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arXiv:2412.02944 · Physica Scripta

Passive polarization-encoded BB84 protocol using a heralded single-photon source

Anju Rani, Vardaan Mongia, Parvatesh Parvatikar, Rutuj Gharate, Tanya Sharma, Jayanth Ramakrishnan, Pooja Chandravanshi, Ravindra Pratap Singh

Published Dec 31, 2025• 2 citations
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Abstract

Abstract The BB84 quantum key distribution (QKD) protocol sets the foundation for achieving secure communication against quantum threats. Since its inception, significant advancements have aimed towards frugal experimental implementations with enhanced security. In this paper, we report a passive polarization encoded BB84 protocol. By passively and randomly encoding the polarization states, the setup avoids active modulation and simplifies design with security standards analogous to entanglement-based QKD. The heralding of a probabilistic single-photon source ensures an extremely low probability of multi-photon emissions evading photon number-splitting attacks. The quality of the single-photon source and thus, the QKD setup is certified by the second-order correlation function, g (2) (0) = 0.006 ± 0.0002. Our protocol provides an optimisation trade-off between the conventional BB84 and the BBM92 protocol. The advantage relies on using fewer detectors (compared to the BBM92 protocol) and no reliance on active quantum random number generators (compared to the standard BB84) to drive Alice’s encoding scheme. Our implementation achieves a quantum bit error rate of 7% and a secure key rate of 5 kbps.

DOI
10.1088/1402-4896/ae3263

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Abstract The BB84 quantum key distribution (QKD) protocol sets the foundation for achieving secure communication against quantum threats. Since its inception, significant advancements have aimed towards frugal experimental implementations with enhanced security. In this paper, we report a passive polarization encoded BB84 protocol. By passively and randomly encoding the polarization states, the setup avoids active modulation and simplifies design with security standards analogous to entanglement-based QKD. The heralding of a probabilistic single-photon source ensures an extremely low probability of multi-photon emissions evading photon number-splitting attacks. The quality of the single-photon source and thus, the QKD setup is certified by the second-order correlation function, g (2) (0) = 0.006 ± 0.0002. Our protocol provides an optimisation trade-off between the conventional BB84 and the BBM92 protocol. The advantage relies on using fewer detectors (compared to the BBM92 protocol) and no reliance on active quantum random number generators (compared to the standard BB84) to drive Alice’s encoding scheme. Our implementation achieves a quantum bit error rate of 7% and a secure key rate of 5 kbps.
Quantum key distribution (QKD) has emerged as a revolutionary technique that can ensure unconditionally secure communication between two distant parties, referred to as Alice and Bob, by exploiting the fundamental principles of quantum physics. Here, we report experimental demonstration of a fully automated QKD system based on the BB84 protocol. A weak coherent pulse source is developed to generate stream of polarization encoded single photons. Our QKD system demonstrates a low QBER of ∼1.2% with sifted key generation rate of ∼70 Kbps at an average photon number per pulse ofμ=0.11\mu=0.11μ=0.11. The final secure key rate of ∼33 Kbps is achieved after performing post processing procedures viz. error correction and privacy amplification. The quantum communication link is established continuously for several hours and the performance is evaluated iteratively. The developed QKD system is shown to have the capability of distributing cryptographic keys securely and seamlessly, under practical operating conditions. Furthermore, we have successfully demonstrated unconditionally secure transmission and reception of an image between Alice and Bob connected over an unsecured public channel by utilizing quantum cryptography.
In this work, we simulate a fiber-based Quantum Key Distribution Protocol (QKDP) BB84 working at the telecoms wavelength 1550 nm with taking into consideration an optimized attack strategy. We consider in our work a quantum channel composed by probabilistic Single Photon Source (SPS), single mode optical Fiber and quantum detector with high efficiency. We show the advantages of using the Quantum Dots (QD) embedded in micro-cavity compared to the Heralded Single Photon Sources (HSPS). Second, we show that Eve is always getting some information depending on the mean photon number per pulse of the used SPS and therefore, we propose an optimized version of the QKDP BB84 based on Quantum Dense Coding (QDC) that could be implemented by quantum CNOT gates. We evaluate the success probability of implementing the optimized QKDP BB84 when using nowadays probabilistic quantum optical devices for circuit realization. We use for our modeling an abstract probabilistic model of a CNOT gate based on linear optical components and having a success probability of sqrt (4/27), we take into consideration the best SPSs realizations, namely the QD and the HSPS, generating a single photon per pulse with a success probability of 0.73 and 0.37, respectively. We show that the protocol is totally secure against attacks but could be correctly implemented only with a success probability of few percent.
Abstract A passive quantum key distribution (QKD) transmitter generates the quantum states prescribed by a QKD protocol at random, combining a fixed quantum mechanism and a post-selection step. By circumventing the use of active optical modulators externally driven by random number generators, passive QKD transmitters offer immunity to modulator side channels and potentially enable higher frequencies of operation. Recently, the first linear optics setup suitable for passive decoy-state QKD has been proposed. In this work, we simplify the prototype and adopt sharply different approaches for BB84 polarization encoding and decoy-state parameter estimation. In particular, our scheme avoids a probabilistic post-selection step that is central to the former proposal. On top of it, we elaborate a simple and tight custom-made security analysis.
Abstract The Quantum Key Distribution protocol can encode a single quantum state and implements an information-theoretically secure key distribution protocol in communication. In the actual QKD experimental system, there are usually two encoding methods which are phase encoding and polarization encoding. Ma et al (Phase-Matching Quantum Key Distribution, Phys. Rev. X., 2018, 83) proposed the phase-matching QKD protocol, which has high transmission and it is an extension of the measurement device independent QKD. This paper successfully gives the polarization scheme of this PM-QKD protocol, the bases in the polarization scheme are arbitrary, and eliminates detector side channel attacks. Furthermore, we give the security analysis and simulation results of the polarization scheme, and compare it with the BB84 protocol. The simulation results show that our protocol is superior to the BB84 protocol in terms of transmission distance under the fixed key rate.
The Bennett-Brassard 1984 (BB84) protocol is one of the simplest protocols for implementing quantum key distribution (QKD). In the protocol, the sender and the receiver iteratively choose one of two complementary measurement bases. Regarding the basis choice by the receiver, a passive setup has been adopted in a number of its implementations, including satellite QKD and time-bin encoding. However, conventional theoretical techniques to prove the security of the BB84 protocol are not applicable if the receiver chooses their measurement basis passively, rather than actively, with a biased probability, followed by measurement with threshold detectors. Here we present a fully analytical security proof against coherent attacks for such a decoy-state BB84 protocol with the receiver’s passive basis choice and measurement with threshold detectors. Numerical simulations under practical situations show that the difference in secure key rate between the active and passive implementations of the protocol is negligible except for long communication distances.
We report a proof-of-principle quantum key distribution experiment using a one-way optical scheme with polarization encoding implementing the BB84 protocol. LiNbO 3 phase modulators are used for generating polarization states for Alice and active basis selection for Bob. This allows the former to use a single laser source, while the latter needs only two single-photon detectors. The presented optical scheme is simple and consists of standard fiber components. Calibration algorithm for three polarization controllers used in the scheme has been developed. The experiment was carried with 10 MHz repetition frequency laser pulses over a distance of 50 km of standard telecom optical fiber.