Abstract
Quantum-computation architecture based on -level systems, or qudits, has attracted considerable attention recently due to their enlarged Hilbert space. Extensive theoretical and experimental studies have addressed aspects of algorithms and benchmarking techniques for qudit-based quantum computation and quantum-information processing. Here, we report a physical realization of a qudit with up to four embedded levels in a superconducting transmon demonstrating high-fidelity initialization, manipulation, and simultaneous multilevel readout. In addition to constructing operations and benchmarking protocols for quantum-state tomography, quantum-process tomography, randomized benchmarking, etc., we experimentally carry out these operations for and . Moreover, we perform prototypical quantum algorithms and observe outcomes consistent with expectations. Our work will hopefully stimulate further research interest in developing manipulation protocols and efficient applications for quantum processors with qudits.
- Received 19 October 2022
- Accepted 3 April 2023
DOI:https://doi.org/10.1103/PhysRevX.13.021028
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
The basic unit of most quantum computing is the quantum bit, or qubit—a two-level quantum system for representing 1s and 0s. But extending qubits to three or more levels could extend the potential speed and capacity of quantum computing even further. Such extended qubits are known as “qudits,” and they have been realized in several physical platforms. One promising platform, due in part to its multilevel structure, is a type of superconducting circuit known as a transmon. Here, we demonstrate high-fidelity initialization, manipulation, and readout of a superconducting transmon qudit with up to four levels.
To use quantum resources more efficiently, we systematically study the theory of universal single-qudit gates and make a physical realization for three and four levels in a superconducting transmon. We accomplish simultaneous four-state readout with fidelity above 91% for each state. To benchmark the performance, we prepare and measure a four-level state, and experimentally estimate the fidelity per gate as greater than 99%. We also implement several rudimentary algorithms to show the efficacy and efficiency of the single-qudit processor unit.
Our experiments demonstrate the feasibility of encoding and processing more than one bit of quantum information in a single superconducting transmon, and we hope it will stimulate more interest in theoretical and experimental studies on qudit-based quantum information processing architecture.
