Quantum sensors can measure extremely small changes in an environment by taking advantage of quantum phenomena like entanglement, where entangled particles can affect each other, even when separated by great distances. Ultimately, say the researchers, they hope to be able to create and use these sensors in applications such as detecting and diagnosing disease, predicting volcanic eruptions and earthquakes, or exploring underground without digging.
Now, by harnessing a unique physics phenomenon, the researchers say they have calculated a way to develop a sensor that has a sensitivity that increases exponentially as it grows, without using more energy.
“This could even help improve classical sensors,” says Prof. Aashish Clerk, co-author of a paper on the research. “It’s a way to build more efficient, powerful sensors for all kinds of applications.”
Quantum sensors use atoms and photons as measurement probes by manipulating their quantum state. Increasing the sensitivity of these sensors – and traditional sensors – often means developing a bigger sensor or using more sensing particles. Even so, say the researchers, such moves only increase the sensitivity of quantum sensors equal to the number of particles that are added.
Wondering if there was a way to increase the sensitivity even more, the researchers say they imagined creating a string of photonic cavities, where photons can be transported to adjacent cavities. Such a string could be used as a quantum sensor. This then brought up the question, if they created a longer and longer chain of cavities, would the sensitivity of the sensor be greater?
In systems like this, say the researchers, photons could dissipate – leak out of the cavities and disappear. But by harnessing a physics phenomenon called non-Hermitian dynamics, where dissipation leads to interesting consequences, they were able to calculate that a string of these cavities would increase the sensitivity of the sensor much more than the number of cavities added. In fact, they say, it would increase the sensitivity exponentially in system size.
Not only that, it would do so without using any extra energy and without increasing the inevitable noise from quantum fluctuations, which would be a huge win for quantum sensors, say the researchers.
“This is the first example of a scheme like this – that by stringing these cavities together in the right way, we can gain an enormous amount of sensitivity,” says Clerk.
To prove the theory, the researchers say are working with other researchers who are building a network of superconducting circuits. These circuits could move photons between cavities in the same manner described in their research paper, which could create a sensor that could improve how quantum information is read out from quantum bits, or qubits.
The researchers say they also hope to examine how to construct analogous quantum sensing platforms by coupling spins instead of photonic cavities, with possible implementations based on arrays of quantum bits.
“We want to know if we can use this physics to improve all kinds of quantum sensors,” says Clerk.