Nanowire Quantum Dots Tuned to Atomic Resonances

Abstract

Quantum dots tuned to atomic resonances represent an emerging field of hybrid quantum systems where the advantages of quantum dots and natural atoms can be combined. Embedding quantum dots in nanowires boosts these systems with a set of powerful possibilities, such as precise positioning of the emitters, excellent photon extraction efficiency and direct electrical contacting of quantum dots. Notably, nanowire structures can be grown on silicon substrates, allowing for a straightforward integration with silicon-based photonic devices. In this work we show controlled growth of nanowire-quantumdot structures on silicon, frequency tuned to atomic transitions. We grow GaAs quantum dots in AlGaAs nanowires with a nearly pure crystal structure and excellent optical properties. We precisely control the dimensions of quantum dots and their position inside nanowires and demonstrate that the emission wavelength can be engineered over the range of at least 30 nm around 765 nm. By applying an external magnetic field, we are able to fine-tune the emission frequency of our nanowire quantum dots to the D 2 transition of 87 Rb. We use the Rb transitions to precisely measure the actual spectral line width of the photons emitted from a nanowire quantum dot to be 9.4 ± 0.7 μeV, under nonresonant excitation. Our work brings highly desirable functionalities to quantum technologies, enabling, for instance, a realization of a quantum network, based on an arbitrary number of nanowire single-photon sources, all operating at the same frequency of an atomic transition.

Wurtzite AlGaAs Nanowires

“…In Fig. 1a, only a few short zincblende insertions, spontaneously formed during the nanowire growth, are visible as darker lines, consistent with our previous observation of a typical density of ~10-30 insertions/µm 13 . The zoom-in in Fig.…”

“…Because of the measured difference in Al content in the core and the shell, we attribute the short-wavelength and long-wavelength branches of the emission to shell and core, respectively. Further details on TEM, EDX and sPL can be found in our previous works 13,17 .…”

Resonant excitation of nanowire quantum dots

“…We note that the exciton linewidth did not vary substantially between the three different excitation techniques (FWHM 110 µeV for above bandgap excitation, 104 µeV for TPE, and 108 µeV for RF), while all of them result in a linewidth far from the lifetime limit. This, rather unexpected result, suggests that the limiting factor is intrinsic to the structure and the local environment around the QDs 35 , and not to the excitation process, even if we have shown in our previous work that some QDs show much narrower linewidths, down to 9.4 µeV 18 .…”

“…In our previous work 18 , we have shown that GaAs QDs can be embedded in AlGaAs nanowires during bottom-up growth in a molecular beam epitaxy reactor, adding new possibilities to the system. For instance, any number of emitters can be precisely positioned within the same nanowire, making the nanowire QDs structure an ideal platform for advanced multi-qubit devices 19,20 that are not possible today with their bulk counterparts.…”

Rational synthesis of atomically thin quantum structures in nanowires based on nucleation processes

“…Recent progresses in epitaxial methods, such as vapor-liquid-solid method and selective-area epitaxy, have resulted in the growth of axial heterostructures in nanowires (NWs) regardless of lattice mismatch, i.e., various materials, such as quantum disks and QDs, could be embedded inside host NWs [4][5][6][7][8] . NW axial heterostructures have great potential for future quantum optical applications because flexible band-gap engineering is possible, and the diameter, height, and density of QDs can be controlled by modifying the host NW's geometry.…”