Rare-earth related electron spins in crystalline hosts are unique material systems, as they can potentially provide a direct interface between telecom band photons and long-lived spin quantum bits. Specifically, their optically accessible electron spins in solids interacting with nuclear spins in their environment are valuable quantum memory resources. Detection of nearby individual nuclear spins, so far exclusively shown for few dilute nuclear spin bath host systems such as the nitrogen-vacancy center in diamond or the silicon vacancy in silicon carbide, remained an open challenge for rare earths in their host materials, which typically exhibit dense nuclear spin baths. Here, we present the electron spin spectroscopy of single Ce^{3+} ions in a yttrium orthosilicate host, featuring a coherence time of T_{2}=124 μs. This coherent interaction time is sufficiently long to isolate proximal ^{89}Y nuclear spins from the nuclear spin bath of ^{89}Y. Furthermore, it allows for the detection of a single nearby ^{29}Si nuclear spin, native to the host material with ∼5% abundance. This study opens the door to quantum memory applications in rare-earth ion related systems based on coupled environmental nuclear spins, potentially useful for quantum error correction schemes.
Rare-earth related electron spins in crystalline hosts are unique material systems, as they can potentially provide a direct interface between telecom band photons and long-lived spin quantum bits. Specifically, their optically accessible electron spins in solids interacting with nuclear spins in their environment are valuable quantum memory resources. Detection of nearby individual nuclear spins, so far exclusively shown for few dilute nuclear spin bath host systems such as the nitrogen-vacancy center in diamond or the silicon vacancy in silicon carbide, remained an open challenge for rare earths in their host materials, which typically exhibit dense nuclear spin baths. Here, we present the electron spin spectroscopy of single Ce^{3+} ions in a yttrium orthosilicate host, featuring a coherence time of T_{2}=124 μs. This coherent interaction time is sufficiently long to isolate proximal ^{89}Y nuclear spins from the nuclear spin bath of ^{89}Y. Furthermore, it allows for the detection of a single nearby ^{29}Si nuclear spin, native to the host material with ∼5% abundance. This study opens the door to quantum memory applications in rare-earth ion related systems based on coupled environmental nuclear spins, potentially useful for quantum error correction schemes.
Light-matter interaction at single quantum object level is a long-lived challenge and dream of physicists. From the 1970s, the development of single ion spectroscopy and the observation of single photon states pave a way to a new era of detecting, and coherently manipulating quantum objects with electromagnetic field at single-ion levels. Later on, the invention of single molecular spectroscopy offers a new approach to investigate single quantum objects in condensed matter, where the sophisticated trapping systems like in ions and cold atoms are not needed, resulting in the discovery of various of single photon emitters embedded in solids. Among all, single quantum dots and single negatively charged nitrogen-vacancy centers in diamond attract most attentions, since their single spins can be coherently manipulated and entangled by the light field giving rise to numerous applications from nanoscale sensing to quantum computing. They are intensively studied as the most promising candidates for the realization of solid-state quantum bits. However, these systems coupled to a complex environment which can result in rapid loss of spin coherence or optical instability. Finding an alternative solid-state single system with remarkable optical and spin properties is the motivation of this dissertation. Rare earth ions doped in inorganic crystal hosts provide promises not only by the high quality factor 4f-4f optical transitions but also by the well preserved and long-lived spin states, with the applications from solid-state laser spectroscopy to quantum information processing. However, for almost three decades, not being able to identify single rare earth elements in solids is the obstacle to achieve their full potential functionality. We demonstrated the first direct optical detection of single rare earth ions (praseodymium) in solids in 2012. This research was covered in my Master Degree Thesis. This dissertation presents experimental progress in optically detecting other single rare earth species in crystals, understanding their fundamental spectroscopy properties and coherently controlling them, which is mainly focused on single trivalent cerium ions in different host materials. Following the optical detection of single cerium ions in yttrium aluminum garnet (YAG), the optical and spin properties of single Ce ions are investigated. Single Ce ions show good photostability under the pulsed laser excitation. Still, like in other solid emitters, photo-induced dynamics of single Ce ions is observed, however, in a counterintuitive way under the continuous laser irradiation. To understand this behavior, we proposed a charge dynamics model, and developed a novel method to suppress this undesired charge dynamics. With this approach, we obtain the photoluminescence excitation spectrum of single Ce ions in YAG under a CW laser excitation. Narrow (~80 MHz) and spectrally stable optical transitions between the lowest Kramers doublets of the ground and the excited states are observed. In comparison with the large inhomogeneous broadening (500 GHz), narrow resonant transitions provide the good selectivity in the spectral domain. Moreover, the single Ce ground spin state presents a spin 1/2 system with anisotropy g factor. It results in the optical selection rules dependent on the directions of the external magnetic field. Under parallel external magnetic field with respect to the quantization axis, only the spin-flip transitions are allowed with high transition contrast. It gives the opportunity to optically initialize the ground spin state of single Ce ions with 97.5% fidelity. The coherent spin properties of single Ce ions can be investigated, after the successful optical initialization. By scanning the microwave frequency, we obtain the electron spin resonance of single Ce spin transitions. We show the spin state has a coherence time of 290 ns, which is dominated by the surrounding aluminum nuclear spin bath and impurities induced electron spin bath. The coherence time can be extended to 2 ms through dynamical decoupling method, which approaches closely to the upper limit 4.5 ms due to spin-lattice relaxation. This result indicates single Ce electron spin can be a good solid-state qubit. With the combination of optical and spin manipulations of single Ce ions, a quantum interface between a single spin and a single photon is observed by monitoring the temporal behavior of circularly polarized emission photons from the ion. We obtain the Larmor precession of the excited spin state, indicating the direct mapping of the excited spin states of single Ce ions onto the polarization states of the fluorescence photons. Furthermore, with both optical and spin access, we all-optically demonstrate coherent population trapping of a single Ce spin qubit. To scale up the system for further applications, we present the nano-scale engineering of rare earth species in YAG crystal, with the acquirement of the production yield of Ce and Pr implantation (53 and 91% respectively). The optical and spin properties of single implanted Ce ions show fairly good performance, which paves the way towards coherent coupling of single rare earth qubits in a small volume. Besides the study of single Ce ions, the spectroscopy properties of single praseodymium ions in YAG crystal are investigated. We obtain the photoluminescence excitation spectrum and the hyperfine splitting of a single praseodymium ion. All-optical control of a single praseodymium ion is achieved. In this dissertation, we solve the key problem of optically detecting, spectrally studying and coherently manipulating single rare earth ions in solids. The developed methods including optical detection, initialization, readout, coherent control and nanoscale production of single rare earth elements in crystals offer novel and powerful tools for understanding and exploring the fundamental spectroscopy properties of single rare earth elements in solids. It paves a way towards constructing scalable quantum network based on single rare earth solid-state qubits.
Probing collective spin dynamics is a current challenge in the field of magnetic resonance spectroscopy and has important applications in material analysis and quantum information protocols. Recently, the rare-earth ion doped crystals are an attractive candidate for making long-lived quantum memory. Further enhancement of its performance would benefit from the direct knowledge on the dynamics of nuclear-spin bath in the crystal. Here we detect the collective dynamics of nuclear-spin bath located around the rare-earth ions in a crystal using dynamical decoupling spectroscopy method. From the measured spectrum, we analyze the configuration of the spin bath and characterize the flip-flop time between two correlated nuclear spins in a long time scale ($\sim $1s). Furthermore, we experimentally demonstrate that the rare-earth ions can serve as a magnetic quantum sensor for external magnetic field. These results suggest that the rare-earth ion is a useful probe for complex spin dynamics in solids and enable quantum sensing in the low-frequency regime, revealing promising possibilities for applications in diverse fields.
Rare-earth ions in crystals are useful in precision measurements and quantum information science because of their exceptional optical and spin coherence properties. We show that the nuclear spin coherence time of 153Eu3+ ions doped into yttrium orthosilicate can be significantly enhanced by driving the environmental nuclear spins in the host crystal. This method of enhancing the spin coherence time can lead to improved precision measurements using rare-earth-doped crystals.
Robust spin-photon interfaces with optical transitions in the telecommunication band are essential for quantum networking technologies. Erbium (Er) ions are the ideal candidate with environmentally protected transitions in telecom-C band. Finding the right technologically compatible host material to enable long-lived spins remains a major hurdle. We introduce a new platform based on Er ions in cerium dioxide (CeO 2 ) as a nearly-zero nuclear spin environment (0.04%) epitaxially grown on silicon, offering silicon compatibility for opto-electrical devices. Our studies focus on Er 3+ ions and show a narrow homogeneous linewidth of 440 kHz with an optical coherence time of 0.72 μs at 3.6 K. The reduced nuclear spin noise enables a slow spin-lattice relaxation with a spin relaxation time up to 2.5 ms and an electron spin coherence time of 0.66 μs (in the isolated ion limit) at 3.6 K. These findings highlight the potential of Er 3+ :CeO 2 platform for quantum networks applications.
Clock-transition-enabled long electron spin coherence of telecom emitters in CeO2
Rare-earth-ion-doped crystals has emerged as a promising platform for quantum technologies, owing to their narrow telecom-band optical emission, long spin memory, and compatibility with silicon integrated photonic architectures. However, the realization of scalable quantum devices requires host materials with intrinsically dilute spin environments to suppress decoherence. In this context, erbium (Er3+) doped cerium oxide (CeO2) is an attractive candidate due to the ultra-low concentration of nuclear spins in the host matrix and its compatibility with silicon-based technologies. Here we perform a comprehensive investigation of the coherence properties of Er3+ electron spin qubit in CeO2 via semiclassical as well as detailed cluster correlation expansion simulations. By systematically exploring magnetic field strength, pulse sequences, erbium concentration, and spin temperature, we identify regimes where decoherence from the spin bath is strongly suppressed. Our investigations illustrate that at dilute doping concentration (of the order of 10 ppb) and sub-Kelvin temperatures, operation near clock transitions enables Hahn-echo coherence times to approach the second timescale even at natural isotopic abundance. Importantly, from a practical standpoint, coherence times on the order of ∼10 ms are expected even at liquid helium temperature (about 2 K) for similar concentrations. Moreover, we demonstrate that an additional enhancement can be obtained with conventional multi-π-pulse dynamical decoupling protocols. Thus, our findings establish Er3+ doped CeO2 as a front-runner for realizing spin qubits, quantum memories, and integrated quantum networks.
Individually addressed Er 3+ ions in solid-state hosts are promising resources for quantum repeaters, because of their direct emission in the telecom band and their compatibility with silicon photonic devices.While the Er 3+ electron spin provides a spin-photon interface, ancilla nuclear spins could enable multiqubit registers with longer storage times.In this work, we demonstrate coherent coupling between the electron spin of a single Er 3+ ion and a single I = 1/2 nuclear spin in the solid-state host crystal, which is a fortuitously located proton ( 1 H).We control the nuclear spin using dynamical-decoupling sequences applied to the electron spin, implementing one-and two-qubit gate operations.Crucially, the nuclear spin coherence time exceeds the electron coherence time by several orders of magnitude, because of its smaller magnetic moment.These results provide a path toward combining long-lived nuclear spin quantum registers with telecom-wavelength emitters for long-distance quantum repeaters.