Nanowerk September 5, 2022 In two-layered molybdenum disulfide, excitation with light produces two different types of electron-hole pairs: intralayer pairs, in which the electron and hole are localized in the same layer of the material, and interlayer pairs, whose hole and electron are in different layers and are therefore spatially separate from one another. The intralayer pairs interact strongly with light. The interlayer excitons are much dimmer but can be shifted to different energies and therefore allow researchers to adjust the absorbed wavelength. They exhibit very strong, nonlinear interactions with one another which play an essential role in many of […]
Tag Archives: Quantum communication
Physicists entangle more than a dozen photons efficiently
Phys.org August 25, 2022 Optical photons represent ideal qubit carriers. However, the most successful technique so far for creating photonic entanglement is inherently probabilistic and, therefore, subject to severe scalability limitations. Researchers in Germany generated up to 14 entangled photons in a defined way and with high efficiency by using a single atom to emit the photons and interweave them in a very specific way, they placed a rubidium atom at the center of an optical cavity and triggered the emission of a photon that is entangled with the quantum state of the atom. By repeating the process several times […]
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 […]
What quantum information and snowflakes have in common, and what we can do about it
Science Daily June 15, 2022 Transducing quantum signals between disparate regimes of the electro-magnetic spectrum remains an outstanding goal. Many remote entanglement protocols require multiple qubit gates both preceding and following the upconversion of the quantum state, and thus an ideal transducer should impart minimal backaction on the qubit. A team of researchers in the US (University of Colorado, NIST) demonstrated readout of a superconducting transmon qubit through a low-backaction electro-optomechanical transducer. The modular nature of the transducer and circuit quantum electrodynamics system used in this work enabled complete isolation of the qubit from optical photons, and the backaction on […]
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
Researchers in Sweden develop light emitter for quantum circuits
Phys.org May 10, 2021 For photons to deliver qubits on-demand in quantum systems, they need to be emitted in a deterministic, rather than probabilistic, fashion. An international team of researchers (Sweden, the Netherlands) has developed a process to harness the single-photon-emitting properties of hexagonal boron nitride (hBN) integrating it with silicon nitride waveguides to emit photons on-demand at room temperature. Their process precisely positions light-particles emitters in an integrated photonic circuit. In a hybrid approach, the team built the photonic circuits with respect to the quantum sources locations using a series of steps involving electron beam lithography and etching, while […]
Researchers realize coherent storage of light over one hour
Phys.org May 10, 2021 One solution for remote quantum communication lies in quantum memories: photons are stored in long-lived quantum memory (quantum flash drive) and then quantum information is transmitted by the transportation of the quantum memory. Researchers in China adopted the spin wave atomic frequency comb (AFC) protocol in a ZEFOZ field (ZEFOZ-AFC) method to implement long-lived storage of light signals. They used dynamical decoupling to protect spin coherence and extend storage time. They demonstrated coherent storage of light in an atomic frequency comb memory over 1 hour with a fidelity of 96.4%. The study meets the basic requirements […]
When memory qubits and photons get entangled
Phys.org March 15, 2021 The implementation of efficient interfaces between photons and stationary qubits is crucial for the rate of information transfer and the scalability of a quantum network. With their experimental setup researchers in Germany demonstrated quantum entanglement between a stationary qubit and a photon out of an optical fiber resonator. They showed the generation of deterministic entanglement at a high fidelity of 90.1(17)% between a trapped Yb ion and a photon emitted into the resonator mode. And achieved a success probability for generation and detection of entanglement for a single shot of 2.5 × 10−3 resulting in 62 Hz entanglement rate. […]
Quantum effects help minimize communication flaws
EurekAlert February 10, 2021 Both quantum computation and quantum communication are strongly deteriorated because quantum superposition state can be destroyed, or entanglement between two or more quantum particles can be lost. An international team of researchers (Austria, UK, Hong Kong, Switzerland, France, Canada) experimentally and numerically compare different ways in which two trajectories through a pair of noisy channels can be superposed. They observed that, within the framework of quantum interferometry, the use of channels in series with quantum-controlled operations generally yields the largest advantages. The results contribute to clarify the nature of these advantages in experimental quantum-optical scenarios and […]
Long-distance and secure quantum key distribution (QKD) over a free-space channel
Phys.org January 25, 2021 Measurement-device-independent quantum key distribution (MDI-QKD) protocol can help in closing all loopholes on detection at once. It has only been successfully implemented using fiber optics. To implement the protocol across free-space channels two main challenges need to be addressed. One is to reduce the gap between theory and practice of QKD, and the other one is to extend the distance of QKD. Researchers in China have developed a robust adaptive optics system – high-precision time synchronization and frequency locking between independent photon sources located far apart to realize free-space MDI-QKD over a 19.2-km urban atmospheric channel. […]