Show HN: Quantum JavaScript (opens in new tab)

And yes—not having any dependencies or anything to install was one of my goals to help anyone get up and running with minimal fuss. I have more to say about that here: https://quantumjavascript.app/contributing.html#JavaScript_s...

You’re asking a really good question—I should probably write page on this to make it more clear; it definitely was NOT clear to me at first either! The short answer is “no.” What you’re seeing there is the Q.Circuit.prototype.try$ function which forces a circuit to choose one of its probable outcomes. I mostly added this in so users could write a simple coin-flip demo and get an actual heads or tails result—you know; feel good about making their first superposition and then collapsing it to a conclusion: Q`H`.try$() ? 'tails' : 'heads'

But it’s the management and redistribution of probabilities during the course of a circuit’s operation that is the real quantum magic—not choosing a series of random outcomes. In fact if you search the entire repo for “Math.random” you’ll see that this try$ function is the only “semi-meaningful” use of randomness. (The other calls to Math.random are either part of some included THREE.js bits for the Bloch Sphere visualizer, or for randomly tilting the click-and-draggable gate tiles in circuit palettes, or for choosing random color + animal names. Yes... Random color + animal names!) Q.getRandomName$()

The way we manage probabilities in a simulator is by representing qubits as a pair of numbers. This should give you a better idea of how that works—and what “superposition” means in this context: https://quantumjavascript.app/Q-Qubit.html

But the weirdest part for me to wrap my head around was that there is no answer until you’ve computed the ENTIRE answer. In a regular computer you can ask what the value of a particular bit is at anytime and that doesn’t effect any other piece of the circuit. But with quantum simulation like this you are mixing all of the ingredients together and it is impossible to pull one out, point to it and say “this particular qubit has this particular value!” Instead you can only know the total state of the system.

You’ve given me a lot to think about in terms of adding more content to Q :)

I need another coffee now...

In that website's playground (https://quantumjavascript.app/playground.html), just write:

   H

Now, /why/ does it jump when measured? We don't know, but physicists have many cool theories.

One of which is that it doesn't really jump, but just that there are many universes created and one shows a 0 and another one shows a 1 (Called the Many-worlds interpretation). As weird as it sounds, it seems like the most promising explanation. There are other theories but they all need to add hacks to make the maths work.

I’d like to really flesh out that page; I’ve now come across so many folks that are amazing at explaining this stuff... It’s just a time crunch to juggle all this as you might imagine ;)

These two videos in particular helped me get started:

1. What is a physical quantum computer? https://www.youtube.com/watch?v=OWJCfOvochA

2. How might one compute using it? https://www.youtube.com/watch?v=F_Riqjdh2oM

quantum.country is a good introduction to quantum computing for people with no background other than linear algebra. Even if you don't understand linear algebra you could probably skim it and get a sense for what's going on.

For reference, here’s some of my original reasoning: https://quantumjavascript.app/contributing.html#JavaScript_s...

It is all javascript all the way down.

1. Doesn’t know anything about this particular subject yet.

2. Is probably very tired from whatever it is they’ve been doing. (Day job, raising kids, just general anxiety keeping them awake all night, etc.)

3. Might be drunk.

So I try to be plain in my language choices, calming when facing something with an aura of complexity (eg. “this thing that you heard is complex is really just a fancy name for these two simple elements combined”), consistent, and to present actual examples instead of everything just being an impenetrable brick of text.

(And then occasionally I break all my rules by throwing in hyperlinks to random tangents / hiding Missy Elliott lyrics in the code / whatevs.)

I have an idea of how to solve it while still keeping gate creation simple—I just need to find some downtime to investigate further :)

There are a few ways to do this in code, so you can pick the style that feels right for you / your particular case: https://quantumjavascript.app/#Quantum_JavaScript

But it’s also easy to make CNOTs in the visual editor. Here’s an animated GIF demonstrating it: https://quantumjavascript.app/tutorials.html#Create_controll...

And for further clarity, here’s a description of the relevant steps in that animated GIF: 1. Drag an Identity gate (the circle) onto your circuit board. 2. Drag a Pauli X gate (the X) onto the same moment (column) of your circuit board. 3. Select both (by tapping on them). 4. Tap on the "C" button to join them into a controlled gate.