One-second coherence for a single electron spin coupled to a multi-qubit nuclear-spin environment

Single electron spins coupled to multiple nuclear spins provide promising multi-qubit registers for quantum sensing and quantum networks. The obtainable level of control is determined by how well the electron spin can be selectively coupled to, and decoupled from, the surrounding nuclear spins. Here we realize a coherence time exceeding a...

Dephasing mechanisms of diamond-based nuclear-spin memories for quantum networks

We probe dephasing mechanisms within a quantum network node consisting of a single nitrogen-vacancy center electron spin that is hyperfine coupled to surrounding C13 nuclear-spin quantum memories. Previous studies have analyzed memory dephasing caused by the stochastic electron-spin reset process, which is a component of optical internode...

Deterministic delivery of remote entanglement on a quantum network

Large-scale quantum networks promise to enable secure communication, distributed quantum computing, enhanced sensing and fundamental tests of quantum mechanics through the distribution of entanglement across nodes ^1-7. Moving beyond current two-node networks ^8-13 requires the rate of entanglement generation between nodes...

Diamond-based quantum networks with multi-qubit nodes

Quantum networks promise to be the future architecture for secure communication and distributed quantum computation. This thesis describes experiments on nitrogenvacancy (NV) centres that lead towards a versatile multi-node quantum network consisting ofmulti-qubit nodes.<br/>The NV centre in diamond is a spinful optically-active crystal defect....

Parameter regimes for a single sequential quantum repeater

Quantum key distribution allows for the generation of a secret key between distant parties connected by a quantum channel such as optical fibre or free space. Unfortunately, the rate of generation of a secret key by direct transmission is fundamentally limited by the distance. This limit can be overcome by the implementation of so-called...

Entanglement distillation between solid-state quantum network nodes

The impact of future quantum networks hinges on high-quality quantum entanglement shared between network nodes. Unavoidable imperfections necessitate a means to improve remote entanglement by local quantum operations. We realize entanglement distillation on a quantum network primitive of distant electron-nuclear two-qubit nodes. The heralded...

Experimental creation of quantum Zeno subspaces by repeated multi-spin projections in diamond

Repeated observations inhibit the coherent evolution of quantum states through the quantum Zeno effect. In multi-qubit systems this effect provides opportunities to control complex quantum states. Here, we experimentally demonstrate that repeatedly projecting joint observables of multiple spins creates quantum Zeno subspaces and...

Repeated quantum error correction on a continuously encoded qubit by real-time feedback

Reliable quantum information processing in the face of errors is a major fundamental and technological challenge. Quantum error correction protects quantum states by encoding a logical quantum bit (qubit) in multiple physical qubits. To be compatible with universal fault-tolerant computations, it is essential that states remain encoded at all...

Robust quantum-network memory using decoherence-protected subspaces of nuclear spins

The realization of a network of quantum registers is an outstanding challenge in quantum science and technology. We experimentally investigate a network node that consists of a single nitrogen-vacancy center electronic spin hyperfine coupled to nearby nuclear spins. We demonstrate individual control and readout of five nuclear spin qubits...

Loophole-free Bell test using electron spins in diamond: Second experiment and additional analysis

The recently reported violation of a Bell inequality using entangled electronic spins in diamonds (Hensen et al., Nature 526, 682–686) provided the first loophole-free evidence against local-realist theories of nature. Here we report on data from a second Bell experiment using the same experimental<br/>setup with minor modifications. We find a...