Free online quantum circuit simulator
No account, no install, no queue. This runs in your browser, so the arithmetic happens on your machine and the answer is exact rather than sampled from a noisy device. Build a circuit by dragging gates onto the wires, and read the outcome probabilities as it changes.
Or try deeper runs on our QCaaS platform
New to the vocabulary? Every term on this page is defined in the quantum computing dictionary
Build a circuit
Two qubits that always agree: never 01, never 10. Measured this way a pair of matched coins looks identical, and the difference only shows up when you measure along a different axis. That is Bell's theorem, and it is not visible in this histogram.
Drag a gate onto a wire, or tap a gate and then a spot.
OPENQASM 2.0;
include "qelib1.inc";
qreg q[2];
creg c[2];
h q[0];
cx q[0],q[1];
measure q -> c;Result
Exact probabilities, computed in this tab, updating as you build. Counts are sampled from them, so the scatter is real shot noise.
|00⟩|11⟩No error bound here, and that is the point.
Nothing above was approximated: at 2 qubits the state is 4 amplitudes and your browser holds all of them exactly. Past roughly 32 qubits no machine can, approximation becomes unavoidable, and the question stops being what the answer is and becomes how far from the truth it might be. That is what the hosted engines measure and certify.
The same platform on a real quantum chemistry problem
The circuit above runs in this tab because ten qubits is small. The console is where the same platform takes a problem from the literature: below is the H2 molecule at its equilibrium bond length, run on a CPU and an NVIDIA GPU, on a Google Cloud TPU, and on two quantum processors, one superconducting from IQM and one trapped-ion from AQT.
None of it is a demonstration. Each row is a real job with a certificate you can open, at the price any customer pays, and a cost estimate in the console is free before anything executes. The method is on the chemistry benchmark.
Run on our engines
The H2 molecule at its equilibrium bond length, whose exact electronic ground state is -1.857275 Ha. Two qubits, so it fits every device we offer. Submitted to each kind of compute we offer, on 16 September 2026. Every figure below is a real job on the service, priced as any customer would be priced.
| Device | Engine | Kind | Qubits | Result | Cost |
|---|---|---|---|---|---|
 | exact.cpu | CPU | 2 | ZZ = -1.0000, the ideal value certificate | $0.0001 |
 | exact.gpu | GPU | 2 | ZZ = -1.0000, the ideal value certificate | $0.0001 |
 | qpu.iqm.garnet | QPU | 2 | ZZ = -0.9326, superconducting, 4,096 shots certificate | $6.239 |
 | qpu.rigetti | QPU | 2 | ZZ = -0.5420, superconducting, 4,096 shots * certificate | $2.041 |
| qpu.rigetti | QPU | 2 | ZZ = -0.5107, the same circuit re-run * certificate | $2.041 |
 | qpu.aqt.ibex | QPU | 2 | ZZ = -0.9200, trapped ion, 100 shots certificate | $2.650 |
| neural.cpu | CPU | 2 | -1.116981 Ha total, 0.0203 Ha above exact certificate | $0.0001 |
 | neural.tpu | TPU | 2 | -1.116981 Ha total, 0.0203 Ha above exact certificate | $0.074 |
A note on the hardware certificates: they state Hellinger fidelity against the exact distribution. For an optimisation circuit that distribution is spread across many outcomes rather than concentrated on one, so the figure is low by construction and is not a measure of whether the device found a good answer. The result column above is.
The same problem is yours to run: every instance here is seeded, so it rebuilds exactly. Open the console and a cost estimate is free before anything executes.
How this compares to Quirk
If you have used Quirk, the well-known browser quantum simulator by Craig Gidney, this will feel familiar: add gates one at a time, watch the outcome probabilities update as you build, no sign-up. Quirk has the richer editor and this is not an attempt to replace it. The difference is what happens after the sandbox.
- Same circuit, bigger engines. A browser tops out around 10 qubits because the state doubles with each one. The same circuit runs here on tensor-network and stabilizer engines past 1,000 qubits, and on real hardware, without being rewritten
- An accuracy statement. Once a circuit leaves exact simulation, every approximate result carries a measured error bound you can cite or verify
- Real QPUs. Eight quantum processors from seven vendors across four modalities, at provider list price, through the same API
For learning the gates, a browser simulator is the right tool and costs nothing. For anything you intend to publish or act on, the question becomes how far the answer might be from the truth, which is what the rest of this platform exists to answer.
Where this stops working
An exact simulation stores one complex amplitude per basis state, so an n-qubit circuit costs 16 × 2n bytes. Each qubit doubles the bill, so the distance between comfortable and impossible is about four qubits.
| Qubits | Amplitudes | Exact state | Runs where |
|---|---|---|---|
| 10 | 1,024 | 16 KiB | This browser tab, instantly |
| 20 | 1,048,576 | 16 MiB | Any laptop |
| 30 | 1.07 x 10^9 | 16 GiB | A well-provisioned workstation |
| 34 | 1.72 x 10^10 | 256 GiB | A large cloud instance |
| 40 | 1.10 x 10^12 | 16 TiB | No single machine |
| 50 | 1.13 x 10^15 | 16 PiB | Not physically possible |
Past that wall the answer has to be approximated, and an approximate answer without a stated error is an assertion rather than a measurement. ZKSF runs the methods that go further, and reports how far from the truth each result might be, measured on the run rather than estimated.
An account with us keeps your jobs, runs them on real quantum hardware, and certifies every result. Sign up at app.zksf.org