Fix image links (#6085)

* Use relative links to the image files
* Update relative links that go up two levels

Author: yinghui-hu

docs/build/circuits.ipynb

@@ -97,7 +97,7 @@
     "id": "77zB_UqkAwCR"
    },
    "source": [
-    "![Circuits and Moments](/cirq/images/CircuitMomentOperation.png)"
+    "![Circuits and Moments](../images/CircuitMomentOperation.png)"
    ]
   },
   {
@@ -454,7 +454,7 @@
     "id": "6633b1d21176"
    },
    "source": [
-    "![Insert Strategies](/cirq/images/InsertStrategy.png)"
+    "![Insert Strategies](../images/InsertStrategy.png)"
    ]
   },
   {

docs/build/ecosystem.md

@@ -1,6 +1,6 @@
 The following document provides an ecosystem overview of how the various tools compatible with Cirq can work together to enable quantum computing research.
 
-![image alt text](/cirq/images/ecosystem.png )
+![image alt text](../images/ecosystem.png)
 
 * **Research Libraries and Tools:** Libraries and tools used for researching new quantum algorithms and designing and preparing experiments on quantum devices.
 

docs/build/gates.ipynb

@@ -103,7 +103,7 @@
    "source": [
     "## Gates versus operations\n",
     "\n",
-    "![Circuits and Moments](/cirq/images/moments.png)\n",
+    "![Circuits and Moments](../images/moments.png)\n",
     "\n",
     "The above example shows the first half of a quantum teleportation circuit,\n",
     "found in many quantum computation textbooks.  This example uses three different\n",

docs/dev/notebooks.md

@@ -21,7 +21,7 @@ We also expect a standard header to be included in all of our notebooks:
 
 Example header:
 
-![notebook header](/cirq/images/notebook_header.png)
+![notebook header](../images/notebook_header.png)
 
 You can use [our template notebook](https://storage.googleapis.com/tensorflow_docs/Cirq/docs/_template.ipynb) to get started - please remember to change the `$$$REPLACE_WITH_TITLE$$$`, `$$$REPLACE_WITH_SITE_URL$$$` and `$$$REPLACE_WITH_NOTEBOOK_PATH$$$` placeholders.
 
@@ -46,7 +46,7 @@ See the [`dev_tools/notebooks`](https://github.com/quantumlib/Cirq/tree/master/d
 In order to speed up the execution of these tests an auxiliary file may be supplied which performs substitutions on the notebook to make it faster (for example it is often useful
 to reduce the number of repetitions in sampling from a simulator).
 
-Tod do this, for a notebook file notebook.ipynb, one can supply a file notebook.tst which contains the substitutes.
+To do this, for a notebook file notebook.ipynb, one can supply a file notebook.tst which contains the substitutes.
 The substitutions are provide in the form `pattern->replacement` where the pattern is what is matched and will be replaced.
 While the pattern is compiled, it is considered best practice to not sure complicated regular expressions.
 Lines in this file that do not have `->` are ignored.  Note that because the pattern is

docs/experiments/quantum_walks.ipynb

@@ -323,7 +323,7 @@
     "looks something like this:\n",
     "\n",
     "\n",
-    "<img src=\"/cirq/images/cycle.png\" style=\"width:550px;height:500px;\">\n",
+    "<img src=\"../images/cycle.png\" style=\"width:550px;height:500px;\">\n",
     "\n",
     "\n",
     "Going back to our original idea of some position vector $\\lvert j\\rangle$, it is apparent that in order to \n",
@@ -476,7 +476,7 @@
     "\n",
     "2. Based on the state of the coin qubit after the flip, either perform the operation $|j\\rangle \\ \\rightarrow \\ |j \\ + \\ 1\\rangle$ or $|j\\rangle \\ \\rightarrow \\ |j \\ - \\ 1\\rangle$ on the register of qubits encoding the position vector of the walker on the graph. This will involve having two operations controlled by opposite states of the coin quibt, each representing a step forward or a step backward on the graph. Thus, our evolution operation will look something like this:\n",
     "\n",
-    "<img src=\"/cirq/images/circ2.png\" style=\"width:400px;height:170px;margin-left:25%\">\n",
+    "<img src=\"../images/circ2.png\" style=\"width:400px;height:170px;margin-left:25%\">\n",
     "\n",
     "\n",
     "If we construct our evolution operator in this fashion, the coin qubit is able to dictate whether the walker \n",

docs/hardware/pasqal/getting_started.ipynb

@@ -87,7 +87,7 @@
     "id": "785bc8599470"
    },
    "source": [
-    "<img src=\"/cirq/images/pasqal/Cirq_pasqal.png\" width=\"700\"/>\n",
+    "<img src=\"../../images/pasqal/Cirq_pasqal.png\" width=\"700\"/>\n",
     "\n",
     "In this notebook, we show how to program a quantum circuit for Pasqal using cirq. The first step is to import cirq, and Pasqal custom classes. We use ``PasqalVirtualDevice`` to showcase how Cirq enforces Pasqal's devices' restrictions throughout the process."
    ]
@@ -102,11 +102,11 @@
     "\n",
     "The QPU of Pasqal is made of neutral atoms controlled by lasers. Individual atoms are trapped at well-defined positions in 1, 2 or even 3D, as shown on the following plot ( [Nature 561, 79 (2018)](https://www.nature.com/articles/s41586-018-0450-2)).\n",
     "\n",
-    "<img src=\"/cirq/images/pasqal/eiffel_tower.png\" width=\"500\"/>\n",
+    "<img src=\"../../images/pasqal/eiffel_tower.png\" width=\"500\"/>\n",
     "\n",
     "We created a custom class in cirq, ThreeDQubit, that corresponds to a qubit placed in 3D space. Let us start by creating a register comprising $36=6\\times6$ qubits in 2D, regularly arranged on a square lattice. It corresponds to the following configuration (image taken from [Nature 561, 79 (2018)](https://www.nature.com/articles/s41586-018-0450-2))\n",
     "\n",
-    "<img src=\"/cirq/images/pasqal/grid_atoms.png\" width=\"300\"/>"
+    "<img src=\"../../images/pasqal/grid_atoms.png\" width=\"300\"/>"
    ]
   },
   {
@@ -257,7 +257,7 @@
    "source": [
     "When the distance between the two qubits involved in the gate is greater than the control radius, as shown for example in the following plot, cirq will raise an error.\n",
     "\n",
-    "<img src=\"/cirq/images/pasqal/r_radius.001.png\" width=\"300\"/><br>"
+    "<img src=\"../../images/pasqal/r_radius.001.png\" width=\"300\"/><br>"
    ]
   },
   {
@@ -291,7 +291,7 @@
     "\n",
     "More precisely, we will implement Grover's algorithm to search for the state $|10\\rangle$, which corresponds to the circuit:\n",
     "\n",
-    "<img src=\"/cirq/images/pasqal/Grover_circuit.png\" width=\"750\"/><br>\n",
+    "<img src=\"../../images/pasqal/Grover_circuit.png\" width=\"750\"/><br>\n",
     "\n",
     "Bear in mind that this is a naïve implementation that can be substantially optimized, particularly in the oracle and the usage of an ancilla, but that is beyond the scope of this tutorial.\n",
     "\n",