DIO Tab¶

The DIO tab provides access to the settings and controls of the digital inputs and outputs. It is available on all SHFQC+ Instruments.

Features¶

Monitor and control of 32-bit DIO port
Configure Trigger Inputs and Marker Outputs
Configure the Internal Trigger settings

Description¶

The DIO tab is the main panel to control the digital inputs and outputs as well as the trigger levels. Whenever the tab is closed or an additional one of the same type is needed, clicking the following icon will open a new instance of the tab.

Table 1: App icon and short description
Control/Tool	Option/Range	Description
DIO		Gives access to all controls relevant for the digital inputs and outputs including DIO, Trigger Inputs, Trigger Outputs, and Marker Outputs.

The QA Channels section shows the settings for the two Trig inputs on the front panel of the Quantum Analyzer channel. The LED status indicator helps in monitoring the input signal state and selecting the threshold. The Marker section allows users to assign internal marker bits to the Mark outputs on the front panel. Alternatively, the outputs can be set to static high or low values. The SG Channels section shows similar settings for the 2, 4, or 6 Signal Generator channels. Additionally, the marker outputs of the Signal Generator channels have a configurable delay, with a resolution of 1 ns. In the System Settings section, the number of repetitions and the holdoff time of the Internal Trigger can be configured. The Internal Trigger is useful for synchronizing the outputs of different channels on the same instrument.

Digital I/O¶

The Digital I/O has 3 operation modes: Manual means controlled manually, QA Sequencer n means controlled by QA Sequencer n, QA there are the 32-bit DIO port is in use.

Figure 2 shows the architecture of the DIO port. It features 32 bits that can be configured byte-wise as inputs or outputs by means of a drive signal. The digital output data is latched synchronously with the falling edge of the internal clock, which is running at 50 MHz. The internal sampling clock is available at the DOL pin of the DIO connector. Digital input data can either be sampled by the internal clock or by an external clock provided through the CLKI pin. A decimated version of the input clock is used to sample the input data. The Decimation unit counts the clocks to decimation and then latches the input data. The default decimation is 5625000, corresponding to a digital input sampling rate of 1 sample per second.

Figure 2: DIO input/output architecture

In Manual mode, each DIO pin can be controlled manually according to Figure 2 and the DIO interface specification is detailed in Specifications.

In QA Sequencer N mode, each DIO pin output can be controlled in the SHFQC+ Readout Pulse Generator Tab Sequencer N (N indicates which Channel) by a SeqC command setDIO.

In QA Results mode, DIO pins are configured to send Readout Result after Thresholding. Table 2 shows the mapping between DIO pins and input/output signals available when using the DIO connector to output qubit state measurement results. The direction is as seen from the SHFQC+ Instrument. In order to use these signals, the Digital I/O Mode and Drive setting have to be chosen accordingly.

Table 2: DIO signal assignment in QA Results Mode
DIOLink signal	DIO pin	Direction	Description
VALID	DIO[0]	OUT	valid bit
CW	DIO[4:1]	OUT	one-hot encoding of Readout Channel
CW	DIO[8:23]	OUT	quantized results for a maximum of 16 State Discriminations
reserved	DIO[24:31]	IN	incoming communication

DIO Result communication belows shows an example of multiple channel readout transmissions through DIO. Every readout is sent in a single message. A one-hot encoding of the readout channel is sent along with the readout on dedicated bits. The valid bit is set for every valid DIO transaction.

Figure 3: DIO Result communication

The QA Results QCCS mode of the DIO interface provides one way of communicating discriminated qubit states between 2 Instruments. For more than 2 Instruments, both qubit states and synchronization becomes essential. The following section explains how the ZSync interface works for both Instrument synchronization and feedback. Please note that ZSync settings are under the Device Tab.

ZSync Interface¶

The ZSync link of the Zurich Instruments' Quantum Computing Control System (QCCS) enables Instrument synchronization and communication on the system level through the Zurich Instruments' PQSC Programmable Quantum System Controller. This architecture is able to support quantum algorithms run in scalable quantum processors.

In particular, the ZSync links distribute the system clock to all Instruments and synchronize all Instruments to sub-nanosecond levels. Besides status monitoring to ensure quality and reliability of qubit tune-up routines, it provides a bidirectional data interface to send readout results to, or obtain sequence instructions from the PQSC.

The ZSync links adhere to strict real-time behavior: all data transfers are predictable to single clock cycle precision. In the SHFQC+, the link is optimized for maximum data transfer bandwidth to the central controller. For example, twice the bandwidth is reserved for results being transferred to the PQSC with respect to the allocated bandwidth for instructions that are received from the PQSC. This enables global feedback and error correction through centralized syndrome decoding and synchronized actions on the global QCCS system level.

Feedback through the PQSC¶

Note

More information on the ZSync, and how to properly link the SHFQC+ with the QCCS can be found in the user manual of the PQSC Programmable Quantum System Controller.

Using the startQA- command, the SHFQA+ or the Quantum Analyzer Channel of the SHFQC+ generates a readout result and forwards it to the PQSC over the ZSync. Depending on the address provided, the PQSC stores it in the register bank - the center of the feedback in the QCCS system. After processing, the PQSC then forwards the results to other devices in the QCCS, such as the SHFSG+.

The register bank requires a readout to have an address and a mask along with the readout data. Each component is sent in a separate ZSync message. The address is sent first, followed by the mask, and then the data, see Figure 4. To reduce latency, the address and the mask are sent during the readout, and the data is then sent as soon as the discriminated qubit results are ready.

Figure 4: Readout Result communication via ZSync

Functional Elements¶

Table 3: Digital input and output channels, reference and trigger
Control/Tool	Option/Range	Description
DIO mode		Select DIO mode
	Manual	Enables manual control of the DIO output bits.
	Sequencer	Enables control of DIO values by the Sequencer.
	Result	Sends discriminated Readout Results to the DIO.
DIO mode		Select DIO mode
DIO mode	Manual	Enables manual control of the DIO output bits.
QA Result Overflow	grey/yellow/red	Red: present overflow condition on the DIO interface during readout. Yellow: indicates an overflow occurred in the past. An overflow can happen if readouts are triggered faster than the maximum possible data-rate of the DIO interface.
DIO bits	label	Partitioning of the 32 bits of the DIO into 4 buses of 8 bits each. Each bus can be used as an input or output.
DIO input	numeric value in either Hex or Binary format	Current digital values at the DIO input port.
DIO output	numeric value in either hexadecimal or binary format	Digital output values. Enable drive to apply the signals to the output.
DIO drive	ON / OFF	When on, the corresponding 8-bit bus is in output mode. When off, it is in input mode.
Format		Select DIO view format.
	Hexadecimal	DIO view format is hexadecimal.
	Binary	DIO view format is binary.
Clock		Select DIO internal or external clocking.
Interface		Selects the interface standard to use on the 32-bit DIO interface. This setting is persistent across device reboots.
	LVCMOS	A single-ended, 3.3V CMOS interface is used.
	LVDS	A differential, LVDS compatible interface is used.
Trigger level		Trigger voltage level at which the trigger input toggles between low and high. Use 50% amplitude for digital input and consider the trigger hysteresis.
50 Ω	50 Ω/1 kΩ	Trigger input impedance: When on, the trigger input impedance is 50 Ω, when off 1 kΩ.
Trigger Input Low status		Indicates the current low level trigger state.
	Off	A low state is not being triggered.
	On	A low state is being triggered.
Trigger Input High status		Indicates the current high level trigger state.
	Off	A high state is not being triggered.
	On	A high state is being triggered.
Marker output signal		Select the signal assigned to the marker output.
Delay (s)		This delay adds an offset that acts only on the trigger/marker output. The total delay to the trigger/marker output is the sum of this value and the value of the output delay node.
Run/Stop		Enable internal trigger generator.
Repetitions		Number of triggers to be generated.
Holdoff		Hold-off time between generated triggers.
Progress		The fraction of the triggers generated so far.
Synchronization		Enable synchronization. Trigger generation will only start once all synchronization participants have reported a ready status. Synchronization checks will be repeated with the same trigger generation settings (holdoff and repetitions) until synchronization is disabled.