Record-efficiency single-photon detector
Demonstrated the highest known system detection efficiency for a near-infrared single-photon detector. Photon-number-resolving, transition-edge sensors (TESs) with maximized absorption across both telecom bands centered at 1550 nm and 1310 nm were fabricated by embedding tungsten films in an optimized optical cavity structure. The TESs have superconducting transition temperatures higher than those for the previous generation, enabling thermal recovery times to be less than 1 microsecond (compared to 5 microsecond decay times previously) while maintaining excellent number discrimination between multiphoton events. Almost complete reduction of coupling losses from input fiber to detector was achieved by AR-coating the fiber, alignment by back-side, through-chip imaging, and assessment of fiber-to-detector spacing via a method originating from swept-frequency laser interferometry. The measured system detection efficiency was a record 95 % +/- 2 % at 1556 nm, characterized over various detector bias points and input power levels and consistent with measurements and simulations of the optical elements and system losses. Single photon detectors with high detection efficiency are a requirement for many quantum information applications and for optical power traceability to the photon.
Contact: Dr.
Sae Woo Nam
|
|
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 |
 |
Photon-pair source
Demonstrated a fiber-based photon pair source with record high coincidence-to-accidental ratio (CAR) of 1300. The photon pairs were generated through spontaneous four-wave mixing (FWM) in dispersion shifted fiber. The record CAR was achieved through careful characterization and minimization of all background photons (including almost complete suppression of the strong Raman scattering in fiber by cooling the fiber to 4 K in a dewar of liquid helium) and through optimized pair production efficiency using data from a seeded FWM measurement. This yielded a high efficiency, low-noise photon pair source that is compatible with existing fiber telecom networks. Photon pair sources are useful in the generation of entangled photon pairs or heralded single photons, for applications such as linear optical quantum computing and entanglement-based quantum key distribution.
Contact: Dr.
Shellee Dyer
|
Millimeter-wave/terahertz imaging system
Developed and demonstrated an ultra-wideband, millimeter-wave/terahertz detector array for use in contraband detection. The modular system of 8-element, linear detector arrays, scalable to a 128-channel THz camera, is based on Nb and NbN superconducting microbolometer detectors co-developed with VTT of Finland. Raster-scanned images of human subjects rank among the best in their class, clearly revealing handguns, ceramic knives, and other contraband hidden under clothing and distinguishing them from wallets, cellphones and other innocuous items. The unique wideband (0.2-1.4 THz) feature of the imaging system enables a high spatial resolution with a reasonable optical system footprint. Modularity is arguably the most important feature of the system, enabling reconfigurable focal plane sampling and lowered costs due to the robustness to lower-yield fabrication processes. Tuning and characterization of the spatial resolution, noise-equivalent temperature difference, and spectral response of the imaging system was accomplished using standard targets, the Aqueous Blackbody Calibration (ABC) source, and variable filters specifically developed for terahertz frequency metrology.
Contact: Dr.
Erich N. Grossman |
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
Millimeter-wave monochromator
Demonstrated a novel, circular variable millimeter-wave monochromator spanning an octave in frequency, with interchangeable ranges. Measured a spectral resolving power of 6, reasonably well matched to the width of recently reported spectral signatures of solid explosives, with less than 0.5 dB insertion loss. Because microbolometers are inherently ultrawideband, such a monochromator enables true terahertz color imaging from a microbolometer based camera.
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
|
