Port and codeword mapping

The port and codeword mapping defines what a control instruction means for the configured device. For example, the default map uses codeword 1 on source port 0 for an X gate on qubit 0, and codeword 4 for acquisition on that qubit.

The mapping belongs to the simulation profile. Programs select entries by source port and codeword; the selected events can address different core-local output ports.

Connections

• Input: source port and codeword from a cw operation.

• Output: a Mapping containing one or more EventSpec values for codeword decoding.

• Owner: the immutable TimingConfig, indexed by port and codeword.

Event specifications

Each EventSpec defines an ideal gate, pulse drive, acquisition, discriminator arm or one output of a paired gate. It specifies the output port, delay and duration. Pulses also have an axis and amplitude; acquisitions have discriminator timing. execution_flag selects an execution condition for single-qubit gates and pulses.

A paired output names a TwoQubitGate in Profile::two_qubit_gates. That definition supplies the backend operation, two targets, resources, duration and two required input endpoints. The default CX uses port 0 with codeword 6 and port 1 with codeword 10. See two-port gate outputs.

The default map assigns codewords 7, 8 and 9 to X gates controlled by last_one, last_zero and equal, respectively, on each qubit’s port.

The event starts at fire_tick + delay and occupies its output port and resources over [start, end). Duration must be positive. An ideal gate changes quantum state at the start of that interval.

Backend support is checked when a program requests the mapping. A profile can therefore contain unused pulse entries when running the Aer backend. Waveforms belong to backend configuration. A pulse mapping selects a waveform by operation; QuTiP supports square, gaussian, drag and samples shapes. See waveform configuration.

Objects and state

Object or member	Representation	Role
Mapping::port and codeword	lookup key	Source control port and digital codeword.
Mapping::actions	vector<EventSpec>	IdealGate, Pulse, Acquire, DiscriminatorArm or GateOutput descriptors.
EventSpec	port and timing with a typed payload	Holds one of GateSpec, PulseSpec, AcquireSpec, DiscriminatorArmSpec or GateOutputSpec.

C++ API.

Reset and errors

Profile validation rejects malformed or duplicate mappings and invalid timing parameters. Lookup rejects unknown ports or codewords. An unsupported requested event fails before timing control acceptance.

Session reset preserves the map. Select a new profile before constructing a new simulator to change these definitions.

Implementation and tests

Source: profile.cpp and profile.hpp.

CTest: config.profile, control.mapping, protocol.readout.

The tests reject unknown port and codeword pairs, duplicate mappings and incompatible acquisition and arm targets. They also check that changing a mapping changes the profile fingerprint. config.profile checks JSON round trips and rejects fields belonging to another event kind.