Session L03: Atomic, Molecular, and Optical Physics III

Quantum Turbulent Structure in Light

A random superposition of plane waves is known to be threaded with vortex line singularities which form complicated tangles and obey strict topological rules. In this work, we use both numerical simulations of random waves and experiments on laser speckle to observe and characterize the dynamics of the vortex tangles. We find that the velocity statistics of the vortices in random waves match those of turbulent quantum fluids such as superfluid helium and atomic Bose-Einstein condensates\footnote{Physical Review Letters 122, 044301 (2019)}. These statistics are shown to be independent of system scale. These results raise deep questions about the role of nonlinearity in the structure of turbulence and the general nature of quantum chaos. Co-authors: Samuel Alperin, Abigail Grotelueschen, Andrew Voitiv, Jasmine Andersen, William Holtzmann, and Leah Huzjak, Department of Physics & Astronomy, University of Denver, and Mark Lusk, Department of Physics, Colorado School of Mines   

Distribution of Free Electrons Ejected Out the Side a Laser Focus at Relativistic Intensities

At laser intensities of 10$^{\mathrm{18}}$ W/cm$^{\mathrm{2}}$, electrons are quickly ionized from atoms and oscillate relativistically. Strong field gradients within a tight laser focus propel these free electrons out the side of the focus. Malka et al. observed that electrons have a strong tendency to be ejected along the direction of the laser polarization. Quesnel and Mora argued that these results must be in error. They developed a theoretical model that contradicted Malka et al. Our theoretical analysis supports the results of Malka et al. and we are setting up an experiment to test these conclusions.   

Decoherence Rates of Coupled Qubits in an Oscillator Environment

Quantum informational systems utilize qubits to store information. Our work focuses on the dynamics of open systems consisting of a qubit coupled to another qubit or oscillator environment.The Wei-Norman algebraic method is the primary technique used to evolve various combined systems. Once the evolution is found, the linear entropy determines the measure of decoherence of the system. We discuss the effects on decoherence of varying the dynamical parameters of the system and on the dependence of the results on selecting the rotating vs. the anti-rotating wave approximation.   

Decoherence of Coupled Oscillators and Qubits

We study the dynamics of open systems of coupled oscillators and qubits in minimal environments. To determine the decoherence of the system, we calculate the linear entropy for various initial states and visualize the dynamics with Husimi functions and Bloch spheres. Increasing the interaction of the system with its environment results in more rapid decoherence. For coupled oscillators under the rotating wave approximation we find periodic linear entropies whereas for the anti-rotating wave approximation the linear entropy can lose periodicity. For a qubit system coupled to an oscillator environment we find oscillatory linear entropies that are pseudo-periodic.   

Evanescent Wave Magnetometer

Atomic magnetometers generally operate by measuring the precession frequency of an atom; this is known as the Larmor frequency and is proportional to the magnetic field strength. Our goal is to make a chip-based nanoscale atomic magnetometer with high sensitivity and fast-scanning capabilities. To achieve this goal, we are using macroscopic techniques to refine experimentation and signal-to-noise ratio of an evanescent wave based magnetometer. The small measurement volume of an evanescent field promises a uniformed population. We draw inspiration from the paper "“Evanescent Wave Magnetometer”" authored by K. F. Zhao (2006). Our atomic magnetometer will use an evanescent field generated from two lasers incident on a cell containing $^{87}$Rb to pump atoms in such a way as to trap most of the population in a dark, spin-polarized, magnetically-stretched ground state. These lasers are combined by a fiber splitter so both maintain the critical angle needed for maximum evanescent field penetration depth. We use an RF source to scan the Larmor frequencies of the $^{87}$Rb atoms. When the RF matches the Larmor precession rate, the atoms leave the dark stretched state and begin scattering photons. We use a lock-in amplifier to detect the absorption and generate the magnetometer output.