Why a Laptop Can Simulate 30 Qubits but Not 50
What the Lab keeps in memory
The Quantum Lab simulates qubits by storing the full quantum state as a list of numbers called amplitudes, one for every possible combination of results. For n qubits there are 2 to the power n combinations. The Qiskit Aer documentation states it plainly: a state vector of n qubits uses 2^n complex values, 16 bytes each. This is the same method used in the circuit builder, with n limited to 3.
The memory table
| Qubits | Amplitudes | Memory at 16 bytes each |
|---|---|---|
| 3 (the Lab) | 8 | 128 bytes |
| 10 | 1,024 | 16 KiB |
| 20 | about 1 million | 16 MiB |
| 30 | about 1.07 billion | 16 GiB |
| 40 | about 1.1 trillion | 16 TiB |
| 50 | about 1.1 quadrillion | 16 PiB |
Each added qubit doubles the memory. A laptop with 16 GiB of memory is just about stuck at 30 qubits for this method, and 50 qubits needs more memory than a typical data centre has in one place. The time to run each gate also doubles with each qubit.
What this does and does not show
- It does show why simulating quantum states exactly is hard for ordinary computers: the cost grows exponentially.
- It does not show that a quantum computer solves every problem faster. Speedups apply to specific problems, such as the square root speedup for search in Grover's Algorithm Explained Step by Step.
- It is not the only method. Some circuits with a special structure, or with limited entanglement, can be simulated with much less memory using other methods, so a "50 qubit wall" is only true for the full state vector approach described here. Real quantum advantage claims depend on the circuit and are argued about between researchers and companies, see Dequantization.
Why the Lab stops at 3 qubits
Three qubits give 8 results, which fit in a single 10 by 10 grid of 100 dots, and the picture stays understandable. A fourth qubit would double the outcomes to 16 and a fifth to 32, and the "What you'll get if you look" grid would stop being readable. The limit is about understanding, not memory: a 3 qubit state takes 128 bytes.
Try it
Build a three qubit circuit in the circuit builder with Spin the coin on every wire. You will see 8 results at about 12 or 13 of 100 each. That grid is the simulator's whole state vector, drawn as a picture. For a gentler start, open Quantum in 5 minutes.
Sources and further reading
- Qiskit Aer: StatevectorSimulator (a state vector of n qubits uses 2^n complex values, 16 bytes each)
- Wikipedia: Quantum logic gate (Hadamard, Pauli-Z and CNOT definitions)
- Wikipedia: Gottesman-Knill theorem (some circuits can be simulated efficiently)
Checked 2026-10-12. The probabilities and memory figures on this page were calculated directly from the formulas shown. This is education, not investment or security advice. QUANTUM (QNT) is an independent community token on Solana and is not affiliated with Quantinuum (Nasdaq: QNT) or Quant Network (QNT on Ethereum).
Frequently asked questions
How many qubits can a normal laptop simulate?
With the full state vector method and 16 bytes per amplitude, about 28 to 30 qubits on a laptop with 16 GiB of memory. Each extra qubit doubles the memory.
Does this mean quantum computers beat simulators at 50 qubits?
Not automatically. Other simulation methods can handle some larger circuits, and whether a particular machine beats classical methods depends on the circuit and is actively debated.
Next read
What Is a Qubit? Superposition and Measurement ExplainedA qubit is the basic unit of a quantum computer. Learn how qubits work, how they are built, and why they are fragile.Read nextAlso useful: Quantum Error Correction Explained | Dequantization: When Classical Computers Catch Up | What Is Quantum Computing? A Plain English Guide
Educational content, not financial advice. QUANTUM (QNT) is independent of Quantinuum (Nasdaq: QNT) and Quant Network (QNT on Ethereum). Live chart | Token facts