Large Dispersive Interaction between a CMOS Double Quantum Dot and Microwave Photons

To implement quantum error-correction, readout must be performed much faster than the coherence time, up to ~100 μs for spins in silicon [1]. With that goal in mind, here we demonstrate the readout of an inter-dot charge transition, the basis of parity readout, in 50 ns with a SNR of 3.3. We do so using dispersive gate sensing with a CMOS split-gate nanowire transistor. This fast readout is achieved firstly by maximising the coherent coupling rate between the microwave photons and the charge dipole. We measure a coupling of 183 MHz owing to the large inter-dot lever arm (0.72) of our asymmetric split-gate device, and the high impedance (560 Ω) of our readout cavity, which comprises of an off-chip superconducting spiral [2] that is inductively coupled to the microwave feedline. Secondly, this inductive coupling is tuned so that the cavity linewidth is similar to the state-dependent shift in the resonant frequency, the regime of optimal state visibility [3].

[1] Veldhorst, M. et al., Nat. Nanotechnol. 9, 981-985 (2014)
[2] Ahmed, I. et al., Phys. Rev. Applied 10, 014018 (2018)
[3] Gambetta, J. et al., Phys. Rev. A. 77, 012112 (2008)