What can detectors detect?

Abstract

This thesis is focused on using a pair of Unruh-DeWitt detectors, which interact locally with a quantum field, to gain information about properties of the field and the underlying spacetime.

First, we consider a massless scalar field with a bandlimit, a hard ultraviolet cutoff. We show that that when UDW detectors interact with a bandlimited field, they are able to become entangled over larger distances then would be expected in the case of no cutoff. The bandlimit introduces some non locality into the interaction, which boosts the nonlocal correlations between the detectors. This boost in entanglement could, in principle, be used to put a lower bound .

Then we study the affect of a quantum controlled switch to the entanglement harvesting protocol. This switch will control when the detectors interact with the quantum scalar field and can allow for them to each couple to the field in a superposition of two times. We show that when a detector interacts with a field at a superposition of times, its transition probability is reduced compared to what it interacted at a mixture of times. This in turn increases the entanglement harvested by a pair of detectors, which can even violate no-go theorems.

Next, we turn our attention to (2+1)-dimensional AdS spacetime. We map out a large amount of the parameter space, tuning both detector and spacetime properties. Most interestingly, we find an "island of seprability" in the parameter space, which occurs at a relatively small Ads length. When the detectors' properties fall in the "island of seprablity", they cannot become entangled through local interactions with the field; however for a good range of parameters around the island, they can.

We then apply the entanglement harvesting protocol to a black hole spacetime, specifically the BTZ black hole. We find an entanglement "death zone" which marks the point where entanglement harvesting is no longer possible as two detectors with fixed proper separation approach the horizon.

Finally, we make a change to the detector model itself. We consider the the center of mass degree of freedom of the detectors to be quantum, and so will it coherently delocalize over the course of the interaction with the quantum field. We find that this delocalization inhibits entanglement harvesting, and it is only in the limit of very heavy and very sharply localized detectors that we recover the case of a pair of UDW detectors classical center center of mass.