RIKEN and Toshiba show a 99.92% two-qubit gate with a simple waveform

[ExoplanetWrench]

Japanese researchers have shown a high quality quantum gate using a refreshingly simple control signal. Quantum Zeitgeist reports that a team from RIKEN and Toshiba demonstrated a parametrically driven iSWAP gate between two fixed frequency transmon qubits with 99.92 percent average fidelity

The qubits are linked by a special coupler called a capacitively shunted double transmon coupler, operated at zero flux bias, a so called sweet spot where it is least sensitive to noise. That makes the result easier to reproduce elsewhere

Fidelity was measured with randomised benchmarking, including leakage, and the gate takes 112 nanoseconds. The researchers said the performance came from a simple analytically defined waveform without predistortion

The authors include Yasunobu Nakamura and Hayato Goto, and the work is published in a Physical Review journal. The gate time is described as relatively long, and most remaining errors come from decoherence rather than control problems

Simple control signals are valuable, because complex pulse shaping becomes a headache when you have thousands of qubits. Reaching above 99.9 percent without tricks suggests the coupler design itself is doing the heavy lifting. Making the gate faster would push the fidelity even higher

Which matters more for scaling, gate speed or simple control? And is Japan becoming a major force in superconducting qubits?

Parametric ISWAP Gate At Zero Flux Boosts Qubitsquantumzeitgeist.com