![This picture shows the two qubit modules (red atom between two blue mirrors) that have been interconnected to… [more] Stephan Welte, Severin Daiss (MPQ)](https://swissquantumhub.com/wp-content/uploads/2021/02/original.jpg)
Today’s quantum computers contain up to several dozen memory and processing units, the so-called qubits. Researchers from the Max Planck Institute of Quantum Optics have successfully interconnected two such qubits located in different labs to a distributed quantum computer by linking the qubits with a 60-meter-long optical fiber.
Over such a distance they realized a quantum-logic gate. It makes the system the worldwide first prototype of a distributed quantum computer.
Simply coupling distant qubits to generate entanglement between them has been achieved in the past, but now, the connection can additionally be used for quantum computations. For this purpose, the researchers employed modules consisting of a single atom as a qubit that is positioned amidst two mirrors. Between these modules, they send one single light quanta, a photon, that is transported in the optical fiber. This photon is then entangled with the quantum states of the qubits in the different modules. Subsequently, the state of one of the qubits is changed according to the measured state of the “ancilla photon”, realizing a quantum mechanical CNOT-operation with a fidelity of 80 percent. A next step would be to connect more than two modules and to host more qubits in the individual modules.
The work has been published in Science.