Scientists find a way to directly measure quantum states, such as momentum, of photons.
Quantum computers and communications promise more powerful machines and unbreakable codes. But to make them work, it's necessary to measure the quantum state of particles such as photons or atoms. Quantum states are numbers that describe particle characteristics such as momentum or energy.
But measuring quantum states is difficult and time-consuming, because the very act of doing so changes them, and because the mathematics can be complex. Now, an international team says they found a more efficient way to do it, which could make it simpler to build quantum-mechanical technologies.
In a study detailed in the Jan. 20 issue of the journal Nature Communications, researchers from the University of Rochester and the University of Glasgow took a direct measurement of a photon's 27-dimensional quantum state. These dimensions are mathematical, not dimensions in space, and each one is a number that stores information. To understand a 27-dimensional quantum state, think about a line described in two dimensions. A line would have a direction in the X and Y coordinates — 3 inches left and 4 inches up, for instance. The quantum state has 27 such coordinates. [Quantum Physics: The Coolest Little Particles in Nature]
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