Transferring of Continuous Variable Squeezed States in 20 km Fiber

Abstract

Transferring of a real quantum state in a long-distance channel is an important task in the development of quantum information networks. For greatly suppressing the relative phase fluctuations between the signal beam and the corresponding local oscillator beam, the usual method is to transfer them with time-division and polarization-division multiplexing through the same fiber. But the nonclassical states of light are very sensitive to the channel loss and extra noise, this multiplexing method must bring the extra loss to the quantum state, which may result in the vanishing of its quantum property. Here, we propose and realize a suitable time multiplexing method for the transferring and measurement of nonclassical states. Only the local oscillator beam is chopped into a sequence of light pulses and transmitted through fiber with continuous orthogonal-polarized signal beam. Finally, when the local oscillator pulses are properly time delayed compared to the signal beam, the quantum state can be measured in the time sequences without the influence of extra noise in the fiber. Our work provides a feasible scheme to transfer a quantum state in relative long distance and construct a practical quantum information network in metropolitan region.

40 km fiber transmission of squeezed light measured with a real local oscillator

“…Firstly, the optical power of the LO decreases exponentially with propagation distance, and therefore, to provide sufficient optical power at the various nodes in the network for enabling low-noise homodyne detection, a significant amount of power must be distributed through the fiber network. In addition to this direct power wastage, the massive power distribution might also lead to deteriorating non-linear optical effects (such as Brillouin scattering) and to distortion of the quantum state of the signal [19,20]. Secondly, transmitting the LO along with the signal is also fundamentally problematic for continuous-variable quantum key distribution (CVQKD), as there are several eavesdropping strategies that explicitly make use of the transmitted LO to corrupt the coherent detection at the trusted receiver, therefore breaching the security of the QKD protocol [21][22][23][24].…”

“…Squeezed states of light have by now been generated for more than three decades [1] and have 17 become a ubiquitous resource in optical quantum information science. Unlike coherent states 18 of light, squeezed light has the outstanding property of exhibiting lower noise uncertainty than 19 the fundamental shot noise in some of its quadratures -known as squeezing -while conjugated 20 quadratures exhibit uncertainties above the shot noise limit -known as anti-squeezing [2,3]. This 21 fundamental quantum property of squeezed states has been the engine of numerous quantum 22 sensing experiments, such as the quantum-enhanced measurements of gravitational waves [4] 23 and vibrational modes of molecules [5,6], and recent quantum computing models including Conceptual schematic of a typical homodyne detection system.…”

40 km Fiber Transmission of Squeezed Light Measured with a Real Local Oscillator

“…Firstly, the optical power of the local oscillator decreases exponentially with propagation distance, and therefore, to provide sufficient optical power at the various nodes in the network for enabling low-noise homodyne detection, a significant amount of power must be distributed through the fiber network. In addition to this direct power wastage, the massive power distribution might also lead to deteriorating non-linear optical effects (such as Brillouin scattering) and to distortion of the quantum state of the signal [19,20]. Secondly, transmitting the local oscillator along with the signal is also fundamentally problematic for continuous-variable quantum key distribution (CVQKD), as there are several eavesdropping strategies that explicitly make use of the transmitted local oscillator to corrupt the coherent detection at the trusted receiver, therefore breaching the security of the QKD protocol [21][22][23][24].…”