Optical quantum memories are essential elements in quantum networks for long-distance distribution of quantum entanglement. Scalable development of quantum network nodes requires on-chip qubit storage functionality with control of the readout time. We demonstrate a high-fidelity nanophotonic quantum memory based on a mesoscopic neodymium ensemble coupled to a photonic crystal cavity. The nanocavity enables >95% spin polarization for efficient initialization of the atomic frequency comb memory and time bin–selective readout through an enhanced optical Stark shift of the comb frequencies. Our solid-state memory is integrable with other chip-scale photon source and detector devices for multiplexed quantum and classical information processing at the network nodes.

We demonstrate optical probing of spectrally resolved single Nd 3+ rare-earth ions in yttrium orthovanadate (YVO4). The ions are coupled to a photonic crystal resonator and show strong enhancement of the optical emission rate via the Purcell effect resulting in near-radiatively-limited single photon emission. The measured high coupling cooperativity between a single photon and the ion allows for the observation of coherent optical Rabi oscillations. This could enable optically controlled spin qubits, quantum logic gates, and spin-photon interfaces for future quantum networks.Rare-earth dopants in solids exhibit long-lived coherence in both the optical and spin degrees of freedom [1, 4]. The effective shielding of 4f electrons leads to optical and radio-frequency transitions with less sensitivity to noise in their crystalline surroundings at cryogenic temperatures. Significant progress in rare-earth based quantum technologies has led to ensemble-based optical quantum memories [1, 3-5] and coherent transducers [7], with promising performance as quantum light-matter interfaces for quantum networks. On the other hand, addressing single ions has remained an outstanding challenge, with the progress hindered by the long optical lifetimes of rare-earth ions and resultant faint photoluminescence (PL). So far, only a few experiments have succeeded in isolating individual praseodymium [8-10], cerium [11][12][13], and erbium [14, 15] ions, though the majority of them did not probe ions via their 4f-4f optical transitions. Recently, several works have demonstrated significant enhancement of spontaneous emissions of rare-earth emitters coupled to a nanophotonic cavity [1,[15][16][17], among which [1, 16] also showed negligible detrimental effect on the coherence properties of ions in nanodevices. These results point at a viable approach to efficiently detect and coherently control individual ions in a chip-scale architecture.Here we demonstrate a nanophotonic platform based on a yttrium orthovanadate (YVO 4 ) photonic crystal nanobeam resonator coupled to spectrally resolved individual neodymium (Nd 3+ ) ions. While the system acts as an ensemble quantum memory when operating at the center of the inhomogeneous line [1], it also enables direct optical addressing of single Nd 3+ in the tails of the inhomogeneous distribution, which show strongly enhanced, near-radiatively-limited single photon emissions. A measured vacuum Rabi frequency of 2π×28.5 MHz signif-icantly exceeds the linewidth of a Nd 3+ ion, allowing for coherent manipulation of spins with optical pulses. Unlike prior experiments [8][9][10][11][12][13], this technique does not hinge on the spectroscopic details of a specific type of ion and can be readily extended to other rare-earths or defect centers. The technique opens up new opportunities for spectroscopy on single ions that are distinct from conventional ensemble measurements, which enables probes for the local nanoscopic environment around individual ions and may lead to new quantum information processing, i...

Quantum memories for light are important components for future long distance quantum networks. We present on-chip quantum storage of telecommunications band light at the single photon level in an ensemble of erbium-167 ions in an yttrium orthosilicate photonic crystal nanobeam resonator. Storage times of up to 10 µs are demonstrated using an all-optical atomic frequency comb protocol in a dilution refrigerator under a magnetic field of 380 mT. We show this quantum storage platform to have high bandwidth, high fidelity, and multimode capacity, and we outline a path towards an efficient erbium-167 quantum memory for light.

Optical networks that distribute entanglement among various quantum systems will form a powerful framework for quantum science but are yet to interface with leading quantum hardware such as superconducting qubits. Consequently, these systems remain isolated because microwave links at room temperature are noisy and lossy. Building long distance connectivity requires interfaces that map quantum information between microwave and optical fields. While preliminary microwave-to-optical transducers have been realized, developing efficient, low-noise devices that match superconducting qubit frequencies (gigahertz) and bandwidths (10 kilohertz – 1 megahertz) remains a challenge. Here we demonstrate a proof-of-concept on-chip transducer using trivalent ytterbium-171 ions in yttrium orthovanadate coupled to a nanophotonic waveguide and a microwave transmission line. The device′s miniaturization, material, and zero-magnetic-field operation are important advances for rare-earth ion magneto-optical devices. Further integration with high quality factor microwave and optical resonators will enable efficient transduction and create opportunities toward multi-platform quantum networks.

Quantum networks will enable a variety of applications, from secure communication and precision measurements to distributed quantum computing. Storing photonic qubits and controlling their frequency, bandwidth, and retrieval time are important functionalities in future optical quantum networks. Here we demonstrate these functions using an ensemble of erbium ions in yttrium orthosilicate coupled to a silicon photonic resonator and controlled via on-chip electrodes. Light in the telecommunication C-band is stored, manipulated, and retrieved using a dynamic atomic frequency comb protocol controlled by linear DC Stark shifts of the ion ensemble’s transition frequencies. We demonstrate memory time control in a digital fashion in increments of 50 ns, frequency shifting by more than a pulse width ( ± 39 M H z ), and a bandwidth increase by a factor of 3, from 6 to 18 MHz. Using on-chip electrodes, electric fields as high as 3 kV/cm were achieved with a low applied bias of 5 V, making this an appealing platform for rare-earth ions, which experience Stark shifts of the order of 10 kHz/(V/cm).

Using Triumf's neutral atom trap, Trinat, for nuclear β decay, we have measured the β asymmetry with respect to the initial nuclear spin in ^{37}K to be A_{β}=-0.5707(13)_{syst}(13)_{stat}(5)_{pol}, a 0.3% measurement. This is the best relative accuracy of any β-asymmetry measurement in a nucleus or the neutron, and is in agreement with the standard model prediction -0.5706(7). We compare constraints on physics beyond the standard model with other β-decay measurements, and improve the value of V_{ud} measured in this mirror nucleus by a factor of 4.

Rare-earth ions in crystals are a proven solid-state platform for quantum technologies in the ensemble regime and attractive for new opportunities at the single ion level. Among the trivalent rare earths, 171 Yb 3+ is unique in that it possesses a single 4f excited-state manifold and is the only paramagnetic isotope with a nuclear spin of 1/2. In this work, we present measurements of the optical and spin properties of 171 Yb 3+ :YVO 4 to assess whether this distinct energy level structure can be harnessed for quantum interfaces. The material was found to possess large optical absorption compared to other rare-earth-doped crystals owing to the combination of narrow inhomogeneous broadening and a large transition oscillator strength. In moderate magnetic fields, we measure optical linewidths less than 3 kHz and nuclear spin linewidths less than 50 Hz. We characterize the excited-state hyperfine and Zeeman interactions in this system, which enables the engineering of a Λ-system and demonstration of all-optical coherent control over the nuclear spin ensemble. Given these properties, 171 Yb 3+ :YVO 4 has significant potential for building quantum interfaces such as ensemble-based memories, microwave-to-optical transducers, and optically addressable single rareearth-ion spin qubits.

Fabrication of high quality factor photonic crystal microcavities in In As P ∕ In P membranes combining reactive ion beam etching and reactive ion etching