Nanoscale and Quantum Photonics Laboratory
Quantum information processing with quantum dot single spins
With collaborators in the Quantum Dot research group at the U.S. Navy Research Laboratory, we are exploring the coupling between single electron and hole spins in a quantum dot and a photon trapped in a photonic crystal cavity. This involves imbedding single InGaAs quantum dots in a very thin heterostructure and then fabricating optical microcavities around single dots. This allows us to control the charging of the dot with a single electron (or hole) and using novel optical techniques, to fully control the spin state of the charge trapped in the dot. The cavity mediates the coupling between the single spin and the exciting light and, when coupled to on-chip waveguides, can allow the spin state to be encoded in the cavity photon and then transferred to a distant dot in another cavity. Thus, we are moving toward the development of an on-chip quantum network, an essential technology for solid-state quantum information processing.
Nanoscale optical emitters in complex photonic environments
With Dr. Raj Basu, we are investigating the coupling of single solid-state emitters in complex soft matter systems. For instance, it has been shown that colloidal quantum dots will exhibit directed self-assembly into long chains when doped in a liquid crystal matrix. This self-assembly may lead to an anisotropy in the emission from the quantum dots and, potentially, photonic coupling between dots in the chain. The ability to switch the emission properties of a solid-state emitter via external electric fields may lead to applications such as fast optical switches and could have implications for hybrid quantum dot laser systems.
Collective optics of nanoscale systems
In concert with Prof. Richard Phillips at the Cavendish Laboratory at the University of Cambridge, we are exploring the interaction of large ensembles of single quantum emitters. We were able to demonstrate for the first time the use of a frequency-swept optical pulse to control the state of a single InGaAs quantum dot. With this technique, we could tailor the inversion profile of an ensemble of quantum dots with a single pulse. If an optical cavity mediated the interaction of these dots, theory predicts that the dynamics of the interaction will drive the system into a novel Bose-Einstein condensate of exciton-polaritons. This interaction of many quantum emitters has implications for the study of exotic states of matter as well as the development of ultra-stable semiconductor lasers.
Silicon vacancy emitters in SiC
SiC has recently emerged as an exciting new materials platform for nanoscale quantum photonics. The silicon vacancy in all the common polytypes of SiC have been shown to be viable spin qubits, even at room temperature. Additionally, nanocrystals of SiC are bio-compatible and emit in the telecom window. Both of these systems have technological benefits that make them potentially disruptive of the current state of the art materials in solid state quanutm information processing and spin imaging in biological systems. In collaboration with Dr. Sam Carter at Navy Research Lab, we are investigating the spectroscopic signature of Si vacancies created via proton irradation with the 2MV Pelletron linear accelerator at USNA. In parallel, William Heuer at USNA is synthesizing small nanocrystals of SiC that can be investigated either in the liquid crystal system or after proton irradiation, a relatively unexplored area of research.
"Spin-Cavity interactions between a quantum dot molecule and a photonic crystal cavity" Nat. Comm. 6, 7665 (2015).
"Cavity-stimulated Raman emission from a single quantum dot spin," Nat. Phot. 8, 442-447 (2014)
"Leveraging crystal anistropy for deterministic growth of InAs quantum dots with narrow optical linewidths," Nano. Lett. ASAP (2013)
"From the artificial atom to the Kondo-Anderson model: Orientation-dependent magnetophotoluminescence of charged excitons in InAs quantum dots," Phys. Rev. B, 87 205308 (2013)
"Coherent optical control of the spin of a single hole in an InAs/GaAs quantum dot," PRL, 108, 017402 (2012)
"Fast preparation of a single-hole spin in an InAs/GaAs quantum dot in a Voigt-geometry magnetic field," Phys. Rev. B, 85, 155310 (2012)
"Population inversion in a single InGaAs quantum dot using the method of adiabatic rapid passage," PRL, 106, 067401 (2011)
Cavity-assisted Raman emssion from a single quantum dot (Nat. Phot. 8 442-447 (2014))
Atomic force microscopy scan of site-controlled InGaAs quantum dots (Nano Lett)
Schematic and SEM image of single quantum dot spin device (Nat. Phot. 7, 329, 2013)
The first demonstration of adiabatic rapid passage in a single solid-state nanostructure (PRL 106 067401 2011)