Fig. 1: Spin qubit array in germanium.
From: Simultaneous single-qubit driving of semiconductor spin qubits at the fault-tolerant threshold
a Scanning electron microscope (SEM) image of the device. The device is comprised of two lithographically defined layers of Ti:Pd constituting the plunger (blue) and barrier (red) gates, as well as an Al ohmic layer (green) forming low resistance ohmic contacts with the quantum well directly. An external magnetic field Bext is applied in-plane with respect to the quantum well. b Latched spin blockade readout mechanism. We consider two separate readout systems Q1Q2 (red) and Q3Q4 (blue), each containing a double quantum dot pair and single hole transistor. By reducing the reservoir tunnel coupling to quantum dot Q2(4) ΓQ2(4), we are able to suppress the (0,1) to (0,2)S transition longer than the typical singlet triplet relaxation rates13 and facilitating a readout integration window of 10 μs. c Ramsey sequences on qubits Q1-4 respectively, at magnetic field Bext = 1 T (circles, lower) and 0.65 T (triangles, upper). Extracted spin dephasing times at 1 T for qubits Q1 (orange), Q2 (yellow), Q3 (purple) and Q4 (green) are T2*,Q1 = 186 ± 19 ns, T2*,Q2 = 119 ± 14 ns, T2*,Q3 = 323 ± 52 ns and T2*,Q4 = 147 ± 26 ns. At 0.65 T the dephasing times increase to T2*,Q1 = 276 ± 22 ns, T2*,Q2 = 166 ± 14 ns, T2*,Q3 = 472 ± 31 ns and T2*,Q4 = 228 ± 15 ns. Data for different magnetic fields is offset by unity for clarity.
