This series covers all areas of research at Perimeter Institute, as well as those outside of PI's scope.
While quantum measurement remains the central philosophical conundrum of quantum mechanics, it has recently grown into a respectable (read: experimental!) discipline as well. New perspectives on measurement have grown out of new technological possibilities, but also out of
attempts to design systems for quantum information processing, which promise to be exponentially more powerful than any possible classical computer. I will try to give a flavour about some of these perspectives, focussing largely on a particular paradigm known as "weak measurement."
The ground-based gravitational-wave telescopes LIGO and Virgo approach the era of first detections. Gravitational-wave observations will provide a unique probe for exploring strong-field general relativity and compact-binary astrophysics. In this talk, I describe recent predictions regarding the distributions of black-hole and neutron-star binary mergers, and progress on solving the inverse problem of turning gravitational-wave observations into astrophysical information.
Causal set quantum gravity is based on the marriage between the concept of causality as an organising principle more basic even than space or time and fundamental atomicity. Causal sets suggest novel possibilities for "dynamical laws" in which spacetime grows by the accumulation of new spacetime atoms, potentially realising within physics C.D. Broad's concept of a growing block universe
One of the main challenges that we face both as individual persons and as a species concerns the distribution and use of resources, such as water, time, capital, computing power or negatively valued
resources like nuclear waste. Also within theoretical physics, one
frequently deals with resources like free energy or quantum entanglement. I will describe a mathematical theory of resources which makes quantitative predictions about how many resources are required for
producing a certain commodity and outline some applications to information theory.
Gravitational radiation promises to teach us many new
things about the universe and the world around us, but all attempts to observe
gravitational waves have so far been unsuccessful. I will discuss some of the challenges we need
to overcome in our quest to detect this elusive form of energy, and how
tackling these challenges is opening new windows on fundamental physics. I will show, specifically, how novel data
analysis strategies have been used to combat detector noise in searches for
Theorists have been studying and classifying entanglement in many-particle quantum states for many years. In the past few years, experiments on such states have finally appeared, generating much excitement. I will describe experimental observations on magnetic insulators, ultracold atoms, and high temperature superconductors, and their invigorating influence on our theoretical understanding.
The Pauli exclusion principle is a constraint on the
natural occupation numbers of fermionic states. It has been suspected for
decades, and only proved very recently, that there is a multitude of further
constraints on these numbers, generalizing the Pauli principle. Surprisingly,
these constraints are linear: they cut out a geometric object known as a
polytope. This is a beautiful mathematical result, but are there systems whose
physics is governed by these constraints?
In one extreme, where the interactions
are sufficiently weak compared to the interactions, electrons form a “Fermi
liquid” – the state that accounts for the properties of simple metals. In the other extreme, where the interactions
are dominant, the electrons form various “Mott” insulating or “Wigner
crystalline” phases, often characterized by broken spatial and/or magnetic symmetries. Corresponding charge and/or magnetically
ordered insulating phases are common in nature.
The global warming
crisis is part of a bigger transformation in which humanity realizes that the
Earth is a finite system and that our population, energy usage, and the like
cannot continue to grow exponentially. While politics and economics pose the
biggest challenges, physicists are in a good position to help make this
transition a bit easier. After a quick review of the problems, we discuss a few
ways physicists can help.