Noel Wan—Large-scale integration of artificial atoms with photonic circuits

welcome uh to the first in the spring series 2021 of nano exploration seminars our speaker today is noel wan from professor dirk england's group noel will join us uh and actually take over in just a moment giving the talk on large-scale integrated quantum photonics with artificial atoms i want to make sure that i welcome you to the seminar series i reminded you that for the sake of everyone have a slightly faster bandwidth if you turn off your video and mute yourself please do so you can send your questions through the chat throughout the seminar those i will make sure i highlight to noel at the end of the seminar or at the end of the seminar you can raise your hand and we'll call upon you and you can ask the question uh verbally all right with that being said uh thank you again for joining us noel please take over thank you vladimir um uh good morning everyone uh today i would like to tell you about the work i've been doing uh over the past six years and in particular how we can possibly build a large-scale logical quantum technology based on solid state systems and some together with some engineering principles so recently there's a lot of excitement about quantum computers so quantum computer is a fundamentally a new model of computation that relies on a couple properties uh in particular massive uh parallelism of the uh of qubits uh as well as entanglement which is a unique correlation between qubits and also interference of of their amplitudes to perform uh useful computation as shown here uh for example is google's quantum computer which you may have seen in the news which perform a sort of computer perform a computation that takes about 200 seconds on your machine but if you were to use to running a super computer the fastest super computer today would take about 10 000 years um but there may be a scaling limit to how large of a quantum computer we can build and in that case we may need to network separate computers together in order to build a larger quantum computer to parallel some of the approaches for example in classical computing so you can think of the network itself as a resource like the internet for distributing quantum information so a quantum network can be thought of basically as an internet of quantum quantum processors sensors or any quantum systems in general and the power of this approach is that if we just have a quantum computer then with n number of qubits or quantum bits then you access a computational hub space of about of 2 to the n and if you just have independent on veterans m of them then you just have m times to the power n scaling however if you manage to build a quantum link between all these systems then potentially you can access a uh a computational hub space of to the power m times n so um typically these are connected by photons so they can be photons and frequencies for example microwave to optical and so that presents us a very exciting opportunity to connect uh in a quantum in a quantum fashion different sorts of quantum technologies for example you can have quantum computers based on trapped ions or silicon dynamic systems or atoms so the way you would do it is you have some sort of quantum link and as i said you can these can be local you know in the same lab or even metropolitan or even intercontinental intercontinental and um the problem always is is photon loss so because of no cloning theorem you would need uh in order to solve this uh this photon loss problem you would also need to place a quantum system in between this uh between these quantum computers and this is known as a quantum repeater um so uh the problem as we all as you're building any technology is that you would need many of these so uh for example here we have a quantum repeater based on the technology i'm going to tell you about but we don't we need more than just one of these and possibly need to build many of them so we need to figure out a way to manufacture these at scale for the pod so these are some of the examples of corn networks that have been realized over the past decade so for example you have trap ions atoms in qubits and also defects in defect qubits in diamond so in boston we are also hard at work for example in our group and together with uh mit lincoln labs we have demonstrated a quantum key distribution over uh over over 40 kilo kilometers of fiber link now the goal is to build a quantum network that transmits quantum information from one node to up to another and to do this we need to store the quant the quantum information in some sort of memory and this is known as a quantum membrane so as you can see that if you're trying to deploy this in a real system in the real world we should be able to the system doesn't uh needs uh not only to be high performing but it also has to be able to be manufactured reasonably well so our platform of choice is the solid-state artificial atoms with optical interfaces so this is the outline my talk today first i'm going to give a really brief introduction to um artificial atoms uh in diamond for quantum technologies and also also for photonics for quantum technologies and in particular i'll be discussing some selected results uh that would help us get towards this uh towards this scalable uh one technology based on artificial items so briefly this is the i'm going to give a brief introduction to diamond so it's a large banger and it's a clean material so it's basically silicon but if you replace all the silicone carbon then you get uh timing so it is mostly spin zero so that's really good for information because now you can have a really clean lattice and because of that we can have uh uh if you have electrons that are trapped in this diamond you can have uh milliseconds of spin connection which is which is not to be long and they behave like like atoms like uh like like a real adam would they have you know they have a state dependent optical radar which basically means that the the brightness of that defect depends on the state of the uh the internal state of the atom so the nice thing about these defects is also they have dopants or and and which have uh nucleus spins and mucous beans are doesn't really interact with their environment so you can even use these nucleus beans as ancillary cubelets to store the confirmation over a minute and the best thing is that there are hundreds of optically active defects in diamond and we've only scratched the surface of what can be used for chrome technologies so this is perhaps the most famous one which is the nitrogen vacancy center which is basically uh two missing carbon atoms in a diamond lattice and one of it is uh being replaced by a nitrogen and the others left vacant so this is the nitrogen vacant center this is one of the workhorse of quantum technologies based on diamond but as i said there are over hundreds of these and in fact you can just buy a book and you know you can study all the spectroscopic lines in diamond and this is the reason why as well if you're if you ever bought uh a jewelry based on diamond they come in various different colors and this basic these colors are basically different defects and different densities in time so there are really lots of opportunities here um but if this excuse me so if so they are so you know is there so great now where's the diamond quantum computer turns out whereas these systems are really exciting for quantum mechanical experiments there are some serious practical challenges that we need to solve in order to make this a scalable coin technology so the first thing is uh diamond is a is uh and the cubits in diameter are quite inefficient and that means that we need to do some sort of photonic engineering in order to make the uh all the relevant rates higher the second thing is this is a solid state system so you can imagine that every every defect and diamond looks slightly different from one another so yes this problem of uh indistinguishability so they look different from each other and they and so they don't interact so we need to also overcome this problem which is it's an active area of research and and perhaps the largest challenge is that whereas we can build small systems uh and we all know from engineering you know that if you want to build something large out of something imperfect then you have this peter and scaling where you know and where you can exponentially suppress uh yields in terms of in terms of the large when you try to build a large system so to solve this there um we propose to use photonics so the first thing that we need to realize is that solid state systems solid state emitters itself have low uh internal efficiencies so if this is a spectrum of the zero of the nv center that i talked about recently uh just a couple of slides ago and you can see there's only one there's this narrow sharp line which is useful for quantum information but then you also have these unwanted sideband emission that's not useful for uh some of the protocols that we want that you that uses the nv for quantum information and this only constitutes three percent of the emissions so you can imagine that our rate really suffers when we try to build a many um qubit systems based on this uh technology and then you have the external efficiency problem excuse me um diamond is a high index material it index a fraction of 2.4 which means that most of the light emitted by the by the emitter is is confined in the in the in about material itself so if you try to just use a you know some high-end optics microscope you only collect one to five percent of the emitted photons and so what people have done usually is they typically build a solid immersion lens and get really fancy in there in the optical setup using adaptive optics and then that brings you to uh to 15 which is remarkable but still far from uh getting us to unity efficiencies so um integrated photonics on the other hand you know it's a really promising technology it allows us to do low loss photon manipulation on the chip and we can potentially get to extraction of photonic correction we near unity efficiencies and most way of is the prospects for really compact and dense integration so for example here there are over hundreds of optical elements on a single chip and that is really the division here where we're trying to build a large rather modestly large quantum system on a fully on on an integrated chip so to build this scalable system we therefore pursue hybrid integration and the principle is as follows so diamond is a is a great host for qubits but it does not you know fulfill the diverse architectural requirements for large scale quantum information processing so in particular uh there's uh optical losses and diamonds is still quite it's still high it's orders of magnitude higher compared to state of the art photonic platform such as silicon nitride and the gymnasium and diamond also does not have uh you know strong optical non-narratives or appears electricity so it's mostly a a passive photonic devices so we set out to with the goal to combine the best uh materials uh for quantum and classic uh for from from both quantum and classical photonics and diamond being the best material today for for one of the best materials to date for quantum and the nitric and silicon nitride being excellent for platforms invisible uh so we we want to combine these these technologies together and this gives us the ability to optimize both materials separately and then heterogeneously integrate them together for example here we can fabricate a photonic integrated circuit based on in this example a little nitride on the sapphire photonics and then also separately fabricate the diamond and then the diamond nano structure and then integrate them after the effect and then you get this sort of hybrid integrated photonics that has this quantum element which is the you know the quantum core which is the diamond containing these artificial atoms with spins and then you perform all your photon manipulation and routing all using a different material that is no loss and has have uh uh can perform active uh active control of this photonic states and then this allows us to shift all the technical complexities of of building a you know monolithic system all into the more mature fabrication platform and then uh use the diamond for what it's good at which is uh for hosting this quantum uh quantum emitters so but to get there first we have to build this diamond nano structures and that turns out to be really challenging because diamond as you all know is a very hard hard material physically and it also doesn't really react with uh with chemicals so fabrication and is typically very challenging with the system so to do that we we adopt this process called the quasi-isotropic etching which allows us to to fabricate such uh suspended nanostructures directly in bulk diamond so the fabrication is as follows first we use ev photography and and reactive etching to define the general shape of the device that we want in diamond and then we we use conformal coating in the form of of atomic layer deposition in order to protect all the side walls and also the top surfaces of the device and then we remove selectively remove the top surface of the of the coating the conformal coating and that leaves the sidewall protected but the top surface is exposed and then what we do is we do reactive ion etching but without any bias so basically the the ions that actually the the gas actually the etch is diamond which is oxygen to form carbon dioxide basically it doesn't have any bias so it reacts uh chemically with the diamond and this basically does a uh isotropic etching along the crystal planes of the dye and by doing a time edge we and after removing the mask we end up with a suspended uh photonic structure directly on the surface of output and these are the fabrication results you can see various steps of fabrication and the final steps of fabrication we end up with with uh really nice uh suspended structures on the surface of bulk time so we did this with one d for one d structures we can make wave guides crystals which are cavities or resonators on a nanoscopic level but we a year later we also managed to extend this process into into some sort of planar photonics platform so that allows us to do significantly more in terms of the uh in terms of the types of devices we can fabricate we can now start to think about um you know importing some of the something more mature design some of the more exciting designs from other platforms directly into diamond and also use it for cavity qed experiments and things like that but the what i really want to talk about today is the the core of this chip which is the quantum photonic uh what we call the quantum photonic chiplet and they are basically an array of of wave guides in diamond and and so this is the fabrication of this so this is basically a for example here shown is an eight channel uh triplet a photonic triplet that we can that suspended in diamond and here is a 16-channel photonic triplet in time and back to this platform back to this image again so what we did then is we fabricated the the photonic integrator circuit and in a different material which is nitrite and we co-designed it such that it fits with this uh with this photonic triplet that i just showed and um now we just have to find a way to integrate these two materials together and the way we uh so but before that i would like to talk about how we um fabricate the artificial atoms in diamonds so we also use a uh fabrication process based on uh focus ion beam so the focus ion beam instead of a is basically like basically like a sem microscope but instead of electrons it's replaced by um some other form of ions in this case we use silicon silicon or germanium and this is basically again like a microscope so it's like it's a focus beam that we shine onto the surface of diamond and then after annealing and some a little bit of chemical treatment and we end up with you know uh under microscope with an array of qubits that look like this so each bright spot here is a it's a color center a corner imaging diamond basically a qubit and this allows us to create in a in a in a regular you know some sort of regular grid in a in a some with somewhat high u uh array of color centers for for subsequent integration and then if you and then we we align the um these triplets using uh even lithography and after fabrication you can see that um you can see under the microscope that you end up with these bright spots in the waveguides and each of this bright spot again is this quantum emitter so we successfully basically integrated these qubits into um into every channel of this of this object's triplet and this is why we like this triplet framework is because you can see here that for this eight channel chiplet you know every each of each and every waveguide in this triplet contains at least one qubit so this can be uh this is basically a really useful uh uh triplet because dao if we just integrate this one by one then we basically get to you know overcome the exponential uh scaling the exponentially suppressed scaling of building a large system by just integra by just using these triplets and then uh uh for integration uh conversely if you just look at this 16 channel chiplet you get to see you see that you know not every um not every waveguide in this triplet contains an emitter and this is you typically the trade-off you know when you try to build you know a hybrid system you know when you have uh you you would like to optimize the you know the size of your your die or your or your triplet in order to maximize the yield of this of this uh in this heterogeneous integration process so again um the way we integrate this quantum photonic chiplets into the into the photonic circuits is we use a pick and place integration so this is literally a what it does is we take a needle and we remove a chiplet one by one and populate this socket in in these triplets and in this photon integrate circuits so now you can see the power of this approach is that we have a linear scaling in the yield so this basically the process of building this large scale system is now not exponential but just linear with the uh with this with this success probability of this process and again the the the photonic integrated circuit is is a nitride on sapphire photonics and there's a reference for that here and the reason why we work with nitrite as our material is that it has high transparency now visible and it is also yes also sound yeah it's also suitable for nonlinear optics so it can also let us use it for active control of the of the photons after the photons emitted by the quantum uh where the quantum emitter is coupled to the photonic copper the photonic circuit and in principle that allows us to build like switches and modulators directly into the uh directly or into the chip which is otherwise unavailable in in diamond so this is the result of our uh assembly process so it's a 128 channel uh photonic chip each of which containing a um at least one qubit so it's about four millimeters big and you know it's both sides here left side right side here image and it's a it's all it's a single chip you know it's all it's all designed and fabricated and assemble in-house it's 16 integrated triplets each of which contains eight channels so 16 times eight gives us 128 and um of these 128 it is of them are we've got a couple and vacancy centers is a type of quantum meter and 40 of them are silicon vacancy centers another type of quantum meter and uh because of because it's now in a different platform we can also use the uh the you know the we can also access the different layers in the photonic circuits in order to build electrodes into it and enable us to control uh the optical transitions of these emitters so this is the uh scm image of the quantum socket and the core so this is the uh there is the nitrite uh photonic integrated circuit the pic and then there's a socket here where it where we can place the diamond and so we place the diamond gear with relatively good accuracy and so shown here in blue is the diamond and yellow is the nitric atomic circuit and this basically allows us to transfer the photons from the diamond emitted from the quantum emitter and diamond into the photonic integrated circuit for uh photon manipulation and the way this hybrid photonics circuit works is as follows so normally if you just have a suspended diamond the more the more profile looks like uh like like this it's highly confined in the high index diamond and if you just have a photonic circuit this is how you look like it's uh it's it's uh also confined nitra in the higher index material and the way we make this uh transfer from the diamond into the nitro is by by tapering that right by introducing a interaction region between the diamond and the nitride so the way this interaction is achieved is by tapering the diamond and also the nitrite such that it forms a a super mode that looks like this and by going through this uh transition uh adiabatically we can basically transfer the light from the diamond layer up here into the nitride with over 95 percent coupling uh efficiencies in design experimentally we get a little bit less we get about 35 expect a percent in experiment uh but we think we know why that is so this is the setup that we use to characterize the setup so the system so the whole chip is placed into a 4k cryostat which has a an objective uh outside the cryostat for imaging purposes and also in it we have a fiber that allows us to breathe out from the photonic circuit so you can have we can perform basically our experiments using either from the top or through the fiber but because these are basically but because this is an integrated system this is the real power of this approach is everything can be interfaced with a fiber network so the one of the measurements that we we did was measuring the the uh you know uh uniquely as a uniquely quantum uh uh phenomena which is photon anti-bunching so because because the the because we are dealing with single emitters here the photons emitted by the uh uh by the single emitters are emitted as single photons so if you try to detect the statistics if you try to measure the statistics of this photons you would see that they emit photons one by one and which means that if you try to measure a coincidence at in along in two detectors you would not see any coincidences between the detectors because the photons are made up one by one and and indeed that's what we see so the photons that are coupled through the from the emitter to through the waveguide and into the fiber and then onto the detectors all have these uh statistics where the the photons have this so-called anti-bunching behavior right they don't and they i mean uh the statistics are basically one by one photon emission and we see that across all channels you know whether it's germanium vacancy or silicon vacancy centers so this basically verifies that the light that we're getting off chip are is is quantum in nature uh so this is the summary of the you know the statistics so basically uh this value here below zero point anything that that is below 0.5 tells us that we are dealing with a single ammeter so basically in all 128 channels we have this quantum statistics of anti-bunching in all in all channels we can do some integrated quantum photonics experiment for example you can send light through the fiber and also detect the emitted photons through the fiber and and do a spectroscopy and so there's no there's no any free space optics involved everything's contributed and we can basically do again we can do spectroscopy and verify we measure the line widths and and measurements like that all with the fiber and this is really useful as an all fiber spectroscopic tool because if you're trying to build you know many of these systems and deploy them in many different repeater stations then you uh you want everything to be utilizing you know the fiber network existing fiber networks and fiber optic-based technologies um we can also measure the the photon fluorescence uh directly on the trip and with high signal noise ratio and we can also see uh photon interference uh effect where if we send a photon through the through the emitter when we send a laser through the emitter we see that the uh the transmission of the laser is extinguished when it passes through the emitter so it's basically like a single atom switch that controls whether or not a laser passes through the waveguide so that's also really exciting and but perhaps first the most important metric here is that if you just take a look at the uh the coherence properties of these photons emitted by these emitters we see that they are all close to the lifetime limit so what what what the lifetime limit is is basically the you know basically the radiative uh lifetime of the emitter so that gives you uh that get in in a fuller transform relation that gives you you know a limit on what kind of bandwidth of a photon that you can get from this emitter so typically if you have uh noise in your system for for example due to fabrication or stray fields in the uh electric fields or magnetic fields that causes wandering of the frequency of the emitter and that basically dephases the the the photon so the temporal shape of the temporal properties of the photons are typically uh degraded in nanostructures and in uh but here we see that uh we recover this so-called lifetime limit in in all of these systems so this is really exciting because we after doing uh significant nanofabrication and also hybrid integration we maintain the the quantum coherence of the of the of the photons emitted by the system and because it's a you know now we have a red like a 3d uh cross section we can start to put electrodes uh in the system so we can put uh uh basically uh different layers of uh electrodes uh go over here for example and this allows by applying voltage this allows us to basically bend the diamond and because when you bend the diamond you're basically distorting the lattice of the defect near the defect and that basically causes the shape of the you know the basically causes the transition of the um optical transition of the system to shift and indeed by by sweeping the voltage we can see that the emitted frequency shifts correspondingly and that allows us to basically tune the um emission of the photons uh by some tens of gigahertz and what we did with that is what was we if we just take a look at different ammeters uh different wave guides we can see that they because as i said these solid state systems are slightly different from one another they all emit at slightly different frequencies or wavelength but by applying voltage we can selectively um align any pair of these three emitters together at distinct voltages and this basically sets the stage for us to do some sort of photon interference between these emitters which is a resource for generating entanglement remote entanglement between these with that i'd like to end with a summary and outlook for my of this platform uh so first we've demonstrated a versatile technology platform for diamond photonics allowing you to fabricate various structures and nanostructures in diamond and then we managed to uh to achieve this logical integration of quantum diamond triplets with photonics which now allows us to build relatively uh uh large uh quantum systems based on uh based on this technology platform and really the next challenge ahead is to really coherently connect all these channels together um in a quantum way so that we can you know use the power of quantum mechanics for this uh uh quantum speed ups in this and quantum security and this network and computing uh protocols but there's a lot of work to be done still so um we've only managed so far to you know demonstrate as as a you know some sort of experimental blueprint how we may build a large relatively large uh quantum system based on uh imperfect and low yield systems but now we have to now that we you know confident that we can we have a path head now really is it's all about bringing in more advanced of the electronics and uh and in order to you know realize uh and make use take advantage of the power of integrated photonics so for example integration of modulators switches and and and detect in detectors in the photon detectors would be crucial in the next step of this technology towards building a um uh integrated quantum computing and scale a scalable quantum computing uh architecture so with that i'd like to acknowledge uh my uh advisor professor england and our collaborators at sandia national labs that has this has allowed us to that has this tool that allows us to build this focused on beam of uh of of quantum meters and their responding agencies and in particular in the lab like thank uh my uh my co-author song julie and sarah moradian and also various other people who contributed uh to to this project um that like to thank you for your attention and i'm open to take questions well thank you so much this was a very inspiring talk it is uh remarkable what uh we now can do thanks to the talents of people like you in uh patterning forming diamond waveguides and then actually imprinting on its optical nanostructures hence allowing us to think about diamond optics i am going to start with some questions i would encourage the audience to send in a chat or by raising a hand additional questions so that we can have uh even more insights into this remarkably good topic um the i mean i guess let me start with uh just the technique of patterning diamond itself which uh i i'm very impressed in the way that you are able to clearly do the etching then by providing some sapphire aluminum oxide to be able to selectively choose how to do isotropic or non-isotropic etching um how does the defect on the edges of the waveguide affect the performance of what you're observing uh is the edge of the waveguide providing you additional interference with your quantum signals uh or certainly it will provide some amount of roughness that might diminish your optical transmission but i guess more importantly does it interfere in any way uh with the observation of your uh resonance responses that you're hoping for yes uh thanks for the really excellent question so yes uh so this is a is a it's a very active area of topic where where people are investigating the effects of nano fabrication on the properties of the embryo itself so as we all wear like surface roughness and um i mean like edge and sidewall roughness things like that obviously it affects the optical uh optical properties of the device however there are also uh potential traps for charges and uh deleterious defects in diamond where they can cause you know uh uh dephasing of the ammeters so basically they are little you know current sources basically that causes magnetic fields and and also uh stock shifts in the in the in the in the in the in the um the emission of the emitter itself so these are you know things that are going to you know shift the frequency of the emitter or uh long scale of fast time scale so these things really affect the properties of their mirrors so i do not have much insight to offer other than the fact that with a good nano fabrication process you eliminate most of these effects and the evidence for that is when you try to measure the coherence of the emitted photons and you see that they are close to what you know what you can achieve uh just you know from the fundamentally from the from the lifetime of the emitter so that means that the effects of this is probably quite reduced currently so maybe i'll extend that question uh by looking at your field affected change in the resonance i believe maybe it was like 27 that showed the ability to apply bias between the top and the bottom electrode and consequently shift the frequency of the response um you associated that shift uh with the lattice strain inside the diamond and consequently lattice strain the vacancy that might be emitting um as opposed to saying that this might be due to the charging of the waveguide or just the presence of the free electrons in vicinity of the emitter um is there a way to distinguish between the two is the second effect i mentioned really not relevant uh because the lattice strain is much more significant could you possibly comment on that yes so that's a very excellent question so this is a really uh uh here we are using this emitter here which is a i think i mentioned is the silicon vacancy or the german vacancy and what's really exciting about these ammeters is that they are symmetric in their in their in their shape so they're actually uh insensitive to electric fields to first order so they don't have a dc stuck shift so and in fact that's what people observe we try to apply electric fields on this mdrs they do not shift to until you apply a strong enough electric field and um so this and so here is basically a it's a it's basically like a diamond mems here it's like a microelectrical structure that uh here's a capacitive uh uh structure that allows us to basically deflect the diamond and that's what we attribute to uh this is called strain killing i guess of the emitter so this is this is likely the the most dominant uh effect in in in the shift of this frequency here that we observe but yeah that's a good that's a really good question i think well i guess the other signature of this is your line width doesn't seem to well it is affected somewhat but in not a direct not a linear way uh it does go from 40 to 80 even 190 uh megahertz which i guess you're still associating though with the distortion of the lattice as opposed to with a presence of charges in the vicinity exactly and um let me see if i have a slide for that so yes so here if we see uh we just apply um a different voltage and we monitor the the frequency of the emitter over a long time scale we can see that yes they move around but within a single millionaire you know within a short time scale they're actually still you know lifetime limited so um so this is more this is probably due to the common drifts in the system and and you can see that as you apply larger then this drift becomes uh of the emitter's frequency and the frequency tend to become uh larger and this is probably due to the fact that now as i mentioned that they were these are symmetric emitters so that they they are quite insensitive to um to to first order uh perturbations in the in the system and by applying large enough strain you're actually they're breaking that symmetry and so that's why you probably see more shifting than in the frequency sometimes but yeah but the effect remains that but the fact remains that the the center frequency itself shifts uh with the uh strongly shifts with the flight applied bias excellent um i understand there are a few questions in the chat um unfortunately i cannot see the questions so i would ask the participants that do have questions um to uh possibly raise your hand uh and uh i will call upon you and you can verbally ask my apologies for that for the technical glitch of me not seeing the actual chat questions great noel great presentation thank you very educational um can i ask you how the etching is done do you guys use like lithography or any specific methodologies yes um so let me see so uh which that was interesting so we use standard uh processing tools like icp rie to etch the mask and the diamond itself uh and then we use um for for the coding of the sidewalls we use atomic layer deposition and in terms of metrology we is mostly just a scanning electron microscopy of the devices got it yeah we may ask a second question and that is uh i notice you use gold cleaning for some of these is there gold plating uh yes so yes i do not have a slide for the fabrication of the electrodes yes they are gold and we did it via liftoff uh not uh yeah i understand the reason you're using gold it's the material it's the emitting power from the gold as a material uh no no we we just wanted a conductor and gold one you know one of the easiest things yeah yeah so thank you very much is there any distinction issues between gold and diamond as you deposited um i assume you need an interstitial layer of some sort oh yes uh we use uh titanium uh yeah the time is running out but let's uh just call upon dimitri i understand to meet you you might also have a question oh yes uh thank you uh thank you for a great talk noel and my question is that related to the inhomogeneity sort of challenge you mentioned at the beginning so how similar are the uh these cubita meters to each other and what is the figure of merit or is there a single figure of merit to sort of uh evaluate quantitatively this in homogeneity thank you thanks for the great question so um so uh as you can as as i've shown here is like even though each of these emitters are you know they have really good coherence properties but the center frequency of these emitters are not quite homogeneous and uh if i remember correctly the numbers are on on the other 50 to 100 gigahertz so they are all narrow you know tens of megahertz but they you know their distribution of the center frequencies or over hundreds of over 50 to 150 to 100 gigahertz and this problem usually gets worse in nanostructures because now you have uh you know built in uh that is strained and things like that that you know and and due to fabrication as well that causes the shift of the uh center frequency and that's why it's really important to implement uh an integrated solution to you know once you integrate these emitters into the circuits you also need an integrated solution controlling them so um so here we for example we've shown that we can control we can shift the frequency by tens of gigahertz as well to compensate for uh this uh inhomogeneities and this experiment here we've shown that even though they you know they start off some tens of gigahertz apart as well you know at applying distinct voltages we can you know choose any pair of them to align to a line to the same spectral band basically um okay thank you thank you um the time is running out but let's just put one more question given how excited the audience is about your talk um if you can just call upon daniel hi uh really nice work on oil so i have a question on how you exactly integrate these chiplets like can you comment a bit more on that yeah sure let me get back to that so as you can see here we use a probe here this is a standard probe that people use in for example focus ion beam uh metrology and this is a tungsten probe that is you know has a very small tip you know the radius of curvature is about one micron i believe and basically this probe sits on a uh on the piezo stage that we move under the microscope and this you know sorry this literally is as as this animation was showing it's we coming and we pick it up and put it into the photonic circuit and yeah is that is that i hope that answer the question answers the question so you just break it out with that needle itself and then it sticks there and then you can nicely transfer to your like yes to your right yeah so it's nice it nicely works out that it's it you know the it sticks to the probe but it sticks but the diamond sticks stronger to the to the circuit than it does to the probe so it all works out well in that sense i'm sure it takes a steady hand to do that oh it's all it's okay it's all piezo control but yeah [Laughter] yeah uh well i and thank you very very much for an extremely uh stimulating talk uh it is indeed uh clear to us that the quantum compute engages upon us and it's indeed advancements of you your colleagues groups like dirk english group that are going to indeed bring it bring that into reality for the rest of us thank you so much for giving us this nano explorations talk let me uh upload you i indeed encourage the audience to do the same and as we are thanking noel i will also uh just announce the next talk the next nano explorations will happen in two weeks from now on february 16th our speaker is uh james mcrae um a mechanical engineering phd candidate and the topic of his talk will be silicate-based composites as heterogeneous integration packaging material for extreme environments so i do hope you can join us in couple of weeks and get another amazing talk by our students noel congratulations on finishing your phd last week and i wish you all the best in your next set of great adventures thank you thank you for joining us today thank you my pleasure bye all the best of all take care you

2021-03-04 15:40

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