Two qudits fully entangled

Newswise —

In the computing realm, we commonly perceive data as saved in the form of ones and zeros - also called binary code. Yet, in our everyday existence, we utilize ten digits to depict all feasible numbers. As an illustration, the number 9 is inscribed as 1001 in binary, demanding three supplementary digits to denote the identical value.

The current quantum computers evolved from the binary framework, but the material systems that hold their quantum bits (qubits) can sometimes encode quantum digits (qudits), as exhibited by a group overseen by Martin Ringbauer from the Experimental Physics Department at the University of Innsbruck. As per ETH Zurich's experimental physicist Pavel Hrmo: "The task for qudit-based quantum computers has been to generate entanglement proficiently amid the information carriers that have high dimensions."

A recent article in the journal Nature Communications details how the group at the University of Innsbruck has accomplished complete entanglement between two qudits, with unparalleled proficiency. This achievement could potentially lead to quantum computers that are more effective and potent than ever before.

Thinking like a quantum computer

The instance of the number 9 elucidates that humans can compute 9 x 9 = 81 in a solitary step, while a classical computer (or calculator) must execute numerous binary multiplication steps behind the scenes by taking 1001 x 1001 before it can exhibit 81 on the display. Although classical computing can manage this task, in the quantum world, computations are naturally vulnerable to noise and external interference. Hence, we must minimize the number of operations necessary to maximize the potential of available quantum computers.

Quantum entanglement is pivotal in any quantum computing calculation. It is one of the distinctive quantum attributes that form the basis for the potential of quantum computers to significantly surpass classical computers in certain operations. However, capitalizing on this potential necessitates the production of sturdy and precise entanglement in higher dimensions.

The natural language of quantum systems

The scientists at the University of Innsbruck have now succeeded in completely entangling two qudits, with each qudit being encoded in up to 5 individual states of Calcium ions. This breakthrough provides theoretical and experimental physicists with a fresh technique to transcend binary information processing. As a result, it could lead to the creation of quicker and more resilient quantum computers.

According to Martin Ringbauer, "Quantum systems possess a plethora of accessible states that can be utilized for quantum computing, instead of restricting themselves to qubits." This more natural language of quantum computing can aid in solving numerous complex issues in fields such as chemistry, physics, and optimization, to name a few.

The study was funded by various organizations including the Austrian Science Fund FWF, the Austrian Research Promotion Agency FFG, the European Research Council ERC, the European Union, and the Federation of Austrian Industries Tyrol, among others.

Publication: Native qudit entanglement in a trapped ion quantum processor. Pavel Hrmo, Benjamin Wilhelm, Lukas Gerster, Martin W. van Mourik, Marcus Huber, Rainer Blatt, Philipp Schindler, Thomas Monz, Martin Ringbauer. Nature Communications 14, 2242 (2023) (Open Access) https://doi.org/10.1038/s41467-023-37375-2