Successfully fabricated a single photon microwave source on an IC

American physicists have taken a step closer to the technology of quantum information transfer on a chip by successfully creating a compatible single-channel microwave broadcast source on an integrated IC (IC).

The source is based on a superconducting tunnel contact, which can be used to " heat up " microwave photons carrying quantum information from one part of the circuit to another. These results have just been published in the journal Nature .

The existing microwave telecommunications systems (also known as quantum encryption) could be one of the devices that outperform traditional security telecommunications equipment, but still cannot achieve. before physicists had the achievements of systems that transmit quantum bits (qubits) in the same circuits as today's computer systems. Photons are one of the good options for conveying qubits, but unless they can be transmitted individually and firmly as required to eliminate the risk that information can be stolen by blocking photons. redundancy.

One way to create a single photon source is to place an atom - a qubit - into a small cavity and stimulate it to a high energy state so that it emits a photon containing qubit states that have been drawn through the cavity. open. But usually cavities are three-dimensional structures, and are often difficult to create links with wires (approximate bidirectional structures) used in integrated circuits.

Figure 1. Model of a single photon source on an integrated circuit (Nature 449 328).

However, recently, the team of Robert Schoelkopf and colleagues at Yale successfully solved this problem, by creating a cavity that is part of the 2D wire and placing a superconducting tunnel contact. acts as a qubit instead of using an atom. This contact contains 2 aluminum particles (Al) separated by an insulating barrier.

Paired electrons (Cooper pairs) according to quantum mechanical mechanism can tunnel through barrier, which means that like real atoms, contact has simple energy levels, in this case corresponds to how many electronic pairs are on the two sides of the barrier. By absorbing a microwave photon, a new pair of electrons will tunnel into the other layer, which should be equal to the excited state. Similarly, the electron pair will tunnel back to its non-excited state by emitting a photon. This means that the existence of a photon at one end of the wire will indicate the state of the qubit at the other end.

Figure 2. The decline of the theoretical and experimental qubits (Nature 449 328).

Unlike the classical information bits only in states 0 or 1, qubits can be in short states between 0 and 1 for a time. To make the contact layer act as a qubit, Schoelkopf and his colleagues placed the magnetic field to bring the contact layer into the excited, non-excited state and the short-lived state.

Microwave waves are often used in classical telecommunications equipment, and the single-photon source of the Schoelkopf group is a step towards using microwaves in quantum information. Currently, they achieve a photon emission efficiency of 38% for the excited state and 12% for a short-lived state, but Schoelkopf told Physics World magazine that the challenge of the group would be to transmit information from the photon back. quantum bits (Detail article published in Nature 449 328).

The Doctrine of Independence