Embed Quirk Editor in Cirq

[tanujkhattar]

Is your feature request related to a use case or problem? Please describe.
Quirk (https://algassert.com/quirk) is an open source quantum circuit editor and simulator. It is a widely used tool for both education and research.
It was proposed in https://tinyurl.com/cirq-visualizations#heading=h.2nfg3hb3jqb to have an integration of the Quirk editor with Cirq. This issue is to discuss the requirements and proposal.

Describe the solution you'd like
Integrate the Quirk editor with Cirq s.t.

• Users should be able to pull up the Quirk editor in ipython notebooks from within Cirq.
• Convert a cirq.Circuit to a Quirk circuit from within the notebook.
• Modify an existing circuit / Build a new circuit using Quirk and export as cirq.Circuit from within the notebook.

[optional] Describe alternatives/workarounds you've considered

• https://github.com/adgt/pyQuirk already exists which can be used to bring up Quirk editor in jupyter notebooks.
• cirq.contrib.circuit_to_quirk_url also exists which can convert any cirq.Circuit to a Quirk URL.
• We can also write another function cirq.contrib.quirk_url_to_circuit which can convert a Quirk URL to a cirq.Circuit to complete the interoperability requirements.

What is the urgency from your perspective for this issue? Is it blocking important work?
P2 - we should do it in the next couple of quarters

[freyam]

Hi.

I would like to work on this issue.

The goals of the issue seem straightforward to add. Let's discuss the finer details in the next Cirq sync.
I will set up the local environment till then and play around with some examples.

[freyam]

Have created a Draft PR with a base module ready.

#4492

[freyam]

@tanujkhattar
Your suggestion to use https://github.com/adgt/pyQuirk works really well, but it's not perfect. Some keywords aren't recognized while exporting a cirq.Cirquit to a QASM. Also, I believe that we don't need the complete set of features provided by Quirk as Users would just be interested in playing around with their personal circuits. Plus, the UI has room for improvement.

Proposed Change

• Fork https://github.com/adgt/pyQuirk/ and make a custom widget for Cirq-specific tasks (call it cirq-pyQuirk perhaps!)

If we continue to simply use adgt's pyQuirk, we will have to implement several helper functions. I am still investigating a workaround for this. Till then, I am rooting for a custom widget.

What do you think?

[freyam]

I have decided to go forward and create a Cirq-specific variant of pyQuirk.

The Goals of the New Widget/Module

• Performance
  pyQuirk might have some additional features that don't exactly align with what Cirq does. We could remove them completely, thus speeding up the load-up time.

• Cirq-like
  pyQuirk might be missing some key features that a Cirq user might want to use to visualize. We could use the existing API to create new features.

• Widget vs Module
  We should also discuss whether we want to make this an ipywidget (not a great idea according to me) or a python module that can be simply imported and used seamlessly.

Let me know what you think about this.