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is desirable to modularize the control hardware (and software) such that the different
channels are independently deployable copies of each other. Each channel
then needs to provide a way to synchronize its signal stream to all other channels.
This synchronization consists of two components: Not only do the signal streams
need to start at the same time t = 0, they also need to progress at the same rate.
The definition of a common starting time t = 0 is usually achieved by a
trigger pulse for which the different channels wait before playing back their signal
sequence. For this, the trigger pulse needs to be distributed to all channels. This
can be done either by splitting the output of a single trigger source and distributing
it to all channels or by a so-called “daisy chain” in which each channel forwards
the trigger signal to the next. Usually, each channel needs to provide facilities to
shift its specific definition of t = 0 by an offset ∆t that compensates for any delays
in the arrival of the trigger pulse or any delays in the delivery of the channel’s
output signal to the respective qubit. The calibration of this delay is best done
with experiments run on the qubits. The type of experiment needed depends on
the involved channels and the type of coupling element used and will be discussed
below.
Actively synchronizing the rate at which the different channels play back their
signals is necessary since affordable clock sources do not natively provide the
desired accuracy. Specifically, the inter-channel phase jitter in the clock signals
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