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Move Over Qubit, There’s a New Q in Town: The Qudit

quantum computing’s


Photo by Zoltan Tasi on Unsplash


With all shouts of new discoveries in quantum computers almost a daily occurrence — and with counter voices such as Professor Peter Cochran’s backing the opinion that most of it is bunkum (and that Quantum Supremacy is decades away at best, too) — no one will be surprised at the latest claims made by a group of scientists at Purdue University, in Indiana. The paper, entitled High-dimensional optical quantum logic in large operational spaces, was published in the journal Quantum Information, and describes in some detail how they have managed, under lab conditions, to create a quantum gate using ‘qudits’ instead of qubits.

But what is a qudit, for heaven’s sake?

A qudit, unlike a qubit, which can be in two states (0 or 1) at any one time, can be in more than two states (0,1,2).


This means, in layman’s terms, you need fewer qudits than qubits to do the same computational work. If the theory translates into practical applications, this could mean processing power could grow even more exponentially than we first thought using qubit processors.

For a long time now researchers have been mulling over whether replacing qubits with another, more efficient and powerful quantum unit, makes sense. With qudits, it seems — especially in regard to current experiments — it does.

The magic of the system was formulated by encoding qudits, four in number, in two ‘entangled’, or joined, photons which were situated separately in time and frequency. Unlike other particles that can easily be disturbed by outside noises such as electromagnetic forces and the like in a phenomenon known as decoherence, an intractable problem in quantum computing.

“This gate allows us to manipulate information in a predictable and deterministic way, which means that it could perform the operations necessary for certain quantum information processing tasks,”

Andrew Weiner, Purdue’s Scifres Family Distinguished Professor of Electrical and Computer Engineering

Yet, qudits offer a solution to this:

Not as sensitive to outside noise as qubits, and as they are placed in time and frequency, qudits offer physicists more choice when it comes to entanglement while also using few photons during the quantum process. This, in turn, leads to longer-lasting coherence and fidelity ratios between the quantum gate.

Photo by Alexander Andrews on Unsplash

Abstract Notion

This is all very theoretical and abstract (you should read the paper), though it could be the start of something that can break new ground in the development of QCs and is great news for advocates of the technology. And with any luck, it could lead to — with the right investment and approach — bringing quantum computers outside the research facilities and university faculties and into the mainstream, with more practical, purpose-driven architectural systems a common feature of everyday life.

Before this happens, however, more tests need to be carried out to prove whether this approach to quantum computing is any better than those currently used, namely superconducting quantum computers, the trapped ion model, the quantum dot approach, topological systems and any others out there.

We’ll keep you posted!

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James Dargan

James Dargan is a writer and researcher at The Quantum Insider. His focus is on the QC startup ecosystem and he writes articles on the space that have a tone accessible to the average reader.

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