The goal of this project is to develop new precision sensing capability based on quantum technology, motivated by the desire to investigate fundamental physics as well as developing improved commercial and military technology.
Measurement is a cornerstone of the natural sciences, with increased measurement precision inevitably leading to the observation of previously unknown phenomena. Currently, atom interferometers provide physicists with a tool for making extremely sensitive measurements. However, the continued endeavour to increase the sensitivity of these devices is currently at a road-block: the limits set by quantum noise. The aim of this project is to use this fundamentally new approach to design practical sensing devices with unprecedented sensitivity.
Atom interferometry provides an important capability that other inertial sensing technologies lack, which is high-precision at low frequencies due to the lack of any long-term systematic drifts in the device. In terrestrial gravitational field and gradient detection, this can provide much higher sensitivities, allowing for new capabilities such as detection of underground structures and hydrology. Atom interferometry will also play an important role in inertial navigation (which is a crucial military capability in GPS denied environments). Here, the atomic sensor would supplement existing (usually high-bandwidth) mechanical sensing technology, by providing periodic re-calibration to correct for long-term drifts, which are currently a limiting factor. This project will apply quantum metrology to improve the sensitivity and bandwidth of these sensors.
There has recently been much interest in the use of quantum entanglement, or quantum squeezing, to enhance the sensitivity of atom interferometry, with recent proof of principle demonstrations in small ‘toy’ interferometers. While these experiments are of fundamental interest and may one day be useful as magnetometers, they lack any spatial path separation so are fundamentally incapable of measuring inertial quantities such as rotations, accelerations, or gravitational fields. It is not simply that these devices need to be refined until they are comparable to the current state-of-the-art. As the method of generating entanglement was based on atom-atom interactions, these devices will never be capable of out-performing the current state of the art precision atomic inertial sensors. The reasons for this are as follows:
- Strong atom-atom interactions are incompatible with the long interrogation times required for inertial sensing. This is because the same interactions that cause the quantum entanglement will inevitably cause an effect known as phase diffusion, which will drastically degrade the sensitivity.
- Increasing the number of particles in a strongly interacting system introduces increasingly complicated multi-mode dynamics, which will inhibit the visibility of the interference fringes.
- Strong interactions inevitably lead to an atomic sample with a broad momentum distribution, which is incompatible with the finely tuned large momentum transfer atomic beam-splitters required for ultra-precise atomic inertial sensors.
The current state of play in precision inertial sensing with atom interferometry is analogous to the situation where a new, much more efficient engine has been developed, but this engine can only be used in a child’s toy car, with no possibility of scaling the technology up to a useful transport solution. This project will design a method of utilising quantum entanglement compatible with current state-of-the-atomic sensors, which will pave the way for a measurement device with unprecedented sensitivity. This project will design a method of utilizing quantum entanglement compatible with current state-of-the-atomic sensors, delivering a measurement device with unprecedented sensitivity. This will be achieved by breaking away from the convention of purely atomic-based atom interferometers, and considering atomic-photonic hybrid devices.
