Communications in Theoretical Physics ›› 2020, Vol. 72 ›› Issue (1): 015101.

• Quantum Physics and Quantum Information •

### Quantum information and microscopic measuring instruments

Alexey V Melkikh()

1. Ural Federal University, Yekaterinburg, Russia
• Received: 2019-08-20 Revised: 2019-10-22 Accepted: 2019-10-31 Published: 2020-01-01

Abstract:

The consideration of measuring instruments as macroscopic bodies leads to neglect of the microscopic processes that occur during measurements. This disregard is not justified in general cases. As an example of measurements using microscopic instruments, the scattering of a photon by an electron with electron interference at two slits (Compton effect) was used. The amount of information that can be obtained in such a process is inversely proportional to the wavelength of the incident photon. At large photon wavelengths (soft measurements), the pure state of the electron can be disrupted by an arbitrarily small extent; accordingly, the amount of information extracted in such an experiment is also arbitrarily small. It is shown that the energy price for a bit obtained in such a measurement tends toward a constant value for increasing the photon wavelength. Microscopic instruments can be used in situations where energy costs for measurements are important.