Ishan Talukdar

Experimental Realization of Quantum-Resonance Ratchets at Arbitrary Quasimomenta

Quantum-resonance ratchets associated with the kicked particle are experimentally realized for arbitrary quasimomentum using a Bose-Einstein condensate (BEC) exposed to a pulsed standing light wave. The ratchet effect for general quasimomentum arises even though both the standing-wave potential and the initial state of the BEC have a point symmetry. The experimental results agree well with theoretical ones which take into account the finite quasimomentum width of the BEC. In particular, this width is shown to cause a suppression of the ratchet acceleration for exactly resonant quasimomentum, leading to a saturation of the directed current.

Directed growth of single-crystal indium wires

Tailored electric fields were used to direct the dendritic growth of crystalline indium wires between lithographic electrodes immersed in solutions of indium acetate. Determination of the conditions that suppress sidebranching on these structures has enabled the fabrication of arbitrarily long needle-shaped wires with diameters as small as 370nm. Electron diffraction studies indicate that these wires are crystalline indium, that the unbranched wire segments are single-crystal domains, and that the predominant growth direction is near ⟨110⟩. This work constitutes a critical step towards the use of simply prepared aqueous mixtures as a convenient means of controlling the composition of submicron, crystalline wires.

Sub-Fourier Characteristics of a δ-kicked-rotor Resonance

We experimentally investigate the sub-Fourier behavior of a δ-kicked-rotor resonance by performing a measurement of the fidelity or overlap of a Bose-Einstein condensate exposed to a periodically pulsed standing wave. The temporal width of the fidelity resonance peak centered at the Talbot time and zero initial momentum exhibits an inverse cube pulse number (1/N3)-dependent scaling compared to a 1/N2 dependence for the mean energy width at the same resonance. A theoretical analysis shows that for an accelerating potential the width of the resonance in acceleration space depends on 1/N3, a property which we also verify experimentally. Such a sub-Fourier effect could be useful for high precision gravity measurements.

The directed-assembly of CdS interconnects between targeted points in a circuit

We demonstrate the one-step dielectrophoretic assembly and interfacing of individual interconnects from populations of 3.7 nm CdS nanoparticles between targeted points in a circuit. We further show that the nanoparticles fuse into bulk CdS during the fabrication process. This finding is significant because it establishes a critical step towards the fabrication of structurally continuous semiconducting interconnects from nanoscopic building blocks.

High-order resonances of the quantum δ-kicked accelerator

We report the observation of high-order resonances of the quantum δ-kicked accelerator using a BEC kicked by a standing wave of light. The signature of these resonances is the existence of quantum accelerator modes. For the first time quantum accelerator modes were seen near 1/2, 2/3 and 1/3 of the half-Talbot time. Using a BEC enabled the internal momentum state structure of the modes and resonances to be studied for the first time. This structure has many similarities to that present in the fractional Talbot effect. We present a theory for this system based on rephasing of momentum orders and apply it to predict the behavior of the accelerator modes around a resonance of any order.