Scalable quantum networks require the efficient generation and storage of entanglement between photonic qubits and quantum memories. Quantum repeaters based on absorptive rare-earth-ion photonic memories offer a promising route toward highly multiplexed quantum networking, but unifying spectrally matched photon sources and quantum memories within a common architecture remains a major challenge. Here we demonstrate an integrated photonic architecture for telecom photon-memory entanglement generation based on dual self-similar silicon carbide microring resonators. Connected by a fiber link, one resonator operates as an entangled photon-pair source, while the other functions as a cavity-enhanced atomic-frequency-comb quantum memory. The memory resonator reaches an ensemble cooperativity of 1.9 after hyperfine initialization and is spectrally matched to the source, enabling storage of entangled telecom photons without spectral modification. We generate and characterize photon-memory entanglement from a quantum interference visibility preserved before and after storage. Harnessing the strong source correlations and the high multimode capacity of the memory, we access high-dimensional entanglement spanning 63 temporal modes, reaching a maximum photon information efficiency of 5.1 Ebits per detected photon and a peak on-chip photon-memory entanglement rate of 5.6 kEbits per second. These results establish a route toward chip-scale quantum networking hardware operating over telecommunications infrastructure.
Scalable quantum networks require the efficient generation and storage of entanglement between photonic qubits and quantum memories. Quantum repeaters based on absorptive rare-earth-ion photonic memories offer a promising route toward highly multiplexed quantum networking, but unifying spectrally matched photon sources and quantum memories within a common architecture remains a major challenge. Here we demonstrate an integrated photonic architecture for telecom photon-memory entanglement generation based on dual self-similar silicon carbide microring resonators. Connected by a fiber link, one resonator operates as an entangled photon-pair source, while the other functions as a cavity-enhanced atomic-frequency-comb quantum memory. The memory resonator reaches an ensemble cooperativity of 1.9 after hyperfine initialization and is spectrally matched to the source, enabling storage of entangled telecom photons without spectral modification. We generate and characterize photon-memory entanglement from a quantum interference visibility preserved before and after storage. Harnessing the strong source correlations and the high multimode capacity of the memory, we access high-dimensional entanglement spanning 63 temporal modes, reaching a maximum photon information efficiency of 5.1 Ebits per detected photon and a peak on-chip photon-memory entanglement rate of 5.6 kEbits per second. These results establish a route toward chip-scale quantum networking hardware operating over telecommunications infrastructure.
Photonic links between disparate quantum technologies−such as photon sources, memories, processors, clocks, and sensors−are key to scaling quantum networks and realizing a versatile quantum internet for secure quantum communication, distributed quantum computing, and entanglement-enhanced metrology. In practice, each technology is most suitably implemented on a different quantum platform; the substantial spectral mismatch between them, along with scarce native telecom interfaces, thus poses a major bottleneck to achieving efficient interconnections over long distances. Here we demonstrate the first deployed two-node hybrid network that operates entirely in the telecom C-band. Our approach uses no quantum frequency conversion or external filtering; instead, we develop a neutral atom single photon source and a solid-state rare-earth quantum memory that both operate in previously unexplored telecom regimes with state-of-the-art performance. The source achieves a high single-photon purity at 46 kcps, and the memory a storage efficiency of 10.6% with high multimode capacity. We leverage the intrinsic tunability of both systems to optimize their spectral overlap and demonstrate microsecond-level storage and retrieval with a large time-bandwidth product. Moreover, we showcase real-world networking competencies such as support for multiplexing across 37 temporal modes and preservation of non-classicality over fibers of 10.6 km (metropolitan) and 49.2 km (laboratory). Our work establishes a backbone for telecom-native quantum repeater links and unlocks a path towards high-bandwidth, large-scale quantum networking.
Reaching a quantum internet of global scale will require a hybrid architecture of ground and satellite quantum repeater nodes [1]. The functional blocks of a generalized quantum repeater are four: the quantum channel; the Bell State measurement; the source of entanglement; and the quantum memory. Over the last 40 years, the technological achievements towards the development of these functional blocks can be categorized in epochs: the first epoch is characterized by the control of a single quantum system, such as the demonstration of entangled photon-pair emission from a non-linear material [2], or the coherent control of the spin in a colour-centre with an optical interface [3]; the second epoch involves the combined control of two quantum systems based on the same platform, such as the three-node network experiments with Rydberg atoms [4] and colour-centres [5]; the third epoch will usher demonstrations of combined control over different quantum systems. This presentation will detail the third-epoch roadmap towards the integration of an entangled photon-pair source (EPPS) and an ensemble-based quantum memory, both operating within the telecommunication C-band. The EPPS leverages the high quality factor of a micro-ring resonator built on a silicon-oninsulator (SOI) platform to achieve high photon-pair generation rates based on spontaneous four-wave mixing (SFWM). Active control of the pair emission wavelength allows preparing photons that fall within the bandwidth of an atomic frequency comb (AFC) carved into the inhomogeously-broadened absorption line of an Erbium-doped Lithium Niobate crystal. The AFC quantum memory stores input photonic quantum states for a fixed storage time, after which it emits a socalled photon echo, so that non-classical correlations between the stored quantum state and its pair can be evaluated. Techniques to increase the spectral overlap between source and memory, as well as to improve the memory storage efficiency are defined in the roadmap. The demonstration of such an integration step will pave the way towards a quantum repeater architecture that finds applications both in ground and space links.
We present the design of an on-chip integrated photon pair source based on Spontaneous Four Wave Mixing (SFWM), implemented on a ring resonator in the 4H Silicon Carbide On Insulator (4H-SiCOI) platform, compatible with a solid state quantum memory in the telecommunications band. Through careful engineering of the waveguide dispersion and micro-ring resonator dimensions, we found solutions where the signal photons are emitted at 1536.48 nm with a bandwidth of ∼150 MHz, enabling the interaction with the hyperfine structure of Er 3+ ions. Simultaneously, the idler photons are generated at 1563.86 nm, matching the central wavelength of a specific channel in a commercial dense wavelength division multiplexing system. The proposed device fulfill all the spectral requirements in a simple ring-bus coupled waveguide configuration with design parameters within the range of reported values for similar resonators, making feasible its manufacturing with current fabrication capabilities.
Reaching a quantum internet of global scale will require a hybrid architecture of ground and satellite quantum repeater nodes [1]. The functional blocks of a generalized quantum repeater are four: the quantum channel; the Bell State measurement; the source of entanglement; and the quantum memory. Over the last 40 years, the technological achievements towards the development of these functional blocks can be categorized in epochs: the first epoch is characterized by the control of a single quantum system, such as the demonstration of entangled photon-pair emission from a non-linear material [2], or the coherent control of the spin in a colour-centre with an optical interface [3]; the second epoch involves the combined control of two quantum systems based on the same platform, such as the three-node network experiments with Rydberg atoms [4] and colour-centres [5]; the third epoch will usher demonstrations of combined control over different quantum systems. This presentation will detail the third-epoch roadmap towards the integration of an entangled photon-pair source (EPPS) and an ensemble-based quantum memory, both operating within the telecommunication C-band. The EPPS leverages the high quality factor of a micro-ring resonator built on a silicon-on-insulator (SOI) platform to achieve high photon-pair generation rates based on spontaneous four-wave mixing (SFWM). Active control of the pair emission wavelength allows preparing photons that fall within the bandwidth of an atomic frequency comb (AFC) carved into the inhomogeously-broadened absorption line of an Erbium-doped Lithium Niobate crystal. The AFC quantum memory stores input photonic quantum states for a fixed storage time, after which it emits a so-called photon echo, so that non-classical correlations between the stored quantum state and its pair can be evaluated. Techniques to increase the spectral overlap between source and memory, as well as to improve the memory storage efficiency are defined in the roadmap. The demonstration of such an integration step will pave the way towards a quantum repeater architecture that finds applications both in ground and space links.
As the reach of quantum technologies extends ever further in communication and information science, a reliable way of transferring quantum information between distant locations becomes ever more crucial. While photons are widely accepted as excellent carriers due to their speed and low decoherence, losses of transmission (in free space or fibre) and the impossibility of cloning quantum information still pose a great challenge. The quantum repeater architecture was suggested as a solution to both problems [1]. In a quantum repeater the information encoded in an input state is transferred to a new one through entanglement swapping, that is then sent on along the channel. In this work we present our advances towards the realisation of a quantum repeater. Our system of choice combines a solid-state quantum memory with a source of photon pairs. The memory is based on a Rare-Earth Doped crystal, where quantum information can be stored in Pr3+ ions as a collective excitation using the Atomic Frequency Comb technique. On demand retrieval of the information is realised by transferring the excitation to a long-lived spin state. Record values of storage times and retrieval efficiencies have been demonstrated in this system [2]. Entangled pairs of single photons are generated by parametric down conversion in a periodically poled crystal placed inside a bow-tie cavity. This allows us to generate narrow band photons pairs, where the signal is spectrally matched to the memory (606nm), while the idler is in the telecom band [3]. Such a configuration allows us to benefit from the high performance of the memory, that also allows for temporal [2] and frequency [4] multimodality, while at the same time overcoming the high optical losses of 606nm photons by pair generation of a telecom photon. The first stepping stone, progress towards which is presented in this work, is the successful demonstration of energy-time entanglement between the telecom idler photon and the signal photon, stored as spin-wave excitation. The entanglement of the original pair is maintained by the memory temporal multimodality. The entanglement analysis will be made through time-bin qubit analysers made of a fibre-based Mach-Zehnder interferometer, for the former, and a solid-state equivalent based on two AFC with different storage times, for the latter [5]. In this direction we have already doubled the efficiency of the AFC storage protocols, that will be beneficial to count rates and signal-to-noise ratio. With respect to [2], we also increased the spectral-matching between the source and the memory [4]. Our experiment will provide an increase in storage time of 3 orders of magnitude with respect to previous demonstrations, as well as introducing for the first time on-demand read-out in a highly multi-mode memory. Demonstration of the successful transfer of quantum information between the signal photon and the long-lived solid-state excitation will open the way to the demonstration of long-distance entanglement between individual nodes in a quantum network.
Multiplexing is essential for improving entanglement distribution rates in quantum communication. Frequency multiplexing provides a promising and scalable path toward large-capacity quantum networks. Further progress requires increasing the number of frequency modes and developing broadband photon-pair sources and quantum memories that are spectrally compatible. Here, we report the integration of a cavity-enhanced spontaneous parametric down-conversion source in the telecom C-band with a frequency-multiplexed atomic frequency comb memory. The bow-tie cavity source was simultaneously resonant at 606 nm and 1550 nm, generating non-degenerate photon pairs exhibiting a clustered frequency-comb spectrum. The atomic frequency comb memory, implemented in Praseodymium-doped Yttrium Orthosilicate crystals, provided up to 83 frequency modes with 123 MHz spacing and enabled broadband storage of 606 nm signal photons. By filtering the main cluster, we obtained 32.7±4.8 effective modes, as confirmed from coincidence measurements. Importantly, we observed strong nonclassical correlations after storage, with cross-correlation values of gs,i(2)=8.1±0.7. Our experimental results demonstrate the feasibility of integrating cavity-enhanced photon-pair sources with rare-earth-ion-doped solid-state memories. The integration reveals a high frequency multiplicity that is essential for scalable quantum networks.