Scalable and Spectrally Uniform Single Photon Sources in Spatially Regular Arrays & Generated Bell States

Universal optical quantum information processing (QIP) requires reliable CNOT gates that are capable of entangling two qubits. Single photon sources including spontaneous parametric down-conversion (SPDC) and semiconductor quantum dots have been demonstrated for CNOT gate operation. However, scaling up QIP systems towards practical applications requires millions of single-photon sources (SPSs), demanding precise positioning of a large number of SPSs for scalable manufacturing.

We present on realizing CNOT gate operation using a spatially regular and spectrally uniform epitaxial quantum dot, mesa top single quantum dots (MTSQDs). The MTSQDs show quantum optical properties meeting all the requirements for QIP [1], with single photon purity >99.5% and two-photon interference (TPI) visibility V=0.948±0.0015 at 4K without Purcell enhancement. In addition, such MTSQDs have large oscillator strength of ~27-29, which is ~3 times larger than typical SAQDs. Using linear optics and single photons emitted from the same MTSQD, we demonstrate a CNOT gate with a success probability of 1/9 and a gate fidelity of F=0.902±0.043 in the ZZ basis. Employing this CNOT gate, we generate a maximally entangled Bell state. The Bell state fidelity is measured to be 0.824±0.010 employing full quantum tomography and density matrix reconstruction. Our results establish that MTSQDs in arrays are highly promising single photon sources ready to next fabricate on-chip scalable photonic quantum information processing systems.