We obtain an explicit formula to calculate the entanglement entropy of bipartite entangled state of general two-mode boson exponential quadratic operator with continuous variables in Fock space. The simplicity and gen...We obtain an explicit formula to calculate the entanglement entropy of bipartite entangled state of general two-mode boson exponential quadratic operator with continuous variables in Fock space. The simplicity and generality of our formula are shown by some examples.展开更多
The developing tendency of continuous-variable （CV） measurement-device-independent （MDI） quantum cryptography is to cope with the practical issue of implementing sealable quantum networks. Up to now, most theoreti...The developing tendency of continuous-variable （CV） measurement-device-independent （MDI） quantum cryptography is to cope with the practical issue of implementing sealable quantum networks. Up to now, most theoretical and experimental researches on CV-MDI QKD are focused on two-party protocols. However, we suggest a CV-MDI multipartite quantum secret sharing （QSS） protocol use the EPR states coupled with optical amplifiers. More remarkable, QSS is the real application in multipartite CV-MDI QKD, in other words, is the concrete implementation method of multipartite CV-MDI QKD. It can implement a practical quantum network scheme, under which the legal participants create the secret correlations by using EPR states connecting to an untrusted relay via insecure links and applying the multi-entangled Greenberger-Horne-Zeilinger （GHZ） state analysis at relay station. Even if there is a possibility that the relay may be completely tampered, the legal participants are still able to extract a secret key from network communication. The numerical simulation indicates that the quantum network communication can be achieved in an asymmetric scenario, fulfilling the demands of a practical quantum network. Additionally, we illustrate that the use of optical amplifiers can compensate the partial inherent imperfections of detectors and increase the transmission distance of the CV-MDI quantum system.展开更多
Continuous-variable quantum key distribution(CVQKD)can be integrated with thermal states for short-distance wireless quantum communications.However,its performance is usually restricted with the practical thermal nois...Continuous-variable quantum key distribution(CVQKD)can be integrated with thermal states for short-distance wireless quantum communications.However,its performance is usually restricted with the practical thermal noise.We propose a method to improve the security threshold of thermal-state(TS)CVQKD by employing a heralded hybrid linear amplifier(HLA)at the receiver.We find the effect of thermal noise on the HLA-involved scheme in near-and-mid infrared band or terahertz band for direct and reverse reconciliation.Numerical simulations show that the HLA-involved scheme can compensate for the detriment of thermal noise and hence increase the security threshold of TS-CVQKD.In near-and-mid infrared band,security threshold can be extended by 2.1 dB in channel loss for direct reconciliation and 1.6 dB for reverse reconciliation,whereas in terahertz band,security threshold can be slightly enhanced for the gain parameter less than 1 due to the rise in thermal noise.展开更多
The fidelity of quantum teleportation of a single-mode squeezed state of light is calculated based on the general theory of quantum-mechanical measurement in the Schrodinger picture. It is shown that the criterion for...The fidelity of quantum teleportation of a single-mode squeezed state of light is calculated based on the general theory of quantum-mechanical measurement in the Schrodinger picture. It is shown that the criterion for the nonclassical state teleportation is different from that for coherent state. F = 1/2 is no longer the rigorous boundary between classical and quantum teleportation for a squeezed state of light. When the quantum entanglement of an Einstein-Podolsky-Rosen （EPR） beam used for teleportation and the parameters of the system are given, the fidelity depends on the squeezing of the input squeezed state. The higher the squeezing is, the smaller the fidelity is, and the lower the classical limitation of fidelity is. The dependence of the optimum gain for teleporting a squeezed vacuum state upon the EPR entanglement is also calculated. The results obtained provide important references for designing experimental systems of teleporting a non-classical state and judging the quality of the teleported quantum state.展开更多
As a highly entangled quantum network, the duster state has the potential for greater information capacity and use in measurement-based quantum computation. Here, we report generating a continuous-variable quadriparti...As a highly entangled quantum network, the duster state has the potential for greater information capacity and use in measurement-based quantum computation. Here, we report generating a continuous-variable quadripartite ＂square＂ cluster state of multiplexing orthogonal spatial modes in a single optical parametric amplifier （OPA）, and further improve the quality of entanglement by optimizing the pump profile. We produce multimode en- tanglement of two first-order Hermite-Gauss modes within one beam in a single multimode OPA and transform it into a duster state by phase correction. Furthermore, the pump-profile dependence of the entanglement of this state is explored. Compared with fundamental mode pumping, an enhancement of approximately 33% is achieved using the suitable pump-profile mode. Our approach is potentially scalable to multimode entanglement in the spatial domain. Such spatial duster states may contribute to future schemes in spatial quantum information processing.展开更多
基金supported by the National Fundamental Research Program under Grant No.2006CB921104National Natural Science Foundation of China under Grant No.60708003
文摘We obtain an explicit formula to calculate the entanglement entropy of bipartite entangled state of general two-mode boson exponential quadratic operator with continuous variables in Fock space. The simplicity and generality of our formula are shown by some examples.
基金Supported by National Natural Science Foundation of China under Grant Nos.61379153,61579725
文摘The developing tendency of continuous-variable （CV） measurement-device-independent （MDI） quantum cryptography is to cope with the practical issue of implementing sealable quantum networks. Up to now, most theoretical and experimental researches on CV-MDI QKD are focused on two-party protocols. However, we suggest a CV-MDI multipartite quantum secret sharing （QSS） protocol use the EPR states coupled with optical amplifiers. More remarkable, QSS is the real application in multipartite CV-MDI QKD, in other words, is the concrete implementation method of multipartite CV-MDI QKD. It can implement a practical quantum network scheme, under which the legal participants create the secret correlations by using EPR states connecting to an untrusted relay via insecure links and applying the multi-entangled Greenberger-Horne-Zeilinger （GHZ） state analysis at relay station. Even if there is a possibility that the relay may be completely tampered, the legal participants are still able to extract a secret key from network communication. The numerical simulation indicates that the quantum network communication can be achieved in an asymmetric scenario, fulfilling the demands of a practical quantum network. Additionally, we illustrate that the use of optical amplifiers can compensate the partial inherent imperfections of detectors and increase the transmission distance of the CV-MDI quantum system.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61572529 and 61871407).
文摘Continuous-variable quantum key distribution(CVQKD)can be integrated with thermal states for short-distance wireless quantum communications.However,its performance is usually restricted with the practical thermal noise.We propose a method to improve the security threshold of thermal-state(TS)CVQKD by employing a heralded hybrid linear amplifier(HLA)at the receiver.We find the effect of thermal noise on the HLA-involved scheme in near-and-mid infrared band or terahertz band for direct and reverse reconciliation.Numerical simulations show that the HLA-involved scheme can compensate for the detriment of thermal noise and hence increase the security threshold of TS-CVQKD.In near-and-mid infrared band,security threshold can be extended by 2.1 dB in channel loss for direct reconciliation and 1.6 dB for reverse reconciliation,whereas in terahertz band,security threshold can be slightly enhanced for the gain parameter less than 1 due to the rise in thermal noise.
基金Supported by the National Natural Science Foundation of China under Grant Nos 60278010, 60238010, and 60478808, the Shanxi Natural Science Foundation under Grant No 20041039, and the Returned Scholar Foundation.
文摘The fidelity of quantum teleportation of a single-mode squeezed state of light is calculated based on the general theory of quantum-mechanical measurement in the Schrodinger picture. It is shown that the criterion for the nonclassical state teleportation is different from that for coherent state. F = 1/2 is no longer the rigorous boundary between classical and quantum teleportation for a squeezed state of light. When the quantum entanglement of an Einstein-Podolsky-Rosen （EPR） beam used for teleportation and the parameters of the system are given, the fidelity depends on the squeezing of the input squeezed state. The higher the squeezing is, the smaller the fidelity is, and the lower the classical limitation of fidelity is. The dependence of the optimum gain for teleporting a squeezed vacuum state upon the EPR entanglement is also calculated. The results obtained provide important references for designing experimental systems of teleporting a non-classical state and judging the quality of the teleported quantum state.
基金National Natural Science Foundation of China(NSFC)(91536222,11674205)Ministry of Science and Technology of the People’s Republic of China(MOST)(2016YFA0301404)+1 种基金Program for the Outstanding Innovative Team of Higher Learning Institution of ShanxiShanxi "1331 Project"
文摘As a highly entangled quantum network, the duster state has the potential for greater information capacity and use in measurement-based quantum computation. Here, we report generating a continuous-variable quadripartite ＂square＂ cluster state of multiplexing orthogonal spatial modes in a single optical parametric amplifier （OPA）, and further improve the quality of entanglement by optimizing the pump profile. We produce multimode en- tanglement of two first-order Hermite-Gauss modes within one beam in a single multimode OPA and transform it into a duster state by phase correction. Furthermore, the pump-profile dependence of the entanglement of this state is explored. Compared with fundamental mode pumping, an enhancement of approximately 33% is achieved using the suitable pump-profile mode. Our approach is potentially scalable to multimode entanglement in the spatial domain. Such spatial duster states may contribute to future schemes in spatial quantum information processing.
