The quantum computers of today grew out of the binary paradigm, but in fact the physical systems that encode their quantum bits (qubit) often have the potential to also encode quantum digits (qudits), as recently demonstrated by a team led by Martin Ringbauer at the department of experi­mental physics at the university of Innsbruck. According to experi­mental physicist Pavel Hrmo at ETH Zurich: “The challenge for qudit-based quantum computers has been to effi­ciently create entanglement between the high-dimensional information carriers.”

The example of the number 9 shows that, while humans are able calculate 9 x 9 = 81 in one single step, a classical computer has to take 1001 x 1001 and perform many steps of binary multi­plication behind the scenes before it is able to display 81 on the screen. Classically, we can afford to do this, but in the quantum world where computations are inherently sensitive to noise and external dis­turbances, we need to reduce the number of operations required to make the most of available quantum computers.

Crucial to any calculation on a quantum computer is quantum entanglement. Yet, exploiting this potential requires the generation of robust and accurate higher-dimensional entangle­ment. The researchers were now able to fully entangle two qudits, each encoded in up to 5 states of individual Calcium ions. This gives both theoretical and experi­mental physicists a new tool to move beyond binary information processing, which could lead to faster and more robust quantum computers.

Martin Ringbauer explains: “Quantum systems have many available states waiting to be used for quantum computing, rather than limiting them to work with qubits.” Many of today's most challenging problems, in fields as diverse as chemistry, physics or optimisation, can benefit from this more natural language of quantum computing. (Source: U. Innsbruck)

Reference: P. Hrmo et al.: Native qudit entanglement in a trapped ion quantum processor, Nat. Commun. 14, 2242 (2023); DOI: 10.1038/s41467-023-37375-2

Link: Quantum Optics & Spectroscopy, University Innsbruck, Innsbruck, Austria