J. R. Guest

Autler-Townes spectroscopy of the 5 S 1 / 2 − 5 P 3 / 2 − 44 D cascade of cold 85 Rb atoms

We study nonlinear optical effects in the laser excitation of Rydberg states. 5S 1 / 2 and 5 P 3 / 2 levels of 8 5 Rb are coupled by a strong laser field and probed by a weak laser tuned to the 5P 3 / 2 -44D Rydberg resonance. We observe high contrast Autler-Townes spectra which are dependent on the pump polarization, intensity, and detuning. The observed behavior agrees with calculations, which include the effect of optical pumping.

Wavelength modulation spectroscopy of single quantum dots

We demonstrate that external cavity diode lasers with large mode-hop-free tuning ranges (up to 80 GHz) together with wavelength modulation spectroscopy can be used to study excitonic transitions in semiconductor nanostructures. Such transitions are characterized by homogeneous linewidths typically on the order of a few GHz. Wavelength modulation spectroscopy offers a high signal-to-noise method for the determination of resonance line shapes. We have used this technique to accurately measure dipole moments and dephasing rates of single semiconductor quantum dot eigenstates. These measurements are important for the use of quantum dots in semiconductor cavities and quantum logic gates, and for an improved understanding of the physics of exciton confinement.

Simple pressure-tuned Fabry–Pérot interferometer

A simple, compact and inexpensive pressure-tuned Fabry–Perot interferometer is presented. It is used as a laser locking reference for optical frequencies where the use of an atomic reference is impractical. The scanning range is several GHz. Absolute positioning of the interferometer with an accuracy of 7MHz rms over a range of 2GHz is possible. The instrument is temperature stabilized and shows long-term drift of 16MHz rms over 48h.

Time averaging of multimode optical fiber output for a magneto-optical trap

We demonstrate a method for increasing the amount of power available for laser cooling applications by using a multimode optical fiber. Through randomization of phase shifts of modes within the fiber on time scales faster than the center-of-mass response time of the atoms, a smooth time-averaged trapping beam is generated. The principle has been demonstrated in a pyramidal magneto-optical trap. The method is particularly suitable for the harnessing of the high output power of broad-area diode lasers for laser cooling.

Optical absorption measurements from single semiconductor quantum dots

Summary form only given. Size fluctuations in ensembles of semiconductor quantum dots lead to inhomogeneous broadening, which mask the intrinsic properties of individual quantum dots. In recent years, many research groups have chosen photoluminescence (PL) to optically probe individual quantum dots due to the sensitivity and simplicity of PL. However, the amount of information extracted from PL is limited. Absorption measurements can complement PL studies and provide important quantitative information such as dipole moments and dephasing rates without any complications arising from spectral and spatial diffusion. The interface fluctuation quantum dots formed in a 6.2 nm GaAs/Al/sub 0.3/Ga/sub 0.7/As quantum well are probed with high spatial resolution through submicron apertures in a 100 nm thick Al mask on the sample surface.

Cold Rydberg gas dynamics and the trapping of cold Rydberg atoms

We study n- and l-mixing dynamics of cold Rydberg atom gases at varying background radiation temperature and Rydberg atom density in a cryogenic magneto-optical trap.

Cold Rydberg atoms and plasmas in strong magnetic fields

We describe our theoretical and experimental efforts to understand cold Rydberg atom gases and plasmas in strong magnetic fields.

Long-lived states in cold Rydberg gases

Summary form only given. Laser-cooled atoms can be excited into Rydberg states to study Rydberg gases at high densities and low atomic velocities. Dense clouds of such atoms undergo virtually complete ionization when their density exceeds a critical value dependent on the principal quantum number n. We report a new regime in which the excited Rydberg population spontaneously evolves into long-lived high-l states, the lifetimes of which exceed the natural lifetimes of the initially excited Rydberg levels by two orders of magnitude. /sup 87/Rb atoms are collected and cooled to 50 /spl mu/K in a magneto optical trap (MOT), which is periodically turned off for 50 ms. 1 ms after the shutdown of the MOT the Rydberg atoms are created via a two-step excitation process using a 5 /spl mu/s long diode laser pulse.

Ponderomotive optical lattices: a method for trapping Rydberg atoms

Summary form only given. Cooling and trapping in atomic systems have ushered in a revolution in the fields of opto-mechanical control, high precision spectroscopy, quantum electrodynamics and quantum information; to date, however, these advances have been restricted almost exclusively to near-ground state atoms. Highly excited atoms, or Rydberg atoms, have been explored for decades as testing grounds for quantum mechanics, quantum chaos, wavepacket manipulation and, more recently, quantum computing. Though the cooling of Rydberg atoms has been proposed and the generation of cold Rydberg atoms from cold ground state atoms has been achieved, the ability to trap cold Rydberg atoms remains an important and unaddressed milestone. We present a method to trap Rydberg atoms in any electronic state based on the weakly-bound nature of the Rydberg electron.

Nano-optics: imaging the resonant nonlinear response of individual localized excitons

Summary form only given. Micro-optical probe techniques have been developed by numerous groups to study and exploit features of excitonic systems since the initial visualization of disorder induced exciton localization in quantum wells by near-field scanning optical microscopy. The most recent work in narrow GaAs quantum wells has demonstrated that these structures have features consistent with quantum dots, including sharp line optical spectra, excited states, and a nonlinear optical response that is distinct from higher dimensional systems. Indeed, many of the optical and electronic features of these systems are similar to simple atomic systems, leading to proposed applications in novel quantum optoelectronic devices. In this paper, we present the first sub-wavelength resolution images of the coherent nonlinear optical response of these strongly localized excitons. Experimental data are collected on a narrow (42 /spl Aring/) single quantum well grown with long growth interruptions. Data is obtained using a 4 K near-field microscope to allow imaging of the system. The measurements are based on homodyne detected differential transmission, which, unlike typical luminescence studies, directly probes all optically accessible excitonic states.