Phys.org April 7, 2022 Spin can be also used as the medium for quantum communication by transferring quantum information with light. But the process of transferring information to the spin of extremely small electrons is challenging and must be performed efficiently. An international team of researchers (Japan, Canada, Germany) has realized the world’s first GaAs gate-controlled quantum dot circuit on a (110)-oriented surface that promises to increase photon-electron spin conversion efficiency. This has the effect of encoding quantum information from incident photons into the electron spins. Because of the way the hole interacts with the GaAs crystal lattice, the g-factor, […]
Category Archives: Quantum communication
Qubits: Developing long-distance quantum telecommunications networks
Science Daily March 22, 2022 An international team of researchers (Switzerland, France) has stored a qubit for 20 milliseconds in crystals doped with europium capable of absorbing light and then re-emitting it. They managed to reach the 100-millisecond mark with a small loss of fidelity. The crystals were kept at -273,15°C, because beyond 10°C above this temperature, the thermal agitation of the crystal destroys the entanglement of the atoms. In theory, it would be enough to increase the duration of exposure of the crystal to radio frequencies, but for the time being, technical obstacles to their implementation over a longer […]
Single-photon source paves the way for practical quantum encryption
Phys.org March 23, 2022 Researchers in Australia have developed an on-demand way to generate photons with high purity in a scalable and portable system that operates at room temperature. They combined hexagonal boron nitride with a hemispherical solid immersion lens, which increases the source’s efficiency by a factor of six. They incorporated the single-photon source into a fully portable device that can perform QKD. They demonstrated that it could produce over ten million single photons per second at room temperature. The streamlined device is easier to use and much smaller than traditional optical table setups allowing the system to be […]
Twin-field quantum key distribution (QKD) across an 830-km fibre
Phys.org January 24, 2022 As the photons carrying signals cannot be amplified or relayed via classical optical techniques to maintain quantum security, the transmission loss of the channel limits its achievable distance. An international team of researchers (Spain, Japan, Canada, China, Russia) has designed an experimental QKD system that could tolerate a channel loss beyond 140 dB and obtain a secure distance of 833.8 km. Furthermore, the optimized four-phase twin-field protocol and set-up make its secure key rate more than two orders of magnitude greater than previous records over similar distances… read more. TECHNICAL ARTICLE 1 , Open Access 2
A nanoantenna for long-distance, ultra-secure communication
Phys.org November 16, 2021 Converting photon-based information to electron-based information are highly inefficient. To increase the efficiency of converting single photons into single electrons in gallium arsenide quantum dots an international team of researchers (Japan, Germany) designed a nanoantenna, consisting of ultra-small concentric rings of gold, to focus light onto a single quantum dot. It resulted in a voltage readout from their device enhancing photon absorption by a factor of up to 9. After illuminating a single quantum dot, most of the photogenerated electrons weren’t trapped there, instead accumulated in impurities or other locations in the device. Nevertheless, these excess […]
A superconducting silicon-photonic chip for quantum communication
Nanowerk November 1, 2021 A key element for achieving discrete-variable QKD is a single-photon detector. Researchers in China heterogeneously integrated, superconducting silicon-photonic chip. Harnessing the unique high-speed feature of the optical waveguide-integrated superconducting detector, they performed optimal Bell-state measurement (BSM) of time-bin encoded qubits generated from two independent lasers. The optimal BSM enables an increased key rate of measurement-device-independent QKD (MDI-QKD), which is immune to all attacks against the detection system and hence provides the basis for a QKD network with untrusted relays. Together with the time-multiplexed technique, they enhanced the sifted key rate by almost one order of magnitude. […]
Quantum holds the key to secure conference calls
EurekAlert June 6, 2021 Traditional quantum communication protocols consume pair-wise entanglement, which is suboptimal for distributed tasks involving more than two users. An international team of researchers (UK, Germany) has demonstrated quantum conference key agreement leveraging multipartite entanglement to efficiently create identical keys between N users with up to N-1 rate advantage in constrained networks. They distributed four-photon Greenberger-Horne-Zeilinger (GHZ) states, generated by high-brightness telecom photon-pair sources over optical fiber with combined lengths of up to 50 km and performed multiuser error correction and privacy amplification. Under finite-key analysis, they established 1.5 × 106 bits of secure key, which were […]
Folding 2D materials gives them new properties useful for quantum communications
Nanowerk May 24, 2021 The use of 2D materials for nonlinear optics are limited by intrinsically small light-matter interaction length and (typically) flat-lying geometries. Researchers in the UK arranged 2D sheets of tungsten (WS2) in a new way to create a 3D arrangement they called a nanomesh. Its unique characteristics are the result of the specific synthesis process they developed. Only light with energy larger than the energy gap can interact with the material in a useful way. If new energy levels are introduced inside this energy gap, the doubling of frequency of the light that passes through the material […]
Detecting photons transporting qubits without destroying quantum information
Phys.org March 25, 2021 Photons that carry qubits over long distances are easily deflected from their path in the air or absorbed in glass fibers—and suddenly, the quantum information is lost. An international team of researchers (Germany, Spain) has developed a physical protocol that can indicate whether the qubit is lost at intermediate stations of the quantum transmission. If this is the case, the transmitter can send the qubit again with significantly less delay than if the loss is noticed only at the receiving end. The protocol only detects the qubit photon and not measure it. They achieved a nondestructive […]
Nanofibers for quantum technologies at room temperature
Nanowerk February 18, 2021 The faithful mapping of information between matter and light can facilitate communication between distant quantum processing nodes. Strong interaction benefits from tightly confined light fields, as well as from many atoms interacting simultaneously with such fields. An international team of researchers (Austria, Germany Israel) realized efficient light-matter interface by gradually thinning an optical fiber down to a diameter of 200 nm, about 600 times narrower than its original width, and about a quarter of the optical wavelength guided by the fiber. Reaching these dimensions resulted in a unique optical field with more than 99% of the […]