Location: Bldg. 216, Rm. E107
We develop novel measurement tools for characterizing nanoscale optical structures and understanding their potential role in quantum and classical information processing, sensing, and metrology. The nanoscale systems under investigation include those created by top-down planar fabrication technology, such as chip-based optical resonators in which light is confined to wavelength-scale dimensions for thousands of optical cycles, those created by bottom-up growth techniques, such as epitaxially-grown semiconductor quantum dots, and systems in which the two are integrated, such as light sources based on quantum dot cavity quantum electrodynamics. Our collaborators include other researchers from the CNST, from the larger NIST community, and from leading academic groups.
Measuring the optical properties of such devices can be difficult because of their size and geometry — they are orders of magnitude smaller than typical laboratory fiber and free-space optics, and the optical response of the nanoscale system under investigation must be separated from background scattered light and other spurious emission sources. One tool we are developing is based on efficient near-field measurement with optical fiber taper waveguide probes. In order to support a variety of measurement needs, we have incorporated these probes into various of experimental instruments: one operating at low-temperature and high-vacuum; one operating at room-temperature and high vacuum; and several operating at ambient pressure and temperature.
Nanostructures under investigation include III-V semiconductor quantum dots and II-VI colloidal quantum dots, both as-grown and in the modified electromagnetic environment created by integrating them into nanofabricated photonic devices. The fiber waveguide allows for efficient photoluminescence and resonant transmission measurements, allowing us to investigate a spectrum of light-matter interactions. These interactions range from the weak coupling regime of modified emission rates and directionality, with relevance to cavity-enhanced detection and novel light sources, to the strong coupling regime in which a single photon and a single quantum dot form a quantum molecule, whose properties might enable the construction of quantum networks for information processing.
We are also using the fabrication capabilities provided by the CNST NanoFab to develop nanophotonic structures for efficient light extraction from single embedded quantum emitters like epitaxially-grown semiconductor quantum dots. Here, a key challenge that we are trying to overcome is the limited amount of accessible fluorescence due to total internal reflection which traps the emitted light within the quantum dot’s host semiconductor environment. We use a combination of detailed electromagnetic simulation, nanofabrication, and measurement to develop new nanostructures that efficiently funnel fluorescence into fiber-optic and free-space collection channels. These methods may prove valuable for developing technologies based on single quantum dots, such as single photon sources for quantum communications and information processing.
Once single photons are extracted, manipulation of their properties of is important for future quantum technologies. We have demonstrated techniques by which the wavelength and temporal shape of single photons can be changed using nonlinear optical frequency conversion and electro-optic modulators. Such operations are a potentially important resource for future hybrid quantum systems, in serving as a means to connect two systems operating at different wavelengths. They may also be useful for sensitive light detection, by converting light in wavelength regions for which existing detectors are inadequate to wavelengths in which high performance options exist.
Finally, we are exploiting on-chip light-matter interactions to develop new metrology tools. Working with the optical MEMS laboratory in CNST, we are developing high bandwidth sensors for atomic force microscopy (AFM) that are both compact and stable. We utilize near-field coupling to high quality factor optical microcavities as a means to transduce the motion of nanocantilevers with high sensitivity, bandwidth, and dynamic range. In these systems, the field inside the optical cavity can be used for displacement and force readout, and also alter the mechanical motion of the nanocantilevers to provide additional functionality in AFM imaging. Finally, we are exploring the possibility of using radiation pressure forces in such cavity optomechanical systems as a means to perform signal transduction, for example, in converting signals from one wavelength band to another.
Optomechanical transduction of an integrated silicon cantilever probe using a microdisk resonator, K. Srinivasan, H. Miao, M. T. Rakher, M. Davanço, and V. Aksyuk, Nano Letters 11, 791-797 (2011).
Quantum transduction of telecommunications-band single photons from a quantum dot by frequency upconversion, M. T. Rakher, L. Ma, O. Slattery, X. Tang, and K. Srinivasan, Nature Photonics 4, 786-791 (2010).
Related LinksCNST Nanoscale Measurement LaboratoriesCurrent Research AreasNanofabrication Research Group
Kartik Srinivasan, Phone 301-975-5938