Demonstration of a small programmable quantum computer with atomic qubits (1603.04512v3)

Abstract: Quantum computers can solve certain problems more efficiently than any possible conventional computer. Small quantum algorithms have been demonstrated on multiple quantum computing platforms, many specifically tailored in hardware to implement a particular algorithm or execute a limited number of computational paths. Here, we demonstrate a five-qubit trapped-ion quantum computer that can be programmed in software to implement arbitrary quantum algorithms by executing any sequence of universal quantum logic gates. We compile algorithms into a fully-connected set of gate operations that are native to the hardware and have a mean fidelity of 98 %. Reconfiguring these gate sequences provides the flexibility to implement a variety of algorithms without altering the hardware. As examples, we implement the Deutsch-Jozsa (DJ) and Bernstein-Vazirani (BV) algorithms with average success rates of 95 % and 90 %, respectively. We also perform a coherent quantum Fourier transform (QFT) on five trappedion qubits for phase estimation and period finding with average fidelities of 62 % and 84 %, respectively. This small quantum computer can be scaled to larger numbers of qubits within a single register, and can be further expanded by connecting several such modules through ion shuttling or photonic quantum channels.

• The paper demonstrates a programmable 5-qubit quantum computer built with trapped ions, showcasing high-fidelity gate operations and algorithmic execution.
• Key results include achieving 98% mean fidelity for two-qubit gates and successfully running quantum algorithms like Deutsch-Jozsa and Bernstein-Vazirani.
• The architecture is modular and scalable, laying groundwork for larger future systems and integration of advanced error correction techniques.

Demonstration of a Small Programmable Quantum Computer with Atomic Qubits

The paper "Demonstration of a Small Programmable Quantum Computer with Atomic Qubits" presents a significant advancement in the domain of quantum computing, focusing specifically on the implementation and operability of a five-qubit trapped-ion quantum computer. Trapped-ion systems are recognized for their versatility and high fidelity, which this paper leverages to demonstrate its capability in executing arbitrary quantum algorithms.

Overview of the Quantum Computing Architecture

The experimental setup described in the paper is based on a linear chain of five trapped-ion qubits. This architecture allows for fully connected and reconfigurable spin-spin Ising interactions, facilitated by counterpropagating Raman beams and a multi-channel acousto-optic modulator (AOM). This setup ensures precise single-qubit rotations as well as two-qubit Ising (XX) gates, with mean operational fidelity reaching 98%. The programmability of the system is a standout feature, achieved through the software-level decomposition of quantum algorithms into sequences of universal quantum logic gates, ultimately translated to native hardware gates.

Implementation of Quantum Algorithms

The paper reports the successful implementation of multiple quantum algorithms, utilizing the inherent programmability of the platform. Notably, it demonstrates the Deutsch-Jozsa (DJ) and Bernstein-Vazirani (BV) algorithms with success probabilities of 95% and 90%, respectively. Additionally, a coherent quantum Fourier transform (QFT) is implemented for applications in phase estimation and period finding, achieving average fidelities of 62% and 84%. These results highlight the system's ability to adapt its gate configurations without modifying the physical hardware, marking a step towards scalable quantum computation.

Technical Specifications and Experimental Control

Trapped-ion systems employed in this paper benefit from long-range interactions, a distinct advantage over solid-state implementations which typically restrict to nearest-neighbor interactions. The qubit coherence time is measured to exceed 0.5 seconds, with potential for extension beyond 1000 seconds under improved magnetic shielding. Experimental control is achieved through precise optical addressing of individual ions, allowing for both global and ion-specific gate operations without the need for intermediary steps such as qubit population shuttling or auxiliary state manipulations.

Implications and Prospects for Future Research

The ion trap quantum computer exemplified in this paper represents a modular and scalable approach. With a single register capable of housing a growing number of qubits, scalability to larger quantum systems is feasible by extending control resources proportionally. This paper sets the stage for future developments that could incorporate multi-zone ion traps for enhanced qubit connectivity or advanced error correction techniques to push gate fidelities beyond 99.9%, a prospect critical for fault-tolerant quantum computing.

In conclusion, the research detailed in this paper underscores the adaptability and high-fidelity operations of trapped-ion quantum computers. While current implementations are limited in qubit number, the groundwork is laid for extensive scalability and enhanced computational power, potentially serving as a cornerstone for future quantum computing advancements.