News for faculty and staff

Contact | Past Issues

Week of April 15, 2013

Research


A better single-photon emitter for quantum cryptography

In a development that could make the advanced form of secure communications known as quantum cryptography more practical, U-M 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.

An atomic force microscope image of a nanowire single-photon emitter. Photo courtesy Pallab Bhattacharya.

Single-photon emitters are essential for quantum cryptography, 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.

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

The semiconducting materials the new emitter is made of are commonly used in LEDs and solar cells. The researchers grew the nanowires 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.

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 first author of the paper is Saniya Deshpande, a graduate student in electrical engineering and computer science.

READER COMMENTS (0) POST A COMMENT 

Leave a comment

All fields are required.




email address will not be shown


Please enter the words you see below for anti-spam purposes:
NO SPAM

 

STAFF SPOTLIGHT

Karen Simpson, student financial assistant, Student Financial Services, on the increase in technology in her 35 years at U-M: “When I first came here we were typing student checks on typewriters. Now, everything is very modernized, very streamlined.”

EVENTS

“Crazy for You,” 7:30 p.m. April 18, 8 p.m. April 19-20 and 2 p.m. April 21, Power Center for the Performing Arts.

View/Submit Events