Quantum Nano-Optics of Semiconductors

Semiconductor Cavity QED with a Single Quantum Dot in a Photonic Crystal Slab Nanocavity

Dr. Hyatt Gibbs and Dr. Galina Khitrova.  Our group was the first to reach the regime of true strong coupling in semiconductor cavity QED using a single quantum dot in a photonic crystal nanocavity [Nature 432, 200 (2004)] - just after it was seen in a micropillar [Nature 432, 197 (2004)].

The focus of our group is to improve and study these quantum devices. Interesting coherent phenomena such as photon-dot entanglement are destroyed by effects that cause decoherence, namely loss of photons from the nanocavity and dephasing of the quantum dot polarization. At present photon loss dominates, so a lot of time is spent measuring the quality factor Q [(cavity mode frequency)/(FWHM frequency linewidth of the cavity mode)] of thousands of nanocavities fabricated by collaborators at Caltech, Professor Axel Scherer and graduate student Uday Khankhoje.

In addition, the study of single quantum dot effects is degraded and complicated by the presence of a very large number of other quantum dots that are close enough in frequency and in spatial position to interfere; consequently ways to grow a single quantum dot exactly where it is wanted and far away from other dots are being explored with Professor Martin Wegener, University of Karlsruhe. If a “single quantum dot on demand” is achieved, a nanocavity can be fabricated around it. Single quantum dot cavity QED is not as advanced as single atom cavity QED, but it does have the advantage that the dot does not move.

Examples of fundamental physics phenomena to be studied: single atom lasing, higher rungs of the Jaynes-Cummings ladder, emission of one and only one photon per pulse (anti-bunching), emission of nonclassical light, etc. Low-energy nonlinear optical switching and interconnecting nanocavities using photonic crystal waveguides are also being pursued.  Instrumentation: a CryoVac microscope cold-bridge cryostat with an internal nanopositioning unit (resolution < 28 nm, motor-driven, and computer programmable) for ultra high stability operation at < 4 K with external high-NA systems for one wavelength resolution; Coherent 899 cw tunable Ti:Sa ring laser and diode lasers; 512x512 Si CCD and a 512 InGaAs linear array; several spectrometers (0.75-m SPEX, 0.25-m SPEX, 0.5-m 3-grating Jarrell-Ash, 0.32-m 3-grating).  08-2009

 Femtosecond Spectroscopy Laboratory

Dr. Hyatt Gibbs and Dr. Galina Khitrova.  The photoluminescence decay time of an ensemble of self-organized quantum dots following 100-fs nonresonant excitation, usually at 780 nm, is measured by a streak camera; the radiative decy time gives the electric dipole moment of a single quantum dot which determines the magnitude of the vacuum Rabi splitting in a nanocavity. Pump/probe nonlinear spectroscopy of quantum wells is performed with a delay line of up to several meters; radiative coupling effects and how they depend upon the spacings between the quantum wells (periodic crystal or Fibonacci-spaced quasicrystal) and the carrier density are studied. Instrumentation: femtosecond Ti:Sa laser (Spectra Physics Tsunami), OPAL optical parametric oscillator system, Hamamatsu 2-ps streak camera (C5680), cryogenically cooled CCD and various other detectors and arrays, two Air Products Heli-Tran cold finger cryostats (one closed-cycle and one flow), and Oxford cold finger cryostat.  08-2009

 Molecular Beam Epitaxy (MBE) Machine

Dr. Hyatt Gibbs and Dr. Galina Khitrova.   A three-chamber Riber 32P MBE (molecular beam epitaxy) system is used for the growth of GaAs/AlGaAs heterostructures on GaAs substrates and GaAlInAs/AlInAs heterostructures on InP substrates including quantum dots, quantum wells, planar microcavities (vertical cavity surface emitting lasers), samples for fabrication of photonic crystal slab nanocavities, and samples to provide gain for split ring resonator metamaterials (with Professor Martin Wegener).

 QNOS research is supported by NSF AMOP, NSF EPDT, NSF ERC CIAN, AFOSR, UofA VP for Research (1988-2010), and TRIF, Arizona’s Technology & Research Initiative Funding enterprise:  http://www.optics.arizona.edu/TRIF.  08-2009