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TNO Quantum
===========
TNO Quantum provides generic software components aimed at facilitating the development
of quantum applications.

TNO Quantum - Communication - QKD Key Rate
==========================================

This repository provides python code to compute optimal protocol parameters for different quantum key distribution (QKD) protocols.

The codebase is based on the following TNO papers:

- Attema et al. - Optimizing the decoy-state BB84 QKD protocol parameters (2021) (doi: `10.1007/s11128-021-03078-0`_)
- Ma et al. - Quantum key distribution with entangled photon sources (2007) (doi: `10.1103/PhysRevA.76.012307`_)


.. _10.1007/s11128-021-03078-0: https://doi.org/10.1007/s11128-021-03078-0
.. _10.1103/PhysRevA.76.012307: http://doi.org/10.1103/PhysRevA.76.012307


The following quantum protocols are being supported:

- BB84 protocol (:py:mod:`~qkd_key_rate.protocols.quantum.bb84`),
- BB84 protocol using a single photon source (:py:mod:`~qkd_key_rate.protocols.quantum.bb84_single_photon`),
- BBM92 protocol (:py:mod:`~qkd_key_rate.protocols.quantum.bbm92`).

The following classical error-correction protocols are being supported:

- Cascade (:py:mod:`~qkd_key_rate.protocols.classical.cascade`),
- Winnow (:py:mod:`~qkd_key_rate.protocols.classical.winnow`).

The presented code can be used to

- determine optimal parameter settings needed to obtain the maximum key rate, 
- correct errors in exchanged sifted keys for the different QKD protocols,
- apply privacy amplification by calculating secure key using hash function. 


Quick Install
-------------

The QKD Key Rate module can easily be installed using pip as follows::

    pip install tno.quantum.communication.qkd_key_rate

Examples
--------
The following code demonstrates how the :py:mod:`~qkd_key_rate.protocols.quantum.bb84` protocol can
be used to calculate optimal key-rate for a specific detector with `attenuation=0.2`.

.. code-block:: python

   from tno.quantum.communication.qkd_key_rate.protocols.quantum.bb84 import (
      BB84FullyAsymptoticKeyRateEstimate,
   )
   from tno.quantum.communication.qkd_key_rate.test.conftest import standard_detector

   detector_Bob = standard_detector.customise(
      dark_count_rate=1e-8,
      polarization_drift=0,
      error_detector=0.1,
      efficiency_party=1,
   )

   fully_asymptotic_key_rate = BB84FullyAsymptoticKeyRateEstimate(detector=detector_Bob)
   mu, rate = fully_asymptotic_key_rate.optimize_rate(attenuation=0.2)

The following example demonstrates usage of the
:py:mod:`~qkd_key_rate.protocols.classical.winnow` error correction protocol.

.. code-block:: python
   
   import numpy as np

   from tno.quantum.communication.qkd_key_rate.base import Message, Permutations, Schedule
   from tno.quantum.communication.qkd_key_rate.protocols.classical.winnow import (
      WinnowCorrector,
      WinnowReceiver,
      WinnowSender,
   )

   error_rate = 0.05
   message_length = 10000
   input_message = Message.random_message(message_length=message_length)
   error_message = Message(
      [x if np.random.rand() > error_rate else 1 - x for x in input_message]
   )
   schedule = Schedule.schedule_from_error_rate(error_rate=error_rate)
   number_of_passes = np.sum(schedule.schedule)
   permutations = Permutations.random_permutation(
      number_of_passes=number_of_passes, message_size=message_length
   )

   alice = WinnowSender(
      message=input_message, permutations=permutations, schedule=schedule
   )
   bob = WinnowReceiver(
      message=error_message, permutations=permutations, schedule=schedule
   )
   corrector = WinnowCorrector(alice=alice, bob=bob)
   summary = corrector.correct_errors()


For more usage examples see the the documentation of the individual modules

   - :py:mod:`qkd_key_rate.protocols.quantum.bb84`
   - :py:mod:`qkd_key_rate.protocols.quantum.bb84_single_photon`
   - :py:mod:`qkd_key_rate.protocols.quantum.bbm92`
   - :py:mod:`qkd_key_rate.protocols.classical.cascade`
   - :py:mod:`qkd_key_rate.protocols.classical.winnow`
   - :py:mod:`qkd_key_rate.protocols.classical.privacy_amplification`


.. toctree::
   :maxdepth: 4
   :caption: Contents:
   :hidden:

   qkd_key_rate



(End)use Limitations
--------------------
The content of this software may solely be used for applications that comply with international export control laws.