1.4. Instantiated Pulse: Program

In qupulse an instantiated pulse template is called a program as it is something that an arbitrary waveform generator (AWG) can execute/playback. It can be thought of as compact representation of a mapping \(\{t | 0 \le t \le t_{\texttt{duration}}\} \rightarrow \mathbb{R}^n\) from the time while the program lasts \(t\) to an n-dimensional voltage space \(\mathbb{R}^n\). The dimensions are named by the channel names.

Programs are created by the create_program() method of PulseTemplate which returns a hardware independent and un-parameterized representation. The method takes a program_builder keyword argument that is propagated through the pulse template tree and thereby implements the visitor pattern. If the argument is not passed default_program_builder() is used instead which is LoopBuilder by default, i.e. the program created by default is of type Loop. The available program builders, programs and their constituents like Waveform and VolatileRepetitionCount are defined in th qupulse.program subpackage and it’s submodules. There is a private qupulse._program subpackage that was used for more rapid iteration development and is slowly phased out. It still contains the hardware specific program representation for the tabor electronics AWG driver. Zurich instrument specific code has been factored into the separate package qupulse-hdawg. Please refer to the reference and the docstrings for exact interfaces and implementation details.

The Loop default program is the root node of a tree of loop objects of arbitrary depth. Each node consists of a repetition count and either a waveform or a sequence of nodes which are repeated that many times. Iterations like the ForLoopPT cannot be represented natively but are unrolled into a sequence of items. The repetition count is currently the only property of a program that can be defined as volatile. This means that the AWG driver tries to upload the program in a way, where the repetition count can quickly be changed. This is implemented via the VolatileRepetitionCount class.

A much more capable program format is LinSpaceNode which efficiently encodes linearly spaced sweeps in voltage space by utilizing increment commands. It is build via LinSpaceBuilder. The main complexity of this program class is the efficient handling of interleaved constant points. The increment and set commands do not only carry a channel and a value but also a dependency key which encodes the dependence of loop indices. This allows the efficient encoding of

for idx in range(10):
    set_voltage(CONSTANT) # No dependencies
    set_voltage(OFFSET + idx * FACTOR) # depends on idx with

for _ in range(10): # loop
    set_voltage(CONSTANT, key=None)
    increment_by(FACTOR, key=(FACTOR,))

The motivation is that increment commands with this capability are available in the HDAWG command table.