New Publication in Physical Review Letters Limits of Measurability of Quantum Jumps Pushed Back


Correct counting determines our modern life – be it the bits in a computer with their two states, the number of positive coronatests, or generally any system that has countable events. But the faster counting is done and the smaller the signals involved are, the more likely data can get lost in the noise. Theoretical physicist Eric Kleinherbers of SFB1242 and CENIDE now developed a new tool with colleagues inside that sheds more light on such data.

Counting statistics are particularly important in the quantum world. Modern measuring instruments are so sensitive that they can detect single quantum jumps. Limiting factors are the time resolution of the detector, the background noise, and the observation time. In addition, detection errors distort the measured information, leading to no or incorrect conclusions about the underlying quantum dynamics.

For their work, the researchers used so-called self-assembled quantum dots, which have similar properties to individual atoms, and employed a trick. The quantum dot is excited with a laser and radiates back light particles (photons) as long as it is "empty." If an additional electron enters the quantum dot, the light current breaks off. Thus, the photons can be used to record the electron occupation in real time, which can then be statistically analyzed.

To test how robust the new evaluation algorithm is, data was intentionally deleted from the original data set, simulating a faulty measurement. "These were typical experimental errors: signals that are too fast for the detector and are therefore "missed" or a spike in the noise that fakes a signal" explains Eric Kleinherbers, lead author of the study. By comparing the original readings with the erroneous data, the researchers were able to demonstrate that the new method of analysis is much more error-tolerant than the standard methods of statistical analysis used previously. This makes the actual behavior of electrons and photons more visible, shedding light on the quantum world. "It's a bit like trying to put a screw in the wall with an improper screwdriver until now," Kleinherbers explains. "It works, but it's not pretty. Now we have the right tool for analyzing the data."

Counting statistics are everywhere: in the evaluation of nerve signals as well as in radioactive decay, in microelectronics as well as in magnetism. While experimental physicists are constantly coming up with new measurement techniques and experiments, theorists are also pushing the boundaries of feasibility with new evaluation methods. The developed method is not only interesting for new measurement results – existing data can now also be examined more closely, as Kleinherbers says. "We are in close exchange with colleagues who now want to see what else might be hidden in their data."

The results were published March 23, 2022, in the journal Physical Review Letters.

DOI: www.doi.org/10.1103/PhysRevLett.128.087701