# 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), 19 Jul 2026, 9:19.

Audio: https://audio.fexingo.com/business/the-hardware-podcast/episode-0120.mp3

In this episode of The Hardware Podcast, Lucas and Luna dive into the emerging world of on-chip quantum dots — nanoscale semiconductor particles that can emit single photons on demand. They explore how researchers at MIT and the University of Chicago are integrating these quantum dots into silicon photonic chips, enabling ultra-secure quantum communication and advanced quantum computing. The hosts break down the physics: quantum dots are tiny crystals that trap electrons, and when excited, they release exactly one photon at a time. This single-photon source is critical for quantum key distribution (QKD) and linear optical quantum computing. Lucas explains the key challenge: getting the quantum dots to emit identical photons consistently, and how recent breakthroughs in strain engineering and cavity coupling are improving indistinguishability. Luna brings up the real-world timeline — maybe five to ten years before we see quantum-dot chips in data centers. They also touch on competitors like nitrogen-vacancy centers in diamond and trapped ions. The episode ends with a low-key ask: listeners can support the ad-free show at buy me a coffee dot com slash fexingo. #QuantumDots #SinglePhotonEmission #SiliconPhotonics #QuantumKeyDistribution #QuantumComputing #Nanotechnology #Semiconductors #ChipDesign #Photonics #Hardware #Technology #FexingoBusiness #BusinessPodcast #MIT #UChicago #OnChip #QuantumCommunication #PhotonicChips Keep every episode free: buymeacoffee.com/fexingo

## Transcript

Lucas: If today's tech conversation gave you something usable, you might be wondering how close we actually are to quantum chips you can buy — and the answer, right now, seems to hinge on a tiny particle called a quantum dot.
Luna: I keep hearing about quantum dots in display tech — Samsung TVs, that kind of thing — but you're talking about something different.
Lucas: Completely different. The quantum dots in a QLED TV are just nanocrystals that convert light colors — useful, but not revolutionary. The quantum dots I'm talking about are being embedded directly into silicon photonic chips to emit single photons, one at a time, on demand.
Luna: And that matters because — for quantum communication or quantum computing, you need a reliable source of individual photons.
Lucas: Exactly. Most quantum cryptography protocols, like quantum key distribution, rely on sending single photons. If you accidentally send two, an eavesdropper could split one off and go undetected. So a deterministic single-photon source — one that guarantees exactly one photon per pulse — is the holy grail.
Luna: And regular lasers can't do that.
Lucas: No. A laser emits a coherent state — you can attenuate it down to an average of, say, 0.1 photons per pulse, but that means most pulses are empty and occasionally you get two. It's probabilistic. A quantum dot, on the other hand, can be excited to emit exactly one photon every time.
Luna: So how do you put a quantum dot inside a chip?
Lucas: There are two main approaches. One is to grow the quantum dots directly on the silicon substrate using epitaxy — basically, you deposit layers of semiconductor materials like indium arsenide on a gallium arsenide wafer, and the strain from the lattice mismatch makes them self-assemble into tiny pyramids, about 20 to 30 nanometers wide. Those are the quantum dots.
Luna: And then you integrate them with photonic waveguides and resonators on the same chip.
Lucas: Right. Researchers at MIT and the University of Chicago have both demonstrated chips where the quantum dot sits inside a microscopic cavity that enhances the photon emission rate and directs the photon into a waveguide. The cavity is often a photonic crystal — a periodic structure of holes that creates a defect where the light is confined.
Luna: Okay, so that sounds like the hardware is working. What's the bottleneck?
Lucas: Indistinguishability. For quantum computing applications, you need photons that are identical in every way — same wavelength, same polarization, same temporal shape. That's really hard because each quantum dot is slightly different due to variations in size and composition.
Luna: So they might emit at slightly different frequencies.
Lucas: Exactly. The typical spread is a few nanometers in wavelength, which is huge for quantum interference. But there have been big advances. One technique is to apply an electric field across the quantum dot — this is called the quantum-confined Stark effect — and you can tune the emission wavelength by adjusting the voltage. Another is to use strain engineering: you put the quantum dot on a piezoelectric material and literally stretch it to shift its energy levels.
Luna: And that works well enough to get two separate quantum dots emitting the same color?
Lucas: In the lab, yes. A group at the University of Chicago reported in 2025 that they achieved two-photon interference with visibility over 90 percent from two different quantum dots on the same chip. That's a huge milestone.
Luna: Quick honest thing — we keep this show ad-free, and a handful of listeners chip in monthly through buy me a coffee dot com slash fexingo, which literally funds making episodes like this one.
Lucas: Yeah, it's a small group, but it makes a big difference. We don't run sponsors, no tracking, just the conversations. Appreciate everyone who's part of that.
Luna: So back to those quantum dots — what's the timeline? When will we see a commercial chip with these on it?
Lucas: I'd say five to ten years for a product you could buy. There are startups like QuiX Quantum in the Netherlands and PsiQuantum in the US that are building photonic quantum computers, but they use different sources — mostly spontaneous parametric down-conversion, which is again probabilistic.
Luna: So quantum dots could leapfrog that approach.
Lucas: Potentially. The big advantage is that quantum dots are compatible with existing semiconductor manufacturing. If you can integrate them into a silicon photonics process, you can scale to millions of sources on a single wafer, which is what you'd need for a fault-tolerant quantum computer.
Luna: Are there other single-photon sources being developed in parallel?
Lucas: Sure. Nitrogen-vacancy centers in diamond, silicon-vacancy centers, trapped ions, even molecules. But quantum dots have the edge because they can be electrically pumped — you just apply a voltage — rather than needing a big laser to excite them. That makes them much more practical for integration.
Luna: And what about the cryogenics? Don't most quantum systems need to be super cold?
Lucas: That's another area where quantum dots are improving. Some can operate at liquid nitrogen temperatures — 77 Kelvin — which is still cold but much easier than the millikelvin temperatures needed for superconducting qubits. Researchers are also working on quantum dots that work at room temperature, using materials like halide perovskites.
Luna: I've read that perovskite quantum dots are really bright, but they're not stable enough yet.
Lucas: Right. They blink — they go dark for random periods — which is a death sentence for deterministic photon emission. So for now, the indium arsenide on gallium arsenide platform is the workhorse.
Luna: So who's leading? Is it mostly academic labs or are big companies investing?
Lucas: Both. Intel has a photonics research group that's been looking at quantum dot lasers for years. IBM has published on quantum dot-based qubits. And there's a European consortium called QUDOT that's specifically targeting on-chip quantum dot sources for quantum networks.
Luna: What about the Chinese ecosystem? They seem to be investing heavily in quantum.
Lucas: They are. The University of Science and Technology of China has demonstrated quantum key distribution over thousands of kilometers using satellites and fiber, but their sources are mainly based on spontaneous parametric down-conversion. They've also shown quantum dot sources in the lab. I'd expect them to move fast once the technology matures.
Luna: One thing that's not clear to me: how do you actually get the photon out of the chip and into a fiber?
Lucas: That's a packaging challenge. You need to couple the waveguide mode on the chip to the mode of a single-mode fiber. That usually involves grating couplers or inverse tapers. The efficiency is often around 50 to 70 percent in research devices, but for commercial products, you'd want 90 percent or more.
Luna: And that's another area where integration helps — if you can do everything on one chip, you avoid those coupling losses.
Lucas: Exactly. That's the whole promise of on-chip quantum optics. You have the source, the waveguides, the modulators, the detectors all on the same silicon substrate. It's the same roadmap as classical silicon photonics, just with quantum dots replacing lasers.
Luna: So if I wanted to follow this closely, what should I keep an eye on?
Lucas: Two things. First, the indistinguishability numbers — watch for papers reporting two-photon interference visibility above 95 percent from electrically pumped quantum dots. Second, yield — how many working quantum dots can you get per chip. Right now, it's often less than 1 percent.
Luna: That's pretty low.
Lucas: It is, but it's improving. With better growth techniques like droplet epitaxy, researchers are getting more uniform dots. And if you can fabricate a million dots per chip and only need a thousand that work, that's fine — you just test and select.
Luna: I like that engineering pragmatism.
Lucas: That's how we got to billions of transistors per chip, right? Redundancy and yield engineering. Quantum dots are following the same path.
Luna: It's fascinating that the same semiconductor industry that gave us classical computing might also give us quantum networks.
Lucas: Exactly. And that's what makes this such an exciting area to watch. The infrastructure is already there — the fabs, the design tools, the packaging know-how. It's really about getting the physics right at the nanoscale.
Luna: Alright, I'm sold. Next time I see a QLED ad, I'll think about the single-photon revolution.
Lucas: It's a very different kind of quantum dot. But who knows — maybe one day your TV will double as a quantum repeater.
Luna: That would be a strange upgrade.
Lucas: That's a wrap for this episode. We'll be back next week with another deep dive into the hardware that's shaping the future.

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