We review concepts and recent work related to creating light-matter interfaces for future quantum networks based on rare-earth ion-doped crystals. More precisely, we explore their unique suitability for creating photon sources, optical quantum memories for light, and qubits that allow quantum information processing. In addition, we review the state-of-the-art of elementary quantum repeater links, and provide suggestions for future research.
Owing to their long excited state lifetimes, rare-earth ions in crystals are widely used in quantum applications. To allow optical readout of the qubit state of individual ions, we propose to dope the crystal with an additional nearby ancilla ion with a shorter radiative lifetime. We show how a Bayesian analysis exhausts the information about the state of the qubit from the optical signal of the ancilla ion. We study the effects of incoherent processes and propose ways to reduce their effect on the readout. Finally, we extend the architecture to ions residing in two remote cavities, and we sho…
We describe a method for creating small quantum processors in a crystal stoichiometric in an optically active rare earth ion. The crystal is doped with another rare earth, creating an ensemble of identical clusters of surrounding ions, whose optical and hyperfine frequencies are uniquely determined by their spatial position in the cluster. Ensembles of ions in each unique position around the dopant serve as qubits, with strong local interactions between ions in different qubits. These ensemble qubits can each be used as a quantum memory for light, and we show how the interactions between qubit…
We demonstrate optical probing of spectrally resolved single Nd rare-earth ions in yttrium orthovanadate. 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.
We propose a scheme for universal quantum computing based on Kramers rare-earth ions. Their nuclear spins in the presence of a Zeeman-split electronic crystal field ground state act as 'passive' qubits which store quantum information. The qubits can be activated optically by fast coherent transitions to excited crystal field states with a magnetic moment. The dipole interaction between these states is used to implement CNOT gates. We compare our proposal with a similar one based on phosphorus donor atoms in silicon and discuss the significantly improved CNOT gate time as compared to rare-earth…
Rare-earth ion doped crystals have proven to be solid platforms for implementing quantum memories. Their potential use for integrated photonics with large multiplexing capability and unprecedented coherence times is at the core of their attractiveness. The best performances of these ions are however usually obtained when subject to a dc magnetic field, but consequences of such fields on the quantum memory protocols have only received little attention. In this article, we focus on the effect of a dc bias magnetic field on the population manipulation of non-Kramers ions with nuclear quadrupole s…
Uniting Quantum Processing Nodes of Cavity-coupled Ions with Rare-earth Quantum Repeaters Using Single-photon Pulse Shaping Based on Atomic Frequency Comb
Quantum networks based on optically addressable spin qubits promise to enable secure communication, distributed quantum computing, and tests of fundamental physics. Scaling up quantum networks based on solid-state luminescent centers requires coherent spin and optical transitions coupled to photonic resonators. Here we investigate single $\mathrm{{}^{171}Yb^{3+}}$ ions in yttrium orthovanadate coupled to a nanophotonic cavity. These ions possess optical and spin transitions that are first-order insensitive to magnetic field fluctuations, enabling optical linewidths less than 1 MHz and spin coh…
On-chip nanophotonic cavities will advance quantum information science and measurement because they enable efficient interaction between photons and long-lived solid-state spins, such as those associated with rare-earth ions in crystals. The enhanced photon-ion interaction creates new opportunities for all-optical control using the ac Stark shift. Toward this end, we characterize the ac Stark interaction between off-resonant optical fields and Nd$^{3+}$-ion dopants in a photonic crystal resonator fabricated from yttrium orthovanadate (YVO$_4$). Using photon echo techniques, at a detuning of 16…
We propose a solid-state based superradiance laser which is almost insensitive to the cavity mirror vibration. Therefore, it can compete with the best frequency-stable local oscillators. The long coherence time and the large optical density of rare-earth-ions (REIs) doped solids are employed to find a regime to demonstrate a steady-state laser emission with linewidth smaller than the atomic decay rate. The experimental parameters are discussed and intracavity photon number and laser linewidth are calculated based on the mean-field theory. A procedure for measuring absolute laser linewidth is p…
Fluoride crystals doped with rare-earth ions (REI) and pair centers in diamond for fast ($10^{-9}\rm{s}$) quantum computers (FQC) are proposed. As specific systems for REI doping, we propose $Ca_{1-x}Sr_{x}F_{2}$ crystals and their analogues. The $^{4}f$-states with different total orbital angular moments of these ions serve as two-level systems (qubits). Suitable REIs are proposed as well. It is established that the pair $SiV$ and $GeV$ centers in diamond are promising systems for fast optical quantum computers operating at elevated temperatures.
Rare-earth ion ensembles doped in single crystals are a promising materials system with widespread applications in optical signal processing, lasing, and quantum information processing. Incorporating rare-earth ions into integrated photonic devices could enable compact lasers and modulators, as well as on-chip optical quantum memories for classical and quantum optical applications. To this end, a thin film single crystalline wafer structure that is compatible with planar fabrication of integrated photonic devices would be highly desirable. However, incorporating rare-earth ions into a thin fil…
Most investigations of rare earth ions in solids for quantum information have used rare earth ion doped crystals. Here we analyse the conversion of quantum information from microwave photons to optical frequencies using crystals where the rare earth ions, rather than being dopants, are part of the host crystal. The potential of large ion densities and small linewidths makes such systems very attractive in this application. We show that, as well as high efficiency, large bandwidth conversion is possible. In fact, the collective coupling between the rare earth ions and the optical and microwave …
Quantum information processing based on magnetic ions are considered potential candidates for applications because they can be modified and scaled up by a variety of chemical methods. For these systems to achieve individual spin addressability and high energy efficiency, we exploited the electric field as a tool to manipulate their quantum behaviours, functioning via spin-orbit coupling. A Ce:YAG single crystal was employed due to that rare-earth ions have strong spin-orbit coupling and with considerations regarding the dynamics and the symmetry requirements. The Stark effect of the Ce3+ ion w…
We have demonstrated electron-electron and electron-nuclear spin manipulations of Gd3+ ion in CaWO4 crystal. The results suggest that the studied system is perspective for multiqubit implementation in quantum computing.
We present a quantum repeater scheme that is based on individual erbium and europium ions. Erbium ions are attractive because they emit photons at telecommunication wavelength, while europium ions offer exceptional spin coherence for long-term storage. Entanglement between distant erbium ions is created by photon detection. The photon emission rate of each erbium ion is enhanced by a microcavity with high Purcell factor, as has recently been demonstrated. Entanglement is then transferred to nearby europium ions for storage. Gate operations between nearby ions are performed using dynamically co…
The possibility of using mixed crystals highly doped with rare earth ions (REIs) as physical systems for creating fast quantum computers with a sampling time of nanoseconds is discussed. The electronic 4f states of rare earth ions with small values of the diagonal elements of the Judd-Ofelt matrix U(2) are proposed as optical frequency qubit levels. CNOT and other conditional gate operations are performed by exciting the rare earth ion into the 4f state with a large diagonal element of U(2), causing a Stark blockade. It is found that the main interaction responsible for this blockade is the qu…
Single dopant atoms or dopant-related defect centers in a solid state matrix provide an attractive platform for quantum simulation of topological states, for quantum computing and communication, due to their potential to realize a scalable architecture compatible with electronic and photonic integrated circuits. The production of such quantum devices calls for deterministic single atom doping techniques because conventional stochastic doping techniques are cannot deliver appropriate architectures. Here, we present the fabrication of arrays of praseodymium color centers in YAG substrates, using…
Investigating Roles of Triple Excitations for High-precision Determination of Clock Properties of Alkaline Earth Metal Singly Charged Ions
Atomic, Molecular and Optical Physics Division, Physical Research Laboratory（物理研究实验室原子、分子与光学物理分部）；Indian Institute of Technology Gandhinagar（甘地纳加尔印度理工学院）
Coupling of a locally implanted rare-earth ion ensemble to a superconducting micro-resonator
我们演示了局部注入到衬底中的稀土离子（Gd $^{3+}$ in Al $_{2}$ O $_{3}$）与超导NbN集总元件微谐振器的耦合。该混合装置是通过控制离子注入稀土离子在明确定义的微米尺寸的区域，对准光刻定义的微谐振器。该技术不会降低保持在$10^{5}$以上的谐振器的内部品质因数。使用微波吸收光谱，我们观察到电子自旋共振与数值模拟的良好协议，并提取相应的耦合率的顺序的$1$ MHz和自旋线宽的$50 - 65$ MHz。
