Nearly a century ago, the German physicist Werner Heisenberg realized that the laws of quantum mechanics put some fundamental limits on how precisely we can measure certain properties of microscopic objects.
However, the laws of quantum mechanics can also provide ways to make more precise measurements than would otherwise be possible.
In new research published in Nature Physics, we outline a way to obtain more precise measurements of microscopic objects using quantum computers. This could prove useful in a wide range of cutting-edge technologies, including biomedical sensing, laser measurement and quantum communications.
We have also been able to push the limits of a variation of Heisenberg’s “uncertainty principle” under certain circumstances, suggesting that different uncertainty principles may be needed in different scenarios.
If you want to examine the properties of a large everyday object like a car, it’s a simple process.
For example, a car has a well-defined position, color and speed. You can measure them one after the other or all at once without any problems. Measuring your car’s position will not change its color or speed.
However, this becomes much more complicated if you are trying to examine microscopic quantum objects such as electrons or photons (which are tiny particles of light).
Certain properties of quantum objects are connected to each other. Measuring one property can influence another property.
Read more: Explainer: Heisenberg’s Uncertainty Principle
For example, measuring the position of an electron will affect its speed and vice versa.
These properties are called “conjugate” properties.
The connection between these properties is a direct manifestation of Heisenberg’s uncertainty principle. It is not possible to simultaneously measure two conjugate properties of a quantum object with any degree of accuracy you want: the more you know about one, the less you know about the other.
While the uncertainty principle imposes a limit on how precise some measurements can be, reaching this limit in practice can be very difficult. However, measuring quantum objects in the greatest amount of detail possible is important for advancing fundamental science as well as developing new technologies.
In our new research, we have designed a way to determine the conjugate properties of quantum objects with greater precision. Our collaborators were then able to perform this measurement in various laboratories around the world.
The new technique revolves around a strange quirk of quantum systems known as entanglement. When two objects are entangled, we can measure them more precisely than if they were not entangled.
Read more: What is quantum entanglement? A physicist explains the science of Einstein’s ‘spooky action at a distance’
We realized that we can use quantum computers, which can precisely control the state of quantum objects, to create two identical quantum objects and entangle them. By measuring entangled objects together, we could determine their properties more precisely than if they were measured individually.
Measuring the two identical quantum objects entangled reduces the noise in the measurement, making it more accurate.
A less noisy future
In theory, it is also possible to entangle and measure three or more quantum systems to achieve even better precision. However, we have not yet been able to do this work experimentally.
The measurement results of three identical objects entangled together were very noisy. However, as quantum computers improve and become more accurate, it may be possible to faithfully measure three copies of a quantum system simultaneously in the future.
One of the strengths of this work is that a quantum improvement can still be observed in very noisy scenarios. This bodes well for future practical applications, such as biomedical measurements, which will inevitably take place in noisy real-world environments.
But the uncertainty principle?
This research also has implications for the aforementioned uncertainty principle.
One interpretation of the uncertainty principle is that it is impossible to measure conjugate properties of quantum objects with unlimited precision. But another interpretation is that measuring one conjugate property of a quantum object must necessarily perturb the second conjugate property by a minimal amount.
In this research, we succeeded in violating an uncertainty principle based on the second interpretation. This suggests that depending on the physical context considered, different uncertainty principles may be required for different scenarios.
A global collaboration
We tested our theory on a total of 19 different quantum computers, which used three different quantum computing technologies: superconductors, trapped ions and photonics. These devices are located in Europe and America and can be accessed via the Internet, allowing researchers around the world to connect and conduct important research.
We conducted the study together with colleagues from the ARC Center of Excellence for Quantum Computing and Communications Technology (CQC2T), in collaboration with researchers from the Materials Research and Engineering Institute at A*STAR in Singapore, the University of Jena, the University of Innsbruck, Macquarie University and Amazon Web Services.