Abstract
In practical quantum communication networks, the scheme of continuous-variable quantum key distribution (CVQKD) faces a challenge that the entangled source is controlled by a malicious eavesdropper, and although it still can generate a positive key rate and security, its performance needs to be improved, especially in secret key rate and maximum transmission distance. In this paper, we proposed a method based on the four-state discrete modulation and a heralded hybrid linear amplifier to enhance the performance of CVQKD where the entangled source originates from malicious eavesdropper. The four-state CVQKD encodes information by nonorthogonal coherent states in phase space. It has better transmission distance than Gaussian modulation counterpart, especially at low signal-to-noise ratio (SNR). Moreover, the hybrid linear amplifier concatenates a deterministic linear amplifier (DLA) and a noiseless linear amplifier (NLA), which can improve the probability of amplification success and reduce the noise penalty caused by the measurement. Furthermore, the hybrid linear amplifier can raise the SNR of CVQKD and tune between two types of performance for high-gain mode and high noise-reduction mode, therefore it can extend the maximal transmission distance while the entangled source is untrusted.
Highlights
Quantum key distribution (QKD) allows two legitimate parties to share the secure key string over an insure quantum channel [1,2,3,4,5]
Note that if there is a symmetric transmission (T1 = T2 ), it can be considered as entangled source in middle (ESIM) continuous-variable QKD (CVQKD) protocol, and if these two transmissions are asymmetric with T1 = 1 (T1 6= T2 ), it can be recovered to the traditional CVQKD protocol where entangled source is generated at Alice or Charlie
We proposed a scheme of four-state discrete modulation with hybrid amplifier to improve the performance of traditional Gaussian modulation CVQKD while the entangle source is untested
Summary
Quantum key distribution (QKD) allows two legitimate parties to share the secure key string over an insure quantum channel [1,2,3,4,5]. The penalty noise caused by detector in Bob side will directly affect the transmission distance performance of CVQKD protocol where the entanglement source is untrusted. The CVQKD scheme with non-traditional light source modulation and non-Gaussian operation, such as the discrete or unimensional modulation and photon subtraction operation, cannot directly implement via NLA. To overcome this problem, the measurement-based NLA (MB-NLA) has been proposed [22,23], which installs a dual homodyne detection ahead of NLA.
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