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SUMMARY:Development of SAW-driven photon detectors and sources in an undop
 ed GaAs/AlGaAs quantum well structure - Antonio Rubino\, Cavendish Laborat
 ory\, University of Cambridge\, UK
DTSTART:20180613T130000Z
DTEND:20180613T140000Z
UID:TALK106816@talks.cam.ac.uk
CONTACT:Dr Kaveh Delfanazari
DESCRIPTION:Advances in controlling single carriers have made it possible 
 to transport single electrons through a quasi-one-dimensional (1D) channel
  [1]\, and back and forth between two distant quantum dots [2\,3] using su
 rface acoustic waves (SAWs)\, with potential applications for quantum comp
 utation. We have developed devices in which both electrons and holes can b
 e induced in an undoped GaAs/AlGaAs well by gates to form a lateral n-i-p 
 junction. SAWs\, generated by a transducer\, collect electrons in the n-re
 gion and transport them into the p-region where they recombine with holes.
  If the stream is composed of single electrons\, the recombination with ho
 les should produce a stream of single photons [4]. Furthermore\, the recom
 bination of spin-polarised electrons can generate circularly polarised pho
 tons\, providing a method of spin readout in a quantum computer and a way 
 for conversion of spin qubits into photon qubits [5].\n\n     The devices 
 contain two types of recessed ohmic contacts\, n-type and p-type\, in an M
 BE-grown undoped GaAs/AlGaAs wafer with a 15nm quantum well. Electrons and
  holes are induced using insulated metal gates. Additional gates on the su
 rface extend the two-dimensional (2D) electron gas and 2D hole gas into th
 e n-i-p junction\, which is a few microns wide. The junction is confined i
 nto a quasi-1D channel laterally by etching and side gates.\n\nWe observe 
 light emission in DC forward bias when the voltage applied is above the fl
 at-band condition. Alternatively\, we can bias the junction 100 mV below t
 he flat-band condition\, so that no current flows until a 1 or 3 GHz SAW d
 rives a current and light emission\, by pumping electrons over the hill in
  the intrinsic region.\n\n     We have characterised this SAW-driven elect
 roluminescence in the regime where less than one electron is transported p
 er cycle on average. Time-resolved electroluminescence has been used to ex
 tract the electron recombination time and to quantify the contributions fr
 om electromagnetic crosstalk and the SAW. In a device without significant 
 crosstalk\, the degree of second-order coherence\, g2(0)\, was measured us
 ing a Hanbury Brown and Twiss interferometer with single-photon detectors\
 , and it shows the signature of antibunching.\n\nWith the use of the same 
 heterostructure\, we have shown that is possible to invert the process so 
 that photons are absorbed in the quantum well and generate electron–hole
  pairs. The photogenerated carriers are separated by metal gates on the su
 rface and transported to charge readers using surface acoustic waves\, all
 owing the possibility to detect the incident photons.\n\n\n[1] Shilton et 
 al.\, J. Phys.: Condens. Matter 8\, L531 (1996).\n[2] McNeil\, R. P. G. et
  al. Nature 477\, 439–442 (2011).\n[3] Hermelin\, S. et al. Nature 477\,
  435–438 (2011).\n[4] Foden\, C. L. et al. Phys. Rev. A 62\, 011803(R)\,
  1–4 (2000).\n[5] Kosaka\, H. et al. Nature 457\, 702–705 (2009)\n\n\n
 \n\n\n
LOCATION:Mott Seminar Room (531)\, Cavendish Laboratory\, Department of Ph
 ysics
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