Introduction to \(C^3\) Toolset

In this section, we go over the foundational components and concepts in \(C^3\) with the primary objective of understanding how the different sub-modules inside the c3-toolset are structured, the purpose they serve and how to tie them together into a complete Automated Quantum Device Bring-up workflow. For more detailed examples of how to use the c3-toolset to perform a specific Quantum Control task, please check out the Setup of a two-qubit chip with C^3 or the Simulated calibration sections or refer to the API Documentation for descriptions of Classes and Functions.

The Building Blocks

There are three basic building blocks that form the foundation of all the modelling and calibration tasks one can perform using c3-toolset, and depending on the use-case, some or all of these blocks might be useful. These are the following:

Quantum Device Model

A theoretical Physics-based model of the Quantum Processing Unit. This is encapsulated by the Model class which consists of objects from the chip and tasks library. chip contains Hamiltonian models of different kinds of qubit realisations, along with their couplings while tasks let you perform common operations such as qubit initialisation or readout. A typical Model object would contain objects encapsulating qubits along with their interactions as drive lines and tasks, if any.

Classical Control Electronics

A digital twin of the electronic control stack associated with the Quantum Processing Unit. The Generator class contains the required encapsulation in the form of devices which help model the behaviour of the classical control electronics taking account of their imperfections and physical realisations. The devices e.g, an LO or an AWG or a Mixer are wired together in the Generator object to form a complete representation of accessory electronics.

Instructions

Once there is a software model for the QPU and the control electronics, one would need to define Instructions or operations to be perform on this device. For gate-based quantum computing , this is in the form of gates and their underlying pulse operations. Pulse shapes are described through a Envelope along with a Carrier, which are then wrapped up in the form of Instruction objects. The sequence in which these gates are applied are not defined at this stage.

Warning

Components inside the c3/generator/ and c3/signal/ sub-modules will be restructured in an upcoming release to be more consistent with how the Model class encapsulates smaller blocks present in the c3/libraries sub-module.

Parameter Map

The ParameterMap helps to obtain an optimizable vector of parameters from the various theoretical models previously defined. This allows for a simple interface to the optimization algorithms which are tasked with optimizing different sets of variables used to define some entity, e.g, optimizing pulse parameters by calibrating on hardware or providing an optimal gate-set through model-based quantum control.

Experiments

With the building blocks in place, we can bring them all together through an Experiment object that encapsulates the device model, the control signals, the instructions and the parameter map. Note that depending on the use only some of the blocks are essential when building the experiment.

Optimizers

At its core, c3-toolset is an optimization framework and all of the three steps - Open-Loop, Calibration and Model Learning can be defined as a optimization task. The optimizers contain classes that provide helpful encapsulation for these steps. These objects take as arguments the previously defined Experiment and ParameterMap objects along with an algorithm e.g, CMA-eS or L-BFGS which performs the iterative optimization steps.

Libraries

The c3/libraries sub-module includes various helpful library of components that are used somewhat like lego pieces when building the bigger blocks, e.g, hamiltonians for the chip present in the Model or envelopes defining a control pulse. More details about these components are available in the Libraries package section.