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: The importance of three-way atom interactions in maintaining coherence

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

Controlling core switching in Pac-man disks

Dec 24, 2014

Magnetic vortices in thin films can encode information in the perpendicular magnetization pointing up or down relative to the vortex core. These binary states could be useful for non-volatile data storage ...

World's most complex crystal simulated

Dec 24, 2014

The most complicated crystal structure ever produced in a computer simulation has been achieved by researchers at the University of Michigan. They say the findings help demonstrate how complexity can emerge ...

Atoms queue up for quantum computer networks

Dec 24, 2014

In order to develop future quantum computer networks, it is necessary to hold a known number of atoms and read them without them disappearing. To do this, researchers from the Niels Bohr Institute have developed ...

New video supports radiation dosimetry audits

Dec 23, 2014

The National Physical Laboratory (NPL), working with the National Radiotherapy Trials Quality Assurance Group, has produced a video guide to support physicists participating in radiation dosimetry audits.

Ultrasounds dance the 'moonwalk' in new metamaterial

Dec 23, 2014

Metamaterials have extraordinary properties when it comes to diverting and controlling waves, especially sound and light: for instance, they can make an object invisible, or increase the resolving power of ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.