The Cluster includes embedded communication features that simplify its modular architecture. These signals are transmitted through the mainframe backplane, enabling communication between internal modules (e.g., SYNQ, LINQ) as well as with external systems via the CMM (e.g., Ethernet, Trigger). The following block diagram illustrates these communication paths and protocols.
Like most instruments, Qblox instruments use a 10 MHz clock as a time reference. To synchronize multiple instruments in your setup, this reference clock must be connected to the REFin SMA connector of all Cluster CMM modules (10 MHz, 1 Vpp nominal @ 50 Ω) (see section cluster_cmm [Link to be added]). In addition, the Cluster.reference_source parameter must be set to external.
The reference clock is typically distributed using a star configuration, where the output from the external clock is split into as many signals as there are clusters. These signals should be delivered through cables of equal length to ensure proper synchronization before being connected to the REFin SMA connector of each Cluster.
Warning
Daisy-chaining the reference clock from one QBlox CMM module to the next is not supported. This does not yield a synchronized system with any reasonable or specified cable length.
To synchronize the start event of the instruments, Qblox SYNQ technology can be used to greatly simplify the process. All modules within a cluster share the same SYNQ network. Clusters can also be daisy-chained to each other to share the same SYNQ network using the SYNQ cable. 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 start their program with the wait_sync instruction (see section Real-time Instructions).
Note
In the case of a single Qblox instrument, the same procedure applies, except the Cluster.reference_source parameter should be set to internal. The Qblox SYNQ technology will then automatically align the timing of all participating sequencers within the instrument to within 300 ps of one another.
Qblox instruments support feedback by using an integrated trigger
network of four parallel trigger lines (16 addresses) that interconnect all sequencers
within the system and allow the user to create low-latency feedback
sequences. Additionally, the external trigger input
on each instrument is connected to the same trigger network. This allows
other instruments to also contribute to any feedback sequence. The
feedback works from any sequencer in any readout module to any sequencer
in any module.
The figure above illustrates the different timing contributions within the instrument. OP and IP represent the output path and input path latencies, respectively. These latencies depend on several factors, including the sequencer type (Control Sequencers , Readout Sequencers, Timetag Sequencers) as well as any options enabled on the path (e.g., NCO, RTP). For most modules with base options, the combined base latency is OP + IP = 149 ns.
The propagation delay refers to the time required for the signal to travel from the output to the input through external cabling. This delay is experiment-dependent; in the data below it is assumed to be 0 ns.The trigger network itself introduces an additional latency of 212–239 ns, depending on when the message is sent relative to the trigger clock.
In total, the feedback time, defined as the duration from the last input sample received to the first output sample sent, is given by:
To help you understand how latency behaves across different sequencer types and configuration options, we’ve separated the information into two tables. The first table shows the base latency values for each sequencer, distinguishing between output and input paths where applicable. This represents the latency without any optional features enabled.
The second table lists the latency modifications introduced by specific options such as RTP, Marker, and TTL. These values represent the change (increase or decrease) from the base latency. Not all options apply to every sequencer or latency direction, so we indicate “N/A” where an option is not applicable.
The figure below shows the four-line trigger network connecting the
external trigger input and all sequencers. Access to this trigger
network is address-based. When triggering the network using the external
trigger input or any of the sequencers, the resulting trigger is
converted into one of fifteen configurable addresses (i.e. 1 to 15). In
turn, any sequencer can subscribe to one or multiple addresses and react
to those incoming triggers using custom sequencer instructions to modify
sequence flow (see section
sequence_processor_operation_instructions).
The trigger network operates on a 28 ns timegrid. This timegrid is
started/aligned during module synchronization using the
[wait_sync]{.title-ref} instruction. Once synchronized, triggers are
sent to the nearest timegrid point in the future. In other words,
triggers that are not sent on this timegrid get a maximum time penalty
of 24 ns. Any trigger that is sent on the trigger network takes 212 ns
to propagate to any receiver on the trigger network, and be available
for conditional operation. A trigger can be sent on the trigger network
once every 252 ns (or 9 timegrid points). The figure below shows an
example of the trigger network timegrid.
Sending triggers on the trigger network can be done via different instructions explains in Feedback Trigger Handling.
💡 Tip — Using the threshold trigger via QCoDeS
Tip
For debugging purposes you can enable the threshold-trigger via QCoDeS (thresholded_acq_marker_en(True)). This feature causes the sequencer to issue a marker pulse independent of the standard trigger network each time the acquisition threshold is exceeded.
Because the threshold-acquisition marker is generated on a 4 ns time grid while most Qblox Q1 sequencer instructions run on a 1 ns time grid, the marker can only appear at multiples of 4 ns. To guarantee the marker is raised exactly when the acquisition finishes, the acquisition end time must be aligned to the 4 ns grid.
If the acquisition finishes at a time that is not divisible by 4 ns, the marker will be delayed until the next 4 ns tick. That introduces an additional timing offset of 1–3 ns, which combined with the instrument’s base input path latency may produce measured latencies such as 131 ns, 132 ns, 133 ns or 134 ns in practice.
If desired, the Qblox instruments can also be triggered by other instruments using an external trigger signal. To achieve this, simply connect the external trigger signal to the TRIGin SMA connector (0–3.3 V, high-Z). Then follow the instructions in the feedback_external_trigger_input [Link to be added] section to configure the external trigger input.
