Georg Harder, Timothy J. Bartley, Adriana E. Lita, Sae Woo Nam, Thomas Gerrits, Christine Silberhorn
The nature of quantum decoherence renders the observation of nonclassical features/properties in large systems increasingly difficult. Optical states are a good candidate to observe nonclassical features since 5 they are less susceptible to environmental effects. Starting with the landmark experiment by Hanbury-Brown and Twiss, the statistical properties of photons have been used in a broad range of contexts, from quantum enhanced metrology, fundamental tests of local realism to quantum information tasks such as Boson sampling and quantum key distribution. However, generating and directly measuring large numbers of photons in well defined optical modes has proven highly challenging. To date, the largest states demonstrating nonclassical distributions with direct photon number measurements consisted of singlephoton modes spanning a Hilbert space of dimension 28 = 256. Here, we show that a nonclassical state in two well defined modes of dimension 20 80 × 80 = 6400 can be efficiently generated and measured. It can further be used to herald nonclassical distributions of up to 50 photons in a single mode. This significantly increases the scale at which quantum optical phenomena can be probed. Moreover, the states we generate are measured with > 65% efficiency in the telecom wavelength band of 1535nm, making them ideal for use in existing telecommunication infrastructure, enabling the next generation of quantum-enhanced technology with large quantum optical states.