Winnipeg Institute
for Theoretical Physics

WITP

WITP Summer Student Symposium 2021
19 Aug 2021, Online

Abstracts

Jiayue Yang
Holographic Complexity of the AdS Soliton
Complexity is an important concept to understand quantum information and some proposals have been put forward to evaluate the complexity of a holographic boundary state. In this report, I will give you a brief introduction to complexity and discuss one of the holographic complexity conjectures: Complexity= Volume conjecture. As an example, I will carry out the complexity calculations of the AdS soliton. Finally, I will talk about my present work on calculating the complexity of general soliton solution and discuss its properties.

Cole Coughlin
Tensor Networks and Geometry
Tensor Networks have already proven to be very useful for a variety of applications including simulating quantum systems, image compression, or exact solutions to NP hard problems. In this talk we will explore some holographic properties of MERA tensor networks which are used to simulate quantum spin chains, and in doing so will link some physical systems with a possibly holographic representation.

Shawna Skelton
MERA networks and Tunnelling in de Sitter Space
Tensor networks have recently garnered attention as a modelling tool for quantum gravity systems, and for de Sitter space (dS) in particular. The Multi-scale Entanglement renormalization ansatz (MERA), designed as an optimization tool for many-bodied ground states, has several distinct dS interpretations. In de Sitter, a quantum tunneling event can create a region of space expanding with a lower potential, and thus lower cosmological constant. With modifications to the typical ansatz, we design a MERA toy model of two-dimensional dS accommodating such regions. We show this construction is consistent with the geometry of two de Sitter spaces joined by a thin domain wall, then compare the growth of the effective Hilbert space dimension and Von Neumann entropy within each section of the model.

Chetna Duggal
Spotting jet-induced star formation in young radio galaxies with Hubble imaging
Imaging the UV continuum from hot massive stars is the best way to study recently triggered and ongoing star formation. With the aim of mapping star forming regions and morphologically separating the generic star formation from that associated with the galaxy-scale jet activity, we obtained high-resolution UV imaging from the Hubble Space Telescope for a sample of nine compact radio sources. Extended UV emission regions are observed in two-thirds of the sample showing strong alignment with the radio-jet orientation. If other mechanisms possibly contributing to the observed UV emission are ruled out, this could be evidence in support of jet-triggered star formation in the early phase of radio galaxy evolution and in turn of the 'positive feedback' paradigm of host-AGN interaction.

Marcelo Rubio
Stabilization and Isotropization of a longitudinally expanding quark-gluon plasma
Experiments at LHC and RHIC show that after a collision of a pair of ultra-relativistic heavy-ions, a plasma composed of highly energetic quarks and gluons is produced. The behaviour of this plasma (or "glasma", as it is called at early stages) is similar to that of an ideal fluid, being its dynamics governed by QCD. The theory predicts that the system expands outward from the collision center, right after the ions collide. Many questions about the dynamics during the expansion arise, in particular whether or not the system reaches thermal equilibrium before dispersing. Given the numerical difficulty of treating the full problem, because of the complexity of QCD theory, in this talk we discuss a simplified model using a scalar field theory with quartic coupling, which shares many of the important properties of QCD. We analyze the role of quantum fluctuations around certain background solutions of interest, and study pressure isotropization. Finally, we comment on some interesting open issues, such as the role of boundary conditions in the isotropization process, and the existence of initial field configurations that allow us to simulate a system with angular momentum.

Mehdi Biderang
Superconductivity of mixed parity and frequency in an anisotropic spin-orbit coupling
We illuminate the superconducting phases in [001]-grown-noncentrosymmetric quantum wells with an anisotropic spin-orbit coupling in the presence of on-site Hubbard interaction. Within the random phase approximation, we investigate the spin-fluctuation-mediated pairing in the presence of Rashba/Dresselhaus antisymmetric spin-orbit couplings. Although the existence of spatial inversion symmetry desires a dominant d-wave pairing for all filling levels, a broken inversion symmetry generates antisymmetric spin-orbit coupling and mixes the even- and odd-parity in the superconducting gap. We study the symmetry of the mixed-parity gap for various strengths of Hubbard interaction. Besides, we consider a superconductor-ferromagnet junction to survey the modifications of superconducting order parameters and observe an admixture of even- and odd-frequencies due to the ferromagnet exchange field.

Hermie Monterde
Types of quantum state transfer and their properties
Undirected graphs are used in quantum information theory to model quantum spin networks, with the vertices and edges representing the qubits and their interactions, respectively. One of the main interests involving quantum spin networks is determining a time t such that the state at a given vertex is transmitted to another vertex with a given probability. By Schrodinger's Equation, the matrix U(t)=exp(itM) governs the evolution of the system at any time t, and it is known that its entries give information about the probability of state transfer between any two vertices of G at time t. In particular, if |U(t)j,k|2=1, then we say that perfect state transfer occurs from vertex j to vertex k at time t, while if |U(t)j,k|2=1 can be made arbitrarily close to 1 by appropriate choices of t, then we say that pretty good state transfer occurs from j to k. On the other hand, if entries on the jth and kth columns of U(t) are zero at time τ except for those indexed by j and k, then we say that fractional revival occurs between vertices j and k at time t. In this talk, we look at the properties perfect state transfer, pretty good state transfer, and fractional revival, and give examples of graphs that admit these quantum phenomena.

Shirin Moein
The Modified Trace Distance of Coherence
We study the problem of minimizing the trace distance between a given Hermitian matrix and the set of diagonal matrices by using a generalization of orthogonality called Birkhoff--James orthogonality. Our results can be applied to the study of quantum coherence---the degree to which a quantum state is in superposition. We characterize quantum states that have maximal modified trace distance of coherence in arbitrary dimensions.

Wade Cowie
Fast Fourier Transforms and Phase Transitions
We are interested in studying phase transitions in three-dimensional Dirac semimetal (3D DSM). I will discuss the basic structure of the problem and point out some of the calculation difficulties. Fast Fourier Transforms are known to be computationally efficient, but they are not normally used to study phase transitions. I will explain why not, and describe a method we have developed to use FFT's to solve integral equations which describe a 3D DSM. I will compare the speed and accuracy of our method with a calculation that uses conventional integration methods.

Brett Meggison
Studying Phase Transitions in Graphene using a Low Energy Effective Field Theory
The possibility of controlling the conductivity of graphene is a promising avenue in the study of using graphene for electronic components. A possible method for controlling graphene's conductivity is straining of the graphene lattice, modeled with fermi-velocity anisotropy in the energy dispersion. We then find the point at which a phase transition occurs by finding the critical coupling of a system of self-consistent, coupled Schwinger-Dyson equations. We show that in the simplest of our models, anisotropy depresses graphene's ability to enter into an insulating state, but that as we relax approximations, we see a reduction in this depression. We take this as motivation to study further modifications of our model.

Kyle Monkman
Operational entanglement of symmetry-protected topological edge states
In my presentation, I will discuss my research on entanglement extracted from a many-body state with topologically protected edge states. I will first discuss the fundamental idea of topologically protected insulators; that is a quantity that cannot be changed without closing the band gap. This quantity can be entanglement, the Wannier center or in the case of my research, it is the long range superposition of the edge states. Viewing this long range superposition as a quantum resource, we can investigate fundamental quantum measurements such as the breaking of Bell's inequality.