Experimental demonstration of tripartite entanglement and controlled dense coding for continuous variables

A tripartite entangled state of bright optical field is experimentally produced using an Einstein-Podolsky-Rosen entangled state for continuous variables and linear optics. The controlled dense coding among a sender, a receiver and a controller is demonstrated by exploiting the tripartite entanglement. The obtained three-mode position correlation and relative momentum correlation between the sender and the receiver and thus the improvements of the measured signal to noise ratios of amplitude and phase signals with respect to the shot noise limit are 3.28dB and 3.18dB respectively. If the mean photon number $\bar{n}$ equals 11 the channel capacity can be controllably inverted between 2.91 and 3.14. When $\bar{n}$ is larger than 1.0 and 10.52 the channel capacities of the controlled dense coding exceed the ideal single channel capacities of coherent and squeezed state light communication.Comment: 8 pages, 4 figure

Dense-coding quantum key distribution based on continuous-variable entanglement

We proposed a scheme of continuous-variable quantum key distribution, in which the bright Einstein-Podolsky-Rosen entangled optical beams are utilized. The source of the entangled beams is placed inside the receiving station, where half of the entangled beams are transmitted with round trip and the other half are retained by the receiver. The amplitude and phase signals modulated on the signal beam by the sender are simultaneously extracted by the authorized receiver with the scheme of the dense-coding correlation measurement for continuous quantum variables, thus the channel capacity is significantly improved. Two kinds of possible eavesdropping are discussed. The mutual information and the secret key rates are calculated and compared with those of unidirectional transmission schemes

Entanglement of nanomechanical oscillators and two-mode fields induced by atomic coherence

We propose a scheme via three-level cascade atoms to entangle two optomechanical oscillators as well as two-mode fields. We show that two movable mirrors and two-mode fields can be entangled even for bad cavity limit. We also study entanglement of the output two-mode fields in frequency domain. The results show that the frequency of the mirror oscillation and the injected atomic coherence affect the output entanglement of the two-mode fields.Comment: 6 pages, 4 figure

Enhanced optical communication and broadband sub-shot-noise interferometry with a stable free-running periodically-poled-KTiOPO4 squeezer

An intrinsically stable type-I optical parametric oscillator was built with a periodically poled KTiOPO4 (PPKTP) crystal to generate a stable bright, continuous-wave, broadband phase-squeezed beam. A 3.2 dB sensitivity enhancement of optical interferometry was demonstrated on weak electrooptic modulation signals within a 20 MHz squeezing bandwidth. This also realized a channel capacity increase beyond that of coherent optical communication.Comment: 9 pages, 4 figs, submitted for publicatio

Detection of Linkage Between Solar and Lunar Cycles and Runoff of the World\u27s Large Rivers

It is an ongoing concern that global hydrological cycle can be likely intensified under context of climate change and anthropogenic actions. Here, our results show that the solar and lunar periodic motions (SLPMs) have substantial impact on the runoff of the world\u27s large rivers. We estimate that SLPMs can produce a change of the world\u27s large rivers runoff by as much as 6.7%. Although climate models suggest that the increased frequency of extreme events is attributed to anthropogenic activities, it is out of our expectation that as much as 73% and 85% of the extreme flood and drought events (based on runoff discharged to the ocean) appear in resonance with SLPMs, respectively. A reevaluation of impacts of SLPMs on changes in the world\u27s river runoff is urgently needed, especially when extreme drought and flood events are on the rise