Fake color scanning electron micrograph of a nano-photon frequency converter containing a ring resonator (blue shaded portion) with light (red portion) injected into the ring resonator. The input signal is represented by a purple arrow and converted to a new frequency (blue arrow) by using two pump lasers (bright red and dark red arrows).
Converting a single photon from one color or frequency to another is an important tool in quantum communication that takes advantage of the subtle relationship between the subatomic properties of photons (particles of light) to safely store and transmit information. Scientists at the National Institute of Standards and Technology have now developed a miniaturized frequency converter using techniques similar to those used to make computer chips.
This tiny device will help improve safety and increase the working distance of next-generation quantum communication systems, make them adaptable for a wide variety of purposes, and make them easy to integrate with other information processing components, and Can be large-scale production.
This new nano-scale optical frequency converter effectively converts photons from one frequency to another while consuming only a small amount of power and adding a very low noise level, ie, the ambient light is uncorrelated with the input signal.
Frequency converters are the key to solving both problems. The optimal frequency at which quantum systems generate and store information is usually much higher than the frequency required to transmit this information over distances of kilometers in fiber optics. Switching photons between these frequencies requires a few hundred terahertz shifts (a THz equal to one trillion cycles per second).
A smaller but still critical frequency mismatch occurs when the shape and composition of two quantum systems that would otherwise be intended to be identical has a small change. These changes cause the system to produce photons with slightly different frequencies rather than the exact duplication that a quantum communication network may require.
The new photon frequency converter, which serves as an example of a nano-photonics project, addresses both the issues at the same time, QingLi, Marcelo Davanco and Kartik Srinivasan report in Nature Photonics. The key component of the IC is a tiny ring resonator with a diameter of about 80 microns (slightly less than the width of a human hair) and a few tenths of microns thick. The shape and size of this ring made of silicon nitride have been optimized to enhance the inherent properties of the material to convert light from one frequency to another. The ring resonator is driven by two pump lasers, each operating on an independent frequency. In a system called four-wave mixing Bragg scattering, the frequency of a photon entering the ring resonator varies by an amount equal to the frequency difference between the two pump lasers.
Like cycling on a track, incident light is circulated hundreds of times before coming out of the resonator, greatly increasing the device's ability to convert photons at low power and low background noise. Unlike previous experiments that used a few watts of power, the system consumed only a few hundredths of a watt of power. More importantly, the amount of added noise is low enough that it can be used in experiments that use single photon sources in the future.
While other technologies have been applied to frequency conversion, "nanophotonics has its benefits as well, making it possible to make devices smaller, easier to customize, lower power consumption, and compatible with mass-manufacturing technologies," Srinivasan said. "Our work is the first demonstration of nanophotonic technology that is suitable for this daunting task of quantum frequency conversion."
This work was done by researchers at the NIST Center for Nanoscience and Technology.
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