Quantum dot devices with modulation doped stacks

A quantum computing device, comprising:

• a quantum processing device, wherein the quantum processing device includes a first quantum well stack region and a second quantum well stack region, an active quantum well layer in the first quantum well stack region, a read quantum well layer in the second quantum well stack region, a doped layer in the first quantum well stack region spaced away from the active quantum well layer by a barrier layer, the doped layer includes a first material and a dopant, the first material has a first diffusivity of the dopant, the barrier layer includes a second material having a second diffusivity of the dopant, and the second diffusivity is less than the first diffusivity;
• a non-quantum processing device, coupled to the quantum processing device, to control voltages applied to gates on the first and second quantum well stack regions;
• and
• a memory device to store data generated by the read quantum well layer during operation of the quantum processing device;
• wherein the first material includes silicon and germanium, the second material includes silicon and germanium, the first material has a first germanium content, the second material has a second germanium content, and the first germanium content is different from the second germanium content.

A quantum dot device, comprising:

• a quantum well stack including a quantum well layer, a first doped layer, a second doped layer, and a barrier layer between the first doped layer and the quantum well layer, wherein the first doped layer includes a first material and a dopant, the first material has a first diffusivity of the dopant, the barrier layer includes a second material having a second diffusivity of the dopant, the second diffusivity is less than the first diffusivity, and the barrier layer is between the first doped layer and the second doped layer;
• and
• gates above the quantum well stack;
• wherein the first material includes silicon or germanium or a combination thereof, and the second material includes silicon or germanium or a combination thereof, a III-V material, or silicon and carbon.

A quantum computing device, comprising:

• a quantum processing device, wherein the quantum processing device includes a first quantum well stack region and a second quantum well stack region, an active quantum well layer in the first quantum well stack region, a read quantum well layer in the second quantum well stack region, a first doped layer in the first quantum well stack region spaced away from the active quantum well layer by a barrier layer, a second doped layer in the first quantum well stack region, the first doped layer includes a first material and a dopant, the first material has a first diffusivity of the dopant, the barrier layer includes a second material having a second diffusivity of the dopant, the second diffusivity is less than the first diffusivity, the barrier layer is between the first doped layer and the second doped layer, the first material includes silicon or germanium or a combination thereof, and the second material includes silicon or germanium or a combination thereof, a III-V material, or silicon and carbon;
• a non-quantum processing device, coupled to the quantum processing device, to control voltages applied to gates on the first and second quantum well stack regions;
• and
• a memory device to store data generated by the read quantum well layer during operation of the quantum processing device.