At scale, fault tolerant on-chip photonic quantum information processing (P-QIP) has been hindered by the lack of (1) on-demand generation of millions of indistinguishable single photons as qubits from (2) quantum emitters in designed spatially ordered arrays. The demonstrated unique shape- and size-controlled mesa-top single quantum dots (MTSQDs) positioned with nm accuracy in designed arrays and exhibiting <2 nanometer spectral nonuniformity offer a promising solution. Here we report CNOT gates with ~90% fidelity using photons from individual MTSQDs at 4 K without Purcell enhancement that enable generating Bell states with fidelity of 0.825 ± 0.010, both underpinned by a two-photon interference (TPI) visibility 0.945 ± 0.005 and single photon purity > 99.5%. Temperature and power dependent studies reveal these remarkable figures-of-merit to originate in single photon superradiance and weak electron-phonon coupling unique to large volume MTSQDs giving large oscillator strength ( ~ 30) thus robustness against temperature. These results show a path to utility scale P-QIP platforms utilizing MTSQD arrays.

Nature is a scientific journal publishing research articles, reviews, and commentary across a wide range of scientific disciplines. Readers can find articles on topics such as biology, chemistry, physics, and environmental science. Additionally, they can learn about  research, scientific discoveries, and advances in understanding the natural world.

Nature

Researchers demonstrate CNOT two-qubit gates with ~90% fidelity using on-demand single photons from mesa-top single quantum dots (MTSQDs) at 4 K without Purcell enhancement. The MTSQDs are shape- and size-controlled, positioned with nanometer accuracy in ordered arrays, and exhibit less than 2 nm spectral nonuniformity. Bell states are generated with fidelity of 0.825 ± 0.010, supported by two-photon interference visibility of 0.945 ± 0.005 and single photon purity above 99.5%. The high performance originates from single-photon superradiance and weak electron-phonon coupling unique to large-volume MTSQDs, yielding large oscillator strength (~30) and temperature robustness. These results outline a path toward utility-scale photonic quantum information processing platforms.

Two-qubit gates using on-demand single-photons from ordered shape and size controlled large-volume superradiant quantum dots