Trying to understand how to make quantum systems useful for sensing can help uncover the secrets of quantum themselves.

“My academic career is still relatively young,” says Dr George Mihailescu, a University College Dublin (UCD) postdoctoral researcher developing advanced quantum sensing techniques.

Mihailescu graduated with a degree in physics from Dublin City University in 2019. Later, he completed a master’s degree in applied mathematics and theoretical physics from UCD. “It was during this time that my interests began to focus more specifically on quantum physics,” he says.

“My master’s thesis looked at how to design efficient protocols for charging quantum batteries, which gave me my first opportunity to work in depth on problems in quantum information and quantum technologies.”

In 2021, Mihailescu began a four-year PhD that focused broadly on understanding complex quantum many-body systems using modern quantum information theory tools.

“Over the course of the PhD, my interests increasingly shifted towards quantum sensing: in particular, whether the complex collective effects that arise in many-body systems could leveraged as a resource for designing more sensitive quantum sensors,” he says.

“Alongside that, I became interested in more practical questions, such as how these sensing protocols can be made robust to noise, imperfections and other detrimental effects that inevitably arise in realistic settings.”

Mihailescu’s work at UCD as a postdoctoral researcher focuses on cooling atoms to extremely low temperatures in order to control their quantum behaviour.

“Our objective is to develop and implement advanced quantum-sensing techniques in these systems, bringing together the theoretical ideas I worked on during my PhD with experiments where those ideas can be tested and applied.”

I was always the child who asked my parents and teachers far too many questions, and I was very curious about the natural world.

One memory that has always stayed with me is reading a children’s book about Einstein. It described the famous debates between Einstein and Bohr about quantum mechanics, including the thought experiments they used to challenge one another’s ideas. Looking back, I think that was probably my first real spark of interest in quantum physics.

During college, I was fortunate to have the opportunity to complete a number of internships in research laboratories. That was when science became much more tangible to me; rather than simply learning established ideas from textbooks, I could see what it meant to work on questions where the answer was not already known.

I think one common misconception is that quantum mechanics only matters for very small particles, like individual atoms or electrons. That is where quantum effects are often easiest to observe, but the theory itself does not suddenly stop applying as systems become larger.

In fact, there is a lot of interest in pushing the boundary between the quantum and classical worlds by demonstrating genuinely quantum behaviour in larger and larger systems.

That is something I find particularly interesting, because it reminds us that quantum mechanics is not just a theory for tiny particles. It is the framework we believe describes nature more generally. The real question is why quantum behaviour becomes so difficult to observe as systems get larger, more complicated and more strongly coupled to their environment.

I think there are two sides to why this research is important. The more obvious one is the potential impact of quantum sensing itself.

If we can learn how to control and use quantum systems in the right way, they can allow us to measure physical quantities with extremely high precision. That could eventually be useful in areas such as navigation, mapping underground structures through tiny variations in gravitational fields, or detecting very weak signals that would otherwise be difficult to observe.

Sensitivity is not only useful for building a better sensor; it can also act as a probe of the underlying physics.

For complicated many-body systems, that can help us identify hidden structure, changes in correlations, transport behaviour, or other physical effects that are not always obvious from more conventional measurements.

So there is a kind of feedback between the two aims – by trying to understand how to make quantum systems useful for sensing, we can also uncover new information about the quantum systems themselves.

Quantum sensing is an interesting area commercially because sensors are already everywhere. We use them in very familiar settings, from thermometers and cars to phones, laptops and industrial systems.

Whether quantum sensors will eventually permeate all of those applications is still an open question, but I think they have a clear role to play in areas where we need a new level of precision or sensitivity.

That could include things such as navigation without relying on satellite signals. This is particularly interesting in environments like the deep ocean, where GPS does not work, and both radio and light are strongly attenuated by sea water.

Highly sensitive quantum sensors could potentially help vehicles navigate by detecting very small changes in quantities such as acceleration, rotation, gravity or magnetic fields, and the same kinds of measurements could also help us map the seafloor or probe underwater structures in ways that are currently very difficult.

Quantum computers and other quantum devices rely on physical effects that are extremely sensitive to their environment. Small fluctuations in temperature, magnetic fields, vibrations or other sources of noise can degrade or destroy the quantum behaviour we are trying to exploit.

Quantum sensors could therefore play a dual role: as technologies with important applications in their own right, but also as part of the infrastructure needed to make other quantum technologies practical and reliable.

One misconception is that simply making a sensor quantum automatically makes it better. Quantum mechanics can, in principle, allow us to achieve levels of sensitivity that would not otherwise be possible, but actually realising that advantage is much more complicated.

The quantum states that give us enhanced sensitivity can also be particularly fragile, so noise, imperfect control and interactions with the surrounding environment can quickly remove the advantage we were hoping to gain.

A large part of the research is therefore not just asking, ‘Can quantum mechanics make this measurement more precise?’ but asking under what realistic conditions that advantage survives and whether we can design protocols that are both highly sensitive and robust.

I think that distinction between what is possible in principle and what can actually be implemented is sometimes lost when quantum technologies are discussed more broadly.

There is also a tendency to think of sensing purely as an application of quantum physics, whereas it can work in the other direction as well. Studying how sensitively a quantum system responds to small changes can itself provide a way of learning about the underlying physics, particularly in complicated many-body systems.

So quantum sensing is not only about building better measurement devices; it can also give us a new way of understanding quantum systems themselves.

One area I would really like to see developed further is our understanding of quantum chaos and, more broadly, how information spreads through complex quantum systems.

In classical physics, chaos is associated with extreme sensitivity to initial conditions: the idea that very small differences at the beginning can eventually lead to completely different outcomes.

Quantum systems do not behave in exactly the same way, but there are closely related questions about how information becomes distributed through a many-body system and how initially simple states evolve into extremely complicated ones.

One concept that comes up here is scrambling. If you perturb one small part of a quantum system, that information can gradually spread across many of its constituent parts until it becomes effectively hidden in complicated correlations throughout the whole system.

Closely connected to that is thermalisation: how an isolated quantum system, evolving according to perfectly reversible quantum mechanics, can nevertheless come to look thermal and apparently lose memory of how it started.

Don’t miss out on the knowledge you need to succeed. Sign up for the Daily Brief, Silicon Republic’s digest of need-to-know sci-tech news.