Quantum Communication Networks Research Articles

Numerical simulation of quantum key distribution network based on wavelength division multiplexing technology

Wavelength division multiplexing (WDM) technology can improve the networking level and overcome the shortcomings of low key rate under the existing technic background of measurement device independent quantum key distribution (MDI-QKD) protocol application. reference frame independent quantum key distribution (RFI-MDI-QKD) protocol cut down on the influence of the reference frame drift on the key distribution system. The decoy state protocol has important development prospects in the development of quantum communication networking. Combining the advantages of of the above protocols to realize RFI-MDI-QKD with WDM, the results show that the key distribution efficiency is improved with the increase in the number of WDM multiplexed channels, which promotes the further exploration and achievement of QKD networking application.

Fidelity optimized multiparty quantum teleportation protocol with quantum Shor codes and OSPF method in imperfect local operations

Relying on the probabilistic nature and entanglement property of quantum state, quantum communication will support the theoretically unconditional security and computational efficiency beyond that of classical communication. In this article, we present a fidelity optimized quantum teleportation protocol for multiparty quantum network communication. Firstly, a special transmission mechanism ensures the secure establishment of the channel between the communicators. Secondly, the quantum information is encoded by Shor codes to resist channel noise. Thirdly, the Open Shortest Path First (OSPF) method is of help for establishing the channel between non-adjacent communicators. In this protocol, the special transmission mechanism guarantees the security of quantum communication. The Shor codes improve the fidelity of quantum information. The OSPF method ensures efficient transmission. The effectiveness of the protocol is verified by experiments. Experimental results show that this protocol provides effective qubit fidelity improvements within the range of noise thresholds of . Compared with existing quantum communication protocols, this protocol has better reliability and fidelity performance.

Detecting quantum capacities of continuous-variable quantum channels

Quantum communication channels and quantum memories are the fundamental building blocks of large-scale quantum communication networks. Estimating their capacity to transmit and store quantum information is crucial in order to assess the performance of quantum communication systems and to detect useful communication paths among the nodes of future quantum networks. However, the estimation of quantum capacities is a challenging task for continuous-variable systems, such as the radiation field, for which a complete characterization via quantum tomography is practically unfeasible. Here we introduce a method for detecting the quantum capacity of continuous-variable communication channels and memories without performing a full process tomography. Our method works in the general scenario where the devices are used a finite number of times, can exhibit correlations across multiple uses, and can change dynamically under the control of a malicious adversary. The method is experimentally friendly and can be implemented using only finitely squeezed states and homodyne measurements.

Controlled quantum teleportation in the presence of an adversary

We present a device independent analysis of controlled quantum teleportation where the receiver is not trusted. We show that the notion of genuine tripartite nonlocality allows us to certify control power in such a scenario. By considering a specific adversarial attack strategy on a device characterized by depolarizing noise, we find that control power is a monotonically increasing function of genuine tripartite nonlocality. These results are relevant for building practical quantum communication networks and also shed light on the role of nonlocality in multipartite quantum information processing.

Simultaneous two-way classical communication and measurement-device-independent quantum key distribution on oceanic quantum channels

Simultaneous two-way classical and quantum (STCQ) communication combines both continuous classical coherent optical communication and continuous-variable quantum key distribution (CV-QKD), which eliminates all detection-related imperfections by being measurement-device-independent (MDI). In this paper, we propose a protocol relying on STCQ communication on the oceanic quantum channel, in which the superposition-modulation-based coherent states depend on the information bits of both the secret key and the classical communication ciphertext. We analyse the encoding combination in classical communication and consider the probability distribution transmittance under seawater turbulence with various interference factors. Our numerical simulations of various practical scenarios demonstrate that the proposed protocol can simultaneously enable two-way classical communication and CV-MDI QKD with just a slight performance degradation transmission distance compared to the original CV-MDI QKD scheme. Moreover, the asymmetric situation outperforms the symmetric case in terms of transmission distance and optical modulation variance. We further take into consideration the impact of finite-size effects to illustrate the applicability of the proposed scheme in practical scenarios. The results show the feasibility of the underwater STCQ scheme, which contributes toward developing a global quantum communication network in free space.

Hyper-parallel nonlocal Toffoli gates assisted by quantum dots inside a double-side optical microcavity

<p indent="0mm">Implementing three-qubit Toffoli gates nonlocally plays an important role in quantum communication networks and distributed quantum computation. Most of previous protocols for implementing quantum Toffolis gate consider only implementing Toffoli gates with one degree of freedom. In this paper, we present a scheme for parallel implementation of nonlocal Toffoli gates in polarization and spatial-mode degrees of freedom assisted by quantum dots inside a double-side optical microcavity. Alice and Bob let photons traverse the double-side optical microcavity sequentially and perform single-particle measurements on electron spin in quantum dots and the entangled photons. Charlie performs single-particle measurements and applies the corresponding unitary operation in polarization and spatial-mode degrees of freedom according to Alice and Bob’s measurement results. Alice and Bob can implement hyper-parallel nonlocal Toffoli gates by performing unitary operations according to Charlie’s measurement result. This protocol has the advantage of having high channel capacity by the hyperentangled state as the quantum channel.

Achieving the ultimate end-to-end rates of lossy quantum communication networks

The field of quantum communications promises the faithful distribution of quantum information, quantum entanglement, and absolutely secret keys, however, the highest rates of these tasks are fundamentally limited by the transmission distance between quantum repeaters. The ultimate end-to-end rates of quantum communication networks are known to be achievable by an optimal entanglement distillation protocol followed by teleportation. In this work, we give a practical design for this achievability. Our ultimate design is an iterative approach, where each purification step operates on shared entangled states and detects loss errors at the highest rates allowed by physics. As a simpler design, we show that the first round of iterations can purify completely at high rates. We propose an experimental implementation using linear optics and photon-number measurements which is robust to inefficient operations and measurements, showcasing its near-term potential for real-world practical applications.

Metropolitan single-photon distribution at 1550 nm for random number generation

Quantum communication networks will connect future generations of quantum processors, enable metrological applications, and provide security through quantum key distribution. We present a testbed that is part of the municipal fiber network in the greater Stockholm metropolitan area for quantum resource distribution through a 20 km long fiber based on semiconductor quantum dots emitting in the telecom C-band. We utilize the service to generate random numbers passing the NIST test suite SP800-22 at a subscriber 8 km outside of the city with a bit rate of 23.4 kbit/s.

Tunable up-conversion single-photon detector at telecom wavelengths

Abstract Up-conversion single-photon detectors (UCSPD) are based on sum-frequency generation of the telecom band single-photons to near-infrared wavelengths at which efficient and low-noise silicon single-photon detectors are available. Moreover, because of high dynamic range of silicon single-photon detectors, UCSPD is suitable for high-speed quantum communication. UCSPDs reported to date, however, have a very narrow fixed window of detectable wavelengths, severely limiting their applications in wavelength-multiplexed quantum networks. In this work, we report a tunable UCSPD module that covers the complete telecom C band, making it suitable for quantum communication networks based on sharing wavelength-multiplexed entangled photons.

Quadripartite EPR steering based on energy-level cascaded four-wave mixing processes

Multipartite quantum steering has important applications in secure quantum communication networks. In this work, three different energy-level cascaded four-wave mixing (FWM) processes are proposed to generate quadripartite quantum steering. The covariance matrix among different modes combination is constructed. The properties of quantum steering of the three cascaded models were studied. The results show that all three model structures can achieve various types of quantum steering, and the steerability varies with the amplitude gain of the FWM processes. The results provide a theoretical basis for the experimental generation of multipartite quantum steering and a significant reference for secure quantum communication.

A new non-entangled quantum secret sharing protocol among different nodes in further quantum networks

As an important branch of quantum secure multi-party computation, quantum secret sharing (QSS) can distribute secret information among dishonest network nodes without revealing the secrets. In this study, a new four-party QSS protocol based on locally indistinguishable orthogonal product (LIOP) states is first proposed for quantum network communication. Then, the general multiparty QSS model based on LIOP states will be expanded. Combined with the property of LIOP states and obfuscating operation, the source node can send the secrets to different destination nodes in the quantum network. Accordingly, it is proven that the destination nodes have to work together to recover the shared secrets against some existing attacks. Furthermore, no entangled resources and complicated operations are required in the presented protocol. We hope the results could make positive effects to the development of quantum secure communication in the future.

Robust one-sided self-testing of two-qubit states via quantum steering

Entangled two-qubit states are the core building blocks for constructing quantum communication networks. Their accurate verification is crucial to the functioning of the networks, especially for untrusted networks. In this work we study the self-testing of two-qubit entangled states via steering inequalities, with robustness analysis against noise. More precisely, steering inequalities are constructed from the tilted Clauser-Horne-Shimony-Holt inequality and its general form, to verify the general two-qubit entangled states. The study provides a good robustness bound, using both local extraction map and numerical semidefinite-programming methods. In particular, optimal local extraction maps are constructed in the analytical method, which yields the theoretical optimal robustness bound. To further improve the robustness of one-sided self-testing, we propose a family of three measurement settings steering inequalities. The result shows that three-setting steering inequality demonstrates an advantage over two-setting steering inequality on robust self-testing with noise. Moreover, to construct a practical verification protocol, we clarify the sample efficiency of our protocols in the one-sided device-independent scenario.

Silicon Photonic Wires for Broadband Polarization Entanglement at Telecommunication Wavelengths

Compact and scalable sources of broadband polarization entanglement at telecommunication wavelengths will pave the way for multiuser long-distance quantum communication at enhanced data rates, but progress toward this goal has been hindered due to large birefringence in conventional silicon-on-insulator nanowaveguides. The authors theoretically demonstrate, via dispersion engineering, the successful generation of polarization-entangled photon pairs over a broad range of wavelengths. This work also provides a strategy to avoid entanglement degradation due to polarization-mode dispersion. The proposed devices will be useful building blocks for large-scale quantum communication networks.

Hyperentangled Time-Bin and Polarization Quantum Key Distribution

Fiber-based quantum communication networks are currently limited without quantum repeaters. Satellite-based quantum links have been proposed to extend the network domain. We have developed a quantum communication system, suitable for realistic satellite-to-ground communication. With this system, we have executed an entanglement-based quantum key distribution (QKD) protocol developed by Bennett, Brassard, and Mermin in 1992 (BBM92), achieving quantum bit error rates (QBER) below 2$\%$ in all bases. More importantly, we demonstrate low QBER execution of a higher dimensional hyperentanglement-based QKD protocol, using photons simultaneously entangled in polarization and time-bin, leading to significantly higher secure key rates, at the cost of increased technical complexity and system size. We show that our protocol is suitable for a space-to-ground link, after incorporating Doppler shift compensation, and verify its security using a rigorous finite-key analysis. Additionally, We discuss system engineering considerations relevant to those and other quantum communication protocols, and their dependence on what photonic degrees of freedom are utilized.

Revival and distribution of Einstein–Podolsky–Rosen steering of a four-mode cluster state in noisy channels

Einstein–Podolsky–Rosen steering is an important resource for constructing secure quantum communication networks. The quantum states carry information transmitted among the spatially separated nodes through the quantum channels, and the steerability of quantum states will reduce or even completely disappear due to the noise in the channels. We theoretically studied the revived steering properties of the quadripartite quantum state. The steering properties versus transmission efficiency and noise amplitude were investigated. Our studies show that when the noise in the channels reaches a certain value, it will lead to the sudden death of steering, and the steerability can be revived over a large range of values by establishing correlated noisy channels. Different types of monogamy relationships are verified in our scheme. These results provide a theoretical foundation for the construction of secure quantum networks.

Experimental demonstration of a local active phase compensation method for a phase encoding quantum key distribution system.

An efficient phase stabilization method is required in quantum key distribution (QKD) systems for stability in practical applications. The existing active phase compensation method has limitations in multi-node network applications, especially in network-scale applications based on measurement-device-independent QKD systems. In this study, we propose a local active phase compensation scheme that can realize phase compensation independently for each interferometer node. We performed experimental demonstrations in the BB84 phase encoding system based on a Faraday-Michelson interferometer. The average QBER rates of the system under two different forms of the reference light were found to be 1.9% and 1.6%. This scheme can also be applied to other QKD systems and has potential for application in future quantum communication networks.

Optimal design and performance evaluation of free-space quantum key distribution systems

Free-space ground-to-ground links will be an integral part of future quantum communication networks. The implementation of free-space and fiber links in daylight inter-modal configurations is however still hard to achieve, due to the impact of atmospheric turbulence, which strongly decreases the coupling efficiency into the fiber. In this work, we present a comprehensive model of the performance of a free-space ground-to-ground quantum key distribution (QKD) system based on the efficient-BB84 protocol with active decoy states. Our model takes into account the atmospheric channel contribution, the transmitter and receiver telescope design constraints, the parameters of the quantum source and detectors, and the finite-key analysis to produce a set of requirements and optimal design choices for a QKD system operating under specific channel conditions. The channel attenuation is calculated considering all effects deriving from the atmospheric propagation (absorption, beam broadening, beam wandering, scintillation, and wavefront distortions), as well as the effect of fiber-coupling in the presence of a partial adaptive optics correction with finite control bandwidth. We find that the channel fluctuation statistics must be considered to correctly estimate the effect of the saturation rate of the single-photon detectors, which may otherwise lead to an overestimation of the secret key rate. We further present strategies to minimize the impact of diffuse atmospheric background in daylight operation by means of spectral and temporal filtering.

Physics-Informed Quantum Communication Networks: A Vision Toward the Quantum Internet

Quantum communications is a promising technology that will play a fundamental role in the design of future networks. In fact, significant efforts are being undertaken by both the quantum physics and the classical communications communities on developing new architectures, solutions, and practical implementations of quantum communication networks (QCNs). Although these efforts led to various advances in today's technologies, there still exists a non-trivial gap between the research efforts of the two communities on designing and optimizing the performance of QCNs. For instance, most prior works by the classical communications community ignore important quantum physics-based constraints when designing QCNs. For example, many existing works on entanglement distribution do not account for the decoherence of qubits inside quantum memories and, thus, their designs become impractical since they assume an infinite lifetime of quantum states. In this article, we bring forth a novel analysis of the performance of QCNs in a physics-informed manner, by relying on the quantum physics principles that underly the different components of QCNs. The need for the physics-informed approach is then assessed and its fundamental role in designing practical QCNs is analyzed across various open research areas. Moreover, we identify novel physics-informed performance metrics and controls that enable QCNs to leverage the state-of-theart advancements in quantum technologies to enhance their performance. Finally, we analyze multiple pressing challenges and open research directions in QCNs that must be treated using a physics-informed approach to lead practically viable results. Ultimately, this work attempts to bridge the gap between the classical communications and the quantum physics communities in the area of QCNs to foster the development of the future communication networks toward the quantum Internet.

New quantum physics, solving puzzles of Wheeler’s delayed choice and a particle’s passing N slits simultaneously and quantum oscillator in experiments

This paper discovers new quantum physics, and gives solutions to puzzles of Wheeler’s delayed choice and a particle’s passing many slits simultaneously by exact quantum physics expressions. We further show new quantum control, new quantum oscillation, new quantum control experiments and new quantum oscillator being able to be installed in quantum communication network etc. We discover that the ability of a photon to hit electrons out in photoelectric effect is complementarily equivalent to the ability of wave of a photon to simultaneously pass through many slits in wave-particle duality. Objective criterion for distinguishing classical and quantum particles is found, and this paper gives applicable realm of quantum theories and new quantum physics expressions of wave-particle duality. All these studies above should be classified as classical and quantum particles, then classical particle and quantum particle wave cannot and can pass many slits, respectively. This paper discovers wave-particle duality’s origin of displaying both wave property from plane wave part of the general Fourier expansion and particle property from the general Fourier expansion coefficients with the particle’s global property and spins etc. We give the superposition state representation of wave-particle duality, further find the collapse of the duality superposition state to wave or particle state. The collapsed wave or particle state is related to the measure of wave or particle property. Then, we explain why sometimes it's a wave or a particle. Our achieved results are truly tested, and we discover new measured attractive state and quantum wave collapse velocity expression.

Purcell Enhancement of Erbium Ions in TiO2 on Silicon Nanocavities.

Isolated solid-state atomic defects with telecom optical transitions are ideal quantum photon emitters and spin qubits for applications in long-distance quantum communication networks. Prototypical telecom defects, such as erbium, suffer from poor photon emission rates, requiring photonic enhancement using resonant optical cavities. Moreover, many of the traditional hosts for erbium ions are not amenable to direct incorporation with existing integrated photonics platforms, limiting scalable fabrication of qubit-based devices. Here, we present a scalable approach toward CMOS-compatible telecom qubits by using erbium-doped titanium dioxide thin films grown atop silicon-on-insulator substrates. From this heterostructure, we have fabricated one-dimensional photonic crystal cavities demonstrating quality factors in excess of 5 × 104 and corresponding Purcell-enhanced optical emission rates of the erbium ensembles in excess of 200. This easily fabricated materials platform represents an important step toward realizing telecom quantum memories in a scalable qubit architecture compatible with mature silicon technologies.