Stimulated emission tomography for frequency-degenerate orbital angular momentum qubits

Abstract

Stimulated parametric down-conversion(StimPDC) can not only effectively mimic quantum correlations of spontaneous parametric down-conversion(SPDC) but also offers amplification of photons in several orders. With this advantage, StimPDC has been exploited in tasks that require higher brightness, such as quantum sensing and quantum state tomography. However, most of the StimPDC research only considers frequency non-degenerate processes. Since many photonic quantum protocols, such as measurement device-independent quantum key distribution(MDI QKD), and entanglement distillation utilizes Hong-Ou-Mandel(HOM) interference, frequency-degenerate photons are preferred. To adress this, we study frequency-degenerate StimPDC and demonstrate stimulated emission tomography(SET) for frequency-degenerate orbital angular momentum qubits. The biggest obstacle in the frequency-degenerate process was noise photons emitted from the seed laser, however, with TCSPC we could separate StimPDC photons and background noise photons. Our results agree with the theoretical prediction of the spiral bandwidth of entangled biphotons.