The researchers were able to translate the information in the light into vibrations in the inner membrane of the quantum tympanic. Image credit: Julian Robinson-Tate
Researchers at the Niels Bohr Institute at the University of Copenhagen have developed a new way to create quantum memory: a small drum can store data sent with light in sonic vibrations, and then forward the data with a new light source when needed. The results suggest that mechanical memory of quantum data may be a strategy to pave the way for an ultra-secure internet with incredible speeds.
The study was published in the journal Physical Review Letters.
Just below Niels Bohr's old office is a basement with scattered desks filled with small mirrors, lasers, and various types of equipment connected by a network of wires and piles of duct tape. It looks like one child's project has gone too far, and their parents are trying in vain to get them to clean up.
While it can be difficult for the untrained eye to discern that these tables are actually home to a series of world-leading research projects, the important thing happens in such a small world that even Newton's laws don't apply. This is where Niels Bohr's heirs to quantum physics are developing cutting-edge quantum technologies.
One of these projects – at least for physicists – is because of the ability of gadgets visible to the naked eye to achieve quantum states. A quantum drum is a small membrane made of ceramic, glass-like material with holes scattered in a neat pattern around the edges.
When the drum is hit by a laser, it begins to vibrate, and it vibrates so fast, and without interference, that quantum mechanics comes into play. This feature has long been a sensation by opening up many possibilities for quantum technology.
Now, the institute's collaboration in various quantum areas has proven that drums can also play a key role in future quantum computer networks. Like modern alchemists, researchers have created a new form of "quantum memory" by converting light signals into sound wave vibrations.
In their just-published research article, the researchers have demonstrated that quantum data from quantum computers emitted in the form of optical signals – for example, via a type of fiber optic cable already used for high-speed internet connections – can be stored as vibrations in a drum and then forwarded.
Image source: University of Copenhagen
Previous experiments have shown researchers that membranes can remain in a fragile quantum state. On this basis, they argue that the drum should be able to receive and transmit quantum data without "decoherence", i.e., lose its quantum state when the quantum computer is ready.
"This opens up great prospects for the day when quantum computers can actually do what we expect. Quantum memory may be the basis for sending quantum information over long distances. So what we're developing is a key part of the foundation of the future internet with quantum speed and quantum security," said Mads Bjerregaard Kristensen, a postdoctoral fellow at the Niels Bohr Institute and lead author of the new research article.
Ultra-fast and ultra-secure
When information is transmitted over long distances between two quantum computers, or between many computers in a quantum internet, the signal will quickly be drowned out by noise. The amount of noise in a fiber optic cable increases exponentially with the length of the cable. Eventually, the data can no longer be decoded.
The classical Internet and other major computer networks solve this noise problem by amplifying the signals of small stations along the transmission route. However, for quantum computers to apply a similar approach, they must first convert the data into an ordinary binary number system, such as the binary number system used by ordinary computers.
It's not going to work. Doing so slows down the network and makes it vulnerable to cyberattacks, as the odds of classical data protection are very low in the future of quantum computers.
"Instead, we want the quantum drum to take on the task. It is already showing great promise because it is ideal for receiving and retransmitting signals from quantum computers. Therefore, our goal is to extend the connection between quantum computers through the stations where the quantum drum receives and retransmits signals, thus avoiding noise while keeping the data in a quantum state," Christensen said.
"In doing so, the speed and advantages of quantum computers, for example, related to certain complex calculations, will extend to networks and the Internet, as they will be achieved by taking advantage of properties such as superposition and entanglement that are characteristic of quantum states.
Mads Bjerregaard Kristensen is the main force behind this new study. Image source: University of Copenhagen
If successful, these space stations will also be able to expand quantum-secure connectivity, and their quantum codes can also be extended by drums. In the quantum internet of the future, these secure signals can be sent across a variety of distances – whether around the quantum network or across the Atlantic.
Flexible, practical, and potentially groundbreaking quantum RAM
Research is being conducted elsewhere as an alternative to an alternative method in which a light source carrying data is pointed at an atomic system and temporarily moves electrons in atoms, but this method has its limitations.
"There's a limit to what you can do with atomic systems because we can't engineer the frequencies of atoms or the light that they can interact with us. Our relatively "large" mechanical systems offer greater flexibility. We can tinker and tweak so that if the new discovery changes the rules of the game, there is a good chance that the quantum drum will be adapted," explains Professor Albert Schliesser, co-author of the research article.
"For better or worse, our ability as researchers primarily determines the limits of how it all works," he noted.
The drum is the latest and most serious rendition of mechanical quantum memory, as it combines a number of characteristics: the drum has low signal loss, i.e. the strength of the data signal is well preserved. It also has the great advantage of being able to handle all optical frequencies, including those used in the fiber optic cables that build the modern internet.
The quantum drum is also convenient because the data can be stored and read when needed. Researchers have achieved a record memory time of 23 milliseconds, making it more likely that the technology will one day become a building block for quantum network systems, as well as quantum computer hardware.
"We started this research very early. Quantum computing and communication are still in the early stages of development, but with the memories we have obtained, one can speculate that quantum drums will one day be used as a kind of quantum RAM, a temporary working memory for quantum information. It will be groundbreaking," the professor said.
More information: Mads Bjerregaard Kristensen et al., Long-lived and efficient opto-mechanical memory for light, Physical Review Letters (2024). DOI： 10.1103/PhysRevLett.132.100802
期刊信息： Physical Review Letters