The foundational element of quantum computers is the qubit. Qubits can be any kind of particle that has quantum properties, such as an electron or a photon. For these qubits to accomplish their job in a quantum computer, they need to interact with each other in a quantum process known as entanglement. 

While photons would make for great qubits because of their speed, they don’t like to interact with each other, or anything else for that matter, making it difficult to achieve quantum entanglement.

Now researchers at the University of Maryland and the Joint Quantum Institute have managed to solve this conundrum with their development of the first single-photon transistor using a semiconductor chip. The resulting device makes possible photon-photon interactions in a compact chip-integrated device, which was the key missing component of an integrated photonic quantum circuit.