Asymmetric Sensing Dot for Scaleable Baseband Readout of Spin Qubits

High fidelity scalable readout is one of the key requirements for quantum computers with more than just a few qubits. Charge sensing dots are in this regard the most sensitive sensors for spin qubit readout. The most widespread readout technique is based on RF reflectometry, satisfying the requirement of high fidelity, but requires bulky, power-hungry components and is not well scalable. A more scalable alternative is to use transistors in close proximity to the qubit [1,2].
For best performance a high output swing of the sensor is desirable. We present experimental results in GaAs of an asymmetric sensing dot (ASD), improving the sensor response by a factor of 15 compared to conventional charge sensing dots. We perform charge sensing using a current biased ASD and observe a 2.36 mV swing in response to a (1,1)→(2,0) transition in a nearby double dot.
The improved voltage swing is due to a device design with a strongly decoupled drain reservoir from the sensor dot, mitigating negative feedback effects.

[1] M. J. Curry et al., APL 2015
[2] L. A. Tracy et al., APL 2016