A quantum random number generator comprising: - an entropy source comprising a radiation source, such as a laser source, - a single photodiode configured for generating photo current based on received light from the radiation source, where the photodiode has a non-unity quantum efficiency for allowing interference of the radiation from the radiation source with a vacuum state to obtain entropy from the vacuum state, or - a single photodiode configured for generating photo current based on received light from the radiation source, and a beam splitter with a non-unity reflectivity or a non-unity transmittivity positioned between the radiation source and the single photodiode, wherein the quantum random number generator is configured such that a vacuum state interfere with the radiation from the radiation source at the beam splitter, - a transimpedance amplifier to convert the photo current into voltage, - an analog-to-digital converter for converting the analog voltage to a digital output, and - a processing unit, wherein the quantum random number generator is configured for establishing a lower bound on the entropy from the vacuum state by at least obtaining parameters from the signal that comes out of the analog-to-digital converter and determining the lower bound on the entropy from the vacuum state by applying a security proof to said parameters, and wherein the processing unit is configured for converting the digital output from the analog-to-digital converter to random numbers based on the established lower bound on the entropy from the vacuum state. - an entropy source comprising a radiation source, such as a laser source, - a single photodiode configured for generating photo current based on received light from the radiation source, where the photodiode has a non-unity quantum efficiency for allowing interference of the radiation from the radiation source with a vacuum state to obtain entropy from the vacuum state, or - a single photodiode configured for generating photo current based on received light from the radiation source, and a beam splitter with a non-unity reflectivity or a non-unity transmittivity positioned between the radiation source and the single photodiode, wherein the quantum random number generator is configured such that a vacuum state interfere with the radiation from the radiation source at the beam splitter, - a single photodiode configured for generating photo current based on received light from the radiation source, where the photodiode has a non-unity quantum efficiency for allowing interference of the radiation from the radiation source with a vacuum state to obtain entropy from the vacuum state, or - a single photodiode configured for generating photo current based on received light from the radiation source, and a beam splitter with a non-unity reflectivity or a non-unity transmittivity positioned between the radiation source and the single photodiode, wherein the quantum random number generator is configured such that a vacuum state interfere with the radiation from the radiation source at the beam splitter, - a transimpedance amplifier to convert the photo current into voltage, - an analog-to-digital converter for converting the analog voltage to a digital output, and - a processing unit,