New quantum debit cards, which can hold unforgeable quantum funds, are constructed using extremely cooled atoms and light particles.

While standard banks often rely on the skill of counterfeiters to detect fake banknotes, quantum banks utilize the no-cloning theorem from physics, rendering counterfeiting impossible. This principle, which states that creating identical copies of quantum information is not feasible, led physicist Stephen Wiessner to propose a protocol in 1983 for generating secure currencies. Julian Laurat and his team at the Kastler Brossel Laboratory in France are actively implementing this groundbreaking concept in advanced experiments.

According to this protocol, banks create banknotes composed of quantum particles, possessing unique properties and existing in specific quantum states, thus ensuring protection against forgery through the no-cloning theorem. Laurat remarks that the protocol showcases an impressive feat of quantum cryptography, though it has not yet been put into practice for actual quantum fund storage.

The research team has made storage feasible by combining memory devices with hard drives. In their experiments, users interact with quantum systems that act as banks by exchanging photons. Each photon can be stored similarly to loading money onto a debit card.

The memory devices used by the team consist of hundreds of millions of cesium atoms, which researchers cool down to nearly absolute zero by bombarding them with lasers. At such extreme temperatures, light can precisely manipulate the quantum state of atoms, but Laurat notes that years were spent identifying the optimal cooling needed for atomic memory to serve as a quantum debit card. Through extensive testing, he and his colleagues demonstrated that users can retrieve photons from atoms without corrupting their states, as long as the process is not tampered with.

Christophe Simon from the University of Calgary emphasizes that the new experiment marks progress toward fully realizing quantum funding. However, the current quantum memory storage time of around six million seconds remains insufficient for practical application. “Another future step is to enhance portability. The long-term goal is to develop quantum memory that can be easily carried, particularly for Quantum Money applications. But we are not there yet,” he states.

The team is focused on extending storage durations, asserting that the protocol can be employed within quantum networks already being established in metropolitan areas across the globe. Additionally, cutting-edge quantum memory not only facilitates ultra-secure long-distance quantum communication but is also instrumental in connecting various quantum computers to more powerful systems.