Engineers enable quantum communication over existing fiber optic cables — new research shows data transmission using quantum teleportation is possible in parallel with a classical network at specific wavelengths

Engineers at Northwestern University have successfully achieved quantum communication in parallel with classical channels by identifying specific wavelengths with minimal interference from classical signals (Source: northwestern.edu). This breakthrough lays the groundwork for quantum communication by leveraging existing infrastructure and sending quantum data alongside classical data. The researchers managed quantum teleportation over a 30.2km fiber optic cable carrying 400 Gbps of classical traffic.

Quantum computing seems to be all the hype these days. Google claims its new quantum chip can solve problems swiftly, which classical computers would otherwise take, and I quote 10 billion years to do; that's 10, followed by 24 zeroes. Quantum entanglement is a phenomenon wherein two particles are linked so that their quantum states (spin, polarization, energy levels, etc.) are connected, regardless of the physical distance. When measuring the state of one particle, the entanglement collapses, revealing the correlated state of the other particle. However, this does not allow for FTL (Faster Than Light) communication in line with the no communication theorem.

Enter Quantum teleportation. This concept combines entanglement with a classical channel, such as the Internet, and is the backbone of this research. It transfers one particle's quantum state to another located elsewhere.

Jordan Thomas, one of the research paper's authors, underlined the essence of quantum teleportation; “By performing a destructive measurement on two photons — one carrying a quantum state and one entangled with another photon — the quantum state is transferred onto the remaining photon, which can be very far away.” A key point to understand here is that the photons aren't transmitted physically. Instead, information encoded within their quantum states is what is sent.

The primary concern with a worldwide network employing quantum teleportation is compatibility; will quantum communication work over classical channels? The likelihood of interference is exceptionally high among the billions of photons being sent concurrently in a fiber optic cable. The research discovered specific wavelengths where the density of classical photons was lower, making such wavelengths suitable for the photons in quantum teleportation. Bell state measurement, or simply state measurement, is performed at the mid-point of the cable. Coupled with other methods to reduce noise and interference, this method can potentially support multiple TB/s of classical data alongside quantum communication.

While it may take years or decades before quantum communication goes mainstream, Prem Kumar, the head of the research team, has high hopes for the future. Based on the current roadmap, the next major milestones are using two pairs of entangled photons instead of one and scaling this experiment to real-world optical fiber networks.