# How Chips Are Using On-Chip Quantum Dots for Single-Photon Emission

An episode of [The Hardware Podcast with Fexingo: Chips, Devices, and Electronics Engineering Conversations](https://invisiblenetwork.ai/podcast/1896799982), 6 Jul 2026, 9:37.

Audio: https://audio.fexingo.com/business/the-hardware-podcast/episode-0095.mp3

In this episode of The Hardware Podcast, Lucas and Luna dive into how chipmakers are embedding quantum dots directly onto silicon to create single-photon emitters. They explore a breakthrough from a joint research team at MIT and the University of Chicago published in Nature Photonics in early 2026, where indium arsenide quantum dots were grown on a silicon photonic chip, achieving over 99% single-photon purity at temperatures above 4 Kelvin. The hosts discuss why this matters for quantum key distribution and optical quantum computing, the engineering challenge of integrating III-V materials with CMOS, and what it means for future on-chip quantum networks. Lucas explains the specific mechanism of quantum confinement, while Luna questions the scalability of current fabrication techniques. #QuantumDots #SinglePhotonEmission #SiliconPhotonics #QuantumComputing #CMOSIntegration #NaturePhotonics #MIT #UniversityOfChicago #IndiumArsenide #QuantumKeyDistribution #OnChipQuantum #IIIVMaterials #QuantumNetworking #HardwareEngineering #ChipDesign #FexingoBusiness #BusinessPodcast #Technology Keep every episode free: buymeacoffee.com/fexingo

## Transcript

Lucas: So earlier this week, a joint team from MIT and the University of Chicago published a paper in Nature Photonics that I think signals a real inflection point for on-chip quantum optics.
Luna: The quantum dot paper? I saw the headline — single-photon emitters on silicon, right?
Lucas: Exactly. They grew indium arsenide quantum dots — that's a iii v semiconductor — directly onto a silicon photonic chip. And they demonstrated single-photon emission with over 99 percent purity at temperatures above 4 Kelvin.
Luna: That purity number is wild. Because anything below 99 percent and you start introducing errors in quantum key distribution or optical quantum computing.
Lucas: Right. And the fact that they're doing this on silicon — not just in a lab with exotic substrates — is what makes it a hardware-engineering story, not just a physics curiosity. They used a technique called 'droplet epitaxy' to grow the dots inside predefined pits etched into the silicon waveguide.
Luna: So they're basically creating an array of identical quantum dots at precise locations, rather than the random nucleation you get with traditional Stranski-Krastanov growth.
Lucas: That's the key advance. In most quantum dot work, you grow a layer and then you have to search for good dots under a microscope. Here, they predefined the positions — thousands of dots per chip — and each one emits single photons on demand when pumped with a laser.
Luna: And they did this at temperatures that are achievable with standard cryocoolers, not millikelvin dilution refrigerators. 4 Kelvin is still cold, but it's practical.
Lucas: Exactly. That's the engineering angle that I think gets underappreciated. A lot of quantum optics work happens at 10 millikelvin — which is expensive, bulky, and slow to cycle. 4 Kelvin opens the door to compact cryogenic packages that could eventually fit in a datacenter rack.
Luna: But let's be honest — iii v on silicon has a long track record of being the technology that's always five years away. What makes this different?
Lucas: Fair question. The difference here is that they solved the lattice mismatch problem not by growing thick buffer layers, but by using the droplet epitaxy in those etched pits. The quantum dot is effectively strain-free because it's confined in all three dimensions by the pit geometry.
Luna: So the silicon itself is doing mechanical work — constraining the dot.
Lucas: Exactly. And that means the optical properties are closer to what you'd get from a free-standing quantum dot, but with the advantage of being integrated into a silicon photonic circuit. They demonstrated on-chip waveguides routing the single photons to a beamsplitter, and showed hong ou mandel interference — that's the two-photon quantum interference effect.
Luna: That's the gold standard for indistinguishable single photons. If you can show hong ou mandel visibility above 90 percent, you've got a practical source for quantum logic.
Lucas: They reported 92 percent visibility. So it's genuinely good. And the chip itself was fabricated using cmos compatible processes — 193-nanometer deep-ultraviolet lithography for the waveguides, and the quantum dot growth was done in a molecular beam epitaxy chamber that's standard in any iii v fab.
Luna: So the question becomes: can you scale this to the thousands of indistinguishable single-photon sources you'd need for a fault-tolerant optical quantum computer?
Lucas: That's the open problem. In this demonstration, they had about a hundred functional dots per chip, but the yield — the fraction of pits that actually produced a good quantum dot — was around 60 percent. For a large-scale system, you'd need yield above 99 percent, and you'd need all the dots to emit at the same wavelength.
Luna: And right now, even with the pit confinement, there's still some variation from dot to dot because of slight differences in size and composition.
Lucas: Right. The team is working on a post-growth tuning technique — applying a local electric field to each dot to shift its emission wavelength into alignment. They showed it works in principle on a few dots, but doing it at scale is a big engineering challenge.
Luna: It reminds me of the early days of silicon photonics for classical data centers. People said you'd never get a good laser on silicon, and then Intel and Luxtera figured out hybrid integration. This feels like that moment for quantum.
Lucas: I think that's the right analogy. The key difference is that here, the emitter is monolithically grown, not hybrid bonded. That's a significant advantage for manufacturing cost and complexity. If the yield and uniformity problems can be solved, this becomes a genuine platform for quantum networks.
Luna: What about the application timeline? Are we talking five years or fifteen?
Lucas: I'd put the first practical quantum key distribution chips — using these emitters for secure communication — at maybe three to five years. For full-scale optical quantum computing, more like ten to fifteen. But the pieces are coming together faster than I expected even two years ago.
Luna: And I think the market is starting to pay attention. I saw that the Defense Advanced Research Projects Agency — DARPA — recently put out a solicitation for on-chip quantum networking components. That kind of funding tends to accelerate things.
Lucas: Yeah, DARPA's 'Quantum-Enhanced Networking' program explicitly calls for integrated single-photon sources on silicon. So there's a pull from the government side, and this mit chicago work directly addresses that need.
Luna: One thing I'm curious about: how does the performance compare to other on-chip single-photon sources? There's been work on color centers in diamond, and on defects in silicon carbide.
Lucas: So the color centers — like the nitrogen-vacancy center in diamond — have the advantage of room-temperature operation for some applications. But their emission is broadband, and they're harder to integrate into photonic circuits because diamond isn't a standard photonic material. The quantum dots have much narrower linewidths and higher indistinguishability, but they need cryogenic temperatures. For quantum repeaters and long-distance entanglement distribution, the quantum dots are probably the better path, because you need that high purity and indistinguishability.
Luna: And silicon carbide defects are promising, but they're still behind in terms of brightness and on-demand emission.
Lucas: Right. So the quantum dot approach, especially on silicon, has a clear roadmap. The next milestone will be demonstrating a two-qubit gate using two quantum dots on the same chip. If that happens in the next year or two, we'll know this is real.
Luna: You know, this kind of deep-dive into a specific fabrication technique is exactly why I love this show. It's not just a high-level overview — you actually explain the mechanism.
Lucas: That's the goal. And it's why we keep the show ad-free — we want to have the freedom to go into this level of detail without worrying about sponsor messages. If you find this kind of content valuable, one way to support it is through buy me a coffee dot com slash fexingo. It helps us keep the show independent and focused on the engineering, not the commercials.
Luna: Yeah, and it really makes a difference. Every contribution lets us spend more time researching episodes like this one.
Lucas: So back to the quantum dots — the paper also demonstrated on-chip detection of the single photons using a superconducting nanowire single-photon detector integrated on the same chip. That's another piece of the puzzle.
Luna: Wait — they integrated the detector too? That's huge. Usually detectors are off-chip, which introduces coupling losses.
Lucas: Exactly. They used a niobium nitride nanowire detector fabricated right on the silicon photonic chip, with efficiency around 70 percent at the quantum dot wavelength. So you've got source, waveguide, and detector all on one chip. That's a complete quantum photonic integrated circuit.
Luna: That basically turns the chip into a self-contained quantum node. You could imagine linking multiple chips via optical fibers to create a quantum network.
Lucas: Exactly. And that's where the technology goes from a lab demo to something that could actually be deployed. There's a lot of work ahead — improving yield, reducing noise, scaling to more dots — but the foundation is there.
Luna: So if someone wanted to get into this field — say, an engineer with a background in CMOS fabrication — what skills would they need?
Lucas: The biggest gap is usually in understanding quantum optics and the iii v growth process. But the cleanroom skills are directly transferable. I think we'll see more cross-training programs, especially at universities that have both a strong semiconductor fab and a quantum research group.
Luna: And for listeners who want to read the paper, it's in the June 2026 issue of Nature Photonics, titled 'Deterministic Single-Photon Emission from Droplet Epitaxy Quantum Dots on Silicon Photonic Circuits.'
Lucas: We'll link to it in the show notes. And I think this is one of those episodes where we'll look back in five years and say — that's when things started to get real.

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