Module channel 

Channel<W> — unified abstraction for gates and noise.

Every operation on a PauliSum (Clifford gate, Pauli rotation, arbitrary unitary, noise channel) maps a single Pauli string to a small weighted sum of Pauli strings. The trait formalizes that mapping; the engine consumes it via the sort-merge pipeline (see engine).

Built-ins in this module:

• Clifford1Q, Clifford2Q — table-driven Clifford gates with MAX_FANOUT = 1.
• PauliRotation — exp(-i·θ·P/2) with MAX_FANOUT = 2 (commuting inputs collapse to fanout-1 at runtime).
• GeneralUnitary1Q, GeneralUnitary2Q — generic unitaries stored as Pauli-expansion tables.
• Depolarizing, Dephasing — coefficient-rescaling noise (MAX_FANOUT = 1).
• AmplitudeDamping — the one built-in with MAX_FANOUT = 2.
• IdentityChannel — pass-through, used in tests and as a neutral composition element.

See design doc §6.

Implementing a custom channel

Implement the trait directly; the engine treats your type as just another Box<dyn Channel<W>> inside a Circuit. Three required methods plus an optional Channel::apply_adjoint override.

use paulistrings::{Channel, OutputBuffer};
use num_complex::Complex64;

/// Multiplies every input coefficient by a complex factor, with no
/// support and `MAX_FANOUT = 1`.
struct GlobalPhase {
    support: [u32; 0],
    factor: Complex64,
}

impl<const W: usize> Channel<W> for GlobalPhase {
    fn max_fanout(&self) -> usize { 1 }
    fn support(&self) -> &[u32] { &self.support }
    fn apply(
        &self,
        input_x: &[u64; W],
        input_z: &[u64; W],
        coeff: Complex64,
        out: &mut OutputBuffer<'_, W>,
    ) {
        out.push(*input_x, *input_z, coeff * self.factor);
    }
}

let ch = GlobalPhase {
    support: [],
    factor: Complex64::new(0.0, 1.0),
};
let _: Box<dyn Channel<1>> = Box::new(ch);

Re-exports

pub use clifford::Clifford1Q;

pub use clifford::Clifford2Q;

pub use identity::IdentityChannel;

pub use noise::AmplitudeDamping;

pub use noise::Dephasing;

pub use noise::Depolarizing;

pub use rotation::PauliRotation;

pub use unitary::GeneralUnitary1Q;

pub use unitary::GeneralUnitary2Q;

Modules

clifford

Clifford gates (table-driven, branchless). See §6.

identity

IdentityChannel — no-op channel that emits its input unchanged.

noise

Noise channels: Depolarizing, Dephasing, AmplitudeDamping. See §6.

rotation

Pauli rotation exp(-i * theta * P / 2). See §6.

unitary

General unitaries pre-decomposed into Pauli expansions. See §6.

Structs

OutputBuffer

Pre-allocated, fixed-capacity SoA scratch buffer for channel outputs.

Traits

Channel

Anything that maps a Pauli string to a small weighted sum of Pauli strings.