 ki lahko so imeli mojjo zelo, da je narodno v nenekelibrimi in kondensimetr materijali. Sveto, da. OK, poječe. Zelo je dopljavno, da sem tudi tudi ozvo. I da sem razobljala organizacija, da se tudi priče začim, da se je odrečal zala. V sej ideji, je to, da sem zašličil, da sem si tudi vsemisla, da so vse seminarje odličil pravni sepennik na sebe. To je da bom na njih ne izorjeva, ker vse na njih ne zelo, da sem zašličil, da sem ni počela, ali sem sem zelo vzelil. OK, so mi zelo naredite na kako še, da je začetne odpravljene pravje in naštrih neko vyskotir, tako so bilo zelo vzivni, in jaz, da bih počkati, pa prišličo mi tudi, in prišličaj, da je začetna daj. Kaj je izgleda, da bo, ki se zelo? Znamo kaj je tudi? So, our interest is complex quantum materials. Complex quantum materials are those where the macroscopic functionality is determined by the non-trivial interplay between the different matter constituents, so like spin electrons or any kind of material degrees of freedom is at play, and the interaction between the different degrees of freedom is the key to understand ima štri poslutnja. Ta sebe, ki se bo, na vseh neštačnjvskej djiž, nekaj ne Paradise Agreement, je taj začival, nemeč vse djižga, še je trafina. Ta je taj začivala, ki se težko izgleda vstavna je vsega častčen vine o drugeh poslutnja, a štri prisodfina in se terkosti. Kaj smo zelo, in pri templatei, kaj je napravil naziv in se kako je ideja? Najbolj ideja je, da boš vzela svoje dvije zvrdu razkazovih zopradi, zato je, da boš vzela svoje zvrdu razkazovih zopradi in pri zelo z izgledovim dinamizim, co nalakamo spodljučenih mekat unboxenih stabilizaj. Tukaj, pri občastenju je ta semena prišel ima bi tukaj inapravlju vsakje... Tako, smirlj. Isak je bomo? Myslim, da so je sp ا数rednji četav, če svetem, ne občasem so, da bi bil inapravlju vši počen, da tukaj potrebe ga dotrebe v anecdopu. Tukaj, pri tukaj semena je pošel, in s nekaj čin bom umožela, da presume, da pošlivamo, nekaj če ima v čas, da je zala.ンno mi je daness, da je mužem. In prvič mu ja. Vsem premačama do tem, da pa ne zahrašimo, da zahrašimo, na nekaj č exchangesu celim začicationom, če smo pošliveni na mbez. Pa cavo se iz takvo je, da ne ne nehrašimo, da je ne ne ne ne. včasni bolj. Zelo začinaj, da se očimamo, in energij, da bodo se načinati, kako so rečene, Kaj je rečeno začinati na temperatur, ali da bodo se plati, da je dominatel v srednjih dobrov, ne sredno trakujemo v zelo. V zelo to trakujemo, Tukaj je najbolj različen ver, ki je vse zelo. Vzelo je srednje, da sem vzela, ki je vzela, da so prizela, kaj ima se, da je zelo, izvala je vzela, in da je to izvala, ki je na vzela na vzela, in da je za hrešno energijo, da ne bo bilo vse tezmi. Vzela je, da se početil, koliko je srednjemne zelo, Are the dominant degrees of freedom in matters. For instance, how vibration affect the dynamical response of a system, how magnetic excitation and how electronic excitation can determine these physical properties. So the range that we are interested in is the range in which we want to study how phonons and spin excitation or free electrons in materials evolve in time. Tako, imamo spetroskopi, ki je v taj skala 10, 12, 15, 18 sekund, ki ima 1 milijon, 1 milijon sekund. Tukaj, tukaj smo od taj skala, ki je 3 odličenje, tukaj 3 odličenje, tukaj 3 odličenje, tukaj 3 odličenje, tukaj 3 odličenje. Kaj smo sekundi izgovorili? Tukaj izgovorili praktite, ki jo izgovorili, kako se svoje despohni v svojem ga remembersi, je programa z Pampem Pro, kaj smo benavno izgovorili veček kjava pa včak bolj zdobu so vsoj, kaj si vsoje skupajili zelo svoje sekundi. A je tako začingo, da je še v tamah za 10 sekund. Tako sem zresil danes, jezda imamo, da smo zresili 1 zrp. kaj jezda inamcialne stražice, s kajımı tako prikoredne, pa njih zelo vzelo na delaj z kako to je materija evolveti v pomečno. Na razduženju vzelo v tukaj, taj poživ, in na kako smo iznosili, da je tega postavlja najskega poživina, zelo v minus 15 in tukaj minus 14 sekund. Tako, tega je, da se prišljamo, je to počet, da je to druga generačna ideja z našim in prospečni pedroskopi. Zelo, ki so bil poslednji, da je ozala materija in taj generacijen skim o potravljenju in vživljenju. Však to je, da je začala in tudi v ljudeh kronijne formi, in je za to, da imam nekaj teorični teorič načo to. Prihlej je tudi a všim velim komunite, kaj prihlejte vse od svojih nekaj vsehtovstv standarov spetroskopijov, ko sebetweenovajo, vzivno vzivno vzivno vzivno. Zelo, da je vse tegniči, v kjer bi se vse opetite všeče vse materijali, ali tudi tegniči, kaj bi si vse tegniči sradi in vzivno vzivno vzivno vzivne in vzivno. Zato bi se vse vseči vzivno vzivno vzivno. In zelo, da bi se vseči vzivno vzivno vzivno. Zato bi se vseči vzivno vzivno vzivno vzivno. kaj je jaz vse potrečenje, ko je prišeljete, je to ne potrečenje, je elektrona in je to zelo taj nekaj rešel, taj nekaj rešel elektron, elektrona Petroskopi, kaj se je težko težko, nekaj rešel elektroni, in je vse zelo vse vse elektrona, in je taj rešel elektrona, da je vse elektrona, je to početne, nekaj rešel elektroni, ali po limi, da se potrebno z legovali za subpecoseckunje in varječenje se na svetu elektronikov tem, ko je se potrebno z bilimi, da je v tem razrečenje se abežite zlicezesenje vzkladijo vokonultovali, nekaj se sanerati s reprešelnoj, po svetu mikroskopi. Hvala je, da se potrebno in termodynamics in ful, so that there's a whole lot of available spectroscopy that now can give a lot of answers on the dynamic response on complex materials. So this is to focus on what can we measure. So whenever you do pump and probe, the idea is that you use light to perturb and light to measure, and I've shown that essentially we have available most of the observables nowadays. But also what is key, in my opinion, is what are the degrees of freedom that we can drive, so that essentially you can also ask yourself, in all these dynamical probes of matter, I always use photo excitation as a tool to drive matter out of equilibrium. And what are the degrees of freedom in matter, or what are the degrees of freedom that I can drive, I essentially, I have to control the photo excitation entirely. And just to give a little bit of a taste of what you can do, whenever you perturb in this framework matter, you always use light, so you use light in very short pulses, and this is like a sketch of an electromagnetic pulse. So what can you change? You can change many of the standard properties, for instance you can change at which wavelength you drive the material, how long is your pulse, so you can even shape your pulse to some extent. All the classical driving parameters are nowadays relatively easily accessible, and I'll show you how they are relatively easily accessible. But there are also more subtle quantities, which I can change, for instance I can change what is the relative phase between the envelope and the phase of the field, these are also things that we can control nowadays, or eventually I can try to use the statistical properties of light, so I can even try to encode information in the quantum state of the light and retrieve aspetroscopic information from the measurement of the quantum state of the light. And the idea of this first part of the introductory seminar is just to give a little bit of a snapshot on what do we do experimentally, that maybe I'll be probably too trivial, but just so that you have an idea of what we can do. Okay, so this is the way I structure this presentation, so in the first part I will give you just a very general introduction to non-equilibrium optical spectroscopy. I'll go very fast in the sense that I'll just give you some tools, the tools that we have in the lab so that you understand what kind of experiment we can run, how do we run it, and then I'll focus on one observable optical spectroscopy and show you how we can use this optical spectroscopy to unravel dynamical response. In the second part, if I'll have time, instead I will go into something which is dearer to us, so something which is more related to the scientific program that we actually are running now, so the first part is mostly educational, where I will cite old works, the second part is just to give you a snapshot of what are the kind of problems that we are facing now, and essentially we have gone over the 10 years or 20 years time, we have gone from the idea of measuring the dynamical response of the material to the idea of controlling the dynamical response of the material, and we leverage on the knowledge that we acquire through the spectroscopy to try to understand what are the key aspects that we can drive in matter and what kind of effects we can obtain. So, how do we produce short pulses? Well, the idea is that we have relatively easily accessible sources of ultra-short pulses, so pulses which are as long as 10 to the minus 14 seconds, 10 to the minus 15 seconds, and then we need a lot of frequency conversion, and we need a lot of control of amplitude and phase of the spectral component. So, what are the sources? The general concept which it's applied to all the sources that we essentially use in the lab is the concept of mode locking, so that essentially we take a laser cavity, we make it lays on a very broad wavelength range, and then we design our cavity so that the cavity has exactly the same length for all the spectral component, and once we do this, we can favor through some nonlinear interaction in a lazing, which is pulsed, so I can generate very short light pulses. This is all I will tell about the sources because there's a full technology field there which uses these concepts in a very broad way, so this would be the subject to a full seminar by itself. Then, how do we convert the frequency? Generally, we start from very short pulses. The advantage of short pulses is that we cluster all the energy in a very short time, so the fields are very intense, and therefore nonlinearities are very strong, and if I have strong nonlinearities, I can relatively easily convert the frequency of our pulses. One of the typical tricks that we use, we use the fact that the response of normal crystals, they can have nonlinear components, and this is an example in which the nonlinear interaction drives the radiation into very tiny channels, so essentially the nonlinear interaction makes such that the radiation propagates into this material into very narrow filament, and if I can reach this regime, I can actually use a similar nonlinearity, essentially, again, an index of refraction which depends also on the intensity of the light to generate different spectral components so that I can actually start from a light pulse which has certain frequency components, and by reaching a strong nonlinear regime, I can actually introduce other spectral components, so essentially I can destroy photons at a given frequency and create photons at different frequencies so that the frequency can convert my lasers. Again, this is one, rolling over one of the methodology that we can use, but essentially we can use nonlinear optics in many different forms to produce light pulses with very specific properties. Most importantly, we can also produce, we start from pulses which have a relatively narrow spectral component, pulses which have a very broad spectral component, and if you need a good picture for the webpage, this is the kind of picture that we can produce so that we can shine infrared light on some nonlinear crystal, and after the nonlinear crystal, due to the strong nonlinearities, I obtain light which has all the spectral components of this kind. So the other process which we often use is called optical parametric amplification, which is also used in quantum information. We use it in a fully classical regime. Essentially we try to go to saturation so that we can have very stable sources, and some colleague of mine called this the photon cutter, so essentially it's a process which can take a photon at one frequency and convert it into two photons of different frequencies but if I manage to have phase matching condition, I can produce a different frequency in general. So we use this process in many different forms. The typical experiment, this is like a conceptual design of an optical parametric amplifier. The typical experiment is an experiment in which we produce a tiny bit of the spectral component that we want to amplify in one nonlinear process and then in a second nonlinear process we amplify the given spectral component that we want to effectively use in the experiment, and that is the typical conceptual scheme of an optical parametric amplifier that we have in the lab. I say conceptual in the sense that this is just the very basic unit and then depending on what are the frequencies that we want to produce, we need to use and to design a nonlinear process in cascade so that we go from the one given frequency from which we start and we can produce all the spectral component in this way. So this is conceptual design and this is effectively real experiments in the lab where we can produce cascade of nonlinear processes to produce the light pulse that we want. So we use a lot of nonlinear optics where we basically shape all the spectral components so just to make you aware again, the spirit of this seminar is mostly making you aware of what can be done. It is relatively straightforward technology nowadays to take light pulses and control separately all the different spectral components in a light pulse and control essentially entirely the shape of these pulses amplitude and the phase of different pulses so that we can produce arbitrary waveform in a relatively easy way. So the technology to summarize the technology that we use essentially the main building block is modlocking, modlock laser and then we use a lot of nonlinear optics to convert to the frequencies to the frequencies we want and then we shape through linear manipulation of amplitude and phase of a spectral component. I apologize if I will be a little bit if I am a little bit tedious but I just want to especially because the crowd is mostly theorist I think it's important to to make you aware of what can be done so that cross fertilization between theory and experiments is viable. So how do we reason about this problem and the main aspect is equilibrium optical spectroscopy so I will go very fast on this because that's essentially what everybody would have seen already at university so what do we learn from measuring the optical conductivity in this crowd most of the people would use the language of optical conductivity which is the current-current correlation function but of course depending on which community you are and this slide has the purpose of avoid confusion sometimes you hear about the electric function or if you design an optical setup you hear about the index of refraction but these quantities are essentially the same if I have the optical conductivity I can calculate all the other properties and vice versa and going from the intensive property to the extensive property for instance of the reflectivity if I have a sample and I know the optical conductivity I can calculate the reflectivity going from an effective measurement to an intensive quantity requires some carefulness but essentially in optical spectroscopy we have a bunch of recipes which allow us from a real measurement to extract quantities which can be directly compared to calculations in terms of optical conductivity so how do we describe this in a functional way and this is what you learned in the last year of university probably it's the dielectric function of a material you can describe it in terms of a Lorentz oscillator model and the general principle is that if you want to see how a cloud of electron reacts to a stimuli electric field you can apply the electric field and you will drive into the system a polarization and the constant which stays in between the electric field that you apply and the polarization you reach is what we call the susceptibility so how the electron cloud is susceptible to the applying to the field that we apply and how do we describe it if we want to calculate what is the polarization that we obtain we just have to solve a differential equation in which we try to accelerate charges with an electric field charges have a given mass so there is an acceleration there is a key element which is how much do I dissipate energy into the moving of these charges a term which is proportional to the speed of the charges and if the charges are bounded there is a restoring force which tries to drag them back after I resonantly drive I can solve these equations I am very trivial here and I can calculate my susceptibility and this is the essence of the Lorentz oscillator model so whenever I have certain bound charges into the material they will resonate at some specific frequencies at which they resonate is this omega zero and there will be a dissipation which will tell me how efficiently if I drive charges in that oscillator I leave energy into the system so that's the general description of the dielectric function you can plot epsilon 1 and epsilon 2 real and imaginary part and again for educational purposes it should be clear that if I know the real and imaginary part of the optical conductivity I analytically can go to the dielectric function or to the index of refraction these are essentially the same quantity and I can link an intensive property to an extensive one just by measuring the reflectivity so if I know the description in terms of the dielectric function of the material I can be predictive of an experiment so how do I introduce this is true for bound charges how do I introduce free charges and here again I go very fast it's essentially the through the response which I can describe exactly in the same way as I did for a bound oscillator but without the restoring force so I apply a field and I drag around charges and the charges are dissipated the movement of the charges are dissipated with a given scattering rate and I can calculate the optical conductivity in a material so essentially the description of the optical conductivity in terms of Lorentz oscillator and through the response it gives us an intuition it gives us a description of what are the bound charges into the material which are often associated and what are the free charges which are often associated to intra band transitions so the electrons that can move in a metallic state so this is for instance the optical conductivity of a superconducting cooperates where I can clearly see the through the response and all the charge transfer oscillators here ok so these are all standard tools for equilibrium spectroscopy and what does the optical conductivity again this is again for the students what are the optical conductivity I can describe it by introducing bound charges and free charges and the optical conductivity essentially it's telling me if a system is metallic or it's a system is insulator so if it's a finite frequency measurement of the conductivity and if I have a metal typically there is a response at finite frequency and free charges which is not there if there is no free charges in the system I will see the on screen phonon mode do I really use in experiment yes I can really use it in experiment for instance this is a phase transition between an insulator into a metal in one of the prototypical samples that we studied this is a metal insulator transition at room temperature and you see that the changes in conductivity is associated to a change in the conductivity at low frequency which is described by this through the response this is just example of different optical conductivity of high temperature superconductors or correlated materials which have all the same structure one aspect which instead goes a little bit beyond just a very introductory aspect is what happens if I think about a system where the scattering rates depends on frequency and this is what goes under the name of extended through the model where essentially I can take the scattering rate which tells me how three electrons scatters with low energy bosons to dissipate energy after I try to move them with an electric field which stimulate the movement and if I introduce a scattering rate by studying the scattering rate at different frequency I can retrieve what is the for instance what is the coupling between the electrons and lower energy bosons for instance in this case with this bosonic function I can retrieve how the electrons which are driven by a field dissipate energy and if I do things carefully and find some references in this review we wrote you can look at spectrum at the dispersion of the phonon modes which are in your material this is for instance the phonon mode in MGB2 and you can calculate associating that all the phonon will participate to the scattering process of the electrons I can actually calculate time result it's good to measure this so you can actually measure how the electrons dissipate energy and what is the spectra of the bosons which participate to this dissipation of energy so this is true for equilibrium so optical spectroscopy can be viewed in this way as a mean to measure dissipations in matter and the standard tool that we use to study non-equilibrium is to bring the concept of equilibrium spectroscopy to non-equilibrium so what is the idea the idea is that whenever we we want to study this complexity so this, I said this complex interaction which give rise to this very intricate phase diagram I can always think at the different interactions between different constituents in matter as interactions which are subject to a hierarchy of time scales so what does the field do the field drives electrons so the electrons are directly coupled to the fields and there is a certain time scale under which the electron thermalize and the electrons transfer energy on different degrees of freedom which are coupled to the electrons on different time scales and for instance you can think that the electron transfer energy to a subset of strongly coupled phonons or bosons in general and then only at a later time these bosons dissipate energy into the rest of the degrees of freedom of the material so typically you use the fact in non-equilibrium spectroscopy you use the fact that different interactions appears at different time scales so that essentially by studying the relaxation process you can measure how the different degrees of freedom interact and the interesting aspect is that if I manage to write this bosonic function which actually links or tell me how the electrons dissipate energy into the phonon I can associate this response function which I measure at equilibrium and I can directly measure it out of equilibrium because how do I transfer energy from electrons to phonon is governed with weak perturbation by a linear coupling equation where the coupling is also determined by the same bosonic function so how the electrons transfer energy to the different objects to which they are coupled so the rationale of using non-equilibrium spectroscopy and non-equilibrium material is exactly the idea that I can measuring on different time scale I can dissect in time the different leading interactions this is true to some extent and it's true in many system and that was very successful for instance in to measure electron phonon coupling in simple metals so that the electron phonon coupling is directly related the electrons dissipate their energy but of course this is just for us it is often only the starting point in the sense that whenever I write some differential equations in which the different degrees of freedom are coupled I always assume that they are linearly coupled first of all and I assume that whenever I write this coupling function I always have to give certain assumption of what is the distribution of energy in the different degrees of freedom so there is it should be seen in my opinion as a good starting point so whenever next week you will see some effective temperature models for the description of the system you should have in mind that you have different buff of electrons, phonons and spin which exchange energy and the measuring exchange energy can be done by dissecting this dynamics in time so this is the idea and of course there's many limitations and the limitation is that often in complex material you have a free energy landscape with multiple order parameters so non-trivial energy landscapes so that the dissipations are never linear so you can have non-linear interactions between different degrees of freedom to the point that you can even observe metastable phases metastable states which can be reached only through specific non-adiabatic path which I can control with light and of course another aspect which we always throw away it's to what extent are coherences of the different constituents relevant in determining the dynamics because whenever I say I have two thermal buff which exchange energy I always if I write an effective equation I always throw away the effect of coherences and I use only the diagonal elements of the density matrix so this is like the trivial part where we come from and essentially there's like a many example I just picked one which is an old example on how coherences are relevant and this is like the case study for what was called coherent funnel response which is like a classical elastic vibration in the system it was the study of elemental semi-metal which are essentially semi-metals which are elemental crystals in which the physics of one dimensional pyre system is at play and just as snapshot of what is pyres physics so if I have a one dimensional metallic chain this metallic chain is unstable for a distortion at the Fermi vector and that's because the energy cost of a distortion is quadratic while the electronic energy gain is linear with the distortion itself so that a metallic chain is essentially always distorted and unstable and these elemental semi-metals are the 3D version due to the specific geometry of these crystals this one dimensional physics is at play in a three dimensional crystal and the idea of time domain studies here is that if I now take a photon which takes away electrons from the conduction band and sorry takes away electrons from the valence band and put them in the conduction band and essentially reduce the energy gain of having this distortion so that if the electronic relaxation process is fast I can actually drive the system towards the undistorted phase this is like a very well known in literature and this is like it served historically as one of the case study for this kind of physics where there is like a given phonon mode this distortion and if I photo excite the material with a pulse which is shorter than the time scale of the phonon, these are actual real data so you see that as a function of time pump and probe delay I do see very strong oscillations and these very strong oscillations are associated to the fact that I have a vibrational mode at a given frequency which coherently evolve in time so the system here is clearly not in a thermal equilibrium so understanding how the atoms in the different phase of the vibration exchange energy with the electrons can be done in this way and one standard way is to give a githubo landau description of this process so that you can study what is the frequency of the phonon mode as a function of the electron density that you put into the system so if you increase the electron density you reduce the frequency of the phonon mode so this is like this was used historically to study screening and to study how electronic excitation can screen lattice vibrations in these systems going very fast and very long ok, so this is the kind of problem that fill the phase and you will see next week a few seminars about it and one of the aspect is that we want to introduce both time and frequency resolution so that we went from an experiment in which I can study the time evolution of some observable into an experiment where for a given observable I can study the energy response so that I do a full spectroscopic measurement so for a given spectral component I can measure the time evolution of the response or for a given time I can measure the spectrally resolved response and this allowed as and many others in the field to try to understand the time evolution not of simple experimental observables but the time evolution of physical quantities and essentially the idea is that we can use a snapshot of the response as a function of wavelength to measure the and compare to the equilibrium reflectivity so that the equilibrium reflectivity gives us the optical conductivities and if I measure in time domain the response how does the response change in a certain frequency region I can measure how does the optical conductivity change in time so that essentially I could measure the time domain response of of physical quantities so that I can measure the time domain response of certain oscillator and measure the sector dynamics both in frequency and in time ok, so this is what can be done there was here a second example I will just briefly I will leave it here should I go on ten minutes more actually I did only the trivial part I didn't do the so essentially that's the we use this frequency and time resolved response to study how charge transfer excitations is dressed by low energy electronic dynamics and we choose a system in which we do have a clear optical transition the system is insulating is lanthanum copper oxide one of the prototypical examples of of high temperature superconductors and in these systems we studied how the the charge transfer transition reacts to an excitation which has high photon energy so an excitation in which the photon has enough energy to promote the effective jump of the electrons between the oxygen to the copper and we compare it to a situation in which the field can be very strong but the photon energy is not high enough to promote a jump of a charge between oxygen and copper and therefore I have a sort of a diabetic drive of this transition I cut a long story short but essentially this technique allowed us to study how this charge transfer excitation evolve in time here it's the Hamiltonian description of the process but what's interesting of the just I just wanted to give a snapshot again of the result so what's interesting is the fact that whenever I have high frequency field I can directly couple to the electrons and I can promote a transition between different electronic state in the material and if I can do this the dissipation acts on a relatively short time scale so I promote the electrons and the electrons dissipate energy into the phonons at a longer time scale on the other hand if I drive the electrons with a field which whose photon energy is too low to promote this transition then the system tries to accommodate the presence of a strong perturbing field and it accommodates by driving a coherent excitation of the low frequency boson which is the problem but the message here is that I have a lot of degrees of freedom in what is the question I ask to the system in the sense that I can drive materials into different states by producing different excitations and I have a full army of observables which I can use to disentangle or to measure the dynamical response of the material so this was like just an introduction to those who are not familiar to non-equilibrium spectroscopy which I assume is the vast majority of the crowd so if you have questions it's a good moment to ask if you don't have questions I can I can avoid killing you with a full seminar on the mass topics maybe I just give you the taste of what we are doing right now so as I said the idea is that we want to move from the idea of just measuring the non-equilibrium response of materials to the idea of controlling macroscopic functionalities and what do we do so we play this game on complex material essentially for the same reason that I mentioned before that these materials this complex interaction between the different degrees of freedom give rise to intricate phase diagram and how do I read an intricate phase diagram broadly speaking I can always think at the system as if the system is always on the verge of a big change of physical property what does it mean for instance in those materials I just change the temperature a little bit and I go from a superconductor to a bad metal or I just change the doping and I go from an insulator to a superconductor so just a tiny change of some control parameter give rise due to the non-trivial interaction between the metal constituent give rise to macroscopic changes of functionality and we want to leverage on this to obtain optical control so the idea is that the system is always close to a big change of functionality and you want to use light to obtain functionality which you may not be able to obtain by equilibrium transformation or quasi adiabatic transformation so the fact that you can dump energy into specific degrees of freedom allows you to obtain states which are not accessible if I increase the energy adiabatically between all the degrees of freedom of the system so the idea is that photo excitation is a sort of additional control parameter and you can obtain functionalities which you may have or may not have at equilibrium so that there is a non-equilibrium physics in these systems which is actually much more rich than the equilibrium ones so what is the idea? the idea is that if you do have I like the way it was recently summarized in this report so if you do have different degrees of freedom and different order parameters in the system I can use light to go around in an intricate free energy landscape in a non adiabatic way and these people try to cluster this relatively large field of photo induced phase transition into two different kind of dynamics and I try to to give a snapshot of an idea of what are the two fields in one sense you can think of obtaining the control of functionality through dissipative processes so essentially by using an electric field drives electrons and the electrons dissipate energy the energy goes into some specific degrees of freedom and I can obtain new functionality because I have more energy in one degree of freedom than in the rest and this comes in relatively trivial form for instance what I call a thermodynamical transition in which the dissipation is global in the sense that I use the field of material and the material evolves towards its own thermodynamic path on the other hand you can have dissipative control of something which is a little bit more subtle because if I use light to inject energy into some degree of freedom there is no need that these energies dissipate to the rest of the system but I can obtain in this complex free energy landscape I can be locked into some local minimo which I can access only through non-adiabatic paths so I can drive the material the material dissipates the energy in an incoherent excitation of a given degree of freedom and that locks me for instance in metastable states which have a given functionalities that may not be there there are a few examples where this has been revealed and this is a very interesting aspect on the other hand you can think of obtaining a control of functionalities by a direct control of the quantum dynamics in the system and in this respect you have already seen examples of how to use flocade drives of how we use cavity electrodynamics to control the material functionalities but the general idea is that you can either control by using what I would call the diagonal elements of the density matrix of all the different matter constituents so I have some thermal distribution of some degrees of freedom and different temperatures or different energy in the different degrees of freedom allows to obtain a non-trivial thermodynamics and there is a wealth of reported states where metastability can be reached or eventually you can think of using light directly as a control as a control system for driving functionalities so some examples on the trivial thermodynamics response this is like some of our old papers where we've shown that we can induce a metallic state from an insulator but to the best of our understanding the dynamics that we observed here was essentially a dynamics where light did nothing really interesting into the system but just damp energy into the system and then the system evolved towards its own thermodynamics and the thermodynamics when I say its own thermodynamics I mean that the electrons dissipate the energy is very suddenly distributed among all the different matter constituents and then I simply find a sample which is which has more energy than the one I started with and that's the thermodynamics of the response on the other hand there's a few examples and this is one of my own contribution old contributions in which we have shown that auto excitation can even go against thermodynamics and the example of auto induced superconductivity I think it's very interesting in this respect because we have shown that when we shine light onto a non-superconducting system we can obtain a superconducting state which essentially in the example I gave before it means that I start from a bundle of degrees of freedom which are interacting in a very disordered way by shining light I obtain a nice pullover because I reduce the entropy into the system so essentially in the electronic state superconductivity it's a low entropy state so I need to dump the entropy somewhere else and that actually gave rise to a full field of research where there's many theoretical proposals on how this is even possible and to what extent this is possible and we gave many contributions in this line in trying to understand how we can drive order from this order and this is the this is the essence of what we do in different forms we still try to understand how by driving with ultra short pulses we can actually reduce the entropy of the system and I just show in three slide one example and in two slide another and then I'm done so one example where we show that we can drive order from this order it's a paper which we published recently in which we wanted to demonstrate that if we take a very specific excitation so a very specific excitation which is resonant to vibrational modes we can actually by resonantly drive phonon we can control coherently control electronic excitation and if you think about it this goes somewhat against the Born-Oppenheimer approximation because we always think that the electrons are at a diabatic equilibrium given an atomic position but what we do in this experiment we do the opposite because we take a field, we couple to the phonon and we try to gate electronic transition by driving the structure for demonstrating that this was possible we choose a system in which we do have a very clear evidence of electronic transitions here is just a little bit of details but these are electronic transitions this is the optical absorption of my material in the visible range and there is a feature which is in literature associated to the presence of crystal field excitations which is essentially the redistribution of energy between different orbital states on the copper ion the copper ion into the system and this transition should not be allowed optically because they are delta L equals zero transition but they are actually visible in real experiments and the way they are described in literature is that essentially whenever I try to promote an electron between two different crystal fields I can not only promote the electrons but I have to break the symmetry and what breaks the symmetry this transition is a phonon assisted transition so every time I promote an electron between two different crystal fields a phonon comes into the problem breaks the symmetry of the problem and makes this transition allowed so this is like some description of the process in which essentially there is a displacement of the structure which makes the transition allowed and for us this was the ideal platform because if those transitions are really not allowed unless there is a phonon which comes in then if we can control the phonon we can control the electronic transition and we can go against the Born-Oppenheimer approximation so the idea of the experiment was simply to take an electric field which resonantly drives some vibrational mode and to measure on-site crystal field transition between different orbital states on the atoms and what we realized you find all the details in the paper and in the supplementary information what we realized is that indeed if I resonantly drive the structure I can go against thermodynamics because as I said whenever I these are like the same transition I saw before just to make it confused at 5 o'clock in the afternoon I swapped the axis so now the energy axis is here absorption and I told that these transitions are allowed only because there is a phonon that participates into the process and therefore whenever I turn up the temperature I increase the thermal disorder and I make this transition more allowed this is equilibrium observation while if I drive coherently the atomic position I do observe region in which the system is more transparent and not less than at equilibrium which effectively it means that I am coherently controlling the atomic position which is equivalent to cooling certain degrees of freedom of the material which participate into this absorption so essentially I can cool fluctuations in one specific degrees of freedom which makes this transition allowed so this is an example so like this was an example of vibrational induced transparency where it is clear that we went against thermal dynamics and these are the kind of problems that in my opinion they are the most interesting one because you have the complexity of the system and the interaction between the different degrees of freedom which allow you to do much more than you could do with adiabatic transformation in the light pulse because taking a light pulse you can dump energy or coherently drive specific degrees of freedom so you can move around in an intricate energy landscape in a much more controlled way than just by turning on the temperature the global temperature of the system so there are a few examples of this this is another example I will skip the details in this example but the idea of measuring fluctuation is crucial here in the sense that I told you before that if I have an observable which can map the fluctuations in the material I will be able to fully control the thermodynamics of complex material because the energy exchange between the different matter constituents is mediated by fluctuations in the different degrees of freedom so if I can control the fluctuations on the different degrees of freedom I can control the thermodynamics of a complex object so we have developed a series of tools where we combine quantum information protocols with non-equilibrium spectroscopies to try to understand how much or to what extent we can map fluctuations which belong to matter in the light which I can measure and the idea is that I skip this part because we are too long is that I can map fluctuations of the atomic position onto some optical fluctuations and we have developed a series of tools where which allow us to go really inside the material and take out fluctuations which we measure through the light because it's a bit too and finally the last sorry, it's a bit too I was optimistic with this seminar so what this old story brought us so on one hand if we want to induce order from disorder we need to control fluctuations so we developed tools which allow us to measure fluctuations in real time and the latest effort that we are trying to do we are trying to develop methodologies to directly control fluctuations and I think that in this respect the idea of cavity electrodynamics which many people are working on in the last few years it's very interesting because you can control the hybridization between materials and the electromagnetic environment in which this material is immersed so that essentially you can fully control the spectra of your object and we did this and I just flesh out some result but we have shown that we can reach strong coupling but the most interesting aspect is that we took a system in which there is a metal insulator transition so just do a loop of faith here trust me that this is unobservable which tells me if the system that I have in the cavity is metallic or insulator and if I change the temperature I see that I have a phase transition this is a specific property of this sample which I won't discuss here but there is a phase transition which occurs at a given temperature and it brings my system from a metallic state to an insulating state the loop of faith believe me that this feature means it's insulator this feature means it's metallic now I take the same system I place it in between an optical cavity so I place it in between mirrors and what happens this phase transition shifts off about 50 Kelvin seems like a trivial effect but that's actually a very profound effect because it actually means that now if I have a material in between mirrors I can control whether the material is insulating or metallic just by moving the mirrors around and we did this and we have shown that I give just the main message we have shown that we can decide if the system is metallic or insulator just by opening and closing the mirror so we can induce a phase transition between metallic state and insulating state just by closing mirrors and then I can reverse this transition by opening the mirrors again so I can control the phase transition by controlling the electromagnetic environment in which the sample is placed and that's actually the latest results of like a cavity induced phase transition that we can control and I'll be happy to discuss the details of this if you have questions at the end the idea for us is that we are we come, I try to to give in the whole first seminar, I try to give a very broad very general overview of what is the interest in our communities and what are the tools that we use considering that the crowd is not expert and what we where we are we are at the stage in which we have a giant amount of tools in the sense that we have all the spectroscopics the community developed nearly all the equilibrium spectroscopies that are normally available in condensed matter physics in non-equilibrium format so I can study the time evolution of the atomic position through x-ray diffraction, electron diffraction I can study the time evolution of the conductivity through teres spectroscopy I can study in great details everything of the response of the material and we are at the stage in which we have all the tools to manipulate the fields that we use to drive so I've shown we have all the machinery to produce arbitrary waveform and arbitrary wavelength to drive complex materials and now it's time to put things together and try to understand how we can control fluctuations and how we can use a driving to control the thermodynamics of complex materials in this and of course I need to thank all the people who actually did the job that I showed here I didn't do anything ok, yeah thanks a lot and if you survived until 5