Satellites may enable better quantum networks

Phys.org  February 10, 2023 Satellite-based quantum links have been proposed to extend the network domain for quantum communication. An international team of researchers (USA – Oak Ridge National Laboratory, University of Illinois, Singapore) developed a quantum communication system, suitable for realistic satellite-to-ground communication and executed an entanglement-based quantum key distribution (QKD) protocol achieving quantum bit-error rates (QBERs) below 2% in all bases. They demonstrated 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. They showed […]

Entangled atoms cross quantum network from one lab to another

Science Daily February 2, 2023 Trapped ions are one of the leading systems to build quantum computers and other quantum technologies. To link multiple such quantum systems, interfaces are needed through which the quantum information can be transmitted. An international team of researchers (Austria, USA – Georgetown University, Switzerland, France) has demonstrated an elementary quantum network of two atomic ions separated by 230 m. The ions were trapped in different buildings and connected with 520(2) m of optical fiber. At each network node, the electronic state of an ion was entangled with the polarization state of a single cavity photon; […]

New quantum computing architecture could be used to connect large-scale devices

Science Daily  January 5, 2023 Quantum information transfer between arbitrary nodes is generally mediated either by photons that propagate between them or by resonantly coupling nearby nodes. The utility is determined by the type of emitter, propagation channel and receiver. Conventional approaches involving propagating microwave photons have limited fidelity due to photon loss and are often unidirectional, whereas architectures that use direct resonant coupling are bidirectional in principle but can generally accommodate only a few local nodes. Researchers at MIT have demonstrated high-fidelity, on-demand, directional, microwave photon emission by using an artificial molecule comprising two superconducting qubits strongly coupled to […]

On-demand storage of photonic qubits at telecom wavelengths

Phys.org  December 6, 2022 Researchers in China processed a fiber-integrated quantum memory at telecom wavelengths based on a laser-written waveguide fabricated in an erbium-doped yttrium silicate. Both ends of the waveguide memory were directly connected with fiber arrays with a fiber-to-fiber efficiency of 51%. Storage fidelity of 98.3(1)% was obtained for time-bin qubits encoded with single-photon-level coherent pulses, which is far beyond the maximal fidelity that can be achieved with a classical measure and prepared strategy. This device featured high reliability and easy scalability, and it can be directly integrated into fiber networks, which could play an essential role in […]

Researchers achieve record entanglement of quantum memories

Phys.org  July 7, 2022 To fully use entanglement over long-distance quantum network links it is mandatory to know it is available at the nodes before the entangled state decays. An international team of researchers (Austria, Germany) demonstrated entanglement between two independently trapped single rubidium atoms generated over fibre links with a length up to 33 km. They generated atom–photon entanglement in two nodes located in buildings 400 m line-of-sight apart and to overcome high-attenuation losses in the fibres converted the photons to telecom wavelength using polarization-preserving quantum frequency conversion. The long fibres guided the photons to a Bell-state measurement setup in which […]

Chaining atoms together yields quantum storage

Phys.org  February 16, 2022 Researchers at Caltech have developed an approach for quantum storage that relies on nuclear spins oscillating collectively as a spin wave. This collective oscillation effectively chains up several atoms to store information. They utilized a qubit made from an ion of ytterbium and embedded the ion in a transparent crystal of yttrium orthovanadate (YVO4) and manipulated its quantum states via a combination of optical and microwave fields. The Yb qubit was used to control the nuclear spin states of multiple surrounding vanadium atoms in the crystal. A unique feature of this system is the pre-determined placement […]

Researchers reach quantum networking milestone in real-world environment

Phys.org  October 6, 2021 A team of researchers in the US (Oak Ridge National Laboratory, Stanford University, Purdue University) implemented flex-grid entanglement distribution in a deployed network connecting nodes in three distinct campus buildings time synchronizing via the Global Positioning System. They quantify the quality of the distributed polarization entanglement via log-negativity, which offers a generic metric of link performance in entangled bits per second. After demonstrating successful entanglement distribution for two allocations of their eight dynamically reconfigurable channels, they realized the first deployed fiber network demonstration of remote state preparation (RSP), a fundamental quantum communications protocol with utility for […]

A 15-user quantum secure direct communication network

Phys.org  September 23, 2021 Researchers in China have created a quantum direct secure communication (QSDC) network based on time–energy entanglement and sum-frequency generation with15 users. They found that fidelity of the entangled state shared by any two users is >97%, when any two users are performing QSDC over 40 km of optical fiber, the fidelity of the entangled state shared by them is still >95%, and the rate of information transmission could be maintained above 1 Kbp/s. The work demonstrates the feasibility of a proposed QSDC network for satellite-based long-distance and global QSDC in the future…read more. Open Access TECHNICAL ARTICLE   

Implementing a 46-node quantum metropolitan area network

Phys.org   September 30, 2021 To achieve a practical quantum network, we need to overcome several challenges including realizing versatile topologies for large scales, simple network maintenance, extendable configuration, and robustness to node failures. To this end, an international team of researchers (China, Germany) developed a field operation of a quantum metropolitan-area network with 46 nodes and showed that all these challenges can be overcome with cutting-edge quantum technologies. They used different topological structures and continuously ran the network for 31 months, by employing standard equipment for network maintenance with an extendable configuration. QKD pairing and key management was done with […]

Quantum networks in our future

Science Daily August 31, 2021 While components of the quantum Internet are under development, the control plane remains undefined. An international team of researchers (Canada, USA – industry) outline their vision for a software-defined quantum network that enables a flexible experimental platform for developing quantum applications for industry. The quantum Internet, like the classical Internet, will be a network of networks. Operation of an industrial quantum network is viewed as a networked control problem, and they propose a time-sensitive network control plane to enable a quantum software-defined network. Measurement-device-independent quantum key distribution is used as an example implementation since it […]