Trapped-Ion Qubits

Chuck Easttom

Mikio Nakahara

Cirac and Zoller proposed in their seminal paper [1] published in 1995 to use ions trapped in an external potential as qubits. Trapped ions are expected to be scalable to a large number of qubits if the trap is segmented into several subtraps. Currently the largest trapped ion register comprises eight qubits, which is the largest among all proposed physical realizations.

Dominik Maxein, Julien Laurat

Benedikt Hampel, D. H. Slichter, Dietrich G. Leibfried +9 more

Atomic ions can be trapped in vacuum with dc and rf electric potentials generated by surface electrode ion traps, and used as qubits in quantum computing applications. Qubit state preparation and control is usually accomplished with laser light while the qubit state readout is achieved by observing qubit-state-dependent fluorescence from the ion while driving an optical cycling transition. The monolithic integration of optical waveguides and single-photon detectors into the ion trap itself provides both light delivery and fluorescence photon counting capability, offering benefits for scaling in trapped ion quantum computing by eliminating the need for free-space optical access to the trap. One promising candidate for integrated high-fidelity trapped-ion qubit state readout are superconducting nanowire single-photon detectors (SNSPDs). However, the joint integration of photonics and superconducting detectors into ion trap chips presents challenges for their design, fabrication, and operation. In this work, we present our progress on the integration of SNSPDs into linear ion traps with integrated photonics designed for Ca+ qubits.

Alexander Hankin, Abdulrahman Mahmoud, Mark Hempstead +2 more

Trapped-ion (TI) qubit architectures have recently become a promising candidate for designing and building quantum computers. In the current noisy-intermediate scale quantum (NISQ) era, TI qubits stand out for their connectivity and reliability over other candidates such as superconducting qubits. However, physical constraints stemming from fine-grained frequency control of TI qubits introduce limitations to the maximum number of trapped-ions in a quantum computing system. This fundamentally challenges the design of large TI-based quantum computers, with various quantum applications requiring a large number of qubits for practical realization.Recent work has proposed TI Quantum Charge Coupled Devices (QCCD) which provides mechanisms to link multiple ion-chains together to address the issue of scalability. While such advances help increase the total qubit count in a TI system, the weak links between ion chains introduce a performance bottleneck and gate-latency penalty. Prior TI modeling toolflows have not explored the performance and scalability implications introduced by weak links on the design of future TI systems; in this work, we directly elevate the weak link as an architectural knob, and present an architecture-level performance modeling framework called VelociTI. We use VelociTI to study the performance trade-offs in a trapped-ion quantum computing design and find that optimal scheduling of qubits can provide a 6.2× speedup in performance.

B. B. Blinov, Dietrich G. Leibfried, Christopher R. Monroe +1 more