Physicists use entanglement to improve quantum measurements

Scientists at the Australian National University (ANU) have discovered a way to achieve more accurate measurements of microscopic objects using quantum computers, in a way that could prove useful in a range of next-generation technologies including biomedical sensing. Examining microscopic quantum objects like photons — tiny particles of light — becomes tricky, because certain properties of quantum objects are connected, and measuring one property can disturb another property. For example, measuring the position of an electron will affect its speed and vice versa.

Such properties are called conjugate properties. This is reportedly a direct manifestation of Heisenberg’s uncertainty principle — it is not possible to simultaneously measure two conjugate properties of a quantum object with arbitrary accuracy. According to lead author and ANU PhD researcher Lorcán Conlon, this is one of the defining challenges of quantum mechanics.

“We were able to design a measurement to determine conjugate properties of quantum objects more accurately. Remarkably, our collaborators were able to implement this measurement in various labs around the world. More accurate measurements are crucial, and can in turn open up new possibilities for all sorts of technologies, including biomedical sensing, laser ranging and quantum communications,” Conlon said.

The new technique revolves around a quirk of quantum systems, known as entanglement. According to researchers, by entangling two identical quantum objects and measuring them together, scientists can determine their properties more precisely than if they were measured individually. Research co-author Dr Syed Assad said that entangling two identical quantum systems can help researchers acquire more information. “There is some unavoidable noise associated with measuring any property of a quantum system. By entangling the two, we’re able to reduce this noise and get a more accurate measurement,” Assad said.

In theory, it is possible to entangle and measure three of more quantum systems to achieve better precision, but in this case the experiments failed to agree with the theory. However, the authors are confident that future quantum computers will be able to overcome these limitations. “Quantum computers with error-corrected qubits will be able to gainfully measure with more and more copies in the future,” Conlon said.

According to Ping Koy Lam, Professor at ANU, one of the key strengths of this work is that a quantum enhancement can still be observed in noisy scenarios. “For practical applications, such as in biomedical measurements, it is important that we can see an advantage even when the signal is inevitably embedded in a noisy real-world environment,” Lam said.

The researchers tested their theory on 19 different quantum computers, across three different platforms: superconducting, trapped ion and photonic quantum computers. These devices are located across Europe and America and are cloud-accessible, allowing researchers from across the globe to connect and carry out their research.

The study was conducted by experts at the ARC Centre of Excellence for Quantum Computation and Communication Technology (CQC2T), in collaboration with researchers from A*STAR’s Institute of Materials Research and Engineering (IMRE). The research findings were published in Nature Physics.

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