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Random number generators (RNGs) have become a vital ingredient for various applications. Especially in the field of quantum cryptography random numbers are essential for an unconditional secure key distribution [1]. Recently generators based on the foundational unpredictability of quantum mechanics have become increasingly popular to produce truly random numbers [2]. Here, we present a generator producing...
We investigate the properties of an atmospheric channel for free space quantum communication with continuous polarization variables. In our prepare-and-measure setup, coherent polarization states are transmitted through an atmospheric quantum channel of 100 m length on the flat roof of our institute’s building. The signal states are measured by homodyne detection with the help of a local oscillator...
Free space QKD over an atmospheric channel was demonstrated in 1996 for the first time. Since then, several prepare-and-measure and entanglement-based schemes have been implemented (for a detailed overview, see). All of these systems use single-photon detectors, and therefore have to employ spatial, spectral and/or temporal filtering in order to reduce background light. In our system, we use an alternative...
In this paper we continue the idea of improving QKD by varying a quantum alphabet. We introduce a protocol for continuous variable QKD, where information is encoded in continuously modulated phase of coherent states of light (continuous phase-shift keying). The corresponding quantum alphabet is a circle in phase space, thus the proposed protocol is in a certain sense in between binary modulation and...
In this paper, we focus on the exchange of quantum states with a prototype setup and present estimated secret bit rates. The continuous-variable QKD protocol employs binary encoding in optical coherent states and postselection. In our experiment, the protocol is adapted to a long range fibre-based setup at the telecommunication wavelength (1550nm). The system employs heterodyne detection, using free-space...
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