Technology of terahertz quantum dot detectors and their applications V Antonov Moscow Institute of Physics and Technology, Russia Royal Holloway University of London, UK THz radiation is a fundamental frequency range having origin in rotational and vibrational modes of molecules THz (FIR ) RHUL, EGHAM, UK

Rotational modes of molecules A diatomic molecule rotating about the common centre of mass of its two atoms Transition between rotational modes with angular momentum l - 1 and l The rotational energy spectrum of HCl measured by absorption Typical energy scale of THz photons corresponds to few meV or K ~ few meV

Identification of materials LIQUIDS Divin,2008 methanol acetone Spectral features are broad because of interaction SOLIDS RDX molecule Kemp,2011 Features of THz technology: -paper, plastics, wood, textiles are transparent for THz radiation -brightness of THz radiation emitted by materials is extremely small -Water/water vapor is strong absorber of THz radiation

Terahertz radiation in nanoscale low temperature systems Komiyama, 2011 Cyclotron radiation emitted by Hall bar in Quantum Hall regime Relaxation of injected electrons at the edge states

Terahertz radiation of HTS Josepson Junction JJ radiation of individual Josephson Junction The upper limit of  JJ  is limited by  /e. It can be up to 7THz Only small part is emitted as coherent JJ radiation (pW out of  W dissipated) Coupling of JJ radiation to the planar metallic antennae is weak. A heating of the JJ becomes strong at high bias (when V=1 mV T m exceeds T B by 3K) Line width of radiation is ~1 GHz Josephson Junction is formed in 200nm thick YBa 2 Cu 3 O 7 film at bi-crystal boundary of sapphire substrate.

QD-SET detector Shift of CBO pattern when one electron is excited Switches of SET current due to electron excitations

Spectral sensitivity of Quantum Dot detector Plasma oscillations in QD Plasma resonance in QD n – sheet carrier concentration m – effective electron mass, 0.07m e in GaAs, 0.014m e in InSb  – dielectric constant, ~13 in GaAs R – radius of the QD,  m For 1.4  m dot  ~ 0.25 THz Plasma resonance in QD At B=0T Plasma resonance in QD At B~3T

QD-SET detector

Detection of JJ radiation Counting of the QD excitations without radiation Suppression of thermal counts is described by: with a=12meV/V Counting of the QD excitations due to JJ radiation Detected power corresponds to 2x W Coherent JJ radiation emitted by JJ is 30 aW out of 80 nW dissipated. Conversion factor is 4x

Detection of JJ radiation Direction of switches of the SET current indicates at the excitations of electrons in/out of the QD Decryption of excitations of the QD

Coherent terahertz radiation of stack of HTS JJ Resonances are determined by geometrical design of resonator. Line width of the radiation is down to 50MHz Power emitted out of substrate ~ 1  W

-We detected a coherent radiation of individual HTS JJ -Radiation of individual HTS JJ is weak, conversion factor is ~ 4x The radiation can be used to study/calibrate sensitive spectral detectors Conclusions

R Shaikhaidarov, A Casey, Royal Holloway University of London, UK Y Harada, K Omitsu, NTT Basic Research labs, Japan A Tzalenchuk, National Physical Laboratory, United Kingdom A Kalaboukhov, S Kubatkin, Chalmers University, Sweden Credits