QUANTUM INFORMATION AND
TERAHERTZ TECHNOLOGY PROJECT

Record QKD lengths with TES detector
Demonstrated QKD of record lengths in fiber using a Transition-edge sensor with Los Alamos National Laboratory.  For QKD systems utilizing BBBSS91 privacy amplification, we demonstrated a link of 185 km.  For a QKD system that is secure from photon-number splitting attack, using a weak coherent source, we demonstrated a fiber link of 68 km.  For a QKD link that implements a decoy state protocol for security, we have demonstrated a link of 108 km.
Contact: Dr. Sae Woo Nam

Record length and rate quantum key distribution link
Sent photons as quantum keys over a record-setting 200-kilometer fiber-optic link in collaboration with NTT Corp. of Japan and Stanford University. The experiment was also the first gigabit-rate experiment—transmitting at 10 Gbits/s -- to produce secure keys. The rate of processed key production—the keys corrected for errors and enhanced for privacy—was much lower due to the long distance involved, and the key was not used to encrypt a digital message as it would be in a complete quantum key distribution (QKD) system. A key aspect of the experiment was the use of ultrafast single-photon detectors, consisting of superconducting niobium nitride nanowires, developed at the Moscow State Pedagogical University in Russia. The detectors have very low false count rates as well as superior timing resolution. Packaging and cooling technology is custom-made at NIST, which offers unique expertise in connecting the single-photon detector chips to optical fiber, in amplifying the detector signals, and in designing refrigeration systems to operate at around 3 K without liquid cryogens. The QKD experiment, using mostly standard components and transmitting at telecommunications wavelengths near 1500 nm, offers an approach for making practical inter-city terrestrial quantum communications networks as well as long-range wireless systems using communicationn satellites.
Contact: Dr. Sae Woo Nam

Single photon source characterized with superconducting detector
Demonstrated, with the Nanostructure Fabrication and Metrology Project, the first use of superconducting single photon detectors (SSPDs) for single photon source characterization. The source was an optically pumped, microcavity-coupled InGaAs quantum dot, emitting single photons at 902 nm. The two SSPDs replaced the silicon Avalanche Photodiodes (APDs) in a Hanbury-Brown Twiss interferometer measurement of the source’s second-order correlation function. The detection efficiency of the superconducting detector system was greater than 2 % (coupling losses included). The SSPD system electronics jitter was 68 ps, versus 550 ps for the APD units, allowing the source spontaneous emission lifetime to be measured with improved resolution. SSPDs offer single-photon counting at fast rates, low jitter, and low dark counts, from visible wavelengths well into the infrared.
Contact: Dr. Sae Woo Nam 

Time-correlated single-photon counting with superconducting detector Demonstrated, in collaboration with the Nanostructure Fabrication and Metrology Project, the advantages of a NbN-based superconducting single-photon detector (SSPD) in a time-correlated, single-photon counting scheme to measure short spontaneous emission lifetimes of quantum wells in the infrared. The instrument response function (IRF) of the SSPD was shown to be Gaussian over nearly five decades of dynamic range. The FWHM of the IRF, which is a measure of the timing jitter, was 68 ps. These response characteristics are of great advantage over those of Si avalanche photodiodes (APDs) for detailed measurement of emission decay curves with high temporal resolution. In contrast, the IRFs of Si APDs exhibit long tails and multi component responses. Quantum well emission out to 1245 nm in wavelength was measured with the SSPD, well beyond the photosensitive range of Si. APDs based on InGaAs or Ge can have reasonable detection efficiencies in the infrared, but have limited available dynamic range. Contact: Dr. Sae Woo Nam

Record-low sensitivity millimeter-wave imaging system Demonstrated a passive millimeter-wave imaging system with a net-equivalent-temperature-difference sensitivity of record 0.13 K. The detectors are cryogenically cooled, super conducting antenna-coupled microbolometers. Images of contraband concealed under clothing were obtained, clearly demonstrating the potential for passive indoor imaging. Contact: Dr. Erich N. Grossman

Terahertz power calibration source
Developed and characterized a novel, aqueous blackbody calibration (ABC) source for calibrating optical power in the mm-wave to terahertz frequency band. The blackbody is a body of water, extremely absorptive in this frequency range, held at a uniform and known temperature in a specially designed container made of expanded polystyrene. The problem of non-zero reflectance at interfaces is solved by a four-reflection, optical trap geometry, the same idea behind trap detectors used in the calibration of optical fiber power meters. The effective emissivity of the source is > 98.5% over the operating band. 'Beta testing' of the calibrator is ongoing at several collaborating institutions. The ABC source represents an effort to bring systematic and traceable radiometric measurement techniques to the millimeter-wave and terahertz bands similar to those well-developed in the optical and infrared bands..
Contact: Dr. Erich N. Grossman

Spectral decomposition of millimeter-wave images
Developed tools and made measurements to accurately decompose the spectral structure of images obtained with a lens/antenna-coupled, cryogenic microbolometer, in collaboration with the Millimetre Wave Laboratory of Finland and UC Santa Barbara. The THz circular variable filter forms a basic monochromator and the aqueous blackbody calibration (ABC) source forms a spectrally flat reference; together they enable absolutely calibrated, ultrawideband, multispectral imaging at the pW power levels appropriate for passive indoor concealed object detection. Real ultrawideband images of personnel consist of superpositions of low frequency images with good clothing penetration but poor spatial resolution and high frequency images with shallower penetration but better spatial resolution. The spectral response of the imaging system obtained from a photomixer-based measurement at UCSB and that from a filtered blackbody measurement at NIST agree at the 5% level.
Contact: Dr. Erich N. Grossman

Millimeter-wave detector testing
Completed the Phase I testing of millimeter-wave detector arrays for the DARPA MIATA program. Measurements of noise spectral density and responsivity to blackbody temperature changes enabled the most direct and accurate measurement of the noise equivalent temperature difference for the zero-bias diode and optical modulator-based detectors from the industry and university participants in the program. Coherent measurements using a swept frequency monochromatic source were made to determine spectral responsivity over the W-band (75 to 110 GHz), and antenna patterns were also measured for some of the detectors using the NIST mm-wave/terahertz antenna range developed by project members. DARPA benefits significantly from the neutral third-party testing role that NIST performs for this program. The detector technology has potential application in areas such as helicopter navigation, firefighting, and concealed weapons detection.
Contact: Dr. Erich N. Grossman