Detection of single ions in a nanoparticle coupled to a fiber cavity
Chetan Deshmukh, Eduardo Beattie, Bernardo Casabone, Samuele Grandi, Diana Serrano, Alban Ferrier, Philippe Goldner, David Hunger, Hugues de Riedmatten
Many quantum information protocols require the storage and manipulation of information over long times, and its exchange between nodes of a quantum network across long distances. Implementing these protocols requires an advanced quantum hardware, featuring, for example, a register of long-lived and interacting qubits with an efficient optical interface in the telecommunication band. Here we present the Purcell-enhanced detection of single solid-state ions in erbium-doped nanoparticles placed in a fiber cavity, emitting photons at 1536 nm. The open-access design of the cavity allows for complete tunability in both space and frequency, selecting individual particles and ions. The ions are confined in a volume two orders of magnitude smaller than in previous realizations, increasing the probability of finding ions separated by only a few nanometers, which could then interact. We report the detection of individual spectral features presenting saturation of the emission count rate and linewidth, as expected for two-level systems. We also report an uncorrected g(2)(0) of 0.24(5) for the emitted field, confirming the presence of a single emitter. Our fully fiber-integrated system is an important step towards the realization of the initially envisioned quantum hardware.
Many quantum information protocols require the storage and manipulation of information over long times, and its exchange between nodes of a quantum network across long distances. Implementing these protocols requires an advanced quantum hardware, featuring, for example, a register of long-lived and interacting qubits with an efficient optical interface in the telecommunication band. Here we present the Purcell-enhanced detection of single solid-state ions in erbium-doped nanoparticles placed in a fiber cavity, emitting photons at 1536 nm. The open-access design of the cavity allows for complete tunability in both space and frequency, selecting individual particles and ions. The ions are confined in a volume two orders of magnitude smaller than in previous realizations, increasing the probability of finding ions separated by only a few nanometers, which could then interact. We report the detection of individual spectral features presenting saturation of the emission count rate and linewidth, as expected for two-level systems. We also report an uncorrected g(2)(0) of 0.24(5) for the emitted field, confirming the presence of a single emitter. Our fully fiber-integrated system is an important step towards the realization of the initially envisioned quantum hardware.
The interaction of single quantum emitters with an optical cavity enables the realization of efficient spin-photon interfaces, an essential resource for quantum networks. The dynamical control of the spontaneous emission rate of quantum emitters in cavities has important implications in quantum technologies, e.g., for shaping the emitted photons' waveform or for driving coherently the optical transition while preventing photon emission. Here we demonstrate the dynamical control of the Purcell enhanced emission of a small ensemble of erbium ions doped into a nanoparticle. By embedding the nanoparticles into a fully tunable high finesse fiber based optical microcavity, we demonstrate a median Purcell factor of 15 for the ensemble of ions. We also show that we can dynamically control the Purcell enhanced emission by tuning the cavity on and out of resonance, by controlling its length with sub-nanometer precision on a time scale more than two orders of magnitude faster than the natural lifetime of the erbium ions. This capability opens prospects for the realization of efficient nanoscale quantum interfaces between solid-state spins and single telecom photons with controllable waveform, for non-destructive detection of photonic qubits, and for the realization of quantum gates between rare-earth ion qubits coupled to an optical cavity.
Abstract The interaction of single quantum emitters with an optical cavity enables the realization of efficient spin-photon interfaces, an essential resource for quantum networks. The dynamical control of the spontaneous emission rate of quantum emitters in cavities has important implications in quantum technologies, e.g., for shaping the emitted photons’ waveform or for driving coherently the optical transition while preventing photon emission. Here we demonstrate the dynamical control of the Purcell enhanced emission of a small ensemble of erbium ions doped into a nanoparticle. By embedding the nanoparticles into a fully tunable high finesse fiber based optical microcavity, we demonstrate a median Purcell factor of 15 for the ensemble of ions. We also show that we can dynamically control the Purcell enhanced emission by tuning the cavity on and out of resonance, by controlling its length with sub-nanometer precision on a time scale more than two orders of magnitude faster than the natural lifetime of the erbium ions. This capability opens prospects for the realization of efficient nanoscale quantum interfaces between solid-state spins and single telecom photons with controllable waveform, for non-destructive detection of photonic qubits, and for the realization of quantum gates between rare-earth ion qubits coupled to an optical cavity.
Single quantum emitters coupled to optical cavities in the Purcell regime can be used as high-efficiency spin-photon interfaces that are essential for building a quantum network. Furthermore, the dynamical control of the spontaneous emission rate of quantum emitters can have important implications in quantum technologies, e.g. for shaping the emitted photons waveform, or for driving coherently the optical transition while preventing photon emission. Here we demonstrate the dynamical Purcell-enhanced emission of a mesoscopic ensemble of erbium ions doped into nanocrystals coupled to a fully-tunable high-finesse fiber-based optical microcavity. Erbium has excellent optical and spin coherence properties at cryogenic temperatures and, in addition, has a transition in the telecom band that can facilitate integration into existing commercial telecom fibers. We show that we can tune the cavity on and out of resonance at a rate of above 8 KHz, which is two orders of magnitude faster that the natural lifetime of the erbium ions (55 Hz), and a factor of five faster than the Purcell enhanced emission (1.8 KHz). This allows us to shape in real time the Purcell enhanced emission of the ions and to achieve full control over the emitted photon’s waveforms. With moderate improvements in our detection efficiency and cavity finesse, this capability will allow for the generation of single telecom photons with controllable wave-shape from single erbium ions and for the realization of quantum processing between rare-earth ion qubits using dipolar interactions.
Encoding information into quantum mechanical properties of a system can lead to applications many fields, including computing and communication. Devices that will enable these applications could be part of a quantum network in the future. Quantum networks can be implemented using nodes that have the ability to generate and store entanglement efficiently for long durations as well as to process quantum information. The nodes also need to be interfaced with photons, which can faithfully carry information over long distances. Single rare-earth ions doped in crystals offer all these capabilities. The main goal of this thesis was to detect a single erbium ion, which operates in the telecommunication wavelength, and to investigate its feasibility as a spin-photon interface. Detecting a single erbium is challenging due to its low emission rate, but it can be aided by Purcell-enhancing its emission via coupling to an optical cavity. In this thesis, we utilize erbium ions doped into nanoparticles, which facilitates their integration into cavities with small mode-volumes. In addition, nanoparticles provide the confinement required to individually manipulate spatially close-by single ion qubits, which is required for dipolar quantum gates. We hence first study the optical coherence properties of Er:Y2O3 nanoparticles at cryogenic temperatures. We identify the limiting mechanisms and identify avenues for improvement in the future. We also study the optical and spin coherence properties of Pr:Y2O3, which is a promising alternative to erbium. Fiber-based microcavities can achieve high Purcell factors as they can simultaneously realize high finesse and small mode-volume. They are also ideally suited to be coupled to nanoparticles due to their tuning capabilities. However, stabilizing such a cavity inside a cryogenic environment is challenging. We hence first describe the construction of a custom setup, which enables us to stabilize the cavity while being coupled to a suitable nanoparticle. Utilizing the first iteration of this setup, we then report on the coupling of Er:Y2O3 nanoparticles to a fiber-based high finesse microcavity. We achieve an average Purcell factor of 14 for a small ensemble of ions, while a small subset of ions show Purcell factor up to 70. We explain the obtained multi-exponential decay behaviour using a detailed model. Furthermore, we demonstrate dynamic control of the Purcell-enhanced emission by tuning the cavity resonance on a time-scale faster than the spontaneous emission rate of the ions. This allows us to extract the natural lifetime of the ions as well as to shape the waveform of the emitted photons. However, we conclude that the achieved signal-to-noise ratio is not high enough to resolve single erbium ions. For the final experiment, we operate the second iteration of the setup, which improves our sensitivity to single erbium ions by more than a factor 50. This enables us to demonstrate the first detection of a single erbium ion in a nanoparticle. The ion exhibits a Purcell factor of 60, leading to a cavity enhanced lifetime of 225 us, and a homogeneous linewidth of 380 MHz. The counts received from the ion show a clear saturation and we measure the second-order auto-correlation of the emitted photons to be 0.59, which reduces to 0.29 after background-subtraction. This is strong evidence that the photons are emitted by a single erbium ion. Our work opens the path for exploring single rare-earth-ions doped into nanoparticles as spin-photon interfaces for quantum information processing. La codificación de la información en las propiedades mecánico-cuánticas de un sistema puede dar lugar a aplicaciones en muchos campos, como la informática y la comunicación. Podemos imaginar que los dispositivos que permitan estas aplicaciones formen parte de una red cuántica en el futuro. Las redes cuánticas pueden implementarse utilizando nodos que tengan la capacidad de generar y almacenar el entrelazamiento de forma eficiente durante largos periodos de tiempo, así como de procesar la información cuántica. Los nodos también necesitan una interfaz con fotones, ya que estos pueden transportar fielmente la información a largas distancias. Los iones individuales de tierras raras dopados en cristales ofrecen todas estas capacidades. El objetivo principal de esta tesis fue detectar un ion individual de erbio, que opera en la longitud de onda de las telecomunicaciones, e investigar su viabilidad como interfaz espín-fotón. La detección de un ion individual de erbio es un reto debido a su baja tasa de emisión, pero esta puede mejorarse mediante el acoplamiento a una cavidad óptica, debido al efecto Purcell. En esta tesis, utilizamos iones de erbio dopados en nanopartículas, lo que facilita su integración a cavidades con volúmenes de modo pequeños. Además, las nanopartículas proporcionan el confinamiento necesario para manipular bits cuánticos de iones individuales cercanos espacialmente, lo cual es necesario para construir puertas cuánticas dipolares. Por ello, estudiamos primero las propiedades de coherencia óptica de las nanopartículas de Er:Y2O3 a temperaturas criogénicas. Identificamos los mecanismos limitantes e identificamos las vías de mejora en el futuro. También estudiamos las propiedades de coherencia óptica y de espín de Pr:Y2O3, que es una alternativa prometedora al erbio. Las microcavidades basadas en fibra pueden alcanzar elevados factores de Purcell, ya que pueden lograr simultáneamente una gran finura y un pequeño volumen de modo. También son idóneas para ser acopladas a nanopartículas debido a su capacidad para ajustar la frecuencia de resonancia. Sin embargo, estabilizar una cavidad de este tipo en un entorno criogénico es un reto. Primero, describimos la construcción de un sistema personalizado que nos permitió estabilizar la cavidad mientras se acoplaba a una nanopartícula adecuada. Utilizando la primera iteración de esta configuración, informamos sobre el acoplamiento de nanopartículas de Er:Y2O3 a una microcavidad de alta precisión basada en fibra. Conseguimos un factor Purcell medio de 14 para un pequeño conjunto de iones, mientras que un pequeño subconjunto de iones mostró un factor Purcell de hasta 70. Explicamos el comportamiento de decaimiento multiexponencial obtenido utilizando un modelo detallado. Además, demostramos el control dinámico de la emisión potenciada por el efecto Purcell ajustando la resonancia de la cavidad en una escala de tiempo más rápida que la tasa de emisión espontánea de los iones. Esto nos permitió extraer el tiempo de vida natural de los iones, así como moldear la forma de onda de los fotones emitidos. Para el experimento final, operamos la segunda iteración de la configuración, que mejoró nuestra sensibilidad a los iones individuales de erbio en más de un factor 50. Esto nos permitió demostrar la primera detección de un ion de erbio en una nanopartícula. El ión presentó un factor Purcell de 60, lo que da un tiempo de vida realzado por la cavidad de 225 us, y un ancho de línea homogéneo de 380 MHz. Los recuentos recibidos del ion mostraron una clara saturación y la medida de autocorrelación de segundo orden de los fotones emitidos resultó en 0,59, que se reduce a 0,29 tras la sustracción de fondo. Esto es una fuerte evidencia de que los fotones son emitidos por un ion individual de erbio. Nuestro trabajo abre el camino para explorar los iones individuales de tierras raras dopados en nanopartículas como interfaces de espín-fotón para el procesamiento de información cuántica
Abstract Europium‐doped nanocrystals constitute a promising material for a scalable future quantum computing platform. Long‐lived nuclear spin states could serve as qubits addressed via coherent optical transitions. In order to realize an efficient spin‐photon interface, we couple the emission from a single nanoparticle to a fiber‐based microcavity under cryogenic conditions. The spatial and spectral tunability of the cavity permits us to place individual nanoparticles in the cavity, to measure the inhomogeneous linewidth of the ions, and to show a multi‐modal Purcell‐enhancement of two transition in Eu 3+ . A halving of the free‐space lifetime to 1.0 ms is observed, corresponding to a 140‐fold enhancement of the respective transition. Furthermore, we observe a narrow optical linewidth of 3.3 MHz for a few‐ion ensemble in the center of the inhomogeneous line. The results represent an important step towards the efficient readout of single Eu 3+ ions, a key requirement for the realization of single‐ion‐level quantum processing nodes in the solid state.
The realization of long-distance quantum communication and the envisioned quantum internet relies on coherent hybrid light-matter interfaces connecting quantum light emitters with quantum memory (QM) systems. Unlike probabilistic photon pair sources such as spontaneous parametric down-conversion, deterministic quantum light emitters enable the on-demand production of pure and bright single- and entangled- photons, essential for scalable quantum networks. In this work, we present the first experimental realization of a coherent hybrid light-matter interface between a chip-integrated InAsP/InP nanowire quantum dot (QD) and a solid-state QM based on Er 3+ ions doped in a glass silica fiber (erbium-doped fiber, EDF). The emission spectrum of the InAsP/InP nanowire QD aligns with the absorption bandwidth of the EDF at 980 nm at cryogenic temperatures, allowing efficient interaction between the two systems. To demonstrate this, we present a spectroscopic characterization of the 4 I215↔ 4 I211 optical transition in EDF at 980 nm. Our measurements reveal substantial inhomogeneous broadening of this optical transition and a long spin population lifetime, underscoring EDF’s potential for broadband QM implementation. We implement an 8 GHz bandwidth multimode QM based on the Atomic Frequency Comb protocol, enabling the storage and retrieval of 59 weak coherent pulses. Furthermore, we characterize single-photon emission from an InAsP/InP nanowire QD at 980 nm and demonstrate its deterministic storage and recall in the EDF QM. Notably, this is achieved without spectral tuning of the QD emission, demonstrating its direct compatibility with a solid-state QM.