Add OTOC documentation (quantumlib#190)

* Add tutorial + index.

* Add to toc.

* Review comments.

docs/_toc.yaml

@@ -55,3 +55,9 @@ toc:
   path: /cirq/experiments/fermi_hubbard/experiment_example
 - title: "Spin-charge separation results"
   path: /cirq/experiments/fermi_hubbard/publication_results
+
+- heading: "Quantum scrambling"
+- title: "Overview"
+  path: /cirq/experiments/otoc
+- title: "Experiment example"
+  path: /cirq/experiments/otoc/otoc_example

docs/otoc/index.md

@@ -0,0 +1,19 @@
+# Information scrambling in computationally complex quantum circuits
+
+Interaction in quantum systems can spread initially localized quantum information 
+into the many degrees of freedom of the entire system. Understanding this process, 
+known as **quantum scrambling**, is the key to resolving various conundrums in physics. 
+
+In [arXiv:2101.08870](https://arxiv.org/abs/2101.08870), we experimentally investigated
+the dynamics of quantum scrambling on a 53-qubit quantum processor. By measuring 
+the time-dependent evolution and fluctuation of out-of-time-order correlators (OTOCs),
+signatures of both mechanisms associated with quantum scrambling, *operator spreading* 
+and *operator entanglement*, were experimentally observed.
+
+This documentation shows how to build quantum circuits used in this experiment and run
+them to reproduce results in this publication.
+
+## Overview
+
+* See the [OTOC experiment example](./otoc_example.ipynb) to detect operator spreading and
+  recreate Figure 1 of the [OTOC paper](https://arxiv.org/abs/2101.08870).