Quantum information protocols are being deployed in increasingly practical scenarios, via optical fibers or free space, alongside classical communications channels. However, entanglement, the most critical resource to deploy to the communicating parties, is also the most fragile to the noise-induced degradations. Here we show that polarization-frequency hyperentanglement of photons can be effectively employed to enable noise-resistant distribution of polarization entanglement through noisy quantum channels. In particular, we demonstrate that our hyperentanglement-based scheme results in an orders-of-magnitude increase in the SNR for distribution of polarization-entangled qubit pairs, enabling quantum communications even in the presence of strong noise that would otherwise preclude quantum operations due to noise-induced entanglement sudden death. While recent years have witnessed tremendous interest and progress in long-distance quantum communications, previous attempts to deal with the noise have mostly been focused on passive noise suppression in quantum channels. Here, via the use of hyperentangled degrees of freedom, we pave the way toward a universally adoptable strategy to enable entanglement-based quantum communications via strongly noisy quantum channels.
Quantum information protocols are being deployed in increasingly practical scenarios, via optical fibers or free space, alongside classical communications channels. However, entanglement, the most critical resource to deploy to the communicating parties, is also the most fragile to the noise-induced degradations. Here we show that polarization-frequency hyperentanglement of photons can be effectively employed to enable noise-resistant distribution of polarization entanglement through noisy quantum channels. In particular, we demonstrate that our hyperentanglement-based scheme results in an orders-of-magnitude increase in the SNR for distribution of polarization-entangled qubit pairs, enabling quantum communications even in the presence of strong noise that would otherwise preclude quantum operations due to noise-induced entanglement sudden death. While recent years have witnessed tremendous interest and progress in long-distance quantum communications, previous attempts to deal with the noise have mostly been focused on passive noise suppression in quantum channels. Here, via the use of hyperentangled degrees of freedom, we pave the way toward a universally adoptable strategy to enable entanglement-based quantum communications via strongly noisy quantum channels.
Entanglement distribution over deployed fiber links is essential for implementing quantum communication protocols. However, environmental noise in deployed fibers, such as classical signals, stray light, and Raman scattering, can significantly degrade entanglement, ultimately destroying the nonlocal correlations required for quantum communication. In this work, we demonstrate noise-resilient quantum communication over 40 km of intra-city deployed fiber, with a total transmission loss of 23.04 dB, by utilizing hyperentanglement in the time-bin and frequency degrees of freedom. By exploiting the frequency anticorrelation of the photon pairs and implementing frequency-to-time mapping using dense wavelength-division multiplexing combined with calibrated delay lines, we realize frequency-resolved detection that discriminates frequency-anticorrelated entangled photon pairs from uncorrelated noise. This enables reliable entanglement distribution with over an order-of-magnitude improvement in signal-to-noise ratio and a substantial increase in Bell-state fidelity, even in high-noise and high-loss conditions of deployed fibers. Moreover, entanglement—initially lost due to entanglement sudden death—is successfully restored, enabling a clear violation of the Bell inequality. These results establish a practical and scalable method for entanglement distribution in noisy and lossy environments, advancing the feasibility of real-world quantum communication over existing fiber infrastructure.
High-dimensional entanglement not only offers a high security level for quantum communication but also promises improved information capacity and noise resistance of the system. However, due to various constraints on different high-dimensional degrees of freedom, whether these advantages can bring improvement to the actual implementation is still not well proven. Here we present a scheme to fully utilize these advantages over long-distance noisy fiber channels. We exploit polarization and time-bin hyperentanglement to achieve high-dimensional coding, and observe significant enhancements in secure key rates and noise tolerance that surpass the capabilities of qubit systems. Moreover, the demonstration achieves a distribution up to 50 km, which is the longest distance for high-dimensional entanglement-based quantum key distribution up to date, to our knowledge. Our demonstration validates the potential of high-dimensional entanglement for quantum communications over long-distance noisy channels, paving the way for a resilient and resource-efficient quantum network.
Photonic entanglement is a fundamental resource in quantum information processing and its distribution between distant parties is a key challenge in quantum communications. Optical satellite links allow transmitting entangled photons over longer distances than currently possible on ground and could provide a path towards global quantum communication networks. The majority of current photonic free-space quantum communication systems, including two recent quantum satellite experiments, use two-dimensional polarization encoding, where each photon can carry at most a single bit of quantum information. Encoding additional qubits in the high-dimensional spatio-temporal degrees of freedom could not only increase channel capacities but also improve robustness with respect to noise and eavesdropping in quantum cryptography. Here, we give an overview of our efforts towards exploiting high-dimensional entanglement in long-distance free-space quantum communications. We report on the results of a first feasibility study, in which we used polarization / energy-time hyperentanglement to increase the dimensionality of the state space and transmit genuine 4-dimensional entanglement via an intra-city free-space link. We discuss how we intend to extend this approach to applications in noise-tolerant large-alphabet quantum key distribution via free-space links, and, ultimately, experiments with satellites.
Hyperentanglement is an effective quantum source for quantum communication network due to its high capacity, low loss rate, and its unusual character in teleportation of quantum particle fully. Here we present a deterministic error-correction scheme for nonlocal spatial-polarization hyperentangled photon pairs over collective-noise channels. In our scheme, the spatial-polarization hyperentanglement is first encoded into a spatial-defined time-bin entanglement with identical polarization before it is transmitted over collective-noise channels, which leads to the error rejection of the spatial entanglement during the transmission. The polarization noise affecting the polarization entanglement can be corrected with a proper one-step decoding procedure. The two parties in quantum communication can, in principle, obtain a nonlocal maximally entangled spatial-polarization hyperentanglement in a deterministic way, which makes our protocol more convenient than others in long-distance quantum communication.
In recent years, quantum communication technology has developed rapidly, and quantum communication schemes based on hyperentangled states have attracted widespread attention due to their efficiency and security. However, in practical communication, maximally hyperentangled states are highly susceptible to environmental noise, which causes them to degrade into non-maximally hyperentangled states. This degradation significantly reduces the fidelity of the quantum information and communication efficiency. In this article, we propose an efficient entanglement concentration scheme to restore degraded polarization-time hyperentangled W states, thereby enhancing the reliability and transmission distance of multiparty quantum communication. The protocol employs the parameter-splitting approach, where the receiver performs local operations on received non-maximally hyperentangled photons by using linear optical elements, achieving hyperentanglement concentration through detector responses and post-selection. This method eliminates the need for auxiliary photons, thereby reducing the use of quantum resources and maintaining operational simplicity. Moreover, the scheme can be extended to N-photon hyperentangled W states. The theoretical calculations demonstrate that the success probability of the protocol is determined by the minimal parameter of the hyperentangled state, exhibiting a monotonic increase as this parameter grows. Under ideal conditions, the maximum success probability approaches unity and the success probability improves with the number of entangled photons increasing. When considering the efficiency of practical optical components, the maximal success probabilities for hyperentangled W states with N = 3, 4, and 5 are found to be 0.856, 0.791, and 0.732, respectively. Consequently, the proposed scheme efficiently concentrates the degraded polarization-time hyperentangled W state into the maximally hyperentangled state. This work is of significant importance for long-distance information transmission and provides theoretical references for implementing long-distance multi-party quantum communication.
Quantum communication is based on the generation of quantum states and exploitation of quantum resources for communication protocols. Currently, photons are considered as the optimal carriers of information, because they enable long-distance transition with resilience to decoherence and they are relatively easy to create and detect. Entanglement is a fundamental resource for quantum communication and information processing, and it is of particular importance for quantum repeaters. Hyperentanglement, a state where parties are entangled with two or more degrees of freedom (DoFs) simultaneously, provides an important additional resource because it increases data rates and enhances error resilience. However, in photonics, the channel capacity, i.e., the ultimate throughput, is fundamentally limited when dealing with linear elements. We propose a technique for achieving higher transmission rates for quantum communication by using hyperentangled states, based on multiplexing multiple DoFs on a single photon, transmitting the photon, and eventually demultiplexing the DoFs to different photons at the destination, using Bell state measurements. Following our scheme, one can generate two entangled qubit pairs by sending only a single photon. The proposed transmission scheme lays the groundwork for novel quantum communication protocols with higher transmission rates and refined control over scalable quantum technologies.