Conference

The question of the time reversibility of quantum mechanics with measurements is one that has been debated for some time. In this talk, I will present new work exploring our ability to distinguish the forward from the time-reverse measurement records of continuous quantum measurements. The question involves both the conditions for the time-reversibility of the quantum trajectory equations of motion, as well as statistical distinguishability of the arrow of time. I will present the case with and without postselection on the final state, and connect the issue to a similar topic in nonequilibrium statistical physics. This work generalizes and pushes the two-time reformulation of quantum mechanics developed by Yakir Aharonov and collaborators beyond arbitrarily weak measurements. I will also discuss how this proposal can be implemented with continuously monitored superconducting quantum circuits. In collaboration with Alexander Korotkov, Justin Dressel, Areeya Chantasri, and Kater Murch Funded by the John Templeton Foundation.

I will present our recent experimental work using electromagnetically induced transparency in laser-cooled atoms to measure the nonlinear phase shift created by a single post-selected photon, and its enhancement through "weak-value amplification." Put simply, due to the striking effects of "post-selective" quantum measurements, a (very uncertain) measurement of photon number can yield an average value much larger than one, even when it is carried out on a single photon. I will say a few words about possible practical applications of this "weak value amplification" scheme, and their limitations. Time permitting, I will also describe other future and past work using "weak measurement," such as our studies quantifying the disturbance due to a measurement and what happens when it destroys interference; and our project to measure "where a particle has been" as it tunnels through a classically forbidden region – our prediction being that it will make it from one side of the barrier to the other without spending any significant time in the middle.

The Square Kilometre Array (SKA) is a next-generation radio telescope scheduled to commence construction in 2018. The SKA will be one of a small set of billion-dollar facilities that collectively span the electromagnetic spectrum, and will be an order of magnitude more sensitive than any other radio facility. The SKA's extraordinary survey capacity will allow it to map the distribution of galaxies and large-scale structure over an unprecedented cosmic volume, providing superb probes of dark matter, dark energy, neutrino physics, magnetogenesis, non-gaussianity and inflation. In addition, pulsar timing with the SKA will provide precision tests of general relativity in the strong field regime, and should allow us to detect gravitational radiation produced by merging supermassive black holes. In this talk, I will provide an overview of the capabilities and science goals for the SKA, highlighting its unique potential for advancing our understanding of cosmology and fundamental physics.

Cosmic background neutrinos are nearly as abundant as cosmic microwave background photons, but their mass, which determines the strength of their gravitational clustering, is unknown. Neutrino oscillation data gives a strict lower limit on neutrino mass, while cosmological datasets provide the most stringent upper limit. Even if the neutrino masses are the minimum required by oscillation data, their gravitational effects on structure formation will nevertheless be detectable in — and in fact required to explain — data within the next decade. I will discuss the physical effects of the cosmic neutrino background on structure formation and present a new signature that may be used to measure neutrino mass with large galaxy surveys.

In a broad class of theories, the relic abundance of dark matter is determined by interactions internal to a thermalized dark sector, with no direct involvement of the Standard Model. These theories raise an immediate cosmological question: how was the dark sector initially populated in the early universe? I will discuss one possibility, asymmetric reheating, which can populate a thermal dark sector that never reaches thermal equilibrium with the SM.

Using lensing of the CMB we can make maps of the dark matter distribution on the largest cosmological scales, perhaps allowing new insights into gravity, particle physics, and cosmology. With high-resolution maps of distant star-forming galaxies we can map dark matter on small scales within individual galaxies, measuring the small-scale clumping properties of dark matter.