Tuna-5 : Topology and allowed gate set
Each of the quantum processors has a specific topology (the way the qubits are connected) and a specific allowed gate set (supported qubit operations).
Tuna-5 consists of five qubits (Q0-Q4) in a starfish configuration with Q2 at the center.
You can execute the following single- and two-qubit gates on this system. Native operations - that is operations that require a single instruction on control hardware - are given in bold, other operations are decomposed using specific decomposition rules for this quantum processor:
-
Single-qubit operations
Rx(angle),Ry(angle),Rz(angle),Rn(angle)X90,Y90,mX90,mY90X,Y,Z,IHS,Sdag,T,TdagCR,CRk
-
Two-qubit operations
CZ,CNOT,SWAP
-
Non-unitary instructions
-
init,measure,reset
More specific, the following operations and commands are not allowed
DisplayDisplay_binaryNot- Binary controlled operations
c- Toffoli
Scheduling user programs: wait/barrier instructions
Programs submitted to Tuna-5 undergo a step of scheduling upon compilation using QuTech’s OpenSquirrel. During scheduling, the operations defined in the user program are rearranged in time according to an as-late-as-possible (ALAP) strategy, in such a way as to execute gates on qubits as late in the sequence of instructions specified by the user, as possible. Scheduling takes into account the duration of various operations in hardware (20 ns for single-qubit operations, 60 ns for two-qubit operations, 800 ns for measurements, and 500 µs for initialization) and various other hardware constraints that are detailed in the fact sheet of Tuna-5.
Users can arbitrarily influence the scheduling of a program through the barrier and wait instructions. The wait is a single-qubit control instruction that allows a user to constrain the optimization of a scheduler by delaying subsequent instructions on the specified qubits(s) by a given time. The instruction takes as arguments a qubit target (q[4] or q[0:4], for example) and the number of cycles (in steps of 20 ns) that the target should be left idling. Please note that wait instructions applied on multiple qubits are scheduled independently for each qubit.
For further details on the wait instruction in cQASM the user is referred to cQASM documentation.
The barrier instruction is a single-qubit control instruction that allows a user to constrain optimization of a scheduler by preventing scheduling of instructions on specified qubit(s) across the barrier. Therefore, the instruction can be used to define a scheduling domain within which ALAP scheduling will also take place.
For further details on the barrier instruction in cQASM the user is referred to cQASM documentation.
For more details on scheduling within the OpenSquirrel please refer to OpenSquirrel
Compiling user programs: gate decomposition
Programs submitted to Tuna-5 undergo a step of gate decomposition upon compilation using OpenSquirrel. Non-native gate operations are decomposed, affecting their overall duration. Furthermore, it should be noted that native gate operations resulting from decomposition are scheduled using quantify scheduler. For a detailed description of the non-native operations supported in the backend, and their respective decompositions, please refer to the fact sheet for Tuna-5. Finally, single-qubit arbitrary rotations are quantized to the nearest multiple of π/36 radians (5°).
Result format: parallel and sequential measurements
The result format strictly depends on the structure of measurements programmed by the user. Therefore, results are organized in a 2-dimensional array where the outer-most dimension encodes the various shots of a circuit requested by the user, and the second dimension encodes the qubit measurement outcomes with the same order as specified in the classical bit register. The user has explicit control on the mapping of qubits measurements to classical bits in the register.
Measurements performed on multiple-qubit targets (q[0:4], for example) are still subject to scheduling. Therefore, barrier instructions should be used when trying to ensure that measurements are performed in parallel.