We demonstrate a photonic circuit with integrated long-lived quantum memories. Precharacterized quantum nodes-diamond microwaveguides containing single, stable, negatively charged nitrogenvacancy centers-are deterministically integrated into low-loss silicon nitride waveguides. These quantum nodes efficiently couple into the single-mode waveguides with >1 Mcps collected into the waveguide, have narrow single-scan linewidths below 400 MHz, and exhibit long electron spin coherence times up to 120 μs. Our system facilitates the assembly of multiple quantum nodes with preselected properties into a photonic integrated circuit with near unity yield, paving the way towards the scalable fabrication of quantum information processors. DOI: 10.1103/PhysRevX.5.031009 Subject Areas: Photonics, Quantum InformationAdvanced quantum information systems, such as quantum computers [1] and quantum repeaters [2], require multiple entangled quantum memories that can be individually controlled [3]. Over the past decade, there has been rapid theoretical and experimental progress in developing such entangled networks using stationary quantum bits (qubits) connected via photons [4][5][6]. Photonic integrated circuits (PICs) could provide a compact, phase-stable, and scalable architecture for such quantum networks. However, the realization of this promise requires near-unity-yield fabrication of high-quality solid-state quantum memories efficiently coupled to low-loss single-mode waveguides.A promising solid-state quantum memory with secondscale spin coherence times is the negatively charged nitrogen-vacancy (NV) center in diamond [7,8]. Its electronic spin state can be optically initialized, manipulated, measured [9,10], and mapped onto nearby auxiliary nuclear memories [11], which allows for quantum error correction [12]. Quantum network protocols based on these unique qualities have been proposed [13,14], and entanglement generation and state teleportation between two spatially separated quantum memories have been demonstrated [15,16]. Translating such entanglement techniques into an on-chip architecture promises scalability, but can only succeed if an efficient photonic architecture can be fabricated with a high yield. So far, waveguide patterning in diamond is challenging, preventing low-loss waveguides in the optical domain around 637 nm, the zero phonon line (ZPL) of the NV. This is in contrast to silicon nitride (SiN)-based photonics, which relies on well-developed fabrication processes [17], is CMOS compatible [18], and has a large band gap (∼5 eV) and high index of refraction (n ¼ 2.1), which makes it ideal for routing the visible emission of NVs.A second challenge in creating a scalable solid-state quantum network architecture is the inherently low yield production of high-quality quantum nodes due to the stochastic process of NV creation. The number of fabrication attempts necessary to create a monolithic network in which all nodes contain NV quantum memories with the desired spectral and spin properties scales exponentially...