Photonic crystals key to quantum networks

US researchers have created a crystal structure that could be used in future quantum networks.

The structure – a photonic crystal – boosts the interaction between electrons and small bursts of light. Built from microscopic layers of a semiconductor and carefully drilled holes, scientists can create cavities where photons become trapped and, effectively, bounce around.

Shuo Sun, a student at the Joint Quantum Institute, in Maryland, US, said: “Our platform has two major advantages over previous work. The first is that the electronic qubit is integrated on a chip, which makes the approach very scalable. The second is that the interactions between light and matter are fast. They happen in only a trillionth of a second – 1,000 times faster than previous studies.”

Currently electronic circuits store information, transmitting it along optical fibres. A quantum network would transmit qubits which would be impossible to decrypt unless you were the intended recipient. By trapping a photon and electron in a small space, the photon can change the quantum properties of the electron and vice versa.

Professor Edo Waks, Associate Professor at Maryland University, said: “These photonic crystals can concentrate light in an extremely small volume, allowing devices to operate at the fundamental quantum limit where a single photon can make a big difference.”

[caption id="attachment_52331" align="alignnone" width="620"] How the quantum switch was created. (S. Kelley/JQI)[/caption]

The photonic crystal contains holes 72nm wide, which allowed photons of certain energy to enter and leave. Inside the cavity, a quantum dot held an electron. If the spin of the electron pointed up, no interaction occurred with the photon. If the spin pointed down, photons left the cavity with reversed polarisation.

These interactions are examples of quantum switches and it is this phenomena that quantum computing and networks will use in the future. In essence quantum networking will allow electrons to store and process quantum information at one location with photons carrying that information to other parts of the network.

Sun said: “The ultimate goal will be integrating photon creation and routing onto the chip itself. In that manner we might be able to create more complicated quantum devices and quantum circuits.”

The findings were published in Nature Nanotechnology.