Approaching quantum-limited imaging resolution without prior knowledge of the object location.

Passive imaging receivers that demultiplex an incoherent optical field into a set of orthogonal spatial modes prior to detection can surpass canonical diffraction limits on spatial resolution. However, these mode-sorting receivers exhibit sensitivity to contextual nuisance parameters (e.g., the centroid of a clustered or extended object), raising questions on their viability in realistic scenarios where prior information about the scene is limited. We propose a multistage detection strategy that segments the total recording time between different physical measurements to build up the required prior information for near quantum-optimal imaging performance at sub-Rayleigh length scales. We show, via Monte Carlo simulations, that an adaptive two-stage scheme that dynamically allocates recording time between a conventional direct detection measurement and a binary mode sorter outperforms idealized direct detection alone when no prior knowledge of the object centroid is available, achieving one to two orders of magnitude improvement in mean squared error for simple estimation tasks. Our scheme can be generalized for more sophisticated tasks involving multiple parameters and/or minimal prior information.

Proposal for the creation and optical detection of spin cat states in Bose-Einstein condensates.

We propose a method to create "spin cat states," i.e., macroscopic superpositions of coherent spin states, in Bose-Einstein condensates using the Kerr nonlinearity due to atomic collisions. Based on a detailed study of atom loss, we conclude that cat sizes of hundreds of atoms should be realistic. The existence of the spin cat states can be demonstrated by optical readout. Our analysis also includes the effects of higher-order nonlinearities, atom number fluctuations, and limited readout efficiency.

Direct observation of coherent population trapping in a superconducting artificial atom.

The phenomenon of coherent population trapping (CPT) of an atom (or solid state "artificial atom"), and the associated effect of electromagnetically induced transparency (EIT), are clear demonstrations of quantum interference due to coherence in multilevel quantum systems. We report observation of CPT in a superconducting phase qubit by simultaneously driving two coherent transitions in a Lambda-type configuration, utilizing the three lowest lying levels of a local minimum of a phase qubit. We observe 60(+/-7)% suppression of the excited state population under conditions of CPT resonance. We present data and matching theoretical simulations showing the development of CPT in time. Finally, we used the observed time dependence of the excited state population to characterize quantum dephasing times of the system.

Cold atom Raman spectrography using velocity-selective resonances.

We have studied velocity-selective resonances in the presence of a uniform magnetic field and shown how they can be used for rapid, single-shot assessment of the ground state magnetic sublevel spectrum in a cold atomic vapor. Cold atoms are released from a magneto-optical trap in the presence of a small bias magnetic field ( approximately 300 mG) and exposed to a laser field comprised of two phase-locked counterpropagating beams connecting the two ground state hyperfine manifolds. An image of the expanded cloud shows the velocity-selected resonances as distinct features, each corresponding to specific magnetic sublevel, in a direct, intuitive manner. We demonstrate the technique with both 87Rb and 85Rb, and show the utility of the technique by optically pumping into particular magnetic sublevels. The results are shown to agree with a theoretical model, and are compared to traditional Raman spectroscopy.

Analysis and optimization of channelization architecture for wideband slow light in atomic vapors.

We carry out an analysis of an earlier proposed "channelization" architecture for wideband slow light propagation and pulse delays in atomic vapors using electromagnetically induced transparency (EIT). In the channelization architecture, a wideband input signal pulse is spatially dispersed in the transverse dimension, sent through an EIT medium consisting of an initially spin-polarized atomic vapor illuminated by a monochromatic, co-propagating pump laser, then spatially recombined. An inhomogenous magnetic field is used to Zeeman shift the atomic vapor into two-photon (Raman) resonance with the signal-pump transitions at all locations. Extending on previous analyses, we show in detail how the reconstructed pulse will be delayed only if a slight mis-match from the two-photon resonance is introduced. If the desired delay is taken as a constrained parameter, we find the bandwidth can be increased by large factor. We present an analytic treatment which optimizes the bandwidth given a desired delay and constraints on the pump power and focusing. We find bandwidth increases on the order of 5 times (100 MHz versus 20 MHz) should be possible for delays of interest (10 ns) to applications in telecommunications and radar. Interestingly, due to the mis-match requirement, we find the channelization can not increase the optimal delay-bandwidth product over conventional slow light.

Stimulated Brillouin scattering in single-mode As(2)S(3) and As(2)Se(3) chalcogenide fibers.

Stimulated Brillouin scattering was investigated for the first time in As(2)S(3) single-mode fibers, and also in As(2)Se(3). The propagation loss and numerical aperture of the fibers at 1.56 mum, along with the threshold intensity for the stimulated Brillouin scattering process were measured. From the threshold values we estimate the Brillouin gain coefficient and demonstrate record figure of merit for slow-light based applications in chalcogenide fibers.

Transfer and storage of vortex states in light and matter waves.

We theoretically explore the transfer of vortex states between atomic Bose-Einstein condensates and optical pulses using ultraslow and stopped light techniques. We find shining a coupling laser on a rotating two-component ground state condensate with a vortex lattice generates a probe laser field with optical vortices. We also find that optical vortex states can be robustly stored in the atomic superfluids for times, in Rb-87 condensates, limited only by the ground state coherence time.