A trapped ion quantum computer with robust entangling gates and quantum coherent feedback

Abstract

Quantum computers are expected to achieve a significant speed-up over classical computers in solving a range of computational problems. Chains of ions held in a linear Paul trap are a promising platform for constructing such quantum computers, due to their long coherence times and high quality of control. Here we report on the construction of a small, five-qubit, universal quantum computer using 88 Sr + ions in an RF trap. All basic operations, including initialization, quantum logic operations, and readout, are performed with high fidelity. Selective two-qubit and single-qubit gates, implemented using a narrow linewidth laser, comprise a universal gate set, allowing realization of any unitary on the quantum register. We review the main experimental tools, and describe in detail unique aspects of the computer: the use of robust entangling gates and the development of a quantum coherent feedback system through EMCCD camera acquisition. The latter is necessary for carrying out quantum error correction protocols in future experiments.

Exploring ab initio machine synthesis of quantum circuits

“…To test and benchmark our circuit synthesis protocols, we generated uniformly Haar-distributed random unitaries 9 as targets, and tried to find circuit representations for them. For each target on N qubits we ran a single attempt to create a circuit performing the same action using the gate set of…”

“…Native gate sets for quantum hardware often consist of a limited number of gates, which express hardware constraints like restricted qubit connectivity or a specific set of supported gates, as is the case e.g. for trapped ions [6][7][8][9][10], superconducting qubits [11][12][13][14], and silicon-based hardware [15][16][17][18][19]. Quantum algorithms, on the other hand, are often prescribed in a gate set that fits the properties of the computation [20].…”