ICFO researchers report in the journal Nature Communications that they have succeeded in quantum teleporting from a photon to a solid-state qubit from a distance of 1 kilometer, using a unique method using multiplexed quantum memory.
Known as quantum teleportation, the method takes advantage of the phenomenon of quantum entanglement to move quantum information between two distant quantum objects, a sender and a receiver. The distinguishing aspect of this method is that information is not physically moved from one location to another; instead, it is destroyed in one location and spawned in the other, without going through a communication channel between the two parties. The entanglement that accompanies the transmission of classical bits in quantum mechanics makes this unexpected behavior possible.
Quantum communication and quantum networks
The ability to move quantum bits over extremely long distances between network nodes using pre-shared entanglement has sparked intense interest in quantum teleportation in the fields of quantum communication and quantum networks. This will facilitate the incorporation of quantum technologies into existing telecommunications networks and increase the ultra-secure communication range made possible by these systems. Quantum teleportation also allows for the transfer of quantum information between various quantum systems, such as between light and matter or between various quantum nodes.
Quantum teleportation was theorized in the early 1990s, and numerous groups around the world have carried out experimental demonstrations. Although the scientific community has considerable knowledge of how to perform these experiments, there is still uncertainty about the practicality of teleporting information that would enable reliable and fast quantum communication over a wide network. It seems reasonable for such an infrastructure to work together with the existing telecom network. To transfer information more accurately and quickly, a feature known as active feed-forward is required to be applied by the quantum teleport protocol to the teleported qubit based on the result of the teleport measurement (transmitted in classical bits).
As a result, the receiver needs a component known as quantum memory that can keep the qubit intact until the post-processing is performed. When the sender and receiver are far apart, this quantum memory must be able to operate in a multiplexed fashion to maximize the information beaming rate. These three needs have not yet been combined in a single representation by any application.
Researchers Dario Lago-Rivera, Jelena V. Rakonjac, and Samuele Grandi from ICFO, under the direction of Hugues de Riedmatten, professor of ICREA at ICFO, recently described long-distance teleportation of quantum information from a photon to a solid-state qubit, a photon stored in a multiplexed quantum memory. They reported that they had succeeded.
The method used an active feedforward system which, when combined with the multimodality of the memory, allowed the teleport rate to be maximized. Long-distance quantum communication was made possible thanks to the compatibility of the proposed architecture with telecommunications channels, allowing for future integration and scalability.
Quantum teleportation works
The group created two experimental installations known in the local language as Alice and Bob. In order to simulate the physical distance between the parties, a 1 kilometer optical fiber was used to connect the two installations.
Three photons were used in the experiment. In the first configuration, called Alice, the scientists used a special crystal to generate two entangled photons: the first photon at 606 nm, known as the signal photon; and the second photon, known as the idler photon, that is compatible with the communication network. When the first photon with a wavelength of 606 nm was produced, “we kept it in Alice and put it in a multiplexed solid-state quantum memory and stored it in memory for later processing. In parallel, we carried the telecom photon produced in Alice to the second experimental setup, known as Bob, over a 1 km optical cable,” says Dario Lago.
The quantum bit they want to carry is encoded by the scientists in the second mechanism, a third photon produced in Bob. The main event of the teleportation experiment occurs when the third photon is created and the second photon reaches Bob from Alice.
The interaction between the second and third photons is known as Bell State measurement (BSM). As a result of this measurement, the states of the second and third photons are mixed. The initial entanglement, or highly correlated joint state, of the first and second photons allowed the BSM to transfer the information contained in the third photon to the first photon, which Alice had stored in its quantum memory at a distance of one kilometer. As Dario Lago and Jelena Rakonjac have pointed out, we can transmit information between two photons that have never interacted before, but are actually combined by a third photon that is entangled with the first.
This experiment stands out because we use a multiplexed quantum memory that can store the first photon long enough; We were still able to process the teleported data as required by the protocol when Alice realized that the interaction had occurred.
The process that Dario and Jelena mentioned was done using the active feedforward method. After the first photon was stored in memory, it changed phase depending on how the BSM resulted. Done this way, the first photon will always have the same state. Without that, half the teleport events would have to be rejected.
Also, thanks to the multimodality of quantum memory, they were able to extend the teleportation rate beyond the constraints set by their 1km range without compromising the quality of the qubit being transported. Overall, this produced a teleportation rate that was limited only by the speed of classical hardware and was three times higher than a single-mode quantum memory.
Quantum Integration and Scalability
The premise of this experiment was work done by this group in 2021, in which they successfully performed entanglement between two multimode quantum memories separated by 10 meters and marked by a photon at a telecommunications wavelength.
As Hugues de Riedmatten underlined, quantum teleportation will be essential to enable high-quality long-distance communication in the future quantum internet. We want to use pre-distributed entanglement to enable quantum teleportation in ever more complex networks. Our quantum nodes are a promising method for deploying technology over long distances in the embedded fiber network due to their solid state and multiplexing capabilities as well as their compatibility with the telecom network.
Further progress is already being considered. On the one hand, the main goal of the team is to advance the technology and maintain speeds and efficiency while expanding the installation to much greater distances. For a future quantum internet that could transmit and process quantum information between remote parties, they also plan to explore and use this approach to move information between various quantum nodes.
📩 19/04/2023 14:17