In this section we explain how to synchronize multiple instruments in your setup including Qblox Pulsar series instruments. Synchronization is based on two aspects:

  1. A shared reference clock, preferably phase aligned, so that all instruments use the same reference to base their operations on.

  2. A synchronized start event, so that all instruments start their operations simultaneously.

The following subsections will go into more detail on how to achieve both aspects.

Reference clock

Like most instruments the Qblox instruments use a 10 MHz clock as a time reference. To synchronize multiple instruments in your setup you will need to connect such a reference clock to the REFin SMA connector of the instruments (10 MHz, 1 Vpp nominal @ 50 Ω) (see section Overview) and set the reference_source() parameter to external. Connecting the reference can be done in two ways:

  1. Through a clock distribution module that distributes a reference clock provided by a reference clock source to all instruments in the setup as shown in the figure below. Care has to be taken that all distributed reference clocks are length matched to keep the clocks phase aligned.

Clock synchronization through clock distribution module.

  1. Through daisy-chaining the reference clock from one Qblox instrument to the next as shown in the figure below. The Qblox instruments have been configured so that when a 50 cm coaxial cable is used to connect the REFout SMA connector of one instrument to the REFin SMA connector of the next, the instrument’s reference clocks are phase align to one another. This removes the need of an additional clock distribution module. The first instrument in the daisy-chain can either use an internal reference source or an external reference if you wish to connect additional non-Qblox instruments. All other Qblox instruments need to be configured to use external reference sources.

Clock synchronization through clock daisy-chain.


To synchronize the start event of the instruments, Qblox SYNQ technology can be used to greatly simply the process. To use this SYNQ technology, the Qblox instruments need to be daisy-chained using the two SYNC ports (see section Overview) as shown in the figure below. Additionally, the sequencer#_sync_en() parameter needs to be set for every sequencer in the instrument participating in the experiment and these same sequencers need to execute the wait_sync instruction (see section Instructions). Note, these last two steps also need to done when only using a single Qblox instrument. The Qblox SYNQ technology will then automatically align the timing of every participating sequencer in all Qblox instruments to within 300 ps of one another.

SYNQ daisy-chain.

Additionally, the marker output channels can be controlled by the sequencers to trigger other non-Qblox instruments, thereby synchronizing them with the Qblox instruments. However, care needs to be taken to compensate for any trigger delay caused by the connection or the triggered instrument itself.


If desired, the Qblox instruments can also be triggered by other non-Qblox instruments. To achieve this, simply connect the trigger signal to the TRIGin SMA connector (0-3.3 V, high-Z) (see section Overview) as shown in the figure below and have any sequencer in the Qblox instrument participating in the experiment execute the wait_trigger instruction (see section Instructions).

External trigger.