Seminars

Quantum simulation with superconducting quantum circuits: coupled harmonic and anharmonic quantum oscillators

Superconducting circuits are demonstrated as analogue quantum simulators of several fundamental Hamiltonians. The testbeds are formed by combinations of coupled of harmonic and anharmonic resonators being operated in the quantum regime. These quantum electromagnetic circuits are based on superconducting thin films and forming linear and non-linear inductors and capacitors being cooled to milliKelvin temperatures. Control and probe pulses are at microwave frequencies and of 10s of nanoseconds duration. The resulting spin dynamics are probed by standard qubit-readout techniques based on circuit quantum electrodynamic.
In this talk I will introduce superconducting quantum circuits, and highlight some quantum simulation experiments: Ultra-strong coupling is demonstrated and probed by moving in the rotating frame (Braumueller et al. Nat. Com 8, 779  (2017)), the level structure of a multi-qubit system coupled to a resonator (Leppaekangas et al. Tavis-Cummings model) is verified experimentally on an eight qubit chip (Yang et al.arXiv:1810.00652), and an experimental approach of simulating the spin-boson model is described (Leppaekangas Phys Rev A 97, 052321 (2018)).

Energy-density-functional results for magic nuclei and the extrapolations to the nuclear matter equations of state for neutron stars

I will discuss results from the references below for the applications of Skyrme energy-density functionals to properties of doubly-magic nuclei, ab-initio calculations of low-density neutron matter, and neutron stars. The correlation between the neutron skin and the slope of the neutron equation of state near a density of 0.10 nucleons/fm^3 discovered in ( 1,2,3) was extended to the differences in the charge radii of mirror nuclei (4). Alternatively, when the Skyrme parameters are constrained by ab-initio calculations of low-density neutron matter, predictions can be made for the neutron skin and the slope of the neutron equation of state (4). The maximum mass of the neutron star depends on the neutron effective mass. A value of [m ∗ n /m](ρ 0 ) = 0.60-0.65 is required to obtain a maximum neutron star mass of 2.1 solar masses (6). With the constraints to the low-density neutron matter and neutron star mass, a value of 12.4(1) km is predicted for the radius of a 1.4 solar mass neutron star.
1) Neutron Radii in Nuclei and the Neutron Equation of State, Phys. Rev. Lett. 85, 5296 (2000).
2) Neutron Radii and the Neutron Equation of State in Relativistic Models, Phys. Rev. C64, 027302 (2001).
3) Constraints on the Skyrme Equations of State from Properties of Doubly Magic Nuclei, Phys. Rev. Lett. 111, 232502 (2013).
4) Constraints on the Skyrme Equations of State from Properties of Doubly Magic Nuclei and ab initio Calculations of Low-Density Neutron Matter, Phys. Rev. C 89, 011307(R) (2014).
5) Mirror Charge Radii and the Neutron Equation of State, Phys. Rev. Lett. 119, 122502 (2017).
6) C. Y. Tsang, B. A. Brown, F.J. Fattoyev, W. G. Lynch, and M. B. Tsang, arXiv:1908.11842v1.

A tale of two nanomaterials

A central theme of our research program is to use nanostructured building blocks to fashion materials with properties that are tailored from the bottom-up, and to study these materials for new scientific insight and potential applications.

In this talk I will present results on 2 such “nanoengineered” materials:

1) gold nanoparticles cross-linked with insulating or semiconducting molecules. This material exhibits a range of interesting behaviour, including an insulator-to-metal transition, single electron charging, and strong electron-electron interactions such as a large Kondo effect.

2) MoS2 flakes functionalized at high temperature with alkanethiols.  The resulting MoS2 is available in quantitative amounts given its low cost solution-based synthesis, soluble in organic solvents, and semiconducting with higher photoluminescence than films grown by chemical vapour deposition.  The functionalized MoS2 flakes can in turn be used as building blocks to explore MoS2-based opto-electronic devices.