Realisation of a spin–photon interface using singlet–triplet qubits in self-assembled quantum dot molecules

Kha Tran, Allan S. Bracker, Michael K. Yakes +3 more

Peter L. McMahon, Kristiaan De Greve

C. Millet

E. Cota, Sergio E. Ulloa, Juan E. Rolon

Y. L. Delley, Martin Kroner, Stefan Fält +2 more

Two-electron charged self-assembled quantum dot molecules exhibit a decoherence-avoiding singlet-triplet qubit subspace and an efficient spin-photon interface. Here, we demonstrate that the cycling transitions originating from auxiliary ground states in the same system allow for an efficient optical read-out of a singlet-triplet qubit. By implementing a spin-selective state transfer to the auxiliary state using a resonant laser field, we observe an improvement approaching two orders of magnitude in fidelity as compared to spin measurement by light scattering directly from the qubit states. Embedding the quantum dot molecule inside a low quality-factor micro-cavity structure should enable single-shot qubit read-out.

Zeng, Zheng

Connecting quantum processors over long distances using photon qubits would enable more complex quantum computing architectures and quantum networks. Recently a protocol to transfer a quantum state from a photonic qubit to a singlet-triplet spin qubit in GaAs/AlGaAs heterostructure has been theoretically demonstrated. In practice, the coherent transfer is facilitated by a hybrid device where a GaAs/AlGaAs gate-defined quantum dot (GDQD) is tunnel coupled to a self-assembled quantum dot (SAQD), in which a conversion between a photon state and a spin state takes place. This work addressed the three requirements of the optical-interface devices based on tunnel coupling between the GDQD and the SAQD: (i) a properly designed GaAs/AlGaAs heterostructure where the two-dimensional electron gas (2DEG) can be electrically tuned into resonance with the InAs SAQD; (ii) high-mobility 2DEG to form and operate a GDQD; (iii) precise alignment between the SAQD and the GDQD. It is proven that the InAs SAQD can be tuned to be charged, discharged, and resonant with the 2DEG by applying a local electric field.