They also provide some possible applications in designing and engineering quantum photonic states, or in simulating complex properties of chemical compounds. At the same time, new methodologies have been developed that allow to treat many-body quantum systems in scenarios that where that was not possible thus far.
The work performed in the project allowed us to successfully reach all the objectives. It gave rise to 128 publications, all of them in leading international journals including 1 Nature, 1 Nature Communications, 25 Phys. Rev. Lett, 5 in Phys. Rev. X and 5 in Phys. Rev. X Quantum. Part of the work was done in collaboration with other scientists, including some experimentalists.
The work has also been presented through more than 50 contributions to international conferences and summer schools as well as seminars and colloquia in many universities and research centers. In addition, the results have appeared in 20 public lectures and 10 times in TV, video channels and newspapers. Some activities are highlighted in "Dissemination and Outputs".
• The analysis of one and few quantum emitters coupled to structured baths modelled by tight-binding models in one (linear), two (square), and three (cubic and other configurations) dimensional lattices. Derivation of non-conventional long-range models.
• In a honey-comb lattice in two dimensions, the effective model has true long-range interactions decaying inversely proportional to the distance without an exponential overall correction.
• In a topological bath (defined by the so-called SSH model) in one dimension, chiral bound sates appear, and mediate a very non-conventional spin model with, eg, a double Neel phase.
• In a fermionic bath (i.e.. similar to the Kondo model), the dynamics can be understood as a renormalization group flow.
• In a waveguide, one can efficiently generate multi-photon Fock states which can be used in metrology applications.
• Proposals for experimental observation of the emerging phenomena with atoms close to photonic crystals, cold atoms in optical lattices, Rydberg atoms in Bose-Einstein condensates, or electrons in magnetic traps.
• A proposal for quantum simulation of chemistry compounds with cold atoms in optical lattices.
• A new technique to measure Renyi entropies in many-body systems.
• A computational variational method for many body system based on Gaussian and non-Gaussian states.
• A computational method to analyze quantum emitters interacting with two dimensional many-body reservoirs or disordered systems based on tensor networks.
• A computational method for quantum problems combining tensor networks and Monte Carlo techniques.
• A computational method for quantum problems combining machine learning and tensor network techniques.
• The introduction of Field Tensor Network states, i.e. Tensor networks in the continuum.
• The proposal for the creation of highly entangled photonic states using Rydberg atoms, atoms close to dielectric, and superconducting devices.
• The analytical result describing super-radiance in the thermodynamic limit, a text-book problem for which only certain approximations existed.
• The experimental simulation of quantum chemistry using quantum dots.
• The extension of methods used to find many-body ground states to finite temperature and its application to systems in lattices.
The results give a quite complete picture of the physical phenomena that occur when atoms interact with a structured bath, including non-Markovian, individual and collective behavior. They also provide some possible applications in designing and engineering quantum photonic states, or in simulating complex properties of chemical compounds. At the same time, new methodologies have been developed that allow to treat many-body quantum systems in scenarios that where that was not possible thus far.
The work performed in the project allowed us to successfully reach all the objectives. It gave rise to 128 publications, all of them in leading international journals including 1 Nature, 1 Nature Communications, 25 Phys. Rev. Lett, 5 in Phys. Rev. X and 5 in Phys. Rev. X Quantum. Part of the work was done in collaboration with other scientists, including some experimentalists.
The work has also been presented through more than 50 contributions to international conferences and summer schools as well as seminars and colloquia in many universities and research centers. In addition, the results have appeared in 20 public lectures and 10 times in TV, video channels and newspapers. Some activities are highlighted in "Dissemination and Outputs".
The state of the art and context of the project is described in the summary above. All the main results of the project, outlined in the previous question, correspond to progress beyond the state of the art. The major breakthrough was the proposal for simulation of quantum chemistry problems. In the section "Major Achievements", we explain in more detail how this and other main objectives of the action were reached.