Quantum physics has become ubiquitous across science over the past few years, often in connection to advances and investment in quantum computing research.
However, it’s ‘quantum sensing’ where much of the investment in quantum technologies is directed and it’s a growing area of research.
It is true that quantum computers will one day offer us increased computing power and efficiency, however the goal of creating a fully-fledged quantum computer is many years away.
This is due to the engineering challenges involved; it is extremely difficult to maintain a qubit (the building block of a quantum computer) in a quantum state long enough to use it. Any outside perturbations cause the system to collapse, rendering it useless. Even the tiniest fluctuations in properties like magnetic and electric fields or temperature can cause the collapse of a quantum state.
This sensitivity presents an obvious challenge to the development of a quantum computer; however, researchers can harness this sensitivity, and access interactions and phenomena at levels well outside the range of conventional sensing approaches.
Today’s quantum sensors have their roots in well-established techniques such as magnetic resonance imaging (MRI), which is founded on similar quantum mechanical principles. In an MRI experiment, individual nuclei are used as qubits, which report on their surrounding environment. Similarly, most modern quantum sensing uses either a nuclear or electronic ‘spin’ as a qubit.
As the name suggests, MRIs measure how the magnetic field environment around hydrogen nuclei affects their behaviour. In many cases, modern quantum sensors are also used as highly sensitive magnetic field detectors. Unlike MRI however, they often combine magnetic field sensitivity with extremely high spatial resolution and the prospect of low cost and portability. Together, these attributes make them useful across a diverse collection of industries and research areas.
For example, one promising application of quantum sensing is the identification of novel materials for use in classical computers.
So, you want to study quantum physics?
To maintain the utility of classical computers into the future, considerations around power consumption and size constraints will need to be addressed. Electrical engineers are interested in new materials, such as graphene and perovskite, which will offer benefits over traditional silicon-based devices.
Quantum sensing is helping to understand the magnetic behaviour of these novel materials; a vital requirement for selecting those worth further development.
As molecular biology has advanced, questions about the nature of intracellular interactions, such as those within or between individual proteins, have become the target of fundamental research. Quantum sensors can offer unique information at a higher resolution than compared to traditional techniques like light microscopy.
Researchers are hopeful that with this new level of detail, quantum sensing can be used to answer questions useful to medical science, such as how to design better drugs, the nature of neuronal signalling and how to more accurately diagnose disease. These goals are being addressed by the new 7-year, ARC Centre of Excellence on Quantum Biotechnology.
Quantum sensing has also seen strong uptake within the mineral resources sector where it can be used to identify new mineral extraction sites via the subtle magnetic fields they produce. SQUID magnetometers (Superconducting Quantum Interference Devices use quantised superconducting states as the sensor) are already deployed for this task and can detect magnetic fields many times smaller than the earth’s.
Finally, given their unique sensitivity, physicists are also interested in the new physical regimes quantum sensors could access. Quantum sensors may end up helping scientists answer some of physics’ most fundamental questions, such as the nature of dark matter or gravity. SQUIDs have recently been deployed at the Simons Observatory in Chile to help detect cosmic microwave background (CMB) radiation. In this case, instead of a magnetic signal, what is detected is the heat created when a CMB photon collides with a SQUID, disrupting its quantum state.
