Phys.org February 11, 2022 Spins in two-dimensional materials offer an advantage, as the reduced dimensionality enables feasible on-chip integration into devices. An international team of researchers (UK, Australia) has reported room-temperature optically detected magnetic resonance (ODMR) from single carbon-related defects in hexagonal boron nitride with up to 100 times stronger contrast than the ensemble average. They identified two distinct bunching timescales in the second-order intensity-correlation measurements for ODMR-active defects, but only one for those without an ODMR response. They observed either positive or negative ODMR signal for each defect. Based on kinematic models, they related this bipolarity to highly tunable […]
Tag Archives: Communications technology
Shifting colors for on-chip photonics
Nanowerk November 24, 2021 Today, most frequency shifters are either too inefficient, losing a lot of light in the conversion process, or they can’t convert light in the gigahertz range. A team of researchers in the US (Harvard University, Caltech, industry) etched coupled ring-resonators and waveguides on thin-film lithium niobate. In the first device, two coupled resonators form a figure eight-like structure. Input light travels from the waveguide entering as one color and emerging as another. It provides frequency shifts as high as 28 gigahertz with about 90% efficiency. It can be reconfigured as tunable frequency-domain beam splitters. The second device […]
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. […]
Intelligent optical chip to improve telecommunications
Phys.org October 15, 2021 An international team of researchers (Canada, France, China, Australia) developed and demonstrated a self-adjusting on-chip optical pulse-shaper based on the concept of temporal coherence synthesis. The scheme enables on-the-fly reconfigurability of output optical waveforms by using an all-optical sampling technique in combination with an evolutionary optimization algorithm. They showed that particle-swarm optimization can outperform more commonly used algorithms in terms of convergence time. The system combines all key ingredients for realizing fully on-chip smart optical waveform generators for next-generation applications in telecommunications, laser engineering, and nonlinear optics. The team’s next steps include the investigation of more […]
Quantum material to boost terahertz frequencies
Science Daily October 20, 2021 An international team of researchers (Germany, Spain, Russia) investigated the ultrafast carrier dynamics in topological insulators (TIs) of the bismuth and antimony chalcogenide family, where they isolated the response of Dirac fermions at the surface from the response of bulk carriers by combining photoexcitation with below-bandgap terahertz (THz) photons and TI samples with varying Fermi level, including one sample with the Fermi level located within the bandgap. They identified distinctly faster relaxation of charge carriers in the topologically protected Dirac surface states, compared to bulk carriers and they observed THz harmonic generation without any saturation […]
Tuning transparency and opacity
Phys.org October 18, 2021 Recently, a new type of wavefront shaping was introduced where the extinction is manipulated instead of the scattered intensity. The underlying idea is that upon changing the phases or the amplitudes of incident beams, the total extinction will change due to interference described by the cross terms between different incident beams. Researchers in the Netherlands have experimentally demonstrated the mutual extinction and transparency effects in scattering media a human hair and a silicon bar. They sent two light beams with a variable mutual angle on the sample. Depending on the relative phase of the incident beams, they […]
Using quantum Parrondo’s random walks for encryption
Phys.org October 15, 2021 Quantum game theory has stimulated some interest in recent years with the advancement of quantum information theory. This interest has led to a resurgence of quantum Parrondo’s games. With two losing games combining to give a winning game, this paradoxical idea is known as Parrondo’s paradox. Researchers in Singapore used chaotic switching between the two losing quantum games, to show that it is possible to achieve Parrondo’s paradox involving a quantum walker playing two-sided quantum coin tossing games. They showed that the framework of chaotic switching in quantum coin tosses can be applied to encryption. This […]
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