What are the issues making the experiment challenging?
In order to successfully perform these experiments, we have to control electrical signals corresponding to one single photon. In comparison, a cell phone emits about 10^23 (100,000,000,000,000,000,000,000) photons per second. Therefore, we need extremely good control over our device in order to isolate it from the environment. The experiments are performed at 10 milli Kelvin (10 milli degrees above absolute zero temperature, 273.13 degree celsius) such that the ambient thermal noise is small and cannot destroy the quantum information.
