High-fidelity fast single-shot electron spin readout above 3.5 K

Electron spin qubits in semiconductors provide a promising platform for large-scale quantum computing due to their small size, long coherence and manufacturability. Typically, readout in spin qubits has been performed using energy-selective readout with extremely high fidelities up to 99.95% at millikelvin temperatures. Despite achieving record fidelities at low electron temperatures, the readout time remains on the order of 1 us to 100 us and comparable to the electron spin coherence time. In this paper we show that by precision engineering the location of two multi-donor quantum dot qubits with respect to the charge sensor we can demonstrate latched parity readout of two electrons in only 175 ns integration time with a fidelity of 99.91% at mK temperatures. Most importantly we show that the strong confinement potential present in donor qubits combined with precision engineering of the tunnel rates allows us to operate our sensors at higher temperatures than before, at 3.7 K using latched spin readout, giving a maximum fidelity of 98.34% in 1.5 us (while maintaining greater than 98% fidelity within 1 us). Our results demonstrate a clear performance improvement of state preparation and measurement using donor systems and offer the real possibility for operation of the surface-code using electron spins in semiconductor qubits.