Stressing Quantum Dots with Rinaldo Trotta

Pranoti Kshirsagar: [00:00:00] Hi, everyone. Welcome to episode 219 of Under the Microscope. I’m your host and today we will find out why stressing quantum dots can surprisingly enhance their functionality. This is in complete contrast to what our previous guest explained to us why relaxing the quantum dots is very important. 

Pranoti Kshirsagar: The science talk is an official science communication partner of the QuanTour project. And today’s guest is the second QuanTour hero. So far, we have had the two co organizers of the QuanTour project feature on Under the Microscope. Today we will introduce you to the second QuanTour hero who will be hosting quantum emitter, which is traveling across 12 different labs over the course of 12 months.

Pranoti Kshirsagar: Today we will understand why stressing quantum dots is important. We will also go into the mysteries of the quantum [00:01:00] entanglement. We will talk more about that. We will understand that. A lot more. We will also understand the material science behind the quantum dots. We will also explore the alignment of the quantum dots and also of course, more about the QuanTour project. There is also a very interesting connection between Armando and today’s guest. Stay tuned to learn more about that. I hope you will enjoy this episode. Let’s get started.

Welcome to Under the Microscope: Meet Rinaldo Trotta

Pranoti Kshirsagar: Welcome to Under the Microscope. My name is Pranoti. I’m your host. And today, I’m very excited to introduce you to our guest, Rinaldo Trotta, who is a professor at the Sapienza University of Rome in Italy. 

Pranoti Kshirsagar: Hi, Rinaldo. How are you? Good.

Rinaldo Trotta: to see you. And thank you for this opportunity. Very excited to be part [00:02:00] of this podcast.

Pranoti Kshirsagar: Let’s get into it. Please. 

Diving Into Quantum Dots and Secure Communication

Pranoti Kshirsagar: Tell me about your research in super simple words. Very

Rinaldo Trotta: So so what we do here at the University of Roma Sapienza. We work with semiconductor nanostructures. our research activity is really at the interface between semiconductor physics and quantum optics. And then we get these very tiny nanostructures they are called quantum dots.

Rinaldo Trotta: And I know that you are by now should be an expert on quantum dots because you had, many talks on that. And and you already know that these tiny nanostructures are able to generate single photons. So particle of light. And then in principle, it is possible to use the single photons to perform secure communication.

Rinaldo Trotta: This is already what you know, but what you do here at Sapienza, actually we get these tiny nanostructures and without stress. So you may remember in previous talks, so that growers are really trying hard to get these nanostructures without stress. And then we actually apply stress on top. And the reason why we do that [00:03:00] is that we want to force these tiny nanostructures to generate not only single photons, but also pairs of polarization entangled photons.

Rinaldo Trotta: This is what we would like to get. And they can do it only in very special conditions, okay? So that’s the reason why we need to apply this stress to the nanostructures in such a way that we get these entangled photons out. And now with these entangled photons, and that’s really the core of our research activity.

Rinaldo Trotta: So as I mentioned, semiconductor physics, so tiny nanostructures, then you apply stress, electric fields, magnetic fields, whatever you can imagine. So external perturbations, and then we get these pairs of entangled photons, and then we use these entangled photons to implement quantum communication protocols, and in particular secure communication.

Rinaldo Trotta: And our dream would be to do that over a really large scale. So over the globe, this is what we would like. So we get the study nanostructures and then we start to send them around. We implement protocols sorry, no nanostructure disentangled for instance, then we implement protocols like teleportation [00:04:00] and entanglement swapping.

Rinaldo Trotta: And yeah, so we send them around and then we try to communicate in an absolute secure way, not only use a single photons, as you might’ve heard before, but using entangled photons.

Pranoti Kshirsagar: Okay, I have so many questions. Okay, I have so many questions. Okay. First question, so Armando mentioned there are two types of quantum dots. There are the colloidal quantum dots, which are spherical, and then there are the epitaxial quantum dots, which are like, if you cut a cookie , then it’s like a semicircle or a bump of sorts.

Pranoti Kshirsagar: So which quantum dots are we, are you talking about?

Rinaldo Trotta: I’m mainly using epitaxial quantum dots actually recently. We are only using those in the past. I had a look at also at the other type of quantum dots, but I think that these ones for quantum technologies are more promising. So the epitaxial quantum dots.

Pranoti Kshirsagar: Okay. Okay. Because the colloidal ones, they are for the LCD screens and blah, blah, blah, blah, blah. All of that. But the ones that you also use, similar to Armando, are these. [00:05:00] 

Rinaldo Trotta: Right. 

Pranoti Kshirsagar: You stress them with electrical and magnetic fields and all kinds of things. So what Armando mentioned that they create like a negative of the bump, then they deposit a material which have a similar lattice constant, lattice constant, lattice 

Rinaldo Trotta: Right. 

Pranoti Kshirsagar: lattice constant, and so that the stress will be less, but then there will still be the epitaxial quantum dots. 

Rinaldo Trotta: And let me be precise. So also the colloidal quantum dots in principle can be used to do quantum, let’s say applications, quantum technologies. These, they can also be used, so far epitaxial quantum dots show the best properties. sources of a single and entangled forms. Okay.

Pranoti Kshirsagar: Okay. Okay. I’m going to add another question that just popped up, but you mentioned, I will come to that. You mentioned entangled something with the, what do entangled interaction, something like that? What is that about? What do you mean by entangled? What? Explain it to me. I don’t understand.

Rinaldo Trotta: Yeah. So to be a little bit technical, I would need to say that entanglement describe so usually in the community we say superposition of correlations. Okay.  I would like to explain in very [00:06:00] simple words. Okay. So imagine you have two particles, okay. And the state of these two particles so the two particles are entangled.

Rinaldo Trotta: Now, quantum mechanics tells you that the quantum state remains completely locked together, okay? And if you perform one measurement, for example, of a polarization of one of these particles, imagine a photon, then this measurement, it will immediately affect the state, the measurement on the other part. I would like to explain you even more in a simple way.

Rinaldo Trotta: So imagine that we have here, I hope you can see those. So we have dices. Okay.

Rinaldo Trotta:  And now imagine that this we can describe these two dices with an, as a, an entangled state. Okay. And for these two dice. And now the point is that if you now look at just one of those, and then you start to roll the dice and then you write down the outcome of the measurement, you may find one, two, three, four, five, six, seven, eight, And then now if someone else does it on the other dice, [00:07:00] what happens is that they will find 1, 2, 3, 4, 5, so on and so forth.

Rinaldo Trotta: So each of them, so the two characters that we usually name, Alice and Bob. So when they look at the outcome of the measurements, they find that the results is completely random. Okay.  They look at their results and then they write down the outcome and then they say, okay, they look at the numbers and they say the result is random.

Rinaldo Trotta: Alice does on this side, Bob does it on the other side, and they both find the outcome random.. nice thing here is that when you compare the results, they are perfectly correlated. Meaning now imagine, I tell you again, I have my dice here and the other, I give you the other dice, okay? You do your measurement, you write down the outcome, okay?

. When you throw it the first time and you find one, I also find one. Now, let me go on 

Rinaldo Trotta: that. Telling you that quantum mechanics is telling you that the state of these two. is completely undetermined.

Rinaldo Trotta: So just imagine that these two dices are the same or same numbers at the same time. But now [00:08:00] you make a measurement on this dice and then you find one

Rinaldo Trotta: instantaneously I will find one on my side. This is two actually, I will find one, on my, okay. So this is what quantum mechanics is telling you.

Rinaldo Trotta: It’s nature. Okay. That’s a very simple thing. I’ve done, these things have to be taken with the tweezers because entanglement, you see it when you go really in the nanoworld, 

Rinaldo Trotta: but microscopic object entanglement is very fragile and it’s extremely hard to see it.

Pranoti Kshirsagar: So when you say entangled, it is the entanglement between the two dice that you showed just now. It, because they are kind of interconnected and that is the entanglement, you have a dice in Italy, I have a dice in Germany and I’m throwing the dice and I’m thinking I’m just talking to Rinaldo. And of course the dice is showing number one or number two, and I think it is random. And Rinaldo, so you also throw the dice while you’re talking and you just see one or two, depending on, and we both think it is random, but actually it is not, [00:09:00] right? Oh my God.

Rinaldo Trotta: exactly. That’s nature.

Pranoti Kshirsagar: If yeah, but this is quantum mechanics. It’s like that. Okay. Okay. Can this happen with three dice? So I have a dice in Germany. You have a dice in Italy and. Armando, let’s say, has a dice in Austria. Can the entanglement be with three dice?

Rinaldo Trotta: It’s rather complicated, but there are scenarios like this. Yes, you can have even multi speak about photons, right? Because we use these nanostructures to generate photons. And then it may happen that in very specific conditions, you can have, for example, several photons which are entangled with each other.

Pranoti Kshirsagar: Oh, and that is why this is secure. I mean, this is where the secure, and there’s so security. This is the element that is important for the secure and less of the communication between you and me or whoever 

Rinaldo Trotta: point is that to really explain you in simple words. So if we do share, so you have a dice, I have the other one. If we do share a perfectly entangled state,

Pranoti Kshirsagar: Yeah.

Rinaldo Trotta: no one else can have even a single part of the share. Okay. So that means that entanglement is a private. So it established a connection [00:10:00] between me and you and no one else in the world can take a share of this entanglement.

Pranoti Kshirsagar: Aha. They can’t tap into it. And even if they do tap into our phones or our connection, they will see the dice showing one and one. But what it means, they wouldn’t know. 

Rinaldo Trotta: Right. 

Pranoti Kshirsagar: Only I have the dice and only you have the dice, which is the key. What Doris was referring to that. I have a key, you have a key. And if a third person tries to unlock the key or try to understand decode then it just gets destroyed

Rinaldo Trotta: Right. 

Pranoti Kshirsagar: but we still have the

Rinaldo Trotta: So we actually, we would need to communicate which kind of measurements we make, right. Without showing the the outcome of the measurement. Okay, we can look at the phone and I can tell you, okay, which kind of measurement are you making? And then I make, for example, the same measurement and then we automatically get the same outcome, depending on the type of entangled state that we are dealing with.

Pranoti Kshirsagar: Okay. Oh, wow. Oh, wow. This is super fascinating. This is super fascinating. Okay. Now [00:11:00] tell me the part about you said the goal is to have to distribute the entanglement all over the globe. What do you exactly mean by that? Does that mean that , let’s say you sitting in Italy and there is a person sitting in Australia that. That this Alice and Bob thing, is that what you mean? Or what exactly do you mean? 

Rinaldo Trotta: The point is that we would like actually to make long distance quantum communication, right? If you have two parties, right, that want to communicate, you may, for example, have one nanostructure here and send a photon, right? So remember that a single nanostructure can generate even a single photon per time.

Rinaldo Trotta: And now what happens is that during the communication distance, right, this photon can get lost,

Pranoti Kshirsagar: Yeah.

Rinaldo Trotta: right? And what happened is that you may have secure communication even with single photons, right? So nanostructure send a single photo, and then you as you heard from Tobias and the others you may have secure communication even with single photons, right?

Rinaldo Trotta: But the point is that this works over [00:12:00] distance of about a hundred kilometers. Okay, and because you basically have photon losses, now you may ask yourself, how can I actually overcome this problem and send, quantum information from here in Italy to Australia is by far more than a hundred kilometers, 

Rinaldo Trotta: right?

Pranoti Kshirsagar: Right.

Rinaldo Trotta: And the point is that, so classical from a classical perspective, you would say, okay, how does it work with the classical signals? So I use amplifiers,

Rinaldo Trotta: But you can’t do that here because you’re dealing with quantum bits.

Pranoti Kshirsagar: Correct.

Rinaldo Trotta: And there is a famous theorem, it’s called no cloning theorem, telling you that you cannot actually copy and amplify.

Rinaldo Trotta: It’s a quantum signal, okay? So it’s just for you to understand. It’s not super precise. But the point is that, so how are you going to do that? And this is a funny thing. Entanglement allows you somehow to increase this communication speed. distance. And how does this work? So I told you that you have a pair of entangled [00:13:00] particles or entangled photons, whatever you want.

Rinaldo Trotta: And now the distance between these two may be, I don’t know, 100 km or so.

Pranoti Kshirsagar: Right.

Rinaldo Trotta: And now imagine that now you have another pair of entangled photons.  

Rinaldo Trotta: There is a procedure which is called entanglement swapping, which I think is one of the best thing I’ve ever seen in my life. That is. So now you take these two inner photons, okay?

Rinaldo Trotta: And you let them you put them in a box, okay? Meaning that actually you are going to to do a measurement on these two photons, okay? And now quantum mechanics tells you that upon, after looking at the results of this measurement, the other two photo gets entangled. 

, if a hundred kilometers is the range, so to say, so then you just build. Towers or these boxes for the swapping so that the signal from, let’s say Mannheim to Rome, if the distance is 800 kilometers, then we need eight points to do this swapping Oh, this is

Rinaldo Trotta: this is a, let’s say a simple version of it. Okay. So if reality, you will need quantum memories. Actually, there are protocols also that do not work with quantum memories. And, this is more complicated than that, but the basic, the core ingredients is really this entanglement [00:14:00] swapping.

Rinaldo Trotta: well. 

Pranoti Kshirsagar: Oh, that is cool. And can we do that with satellites and stuff? Or

Rinaldo Trotta: Oh, yes, of 

Pranoti Kshirsagar: We can, of course, we can do it with satellites.

Pranoti Kshirsagar: Okay, Okay, because that will save us the Yeah.

Rinaldo Trotta: There was an experiment a few years ago where actually they managed to, to distribute entangle photons using satellite yeah, I can’t remember the distance. But it just was direct

Pranoti Kshirsagar: That is so cool!

Rinaldo Trotta: From the satellite. This was an incredible experiment done in China.

Pranoti Kshirsagar: Oh, wow, that is awesome. Okay. Okay. Okay. Okay. Okay, 

The Material Science Behind Quantum Dots

Pranoti Kshirsagar: then let me ask you this question And then we will move on to the next one But first I want to know Armando was super keen on unstressing or relaxing the quantum dots Why do you want to stress them? Let them be they’re already stressed. Why do you want to stress the quantum dots?

Pranoti Kshirsagar: What pleasure do you get from torturing the quantum dots?

Rinaldo Trotta: Well, I mean, the point is that I mentioned at the beginning. That these quantum dots can generate entangled photons in these three into very specific conditions.

Pranoti Kshirsagar: Oh, yes,

Rinaldo Trotta: Very specific. Okay. You may remember that this is actually [00:15:00] related to the symmetry of the confining potential of electrons and holes confined inside this quantum dots.

Rinaldo Trotta: However, to make it very simple, I want to, show you just the idea the theory is telling you. So you see, you have, we have a small 

Rinaldo Trotta: ball.

Pranoti Kshirsagar: Yeah,

Rinaldo Trotta: Theory, so imagine that this is a quantum dot, okay, super simplified in version.. And I now am telling you that theory tells us that you can get entangled photons only when this is round. I’m oversimplifying it, but it’s the symmetry of the confining potential, okay? Meaning that you can get entangled photons if this dot is round. So let me allow to say this.  

Rinaldo Trotta: Now the point is that every quantum dot is slightly different from the other, and it’s not round. So that means that now, if you take a quantum dot, it’s like this, naturally, it doesn’t give you this entangled photons.

Pranoti Kshirsagar: Aha, Okay.

Rinaldo Trotta: the reason why I want to stretch them, electric field, magnetic field. Okay. So we want to start from a configuration, which is like this. [00:16:00] And then you squeeze this ball now, 

Pranoti Kshirsagar: Uh 

Rinaldo Trotta: and then you make it round. And when you do it, so you get entangled photons. So once again, this is dot without stress, but it has a certain shape.

Rinaldo Trotta: And now I stress it, or I apply electric field, magnetic field, and then somehow the shape looks like this. And then it gives you an entanglement.

Pranoti Kshirsagar: Oh, so for it to perform and emit the photons, you need to change the shape. For example, so that is why you do the, so what you’re doing is you are manipulating the quantum dots in order for them to emit photons. Doesn’t Armando then also have an issue? If his quantum dots are relaxed that they are not able to emit the photons or is it dependent on the material, which is why you need to stress your quantum dots. But Armando doesn’t need to stress his quantum. Is that what is the difference here? What? 

Rinaldo Trotta: Well, so The point is that, so Armando can in principle with his machine, so he showed you the oven, the point is [00:17:00] that with his machine, he can make the quantum dot as close as possible to a sphere, 

Rinaldo Trotta: okay? So that’s it. And then if he manages to do that, then he also gets entangled for it.

Rinaldo Trotta: It’s the same 

Pranoti Kshirsagar: Ah, okay.

Rinaldo Trotta: But there is a but, okay? And you should not forget this nanostructure is composed of several thousands of atoms. Okay? And it’s rather difficult to control the shape of this nanostructure, the symmetry, I should say with the required accuracy. So the point is that he Armando tries to do that, okay, but, not always he manages.

Rinaldo Trotta: So that’s the point. And also he needs quantum dots. So we actually can use a strain, electric 

Rinaldo Trotta: field, to, restore his structural symmetry, and then to force the quantum dots to give us entanglement.

Pranoti Kshirsagar: Ah. Okay. Okay. Okay. Okay. Okay. Okay. Okay. And then, so what is the material of your quantum dots? [00:18:00] Because I think Armando mentioned he had the gallium arsenide kind of, so which what quantum dots do you have? What is the material of your quantum dots or which is your favorite material for quantum dots so that you can manipulate them and stress them to get the most out of it?

Rinaldo Trotta: Yeah, so the my favorite quantum dots are Armando’s quantum dots.

Pranoti Kshirsagar: Oh, really? Oh, come on. You can’t say that. I was just like, I was trying to fuel a fire and start a feud between, oh, Armando’s quantum dots are not always the best. And that’s where, come on, Rinaldo, give me some drama here. 

Rinaldo Trotta: No, well, I have to say that Armando explained to you that he, that, it took him a lot of time to fabricate these nanostructures without stress. And he also invested a lot of time to make them as symmetric as possible,

Pranoti Kshirsagar: Correct. Yeah.

Rinaldo Trotta: but still you need a little bit of strain to, to really make them perfect for entangled photon generation.

Pranoti Kshirsagar: Correct. Correct. Correct. So you’re still sticking with Armando’s quantum dots are your favorite. Are you going to tell me a different answer when we stop recording? Like for sure. So cause you know that Armando is going to [00:19:00] watch this video. Ah,

Rinaldo Trotta: Amanda for many years, so we know very well each other. And I really believe that he’s quantum state of the art

Pranoti Kshirsagar: Okay. Well, I tried guys, everyone listening or watching. I tried to get some drama with the QuanTour heroes, but I will try probably later on. We are about to take a short break, but stay tuned because when we return, we will dive deep into the career journey of our guest today. It is always inspiring to see the paths that lead scientists to where they are now. Don’t miss it.. 

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Thank you for listening. Thank you for watching and let’s get back to the episode. 

Pranoti Kshirsagar: Tell me about your career journey to becoming a professor at the, in Rome, in Italy.

 I actually studied Yeah.  I did my master here. Then I did my PhD here. And then one year of postdoc, and then it was after a while I said, okay, I maybe try to challenge myself and then, let’s go outside Italy. And actually I went to Dresden.

Pranoti Kshirsagar: Ooh. Is that where you met Armando?

Rinaldo Trotta: Right, right, right. Yeah. So so I went to Dresden actually and actually at that time I didn’t know that Armando was there. So it was so I actually applied to the, really the big boss there, Oliver Schmidt. And then, they ended up working with Armando. [00:22:00] And then when Armando actually moved to Linz, I actually followed. Yeah, it was I got a position as a university assistant. It was a possibility, let’s say, to do my tenure track. 

Rinaldo Trotta: And yeah, I went there and then it was so I had no labs at the beginning. We started with empty rooms. I built up the lab. And then I started also to build up a group 

Rinaldo Trotta: there named Nanophotonics.

Rinaldo Trotta: And then after I think I stayed there for something like five years, something like that. Then I did my habilitation in Austria, then I became a professor in Austria, 

Rinaldo Trotta: and then I got an ERC starting grant. 

Pranoti Kshirsagar: The early career researcher from the EU.

Rinaldo Trotta: from the EU, Right. 

Rinaldo Trotta: Right. And yeah. And then I had somehow the possibility to go back to Italy with this grant. 

Rinaldo Trotta: And, also here I got empty rooms. And I had to build up the lab again from scratch, 

Rinaldo Trotta: the group, 

Pranoti Kshirsagar: didn’t you just move the lab from Linz to Rome?

Rinaldo Trotta: not so easy, right? So [00:23:00] it was it was quite tough I have to say, but in the end, everything worked really well. And, yeah, so I have to say that I’m quite happy here. So I have my own lab, I have my own group and we do the research we want. So you see, that’s the reason why we get this tight connection with Armando, right?

Rinaldo Trotta: So we worked together 

Rinaldo Trotta: Many years.

Pranoti Kshirsagar: You two go way back. So it will be difficult for me to introduce some sort of feud because it’s like you grew up together becoming professors. It’s also interesting that you met in Dresden and It’s quite it’s quite interesting because, well, I’m based in Germany.

Pranoti Kshirsagar: So for me, it’s like Armando is in Austria. You are in Italy, but you met in Germany

Rinaldo Trotta: Right.

Pranoti Kshirsagar: For whatever it’s worth. See, I’m looking for some drama here and you’re not giving me any. This is really cool. And also setting up the labs and starting from empty rooms is something that a lot of people who are even scientists or like masters or bachelor’s students, or even PhDs in some [00:24:00] cases, they have never even thought about it, that actually everything, all the fancy toys you see around you in the lab, at some point it was an empty room, which your PI or your PI’s PI had to build from scratch.

Pranoti Kshirsagar: This is something that we think.

Rinaldo Trotta: twice,

Pranoti Kshirsagar: Yes, you did it twice. You are a pro now. You can be the go to consultant for starting the lab from scratch.

Rinaldo Trotta: but I confess that I don’t want to do it anymore.

Pranoti Kshirsagar: I don’t know. You don’t do it. You just help others do it and you watch from the sidelines while you instruct them how to,

Rinaldo Trotta: Right.

Pranoti Kshirsagar: I’m I’m assuming also there is a lot of paperwork and admin stuff, which Armando also spoke about that. The admin, the bureaucracy sucks the joy out of the research. Okay. So you have moved around quite a bit. You started in Rome, then you went to Dresden, then you went to Linz. You were there for quite some time and now you’re back in Rome. So it sounds to me that you have been involved in a lot of interesting research projects.

Pranoti Kshirsagar: So now [00:25:00] I don’t want you to hate me, but if I ask you. To pick one research project that you are most proud of, can you pick one and explain it to us in simple words in the section we call In Other Words?

Rinaldo Trotta: Only one, you said.

Pranoti Kshirsagar: Only one, sorry, only one.

Rinaldo Trotta: The one really that I’m sentimentally bound to somehow the project is, as I mentioned, growers were trying really to get these structural symmetry as close as possible.

Rinaldo Trotta: Quantum mechanics is telling you that you can’t do that. We were really wondering why and how, and then somehow we found the key, and then we understood why. 

Rinaldo Trotta: What we discovered, that since every quantum dot is different from the other. The trick is to use two different stresses. You use one stress. to rotate and then you use the other one to make it symmetric. That’s my favorite thing.

Pranoti Kshirsagar: That is brilliant! Of course, now that you say it, it’s like simple, obviously, duh. Oh, wow. [00:26:00] That is brilliant. But so how can I imagine this? So you have an array of quantum dots. So you have, let’s say eight by eight, that means 64 quantum dots. 

Exploring Quantum Dots and Their Alignment

Pranoti Kshirsagar: And some of them are aligned. these are the hero quantum dots, which are standing straight. So that if you apply. stress along its axis in parallel, then it becomes a spherical.

Rinaldo Trotta: What you have to do, you have to adjust the magnitude of your perturbation for each specific quantum dot. 

Tuning Quantum Dots for Entangled Photon Generation

Rinaldo Trotta: And then you need to tune the stress on each of these quantum dots individually if you want to tune them all for entangled photon generation.

Rinaldo Trotta: We demonstrated you can take any quantum dot and tune it for entangled photon generation. And actually we built up a device that uses three different stresses, not only two, but three.

Rinaldo Trotta: But the idea is very simple, right? You start stretching in all directions until you get what you want. This is basically the physics. 

Pranoti Kshirsagar: So you need localized forces. You [00:27:00] need control very locally so that you don’t disturb the neighboring quantum dots in the vicinity.

Rinaldo Trotta: That’s actually what we would like to do in the future. 

Rinaldo Trotta: The moment, we get our substrate 

Rinaldo Trotta: with many many quantum dots. 

Rinaldo Trotta: And then we pick up the one we like. 

Rinaldo Trotta: Okay. And then we start applying stresses in different directions. And then we choose that one for entangled photon generation.

Rinaldo Trotta: And of course, you got it right. The, the stress that we use to tune that one for entanglement. It’s not suitable to tune. Okay, so you need to change this. So that means that if you want to have many of those, you need to be able to apply locally stress. And this is something actually is a topic for future research.

Pranoti Kshirsagar: Do you even want the quantum dots next to each other? Let’s say, 100 nanometers or so, or do you not care? You just want one quantum dot on one substrate and that’s enough.[00:28:00] 

Rinaldo Trotta: Well, I mean, we would like to get a low density of quantum dots 

Rinaldo Trotta: and the reason is simple. We look at these quantum dots with our microscope. We don’t want to look at more than one per time, so we would like them to be apart, let’s say, a micron or so.

Pranoti Kshirsagar: Okay. And how big are your quantum dots? Because now Armando taught me that the way you measure like what you’re reporting is the height of the quantum dots and not the spread.

Pranoti Kshirsagar: So Right. are your quantum dots?

Rinaldo Trotta: So the quantum dot are a few nanometers in height, like five, six, but it depends, actually. And in the plane, so it can be 20, 30, 40 nanometers.

Pranoti Kshirsagar: Bumpy quantum dots.

Pranoti Kshirsagar: bumpy.

Pranoti Kshirsagar: dots, which you like to stress. Okay. But hey, you said that when you imagine this baseball ball which you want to make a sphere.

Pranoti Kshirsagar: But if your quantum dots are bumpy, like bumps or like slices of cookie how do you make them like, [00:29:00] which access are you going for? I, how do you make them spherical? Okay. I’m feeling like I’m asking you all your secrets, which you probably want to publish too. 

Rinaldo Trotta: Actually, there is no secret. I mean , of course, I oversimplified, right? And the point is that what is important is not the shape of the dot, but actually it’s natural symmetry. Can be proved from a theoretical point of view that the problem lies in 2D.

Rinaldo Trotta: Okay, and in 2D, you may have either a circle or an ellipse, okay, from a theoretical perspective. But you have to be precise. You cannot really measure high quality entanglement if this is not the case. 

Pranoti Kshirsagar: Okay. Okay. I understand now. Okay. Okay. So now your quantum dots, you stress them to make them better so that they will emit photons. 

The QUANTOR Project: A Quantum Dot Journey Across Europe

Pranoti Kshirsagar: Now tell me, about the QUANTOR project. The quantum source, which is traveling around Europe.

Pranoti Kshirsagar: 12 different labs, 12 months one source. Doris and Tobi , I have two votes now. Ten more to [00:30:00] go. Okay. Unite them all. I’m going to use that. I want the drama. So now talking about the science of it. So there are these concentric circles like a dart board and you have your quantum dots that are ready.

Pranoti Kshirsagar: And how are you going to do it? I asked the same question to Armando, but I want you to explain it to me as well.

Pranoti Kshirsagar: Well, actually its quite interesting cause I am also working pretty much on these, 

Rinaldo Trotta: kind of structures. Okay. So the one that is to look at the properties of the chip traveling across Europe. And the reason is it’s very simple to understand because now this you have this chip, right? And I would be very happy to see the properties of the quantum dot embedded in this dart like structure.

Rinaldo Trotta: But now this time, not only looking at the single photons, but what I would like to see is whether. It is a sphere or an ellipse. 

Rinaldo Trotta: And then to see what that kind of source can be used not only to generate single photons, but also entangled photons. So we will get this source, actually it is here, and [00:31:00] we will look carefully at all the properties.

Rinaldo Trotta: But this time, since we are interested in entangled photons, we look also at this symmetry, structural symmetry, to see whether in principle it’s possible to get entangled photons

Pranoti Kshirsagar: the dot is already inside the bullseye. And you’re going to do the measurement and then you’re going to do the entanglement. So you will put two rings next to each other. Are you also going to do this swapping thingy where you put three rings next to each other and then you’re like doing the information transfer or am I like going too far here?

Rinaldo Trotta: It’s really important to see all the properties of the source. We did already something similar that, this bullseye cavity with the dot inside.

Rinaldo Trotta: I told you that if you want to use it to generate entangled photons, the dot should have a certain structure of symmetry. 

Rinaldo Trotta: And I’m very curious to see, but probably the dot which is inside the bullseye will not have this symmetry. And now it gets interesting, right, in the future to have this bullseye cavity and start to stretch it around and then to see whether it gets, [00:32:00] that you can get entangled photons out.

Pranoti Kshirsagar: Are you going to do that with the source that you receive like today that you have the QuanTour source or you’re going to do it with your bullseye structure with the quantum dot inside

Rinaldo Trotta: We actually did it already with our bullseye structure. 

Rinaldo Trotta: And we are not going to do it with a chip we recieved simply because it has to, continue

Pranoti Kshirsagar: It’s journey. You don’t want to play with it.

 The source has arrived. It is in Rome. We saw on Instagram that the source, in the aluminum suitcase, took a train from Linz to Rome. It’s in the same building as you where you’re sitting. So have you seen the source yet? What is what was that like? Tell me your experience of opening the suitcase.

Rinaldo Trotta: After conversation, I go to the lab and I will open it.. So stay posted on Instagram because we will we 

Rinaldo Trotta: show 

Rinaldo Trotta: you, 

Pranoti Kshirsagar: By the time the podcast comes out, there would have been already reels on Instagram, quantour.eu, where Rinaldo is opening suitcase and we’re looking at the source or he’s looking and he and his team is [00:33:00] looking at the source. That is brilliant. Do you also have a sticker ceremony planned?

Rinaldo Trotta: do, 

Pranoti Kshirsagar: I will not ask you questions about that because I want to be surprised with what kind of sticker ceremony do you do? Because the one in Linz was also quite a lot of fun. 

Rinaldo Trotta: Was there as well.

Pranoti Kshirsagar: You were there as well. Oh, for the workshop?

Pranoti Kshirsagar: So you already know the behind the scenes and everything. Okay, perfect. Perfect. Looking forward to the pictures and the videos of you opening the suitcase, source, and then also the sticker ceremony. Now let shift gears a little bit and tell me, other than the research aspect, which I think you like a lot, I feel like you like, you really love the research, but there is more to you as a professor or as a scientist than the mere research, so to say. So what else do you like about being a scientist or being a professor now? 

The Joy of Teaching and Building International Networks

Rinaldo Trotta: mainly I would say. Teaching is really something that 

Rinaldo Trotta: really like. 

Rinaldo Trotta: The [00:34:00] interaction with students, I really try my best to pass passion and my knowledge to students. And I’m actually coordinating an Erasmus Mundus

Rinaldo Trotta: here at Sapienza, where you basically get many international students.

Rinaldo Trotta: And then I had the pleasure and the opportunity, to teach physics, actually quantum optics.

Rinaldo Trotta: These experiences really, I’m really having a lot of fun with it. I’m learning a lot about different cultures and that’s something really important, I believe. And I really believe that teaching is a way to bridges cultures. So teaching science is really something that I really like. And the other thing, of course, I told you that I built up two labs and I really enjoy my life in the lab. If you are there and then you work with the right people, I mean, this is something really special.

Rinaldo Trotta: Okay. And I can tell you that I made a lot of friends all around the world. Actually in June, I’m going to [00:35:00] to visit a friend, he built up another lab in Germany.

Rinaldo Trotta: I created my lab here and then now I’m going to do experiments with him. Then he comes here he will do experiment with me in my lab. This is something that, very good friends, colleagues, friends, and good connections. I think that this is really special of our job. Also, when you go to conferences and you have the possibility to discuss with so many people, I think that this is something special about our job.

Pranoti Kshirsagar: That is so cool. A few episodes ago, we had a guest who who had a term for it. And she said, it’s like an international network of science besties. You find interesting labs and then you find interesting people, of course, and then spending time. It’s like a. Yeah. Yeah. It’s the best figuring the science out, doing the research, doing the experiments in the lab.

Pranoti Kshirsagar: It’s just brilliant. I love that. I completely agree. I wish I could go back to that. That would be, you know what, I’m going to visit you at some point. I will do some sort of SEM [00:36:00] images for you.

Pranoti Kshirsagar: And also, I’m glad that you love teaching because we need professors such as you who actually enjoy teaching and shape the next generation of scientists. I think that is very important. 

Rinaldo Trotta: Because somehow there is not enough training on quantum technologies. These Erasmus Mundus is really focused on that quantum science and technology, and we are trying to, , train the next generation of quantum physicists, quantum engineers, whatever you want to call them.

Rinaldo Trotta: And, 

Rinaldo Trotta: I think that’s really important.

Pranoti Kshirsagar: Are you also, Armando is involved Quanta project, which is the quantum science community in Austria. Do you have something similar in Italy? I think you had mentioned something like national Quantum Science and Technology Institute.

Pranoti Kshirsagar: Do you wanna tell me a bit more about that?

Rinaldo Trotta: Yeah, this is actually is a really important initiative in Italy, this NQSTI, this is how we call it. So quantum science and technology, where there are several entities working [00:37:00] together on the different aspects of quantum science and technology, both fundamental, quanta that you mentioned where Armando is really focused on fundamental physics.

Rinaldo Trotta: So this one here is focused on both. So fundamental science and also applied science,

Pranoti Kshirsagar: Okay.

Rinaldo Trotta: quantum science. I think this is a really special occasion because within this institute now, so there are many groups all around Italy and we are working together. I think this is really important to, to push also on the national level, quantum science and technology.

Rinaldo Trotta: And this is really a unique opportunity.

Pranoti Kshirsagar: So NQSTI National Quantum Science and Technology Institute. Is it then based in Rome or does it have like several different locations or how does that work? 

Rinaldo Trotta: It involves all many different groups across Italy. 

Rinaldo Trotta: Okay. So I would say that it’s de localized, 

Rinaldo Trotta: uh, across 

Pranoti Kshirsagar: Oh, okay. Okay. Okay.

Rinaldo Trotta: Italy. And of course, I mean many [00:38:00] ceremonies. Also the kickoff meeting was here in Rome. Rome is The heart. 

Rinaldo Trotta: the central part of of Italy. 

Pranoti Kshirsagar: Mm 

Rinaldo Trotta: City. So, but de localized. Okay. So many different 

Pranoti Kshirsagar: Okay. 

Rinaldo Trotta: working together across Italy.

Pranoti Kshirsagar: Huh. Okay. Okay. I’m definitely going to check out and inform myself a lot more about NQSTI which is the National Quantum Science and Technology Institute all the initiatives that are going on because this is 

Pranoti Kshirsagar: definitely, definitely interesting. We would be right back after this short break up next, we ask our guests a fascinating question. If they could have three wishes to improve their research experience. What would they ask for? It’s going to be a very interesting conversation, so don’t go anywhere. 

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Wishes for the Future of Research and Academia

Pranoti Kshirsagar: It sounds to me other than the having to set up the lab two times, it sounds to me, Rinaldo, your experience in research has been amazing of course, but if you had three wishes to improve your research experience, what would you ask for? And I’m not promising anything here.

Rinaldo Trotta: What I can say for sure that, I would definitely love to have more time for research and also for teaching. as I told you I love doing research. I love staying in the lab, but I also love teaching.

Rinaldo Trotta: And the point is that as soon as you go on with your career, you’re going to have a lot of fun.

Rinaldo Trotta: You get more duties, you are in commissions, you have to deal with many different things. You have to write reports, and then you have to write grants. You know how it works, right? But the point is that now it’s become a little bit too much of a bureaucracy. It was really, it’s really a lot.

Rinaldo Trotta: And then you end up, during the day working more than [00:41:00] 10 hours, 12 hours. And sometimes you don’t really do research or science. 

Rinaldo Trotta: And this this a bit, a bit annoying and I think that they should I’d really love to have less duties and more time to stay in the lab. This is one thing.

Rinaldo Trotta: Then the other thing is for sure is that I believe that I have many young researchers working with me and, they are really struggling to find permanent position, I was kind of lucky, I also suffered somehow and I think that I think it cannot be that brilliant scientists have to fight really a lot to, to get a permanent position and to follow their dream to do science.

Rinaldo Trotta: I think that they would really wish they could get permanent position. I would be really sad if somehow they have to leave academia because they can’t find a permanent position. 

Rinaldo Trotta: That’s that I would be really sad. That’s something that definitely I would like to improve in the system. I would love that it would be easier for good researchers.

Pranoti Kshirsagar: [00:42:00] To stay. More time. lesser bureaucracy and more permanent positions for young researchers, because I agree with you.

Pranoti Kshirsagar: It’s a pity that academia or science or research loses out on some excellent talent and brilliant minds because of the Organizational structures or the lack of organizational structures in some cases.

Rinaldo Trotta: They may have the possibility to, they are so good, right? That in principle they could go abroad. And then, this is something that’s also, I mean, as Italian, I would not love to have to see, good. I mean, it’s good to go around. I told you, right? It’s definitely good. Actually, I learned a lot traveling across Europe and then visiting many labs doing postdocs here and there. But, at some point after a few years of postdocs, I think it’s good that, that they find their own way.

Pranoti Kshirsagar: Yes, absolutely. Also that takes the pressure off, right? I mean a bit of traveling around with temporary contracts with postdoc-ing here or there Across the different labs. It’s [00:43:00] great. It also adds value. But I think there should be the option of having a permanent position. And if you still want to continue to go from one lab to the other, you can still do it. It’s not like everyone has to be in one place at all times. I hope your wish comes true. And again, not every researcher everyone who is from Italy or has started their research journey in Italy have to come back, but it’s good to have that option that, Hey, well, I do have an option of a permanent position, but I prefer to stay wherever they are. 

Rinaldo Trotta: So if, then if someone wants to go somewhere else across Europe or, you know, over the world, find a permanent position there is no problem at all. But I mean, from our side as Italian, I would say that it’s not good that we lose brilliant people. And then it would be because they can’t find the position here, right?

Rinaldo Trotta: So this is even if they want, I mean, if you want to go abroad, that’s fine, we have this flux of brilliant minds going outside. It would be, that’s [00:44:00] not the problem. If you would also have flux of incoming brilliant minds, and this is not, the flux is not balanced. I would say. 

Pranoti Kshirsagar: Finding that balance is it would be good to have that sort of a balance. Yes, definitely. Completely understand. And I wish I had the magic wand to grant all three wishes of you have more time in the lab, less bureaucracy. And permanent contracts for everyone who wants them. I would like to believe that we are working towards it with professors like people like you, Armando, Tobi or Doris, you being in the in the positions like decision making or decision influencing positions to change the structures from the inside. So that. The next generation of scientists or next, next to next generation of scientists will have lesser bureaucracy while setting up the lab like you did twice. I don’t even want to ask you how many papers you have to fill and how long it I, that’s a separate [00:45:00] podcast altogether, I feel,

Rinaldo Trotta: But it was a lot of fun. Lots of bureaucracy, lots of work, but it was so funny. I have to 

Rinaldo Trotta: say. 

Pranoti Kshirsagar: Yeah. But now it’s fun. Right? When you were doing it, was it fun?

Rinaldo Trotta: Also at that time, it was stressful. That’s for sure. Right. But, in the lab and in certain things, the way you want, because that’s also another thing. The way you want, then you are really it’s really fun. I have to say. Lots of stress, but also fun.

Pranoti Kshirsagar: but it

Pranoti Kshirsagar: is worth it. It’s like childbirth. It is a lot of stress, but it is worth it because then you love the lab and you love the child. Okay. Perfect. Rinaldo, this has been wonderful. I really enjoyed speaking with you and thank you very much for teaching me about the stressed quantum dots and why you stress them and why you have to stress them. Apologies to the listeners or watchers. I did not find a way to create more drama with the QuanTour heroes. So with Armando, with Rinaldo, with Tobi and Doris, because they all [00:46:00] seem to be getting along like for some reason. So now my bets are on the next guest from Spain, maybe there I can try a little bit, maybe. I will try my best, but before I let you go, sorry.

Rinaldo Trotta: that you are going to try hard. 

Pranoti Kshirsagar: I’m 

Pranoti Kshirsagar: trying to try hard. 

Rinaldo Trotta: will work.

Pranoti Kshirsagar: I will get there. I will get there somehow I will get there and I will get the feud and then when all of you are in one room There would be like sparks flying and I would be sitting in the corner filming all of that for content for let’s start to put it on youtube. That would be brilliant

Pranoti Kshirsagar: No, please tell me one last question I have for you. So in addition to featuring on our podcast Under the Microscope, you also get the keys to the Twitter account or X account called Real Scientist Nano, which maybe will be rebranded into Under the Microscope, but you basically get one entire week on the Twitter account, [00:47:00] which has more than 3, 400 followers. What can those followers expect in the week that you are tweeting from that account or X ing from that account? No pressure. No pressure.

Rinaldo Trotta: mean, we actually have maybe several plans. Okay. So we want to show Rome a little bit because, there are some places that it’s really wonderful. And and there are some 

Rinaldo Trotta: connections also to what we. what we study with secure communication and the landscape. So we, so there are a couple of things and then there are many ideas.

Rinaldo Trotta: So we show you the labs, some of the instruments, we look at the source. And then we look at whether there is a structural symmetry right that I mentioned before. And also that maybe there will be other surprises. So we plan also to, to show you what is a typical day of a professor or PhD students here working in Rome. 

Pranoti Kshirsagar: So a bunch of fun and, [00:48:00] Science y things as well. That is brilliant. That is brilliant. Looking forward to having you on Real Scientist Nano. This has been wonderful. Thank you very much for that.

Rinaldo Trotta: coming. It was a pleasure for me. Thank you very much.