Fluxonium Qubit Retains Information For 1.43 Milliseconds – 10x Longer Than Before

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Superconducting quantum technology has long promised to bridge the divide between existing electronic devices and the delicate quantum landscape beyond. Unfortunately progress in making critical processes stable has stagnated over the past decade. 

Now a significant step forward has finally been realized, with researchers from the University of Maryland making superconducting qubits that last 10 times longer than before. 

What makes qubits so useful in computing is the fact their quantum properties entangle in ways that are mathematically handy for making short work of certain complex algorithms, taking moments to solve select problems that would take other technology decades or more. 

Unfortunately, those critical properties don't just entangle with other qubits – they can mesh with anything in their environment, often before their precious information can be measured. 

Now researchers have built what's known as a fluxonium qubit that can retain information for 1.43 milliseconds. That might seem like a super-short flash of time, but it's a 10x upgrade on the previous record. 

There's more than one way to build a qubit, and each approach has its own supporters. 

Fluxonium is a kind of qubit based on the operations at important junctions in a superconducting circuit. 

One big benefit of using superconducting systems to measure the quantum properties of electrons is that they're already based on electronic circuits – something we have plenty of experience producing. 

This is one of the reasons that fluxonium qubits are in theory better suited for larger systems and limiting errors. But until now the coherence times (the time that data can be logged for) have been too small to be useful. 

This latest advance puts fluxonium qubits back in the running with transmon qubits, which are the type of superconducting qubit currently favored by the likes of Google and IBM for their quantum computers. 

"Notably, even in the millisecond range, the coherence time is limited by material absorption and could be further improved with a more rigorous fabrication," write the researchers in their published paper. 

"Our demonstration may be useful for suppressing errors in the next generation quantum processors." 

In other words, the researchers are confident that fluxonium qubits can go even further in terms of coherence and stability. That's going to be important as scientists look to scale up their quantum computing systems using a variety of metrics. 

Key to the improvement here were tweaks to the operating frequency and circuit parameters, which pushed up the qubit's relaxation time: the time when it's passing between its possible states, during which data can be logged. 

Clearly there's a lot of ground still to cover to get qubits ready for practical use – most of the time, they still need ultra-low temperatures to operate in, for example – but if we're jumping forward 10x with each new study, our quantum computing future might be here faster than we think. 

"Much work is still required to build large-scale superconducting processors with millisecond-range coherence times, and our case study demonstrates the short-term feasibility of this goal," write the researchers. 

The research has been published in Physical Review Letters.