Researchers demonstrate a new way to drive a single hole spin qubit in a germanium device using very little radio‑frequency power. The work addresses a practical problem: conventional electric dipole spin resonance (EDSR) can need substantial rf drive power at the low magnetic fields that give the best qubit coherence and readout. That extra power causes heating and crosstalk, which make it harder to scale up devices.

The team implements a “flopping‑mode” qubit. In this design one spin is shared, or delocalized, across a double quantum dot. That arrangement keeps the qubit partly protected from charge noise (a common source of errors) while at the same time making electric driving much more efficient. The authors mapped out where the qubit coherence is best by changing the direction of the magnetic field. They were able to operate at a nearly in‑plane magnetic field of 5 millitesla and use only −52 dBm of drive power at the device, far below the roughly −27 dBm reported for conventional planar germanium EDSR at similarly low fields.

The device shows good coherence and control. Reported values include a free induction decay time T2* = 1.4 μs, a Hahn echo time T2^Hahn = 11.5 μs, a CPMG32 echo time T2^(φ,CPMG32) = 130 μs, and an energy relaxation time T1 = 226 μs. Single‑qubit gates reached up to 99.76% fidelity with a π‑pulse time tXπ = 88 ns. These numbers show that low‑power driving did not come at the cost of dramatically worse coherence or control.

The authors also examined how the qubit relaxes and found behavior consistent with a two‑photon Orbach process. In plain terms, this is a phonon‑assisted relaxation path that involves a virtual or real higher energy state and two phonons. Identifying this mechanism points to concrete ways to reduce relaxation in future devices, for example by changing level spacings or the device environment to suppress that phonon channel.