qkdQKD with the hardware in the loop

Excess noise is an output assembled from measured hardware parameters, not an input.

Excess noise is an output

The budget is assembled from laser linewidth, electronic noise, quantum efficiency, DAC and ADC bit depth, pilot power ratio, symbol rate and fibre length. The key rate follows from it.

DSP in the loop

Pilot-assisted phase recovery and carrier-frequency-offset estimation run over simulated symbols. Their residual phase error is an excess-noise term.

Discrete and continuous

Gaussian modulation and M-PSK; BB84-WCP with decoy states, six-state, SARG04, B92, DPS, COW; BBM92 and E91; both untrusted midpoints, CV-MDI and MDI-BB84, each on a Rust engine.

Every plane is named

Excess noise requires ref=. Detector trust is a separate flag, a statement about the adversary.

It refuses rather than approximates

A configuration with no published bound raises and names the restriction: a trusted detector on the analytic discrete-modulation bound, or a device-independent CHSH claim.

Native Rust core

Symplectic covariance, a truncated number basis, the symbol pipeline, the cone solvers and every key-rate formula, in f64 on CPU with rayon. Dispatch asks for a precision, not a device.

What this is

A Python package over a native Rust core (qkd._core, PyO3, abi3-py311). Getting Started installs it.

What you can get a number out of

The protocol matrix; Usage by example runs each row.

Three things to know before quoting a number

Verification is graded on two axes: Validation.
Most q.Link families are asymptotic: Security.
Every q.Link run is CPU: the GPU path.

Where next

Architecture; Conventions.