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SUMMARY:Measuring photon-assisted shot noise in capacitively-coupled quant
 um point contacts - Dr Yodchay Jompol\, Mahidol University
DTSTART:20141215T141500Z
DTEND:20141215T151500Z
UID:TALK56691@talks.cam.ac.uk
CONTACT:Teri Bartlett
DESCRIPTION:The physics  of  quantum  shot  noise  becomes  particularly i
 nteresting  when  the  bias  voltage\ncausing a current noise is close to 
 the noise measurement frequency (eV ≡ hv). However\, the \nhigh-frequenc
 y noise measurements are usually limited to few GHz due to the large misma
 tch between \nhigh impedance of the quantum conductor and low impedance of
  the external circuit. To circumvent \nthis problem\, on-chip detection sc
 hemes have been developed using Quantum Dots or SIS junctions. \nThese dev
 ices reduce shunting ground capacitance which would otherwise lower the co
 upling and hence \nthe frequency bandwidth. However\, the proximity (few t
 ens of microns) between those emitter and \ndetector still introduces enou
 gh capacitive shunting that prevents the measurements at very \nhigh-frequ
 ency noise (up to THz).\n\nIn this talk\, I will present an experimental r
 ealisation of a novel on-chip shot noise detection \nscheme using photon-a
 ssisted effect in capacitively-coupled quantum point contacts (QPCs). This
  \nquantum effect differs from the ordinary "transport" shot noise because
  it does not need an \napplication of a dc bias\, but is due to probabilis
 tic scattering of the electron-holes pairs \npartitioning between left and
  right contacts. This results in a current noise called \nphoton-assisted 
 shot noise (PASN). For a QPC\, both the photocurrent and PASN are proporti
 onal to \nD(1-D)\, where D is the transmission of the QPC. Our experiment 
 is realised using a set of quantum \npoint contacts\, one of which serves 
 as a QPC emitter that generates high-frequency shot noise at \nanother QPC
 \, called QPC detector. This QPC detector is used to capture and convert t
 he high- \nfrequency current fluctuation from the QPC emitter into the mea
 sureable (low-frequency) voltage\nfluctuation with application of an on-ch
 ip interdigitated capacitor. We show that when the QPC \nemitter is dc bia
 sed\, the measured current by the QPC detector is proportional to DE(1-DE)
 \, where \nDE/DD is the transmission of the emitter/detector. We also demo
 nstrate that by varying both DE and \nDD for a given Vds the measured sign
 al is qualitatively proportional to the product ~ DD(1-DD)  \nDE(1-DE).  T
 his  new  way  of  on-chip  detection  scheme  should  find  fundamental\n
 applications in electronic quantum physics.\n
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
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