The Quantum Kitchen
The exciting thing is getting to cook
I really like the analogy of algorithms as recipes. I think it’s one of the few effective analogies out there, in the sense that most people have a good feel for the reference point, and the mapping between the algorithms and recipes is reasonably tight.
We can extend the analogy to quantum computing. Other people have made similar connections in the past (here, here, here, and here).
In this post, I take a different approach.
Extending the algorithm-as-recipe analogy
If an algorithm is like a recipe, then we can think of the inputs to the algorithm as ingredients in the recipe. An algorithm also has operations the same way that a recipe has techniques (e.g. grate this, mix these two things together, bake it all for 30 mins). And an algorithm is usually executed on a computer, the same way that a recipe is usually executed in a kitchen.
Running an algorithm produces an output, much like following a recipe produces a dish. But a dish on its own isn’t necessarily a meal. A meal is what you get when that dish is combined with other dishes, served for a particular purpose, and eaten (maybe a stretch by this point, but stay with me). In the same way, an application is what happens when the output of an algorithm is used as part of a broader workflow to do something meaningful.
We can summarize the mapping as follows:
recipe ↔ algorithm
ingredients ↔ inputs
techniques ↔ operations
kitchen ↔ computer
dish ↔ output
meal ↔ application
A standard kitchen, like the one you cook in, obeys the laws of classical physics.1
But now imagine that your kitchen is a quantum kitchen.
The quantum kitchen
A quantum kitchen obeys a completely new set of physical laws: the laws of quantum physics.
In this quantum kitchen, you have a bunch of exotic ingredients that you’ve never seen in a regular kitchen. And you have a bunch of exotic techniques that you’ve never had access to in a regular kitchen.
But it’s up to you to come up with quantum recipes.
And since it will be very expensive to build this quantum kitchen, we want those recipes to either prepare certain meals more quickly than the same meals prepared in a regular kitchen, or you want those recipes to make meals that are better in different ways, for example, more tasty, or healthier, or prepared with less expensive ingredients, or in larger batches.
Barbie and The Sims
Unfortunately, we don’t have a fully-functional quantum kitchen yet.
What we do have is the analogue of a quantum Barbie kitchen.2 And we also have the analogue of a—potentially larger—quantum kitchen inside a game like The Sims.3
What’s neat is that, despite this, we’ve already been able to create quantum recipes that can be executed in existing Barbie kitchens, that are able to prepare certain kinds of dishes more quickly than you could in a regular full-sized kitchen4.
The problem is that no one wants to eat those specific dishes56.
Meals that people want to eat
It turns out that we don’t actually have very many proven quantum recipes for meals that people want to eat (not yet anyway)7.
But we know that one of these recipes8 makes it possible to prepare a certain dish9 much, much more quickly than you could in a regular kitchen with a regular recipe. This dish is used in a meal (a poisonous meal?)10 that is so important, that being able to make it more quickly, is almost enough of a motivation on its own to build one of these quantum kitchens. In fact, almost every major government has a strong interest in having one.
Can we create new recipes?
If we only have a few proven quantum recipes for meals that people want to eat, can we come up with others?
We have reasons to believe that we can, but only for some specific kinds of dishes, so we still need regular kitchens to continue to make many of the dishes we already know how to make, as quickly as possible.
A more exciting possibility is that we might be able to make dishes that we’ve never made before, or even imagined being made in a regular kitchen.
In both cases, however, we need to create more quantum recipes.
How do you create new recipes?
I often wonder about this when I’m eating something. How did someone think to combine these ingredients in this particular way? Occasionally, some brilliant chef might have had some special insight, but the typical answer is trial and error.
We’ve been lucky that a few people have been able to come up with a handful of quantum recipes in the abstract, and we’ve been lucky that we know some special tricks for confirming that these recipes will be faster than regular recipes, without having to actually prepare the meal.
But to really come up with new exotic recipes, we need to get into the kitchen and play around, to get our hands dirty, to accidentally combine things together that don’t make sense at first, to let something sit on the counter for too long, and have it surprise us.
We can only do that once a fully functional quantum kitchen gets built and we can cook in it.
The exciting part is getting to cook
The space of possible quantum recipes is structured in a way that we don’t fully understand yet. We can reason about it abstractly. We can prove a few things on paper. We can test small examples in the Barbie kitchen or simulate them in the Sims kitchen. But we don’t have the kind of hands-on experience, in a real quantum kitchen, that lets us develop intuition.
If you talk to chefs11 in the field, this is often what motivates them. Not the promise of specific meals, but the chance to explore a new kind of kitchen, unlike any they’ve ever cooked in before. To see what happens when you actually start combining these exotic ingredients in unusual ways.
What we know and have built so far has allowed a small number of genuinely new recipes to be discovered, and it’s given us hints about what might lie beyond them.
The hope is not that a fully functional quantum kitchen will suddenly reveal a menu of obvious new meals, but that spending time inside this kitchen will gradually expand our sense of what’s even cookable. That’s what’s exciting to me.
Bon appetit!
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At least on the scale on which the cook operates.
Existing quantum hardware with several hundred physical qubits or a handful of logical qubits.
Quantum computer emulators like NVIDIA’s cuQuantum.
The various random circuit sampling and Boson sampling demos.
They don’t have any practical applications.
Ok, maybe a few physicists might want to eat some of the recent dishes demonstrated by Google and Quantinuum, but they won’t be immediately commercially interesting to most food companies.
Scott Aaronson recently summed it up nicely:
One more time for those in the back: the main known applications of quantum computers remain (1) the simulation of quantum physics and chemistry themselves, (2) breaking a lot of currently deployed cryptography, and (3) eventually, achieving some modest benefits for optimization, machine learning, and other areas (but it will probably be a while before those modest benefits win out in practice). To be sure, the detailed list of quantum speedups expands over time (as new quantum algorithms get discovered) and also contracts over time (as some of the quantum algorithms get dequantized). But the list of known applications “from 30,000 feet” remains fairly close to what it was a quarter century ago, after you hack away the dense thickets of obfuscation and hype.
Shor’s algorithm
Factoring
Breaking the cryptographic codes that are currently used to protect most of today’s digital communications.
Researchers