Advancing secure communications: A better single-photon emitter for quantum cryptography

Apr 09, 2013 by Nicole Casal Moore
An atomic force microscope image of a nanowire single photon emitter. Credit: Pallab Bhattacharya

(Phys.org) —In a development that could make the advanced form of secure communications known as quantum cryptography more practical, University of Michigan researchers have demonstrated a simpler, more efficient single-photon emitter that can be made using traditional semiconductor processing techniques.

Single-photon emitters release one particle of light, or photon, at a time, as opposed to devices like lasers that release a stream of them. Single-photon emitters are essential for , which keeps secrets safe by taking advantage of the so-called observer effect: The very act of an eavesdropper listening in jumbles the message. This is because in the quantum realm, observing a system always changes it.

For quantum cryptography to work, it's necessary to encode the message—which could be a bank password or a piece of military intelligence, for example—just one photon at a time. That way, the sender and the recipient will know whether anyone has tampered with the message.

While the U-M researchers didn't make the first single-photon emitter, they say their new device improves upon the current technology and is much easier to make.

"This thing is very, very simple. It is all based on silicon," said Pallab Bhattacharya, the Charles M. Vest Distinguished University Professor of Electrical Engineering and Computer Science, and the James R. Mellor Professor of Engineering.

Bhattacharya, who leads this project, is a co-author of a paper on the work published in Nature Communications on April 9.

Nanowires growing on silicon. Credit: Pallab Bhattacharya

Bhattacharya's emitter is a single nanowire made of with a very small region of gallium nitride that behaves as a quantum dot. A quantum dot is a that can generate a bit of information. In the of conventional computers, a bit is a 0 or a 1. A can be either or both at the same time.

The the new emitter is made of are commonly used in LEDs and solar cells. The researchers grew the on a wafer of silicon. Because their technique is silicon-based, the infrastructure to manufacture the emitters on a larger scale already exists. Silicon is the basis of modern electronics.

"This is a big step in that it produces the pathway to realizing a practical electrically injected single-photon emitter," Bhattacharya said.

Key enablers of the new technology are size and compactness.

"By making the diameter of the nanowire very small and by altering the composition over a very small section of it, a quantum dot is realized," Bhattacharya said. "The quantum dot emits single-photons upon electrical excitation."

The U-M is fueled by electricity, rather than light—another aspect that makes it more practical. And each photon it emits possesses the same degree of linear polarization. Polarization refers to the orientation of the electric field of a beam of light. Most other single-photon emitters release light particles with a random polarization.

"So half might have one polarization and the other half might have the other," Bhattacharya said. "So in cryptic message, if you want to code them, you would only be able to use 50 percent of the photons. With our device, you could use almost all of them."

This device operates at cold temperatures, but the researchers are working on one that operates closer to room temperature.

The paper is titled "Electrically-driven polarized single-photon emission from an InGaN quantum dot in a GaN nanowire." The first author is Saniya Deshpande, a graduate student in electrical engineering and computer science. The work is supported by the National Science Foundation. The device was fabricated at the U-M Lurie Nanofabrication Facility.

Explore further: Physicists design quantum switches which can be activated by single photons

Related Stories

First noiseless single photon amplifier

Nov 12, 2012

Research physicists have demonstrated the first device capable of amplifying the information in a single particle of light without adding noise.

Towards 'unbreakable' message exchange

Aug 03, 2012

Single particles of light, also known as photons, have been produced and implemented into a quantum key distribution (QKD) link, paving the way for unbreakable communication networks.

Recommended for you

Could 'Jedi Putter' be the force golfers need?

Apr 18, 2014

Putting is arguably the most important skill in golf; in fact, it's been described as a game within a game. Now a team of Rice engineering students has devised a training putter that offers golfers audio, ...

User comments : 0

More news stories

NASA's space station Robonaut finally getting legs

Robonaut, the first out-of-this-world humanoid, is finally getting its space legs. For three years, Robonaut has had to manage from the waist up. This new pair of legs means the experimental robot—now stuck ...

Ex-Apple chief plans mobile phone for India

Former Apple chief executive John Sculley, whose marketing skills helped bring the personal computer to desktops worldwide, says he plans to launch a mobile phone in India to exploit its still largely untapped ...

Filipino tests negative for Middle East virus

A Filipino nurse who tested positive for the Middle East virus has been found free of infection in a subsequent examination after he returned home, Philippine health officials said Saturday.

Egypt archaeologists find ancient writer's tomb

Egypt's minister of antiquities says a team of Spanish archaeologists has discovered two tombs in the southern part of the country, one of them belonging to a writer and containing a trove of artifacts including reed pens ...