Fast and reliable detection is essential for probing quantum systems before fragile information is lost. In a new study, the researchers show that a nonlinear resonator can deliver a near-perfect readout signal without meeting the usual impedance-matching requirements that normally limit detector speed. By deliberately driving the resonator into a nonlinear regime, they found a way to boost the signal that opens the door to much faster charge detection in quantum devices.
“The goal is to detect the presence of an electric charge in a quantum system”, says Harald Havir, who defended his PhD thesis last year.
“The challenge with doing this is to perform the readout fast, so that the information carried by the electron isn’t lost in time. The quicker the better, so to speak.”
Increase the speed while maintaining the signal strength
If a sensor produces a certain signal, you normally need to read it at a rate that matches the sensor's impedance – something that slows down the detection process involving tiny nanodevices. To handle these matching requirements is a typical electrical engineering problem.
“You need to match it – but this study has found a way to break this rule, and gives you more freedom”, says Ville Maisi.
And they actually found this out by accident. During work on his doctoral thesis, Harald Havir and his colleagues were conducting tests of the resonator's signal strength. When they increased the input power to enhance the signal, the very nature of the signal changed.
Nonlinearity altered the scene
“The response strength all of a sudden increased by a factor of five. I first got confused and felt like something strange had happened. But it was due to the nonlinearity”, says Harald Havir.
“This triggered our curiosity about what was happening”, says Ville Maisi.
In a linear system, the output acts in proportion to an input, such as the number of photons oscillating in a resonator, as you increase the input power. In nonlinear systems, this is no longer the case.
“A linear resonator that is usually used in these kinds of detectors results in an amplitude change on resonance”, says Ville Maisi.
“Since the resonator was nonlinear, we ended up getting something completely different. The nonlinearity changes the frequency of the resonator, and hence the whole response moves away. This is the mechanism behind the sudden increase”, continues Ville Maisi.
No need for matching
The oscillating resonator was, in other words, changing the whole operation principle of the detector. The goal of making a more sensitive detector for fast speed was achieved.
“We changed the requirement for the resonator so that it doesn’t need to match the sensor, making it possible to probe a quantum system faster. I want to emphasize that the results are relevant even for other fields, as long as they can find a nonlinear system to read out their sensor”, says Harald Havir.
“The principle applies to any system that oscillates: pendulums, waves... This concerns fundamental conditions in many fields”, concludes Ville Maisi.
- “Near-unity charge readout signal in a nonlinear resonator without matching the sensor dissipation” in Nature Communications
- Authors: Harald Havir, Andrea Cicovic, Pierre Glidic, Subhomoy Haldar, Sebastian Lehmann, Kimberly A. Dick & Ville F. Maisi
