Physicists have used entanglement to “extend” the uncertainty principle, improving quantum measurements

Nearly a century ago, German physicist Werner Heisenberg realized that the laws of quantum mechanics place some fundamental limitations on how accurately certain properties of microscopic objects can be measured.

However, the laws of quantum mechanics can also offer ways to make measurements more precise than would otherwise be possible.

in a new search Published in Nature Physics, we have identified a method to achieve more accurate measurements of microscopic objects using quantum computers. This could be useful in a wide range of next-generation technologies, including biomedical sensing, laser ranging, and quantum communications.

We were also able to push the limits of one form of Heisenberg’s Uncertainty Principle in certain circumstances, which suggests that different uncertainty principles may be necessary in different scenarios.

quantitative uncertainty

If you want to examine the characteristics of something as big for everyday use as a car, this is a simple process.

For example, a car has a well-defined position, color, and speed. You can measure them one by one or all at once without problems. Measuring your vehicle’s position will not change its color or speed.

However, this gets more complicated if you are trying to examine microscopic quantum objects such as electrons or photons (which are very small particles of light).

Certain properties of quantum objects are related to each other. Measurement of one characteristic can affect another property.

Read more:
Explanation: Heisenberg’s Uncertainty Principle

For example, measuring the position of an electron will affect its speed and vice versa.

These properties are called “associated” properties.

The link between these properties is a direct manifestation of Heisenberg’s uncertainty principle. Two closely spaced properties of a quantum object cannot be measured simultaneously with any degree of precision you would like: the more you know about one, the less you know about the other.

While the uncertainty principle imposes a limit on how accurate some measurements can be, in practice reaching that limit can be very difficult. However, measuring quantum objects in as much detail as possible is important for the development of basic science as well as the development of new technologies.

tangled objects

In our new research, we have designed a method to more accurately define the conjugate properties of quantum objects. Our collaborators were then able to make this measurement in different laboratories around the world.

The new technique revolves around a strange anomaly in quantum systems, known as entanglement. When two objects are entangled, we can measure them more accurately than if they were not entangled.

Read more:
What is quantum entanglement? A physicist explains the science of Einstein’s “frightening 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 can determine their properties more accurately than if they were measured individually.

The measurement of the two entangled quantum objects reduces the noise in the measurement, making it more accurate.

Less noisy future

Theoretically, it is also possible to entangle and measure three or more quantum systems to achieve better precision. However, we have not been able to perform this work experimentally yet.

The results of measuring three identical entangled objects were very noisy. However, as quantum computers improve and become more accurate, it may be possible to faithfully measure three versions of a quantum system simultaneously in the future.

An advanced cooling device for a quantum computer, on a black background.
Quantum computers of the future may be less noisy.

One of the main strengths of this work is that the 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.

What about the uncertainty principle?

This research also has implications for the uncertainty principle mentioned above.

One explanation of the uncertainty principle is that it is impossible to measure the conjugate properties of quantum objects with infinite precision. But another explanation is that measuring one conjugate property of a quantum object must necessarily disturb the second conjugate property by a minimal amount.

In this paper, we were able to violate the uncertainty principle based on the second explanation. This indicates that depending on the physical environment being considered, different uncertainty principles may be necessary for different scenarios.

Global collaboration

We tested our theory on a total of 19 different quantum computers, which used three different quantum computing techniques: superconductors, trapped ions, and photonics. These devices are located all over Europe and America and are accessible online, allowing researchers from all over the world to connect and conduct important research.

We conducted the study with colleagues at ARC’s Center of Excellence for Quantum Computation and Communication Technology (CQC2T), in collaboration with researchers from A*STAR’s Institute of Materials Research and Engineering in Singapore, the University of Jena, and the University of Jena. Innsbruck, Macquarie University and Amazon Web Services.

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