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News — Researchers have developed a new way to speed up quantum measurements, a vital building block for the next generation of quantum technologies.

Accurate and fast quantum measurements will be crucial for quantum technologies, but quantum systems are fragile and susceptible to disturbance which can cause errors. Previous work in this area presented a fundamental challenge – scientists were only able to increase the accuracy of measurements in quantum systems by sacrificing speed.

A team of quantum experts, led by the University of Bristol, have struck upon a novel way to overcome this problem, published in a Physical Review Letters journal .

The method involves trading ‘space’ for time by using additional qubits – the basic units of information used in quantum computing. Unlike the binary bits used in today’s computers, qubits can act as though they have components in multiple states at the same time until measured, a concept known as superposition.

But to perform a measurement in quantum computing, you need to probe a qubit, and to be certain of the result, you have to probe the qubit for a long time.

Chris Corlett, a PhD student at the University’s School of Physics, and first author on the paper, explained: “Imagine you are shown a picture of two glasses of water – one with 25ml and the other with 20ml, and you have to determine by sight which glass has more water in it. If you’re only shown the picture for one second you might struggle to tell which glass is more full but if you’re shown the picture for two seconds, then you can be more confident you chose the glass with more water in it.

“In our scheme, by including an additional qubit you increase the amount of information the probe can gather in a fixed amount of time, so we can be more confident about our answer. Adding the qubit is like doubling the volume of each glass to 50ml and 40ml, making it easier to distinguish which is more full in a shorter amount of time due to the greater difference between the two volumes.

“A significant benefit of our approach is that this relationship continues with additional qubits – so for example if you added a third qubit and, by analogy, the volume of the glasses now appears as 75ml and 60ml, you would be able to tell which was greater, with confidence, in just 0.66 seconds – this is the intuition behind our solution.”

Chris made the breakthrough working with his supervisors Professor Noah Linden, Professor of Theoretical Physics, and Dr Paul Skrzypczyk, Associate Professor of Physics, along with collaborators from the University of Oxford, Strathclyde University, and Sorbonne Université in Paris.

Remarkably, the team’s process allows the quality of a measurement to be maintained, or even enhanced, even as it is sped up. The method could be applicable to a broad range of leading quantum hardware platforms. As the global race to build the highest performance quantum technologies continues, the scheme has the potential to become a standard part of the quantum read-out process.