Circuit Builder
Free-form circuit building — single-qubit circuits are free for everyone, multi-qubit circuits need Pro, and noise channels need Pro+. Drag to reorder, scrub through each step, and check your work against real targets.
Qubit count
Wires
Circuit sequence
No operations yet — add gates below.
Timeline — step through the circuit
Step 0 / 0 — initial state
Add single-qubit gate
Hover or focus a gate above to see what it does mathematically.
H X Y Z I S T — add that gate to the currently selected qubit (the "qubit" dropdown above)
Ctrl+Z (or Cmd+Z) — undo · Ctrl+Y or Ctrl+Shift+Z — redo
Click a gate chip to select it, Shift+click to select a range, Ctrl/Cmd+click to add one
Ctrl+C / Ctrl+V — copy / paste the selected gate(s)
Delete or Backspace — remove the selected gate(s)
Drag a chip's ⋮⋮ handle, or use its ◀/▶ buttons, to reorder it
Esc — clear the current selection
Preset circuits
Deutsch–Jozsa and Teleportation aren't available yet — they need circuit primitives (an oracle gate, mid-circuit measurement with classical control) this builder doesn't support. They'll be added once that engine work exists.
Export & share
System type
Isolated
Open
Noise channel
Kraus operators — ρ' = Σᵢ Kᵢ ρ Kᵢ†
Circuit diagram
Click a column to select that gate. Lime/red columns have already run at the current timeline step; grey columns haven't yet.
How noise is modeled here at n>1. The joint state above is always the exact pure-state evolution. With Open switched on, each qubit's Bloch sphere and purity/entropy below are computed from its own reduced density matrix (tracing out every other qubit), then the selected noise channel is applied to that reduced description — the same math F5 uses, just aimed at every qubit inside the register individually. It's not a full multi-qubit open-system simulation (that engine doesn't exist yet); it's an honest, engine-accurate approximation.
Challenge — build it yourself
Starting a challenge resets the circuit to a blank one at the right qubit count — build the target state using the palette above, then check your work. Success is judged by state fidelity against the real target, not multiple choice.