Aurelia Butler

Researchers at the University of the Witwatersrand in Johannesburg, South Africa, have demonstrated a record setting quantum protocol for sharing a secret amongst many parties. The team created an 11-dimensional quantum state and used it to share a secret amongst 10 parties. By using quantum tricks, the secret can only be unlocked if the parties trust one another. The work sets a new record for the dimension of the state (which impacts on how big the secret can be) and the number of parties with whom it is shared and is an important step towards distributing information securely across many nodes in a quantum network.
Laser & Photonics Reviews published online the research by the Wits team led by Professor Andrew Forbes from the School of Physics at Wits University. In their paper titled: Experimental Demonstration of 11-Dimensional 10-Party Quantum Secret Sharing, the Wits team beat all prior records to share a quantum secret.
“In traditional secure quantum communication, information is sent securely from one party to another, often named Alice and Bob. In the language of networks, this would be considered peer-to-peer communication and by definition has only the two nodes: sender and receiver,” says Forbes.
“Anyone who has sent an email will know that often information must be sent to several people: one sender and many receiving parties. Traditional quantum communication such as quantum key distribution (QKD) does not allow this, and is only of the peer-to-peer form.”
Using structured light as quantum photon states, the Wits team showed how to distribute information from one sender to 10 parties. Then, by using some nifty quantum tricks, they could engineer the protocol so that only if the parties trust one another can the secret be revealed.
“In essence, each party has no useful information, but if they trust one another then the secret can be revealed. The level of trust can be set from just a few of the parties to all of them,” says Forbes. Importantly, at no stage is the secret ever revealed through communication between the parties: they don’t have to reveal any secrets. In this way a secret can be shared in a fundamentally secure manner across many nodes of a network: quantum secret sharing.
“Our work pushes the state-of-the-art and brings quantum communication closer to true network implementation,” says Forbes. “When you think of networks you think of many connections, many parties, who wish to share information and not just two. Now we know how to do this the quantum way.”
The team used structured photons to reach high dimensions. Structured light means ”Patterns of light” and here the team could use many patterns to push the dimension limit. More dimensions mean more information in the light, and translates directly to larger secrets.

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Researchers have solved a major problem for optical wireless communications — the process by which light carries information between cell phones and other devices. Light-emitting diodes (LEDs) pulse their light in a coded message that recipient devices can understand.
Now, a team of researchers based in Japan has married the two options into the ideal combination of long lasting and fast LEDs. They published their results on July 22 in Applied Physics Letters.
“A key technology for faster modulation is to decrease the device si earch for Advanced Materials at Tohoku University. “However, this tactic creates a dilemma: although smaller LEDs can be modulated faster, they have lower power.”
Another issue is that both visible and infrared optical wireless communications can have significant solar interference, according to Kojima. To avoid confusion with visible and infrared solar light, the researchers aimed to improve LEDs that specifically communicate via deep ultraviolet light, which can be detected without solar interference.
“Deep ultraviolet LEDs are currently mass produced in factories for applications related to COVID-19,” Kojima said, noting that deep ultraviolet light is used for sterilization processes as well as in solar-blind optical wireless communications. “So, they’re cheap and practical to use.”
The researchers fabricated the deep ultraviolet LEDs on sapphire templates, which are considered an inexpensive substrate, and measured their transmission speed. They found that the deep ultraviolet LEDs were smaller and much quicker in their communications than traditional LEDs at that speed.
“The mechanism underlying this speed is in how a lot of tiny LEDs self-organize in a single deep ultraviolet LED,” Kojima said. “The tiny LED ensemble helps with both power and speed.”
The researchers want to use the deep ultraviolet LEDs in 5G wireless networks. Many technologies are currently under testing to contribute 5G, and Li-Fi, or light fidelity, is one of the candidate technologies.
“Li-Fi’s critical weakness is its solar dependency,” Kojima said. “Our deep ultraviolet LED-based optical wireless technology can compensate for this problem and contribute to society, I hope.”
This work was supported in part by Five-Star Alliance and the Japan Society for the Promotion of Science.

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A way of shrinking the devices used in quantum sensing systems has been developed by researchers at the UK Quantum Technology Hub Sensors and Timing, which is led by the University of Birmingham.
Sensing devices have a huge number of industrial uses, from carrying out ground surveys to monitoring volcanoes. Scientists working on ways to improve the capabilities of these sensors are now using quantum technologies, based on cold atoms, to improve their sensitivity.
Machines developed in laboratories using quantum technology, however, are cumbersome and difficult to transport, making current designs unsuitable for most industrial uses.
The team of researchers has used a new approach that will enable quantum sensors to shrink to a fraction of their current size. The research was conducted by an international team led by University of Birmingham and SUSTech in China in collaboration with Paderborn University in Germany. Their results are published in Science Advances.
The quantum technology currently used in sensing devices works by finely controlling laser beams to engineer and manipulate atoms at super-cold temperatures. To manage this, the atoms have to be contained within a vacuum-sealed chamber where they can be cooled to the desired temperatures.
A key challenge in miniaturising the instruments is in reducing the space required by the laser beams, which typically need to be arranged in three pairs, set at angles. The lasers cool the atoms by firing photons against the moving atom, lowering its momentum and therefore cooling it down.
The new findings show how a new technique can be used to reduce the space needed for the laser delivery system. The method uses devices called optical metasurfaces — manufactured structures that can be used to control light.
A metasurface optical chip can be designed to diffract a single beam into five separate, well-balanced and uniform beams that are used to supercool the atoms. This single chip can replace the complex optical devices that currently make up the cooling system.
Metasurface photonic devices have inspired a range of novel research activities in the past few years and this is the first time researchers have been able to demonstrate its potential in cold atom quantum devices.
Dr Yu-Hung Lien, lead author of the study, says: “The mission of the UK Quantum Technology Hub is to deliver technologies that can be adopted and used by industry. Designing devices that are small enough to be portable or which can fit into industrial processes and practices is vital. This new approach represents a significant step forward in this approach.”
The team have succeeded in producing an optical chip that measures just 0.5mm across, resulting in a platform for future sensing devices measuring about 30cm cubed. The next step will be to optimise the size and the performance of the platform to produce the maximum sensitivity for each application.

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Researchers have solved a 20-year-old problem in quantum information theory on how to calculate entanglement cost — a way to measure entanglement — in a manner that’s efficiently computable, useful, and broadly applicable in several quantum research areas. More

A typical recycling process converts large quantities of items made of a single material into more of the same. However, this approach isn’t feasible for old electronic devices, or “e-waste,” because they contain small amounts of many different materials that cannot be readily separated. Now, in ACS Omega, researchers report a selective, small-scale microrecycling strategy, which they use to convert old printed circuit boards and monitor components into a new type of strong metal coating.
In spite of the difficulty, there’s plenty of reason to recycle e-waste: It contains many potentially valuable substances that can be used to modify the performance of other materials or to manufacture new, valuable materials. Previous research has shown that carefully calibrated high temperature-based processing can selectively break and reform chemical bonds in waste to form new, environmentally friendly materials. In this way, researchers have already turned a mix of glass and plastic into valuable, silica-containing ceramics. They’ve also used this process to recover copper, which is widely used in electronics and elsewhere, from circuit boards. Based on the properties of copper and silica compounds, Veena Sahajwalla and Rumana Hossain suspected that, after extracting them from e-waste, they could combine them to create a durable new hybrid material ideal for protecting metal surfaces.
To do so, the researchers first heated glass and plastic powder from old computer monitors to 2,732 F, generating silicon carbide nanowires. They then combined the nanowires with ground-up circuit boards, put the mix on a steel substrate then heated it up again. This time the thermal transformation temperature selected was 1,832 F, melting the copper to form a silicon-carbide enriched hybrid layer atop the steel. Microscope images revealed that, when struck with a nanoscale indenter, the hybrid layer remained firmly affixed to the steel, without cracking or chipping. It also increased the steel’s hardness by 125%. The team refers to this targeted, selective microrecycling process as “material microsurgery,” and say that it has the potential to transform e-waste into advanced new surface coatings without the use of expensive raw materials.

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