Module surface_code 

Surface Code Error Correction Simulation

Simulates a distance-3 rotated surface code with:

• 9 data qubits (3 x 3 grid)
• 4 X-type stabilizers (plaquettes, detect Z errors)
• 4 Z-type stabilizers (vertices, detect X errors)
• 8 ancilla qubits (one per stabilizer)

Each QEC cycle performs:

1. Noise injection – random Pauli errors on data qubits.
2. Stabilizer measurement – entangle ancillas with data qubits and measure the ancillas to extract the error syndrome.
3. Decoding – a simple lookup decoder maps the syndrome to a correction (placeholder; production systems would use MWPM).
4. Correction – apply compensating Pauli gates.

Qubit layout (distance 3)

Data qubits:        Ancilla assignment:
  d0  d1  d2          X-anc: 9, 10, 11, 12
  d3  d4  d5          Z-anc: 13, 14, 15, 16
  d6  d7  d8

X stabilizers (plaquettes):

• X0 (anc 9): {d0, d1, d3, d4}
• X1 (anc 10): {d1, d2, d4, d5}
• X2 (anc 11): {d3, d4, d6, d7}
• X3 (anc 12): {d4, d5, d7, d8}

Z stabilizers (boundary vertices):

• Z0 (anc 13): {d0, d1}
• Z1 (anc 14): {d2, d5}
• Z2 (anc 15): {d3, d6}
• Z3 (anc 16): {d7, d8}

Structs

SurfaceCodeConfig

Configuration for a surface code error correction simulation.

SurfaceCodeLayout

Physical layout of a surface code: which data qubits participate in each stabilizer, and the ancilla qubit assigned to each stabilizer.

SurfaceCodeResult

Result of a surface code simulation.

Functions

run_surface_code

Run a surface code error correction simulation.