# Capacitor¶

class qucat.C(node_minus, node_plus, *args)[source]

A class representing a capacitor

Parameters
• node_minus (integer) – Index corresponding to one node of capacitor

• node_minus – Index corresponding to the other node of the capacitor

• args (<float> or <str> or <float>,<str>) – Other arguments should be a float corresponding to the capacitance, a string corresponding to the name of that value (ex: “C”), or both. If only a label is provided, a value for should be passed as a keyword argument in subsequent function calls (ex: C = 1e-9) This is the best way to proceed if one wants to sweep the value of this capacitor. Indeed, the most computationally expensive part of the analysis is performed upon initializing the circuit, subsequently changing the value of a component and re-calculating a quantity such as the anharmonicity can be performed much faster.

zpf(mode, quantity, **kwargs)

Returns contribution of a mode to the zero-point fluctuations of a quantity for this component.

The quantity can be current (in units of Ampere), voltage (in Volts), charge (in electron charge), or flux (in units of the reduced flux quantum, $$\hbar/2e$$).

Parameters
• mode (integer) – Determine what mode to consider, where 0 designates the lowest frequency mode, and the others are arranged in order of increasing frequency

• quantity (string) – One of ‘current’, ‘flux’, ‘charge’, ‘voltage’

• kwargs – Values for un-specified circuit components, ex: L=1e-9.

Returns

contribution of the mode to the zero-point fluctuations of the quantity

Return type

float

Notes

This quantity is calculated by multiplying the voltage transfer function $$T_{rc}$$ (between a reference component $$r$$ and the annotated component $$c$$ ), with $$X_{zpf,m,r}$$, the zero-point fluctuations of $$\hat{X}$$ at the reference component.

Note that resistors make the transfer function $$T_{rc}$$, and hence this quantity, complex.

For more detail on the underlying theory, see https://arxiv.org/pdf/1908.10342.pdf.