Quantum metrology for accelerating future searches for fundamental physics including gravitational-wave observation

Abstract

Searches for fundamental physics such as gravitational waves, dark matter, and quantum gravity are now reaching the quantum limit around a century since the invention of quantum mechanics. To push past the fundamental quantum noise and accelerate the discovery of new physics, we need to understand and exploit the interplay of quantum information and quantum metrology. In this thesis, we advocate for a new perspective on the design of gravitational-wave interferometers and other precision waveform sensors, one centred on optimising the sensitivity through studying and manipulating the relevant quantum information-theoretic quantities with practical considerations for loss and classical noise. We demonstrate this approach with a series of papers proposing various measurement schemes, initial quantum states, and quantum control sequences to achieve the fundamental quantum limits of different waveform estimation problems. We suggest that the ultimate potential sensitivity of present experimental designs remains untapped: present in the capability of the device but not yet accessed. In particular, we show that a quantum advantage exists in sensing non-stationary or stochastic waveform signals or those with a wide range of possible frequencies. We discuss the implications of these results and how to realise them for future searches for fundamental physics.