Update the link to Nielsen's notes. (#903)

* Update intro_workshop_exercises.ipynb

* Update jordan_wigner_and_bravyi_kitaev_transforms.ipynb

docs/tutorials/intro_workshop_exercises.ipynb

@@ -122,7 +122,7 @@
     "operator*, and we refer to creation and annihilation operators as\n",
     "fermionic *ladder operators*.\n",
     "    \n",
-    "The canonical anticommutation relations impose a number of consequences on the structure of the vector space on which the ladder operators act; see [Michael Nielsen's notes](http://michaelnielsen.org/blog/archive/notes/fermions_and_jordan_wigner.pdf) for a good discussion.\n",
+    "The canonical anticommutation relations impose a number of consequences on the structure of the vector space on which the ladder operators act; see [Michael Nielsen's notes](https://futureofmatter.com/assets/fermions_and_jordan_wigner.pdf) for a good discussion.\n",
     "\n",
     "The electronic structure Hamiltonian is commonly written in the form\n",
     "$$\n",

docs/tutorials/jordan_wigner_and_bravyi_kitaev_transforms.ipynb

@@ -136,7 +136,7 @@
     "-   The annihilation operators $a_p$ act on this basis as follows:\n",
     "    $$\\begin{aligned} a_p \\lvert n_0, \\ldots, n_{p-1}, 1, n_{p+1}, \\ldots, n_{N-1} \\rangle &= (-1)^{\\sum_{q=0}^{p-1} n_q} \\lvert n_0, \\ldots, n_{p-1}, 0, n_{p+1}, \\ldots, n_{N-1} \\rangle \\,, \\\\ a_p \\lvert n_0, \\ldots, n_{p-1}, 0, n_{p+1}, \\ldots, n_{N-1} \\rangle &= 0 \\,.\\end{aligned}$$\n",
     "    \n",
-    "See [here](http://michaelnielsen.org/blog/archive/notes/fermions_and_jordan_wigner.pdf) for a derivation and discussion of these\n",
+    "See [here](https://futureofmatter.com/assets/fermions_and_jordan_wigner.pdf) for a derivation and discussion of these\n",
     "consequences.\n",
     "\n",
     "## Mapping fermions to qubits with transforms\n",