48 research outputs found
Squeezed Light and Entangled Images from Four-Wave-Mixing in Hot Rubidium Vapor
Entangled multi-spatial-mode fields have interesting applications in quantum
information, such as parallel quantum information protocols, quantum computing,
and quantum imaging. We study the use of a nondegenerate four-wave mixing
process in rubidium vapor at 795 nm to demonstrate generation of
quantum-entangled images. Owing to the lack of an optical resonator cavity, the
four-wave mixing scheme generates inherently multi-spatial-mode output fields.
We have verified the presence of entanglement between the multi-mode beams by
analyzing the amplitude difference and the phase sum noise using a dual
homodyne detection scheme, measuring more than 4 dB of squeezing in both cases.
This paper will discuss the quantum properties of amplifiers based on
four-wave-mixing, along with the multi mode properties of such devices.Comment: 11 pages, 8 figures. SPIE Optics and Photonics 2008 proceeding (San
Diego, CA
Generating the local oscillator "locally" in continuous-variable quantum key distribution based on coherent detection
Continuous-variable quantum key distribution (CV-QKD) protocols based on
coherent detection have been studied extensively in both theory and experiment.
In all the existing implementations of CV-QKD, both the quantum signal and the
local oscillator (LO) are generated from the same laser and propagate through
the insecure quantum channel. This arrangement may open security loopholes and
also limit the potential applications of CV-QKD. In this paper, we propose and
demonstrate a pilot-aided feedforward data recovery scheme which enables
reliable coherent detection using a "locally" generated LO. Using two
independent commercial laser sources and a spool of 25 km optical fiber, we
construct a coherent communication system. The variance of the phase noise
introduced by the proposed scheme is measured to be 0.04 (rad^2), which is
small enough to enable secure key distribution. This technology also opens the
door for other quantum communication protocols, such as the recently proposed
measurement-device-independent (MDI) CV-QKD where independent light sources are
employed by different users.Comment: 11 pages, 10 figure