Applied Physics Seminar

Quantum networks enable the distribution of quantum information that is generated, processed and stored in local nodes [1]. Setting up a quantum network requires the generation of entanglement between widely separated qubits combined with local long-lived quantum registers. Here we present our recent results towards the realization of scalable quantum networks with solid-state qubits. We have entangled two spin qubits, each associated with a nitrogen vacancy center in diamond [2]. The two diamonds reside in separate setups three meters apart from each other. With no direct interaction between the two spins to mediate the entanglement, we make use of a scheme based on quantum measurements: we perform a joint measurement on photons emitted by the NV centers. The detection of the photons projects the spins into an entangled state. We verify the generated entanglement by single-shot readout of the spin qubits in different bases and correlating the results.

Furthermore, we show that this entanglement serves as a valuable resource and demonstrate a key functionality of a quantum network: the transmission of a quantum state via quantum teleportation. By first creating entanglement between distant NV-centers and then consuming this entanglement in a local Bell-state measurement between the electronic spin and the nitrogen nuclear spin on Alice side, we can teleport an arbitrary quantum state of the nitrogen spin onto the electron spin on Bob's side [3].

Analysis shows that the obtained fidelities are in principle high enough for a loophole-free violation of Bell's inequalities. We will present our latest efforts towards reaching this ultimate goal.