Quantum Networking & Communications: Quantum Internet & Entanglement
Quantum internet news: quantum communications, quantum repeaters, entanglement distribution, quantum teleportation. Network architecture updates.
Quantum networking connects distant quantum processors via entanglement distribution, enabling distributed quantum computing, provably secure communications, and quantum sensor arrays.
India's Quantum Networking and Communications Initiatives
India's National Quantum Mission includes quantum communication as a major vertical with specific deliverables: satellite-based secure quantum communications between ground stations over 2000 kilometers; long-distance secure quantum communications with other countries; inter-city quantum key distribution over 2000 km; and multi-node quantum networks with quantum memories.
The IITM C-DOT Samgnya Technologies Foundation at IIT Madras serves as the Thematic Hub on Quantum Communication. Established in partnership with the Centre for Development of Telematics (C-DOT), the hub focuses on quantum cryptography, post-quantum security, QKD networks, quantum memory, quantum repeaters, and satellite-enabled quantum communication.
ISRO plans satellite-based quantum communication missions to demonstrate space-based quantum links. The Society for Applied Microwave Electronics Engineering & Research (SAMEER) in Mumbai develops indigenous QKD systems. The Centre for Development of Telematics (C-DOT) integrates quantum communication with national telecom infrastructure.
The NQM targets operational quantum communication networks connecting major Indian cities, with potential applications in government secure communications, financial transaction security, and defense applications.
quantum-computingQuantum Communication Secured by Choosing Measurement Basis Offers Ultimate Privacy
Scientists have developed a novel protocol for one-way quantum secure direct communication, utilising the choice of measurement basis as the secret key. Santiago Bustamante and Boris A. Rodríguez, both from Universidad de Antioquia, alongside Elizabeth Agudelo of TU Wien, demonstrate a system where information is encoded and decoded through measurements performed in either the computational or Hadamard basis. This research is significant because it establishes information-theoretic security against BB84-symmetric attacks using finite ensembles of entangled pairs and a public channel. Importantly, the protocol requires no local unitary operations by the receiver, making it particularly suitable for practical implementation in network configurations such as star networks. This research addresses the fundamental question of distinguishing ensembles described by identical compressed density operators and introduces a method for encoding and decoding classical information through measurements in either the computational or Hadamard basis. Employing quantum wiretap channel theory, the study rigorously assesses the secure net bit rates and certifies the information-theoretic security of various implementations against BB84-symmetric attacks. A key advantage of this model is the elimination of local unitary operations required by the receiver, making it particularly suitable for practical implementation in star network configurations. The work builds upon the concept of finite ensembles of entangled EPR pairs, each shared between two parties, Alice and Bob, and explores how local measurements influence the transmission of a single bit of information. Researchers define a compressed density operator as the state of an average entity within an ensemble, acknowledging that this operator may not fully capture all information about the ensemble’s preparation. By measuring qubits in either the computational or Hadamard basis, Alice and Bob induce correlated collapses in their res
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quantum-computingNu Quantum Opens Trapped-Ion Quantum Networking Laboratory in Cambridge - HPCwire
Nu Quantum Opens Trapped-Ion Quantum Networking Laboratory in Cambridge HPCwire
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quantum-computingNu Quantum Opens Trapped-Ion Networking Laboratory in Cambridge
Nu Quantum Opens Trapped-Ion Networking Laboratory in Cambridge Nu Quantum has announced the opening of a new trapped-ion networking laboratory in Cambridge, UK, marking the first dedicated industrial R&D facility for distributed trapped-ion quantum computing in Europe. The state-of-the-art facility doubles the company’s existing research infrastructure and serves as the primary testbed for its Entanglement Fabric roadmap. The lab is designed to prove the company’s Qubit-Photon Interface (QPI) technology with trapped-ion qubits, transitioning from theoretical modeling to in-house experimental validation of modular, multi-node quantum architectures. The technical core of the new facility is the advancement of Nu Quantum’s QPI, which utilizes optical microcavity technology to enhance the interaction between stationary qubits and flying photons. These interfaces employ nanostructured mirrors with active stabilization—achieving cavity length control with a precision of <5 picometres—to ensure resonance with specific qubit wavelengths. By integrating these microcavities into custom-built ion traps, the system facilitates high-rate, high-fidelity entanglement links between discrete quantum processing units (QPUs). This hardware-agnostic approach is designed to interconnect clusters of commercial processors into a distributed fabric, aiming to exceed current state-of-the-art remote entanglement rates and fidelities. The expansion follows Nu Quantum’s $60 million Series A funding round, the largest for a pure-play quantum networking company globally. The investment supports a growth phase focused on recruiting specialist Atomic, Molecular, and Optical (AMO) physics talent and expanding international operations. The laboratory integrates a specialized laser suite with wavelength stabilization developed in partnership with the National Quantum Computing Centre (NQCC). Collaborative efforts also involve the University of Sussex, Cisco, and Infineon Technologies, the lat
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quantum-computingTheory of quantum error mitigation for non-Clifford gates
AbstractQuantum error mitigation techniques mimic noiseless quantum circuits by running several related noisy circuits and combining their outputs in particular ways. How well such techniques work is thought to depend strongly on how noisy the underlying gates are. Weakly-entangling gates, like $R_{ZZ}(\theta)$ for small angles $\theta$, can be much less noisy than entangling Clifford gates, like CNOT and CZ, and they arise naturally in circuits used to simulate quantum dynamics. However, such weakly-entangling gates are non-Clifford, and are therefore incompatible with two of the most prominent error mitigation techniques to date: probabilistic error cancellation (PEC) and the related form of zero-noise extrapolation (ZNE). This paper generalizes these techniques to non-Clifford gates, and comprises two complementary parts. The first part shows how to effectively transform any given quantum channel into (almost) any desired channel, at the cost of a sampling overhead, by adding random Pauli gates and processing the measurement outcomes. This enables us to cancel or properly amplify noise in non-Clifford gates, provided we can first characterize such gates in detail. The second part therefore introduces techniques to do so for noisy $R_{ZZ}(\theta)$ gates. These techniques are robust to state preparation and measurement (SPAM) errors, and exhibit concentration and sensitivity—crucial statistical properties for many experiments. They are related to randomized benchmarking, and may also be of interest beyond the context of error mitigation. We find that while non-Clifford gates can be less noisy than related Cliffords, their noise is fundamentally more complex, which can lead to surprising and sometimes unwanted effects in error mitigation. Whether this trade-off can be broadly advantageous remains to be seen.Featured image: An illustration of probabilistic error cancellation (PEC) generalized to $R_{ZZ}$ gates with a non-Clifford angle. The gate noise can be accurate
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quantum-computingScientists Report Deterministic Entanglement-Assisted Quantum Communication Over 20-km Fiber Channel
Insider Brief Researchers experimentally demonstrated deterministic entanglement-assisted quantum communication over 20.121 km of optical fiber, extending dense coding from laboratory-scale tests to metropolitan-scale distances. The work uses an improved continuous-variable quantum dense coding scheme that independently transmits entangled states and local oscillator beams to reduce fiber noise and prevent decoding with classical coherent states alone. Measurements show higher signal-to-noise ratios and increased channel capacity than classical communication across long fiber links, particularly at larger average photon numbers. Schematic of the experimental setup for continuous-variable entanglement-assisted quantum comumication. (Xiaolong Su et al.) PRESS RELEASE — Entanglement-assisted quantum communication has substantial advantages in surpassing the power of classical communication by utilizing the entangled state. As a typical entanglement-assisted quantum communication encoding scheme, quantum dense coding enables two communication parties to enhance the channel capacity with the shared quantum entanglement. In continuous-variable quantum dense coding, the classical signals are encoded on both amplitude and phase quadratures of one entangled beam. Owing to the deterministic advantage in the generation and detection of continuous-variable entangled states, the combination of continuous-variable quantum dense coding enables the implementation of deterministic entanglement-assisted quantum communication. Since the first experimental demonstration of quantum dense coding with entangled photon pairs, it has been experimentally demonstrated in several physical systems, including optical system, nuclear magnetic resonance system, and atomic system. However, most demonstrations of entanglement-assisted quantum communication with dense coding still remain in proof-of-principle experiments. The implementation of quantum dense coding in practical fiber channels is of gr
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quantum-computingInternational Conference on Quantum Communication and Security
International Conference on Quantum Communication and Security Acronym: ICQCSDates: Monday, March 16, 2026 to Friday, March 20, 2026Web page: https://icqcs.sciencesconf.org/Registration deadline: Sunday, March 1, 2026Submission deadline: Sunday, March 1, 2026Tags: quantum cryptographyQKDquantum networkspost-quantum cryptographyICQCS 2026 is a five-day conference organized by MSCA QSI and DIM QuanTiP dedicated to quantum-safe communications, explicitly bringing together communities that are too often split across venues: 🔹 Post-quantum cryptography (PQC) 🔹 QKD theory & protocols 🔹 Experimental QKD + network integration …plus beyond-QKD quantum cryptography and quantum networks, with a program mixing keynote-tutorials, invited talks, posters, and an industry session. 📍 Paris (Campus des Cordeliers) 📅 March 16–20, 2026 📝 Free participation (registration mandatory) 🖼️ Posters: everyone is welcome to present! 🎙️ Speakers listed on the conference website include Rotem Arnon, Hugues de Riedmatten, Martin Albrecht, Giulio Malavolta, Boris Korzh, Qiang Zhang, and others. If you’re working anywhere near PQC, QKD, quantum networks, or quantum security, ICQCS is a unique chance to learn directly from leading researchers across these closely connected areas—and to connect with people bridging theory, protocols, and real-world implementations! Log in or register to post comments
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quantum-computingInternational Conference on Quantum Communication and Security ICQCS 2026
International Conference on Quantum Communication and Security ICQCS 2026 Acronym: ICQCSDates: Monday, March 16, 2026 to Friday, March 20, 2026Web page: https://icqcs.sciencesconf.org/Registration deadline: Sunday, March 1, 2026Submission deadline: Sunday, March 1, 2026Tags: quantum cryptographyQKDquantum networkspost-quantum cryptographyICQCS 2026 is a five-day conference organized by MSCA QSI and DIM QuanTiP dedicated to quantum-safe communications, explicitly bringing together communities that are too often split across venues: 🔹 Post-quantum cryptography (PQC) 🔹 QKD theory & protocols 🔹 Experimental QKD + network integration …plus beyond-QKD quantum cryptography and quantum networks, with a program mixing keynote-tutorials, invited talks, posters, and an industry session. 📍 Paris (Campus des Cordeliers) 📅 March 16–20, 2026 📝 Free participation (registration mandatory) 🖼️ Posters: everyone is welcome to present! 🎙️ Speakers listed on the conference website include Rotem Arnon, Hugues de Riedmatten, Martin Albrecht, Giulio Malavolta, Boris Korzh, Qiang Zhang, and others. If you’re working anywhere near PQC, QKD, quantum networks, or quantum security, ICQCS is a unique chance to learn directly from leading researchers across these closely connected areas—and to connect with people bridging theory, protocols, and real-world implementations! Log in or register to post comments
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quantum-computingPhD Projects in Theoretical Quantum Optics and Quantum Information at he Niels Bohr Institute
PhD Projects in Theoretical Quantum Optics and Quantum Information at he Niels Bohr Institute Application deadline: Sunday, March 15, 2026Research group: Theoretical quantum optics group at the Niels Bohr InstituteTheoretical quantum optics group at the Niels Bohr InstituteEmployer web page: Theoretical Quantum Optics GroupJob type: PhDTags: quantum opticsQuantum theoryquantum informationThe Niels Bohr Institute invites applicants for two PhD fellowships in Theoretical Quantum Optics and Quantum Information. The projects will be part of the theoretical quantum optics group and the Center for Hybrid quantum Networks (Hy-Q). The starting date is (expected to be) 1 September 2026 or as soon as possible thereafter. An earlier starting date may also be a possibility. The projects Two different projects are available Quantum Internet technology. This project will be part of the Quantum Internet Alliance (QIA), a joint European network aiming at bulding the world’s first quantum internet protype within the duration of the Ph.D. project. The successful candidate will develop physical models of the system being built with the aim of predicting and optimizing its performance. In addition the project will develop general theories for quantum internet technologies and methods for describing them. Scalable quantum information processing based on quantum dots. The projects aims at developing theories for how to implement quantum information processing with quantum dots strongly coupled to light and will be a collaboration with experimentalists at the Niels Bohr Institute, Ruhr-Universität Bochum and the University of Basel. The goal is to both develop concrete proposals for experiments which can be implemented in the near future and long term architectures for quantum information processors. Who are we looking for? We are looking for candidates within the field of Physics, Quantum Information Processing or related areas. Applicants can have a background f
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quantum-computingNu Quantum opens trapped‑ion quantum networking laboratory in Cambridge - New Electronics
Nu Quantum opens trapped‑ion quantum networking laboratory in Cambridge New Electronics
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quantum-computingBeyond Wigner: Non-Invertible Symmetries Preserve Probabilities
--> Quantum Physics arXiv:2602.07110 (quant-ph) [Submitted on 6 Feb 2026] Title:Beyond Wigner: Non-Invertible Symmetries Preserve Probabilities Authors:Thomas Bartsch, Yuhan Gai, Sakura Schafer-Nameki View a PDF of the paper titled Beyond Wigner: Non-Invertible Symmetries Preserve Probabilities, by Thomas Bartsch and 2 other authors View PDF Abstract:In recent years, the traditional notion of symmetry in quantum theory was expanded to so-called generalised or categorical symmetries, which, unlike ordinary group symmetries, may be non-invertible. This appears to be at odds with Wigner's theorem, which requires quantum symmetries to be implemented by (anti)unitary -- and hence invertible -- operators in order to preserve probabilities. We resolve this puzzle for (higher) fusion category symmetries $\mathcal{C}$ by proposing that, instead of acting by unitary operators on a fixed Hilbert space, symmetry defects in $\mathcal{C}$ act as isometries between distinct Hilbert spaces constructed from twisted sectors. As a result, we find that non-invertible symmetries naturally act as trace-preserving quantum channels. Crucially, our construction relies on the symmetry category $\mathcal{C}$ being unitary. We illustrate our proposal through several examples that include Tambara-Yamagami, Fibonacci, and Yang-Lee as well as higher categorical symmetries. Comments: Subjects: Quantum Physics (quant-ph); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th); Quantum Algebra (math.QA) Cite as: arXiv:2602.07110 [quant-ph] (or arXiv:2602.07110v1 [quant-ph] for this version) https://doi.org/10.48550/arXiv.2602.07110 Focus to learn more arXiv-issued DOI via DataCite (pending registration) Submission history From: Sakura Schafer-Nameki [view email] [v1] Fri, 6 Feb 2026 19:00:00 UTC (488 KB) Full-text links: Access Paper: View a PDF of the paper titled Beyond Wigner: Non-Invertible Symmetries Pre
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quantum-computingQuantum Cryptography’s Arithmetic Boost Promises More Secure Communications Networks
Researchers investigating continuous variable quantum key distribution (CVQKD) reconciliation protocols have focused on optimising the sharing of secure keys between parties. Rávilla R. S. Leite, Juliana M. de Assis, and Micael A. Dias, alongside Francisco M. de Assis and colleagues, present a detailed analysis of Arithmetic Reconciliation, a protocol notable for its reduced complexity and improved performance at low signal-to-noise ratios. Their work, detailed in this paper, establishes realistic reconciliation efficiencies through mutual information estimation and key sequence matching rates of 0.83 and 0.92. These findings demonstrate the feasibility and potential of Arithmetic Reconciliation for practical CVQKD systems, offering a promising pathway towards enhanced secure communication. Quantization efficiency is estimated for binary-input-continuous-output channels retaining soft information for decoding, achieving efficiencies exceeding 0.95 at low signal-to-noise ratios. Simulation results further validate the entire reconciliation procedure, utilising a Low Density Parity Check (LDPC) code across a signal-to-noise ratio range of 2 to 7 dB, dependent on the code rate employed. Unlike discrete variable QKD, continuous variable QKD benefits from easier implementation with existing telecommunications equipment and the potential for room temperature operation, making it a more practical solution for secure communication networks. The core innovation lies in the mapping of continuous random variables to their Cumulative Distribution Function, projecting them onto the unit interval and simplifying the quantization process. This approach leverages the intrinsic randomness of quantum measurements, eliminating the need for sophisticated decoding procedures or external random number generators, and resulting in statistically well-behaved bit strings for key extraction. This mapping facilitated quantization and enabled a binary representation of the variable through its
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quantum-computingQuantum Advice Cuts Communication Needed to Wake up Networks of Nodes
Researchers are tackling the fundamental distributed wake-up problem, investigating how to efficiently activate sleeping nodes in a network given limited initial knowledge. Peter Robinson and Ming Ming Tan, both from Augusta University, present novel upper and lower bounds on message complexity within the routing model. Their work establishes an algorithm achieving a message complexity of with high probability, utilising bits of advice per node and surpassing previous limitations in dense graphs. Complementing this, Robinson and Tan demonstrate a lower bound of for wake-up without advice, a result with broad implications as many core graph problems, including single-source broadcast and spanning tree construction, inherently rely on solving wake-up first. This research addresses a fundamental challenge in network communication: efficiently waking up all nodes in a network after an adversary activates only a subset. The work introduces a novel distributed advising scheme that, given α bits of advice per node, successfully wakes up all nodes with a message complexity of O q n3 2max{⌊(α−1)/2⌋,0} · log n with high probability. This result surpasses the Ω n2 2α barrier previously known for classical algorithms in sufficiently dense graphs, demonstrating a substantial improvement in efficiency. The core of this advancement lies in leveraging quantum communication capabilities to minimize the number of messages required for wake-up. Researchers demonstrate that by utilising α bits of advice per node, the algorithm achieves a message complexity scaling with the cube of the number of nodes, n, and a logarithmic factor. This contrasts sharply with classical approaches, which face inherent limitations in message efficiency. Complementing this algorithmic achievement is a rigorous lower bound proof, establishing that wake-up requires a quantum message complexity of Ω n3/2 even without any advice. This bound holds regardless of the allotted computation time, highlighting a funda
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quantum-computingQuantum Networks’ Errors Tackled with New Noise-Reduction Technique
Errors represent a substantial obstacle to realising practical quantum computation. Maria Gragera Garces from the University of Edinburgh, alongside collaborators, investigates Zero Noise Extrapolation (ZNE) as a means of tackling these errors specifically within distributed quantum systems. Their research compares applying ZNE globally, before circuit partitioning, with a local approach where ZNE is applied to individual sub-circuits. By modelling distributed computation via noisy teleportation between quantum processing units, the team evaluated both strategies across different system sizes and noise profiles. The findings demonstrate that global ZNE offers better scalability, achieving error reductions of up to across six quantum processing units, and surprisingly reveal that increasing their number can actually improve mitigation despite increased communication demands. This work therefore illuminates crucial trade-offs in distributed quantum error mitigation and provides valuable insight into optimising circuit design and partitioning strategies for future quantum networks. The research addresses a gap in understanding how error mitigation techniques, effective on standalone quantum processors, behave when applied to distributed systems. Experiments were conducted using three algorithms from the MQT Bench suite: Greenberger-Horne-Zeilinger (GHZ) state preparation, Deutsch-Jozsa (DJ), and W state preparation, providing a diverse assessment across varying circuit structures and computational patterns. Local gates were subjected to a base noise level, denoted as pLocal, representing the probability of a qubit error during gate operation under a depolarizing channel model. Non-local operations, simulating communication between quantum processing units, experienced amplified noise, pcomm = α · pLocal, where α ranged from 1.0 to 1.2 to represent elevated communication error rates. The study systematically varied pLocal from 0.001 to 0.02 and tested partition counts r
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quantum-computingLaser‑written glass chip pushes quantum communication toward practical deployment
As quantum computers continue to advance, many of today's encryption systems face the risk of becoming obsolete. A powerful alternative—quantum cryptography—offers security based on the laws of physics instead of computational difficulty. But to turn quantum communication into a practical technology, researchers need compact and reliable devices that can decode fragile quantum states carried by light.
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quantum-computingQuantum Teleportation Between Cities Moves Closer with New Hardware Blueprint
Scientists at Delft University of Technology, including Soubhadra Maiti, Guus Avis and Sounak Kar, have delved into the intricate requirements for teleportation within an intercity quantum network. Their research, co-led by Stephanie Wehner, addresses the hardware prerequisites needed to achieve a fidelity level that matches classical limits in such networks. By formulating optimisation problems and deriving analytical expressions based on simplified noise models, they explore how different hardware configurations can impact teleportation fidelity and rates. The study highlights the potential for current technology to support metropolitan-scale teleportation but identifies necessary enhancements for intercity applications. Their work not only advances our understanding of quantum communication networks but also provides a roadmap for future technological developments in this field. Analytical modelling of fidelity and rate for intercity quantum teleportation reveals significant challenges to practical implementation Scientists have identified the minimal hardware improvements needed to achieve quantum teleportation across intercity distances. This work details the requirements for an end-to-end expected teleportation fidelity of 2/3, representing the classical limit for reliable quantum communication. Researchers formulated the problem as an optimisation task, using hardware parameters as variables to determine the necessary device capabilities. Closed-form analytical expressions were derived for teleportation fidelity and rate, accounting for heterogeneous hardware including quantum repeater chains with memory limitations. These derivations are based on the timing of link generation within both metropolitan networks and the long-distance backbone, and were validated using simulations on the NetSquid platform. The resulting analytical expressions allow for efficient exploration of potential hardware configurations without relying on computationally intensive simulat
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quantum-computingQuantum Networks Overcome Fragility to Synchronise Learning across Distances
Researchers are tackling the significant hurdles to realising robust distributed quantum neural networks (DQNNs) over existing internet infrastructures. Kuan-Cheng Chen from Imperial College London, Samuel Yen-Chi Chen from Brookhaven National Laboratory, and Mahdi Chehimi from American University of Beirut, alongside Burt et al., present a novel Consensus-Entanglement-Aware Scheduling (CEAS) framework that simultaneously optimises consensus protocols and manages entanglement. This co-design approach enables robust synchronous training across distributed processors by integrating fidelity-weighted aggregation and decoherence-aware entanglement scheduling, effectively treating entangled Bell pairs as limited resources. The resulting architecture not only offers theoretical convergence guarantees under varying noise conditions but also demonstrates a 10-15 percentage point accuracy improvement over existing methods when subjected to coordinated attacks, representing a crucial step towards scalable, fault-tolerant distributed machine learning. These challenges stem from the fragile nature of entanglement and the demanding synchronisation requirements of distributed learning. Researchers introduce a Consensus, Entanglement-Aware Scheduling (CEAS) framework that co-designs quantum consensus protocols with adaptive entanglement management to enable robust synchronous training across distributed quantum processors. CEAS integrates fidelity-weighted aggregation, where parameter updates are weighted by quantum Fisher information to suppress noisy contributions. Fidelity-weighted consensus and dynamic entanglement brokerage for distributed quantum neural network training Scientists are developing a consensus-driven, entanglement-aware scheduling framework to enable efficient training of distributed quantum neural networks (DQNNs). The framework integrates fidelity-weighted consensus voting with dynamic entanglement brokerage, allowing each node to evaluate the quality of its
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quantum-computingQuantum Communication Breaks 11km Barrier Using Free Space and Fibre Optics
Researchers are pioneering robust communication methods for emerging space-ground networks, and a new study demonstrates a significant advance in quantum secure direct communication. Ze-Zhou Sun, Yuan-Bin Cheng, and Yu-Chen Liu, all from the Beijing Academy of Quantum Information Sciences at Tsinghua University, alongside Guo et al., have successfully implemented phase-encoded quantum key distribution over a combined 11.4km heterogeneous free-space and fibre link. This work overcomes long-held limitations regarding the suitability of phase encoding for free-space transmission, previously favoured for fibre optics, and establishes its viability for cross-medium integration. By achieving stable operation over 1400m of urban free-space with high interference visibility and low bit error rates, and seamlessly coupling this to a 10km fibre link, the team showcases a pathway towards simplified and compatible quantum networks, potentially extending to satellite-to-ground distances exceeding 30km. Turbulence compensation enables robust free-space to fibre quantum key distribution Scientists have demonstrated phase-encoded quantum communication over a 1.4km urban free-space channel, a feat previously considered impractical due to atmospheric disturbances. This work overcomes long-standing challenges in free-space quantum networking, establishing a viable pathway for integrating quantum signals across different transmission media. The system maintained stable operation for nearly one hour, achieving 99.07% interference visibility and an average quantum bit error rate of 2.38%, showcasing remarkable resilience to environmental factors. Crucially, the free-space quantum states were directly coupled into a 10km optical fiber, confirming seamless interoperability between free-space and fiber networks. This achievement hinges on effective compensation for turbulence-induced phase drifts between successive picosecond pulses, a significant technical hurdle in free-space quantum comm
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quantum-computingQuantum Channel Transposition Now Possible with Just One Measurement, Research Confirms
Researchers are increasingly focused on understanding how to physically realise transformations of quantum channels, such as transposition and the adjoint, given only access to an unknown channel. Chengkai Zhu, Ziao Tang, and Guocheng Zhen, all from the Thrust of Artificial Intelligence, Information Hub at The Hong Kong University of Science and Technology (Guangzhou), alongside Yinan Li, Ge Bai, and Xin Wang, have established a clear hierarchy of physical realisability for these transformations. Their work is significant because it demonstrates that while the transpose can be implemented exactly with a single query, the complex conjugate and adjoint transformations are fundamentally more difficult to achieve via completely positive supermaps. The team circumvented this impossibility for the complex conjugate by developing an optimal virtual protocol based on quasi-probability decomposition, and importantly, they propose a new protocol for estimating expectation values from the Petz recovery map with improved efficiency. This work establishes a clear hierarchy for physically implementing transformations of unknown quantum channels, specifically addressing the transpose, complex conjugate, and adjoint. Researchers demonstrate a probabilistic method for precisely implementing the transpose transformation with a single query to the unknown channel, a result with implications for quantum information processing. The study rigorously proves that direct physical implementation of the complex conjugate and adjoint transformations is impossible using conventional quantum supermaps, even with probabilistic approaches. To circumvent this fundamental limitation, the team designed a novel “virtual protocol” leveraging quasi-probability decomposition, effectively enabling estimation of these otherwise unrealizable transformations. This virtual protocol is proven optimal in terms of the diamond norm, a measure of map similarity. A key application of this research lies in improved
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quantum-computingMinimising the number of edges in LC-equivalent graph states
AbstractGraph states are a powerful class of entangled states with numerous applications in quantum communication and quantum computation. Local Clifford (LC) operations that map one graph state to another can alter the structure of the corresponding graphs, including changing the number of edges. Here, we tackle the associated edge-minimisation problem: finding graphs with the minimum number of edges in the LC-equivalence class of a given graph. Such graphs are called minimum edge representatives (MER) and are crucial for minimising the resources required to create a graph state. We leverage Bouchet's algebraic formulation of LC-equivalence to encode the edge-minimisation problem as an integer linear program (EDM-ILP). We further propose a simulated annealing (EDM-SA) approach guided by the local clustering coefficient for edge minimisation. We identify new MERs for graph states with up to 16 qubits by combining EDM-SA and EDM-ILP. We extend the ILP to weighted-edge minimisation, where each edge has an associated weight, and prove that this problem is NP-complete. Finally, we employ our tools to minimise the resources required to create all-photonic generalised repeater graph states using fusion operations.Featured image: An example of how edge-minimisation works. Both graph states are local Clifford equivalent.Popular summaryOur algorithms for edge-minimisation find LC-equivalent graph states (locally equivalent graphs) that have minimum number of edges to a given graph state. This allows for the simplification of the required graph, which can be leveraged to save resources required for graph state creation.► BibTeX data@article{Sharma2026minimisingnumberof, doi = {10.22331/q-2026-02-09-2001}, url = {https://doi.org/10.22331/q-2026-02-09-2001}, title = {Minimising the number of edges in {LC}-equivalent graph states}, author = {Sharma, Hemant and Goodenough, Kenneth and Borregaard, Johannes and Rozp{\k{e}}dek, Filip and Helsen, Jonas}, journal = {{Quantum}}, issn =
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quantum-computingMicroCloud Hologram (NASDAQ: HOLO) Advances Quantum Communication with Brownian State Breakthrough
MicroCloud Hologram Inc. (NASDAQ: HOLO) has achieved a breakthrough in quantum communication, developing a transmission scheme for GHZ and W states utilizing a novel Brownian state quantum channel. Announced February 6, 2026, the Shenzhen-based technology service provider has established an efficient mechanism for transmitting multi-particle entangled states – a crucial step towards practical quantum networks. This innovation hinges on leveraging the unique characteristics of a special four-particle entangled state, the Brownian state, to forge stable quantum links. According to the company, this scheme “not only perfects the theoretical system of quantum teleportation but also provides new technical paths for information transmission in large-scale quantum systems,” paving the way for more robust and scalable quantum communication technologies. GHZ & W State Transmission via Brownian State Quantum Channels MicroCloud Hologram Inc. This development establishes “an efficient transmission mechanism for multi-particle entangled states,” according to the company, by constructing specialized quantum channels and measurement systems. Unlike conventional methods, the scheme leverages the unique properties of a Brownian state – a specific four-particle entangled state – to create stable quantum links for information transfer. The technical core of this innovation lies in the application of quantum Fourier transform for quantum state projection measurement and the precise orchestration of quantum gate operations. Researchers meticulously designed the sequence of these gates to reconstruct quantum states at the receiving end, perfecting the theoretical underpinnings of quantum teleportation and opening avenues for large-scale quantum systems. When transmitting a three-particle GHZ state, the sender performs a joint measurement, establishing “quantum correlation between the transmission state and the channel state.” Crucially, specially designed measurement devices ensure
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