Minecraft qCraft interview: the mod that lets you build quantum computers with blocks

Duncan Geere at

Daniel Ratcliffe is the creator of the influential Minecraft mod ComputerCraft, which allows players to code for in-game computers. But his latest project, qCraft, is even more audacious - teaching quantum computing to the next generation of programmers. We spoke to him to find out what it was like working with Google, why modpacks dominate Minecraft mod discovery and how to teleport a house to the bottom of the ocean.

PC Gamer: Thanks for talking to us, Dan! Let's start with the basics - what is qCraft and where did the idea come from?

Ratcliffe: Well, it was all Google's idea. Basically Google reckons that in 20 years time we'll have quantum computers, which are computers that operate completely differently to the ones that exist today in really non-intuitive ways. They want to get in on the ground floor of this, and so it's in their interest that programmers in ten to twenty years time understand this stuff. Kids like Minecraft, so they had the idea of making a Minecraft mod to start teaching quantum intuition to the programmers of tomorrow at an early age.

The mod adds a bunch of blocks that act in ways that are unexpected but are sort of similar to the non-intuitive principles of quantum mechanics. The three principles that we're showing are entanglement - that the states of things that are far apart can be linked, observer-dependency - which is how things can have different states depending on how you measure them or where you measure them from, and superposition - which is the idea that until you measure something it has many states at once, and they don't decide a state until you look at them.

PC Gamer: So how did Google come to get in touch with you?

Ratcliffe: Well, Google contacted TeacherGaming, who do MinecraftEDU, which is the version of Minecraft that they sell to schools. They contacted me because I've been doing some work with them related to my other mod, ComputerCraft, and they knew me. Then, once I was hooked up with them, Google introduced us to a physicist from Caltech and then between us, the four parties, we designed the mod. It was a push and pull between making something that's fun for a game and making something that's a complete simulation of quantum physics and I think we landed somewhere in the middle on that.

PC Gamer: That must have been a pretty cool email to get - how did you feel when it landed in your inbox?

Ratcliffe: Yeah, it was really cool - I got paid to make a Minecraft mod! That's something I've been doing for free, for fun, for a long time. Plus, with a name like Google attached, it's had loads of attention that I wouldn't normally got for my work.

PC Gamer: You mentioned the conflict between making it accurately reflect reality and making it fun. What were some of the things that you came across that you could have put in but it wasn't fun?

Ratcliffe: Well, we made two versions of it. Basically I went and read a book on quantum physics and then I read a bit about quantum computing, and then I set out to make a simulator of the kind of things you can do on quantum computers. What we ended up with was a really complicated system that was really hard to understand. Even if you did understand it, and spent a long time building stuff, it was really hard to build something that was actually useful in your world - because we don't have actual quantum computers yet, you just end up with very complicated mechanisms for generating random numbers.

So we went back and asked: "What are the actual principles that people want to know?" and "What are the simplest ways we can represent those concepts?" So we picked interpretations that allowed us to design interesting traps and puzzles in our worlds.

PC Gamer: What's next for the mod? Are there other aspects of quantum mechanics that you think could be easily replicated in Minecraft?

Ratcliffe: I think I'd like to make what we've built a bit more integrated, so you can use it with other mods. At the moment there's no way to automate anything in there. It would be nice if we made it a bit more mechanical, so that people could build really complicated contraptions with it.

PC Gamer: How about mashing it together with your other mod? Might we see Quantum ComputerCraft?

Ratcliffe: That ties into the automated thing. If I could make both of those mods talk to Redstone, the stuff in Minecraft, I think that would multiply the possibilities of what people can do.

YouTuber, Pr0tonium, recreated a version of the famous Schroedinger's cat quantum conundrum using qCraft using dynamite and some wool.

PC Gamer: The way that you're releasing it - telling people to grab a mod pack rather than bothering with A standalone download - is interesting. Why did you go that route?

Ratcliffe: It's mostly the numbers - to get a bigger audience for Google's sake. If you talk to the people that run the mod packs and get their figures for how many people use them, you'll see that there are massively, massively more people playing mods through mod packs than directly downloading and installing them themselves.

The reason is that installing mods yourself is still a bit tricky - especially if you're pushing towards an educational audience that's not already versed in the world of Minecraft modding. Instead, these mod packs are really good - you just download them and it's one click and you get all these mods. It's quite a process to set all that up manually.

It's an easy way to get an audience. It helped that I'm friendly with the people that run the FeedTheBeast modpack and Joel (Minecraft Teacher), who is the person at MinecraftEdu I was working with, has friends in the Technic mod pack. We managed to use those connections to get included on day one, which is a very rare thing - normally you have to run the public gauntlet before a mod pack will include you.

PC Gamer: What's the best thing you've seen made with it so far?

Ratcliffe: There hasn't been a lot yet because people are still figuring it out. There was a video the other day where somebody built a house and then they teleported their house underwater to the bottom of the sea.

With the entanglement, we stretched the concept so that you can entangle two regions of space, and therefore transport matter between the two by swapping the blocks. So you can define a big area, define another area somewhere else and then build you house in one place, power it up, and then the house gets swapped with the stuff at the other end.

In this case, the water disappeared and the house went down there, and then you had a big block of water where the house was.

The Mike Crafting YouTube channel features several experiments with qCraft, including our favourite, the teleporting house. Watch Mike move a house into the ocean with the aid of a quantum computer.

PC Gamer: Obviously this is an educational exercise at the end of the day. Why do you think that Minecraft is such a powerful educational tool?

Ratcliffe: It's because kids are so invested in it - kids spend so much time playing Minecraft. When you're playing Minecraft, a lot of what you're doing is finding out how the Minecraft world works - how to craft things, what you can find, what you can build, what you can construct out of redstone. The basic experience of playing Minecraft is a learning experience anyway - you have to look things up on wikis, you have to talk to your friends and find out what they've built. If you're already in that world where you're continually investigating and learning and discovering things, it's quite nice to put real educational things in there, so that players will discover them and learn them while they're playing.

PC Gamer: Did you find that the physicists had quite a good understanding of what Minecraft is and the possibilities behind it already?

Ratcliffe: It was about 50:50. You had people who played it and knew it completely, and a couple of people that had never played it. But it was quite easy to get them up to speed.

PC Gamer: Finally, I know you said on Twitter that you're going to talk more at Minecon about what the future of the mod holds, but there is going to be more updates? Are you planning on expanding it?

Ratcliffe: Yeah, I think so. I don't know how much I'm allowed to say at the moment about the Minecon stuff, but it's in two weeks time so it'll be public then. There'll be some of the quantum physicists that have been helping us. They'll be talking a bit more about the science behind it, because it's all part of Google's larger plans to teach quantum physics to people.

If you want to give qCraft a try and explore the weird world of quantum mechanics yourself, the easiest way to to grab the latest version of one of several popular mod packs, including FTB Unleashed, Tekkit and Hexxit. Full download and installation instructions can be found on the qCraft website.