Breakthrough for photons in the microwave frequency range

Feb 22, 2011
Schematic illustration of the microchip produced in the ETH Zurich FIRST cleanroom, showing the photon source in the upper half and the beam splitter in the lower half. Credit: ETH Zurich

Photons in the microwave frequency range are important in quantum research - for quantum information processors, for example. Now, for the first time, researchers have achieved the controlled production of single photons in the microwave region and successfully detected them with highly sensitive measuring instruments - although they are 100,000 times weaker than the photons emitted by an electric light bulb.

When released by a conventional light or radiation source hit a detector, they trigger an comparable to a single “click” of a Geiger counter, which rattles when radioactive particles strike it. However, unlike optical photons, until now there have been no detectors that can detect single photons at particularly low frequencies, such as the microwave frequency range. The intensity of these microwave photons is much too weak for this. The research group led by ETH Zurich Professor Andreas Wallraff from the Department of Physics has now been able to characterise such low-intensity photons even without any “clicking” detectors by using a special apparatus and method. Physicists need techniques of this kind, for example to research the fundamental principles of quantum mechanics or to enable efficient information transmission in optical data communication.

Detector and emitter in one

In the interdisciplinary collaboration between Wallraff’s group, the Master student Deniz Bozyigit from the Department of Information Technology and Electrical Engineering and Canadian scientists, the researchers integrated a light source that generates single microwave photons onto a microchip. The frequency range of these photons is a few gigahertz, similar to the electromagnetic radiation of mobile phones and microwave ovens. With this innovative arrangement, a single photon is generated with an accuracy controlled to within a few nanoseconds and at a total rate of two million times per second. The scientists also constructed a highly sensitive and efficient measuring device, similar to that used for optical photons, on the same microchip in order to show that this apparatus really does generate only single photons.

Only one way possible

In the case of optical photons, a half-mirrored beam splitter is used for this purpose. The photons can either be reflected or pass through the beam splitter, with equal probability. For each of these two alternatives there is a detector which identifies the reflected or transmitted photon. According to the laws of quantum mechanics, an individual photon generated by a photon source can never be half-reflected and half-transmitted. It must opt for one of the two alternatives. In this case the light is no longer described by its wave properties as in classical physics; the photons behave like particles. If only one of the detectors “clicks”, this proves that the source really does generate only single photons.

Wallraff explains how single photons have now been successfully recorded in this way even in the microwave frequency range: “Until now it was thought that these correlations – characterizing the properties of the photons and how they behave at a beam splitter – could be measured only if the detector detects the photons with a “click”, like a particle. Since the intensity of photons in the microwave frequency range is too weak for this, we amplify the signals of the incoming photons and then measure the amplitude of the field generated by the photons”. To cope with the immense volume of data from these measurements, amounting to more than 1,000 gigabytes per hour, the researchers also needed to develop an innovative system which can process this data in real time. From the statistics thus obtained, and by using the newly developed method, they were able to prove that only a single photon is emitted and, as expected, this took either one or the other of the possible routes.

Very promising for information processing

If it proves possible to manipulate and measure individual photons in the microwave frequency range, this measuring unit could become a component of a quantum computer: single photons strike a beam splitter and transmit information quantum mechanically across an integrated microchip, and are then detected. According to the physicist, this could allow information processing procedures to be carried out more efficiently in the future.

Explore further: High power laser sources at exotic wavelengths

More information: Bozyigit D et al.: Antibunching of microwave-frequency photons observed in correlation measurements using linear detectors, Nature Physics 7, 154–158 (2011) doi:10.1038/nphys1845

Related Stories

Shining light in quantum computing

Sep 12, 2006

University of Queensland scientist Devon Biggerstaff is investigating ways to manipulate light in a process that will help shape future supercomputers and communication technology.

Quantum electronics: Two photons and chips

Jan 20, 2006

Scientists at Toshiba Research Europe Limited (Cambridge, UK) believe they are on to a way of producing entangled twins of photons using a simple semiconductor electronic device. Such a chip-based source of entangled photons ...

NIST researchers create 'quantum cats' made of light

Sep 01, 2010

Researchers at the National Institute of Standards and Technology have created "quantum cats" made of photons (particles of light), boosting prospects for manipulating light in new ways to enhance precision ...

Recommended for you

High power laser sources at exotic wavelengths

Apr 14, 2014

High power laser sources at exotic wavelengths may be a step closer as researchers in China report a fibre optic parametric oscillator with record breaking efficiency. The research team believe this could ...

Combs of light accelerate communication

Apr 14, 2014

Miniaturized optical frequency comb sources allow for transmission of data streams of several terabits per second over hundreds of kilometers – this has now been demonstrated by researchers of Karlsruhe ...

User comments : 0

More news stories

CERN: World-record current in a superconductor

In the framework of the High-Luminosity LHC project, experts from the CERN Superconductors team recently obtained a world-record current of 20 kA at 24 K in an electrical transmission line consisting of two ...

Glasses strong as steel: A fast way to find the best

Scientists at Yale University have devised a dramatically faster way of identifying and characterizing complex alloys known as bulk metallic glasses (BMGs), a versatile type of pliable glass that's stronger than steel.

Patent talk: Google sharpens contact lens vision

(Phys.org) —A report from Patent Bolt brings us one step closer to what Google may have in mind in developing smart contact lenses. According to the discussion Google is interested in the concept of contact ...

Tech giants look to skies to spread Internet

The shortest path to the Internet for some remote corners of the world may be through the skies. That is the message from US tech giants seeking to spread the online gospel to hard-to-reach regions.

Wireless industry makes anti-theft commitment

A trade group for wireless providers said Tuesday that the biggest mobile device manufacturers and carriers will soon put anti-theft tools on the gadgets to try to deter rampant smartphone theft.