Fast spin-valley-based quantum gates in Si with micromagnets

Abstract

An electron spin qubit in silicon quantum dots holds promise for quantum information processing due to the scalability and long coherence. An essential ingredient to recent progress is the employment of micromagnets. They generate a synthetic spin–orbit coupling (SOC), which allows high-fidelity spin manipulation and strong interaction between an electron spin and cavity photons. To scaled-up quantum computing, multiple technical challenges remain to be overcome, including controlling the valley degree of freedom, which is usually considered detrimental to a spin qubit. Here, we show that it is possible to significantly enhance the electrical manipulation of a spin qubit through the effect of constructive interference and the large spin-valley mixing. To characterize the quality of spin control, we also studied spin dephasing due to charge noise through spin-valley mixing. The competition between the increased control strength and spin dephasing produces two sweet-spots, where the quality factor of the spin qubit can be high. Finally, we reveal that the synthetic SOC leads to distinctive spin relaxation in silicon, which explains recent experiments.

Electrical manipulation of a single electron spin in CMOS using a micromagnet and spin-valley coupling

“…It is worth noting that measurement further on the hotspot is prevented by fast relaxation during readout. This increase of EDSR Rabi frequency at the hotspot is related to the presence of a second drive mechanism which involves the presence of valley mixing in the silicon QD combined with synthetic SOC 35 . More precisely, the microwave electric field allows a transition from two different valleys but same spin ( v À ; # j i and v þ ; # j i) and the synthetic SOC couples the two opposite spins in different valleys ( v À ; " j i and v þ ; # j i) which eventually leads to an opposite spin and same valley transition ( v À ; " j i to v À ; # j i) 36 .…”

“…Though, we do not observe a clear enhancement of the quality factor as was proposed in ref. 35 . We therefore need to understand further the noise spectrum of the qubit and in particular the influence of charge noise.…”

Electrical manipulation of a single electron spin in CMOS with micromagnet and spin-valley coupling

“…It is worth noting that measurement further on the hotspot is prevented by fast relaxation during readout. This increase of EDSR Rabi frequency at the hotspot is related to the presence of a second drive mechanism which involves the presence of valley mixing in the silicon QD combined with synthetic SOC [28]. More precisely, the microwave electric field allows a transition from two different valleys but same spin (|v -, ↓ and |v + , ↓ ) and the synthetic SOC couples the two opposite spins in different valleys (|v -, ↑ and |v + , ↓ ) which eventually leads to an opposite spins and same valley transition (|v -, ↑ to |v -, ↓ ) [33].…”

“…Though, we do not observe a clear sweetspot in quality factor as was proposed in ref. [28]. We therefore need to understand further the noise spectrum of the qubit and in particular the influence of charge noise.…”