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arXiv:2603.12777 · IEEE Transactions on Communications

Quantum CDMA-based Continuous Variable Quantum Key Distribution using Chaotic Phase Shifters

Shahnoor Ali, Neel Kanth Kundu, Sourav Chatterjee

quant-phSubmitted Mar 13, 2026• Announced Mar 16, 2026• 0 citations
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Abstract

We present a quantum code-division multiple-access (q-CDMA) framework for multiuser continuous-variable quantum key distribution (CV-QKD) over a shared quantum channel. The proposed architecture employs chaotic phase shifters to encode and decode quantum states, enabling efficient multiplexing and demultiplexing of signals generated by multiple transmitters. In this scheme, quantum states from different users are chaotically phase-encoded and combined through a beam splitter network before transmission. At the receiver, synchronized chaotic phase shifters are used for decoding, followed by an inverse beam splitter structure to recover the individual user signals. This chaotic synchronization allows reliable state recovery and secure key establishment between each sender-receiver pair. For an arbitrary number of users, we derive the input-output quadrature relations describing the multiuser q-CDMA CV-QKD system. Using this model, we evaluate the achievable secret key rate under collective attacks with reverse reconciliation. We further investigate the impact of key system parameters including the correction factor, multiuser interference noise, environmental noise, and channel transmittance. A comparison between the asymptotic and finite-size regimes is also presented to highlight the associated performance trade-offs. These results provide a theoretical framework for assessing the performance of q-CDMA-based CV-QKD and support the development of scalable and secure multiuser quantum communication networks.

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We present a quantum code-division multiple-access (q-CDMA) framework for multiuser continuous-variable quantum key distribution (CV-QKD) over a shared quantum channel. The proposed architecture employs chaotic phase shifters to encode and decode quantum states, enabling efficient multiplexing and demultiplexing of signals generated by multiple transmitters. In this scheme, quantum states from different users are chaotically phase-encoded and combined through a beam splitter network before transmission. At the receiver, synchronized chaotic phase shifters are used for decoding, followed by an inverse beam splitter structure to recover the individual user signals. This chaotic synchronization allows reliable state recovery and secure key establishment between each sender-receiver pair. For an arbitrary number of users, we derive the input-output quadrature relations describing the multiuser q-CDMA CV-QKD system. Using this model, we evaluate the achievable secret key rate under collective attacks with reverse reconciliation. We further investigate the impact of key system parameters including the correction factor, multiuser interference noise, environmental noise, and channel transmittance. A comparison between the asymptotic and finite-size regimes is also presented to highlight the associated performance trade-offs. These results provide a theoretical framework for assessing the performance of q-CDMA-based CV-QKD and support the development of scalable and secure multiuser quantum communication networks.
In this paper, we propose a quantum code division multiple access (q-CDMA) based continuous-variable quantum key distribution (CV-QKD) system. In the proposed system, the quantum states of two senders (Alice1,2) are chaotically encoded through chaotic phase shifters and then transmitted over a quantum channel. At the receiver, the quantum states are decoded via chaos synchronization to separate the quantum states sent by the different senders and received by the two receivers (Bob1,2) separately. We characterize the input-output relation of the quadrature between the two senders and receivers and then analyze the secret key rate (SKR) of the q-CDMA-based CV-QKD system. Our numerical results reveal that the q-CDMA approach can significantly enhance the SKR for both users when compared to the single-user case without the q-CDMA approach.
In recent years, continuous-variable quantum key distribution (CV-QKD) has become a promising paradigm for enabling secure communication among multiple end users sharing the same telecommunication backbone. CV-QKD with reverse reconciliation naturally enables scalability from conventional point-to-point links to quantum access networks based on passive quantum broadcasting channels. Here, we report an experimental demonstration on an active 1:41:41:4 multi-user CV quantum network (QN) in the finite-size regime. With 1.25⋅1091.25\cdot10^91.25⋅109 coherent states exchanged on each 11km11\text{km}11km quantum channel, the highest performance for secret key generation totaling 1.9⋅10−11.9\cdot10^{-1}1.9⋅10−1 bits/channel use. Furthermore, we investigate adaptable CV-QN protocols that comprehensively allow network operation in various security and key rates requirements of individual users. The results establish the practical security of CV-QN compatible with existing telecommunication for broad deployment, and allowing additional degree of freedom for connected end users in existing infrastructures.
In this paper, we propose a novel architecture of the satellite continuous-variable quantum key distribution (CV-QKD) system that can not only support multiple users but also enhance the security. The satellite CV-QKD system is based on a code-division multiple access (CDMA) technique to simultaneously transmit multiple key streams from a trusted satellite to a ground station, which passively forwards these key streams to multiple users nearby via optical fibers. Our proposed architecture avoids using multiple ground stations that result in high costs. We analyze the performance of the proposed system under the negative impacts of atmospheric attenuation and atmospheric turbulence, as well as beam spreading and pointing error loss. Especially, the impact of multiple user interference is also considered in our analysis. The numerical results show that the proposed QKD system using CDMA can support multiple users, whose performance metrics such as quantum bit-error rate (QBER), sifted probability, and secret key rate meet the designed targets. The eavesdroppers suffer high QBER and low sifted probability, thus the security is guaranteed.
A crucial open problem inS large-scale quantum networks is how to efficiently transmit quantum data among many pairs of users via a common data-transmission medium. We propose a solution by developing a quantum code division multiple access (q-CDMA) approach in which quantum information is chaotically encoded to spread its spectral content, and then decoded via chaos synchronization to separate different sender-receiver pairs. In comparison to other existing approaches, such as frequency division multiple access (FDMA), the proposed q-CDMA can greatly increase the information rates per channel used, especially for very noisy quantum channels.
We propose a scheme for continuous-variable quantum key distribution (CV-QKD) using the subcarrier multiplexing technique which was employed in microwave photonics. This scheme allows distribution of NNN channels with independent Gaussian-modulated CV-QKD in parallel with one laser source and several phase modulators. We analyze the influence of nonlinear signal mixing and security in the asymptotic limit. Results indicate that by using this multiplexing technique, each channel will have a non-Gaussian extra source noise, resulting in slight shortening of the maximum transmission distance, while the total secret key rate can be considerably increased. This scheme could also be used for key distribution for multiple users, and combined with wavelength division multiplexing devices it has potential to be used for construction of a CV-QKD network.
Abstract We propose a high-rate phase reference scheme for continuous-variable quantum key distribution (CV-QKD). In this scheme, a transmission mode has been employed in which several quantum signal pulses are accompanied by a pair of reference pulses, calibrating the measurement bases of the communicating parties. Within a certain range, and with the ratio between quantum signal pulses and reference pulses increased, the secret key rate approaches that of the traditional CV-QKD scheme (which is a scheme without phase noise). Compared with general CV-QKD schemes, which adopt the transmission mode of a quantum signal pulse plus a pair of reference pulses, this scheme has a higher spectral efficiency, enabling high-rate CV-QKD. In addition, we reduce the interference of strong reference pulses with weak quantum signal pulses by using a pair of polarization beam splitters with a dynamic polarization controller. Simulation results demonstrate that we achieve a higher secret key rate than the self-coherent phase reference scheme. This provides a pathway towards large-scale quantum communication networks.