Abstract
Hardware efficient transpilation of quantum circuits to a quantum devices native gateset is essential for the execution of quantum algorithms on noisy quantum computers. Typical quantum devices utilize a gateset with a single two-qubit Clifford entangling gate per pair of coupled qubits, however, in some applications access to a non-Clifford two-qubit gate can result in more optimal circuit decompositions and also allows more flexibility in optimizing over noise. We demonstrate calibration of a low error non-Clifford Controlled-$\frac{\pi}{2}$ phase (CS) gate on a cloud based IBM Quantum computing using the Qiskit Pulse framework. To measure the gate error of the calibrated CS gate we perform non-Clifford CNOT-Dihedral interleaved randomized benchmarking. We are able to obtain a gate error of $5.9(7) \times 10^{-3}$ at a gate length 263 ns, which is close to the coherence limit of the associated qubits, and lower error than the backends standard calibrated CNOT gate.
Highlights
Quantum computation holds great promise for speeding up certain classes of problems; near-term applications are heavily restricted by the errors that occur on presentday noisy quantum devices [1]
We describe the protocol for estimating the average gate error of the CS gate using interleaved CNOT-dihedral randomized benchmarking, which is a natural generalization of the CNOT-dihedral RB procedure described in [17] with interleaved RB [13] to estimate individual gate fidelities for the CS = ⎜⎜⎜⎝00
To benchmark performance of the non-Clifford gate we performed an experimental demonstration of twoqubit interleaved CNOT-dihedral RB, which allows efficient and robust characterization of a universal gate set containing the CS gate
Summary
Quantum computation holds great promise for speeding up certain classes of problems; near-term applications are heavily restricted by the errors that occur on presentday noisy quantum devices [1]. In some cases it may be favorable to introduce an additional two-qubit gate to a gate set if it enables more hardware-efficient compilation of relevant circuits; this adds the overhead of additional calibration and characterization of the gate errors One such gate is the controlled-phase (CS) gate, which is a non-Clifford two-qubit entangling gate that is universal when combined with the Clifford group [17]. The CS gate is attractive to fixed-frequency transmon qubit systems as it can be implemented√using the CR interaction, since it is locally equivalent to CNOT This means it can be calibrated using the same techniques as the CNOT gate, but with a shorter gate duration or lower power, potentially leading to a higher-fidelity two-qubit gate when calibrated close to the coherence limit. Pulse-level calibration was done using Qiskit Pulse [22], and the RB and QPT experiments were implemented using the open source Qiskit computing software stack [23] through the IBM Quantum cloud provider
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