Qubits based on trapped ions can be prepared and manipulated with record-breaking accuracy, offering a promising scalable platform for quantum computing.
Several platforms are being considered as hardware for quantum technologies. For quantum computing (QC), superconducting qubits and artificially trapped ions are among the leading platforms, but many others also show promise, e.g. photons, cold atoms, defect centers including Rare-Earth (RE) ions. So far, results are limited to the regime of noisy intermediate scale qubits (NISQ), with a small number of qubits and a limited connectivity, and it is likely that future QC hardware will utilize several existing platforms in different ways. Thus, it currently makes sense to invest resources broadly and explore the full range of promising routes to quantum technology. Rare-earth ions in solids constitute one of the most versatile platforms for future quantum technology. One advantage is good coherence properties even when confined in strong natural traps inside a solid-state matrix. This confinement allows very high qubit densities and correspondingly strong ion-ion couplings. In addition, although their fluorescence is generally weak, cavity integration can enhance the emission greatly and enable very good connections to photonic circuits, including at the telecom wavelengths, making them promising systems for long-term scalability. The primary aim of this roadmap is to provide a complete picture of what components a RE quantum computer would consist of, to describe the details of all parts required to achieve a scalable system, and to discuss the most promising paths to reach it. In brief, we find that clusters of 50-100 single RE ions can act as high fidelity qubits in small processors, occupying only about (10 nm)^3. Due to the high capacity for integration of the RE systems, they be optically read out and connected to other such clusters for larger scalability. We make suggestions for future improvements, which could allow the REQC platform to be a leading one.
We implement all single-qubit operations with fidelities significantly above the minimum threshold required for fault-tolerant quantum computing, using a trapped-ion qubit stored in hyperfine "atomic clock" states of 43 Ca þ .We measure a combined qubit state preparation and single-shot readout fidelity of 99.93%, a memory coherence time of T Ã 2 ¼ 50 sec, and an average single-qubit gate fidelity of 99.9999%.These results are achieved in a room-temperature microfabricated surface trap, without the use of magnetic field shielding or dynamic decoupling techniques to overcome technical noise.
Quantum phenomena of superposition paved the way for the quantum computer demonstrations utilizing different approaches of qubit creation and manipulation, such as, based on trapped ions, neutral atoms, nitrogen vacancies, photonic integrated circuits, superconducting loops, etc. The trapped-ion-based platform demonstrated record long coherence times, high-fidelity gates, qubit connectivity and potential for fault-tolerant operation [1]. Number of atomic species have been investigated as basis for qubits and various qubit types along with state-preparation and measurement (SPAM) techniques have been developed. These qubit initialization and readout operations as well as atomic ion preparation stages of photoionization and atom cooling are implemented by single-frequency lasers with narrow emission linewidths at frequencies corresponding to electronic transitions in atomic ion specie. Therefore, several single-frequency lasers with well-defined parameters such as linewidth, output power, polarization, intensity noise are required for trapped-ion-based quantum computer. Considering that currently there are about 11 ion species being employed as qubits, thus more than 100 different laser wavelengths are required across the spectrum. For practical use, scalability of quantum computer is required, i.e., steady increase of qubits number without the loss of quantum system control. Therefore, availability and performance of single-frequency stabilized laser systems with tailorable emission parameters is one of pre-requirements for quantum information processing field development and commercialization success.