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Experimental investigation of transmission characteristics of continuous variable entangled state over optical fibers

## Experimental investigation of transmission characteristics of continuous variable entangled state over optical fibers

Wan Zhen-Ju, Feng Jin-Xia, Cheng Jian, Zhang Kuan-Shou
• #### Abstract

Continuous variable (CV) quantum entanglement is an essential resource for quantum computation and communication protocols. The use of CV quantum entanglement at a telecommunication wavelength of 1.5m in combination with existing fiber telecommunication networks offers the possibility to implement long-distance quantum communication protocols like quantum key distribution (QKD) and applications such as quantum repeaters, quantum teleportation in the future. In spite of the fact that the optical power attenuation of light in a standard telecommunication fiber is lowest at a wavelength of 1.5m, the entangled states will interact with fiber channels and the disentanglement will occur. It is one of the important factors restricting the development of long distance quantum information. In this paper, CV entangled state at 1.5m telecommunication band is obtained by using a type-II periodically poled KTP (PPKTP) crystal inside a nondegenerate optical parametric amplifier (NOPA). A wedged PPKTP is used for implementing frequency-down-conversion of the pump field to generate the optically entangled state and achieving the dispersion compensation between the pump and the subharmonic waves. By controlling the temperature and the length of the PPKTP crystal, a triply resonant optical parametric oscillator with a threshold of 80 mW is realized. Einstein-PodolskyRosen (EPR)-entangled beams with quantum correlation of 8.3 dB for both the amplitude and phase quadratures are experimentally generated by using a single NOPA at a pump power of 40 mW and an injected signal power of 10 mW when the relative phase between the pump and injected signal is locked to . The generated entangled state is coupled into a single-mode optical fiber, and the transmission characteristics of the generated EPR entangled beams through standard single-mode fibers are investigated experimentally and theoretically. A fiber polarization controller is used to compensate for the polarization state variation induced by random fluctuations of birefringence of the single mode fiber when the light propagates along the fiber, and to keep the polarization of light linear at the fiber output. A 0.21 dB quantum entanglement could still be observed for the EPR-entangled beams transmitted through a 50-km-long single-mode fiber. The theoretical prediction considering the excess noise in fiber channel is in good agreement with the experimental result. The generated CV quantum entanglement is highly suitable for the required experiments, such as CV measurement-device-independence QKD based on standard fibers, owing to the fact that the tolerance of the excess noise in the quantum channel can be enhanced significantly with respect to a coherent state if EPR-entangled beams are used.

#### Authors and contacts

###### Corresponding author: Feng Jin-Xia, fengjx@sxu.edu.cn
• Funds: Project supported by the National Key Research and Develop Program of China (Grant No. 2016YFA0301401) and the Fund for Shanxi 1331 Project Key Subjects Construction, China (Grant No. 1331KS).

#### References

 [1] Briegel H J, Dur W, Cirac J I, Zoller P 1998 Phys. Rev. Lett. 81 5932 [2] Braunstein S L, Kimble H J 1998 Phys. Rev. Lett. 80 869 [3] Li X Y, Pan Q, Jing J T, Zhang J, Xie C D, Peng K C 2002 Phys. Rev. Lett. 88 047904 [4] Su X L, Wang W Z, Wang Y, Jia X J, Xie C D, Peng K C 2009 Europhys. Lett. 87 20005 [5] Lee N, Benichi H, Takeno Y, Takeda S, Webb J, Huntington E, Furusawa A 2011 Science 332 330 [6] Madsen L S, Usenko V C, Lassen M, Filip R 2012 Nat. Commun. 3 1083 [7] Duan L M, Guo G C 1997 Quantum Semiclassic. Opt. 9 953 [8] Shelby R M, Levenson M D, Bayer P W 1985 Phys. Rev. Lett. 54 939 [9] Corney J F, Drummond P D, Heersink J, Josse V, Leuchs G, Andersen U L 2006 Phys. Rev. Lett. 97 023606 [10] Deng C Y, Hou S L, Lei J L, Wang D B, Li X X 2016 Acta Phys. Sin. 65 240702 (in Chinese)[邓春雨, 侯尚林, 雷景丽, 王道斌, 李晓晓 2016 物理学报 65 240702] [11] Marcikic I, Riedmatten H, Tittel W, Zbinden H, Legr M, Gisin N 2004 Phys. Rev. Lett. 93 180502 [12] Rosenberg D, Harrington J W, Rice P R, Hiskett P A, Peterson C G, Hughes R J, Lita A E, Nam S W, Nordholt J E 2007 Phys. Rev. Lett. 98 010503 [13] Schmitt-Manderbach T, Weier H, Furst M, Ursin R, Tiefenbacher F, Scheidl T, Perdigues J, Sodnik Z, Kursiefer C, Rarity J G, Zeilinger A, Weinfurter H 2007 Phys. Rev. Lett. 98 010504 [14] Valivarthi R, Puigibert M I G, Zhou Q, Aguilar G H, Verma V B, Marsili F, Shaw M D, Nam S W, Oblak D, Tittel W 2016 Nat. Photon. 10 676 [15] Sun Q C, Mao Y L, Jiang Y F, Zhao Q, Chen S J, Zhang W, Zhang W J, Jiang X, Chen T Y, You L X, Li L, Huang Y D, Chen X F, Wang Z, Ma X, Zhang Q, Pan J W 2017 Phys. Rev. A 95 032306 [16] Biswas A, Lidar D A 2006 Phys. Rev. A 74 062303 [17] Maniscalco S, Olivares S, Paris M G A 2007 Phys. Rev. A 75 062119 [18] Barbosa F A S, Faria A J, Coelho A S, Cassemiro K N, Villar A S, Nussenzveig P, Martinelli M 2011 Phys. Rev. A 84 052330 [19] Coelho A S, Barbosa F A S, Cassemiro K N, Villar A S, Martinelli M, Nussenzveig P 2009 Science 326 823 [20] Barbosa F A S, Coelho A S, Faria A J, Cassemiro K N, Villar A S, Nussenzveig P, Martinelli M 2010 Nature Photon. 4 858 [21] Deng X W, Tian C X, Su X L, Xie C D 2017 Sci. Rep. 7 44475 [22] Jouguet P, Kunz-Jacques S, Leverrier A, Grangier P, Diamanti E 2013 Nature Photon. 7 378 [23] Black E D 2001 Am. J. Phys. 69 79 [24] Sun Z N, Feng J X, Wan Z J, Zhang K S 2016 Acta Phys. Sin. 65 044203 (in Chinese)[孙志妮, 冯晋霞, 万振菊, 张宽收 2016 物理学报 65 044203] [25] Zhang J, Peng K C 2000 Phys. Rev. A 62 064302 [26] Duan L M, Giedke G, Cirac J I, Zoller P 2000 Phys. Rev. Lett. 84 2722 [27] Deng X W, Hao S H, Tian C X, Su X L, Xie C D, Peng K C 2016 Appl. Phys. Lett. 108 081105

#### Cited By

•  [1] Briegel H J, Dur W, Cirac J I, Zoller P 1998 Phys. Rev. Lett. 81 5932 [2] Braunstein S L, Kimble H J 1998 Phys. Rev. Lett. 80 869 [3] Li X Y, Pan Q, Jing J T, Zhang J, Xie C D, Peng K C 2002 Phys. Rev. Lett. 88 047904 [4] Su X L, Wang W Z, Wang Y, Jia X J, Xie C D, Peng K C 2009 Europhys. Lett. 87 20005 [5] Lee N, Benichi H, Takeno Y, Takeda S, Webb J, Huntington E, Furusawa A 2011 Science 332 330 [6] Madsen L S, Usenko V C, Lassen M, Filip R 2012 Nat. Commun. 3 1083 [7] Duan L M, Guo G C 1997 Quantum Semiclassic. Opt. 9 953 [8] Shelby R M, Levenson M D, Bayer P W 1985 Phys. Rev. Lett. 54 939 [9] Corney J F, Drummond P D, Heersink J, Josse V, Leuchs G, Andersen U L 2006 Phys. Rev. Lett. 97 023606 [10] Deng C Y, Hou S L, Lei J L, Wang D B, Li X X 2016 Acta Phys. Sin. 65 240702 (in Chinese)[邓春雨, 侯尚林, 雷景丽, 王道斌, 李晓晓 2016 物理学报 65 240702] [11] Marcikic I, Riedmatten H, Tittel W, Zbinden H, Legr M, Gisin N 2004 Phys. Rev. Lett. 93 180502 [12] Rosenberg D, Harrington J W, Rice P R, Hiskett P A, Peterson C G, Hughes R J, Lita A E, Nam S W, Nordholt J E 2007 Phys. Rev. Lett. 98 010503 [13] Schmitt-Manderbach T, Weier H, Furst M, Ursin R, Tiefenbacher F, Scheidl T, Perdigues J, Sodnik Z, Kursiefer C, Rarity J G, Zeilinger A, Weinfurter H 2007 Phys. Rev. Lett. 98 010504 [14] Valivarthi R, Puigibert M I G, Zhou Q, Aguilar G H, Verma V B, Marsili F, Shaw M D, Nam S W, Oblak D, Tittel W 2016 Nat. Photon. 10 676 [15] Sun Q C, Mao Y L, Jiang Y F, Zhao Q, Chen S J, Zhang W, Zhang W J, Jiang X, Chen T Y, You L X, Li L, Huang Y D, Chen X F, Wang Z, Ma X, Zhang Q, Pan J W 2017 Phys. Rev. A 95 032306 [16] Biswas A, Lidar D A 2006 Phys. Rev. A 74 062303 [17] Maniscalco S, Olivares S, Paris M G A 2007 Phys. Rev. A 75 062119 [18] Barbosa F A S, Faria A J, Coelho A S, Cassemiro K N, Villar A S, Nussenzveig P, Martinelli M 2011 Phys. Rev. A 84 052330 [19] Coelho A S, Barbosa F A S, Cassemiro K N, Villar A S, Martinelli M, Nussenzveig P 2009 Science 326 823 [20] Barbosa F A S, Coelho A S, Faria A J, Cassemiro K N, Villar A S, Nussenzveig P, Martinelli M 2010 Nature Photon. 4 858 [21] Deng X W, Tian C X, Su X L, Xie C D 2017 Sci. Rep. 7 44475 [22] Jouguet P, Kunz-Jacques S, Leverrier A, Grangier P, Diamanti E 2013 Nature Photon. 7 378 [23] Black E D 2001 Am. J. Phys. 69 79 [24] Sun Z N, Feng J X, Wan Z J, Zhang K S 2016 Acta Phys. Sin. 65 044203 (in Chinese)[孙志妮, 冯晋霞, 万振菊, 张宽收 2016 物理学报 65 044203] [25] Zhang J, Peng K C 2000 Phys. Rev. A 62 064302 [26] Duan L M, Giedke G, Cirac J I, Zoller P 2000 Phys. Rev. Lett. 84 2722 [27] Deng X W, Hao S H, Tian C X, Su X L, Xie C D, Peng K C 2016 Appl. Phys. Lett. 108 081105
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•  Citation:
##### Metrics
• Abstract views:  197
• Cited By: 0
##### Publishing process
• Received Date:  04 July 2017
• Accepted Date:  21 September 2017
• Published Online:  20 January 2018

## Experimental investigation of transmission characteristics of continuous variable entangled state over optical fibers

###### Corresponding author: Feng Jin-Xia, fengjx@sxu.edu.cn;
• 1. State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Taiyuan 030006, China;
• 2. Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
Fund Project:  Project supported by the National Key Research and Develop Program of China (Grant No. 2016YFA0301401) and the Fund for Shanxi 1331 Project Key Subjects Construction, China (Grant No. 1331KS).

Abstract: Continuous variable (CV) quantum entanglement is an essential resource for quantum computation and communication protocols. The use of CV quantum entanglement at a telecommunication wavelength of 1.5m in combination with existing fiber telecommunication networks offers the possibility to implement long-distance quantum communication protocols like quantum key distribution (QKD) and applications such as quantum repeaters, quantum teleportation in the future. In spite of the fact that the optical power attenuation of light in a standard telecommunication fiber is lowest at a wavelength of 1.5m, the entangled states will interact with fiber channels and the disentanglement will occur. It is one of the important factors restricting the development of long distance quantum information. In this paper, CV entangled state at 1.5m telecommunication band is obtained by using a type-II periodically poled KTP (PPKTP) crystal inside a nondegenerate optical parametric amplifier (NOPA). A wedged PPKTP is used for implementing frequency-down-conversion of the pump field to generate the optically entangled state and achieving the dispersion compensation between the pump and the subharmonic waves. By controlling the temperature and the length of the PPKTP crystal, a triply resonant optical parametric oscillator with a threshold of 80 mW is realized. Einstein-PodolskyRosen (EPR)-entangled beams with quantum correlation of 8.3 dB for both the amplitude and phase quadratures are experimentally generated by using a single NOPA at a pump power of 40 mW and an injected signal power of 10 mW when the relative phase between the pump and injected signal is locked to . The generated entangled state is coupled into a single-mode optical fiber, and the transmission characteristics of the generated EPR entangled beams through standard single-mode fibers are investigated experimentally and theoretically. A fiber polarization controller is used to compensate for the polarization state variation induced by random fluctuations of birefringence of the single mode fiber when the light propagates along the fiber, and to keep the polarization of light linear at the fiber output. A 0.21 dB quantum entanglement could still be observed for the EPR-entangled beams transmitted through a 50-km-long single-mode fiber. The theoretical prediction considering the excess noise in fiber channel is in good agreement with the experimental result. The generated CV quantum entanglement is highly suitable for the required experiments, such as CV measurement-device-independence QKD based on standard fibers, owing to the fact that the tolerance of the excess noise in the quantum channel can be enhanced significantly with respect to a coherent state if EPR-entangled beams are used.

Reference (27)

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