As a key component of quantum networks, the quantum router distributes quantum information among different quantum nodes. The silicon-vacancy (SiV) center in diamond offers a promising platform for quantum technology due to its strong strain-induced coupling with phonons. However, the development of a practical quantum router faces the challenges of achieving long-range entanglement and suppressing decoherence. Here, we propose a non-Markovian quantum router based on a diamond waveguide embedded with an array of SiV centers as the quantum nodes. Unlike conventional channel-switching methods, our design enables parallel quantum-state transfer from a single input node to multiple target nodes, analogous to a classical WiFi router. We demonstrate that persistent entanglement and suppressed decoherence of the SiV centers over long distances are achievable when bound states are present in the energy spectrum of the total system formed by the SiV centers and the phonon waveguide. Our scheme enriches the implementation of quantum routing and prompts the development of solid-state quantum networks.
Quantum networks enable applications ranging from quantum secure communication to distributed quantum computing and quantum-enhanced non-local sensing. Silicon-vacancy (SiV) centers in diamond nano-photonic cavities are a strong candidate platform for quantum networking due to their access to multiple qubits, high operation fidelities, and an efficient matter qubit-photon interface. In this thesis, I provide a background overview of both the field of quantum networking in general and the experimental platform of SiVs in diamond nano-photonic cavities. The thesis shows experimental demonstrations of SiVs from the last six years, including the development of the 29SiV as a quantum node with a two-qubit register and the subsequent remote entanglement of two such nodes over a metropolitan fiber. With this two-node network of SiVs, we implement two quantum networking applications. The first application, blind quantum computing, allows a user to remotely run an arbitrary algorithm on a quantum computer by controlling the measurement basis of photons they receive from the quantum computer, while the quantum computer receives no information about the implemented algorithm. We demonstrate a full blind quantum gate set required to implement an arbitrary quantum algorithm with information-theoretic security. The second application is entanglement-assisted remote optical interferometry. This experiment shows how remotely entangled SiVs can assist the phase sensitivity of long-baseline telescope arrays to better observe weak thermal photonic signals. I finally provide some remarks and propose future directions for the SiV as a quantum networking platform
Entangling spatially separated quantum bits is an important tool for quantum key distribution, quantum sensing, and scalable quantum computing. The negatively charged silicon-vacancy center in diamond (SiV) is unique in its potential for efficient, high-fidelity gates with optical photons, which is the prerequisite for entangling networks of separated quantum bits. We have recently implemented a scheme to entangle SiVs with different optical transition frequencies, overcoming the inhomogeneous distribution common in solid-state optical qubits. Additionally, we have engineered high fidelity gates between the SiV spin and the spin of the
29Si nucleus, which can serve as a long-lasting quantum memory. These two advances present the prospects for entanglement distillation, device-independent quantum key distribution and distributed quantum sensing.
Quantum networks hold the promise of secure communication, guaranteed by fundamental laws of physics. Building such networks, however, requires quantum nodes that can relay this quantum information. Here, the authors address practical considerations necessary for building a quantum network node using silicon-vacancy color centers (SiVs) in diamond. Specifically, they describe improvements in nanophotonic cavity design and fabrication, as well as the roles that strain, spin bath, and heating have in performing spin-photon and spin-spin entanglement experiments with SiVs at 100-mK temperatures.
We propose and analyze a novel realization of a solid-state quantum network, where separated silicon-vacancy centers are coupled via the phonon modes of a quasi-one-dimensional diamond waveguide. In our approach, quantum states encoded in long-lived electronic spin states can be converted into propagating phonon wave packets and be reabsorbed efficiently by a distant defect center. Our analysis shows that under realistic conditions, this approach enables the implementation of high-fidelity, scalable quantum communication protocols within chip-scale spin-qubit networks. Apart from quantum information processing, this setup constitutes a novel waveguide QED platform, where strong-coupling effects between solid-state defects and individual propagating phonons can be explored at the quantum level.
The construction of a quantum internet, an interconnected network which can distribute and store quantum states, is an essential step towards the development of next generation quantum technologies, including unconditionally secure communication, enhanced metrology, and distributed quantum computing. Development of these networks require functional nodes consisting of stationary registers with the capability of high-fidelity quantum information processing and storage, which efficiently interface with photonic qubits. This thesis outlines one emerging platform for building a quantum network node using the silicon-vacancy color center in diamond (SiV). Although previous work has established the SiV as a superior optical emitter capable of strong light-matter coupling, its feasibility as a quantum memory has remained elusive, primarily due to coupling to thermal phonons. This suggests two branching research directions: one where this coupling is investigated and characterized as a nanoscale sensor, and one where this coupling is supressed in order to realize the SiV as a quantum information processor. This thesis begins by highlighting the extreme phonon sensitivity as a metrological tool, where an ensemble of SiVs are used as an all-optical thermometer, capable of \SI{70}{\milli\kelvin} precision at room temperature. When incorporated into nanodiamonds, the sensing properties deviate by less than
1% between nanodiamonds, enabling calibration-free thermometry for sensing and control of complex nanoscale systems. For quantum information tasks, coherent control of the SiV electronic spin qubit is enabled by suppressing phonon-induced dephasing by five orders of magnitude at temperatures below \SI{500}{\milli\kelvin}. By aligning the magnetic field along the silicon-vacancy symmetry axis, optical transitions are highly spin-conserving, allowing for single-shot readout of the qubit with high fidelity. This coherent control is used to demonstrate a spin coherence time
T2> \SI{13}{\milli\second} and spin relaxation time
T1> \SI{1}{\second} at \SI{100}{\milli\kelvin}. Finally, SiV quantum memories are packaged into a fully integrated quantum network node by incorporating SiV qubits into nanophotonic cavities. The efficient SiV-cavity coupling (with cooperativity
C>30) provides a nearly-deterministic interface between photons and the spin qubit, which enables heralded single-photon storage. Coherent coupling to nearby \cnuc\ nuclear spins (with nearly second-long coherence times) enables multi-qubit registers and paves the way towards large-scale quantum networks.
Multiparticle entanglement is of great significance for quantum metrology and quantum information processing. We present here an efficient scheme for generating stable multiparticle entanglement in a solid-state setup, where an array of silicon-vacancy centers are embedded in a quasi-one-dimensional acoustic diamond waveguide. In this scheme, the continuum of phonon modes induces a controllable dissipative coupling among the SiV centers. We show that, by an appropriate choice of the distance between the SiV centers, the dipole-dipole interactions can be switched off due to destructive interference, thus realizing a Dicke superradiance model. This gives rise to an entangled steady state of SiV centers with high fidelities. The protocol provides a feasible setup for the generation of multiparticle entanglement in a solid-state system.