2. Sequence edition¶
Once the Exopy application started, select the Pulses workspace to create a new sequence. The following section will guide through the required steps and explain the principle of pulse synthesis in Exopy.
Contents
2.1. Creating a sequence¶
When selecting the Pulses workspace, the.measurement edition panels are replaced by three panels :
one is dedicated to the edition of a sequence
the second, tabbed beind the first, can be used to edit the variables of the sequence (more on their use will be said later on).
the thrid one is nothing else than a log panel similar to the one present in the.measurement edition workspace.
Note
Currently the workspace supports only editing a single sequence at a time.
When starting the editor contains a blank sequence. You can either start from there or load an existing sequence using the File menu. From the same menu you can save the sequence (Ctrl+S can also be used).
A pulse sequence is made of two things :
the sequence of pulses itself which can contain subsequences.
a compilation context responsible of compiling the pulse sequence and transferring it to a waveform geenrator.
For simplicity sakes, we will first decribe the role of the pulses and sequences but keep in mind that some settings can only be performed once a context is selected.
Note
The edition of the pulse sequence is concentrated in a single scrollable area. To avoid undesired modification of some settings it is advised to only scroll when the mouse is over the scrool bar.
2.1.1. Adding a pulse¶
When a sequence is empty, it displays two buttons : one dedicated to the addition of a pulse the other to the addition of a sequence. Clicking on the one dedicated to the pulse will immediately insert a new pulse in the sequence and the two previously diplayed buttons will disappear.
Note
Just like when editing the tasks composing a.measurement, the button of the left of each item (pulse/sequence) can be used to add new items, move items or delete items.
The inserted pulse is blank. First you should determine its kind. A pulse can be either Logical or Analogical. A logical pulse as its name indicates can only take two values 0 or 1. By convention during the pulse duration its take the value 1. By contrast an analogical pulse is arbitrary and hence requires more settings that will be detailed later on.
Once the kind chosen, if you have selected a context, you can then specify on which channel should the pulse be played. Depending on its kind, only the matching channels will be proposed.
Note
The contexts provide the possibility to invert the meaning of a logical channel.
One setting common to all kind of pulse is the timing of the pulse, which can be specified in three different ways : start/stop, start/duration, or duration/stop. In each case, the two required parameters can be specified using formulas with variables in between {}.
The accessible variables, listed by the autocompletion, are the following :
the global variables declared on the root sequence (discussed later)
the local variables declared in a subsequence (discussed later)
the start/stop/duration of any pulse or sequence (in the form i_start, …) where i is the index of the pulse or sequence. This include the ones of pulses occuring after the edited pulse.
To avoid editing sequences more than necessary, it is advised to avoid hardcoding durations but rather use variables and express the constraints between the pulses using their timing information.
Note
The pulses being indexed rather than named, one should be careful when inserting, moving or deleting a pulse as this will lead to a re-indexing of the pulses.
As previously mentionned, the above information are sufficient to specify a logical pulse but not an analogical one. Analogical pulses need additional parameters provided by their shape and an optional modulation.
The shape of a pulse can be chosen from an existing list of shapes providing different parameters. As it is very common in some experiments to use such pulses to drives mixers, an additional sinusoïdal modulation can be added. In such a case the output pulse will be a sinuoïdal signal whose amplidtude is given by the shape. As can be expected one can specify the frequency and phase of the modulation.
For simple sequences using only pulses is sufficient, however if a more complex/versatile
structure is required subsequence can be used. For example, the ConditionalSequence
can be used to include its child pulses on a given condition making it easy to
compile a witness sequence missing the active part.
2.1.2. Adding a sequence¶
Adding a sequence is very similar to a adding a task to a task hierarchy. When clicking the button, you will be prompted to choose the kind of sequence to add and provide some informations. Once this is done the sequence will be inserted.
Depending on the sequence you will have to adjust specific parameters but some of them are common (and also apply to a point to the root sequence):
should the sequence have a fixed duration ? This is particularly useful is a specific duty cycle should be respected. When activated you will have to specify the timing of the sequence just like for a pulse and teh context will take care to fill in any necessary blank. Note that the timing infos of a sequence are only accessible in the formula fields if the sequence as a fixed duration.
the local variables of the sequence. Local variables of a sequence are only visible to its child items and can be used to avoid writing multiple times the same formula.
Your sequence is now ready (up to the selection of the channels) and it is time to select a context.
2.1.3. Choosing a context¶
The context is responsible for compiling the sequence and transferrring it to the instrument. During compilation, all the formulas are evaluated and the sequence is simplified before being transferred to the instrument.
As a context is linked to a particular instrument, it knwows the available channels.
The context can offer different parametrization, the default ones being :
the unit used for representing the time in the sequence. By default the unit is the mus.
the logical channels whose meaning should be inverted (an absence of pulse becoming a logical 1, a presence a 0)
Warning
Currently the context does not support using arbitrary formulas.
Note
Because some optimizations of the compilation may be specific to the waveform generator used the context can work only with specific drivers.
2.1.4. Using the external variables¶
It is often desirable to parametrize a pulse sequence, for example performing a Rabi oscillation measurement requires to vary duration of the driving pulse. Such a parametrization is possible through the use of the root sequence external variables. Contrary to the local variables, the externals variables will be accessible from the task used to transfer the sequence to the instrument.
These variables can be edited from the second tab of the workspace. Their value will be specified mainly through the transfer task but are needed here too to allow to check that the sequence can be compiled as explained in the next section.
2.2. Checking that the sequence compile¶
Once your sequence written and saved, it may be a good idea to check that it can be compiled. To check it, click on the compile button at the bottom right corner. This will open a dialog,
From this dialog, you can edit the external variables and attempt to compile the sequence. If the compilation succeed the compilation duration will appear in green, if not in red and the compilations errors will be visible in the errors tabs.
Note
At the moment it is not possible to transfer a pulse sequence directly from the pulse sequence edition workspace.