Phys.org April 15, 2024 Nonlocality is crucial for device-independent technologies like quantum key distribution and randomness generation. It quickly deteriorates in the presence of noise, and restoring nonlocal correlations requires additional resources incurring a significant resource overhead. An international team of researchers (Australia, France, USA – NIST, Boulder, CO) experimentally demonstrated that single copies of Bell-local states, incapable of violating any standard Bell inequality, could give rise to nonlocality after being embedded into a quantum network of multiple parties. They subjected the initial entangled state to a quantum channel that broadcast part of the state to two independent receivers and […]
Category Archives: Communications technology
The world is one step closer to secure quantum communication on a global scale
Phys.org March 25, 2024 An on-demand source of bright entangled photon pairs is needed for quantum key distribution (QKD) and quantum repeaters. The generation of such pairs is based on spontaneous parametric down-conversion (SPDC) in non-linear crystals. However, SPDC pair extraction efficiency is very limited when operating at near-unity fidelity. In principle quantum dots in photonic nanostructures can overcome this limit, but the devices with high entanglement fidelity have low pair extraction efficiency. An international team of researchers (Canada, the Netherlands, Sweden) has demonstrated a measured peak entanglement fidelity of 97.5% ± 0.8% and pair extraction efficiency of 0.65% from an InAsP […]
New type of tunable filter reveals the potential for terahertz wireless communications
Phys.org March 11, 2024 Researchers in Japan constructed a tunable Fabry–Perot interferometer (FPI) by controlling the effective refractive index of pitch-variable subwavelength gratings (PV-SWGs) that were incorporated into an FP cavity. The period of the PV-SWG could be varied to change the effective refractive index and shift the optical resonant frequency of the FPI. Compared with conventional methods that tune the optical resonance by adding fillers or deforming the cavity, the FPI obtained a higher transmission and quality factor (Q-factor) for the transmittance peak, and its resonant frequency could be shifted by simply stretching the PV-SWG. According to the researchers […]
Single sideband modulation technique can relax the bandwidth restriction
Phys.org September 26, 2023 The highest frequency achievable for microwave signals is limited by the bandwidths of optoelectronic devices. To maximize the microwave frequency with a limited bandwidth of a photodetector (PD) and relieve the bandwidth bottleneck, researchers in China proposed to generate microwave signals with the single sideband (SSB) format by beating a continuous wave (CW) light with an optical SSB signal. By simply adjusting the frequency difference between the CW light and the carrier of the optical SSB signal, the frequency of the generated microwave SSB signal was changed correspondingly. In the experiment, amplitude shift keying (ASK) microwave […]
Device offers long-distance, low-power underwater communication
MIT News September 6, 2023 Researchers at MIT have designed, evaluated, and implemented Van Atta Acoustic Backscatter (VAB), a technology that enables long-range, ultra-low-power networking in underwater environments. VAB is scalable underwater backscatter architecture that bridges recent advances in RF backscatter (Van Atta architectures) with ultra-low-power underwater acoustic networks. Their design introduces multiple innovations across the networking stack to overcome unique challenges that arise from the electro-mechanical properties of underwater backscatter and the challenging nature of low-power underwater acoustic channels. They implemented and evaluated their design in over 1,500 real-world experimental trials in a river and the ocean. In stationary […]
Researchers demonstrate high-fidelity transmission of information via novel electronic-optical system
Phys.org August 29, 2023 Free-space optical information transfer through diffusive media is critical in many applications but remains challenging due to random, unknown perturbations in the optical path. Researchers at UCLA demonstrated an optical diffractive decoder with electronic encoding to accurately transfer the optical information of interest through unknown random phase diffusers along the optical path. The model comprised a convolutional neural network-based electronic encoder and successive passive diffractive layers that were jointly optimized. After their joint training using deep learning, their hybrid model could transfer optical information through unknown phase diffusers, demonstrating generalization to new random diffusers. The model […]
New technique measures structured light in a single shot
Phys.org August 8, 2023 Orbital angular momentum (OAM) spectrum diagnosis is a fundamental building block for diverse OAM-based systems. Among others, the simple on-axis interferometric measurement can retrieve the amplitude and phase information of complex OAM spectra in a few shots. Yet, its single-shot retrieval remains elusive, due to the signal–signal beat interference inherent in the measurement. Researchers in Switzerland have introduced the concept of Kramers–Kronig (KK) receiver in coherent communications to the OAM domain, enabling rigorous, single-shot OAM spectrum measurement. They explained in detail the working principle and the requirement of the KK method and applied the technique to […]
Lights could be the future of the internet and data transmission
Phys.org July 25, 2023 The modulation characteristics of perovskite LEDs are not clear. An international team of researchers (UK, Switzerland) has developed a new approach for realizing fast perovskite photonic sources on silicon based on tailoring alkylammonium cations in perovskite systems. They showed the recombination behaviour of charged species at various carrier density regimes relevant for their modulation performance. By integrating a Fabry–Pérot microcavity on silicon, they demonstrated perovskite devices with efficient light outcoupling and achieved device modulation bandwidths of up to 42.6 MHz and data rates above 50 Mbps, with further analysis suggesting that the bandwidth may exceed gigahertz levels. According […]
Protecting light communication with random objects
Phys.org July 17, 2023 Researchers in the Netherlands have developed an optical communication system with two scattering layers to hide both the sender and receiver, by measuring the correlation of the intermediate speckle generated between the two layers. The binary message is modulated as spatially shaped wavefronts, and the high number of transmission modes of the scattering layers allowed for many uncorrelated incident wavefronts to send the same message, making it difficult for an attacker to intercept or decode the message and thus increasing secrecy. They collected 50,000 intermediate speckle patterns and analyzed their correlation distribution using the Kolmogorov-Smirnov (K-S) […]
China has begun launching its own satellite internet network
Phys.org July 17, 2023 On Sunday, July 9, launched a prototype internet satellite from China’s Jiuquan Satellite Launch Center in Inner Mongolia. The satellite will conduct several tests to validate the broadband satellite technology. The long-term aim of the project is to create a constellation of 13,000 satellites code-named “Guo Wang”. They intend to create two constellations (GW-A59 and GW-2) with a coverage of 37.5 to 42.5 GHz (space-to-Earth) and 47.2 to 51.4 GHz (Earth-to-space). According to multiple sources, this constellation is part of a wider effort by China to stake its claim to the growing satellite internet market. The […]