arXiv subjects

J. Leach

Publications and source records attributed to J. Leach.

7 recordsLinked to original sources

arXiv2025

Parametric Analysis of First High-Gain Vertical Fe-doped Ultrafast Ga2O3 Photoconductive Semiconductor Switch

We investigate, as part of a Lawrence-Livermore-National-Laboratory (LLNL) sponsored-research work initiated in February of 2021, the parametric performance analysis of ultra-wide bandgap (UWBG) Fe-doped Ga2O3 photoconductive semiconductor switch (FG-PCSS) with embedded electrode. The detailed SILVACO based simulation of the FG-PCSS uses experimentally obtained lifetime, absorption coefficient, and mobility data. The key analysis results, demonstrated first to the sponsor LLNL in 2022, focus on the performance of the FG-PCSS under relatively high electric field and optical-excitation energy with specific regard to current gain, quantum efficiency, on-state resistance, and impact of beam position. The parametric analysis indicates that a high-gain operation yielding a low-cost laser beam for the FG-PCSS is possible.

physics.app-ph↗

arXiv2013

Characterization of high-dimensional entangled systems via mutually unbiased measurements

Mutually unbiased bases (MUBs) play a key role in many protocols in quantum science, such as quantum key distribution. However, defining MUBs for arbitrary high-dimensional systems is theoretically difficult, and measurements in such bases can be hard to implement. We show experimentally that efficient quantum state reconstruction of a high-dimensional multi-partite quantum system can be performed by considering only the MUBs of the individual parts. The state spaces of the individual subsystems are always smaller than the state space of the composite system. Thus, the benefit of this method is that MUBs need to be defined for the small Hilbert spaces of the subsystems rather than for the large space of the overall system. This becomes especially relevant where the definition or measurement of MUBs for the overall system is challenging. We illustrate this approach by implementing measurements for a high-dimensional system consisting of two photons entangled in the orbital angular momentum (OAM) degree of freedom, and we reconstruct the state of this system for dimensions of the individual photons from d=2 to 5.

quant-ph↗

arXiv2010

Entangled topological features of light

We report the entanglement of topological features, namely, isolated, linked optical vortex loops in the light from spontaneous parametric down-conversion (SPDC). In three dimensions, optical vortices are lines of phase singularity and vortices of energy flow which percolate through all optical fields. This example of entanglement is between features that extend over macroscopic and finite volumes, furthermore, topological features are robust to perturbation . The entanglement of photons in complex three-dimensional(3D) topological states suggests the possibility of entanglement of similar structures in other quantum systems describable by complex scalar functions, such as superconductors, superfluids and Bose-Einstein condensates.

quant-ph↗

arXiv2008

Hydrodynamic Interactions in Two Dimensions

We measure hydrodynamic interactions between colloidal particles confined in a thin sheet of fluid. The reduced dimensionality, compared to a bulk fluid, increases dramatically the range of couplings. Using optical tweezers we force a two body system along the eigenmodes of the mobility tensor and find that eigen-mobilities change logarithmically with particle separation. At a hundred radii distance, the mobilities for correlated and anti-correlated motions differ by a factor of two, whereas in bulk fluids, they would be practically indistinguishable. We derive the two dimensional counterpart of the Oseen hydrodynamic tensor which quantitatively reproduces the observed behavior. These results highlight the importance of dimensionality for transport and interactions in colloidal systems and proteins in biological membranes.

cond-mat.soft↗

arXiv2007

Parametric Resonance of Optically Trapped Aerosols

The Brownian dynamics of an optically trapped water droplet are investigated across the transition from over to under-damped oscillations. The spectrum of position fluctuations evolves from a Lorentzian shape typical of over-damped systems (beads in liquid solvents), to a damped harmonic oscillator spectrum showing a resonance peak. In this later under-damped regime, we excite parametric resonance by periodically modulating the trapping power at twice the resonant frequency. The power spectra of position fluctuations are in excellent agreement with the obtained analytical solutions of a parametrically modulated Langevin equation.

cond-mat.stat-mech↗

arXiv2006

Optical ferris wheel for ultracold atoms

We propose a versatile optical ring lattice suitable for trapping cold and quantum degenerate atomic samples at discrete angular positions. We demonstrate the realisation of intensity patterns generated from Laguerre-Gauss ($\exp(i \ellθ)$) modes with different $\ell$ indices. The ring lattice can have either intensity maxima or minima, suitable for trapping in red or blue detuned light, and it can be rotated by introducing a frequency shift between the Laguerre Gauss modes. The potential wells can be joined to form a uniform ring trap, making it ideal for studying persistent currents and the Mott insulator transition in a ring geometry.

physics.optics↗

arXiv2005

Vortex knots in light

Optical vortices generically arise when optical beams are combined. Recently, we reported how several laser beams containing optical vortices could be combined to form optical vortex loops, links and knots embedded in a light beam (Leach et al 2004). Here, we describe in detail the experiments in which vortex loops form these structures. The experimental construction follows a theoretical model originally proposed by Berry and Dennis, and the beams are synthesised using a programmable spatial light modulator and imaged using a CCD camera.

physics.optics↗