Initiating a Circuit object

The Circuit class supports all superconducting circuits consisting of capacitances, inductances, and Josephson junctions. A Circuit object can be initiated in two different ways:

  • By providing a yaml file that describes the circuit graph

  • By providing a symbolic Hamiltonian which represents the circuit (described here)

In this notebook, we will demonstrate how to define a circuit graph.

Defining a Circuit Graph

We will describe the circuit graph using a yaml file. For example, consider the circuit of the zero-\(\pi\) qubit.

Consider the circuit of the zero-pi qubit:

zero-pi circuit

The above circuit is specified branch by branch, using the following syntax:

[1]:

zp_yaml = """# zero-pi
branches:
- [JJ, 1,2, EJ=10nA, ECJ=200pF]
- [JJ, 3,4, EJ, 20GHz]
- [L, 2,3, EL=10uH]
- [L, 4,1, 0.008]
- [C, 1,3, 0.02]
- [C, 2,4, 0.02]
"""

Summary of the above input file (a detailed description is given in the next page):

The input is just a collection of branches which make the circuit. Each branch connecting node \(n_i\) to \(n_f\) is a list with the following items:

  • branch type:

    • JJ for Josephson junction,

    • L for inductance,

    • C for capacitance

  • initial node index: \(i\)

  • final node index: \(f\)

  • branch parameters corresponding to the branch type:

    • JJ: EJ, ECJ

    • L: EL

    • C: EC

Once a YAML description has been prepared (either inline as a string, or saved as a .yaml file), a Circuit object can be constructed via the named constructors:

  • scq.Circuit.from_yaml_string(yaml_text, ...) for an inline string;

  • scq.Circuit.from_yaml_file(path, ...) for a YAML file on disk.

Deprecated form. The earlier Circuit(input_string=..., from_file=True/False) constructor still works, but passing from_file explicitly now emits a DeprecationWarning. New code should use the named constructors above.

Graphical user interface (GUI) for defining custom circuits

Superconducting Circuit Builder (developed by Ben McDonough) is a separate package that offers the GUI for defining custom circuits: the user can draw a circuit, and can export a corresponding YAML string of the circuit. The package is available here.