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arXiv:1501.05517 · Journal of Lightwave Technology

Orthogonal Frequency-Division Multiplexed Quantum Key Distribution

Sima Bahrani, Mohsen Razavi, Jawad A. Salehi

Published Sep 4, 2015• 31 citations
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Abstract

We propose orthogonal frequency-division multiplexing (OFDM), as a spectrally efficient multiplexing technique, for quantum key distribution at the core of trusted-node quantum networks. Two main schemes are proposed and analyzed in detail, considering system imperfections, specifically, time misalignment issues. It turns out that while multiple service providers can share the network infrastructure using the proposed multiplexing techniques, no gain in the total secret key generation rate is obtained if one uses conventional passive all-optical OFDM decoders. To achieve a linear increase in the key rate with the number of channels, an alternative active setup for OFDM decoding is proposed, which employs an optical switch in addition to conventional passive circuits. We show that by using our proposed decoder, the bandwidth utilization is considerably improved as compared to conventional wavelength-division multiplexing techniques.

DOI
10.1109/jlt.2015.2476821

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We propose orthogonal frequency-division multiplexing (OFDM), as a spectrally efficient multiplexing technique, for quantum key distribution at the core of trusted-node quantum networks. Two main schemes are proposed and analyzed in detail, considering system imperfections, specifically, time misalignment issues. It turns out that while multiple service providers can share the network infrastructure using the proposed multiplexing techniques, no gain in the total secret key generation rate is obtained if one uses conventional passive all-optical OFDM decoders. To achieve a linear increase in the key rate with the number of channels, an alternative active setup for OFDM decoding is proposed, which employs an optical switch in addition to conventional passive circuits. We show that by using our proposed decoder, the bandwidth utilization is considerably improved as compared to conventional wavelength-division multiplexing techniques.
We introduce a reliable scheme for continuous-variable quantum key distribution (CV-QKD) by using orthogonal frequency division multiplexing (OFDM). As a spectrally efficient multiplexing technique, OFDM allows a large number of closely spaced orthogonal subcarrier signals used to carry data on several parallel data streams or channels. We place emphasis on modulator impairments which would inevitably arise in the OFDM system and analyze how these impairments affect the OFDM-based CV-QKD system. Moreover, we also evaluate the security in the asymptotic limit and the Pirandola-Laurenza-Ottaviani-Banchi upper bound. Results indicate that although the emergence of imperfect modulation would bring about a slight decrease in the secret key bit rate of each subcarrier, the multiplexing technique combined with CV-QKD results in a desirable improvement on the total secret key bit rate which can raise the numerical value about an order of magnitude.
In this paper, we investigate the performance of orthogonal frequency division multiplexed quantum key distribution (OFDM-QKD) in an integrated quantum-classical wavelength-division-multiplexing system. The presence of an intense classical signal alongside the quantum one generates Raman background noise. Noise reduction techniques should, then, be carried out at the receiver to suppress this crosstalk noise. In this work, we show that OFDM-QKD enables efficient filtering, in time and frequency domains, making it an attractive solution for the high-rate links at the core of quantum-classical networks.
This paper addresses multi-user quantum key distribution networks, in which any two users can mutually exchange a secret key without trusting any other nodes. The same network also supports conventional classical communications by assigning two different wavelength bands to quantum and classical signals. Time and code division multiple access (CDMA) techniques, within a passive star network, are considered. In the case of CDMA, it turns out that the optimal performance is achieved at a unity code weight. A listen-before-send protocol is then proposed to improve secret key generation rates in this case. Finally, a hybrid setup with wavelength routers and passive optical networks, which can support a large number of users, is considered and analyzed.
Recently, extensive research attention has been dedicated to enabling Orthogonal Frequency-Division Multiplexing (OFDM) waveforms to be compatible with a modern communication system. Encoding data as OFDM wavelengths still has a lot of problems, like the peak-to-average power ratio (PAPR) and the cyclic prefix (CP), which are important factors that affect how efficiently the spectrum is used. To meet the quality-of-service requirements imposed by communication system applications, this paper proposes to replace the classical encoding and decoding schemes, classical channel, discrete Fourier transform (DFT), and inverse discrete Fourier transform (IDFT) with their classical counterparts. This new quantum OFDM transmission scheme allows for the preparation of a quantum OFDM symbol without the need to incorporate a CP. To validate the accuracy of the suggested quantum OFDM transmission scheme, we compared it with the most widely recognised reference quantum transmission scheme. We have demonstrated that increasing the channel resistivity results in a higher probability of correctly measuring the quantum state in the quantum OFDM transmission scheme compared to the reference quantum transmission scheme. The results are verified by IBM's Qiskit.
Physical layer key generation from the wireless channel is an emerging area of interest to provide confidentiality and authentication. One of the main challenges in this domain is to increase the length of the generated secret key while maintaining its randomness and uniformity. In this letter, new dimensions for wireless channel-based key generation are proposed for orthogonal frequency division multiplexing (OFDM) systems. The novel perspective of the proposed work lies in the generation of key bits not only from the magnitudes of OFDM subchannels as it has conventionally been done but also from the number and positions/indices of those subchannels, whose channel gains are above the mean of the respective subblock. The effectiveness of the proposed algorithms is evaluated in terms of key generation rate and key mismatch rate. It is shown in the simulation results that the involvement of the proposed dimensions can double the key generation rate compared to conventional algorithms.
Quantum key distribution (QKD) can theoretically accomplish unconditionally secure communication with the support of quantum mechanics. The point-to-point QKD system has already been well developed, and the focus of advanced research has shifted more toward QKD networks. However, it is still unclear how to achieve the maximum secret key rate within the limited physical bandwidth in QKD networks. In this paper, we propose an orthogonal frequency division multiplexing continuous-variable QKD access network (CV-QAN), which improves the bandwidth utilization efficiency to the Nyquist limit. Specifically, each quantum network unit prepares a carrier-modulated Gaussian-modulated coherent state so that they become orthogonal in the frequency domain when received by the quantum line terminal. Crosstalk arising from the multi-path effect among multi-mode quantum states was effectively suppressed through the implementation of a cyclic prefix. In this theory, we have demonstrated the feasibility of this scheme through the continuous-mode Gaussian information theory. In this experiment, we conducted a local local oscillator (LLO) CV-QAN experiment within the existing passive optical network architecture. The network capacity of CV-QAN is 7, and the secret key rate of each user reaches 4.06 and 0.87 Mbps at 25 km in the asymptotic case and the finite-size effect, respectively. This achievement has established an efficient and simple QAN based on digital signal processing, laying the foundation for the practicality and commercialization of large-scale quantum networks.