Quantum computing has made technological advances that allow for general adoption, so many ancillary research areas need to be explored before it can be used in the real world.Chinese researcher Succeeded in entangling two quantum memories (Devices that can store information about quantum states for later retrieval) Crossing the greatest distance ever recorded – 12.5 Km. This step brings the concept of the quantum internet closer to reality. This is what enables distributed communication between quantum computers.
working with University of Science and Technology of China Jinan Institute of Quantum Technology (opens in new tab), researchers have shown that entangled quantum memories can maintain coherence even when there is an urban environment between them. This is because it was a known component of entanglement, a process in which two quantum units (such as qubits and quantum memories) are related to each other and whose state, or content, cannot be independently described.
In theory, entanglement can be maintained regardless of distance. The problem is that the sensitivity of a quantum unit to environmental disturbances, such as electromagnetic or thermal interference (also called noise), has the side effect of collapsing its state, leading to loss of coherence and entanglement, i.e. loss of information.
Building on their previous 2020 experiment, the researchers successfully entangled two different qubits over a 50km fiber optic cable. However, the feat was accomplished within the same lab. The fiber was scaled as much as possible without environmental interference breaking the qubit entanglement. It also made it easier to control the qubit’s environment.
The evolution of this early effort, transferring photons between two different labs, speaks to improved stability of quantum transmission and quantum entanglement.
“In 2020, we published paper In this study, we demonstrate the entanglement of two quantum memories over a 50-km fiber link,” Xiao-Hui Bao, one of the researchers who conducted the study, told Phys.org. I’m here. “In that experiment, the two memories of his that we used were both located within one lab, so they weren’t completely independent. completely independent and a long distance between them.”
Today, physics requires constant transmission of quantum information through traditional methods such as fiber optic cables. Therefore, the researcher created two quantum ensembles (one for each lab). In the first lab, they entangled his one quantum memory A and lasered it to add energy (a process called excitation).
This extra energy is quickly released as a photon when the quantum memory spontaneously returns to its ground state. Moreover, these photons are inherently entangled according to the quantum memory that emitted them. The researchers then used a fiber optic cable to transport this emitted photon from its original node, node 1, to its destination node, node 2, over 12.5 km.
The arrival of this photon at node 2 means that researchers can now use that quantum state information to entangle a new quantum memory, B. Two different quantum memories are said to be entangled, despite being 12.5 km apart, because they share the same state (or at least a correlatively equivalent state) as the original quantum memory.
Transmitting a single photon through 12.5 km of optical fiber without loss of fidelity is a daunting task. Especially considering the low energy level of the emitted photons (near infrared at 725 nm), they are particularly susceptible to interference from high energies. level particles or waves. To avoid the low energy of the photons, the researchers said,Instead, a quantum frequency conversion technique that shifts the photon wavelength to 1342 nm significantly improves the overall transmission efficiency. ”
This work facilitates the advent of the quantum internet, where quantum information can be sent from one node to another more efficiently and more securely. Additionally, photons are very sensitive to external interference (remember noise?), so if you intercept them and try to access their contents, they will decay and you will lose the information you need. This could lead to a new era of quantum secure communications.
It also opens the door to distributed operation of quantum computers. Instead of being placed in a single building, quantum computers can follow a distributed design, with the same quantum computer transmitting the required information from one node to another as needed. A remarkable and necessary step towards a quantum future.