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Show HN: Play with real quantum physics in your browser (quantum.orgsoft.org)

156 points by mattvr ↗ HN
I wanted to make the simplest app to introduce myself and others to quantum computing.

Introducing, Schrödinger's Coin. Powered by a simple Hadamard gate[0] on IBM quantum, with this app you can directly interact with a quantum system to experience true randomness.

Thoughts? Could you see any use cases for yourself of this? Or, does it inspire any other ideas of yours? Curious what others on HN think!

[0] https://en.wikipedia.org/wiki/Quantum_logic_gate#Hadamard_ga...

77 comments

[ 3.1 ms ] story [ 147 ms ] thread
jwpapi
A physical coin is biased?
helboi4
I feel like when I flip a physical coin it pretty much always lands on exactly the same side unless I flip it real wierd.
scottmsul
I just see a bunch of spinning coins forever and nothing happens with no way to stop it...
ryan-duve
When I click the coin I see an animation of 7-8 blurry coins spinning. Further clicking seems to have no effect. Is something else supposed to happen?
sinan
Technical Details section of help says: "In some cases, you may have to wait multiple minutes for a result."
mattvr
Yes, sorry, server was a bit overloaded. It should be more reliable now.
asparagui
Cool idea! This is a really clever way to demo a real-world circuit!
brap
Is this truly live or did they batch random numbers ahead of time?
sinan
Technical Details section of help explains "we buffer batches of coin flips in advance to ensure a responsive experience. Your coin flips are always drawn directly from a quantum circuit, though no necessarily in real-time."
Rooster61
In reality, it's a room full of interns flipping quarters and averaging their results in "real time"
Diti
Am I wrong, or would that mean this “quantum flip” can be biased by race conditions, round robin, CDNs, things like that?
rahulstein
yea its not truly random. not sure how predictable the batching or caching is
Rooster61
Considering this states its talking to an actual quantum computer somewhere(at least that's what I'm led to believe by the "Connected to <some instance somewhere>" in the bottom right), I'd imagine this has gotten hugged to death, and hence why we are only seeing the spinning coins rather than it actually resolving.
mattvr
You are precisely right.
Traubenfuchs
My observation is too weak, the coins keep spinning.

Maybe I am so disconnected from the rest of reality, I count as absolute, non destructive observer?

inurqubits
Do you by any chance have a friend named Wigner?
SaberTail
You're now entangled with the system, and so we will need someone else to observe you.
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__MatrixMan__
I've wondered for a long time what the user experience for quantum computing will look like. I had imagined some library with a type for "qbit" and an dsl for making them interact in certain ways and then some kind of async thing where your classical code could run locally while periodically shuttling data to and from wherever the quantum computer is.

This isn't quite that but I guess it's a first step.

inurqubits
They already exist

    import numpy as np
    from qiskit import QuantumCircuit

    # 1. A quantum circuit for preparing the quantum state |000> + i |111> / √2
    qc = QuantumCircuit(3)
    # generate superposition
    qc.h(0)  
    # add quantum phase   
    qc.p(np.pi / 2, 0)  
    # 0th-qubit-Controlled-NOT gate on 1st qubit
    qc.cx(0, 1)   
    # 0th-qubit-Controlled-NOT gate on 2nd qubit 
    qc.cx(0, 2)
__MatrixMan__
Thanks for the pointer to qiskit, I'm gonna go learn...
ziofill
Tangent, but interesting: how do you get fair samples from a biased coin? 1. You take a string of biased samples like 001011100101 2. you split it in pairs 00 10 11 10 01 01 3. you keep only pairs with a zero and a one in them 10 10 01 01 4. You assign 0 and 1 to them, e.g. 1 1 0 0, this is a fair sampling from an unbiased coin

Why does it work? Because even if p(0) ≠ p(1), p(01) = p(10).

Exuma
Damn, that is cool
amelius
It's a nice trick, but it requires a lot of extra coin flips. Imagine you have a coin with p(1)=0.501, and you want 1000 random bits. With the proposed method, this will take about 4000 coin flips. Surely, since the coin is quite close to being fair, it should be possible to do it with far fewer flips ...
randomcatuser
how do you get biased samples from a fair coin? (say, 0.3)

(this one has less wow, i guess)

1. You take a string of fair samples 0101011101010 2. you split it into chunks of 3 (8 possibilities, so each one is 0.125 chance) 3. 000, 001, 010 -> 1, and all the rest is 0, which will get 0.275 chance

Any better approaches?

layer8
However, that stops working as soon as you have a biased coin with memory. ;)
jsmcgd
Instead of discounting some of the results, can we alternate the value of the coin each toss? So on the first flip, heads is 0 and tails is 1, then on the next flip, heads is 1 and tails is 0.
hansvm
That'll obtain the right average but won't have the same pairwise relations as an independent, unbiased coin.

That's probably easiest to see if you imagine approaching an infinitely biased coin (100% heads, 0% tails). Your strategy alternates between 0 and 1 almost always. The listed strategy throws away most flips but gives actualy unbiased results when a pair does pass.

Another way to look at it is from an entropy perspective. An unbiased, independent coin flip has 1 bit of entropy. A biased coin with, e.g., 99% heads has 0.0807 bits of entropy. On average, you need at least 12.377 such flips to emulate an unbiased, independent flip. Any strategy without some sort of rejection/continuation/... (like your proposal) is doomed to fail.

I haven't checked if their proposal is actually optimal. Empirically, it's suggestive of having room for improvement. I'm seeing something like 101 flips on average instead of 12.377 for that 99% bias example.

hatthew
A general direction you could go is to use blocks greater than 2. For example, you flip the coin exactly 64 times, and discard the result unless there is exactly 1 tails and 63 heads. This happens about 22% of the time, so it's on average 290 flips to get a single sample. When you do get that sample, you convert the single tails' position within that 64 block into binary, and get a 6 bit number uniformly distributed 0-63, i.e. you get 6 bits of entropy. So on average 6/290=0.02 bits of entropy per flip, twice as good as using blocks of 2, though only a quarter as good as the theoretical upper bound.

I picked "block of 64 with only a single tails" since it was simple, and I'm sure a mathematician could figure out how to optimize it much more, but my general point is to agree that there's definitely ways to get closer to the theoretical upper bound you mentioned.

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herodotus
Nice idea, but watching the spinning coins made me a bit nauseous. I had to go away from the page.
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mattvr
Sorry about that. I toned down the animation and fixed the infinite spin issue – curious if it's more comfortable now.
its-summertime
from the console

> Failed to get quantum result from server

cloudflare connection timed out

mattvr
Hey HN! Creator here. Sorry for the downtime and dizzying spinning coins.

I was surprised to see this on the frontpage this morning and the scale is pushing the limits of our quantum randomness generator

It should be working again now as I'm pushing fixes. Thanks for your patience.

inurqubits
It's not true that computer randomness is predictable, all recent computers have entropy sources which are essentially quantum in nature - thermal noise.
n8m8
Thermal noise entropy is probably good enough for most practical uses, but it's still fundamentally producing a seed value that can be captured, misused, or bruteforced, right? Also curious if there are monte-carlo models looking at this to see "how uniformly random" they look.

Edit: I think figure 3 in this study is what I'm looking for. They define the inconsistency I described as "spectral pivoting".

> This discrepancy is because the Mermin-Wagner-Hohenberg theorem holds in the thermodynamic limit, while these simulations are for finite lattices

I think thermodynamic limit here means, it needs to be way too hot?

https://arxiv.org/html/2403.09078v1

sobellian
In practice it would be very difficult to predict RDRAND outputs. Even so I believe the truly paranoid can use RDSEED to skip the PRNG step. Not qualified at all to talk about how they de-bias the measurements.
stared
Thank you for sharing!

As a small remark, classical and quantum coins are equally susceptible to bias. So the initial intro is a bit misleading.

boothby
People using quantum computers for random uncorrelated 50/50 bitstrings makes me unreasonably angry (disclaimer: employer in profile, this is my personal opinion). At best, it's just a test of how well we've got the calibration dialed in, how isolated the qubits are, etc. Fine as a test "does the machine do what its manufacturer claims," but otherwise a tragic waste of resources. Hardware RNGs can beat any quantum computer on bandwidth and reliability for a few pennies, versus a multimillion dollar behemoth.

That said... as a demo of a stack using quantum cloud compute, it's all in good fun and I shouldn't be a stick in the mud.

nineplay
Question from someone who's not going to even pretend to understand quantum physics..

The explanation says the visualization shows the coin in all possible states. I'm trying to count quickly and it seems like about 8. Does all possible states mean there's an infinite number and 8 are shown for visualization purposes, or is there a finite predictable number of possible states.

shalg
Quantum mechanics tells us that the qubit (coin) can exist in any linear superposition of heads and tails. To express this you write a|heads> + b|tails> the only constraint is that a^2 + b^2 must equal 1. Now why would that be the constraint? It is because a^2 and b^2 are the probabilities of measuring heads and tails respectively.

In this example the coin is put into the state where an and b equal 1/sqrt(2) to give an equal probability of each outcome. So there is exactly one state associated with the coin. Now this state does lead to two possible outcomes but the underlying state (that can not be directly observed) is exactly one thing.

shalg
Oh and to be clear the visualization is nonsense it doesn’t relate to anything.
hoten
Got 2 tails in a row. Must be broken.
westurner
Quantum logic gate > Universal logic gates: https://en.wikipedia.org/wiki/Quantum_logic_gate#Universal_q...

From https://news.ycombinator.com/item?id=37379123 :

> [ Rx, Ry, Rz, P, CCNOT, CNOT, H, S, T ]

From https://news.ycombinator.com/item?id=39341752 :

>> How many ways are there to roll a {2, 8, or 6}-sided die with qubits and quantum embedding?

From https://news.ycombinator.com/item?id=42092621 :

> Exercise: Implement a QuantumQ circuit puzzle level with Cirq or QISkit in a Jupyter notebook

ray-pH/quantumQ > [Godot] "Web WASM build" issue #5: https://github.com/ray-pH/quantumQ/issues/5

westurner
From https://quantumflytrap.com/scientists/ :

> [Quantum Flytrap] Virtual Lab is a virtual optical table. With a drag and drop interface, you can show phenomena, recreate existing experiments, and prototype new ones.

> Within this environment it is possible to recreate interference, quantum cryptography protocols, to show entanglement, Bell test, quantum teleportation, and the many-worlds interpretation.

ellis0n
I watched how it works, but it seems the rotation is just an animation and a fake. There are two requests: /flip and /info. When you click mouse button, the /flip request is GET immediately and it returns a result of 1(eagle) or 0. After that the coin animation begins with requests to /info which always returns the same response for no clear reason. After several /info requests the coin eventually stops without receiving any new results.

$ curl https://quantum.orgsoft.org/info

{"status":"ok","message":"Connected to IBM Eagle r3 (127 qubits)","display_name":"Eagle r3 (127 qubits)","alias":"ibm_kyiv","version":"1.20.22","num_qubits":127,"processor":"Eagle r3","url":"https://quantum.ibm.com/services/resources?system=ibm_kyiv"}

$ curl https://quantum.orgsoft.org/flip

1

PcChip
Well yeah, the result from ibm quantum is either a 1 or 0 i suppose. Did you expect the quantum computer to draw you the coins through your phone too?
ellis0n
The coin animation is non-quantum. I thought it was a bug and it doesn’t work as the author intended.
lazyeye
I wonder what the cost of running this website is?
deadbabe
In the many worlds interpretation, if one connected this computer to a machine that would instantly kill you if the result was heads, you as the observer should find that you never die, but rather that the machine always seems to come up tails. Is that correct? Might be cool for some kind of euthanasia patient to experience.
apt-apt-apt-apt
If it maimed you horribly instead, you'd quickly find that you'd still have to deal with the consequences.
doctoboggan
A few years ago I heard a story on NPR about someone who built a site that also used the IBM quantum backend. They had you input a question about what you should do with your life (I think the example was "Should I grow a beard?"). Then the quantum backend would give you a yes or no answer.

The idea here is that if you believe the many worlds interpretation then that quantum decision splits the universe in two, and in one universe you grow a beard, and in the other you don't.

I thought it was a fun idea.

depingus
That is a fun idea. With enough quantum computing power, we might be able to spawn enough universes fast enough to crash The Simulation. Maybe even escape containment and access the quantum hypervisor!
ge96
Only to discover there is another layer
52-6F-62
Isn’t that what happens without the need of a quantum computer…