Researchers develop first-of-its-kind quantum gate

A recent study led by quantum researchers at the Department of Energy’s Oak Ridge National Laboratory proved popular among the science community interested in building a more reliable quantum network.

The study, led by ORNL’s Hsuan-Hao Lu, details development of a novel quantum gate that operates between two photonic degrees of freedom—polarization and frequency. (Photonic degrees of freedom describe different properties of a photon that can be controlled and used to store or transmit information.) When combined with hyperentanglement, this new approach could enhance error resilience in quantum communication, helping to pave the way for future quantum networks.

Their work was published in the journal Optica Quantum.

“Photons, the smallest packets of electromagnetic energy, are viable carriers of information across quantum networks,” said Lu. “Each photon has multiple degrees of freedom—such as path, polarization and frequency—that can carry quantum information. The quantum connection between photons, known as entanglement, enables protocols like quantum teleportation. However, this connection is highly sensitive to environmental conditions, which can introduce errors during transmission.”

Through hyperentanglement, which is the entanglement of multiple degrees of freedom between two photons, Lu and his team determined that communication could be more reliably shared.

“Imagine you have a photon that’s horizontally polarized, which corresponds to a communication bit value of zero, for example. As it travels through fiber, its polarization could change randomly, introducing errors in communication,” Lu said. “The techniques we developed here, when combined with hyperentanglement, have the potential to suppress these errors in a networking task.”

Researchers on the project established that this hyperentanglement could be manipulated through a novel quantum gate and used in an application, namely improving the ability to communicate via a quantum network.

Lu’s research complements that of his ORNL colleague Alex Miloshevsky in his paper titled, “CMOS photonic integrated source of broadband polarization-entangled photons.” Miloshevsky’s paper was also published in Optica Quantum.

The next step for this research is to deploy this new technology on ORNL’s quantum network.