Physicists pressed light to the quantum limit

A group of physicists from the University of Toronto have found a new technique that can force light to the fundamental quantum limit. This finding has potential applications for high-precision measurement, new generation atomic clocks, new quantum computing, and the most basic understanding of the universe.

Krister Shalm, Rob Adamson and Aephraim Steinberg of the Department of Physics and the Quantum Control and Information Center at U of T, published their findings in the January 1 issue of the international journal Nature.

Dr. Krister Shalm explains: 'Accurate measurement is a very important part of experimental science: accuracy in measurement is directly proportional to the amount of information that can be obtained. In the quantum world, everything is smaller, the exact factor in measurement is often avoided. '

Light is one of the most accurate measuring tools in physics and is used to find answers to basic questions in science from relativism to quantum gravity. However, light also has limitations in the world of advanced quantum technology.

The smallest element of light is the photon and it is so small that a normal light bulb emits billions of photons in a millionth of a second. Professor Aephraim Steinberg explains: "Despite the unimaginable nature of these tiny particles, modern quantum technology relies on these photons to contain and control information. However, it is uncertain. shield, also known as quantum noise, interferes with the information gathering process'.

Development process of triphoton pressing state. Quantum uncertainty in the triphoton is expressed as water droplets on a "squeezed" sphere. (Photo: Victoria Feistner) Pressing is a method of increasing certainty in a number of positions such as position or speed but also has a price. He said: 'If you force to increase the certainty of an attribute, the uncertainty of an additional attribute will increase.'

In U of T's experiment, physicists combined three separate photon types together in an optical fiber to create a triphoton. Steinberg said: 'A strange feature of quantum physics is that when some identical photons are combined, like optical fibers are used to transmit the internet to your home, they experience a' crisis. identity ', and no one can know what a single photon is doing'. The authors then pressed the triphoton state to encode the encoded quantum information in the polarization of triphoton. (Polarized is the attribute of light, the basis of 3D films, lusting glazing, and a host of advanced technologies such as quantum cryptography).

In the previous study, scientists thought that the pressing method could be used indefinitely, ignoring the development of uncertainty in ways that were not worth considering.'However the world of polarization, like the Earth, is not flat,' Steinberg observed.

He explained: 'The state of polarization can be visualized as a small continent floating on a sphere. When we force the triphoton continent, first of all it takes place as the original experiment. But when we squeeze to a certain extent, the continent extends too much and begins to cover the surface of the sphere '.

'All previous experiments are restricted to small areas where the sphere, like where you live, looks like a flat surface. This task needs to determine the triphoton on a sphere, easily visualized and applied. Accordingly, we show for the first time that the nature of polarization creates different states and gives a limit to the ability to squeeze '.

Rob Adamson said: 'Creating this special combination state allows the limits of the pressing method to be studied thoroughly. For the first time we have demonstrated the technique of creating any desired triphoton state and showing that the spherical nature of the polarization state of light is an inevitable result. This is simply: to visualize the quantum state of light, shining light on a sphere '.