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Tripartite Entanglement Swapping of Bright Light Beams

Jietai Jing, Changde Xie, Kunchi Peng

Published Jan 1, 2003• 1 citation
OpenAlex

Abstract

We propose a new and experimentally realizable continuous variable quantum communication protocol named tripartite entanglement swap-ping. Three optical modes, which are not in a tripartite entangled state initially, can be entangled by means of the direct detections of Bell-states, the amplitude and phase modulators, and the beamsplitters. The initial bipartite and tripartite entangled states are produced with the bright single mode quadrature squeezed state of light and linear optics. We analystically proved that tripartite entanglement swapping can be accomplished with two schemes in which a tripartite entangled state or two bipartite entangled states serve as quantum channel respectively. The direct detection of Bell-state is applied in the proposed schemes, thus the needs for local beams used in homodyne detectors and the trouble for mode matching are significantly avoided.

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We propose a new and experimentally realizable continuous variable quantum communication protocol named tripartite entanglement swap-ping. Three optical modes, which are not in a tripartite entangled state initially, can be entangled by means of the direct detections of Bell-states, the amplitude and phase modulators, and the beamsplitters. The initial bipartite and tripartite entangled states are produced with the bright single mode quadrature squeezed state of light and linear optics. We analystically proved that tripartite entanglement swapping can be accomplished with two schemes in which a tripartite entangled state or two bipartite entangled states serve as quantum channel respectively. The direct detection of Bell-state is applied in the proposed schemes, thus the needs for local beams used in homodyne detectors and the trouble for mode matching are significantly avoided.
A scheme achieving quantum entanglement swapping between two pairs of bright EPR optical beams is theoretically proposed. Two pairs of coherent EPR beams are produced from two independent nondegenerate optical parametric amplifiers. The entanglement swapping is demonstrated by means of a half of each EPR beam. The measuring process entangles other two halves of EPR beams that have never directly interacted with each other. In the proposed system, the direct detection of Bell-states is applied instead of usual homodyne detetion. Due to that the local oscillator is not needed, the technic trouble for mode-matching is overcome and the efficiency of the detection can be increased in experiments.
A scheme for the entanglement swapping of entangled states with continuous variable is presented, in which the bipartite maximally entangled coherent state serves as the quantum channel.With the help of the idea of teleportation,using beam splitter and phase-shifter,entanglement swapping of tripartite entangled coherent state can be realized.In this scheme,the entanglement swapping is failure only for one measurement process.The failure probability is very small.The detail results show that the probability and the minimum of total average fidelity for successful swapping an arbitrary tripartite entangled coherent state is nearly 1 when the mean number of photons is larger than 2.
Quantum entanglement shared by more than two partites is the essential bases for developing quantum communication networks and quantum computation. The multipartite entanglement of continuous variables can be generated by distributing or combining squeezed states of light using linear optics. We experimentally obtained a tripartite entangled state of bright optical field by means of a nondegenerate optical parametric amplifier (NOPA) and optical beam-splitters. The NOPA is operated in the state of parametric deamplification by locking the relative phase between the pump laser and the injected seed wave to (2n+1)π, so the generated Einstein-Podolsky-Rosen (EPR) beam for continuous variables is an entangled state of light with the quantum correlation of phase quadratures and the quantum anticorrelation of amplitude quadratures [1]. The output EPR beam consists of two frequency-degenerate optical modes with horizontal and vertical polarizations which are distributed to three parties with two linear beam-splitters. We have theoretically and experimentally demonstrated the three parties are in a tripartite entangled state with three-mode “position” (amplitude quadrature) correlation and relative “momentum” (phase quadrature) correlation [2]-[4]. The obtained GHZ-like state is a fully inseparable tripartite continuous-variables state violating the three inequalities used for the criterion of the inseparability [5][6]. The controlled dense coding quantum communication is experimentally accomplished by exploiting the tripartite entanglement. The three entangled modes are sent to a sender (Alice), a receiver (Bob) and a controller (Claire), respectively. The information transmission capacity of the quantum channel between Alice and Bob is controlled by Claire. The channel capacity completed under Claire’s help is always larger than that without her help.
A pair of entangled states of light with classical coherence and independent quantum fluctuations has been produced from two home-designed and home-made non-degenerate optical parametric amplifiers. Utilizing these entangled states we have experimentally demonstrated unconditional entanglement swapping for continuous variables, i.e. quantum teleportation of an entangled state. Based on the direct detection of Bell states and entanglement collapse, two optical beams which have never directly interacted with each other are entangled together. The degrees of quantum correlation resulting from the entanglement swapping have been determined by direct measurement to be 1.23dB and 1.12dB below the shot noise limit for the amplitude and phase quadratures, respectively. The theoretical calculation and experimental measurements are in reasonable agreement.
We present a protocol for performing entanglement swapping with intense pulsed beams. In a first step, the generation of amplitude correlations between two systems that have never interacted directly is demonstrated. This is verified in direct detection with electronic modulation of the detected photocurrents. The measured correlations are better than expected from a classical reconstruction scheme. In an entanglement swapping process, a four-partite entangled state is generated. We prove experimentally that the amplitudes of the four optical modes are quantum correlated 3 dB below shot noise, which is consistent with the presence of genuine four-party entanglement.