An interdisciplinary team at the Advanced Quantum Testbed (AQT) at Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California, Berkeley’s Quantum Nanoelectronics Laboratory (QNL) achieved a technical breakthrough using qutrits—three levels of system—of a superconducting quantum processor. .
The team has successfully linked two transmon qutrits with gate fidelity higher than previous works, thus getting closer to enabling ternary logic to encode more information than their binary counterparts—qubits.
Published in Communication in Nature in December 2022 and shown as an editor’s highlight, this experimental success drives the research and development of the AQT qutrit, including previous experimental successes published in 2021 in Physical Review X and Physical Review Letters. Ternary quantum information processors offer significant potential advantages in quantum simulation and error correction, as well as the ability to improve certain quantum algorithms and applications.
Application of ternary quantum information processing
A superconducting circuit, like a qubit, uses microwave-induced logical gate operations for control. However, ternary quantum logic has a more complex state space and noise environment, which makes one and two qutrit-logic gates at short times difficult to control.
Recent advances in materials science and device design have improved the connectivity of superconducting devices, making it easier to control qutrits, which are often more susceptible to noise. To fully utilize the power of a qutrits processor, however, it is necessary to implement operations with high control over individual qutrits, but also to cover neighboring qutrits with high fidelity and flexibility. control.
Research teams have already demonstrated single qutrit operations with high fidelity. However, gate mining speed has been compromised so far by relying on a slow and static interaction that is always “on.” Facilitating this static interaction without the ability to tune it adds unwanted noise, crosstalk, and errors to the system.
The team leading the demonstration expanded on AQT’s state-of-the-art research to implement faster, flexible, and tunable microwave-activated entanglement between two transmon qutrits with fixed frequency and fixed coupling. This new method of qutrit entanglement has created two universal two-qutrit gates, the controlled-Z gate (CZ) and the controlled-Z inverse gate (CZ+).
Using cycle benchmarking methods from AQT’s previous qutrit work with industry collaborator, Keysight Technologies, the team measured a process fidelity for the two-qutrit entangling gate of up to 97.3%, reducing infidelity from previous efforts by by a factor of almost four. In addition, for the first time in the study of qutrits, AQT researchers applied and generalized another established protocol—cross-entropy benchmarking—for gate noise detection and fidelity determination. in gate operations.
Exploring new frontiers in quantum physics
Noah Goss, a graduate student researcher at AQT and QNL, is the paper’s lead author. Goss is excited about advancing the understanding of quantum mechanics with qutrit gates.
“A combination of the different works of AQT and QNL has enabled us to reach this point, where we can identify and understand the physics with the qutrit logic gate well. We synthesize a lot of previous skills, and took it a step further experimentally, by introducing an interaction for qutrits with a high degree of control and which had not been studied before,” said Goss.
The AQT team demonstrated in 2021 how to deploy a microwave-activated tunable coupling between fixed frequency qubits. To do this for qutrits, Goss and team applied and described the differential AC Stark shift for two fixed frequency transmon qutrits. AC Stark switching uses microwave light to produce small changes in the transition frequencies and energy level structure of the coupled qutrit system to tune the coupling between the two qutrits.
“We learned how to create entanglement with two qutrit gates without sacrificing one qutrit gates. And, if you compare the fidelity achieved in the experimental demonstration with qutrits , it competes perfectly with state-of-the-art three-qubit gates, despite being in a much larger space,” Goss said.
Build a quantum-ready vision
The creation of high-fidelity qutrit gates introduces the complexity of all aspects of quantum computing. AQT offers an ideal training laboratory for these types of wide-ranging, cutting-edge explorations with highly complex superconducting processors. AQT also trains the next generation of scientists and engineers through research opportunities and open access to the lab’s testbed. In the third year of the testbed user program, the team’s experimental work has sparked more interest in future research collaborations.
“It’s fun and cool to continue building on previous works while driving a qutrit R&D direction forward, from a very different angle than most other academia and industry. AQT is a great place for such exploration. There are still many details to be worked out and a lot of physics to be done in this growing subfield of qutrits,” Goss said.
The physics studied in this work to create a qutrit entanglement between two fixed frequency transmons can be used in different hardware architectures, including those with tunable coupling, or different superconducting circuits like fluxonium.
Noah Goss et al, High-fidelity qutrit entangling gates for superconducting circuits, Communication in Nature (2022). DOI: 10.1038/s41467-022-34851-z. www.nature.com/articles/s41467-022-34851-z
Provided by Lawrence Berkeley National Laboratory
Citation: Toward ternary quantum information processing: Success in creating two qutrit entangling gates with high fidelity (2023, July 6) retrieved on July 6, 2023 from https://phys.org/news /2023-07-ternary-quantum-success-generating- duha-qutrit.html
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