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New Discovery Challenges Heisenberg's Uncertainty Principle, Advancing Quantum Mechanics

First Posted: Mar 04, 2013 09:39 AM EST

Heisenberg's famous Uncertainty Principle may not be as uncertain as once thought. Researchers have applied a recently developed technique to directly measure the polarization of light, which overcomes some important challenges of the principle and is also applicable to qubits, the building blocks of the quantum information theory.

The findings, published in the journal Nature Photonics, used a direct measurement technique that was first developed in 2011 by scientists at the National Research Council, Canada. It was first created in order to measure the wavefunction, which is a way of determining the state of a quantum system.

The Uncertainty Principle itself is used in quantum mechanics. It's any of a variety of mathematical inequalities asserting a fundamental limit to the precision with which certain pairs of physical properties of a particle can be known simultaneously. This is why the direct measurement of the wavefunction has long seemed impossible--certain properties of a system could only be known poorly if other related properties were known with precision.

The newest findings from researchers challenge this long-held belief, though. Previously, researchers only were able to use a technique called quantum tomography to measure the information in these states indirectly. Yet the new technique that this experiment employed allowed them to measure information directly. The scientists measured the polarization states of light, the directions in which magnetic fields of the light oscillate. The key result was that it was actually possible to measure key related variables of a quantum particle or state directly.

So how did they do it? The researchers used the position and momentum of light as the indicator of the polarization state. In particular, they then used two birefringement crystals, which cause a spatial separation when light passes through them, of different thicknesses. One of the crystals was thicker than the other, and the researchers were able to take two measurements from the experiment by using a technique so that the system is not disturbed significantly after the first property is measured. They repeated the process several times in order to build up accurate statistics.

In addition to challenging the Uncertainty Principle, the scientists were also able to gain a full, direct characterization of the polarization states of the light. It's a huge step forward for quantum mechanics, and may change the way scientists approach the field. In the future, the researchers involved in the study plan to apply the technique to other systems in order to measure the form of a "mixed" quantum state.

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