Recently, there has been a growing focus on quantum communication due to its inherent security advantages. However, there are still many challenges that need to be addressed, such as the distribution of entangled states over long distances, closing the Bell test loopholes , and increasing the key rate. In this work, we present an innovative device-independent Quantum Key Distribution (QKD) protocol based on the distribution of near-maximally entangled multiphoton states across long distances. Our proposed strategy employs the resources available within the current landscape of integrated quantum photonic technology, including the utilization of squeezed vacuum states and photon-number-resolving detectors. Besides, this protocol enables entanglement sharing and quantum communication in free space.
Recently, there has been a growing focus on quantum communication due to its inherent security advantages. However, there are still many challenges that need to be addressed, such as the distribution of entangled states over long distances, closing the Bell test loopholes , and increasing the key rate. In this work, we present an innovative device-independent Quantum Key Distribution (QKD) protocol based on the distribution of near-maximally entangled multiphoton states across long distances. Our proposed strategy employs the resources available within the current landscape of integrated quantum photonic technology, including the utilization of squeezed vacuum states and photon-number-resolving detectors. Besides, this protocol enables entanglement sharing and quantum communication in free space.
We propose a protocol to perform long-range distribution of near-maximally entangled multiphoton states, allowing versatile applications such as quantum key distribution (QKD) and quantum metrology which can provide alternatives to state-of-the-art protocols. Our scheme uses resources available within the current integrated quantum photonic technology: squeezed vacuum states and photon-number-resolving detectors. The distributed entanglement can be certified by Bell tests which have the potential to be loophole free, and may be directly used in well-established QKD protocols. Generally, this provides measurement-device-independent levels of security, which may be upgraded to fully device-independent security if the Bell test is loophole free. In both cases, the protocol is robust to extremely high transmission losses, matching the optimal $O(\sqrt{\ensuremath{\eta}})$ scaling of key rate with channel transmittance.
Device-independent quantum key distribution (DI-QKD) enables information-theoretically secure key exchange between remote parties without any assumptions on the internal workings of the devices used for its implementation. However, its practical deployment remains severely constrained by the need for loophole-free Bell inequality violations, which are highly susceptible to losses and detection efficiencies. In this paper, we propose two long-distance DI-QKD protocols based on a heralding scheme using single-photon interference. Our protocols consist of only standard quantum optics tools such as two-mode squeezed states, displacement operations, and on-off detectors, making them experimentally accessible. To further enhance robustness against realistic imperfections, we integrate a classical noisy preprocessing technique during post-processing. We calculate key rates of the protocols by numerical optimization and show the supremacy of this implementation over existing protocols in terms of communication distances.
Abstract Device-independent quantum key distribution (DI-QKD) provides the gold standard for secure key exchange. Not only does it allow for information-theoretic security based on quantum mechanics, but it also relaxes the need to physically model the devices, thereby fundamentally ruling out many quantum hacking threats to which non-DI QKD systems are vulnerable. In practice though, DI-QKD is very challenging. It relies on the loophole-free violation of a Bell inequality, a task that requires high quality entanglement to be distributed between distant parties and close to perfect quantum measurements, which is hardly achievable with current technology. Notwithstanding, recent theoretical and experimental efforts have led to proof-of-principle DI-QKD implementations. In this article, we review the state-of-the-art of DI-QKD by highlighting its main theoretical and experimental achievements, discussing recent proof-of-principle demonstrations, and emphasizing the existing challenges in the field.
The security of quantum key distribution (QKD) usually relies on that the users' devices are well characterized according to the security models made in the security proofs. In contrast, device-independent QKD-an entanglement-based protocol-permits the security even without any knowledge of the underlying quantum devices. Despite its beauty in theory, device-independent QKD is elusive to realize with current technologies. Especially in photonic implementations, the requirements for detection efficiency are far beyond the performance of any reported device-independent experiments. In this Letter, we report a proof-of-principle experiment of device-independent QKD based on a photonic setup in the asymptotic limit. On the theoretical side, we enhance the loss tolerance for real device imperfections by combining different approaches, namely, random postselection, noisy preprocessing, and developed numerical methods to estimate the key rate via the von Neumann entropy. On the experimental side, we develop a high-quality polarization-entangled photon source achieving a state-of-the-art (heralded) detection efficiency about 87.5%. Although our experiment does not include random basis switching, the achieved efficiency outperforms previous photonic experiments involving loophole-free Bell tests. Together, we show that the measured quantum correlations are strong enough to ensure a positive key rate under the fiber length up to 220 m. Our photonic platform can generate entangled photons at a high rate and in the telecom wavelength, which is desirable for high-speed generation over long distances. The results present an important step toward a full demonstration of photonic device-independent QKD.
Entanglement-based quantum key distribution (e-QKD) is a cornerstone of quantum-secure communication, offering advantages in device-independent security, compatibility with quantum networks, and resilience to specific attacks. While the probabilistic nature of entangled photon generation has slowed down experimental adoption compared to prepare-and-measure approaches, deterministic solid-state emitters—particularly epitaxial quantum dots (QDs)—have recently emerged as promising candidates for scalable, high-rate implementations. In this review, we survey the main e-QKD protocols along with their practical requirements and assess current technologies for entangled photon pair generation. We place particular emphasis on the state of the art in QD-based entangled photon sources, analyzing design strategies and performance metrics that directly impact secure key generation. Recent experimental advances demonstrating entanglement distribution and e-QKD with QDs over both fiber and free-space channels are discussed in detail. We conclude with an outlook on remaining challenges in source engineering, transmission capacity, and system integration, highlighting the potential of QDs to enable next-generation quantum communication technologies.
Quantum Key Distribution (QKD) offers a revolutionary method for achieving information-theoretic security in communication systems by leveraging quantum mechanical principles. With foundational protocols like BB84 and newer innovations such as phase-matching and device-independent QKD, the field has rapidly progressed from theoretical constructs to real-world prototypes. Recent advancements in integrated photonics, high-speed key generation, and satellite-based systems suggest a transformative potential for global cybersecurity infrastructure. However, significant challenges remain in extending secure communication distances, ensuring practical implementation security, reducing cost and size of components, and integrating QKD into existing network architectures. This paper reviews the state-of-the-art in QKD, discusses emerging trends such as chip-based and layered QKD systems, evaluates satellite and free-space deployments, and examines the practical limitations and solutions for long-distance and high-rate secure communications. It concludes by highlighting future directions including standardization, hybrid classical-quantum infrastructures, and software-defined QKD networks.