The Forbes Group | Washington State University

^{Department of Physics and Astronomy}_{The Forbes Group
Homepage}

Quantum Dynamics from Cold Atoms to Neutron Stars

Introduction

In our group we study the dynamical properties of quantum many-body systems ranging from cold atoms trapped in one of the coolest places in the universe -- to the neutron stars where matter is compressed to such extremes that a teaspoon would weight more than a mountain.

Vortices in a rotating BEC with a pinning site and tracer particles.

super_hydro: Exploring Superfluids¶

Nobel laureate Richard Feynman said: "I think I can safely say that nobody really understands quantum mechanics". Part of the reason is that quantum mechanics describes physical processes in a regime that is far removed from our every-day experience – namely, when particles are extremely cold and move so slowly that they behave more like waves than like particles.

This application attempts to help you develop an intuition for quantum behavior by exploiting the property that collections of extremely cold atoms behave as a fluid – a superfluid – whose dynamics can be explored in real-time. By allowing you to interact and play with simulations of these superfluids, we hope you will have fun and develop an intuition for some of the new features present in quantum systems, taking one step closer to developing an intuitive understanding of quantum mechanics.

Beyond developing an intuition for quantum mechanics, this project provides an extensible and general framework for running interactive simulations capable of sufficiently high frame-rates for real-time interactions using high-performance computing techniques such as GPU acceleration. The framework is easily extended to any application whose main interface is through a 2D density plot - including many fluid dynamical simulations.

Negative-Mass Hydrodynamics¶

Negative mass is a peculiar concept. Counter to everyday experience, an object with negative effective mass will accelerate backward when pushed forward. This effect is known to play a crucial role in many condensed matter contexts, where a particle's dispersion can have a rather complicated shape as a function of lattice geometry and doping. In our work we show that negative mass hydrodynamics can also be investigated in ultracold atoms in free space and that these systems offer powerful and unique controls.

Michael McNeil Forbes

Michael McNeil Forbes¶

Our universe is an incredible place. Despite its incredible diversity and apparent complexity, an amazing amount of it can be described by relatively simple physical laws referred to as the Standard Model of particle physics. Much of this complexity "emerges" from the interaction of many simple components. Characterizing the behaviour of "many-body" systems forms a focus for much of my research, with applications ranging from some of the coldest places in the universe - cold atom experiments here on earth, to nuclear reactions, the cores of neutrons stars, and the origin of matter in our universe.

Kyle Elsasser

Kyle Elsasser¶

Kyle was raised on a farm in the mountains of northern Idaho before becoming a Nuclear Reactor Technician on US Navy submarines and later a firefigher/EMT back in his hometown. His curiosity got the better of him and he attended Eastern Washington University, completing a bachelor's degree in Physics and one in Mathematics in 2017 before continuing to Washington State University to pursue his PhD in Physics.

Currently, he is working jointly under Dr Forbes and Dr Bose to re-derive the Tolman-Oppenheimer-Volkoff (TOV) equations for arbitrary rotation speeds, and has interest in investigating the mechanisms that cause neutron star glitching.

Chunde Huang

Chunde Huang¶

Chunde comes from China where he got his bachelor degree (Software Engineering) and master degree (Computer Science) from Xiamen University, his major research was computer vision and machine learning. He worked as a professional software engineer for three years with experience on embed system framework development (C++ middleware for Android OS), smart traffic surveillance (object detection and tracking) and distribute system (Content Distribution Network). He started his pursuit of Ph. D in physics in 2013 at WSU.

Praveer Tiwari

Praveer Tiwari¶

Praveer comes from India where he got his BSc-MSc(Research) degree(Physics) from Indian Institute of Science, his major research was on Accretion Disk Modeling and Gravitational Wave Data Analysis. He started his pursuit of Ph.D in physics in 2016 at WSU. Since 2017, he worked in professor Jeffrey McMahon Group learning different aspects of machine learning and computational condensed matter.

Currently, he is working jointly under Dr Forbes and Dr Bose. He is working on constraining the parameters of the equation of state of neutron stars using the gravitation wave detection. He is also working on employing novel machine learning techniques to characterize different aspects of gravitational wave detections.

Ted Delikatny

Ted Delikatny¶

Ted simulates various phenomena related to quantum turbulence in superfluids, including the dynamics and interactions of vortices, solitons, and domain wall dynamics. Currently Ted is working to understand the phenomenon of self-trapping in BECs with negative-mass hydrodynamics.

Khalid Hossain

Khalid Hossain¶

Khalid comes from Bangladesh where he got his MS in theoretical physics from University of Dhaka. Currently Khalid is simulating two-component superfluid mixtures - Spin-Orbit Coupled Bose Einstein Condensates (BECs) and mixture of Bose and Fermi superfluids. In particular, the interest is in detecting the entrainment (dragging of one component with another) effect, which may shed light on the astrophysical mystery of neutron star glitching.

Saptarshi Sarkar

Saptarshi Rajan Sarkar¶

Saptarshi is currently looking at quantum turbulence in a axially symmetric Bose-Einstein condensate, in which a shockwave is created by a piston. The axially symmetric simulation, although missing some key features like Kelvin waves and vortex reconnections, has a considerably less computational cost, while retaining the shock behaviour. He is also interested in learning about the vortex filament model to look into quantum turbulence in detail.

Ryan Corbin

Ryan Corbin¶

Ryan hails from the greater Seattle area. His current research focuses on DFT simulations of nuclei.

Popular Explanations

Here are resources that explain some of the physics at the core of our research in a fun way:

Atoms As Big As Mountains — Neutron Stars Explained (YouTube)

Prerequisites: Models¶

This post describes various models that are useful for demonstrating interesting physics.

Thermodynamics¶

This post discusses how phase equilibrium is established. In particular, we discuss multi-component saturating systems which spontaneously form droplets at zero temperature. This was specifically motivated by the discussion of the conditions for droplet formation in Bose-Fermi mixtures 1801.00346 and 1804.03278. Specifically, the following conditions in 1804.03278:

\begin{gather} \mathcal{E} < 0, \qquad \mathcal{P} = 0; \tag{i}\\ \mu_b\pdiff{P}{n_f} = \mu_f\pdiff{P}{n_b}; \tag{ii}\\ \pdiff{\mu_b}{n_b} > 0 , \qquad \pdiff{\mu_f}{n_f} > 0, \qquad \pdiff{\mu_b}{n_b}\pdiff{\mu_f}{n_f} > \left(\pdiff{\mu_b}{n_f}\right)^2. \tag{iii} \end{gather}

1801.00346: https://arxiv.org/abs/1801.00346 1804.03278: https://arxiv.org/abs/1804.03278

Correlation Plot

Uncertainties¶

Here we discuss the python uncertainties package and demonstrate some of its features.

Galileo

Galilean Covariance¶

In his "Dialogue Concerning the Two Chief World Systems", Galileo put forth the notion that the laws of physics are the same in any constantly moving (inertial) reference frame. Colloquially this means that if you are on a train, there is no experiment you can do to tell that the train is moving (without looking outside).

This post will explain formally what Galilean covariance means, clarify the difference between covariance and invariance, and elucidate the meaning of Galilean covariance in classical and quantum mechanics. In particular, it will explain the following result obtained by simply changing coordinates, which may appear paradoxical at first:

Consider a modern Lagrangian formulation of a classical object moving without a potential in 1D with coordinates $x$ and $\dot{x}$, and the same object in a moving frame with coordinates $X = x - vt$ and $\dot{X} = \dot{x} - v$. The Lagrangian and conjugate momenta in these frames are:
\begin{align} L[x, \dot{x}, t] &= \frac{m\dot{x}^2}{2}, & p &\equiv \pdiff{L}{\dot{x}} = m\dot{x},\\ L_v[X, \dot{X}, t] &= \frac{m(\dot{X}+v)^2}{2}, & P &\equiv \pdiff{L_v}{\dot{X}} = m(\dot{X}+v) = p. \end{align}
Perhaps surprisingly the conjugate momentum $P$ is the same in the moving frame whereas Galilean invariance implies that one should have a description in terms of $P = m\dot{X} = p - mv$. The later description exists, but requires a somewhat non-intuitive addition to the Lagrangian of a total derivative.

Read more…

Kamiak Cluster at WSU¶

Here we document our experience using the Kamiak HPC cluster at WSU.

Resources¶

Kamiak Specific¶

Kamiak Users Guide: Read this.
Service Requests: Request access to Kamiak here and use this for other service requests (software installation, issues with the cluster, etc.)
Queue List: List of queues.

General¶

SLURM: Main documentation for the current job scheduler.
Lmod: Environment module system.
Conda: Package manager for python and other software.

Prerequisites¶

This post describes the prerequisites that I will generally assume you have if you want to work with me. It also contains a list of references where you can learn these prerequisites. Please let me know if you find any additional resources particularly useful so I can add them for the benefit of others. This list is by definition incomplete - you should regard it as a minimum.

michael.forbes+blog@gmail.com

Many-body Quantum Mechanics¶

In this notebook, we briefly discuss the formalism of many-body theory from the point of view of quantum mechanics.

Washington State University