Royal Holloway University of London Towards passive terahertz imaging using a semiconductor quantum dot sensor Vladimir Antonov Royal Holloway University of London http://www.teraeye.com

Acknowledgments Royal Holloway, UK : H Hashiba Tokyo University&JST, Japan: Prof. S Komiyama, Drs. J Chen, O Astafiev (NEC) ISSP RAN, Russia: Dr. L Kulik NPL, UK: Dr A Tzalenchuk, Dr S Gibling and P Kleinschmidt Chalmers University, Sweden: Prof. P Delsing, Dr S Kubatkin Optisense LTD: M Andreo

Passive Imaging with superconducting bolometer by VTT-NIST Nb superconducting bolometer Detection of hidden weapon Courtesy of VTT-NIST

Some numbers for consideration Noise Equivalent Temperature Difference (NETD) imposed by the temperature contrast, or variation of spectral intensity (spectral fingertips) < 0.1K Background limited noise BLIP~ T(F/n)1/2 , where F - frame rate (10Hz), n - number of detected photons (108), ~0.05K Detector should have NETD better than 0.1K and counting rate around 108 photons/sec

Some numbers for consideration Plank’s law There is a difference in ~1010 photons/sec (~10-23J) for black body radiation at 300K and 305K in bandwidth from 0.5 to 0.7 THz. Passive imaging U, 10-21 J /(Hz m3) f , THz T=305K U, 10-19 J /(Hz m3) T=300K f , THz

Finger prints of explosives Complex materials has a unique fingerprints in spectrum T=300K JF Federici et all ’05

QD as a spectral sensitive detector Layout of the QD in 2DEG SEM images of the QD Resonance curve APL ’02 B (Tesla) 1 2 3 4 5 20 40 60 Frequency  (/cm) c  0 QD in magnetic field Zero filed Plasma resonance in QD

Log-periodic circular antenna (0.2-3Thz) QD-SET detector Log-periodic circular antenna (0.2-3Thz) coupled with QD sensor Energy diagram Dark switches and photo-response original peaks shifted DVg SET response to QD excitation

Modeling of QD-SET SET SG1 CG Offset charge at SET SG2 QD QSET -Vc NSET NSET+1 -Vc

Formation of QD Individual SET trace 2D map of SET current Charging of the QD

Photosignal at 0.3K T=0.3K T=0.05K

Photo response and dark counts Noise Equivalent Power~ 10-20 Watt/Hz1/2 NETD = NEP/(2hkBDnt1/2) ~0.01K Quantum Efficiency ~1% Spectral bandwidth ~ 1% Operation temperature is limited by SET (up to 4K) APL, JAP, PRB, IEEE ’04-07

Photosignal at 0.5-0.7K

2D maps of QD-SET VS, V VS, V VC, V VC, V Emitter is OFF Emitter is ON Physica E ’06 PRB’06

Detector of different designs A lateral sensor with QD crossing the channel A lateral sensor with QD outside channel A lateral sensor with QD inside channel A vertical sensor

QD outside of 2DEG channel Gate QD-SET

QD inside the 2DEG channel

QD in high magnetic field LL0 LL1 SEM picture of the QD 1m NATURE, 2000

QD in high B QD under illumination Time traces of QD conductance Spectral sensitivity of the detector

QD in high B LL1­ I II QD has three levels: LL0­,LL0¯, Lifetime of excitations PRB, 2002

LT THZ microscope of Tokyo University Ikushima, Komiyama APL, 2006

LT THZ microscope of Tokyo University

Future plans: Quantum Dot in DQW heterostructure Schematic view Inter-well excitation in asymmetric DQW ~1 THz

Near-field antennae Simulation of near-field antennae Simulation of E-field

Near-field antenna

Challenges Room Temperature Imaging QD detector: which type? Room Temperature Imaging Source of THz radiation for in-situ calibration Physics of isolated QD in DW heterostructures

Vertical sensor in DQW heterostructure An et all, PRB’07