Featured Research

from universities, journals, and other organizations

New Quantum Dot Transistor Counts Individual Photons

Date:
October 15, 2007
Source:
National Institute of Standards and Technology
Summary:
Researchers have designed and demonstrated a transistor containing quantum dots that can count individual photons. The semiconductor device could be integrated easily into electronics for applications such as quantum key distribution for 'unbreakable' encryption using single photons.

NIST's modified field-effect transistor can count single photons, or particles of light. When light enters through the transmission window (see electron micrograph of top of device), it penetrates the gallium arsenide absorbing layer and separates electrons from the ‘holes’ they formerly occupied. Quantum dots (red dots) trap the positively charged holes, while electrons flow into the channel (green Xs). By measuring the channel current, researchers can determine the number of photons absorbed.
Credit: NIST

A transistor containing quantum dots that can count individual photons (the smallest particles of light) has been designed and demonstrated at the National Institute of Standards and Technology (NIST). The semiconductor device could be integrated easily into electronics and may be able to operate at higher temperatures than other single-photon detectors--practical advantages for applications such as quantum key distribution (QKD) for "unbreakable" encryption using single photons.

The NIST device, described in a new paper,* can accurately count 1, 2 or 3 photons at least 83 percent of the time. It is the first transistor-based detector to count numbers of photons; most other types of single-photon detectors simply "click" in response to any small number of photons. (See table for a comparison of various types of single-photon detectors used at NIST.)

Counting requires a linear, stepwise response and low-noise operation. This capability is essential for advanced forms of precision optical metrology--a focus at NIST--and could be used both to detect photons and to evaluate single-photon sources for QKD. The new device also has the potential to be cooled electronically, at much higher temperatures than typical cryogenic photon detectors.

Dubbed QDOGFET, the new detector contains about 1,000 quantum dots, nanoscale clusters of semiconductors with unusual electronic properties. The NIST dots are custom-made to have the lowest energy of any component in the detector, like the bottom of a drain. A voltage applied to the transistor produces an internal current, or channel. Photons enter the device and their energy is transferred to electrons in a semiconductor "absorbing layer," separating the electrons from the "holes" they formerly occupied.

As each photon is absorbed, a positively charged hole is trapped by the quantum dot drain, while the corresponding electron is swept into the channel. The amount of current flowing in the channel depends on the number of holes trapped by quantum dots. By measuring the channel response, scientists can count the detected photons. NIST measurements show that, on average, each trapped hole boosts the channel current by about one-fifth of a nanoampere. The detector has an internal quantum efficiency (percentage of absorbed photons that result in trapped holes) of 68 18 percent, a record high for this type of photon detector.

The QDOGFET currently detects single photons at wavelengths of about 800 nanometers. By using different semiconductor materials, NIST researchers hope to make detectors that respond to the longer near-infrared wavelengths used in telecommunications. In addition, researchers hope to boost the external quantum efficiency (percentage of photons hitting the detector that are actually detected), now below 10 percent, and operate the device at faster speeds.

The research is supported in part by the Disruptive Technology Office. The authors include one from Los Alamos National Laboratory and one from Heriot-Watt University, Edinburgh, UK.

* E.J. Gansen, M.A. Rowe, M.B. Greene, D. Rosenberg, T.E. Harvey, M.Y. Su, R.H. Hadfield, S.W. Nam and R.P. Mirin. Photon-number-discriminating detection using a quantum dot, optically gated, field-effect transistor. Nature Photonics. 1, 585 - 588 (2007). Published on-line Oct. 1, 2007.


Story Source:

The above story is based on materials provided by National Institute of Standards and Technology. Note: Materials may be edited for content and length.


Cite This Page:

National Institute of Standards and Technology. "New Quantum Dot Transistor Counts Individual Photons." ScienceDaily. ScienceDaily, 15 October 2007. <www.sciencedaily.com/releases/2007/10/071011180823.htm>.
National Institute of Standards and Technology. (2007, October 15). New Quantum Dot Transistor Counts Individual Photons. ScienceDaily. Retrieved July 25, 2014 from www.sciencedaily.com/releases/2007/10/071011180823.htm
National Institute of Standards and Technology. "New Quantum Dot Transistor Counts Individual Photons." ScienceDaily. www.sciencedaily.com/releases/2007/10/071011180823.htm (accessed July 25, 2014).

Share This




More Matter & Energy News

Friday, July 25, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

TSA Administrator on Politics and Flight Bans

TSA Administrator on Politics and Flight Bans

AP (July 24, 2014) TSA administrator, John Pistole's took part in the Aspen Security Forum 2014, where he answered questions on lifting of the ban on flights into Israel's Tel Aviv airport and whether politics played a role in lifting the ban. (July 24) Video provided by AP
Powered by NewsLook.com
Creative Makeovers for Ugly Cellphone Towers

Creative Makeovers for Ugly Cellphone Towers

AP (July 24, 2014) Mobile phone companies and communities across the country are going to new lengths to disguise those unsightly cellphone towers. From a church bell tower to a flagpole, even a pencil, some towers are trying to make a point. (July 24) Video provided by AP
Powered by NewsLook.com
Algonquin Power Goes Activist on Its Target Gas Natural

Algonquin Power Goes Activist on Its Target Gas Natural

TheStreet (July 23, 2014) When The Deal's Amanda Levin exclusively reported that Gas Natural had been talking to potential suitors, the Ohio company responded with a flat denial, claiming its board had not talked to anyone about a possible sale. Lo and behold, Canadian utility Algonquin Power and Utilities not only had approached the company, but it did it three times. Its last offer was for $13 per share as Gas Natural's was trading at a 60-day moving average of about $12.50 per share. Now Algonquin, which has a 4.9% stake in Gas Natural, has taken its case to shareholders, calling on them to back its proposals or, possibly, a change in the target's board. Video provided by TheStreet
Powered by NewsLook.com
Robot Parking Valet Creates Stress-Free Travel

Robot Parking Valet Creates Stress-Free Travel

AP (July 23, 2014) 'Ray' the robotic parking valet at Dusseldorf Airport in Germany lets travelers to avoid the hassle of finding a parking spot before heading to the check-in desk. (July 23) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

    Health News

      Environment News

        Technology News



          Save/Print:
          Share:

          Free Subscriptions


          Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

          Get Social & Mobile


          Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

          Have Feedback?


          Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
          Mobile: iPhone Android Web
          Follow: Facebook Twitter Google+
          Subscribe: RSS Feeds Email Newsletters
          Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins