Improvements to the CircuitZoo purification circuits (#37)

---------

Co-authored-by: Alexandru Ariton <anduariton1234@gmail.com>
Co-authored-by: Stefan Krastanov <stefan@krastanov.org>

docs/src/references.bib

@@ -204,3 +204,29 @@ @article{choi2019percolation
   year={2019},
   publisher={Nature Publishing Group}
 }
+
+@article{keisuke2009doubleselection,
+  title={Entanglement purification with double selection},
+  author={Keisuke Fujii and Katsuji Yamamoto},
+  journal={Phys. Rev. A 80, 042308},
+  year={2009},
+  url={https://doi.org/10.1103/PhysRevA.80.042308},
+  doi={https://doi.org/10.1103/PhysRevA.80.042308}
+}
+
+@article{krastanov2019optimised,
+  title={Optimized Entanglement Purification},
+  author={Stefan Krastanov, Victor V. Albert, and Liang Jiang},
+  year={2019},
+  url={https://arxiv.org/pdf/1712.09762.pdf},
+  journal={Arxiv}
+}
+
+@article{naomi2013topological,
+  title={Topological quantum computing with a very noisy network and local error rates approaching one percent},
+  author={Naomi H. Nickerson, Ying Li, Simon C. Benjamin},
+  url={https://www.nature.com/articles/ncomms2773},
+  year={2013},
+  journal={Nature}
+}
+