Quantum computer simulator
A quantum computer simulator is a program on an ordinary computer that calculates what a quantum computer would do with a quantum program. On Qubitwerk you can try this for free in your browser, without signing up: measure qubits, build circuits and open a combination lock with a simulated quantum search.
What does a quantum computer simulator do?
A simulator stores the state of all qubits as a long list of numbers, the amplitudes. Every step of a quantum program, every gate, changes these numbers according to fixed rules. At the end, the simulator draws measurement results just as a real quantum computer would deliver them, for example 2,048 measurements in a row.
A simulator calculates ideally: without noise and without hardware errors. The randomness of a measurement comes from a random number generator. That makes it well suited for learning, for checking quantum programs and as a benchmark for real devices.
Why simulating quickly gets hard
Every additional qubit doubles the length of the list. In double precision, each amplitude needs 16 bytes. For 20 qubits that is 16 MiB, for 30 qubits 16 GiB, roughly the memory of a good laptop. For 35 qubits it is already 512 GiB, and for 50 qubits 16 PiB.
In November 2025, Forschungszentrum Jülich simulated 50 qubits on the JUPITER supercomputer, reducing the memory needed by a factor of eight with compression. For suitable circuits there are also more compact methods that need much less memory. The actual effort therefore always depends on the circuit, too.
What you can simulate on Qubitwerk
In the circuit playground you build your own quantum circuits with up to three qubits and the gates H, X, Z and CNOT and see immediately which measurement results come out.
In the experiments, our PC with an RTX 3090 graphics card calculates for you: experiment cards about coins, waves and twins, a treasure search and the combination lock. There our simulator searches for your seven-digit test code with 24 qubits, or even an eight-digit one with 27 qubits if you like. In the diamond lab you control a simulated qubit with microwave pulses.
Try it: does the quantum search find your code? Our own simulator
Qubitwerk is Coolblack GmbH’s own simulator. In a research test we computed a complete 35-qubit circuit on an ordinary PC with an Intel Core i9 and an RTX 3090. For twelve mixed test jobs, our research prototype took 12.23 seconds, the widely used tool Qiskit Aer on the same PC 24.58 seconds.
All measurement conditions and accuracy checks are on our research page.
Simulator or real quantum computer?
A simulator is exact and error-free, but limited by memory and computing time. A real quantum computer does not have this limit in the same way, but struggles with noise and errors and is mostly only available via the cloud.
The two complement each other: new quantum programs are checked in a simulator first. And simulators show from which size a real quantum computer can have an advantage at all.
Frequently asked questions about quantum computer simulators
Is there a free online quantum computer simulator?
Yes. On Qubitwerk you can build quantum circuits, measure qubits and open a combination lock with a simulated quantum search, without signing up. Our PC calculates the experiments, and you see the result in your browser.
How many qubits can an ordinary PC simulate?
With the complete state list, about 30 qubits if 16 GiB of memory is free. Every additional qubit doubles the requirement. Large memory, graphics cards or more compact methods allow more; in a research test we computed 35 qubits on one PC.
Is a simulator as good as a real quantum computer?
For small programs it is even more accurate, because it has no hardware errors. For very many qubits, however, no ordinary computer is enough; that is where real quantum computers are needed.
Do I need programming skills?
No. On Qubitwerk you choose gates by tapping or try ready-made experiments. No expert knowledge is needed.
Which quantum computer simulators are there?
Besides Qubitwerk there is, for example, Qiskit Aer from IBM, a widely used programming tool. Large research centres such as Jülich run their own simulators on supercomputers.
- What is a quantum computer? Explained simply
- What is a qubit?
- Superposition explained simply
- Entanglement explained simply
- Grover’s algorithm explained
- Can a quantum computer break encryption?
Sources
- De Raedt et al.: JUQCS-50, simulating 50 qubits on the JUPITER supercomputer (arXiv, November 2025)
- German Federal Government: Quantum computing briefly explained (German)
As of 31 October 2026
Start your first simulation.
Build a circuit in the playground or let the combination lock calculate. No sign-up.