Abstract

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 surface acoustic waves (SAWs), with potential applications for quantum computation. We have developed devices in which both electrons and holes can be 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-region and transport them into the p-region where they recombine with holes. If the stream is composed of single electrons, the recombination with holes should produce a stream of single photons [4]. Furthermore, the recombination of spin-polarised electrons can generate circularly polarised photons, providing a method of spin readout in a quantum computer and a way for conversion of spin qubits into photon qubits [5].

The devices contain two types of recessed ohmic contacts, n-type and p-type, in an MBE-grown undoped GaAs/AlGaAs wafer with a 15nm quantum well. Electrons and holes are induced using insulated metal gates. Additional gates on the surface extend the two-dimensional (2D) electron gas and 2D hole gas into the n-i-p junction, which is a few microns wide. The junction is confined into a quasi-1D channel laterally by etching and side gates.

We observe light emission in DC forward bias when the voltage applied is above the flat-band condition. Alternatively, we can bias the junction 100 mV below the flat-band condition, so that no current flows until a 1 or 3 GHz SAW drives a current and light emission, by pumping electrons over the hill in the intrinsic region.

We have characterised this SAW-driven electroluminescence in the regime where less than one electron is transported per cycle on average. Time-resolved electroluminescence has been used to extract the electron recombination time and to quantify the contributions from electromagnetic crosstalk and the SAW. In a device without significant crosstalk, the degree of second-order coherence, g2(0), was measured using a Hanbury Brown and Twiss interferometer with single-photon detectors, and it shows the signature of antibunching.

With 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 surface and transported to charge readers using surface acoustic waves, allowing the possibility to detect the incident photons.

[1] Shilton et al., J. Phys.: Condens. Matter 8, L531 (1996). [2] McNeil, R. P. G. et al. Nature 477, 439–442 (2011). [3] Hermelin, S. et al. Nature 477, 435–438 (2011). [4] Foden, C. L. et al. Phys. Rev. A 62 , 011803®, 1–4 (2000). [5] Kosaka, H. et al. Nature 457, 702–705 (2009)