| Precise measurement of microwave electric fields is of central importance in a wide range of fields such as communication,remote sensing and cosmology.Currently,traditional microwave measurement system is based on metal antennas and microwave circuits,which has caused its sensitivity to be limited by Johnson-Nyquist noise and its measurement accuracy is affected by antenna size effect and disturbance of antenna to measured electric field,making it difficult to achieve either ultra-sensitive or accurate measurements.As modern science and technology rapid advance,various fields have put forward higher requirements on the sensitivity and accuracy of microwave measurement,making traditional system became overwhelmed.With the development of quantum technology,especially quantum sensors such as atomic clocks and atomic magnetometers have achieved great success,showing performance beyond their classic counterparts,people have begun to develop microwave electric field sensors based on quantum systems.The representative work of microwave electric field sensor based on quantum system at present is atomic electrometer,which solves problem of metrological traceability of traditional system,and its theoretical sensitivity is limited by quantum projection noise,which is far superior to traditional systems.However,when atomic electrometer performs a weak microwave measurement,its readout signal is proportional to the square of input microwave electric field intensity,and has property of variance measurement.Variance measurement leads to an increase in sensitivity of electric field strength by only √10 each time when amplitude of measurement system’s classical technology noise is reduced by an order of magnitude.This makes it extremely difficult for atomic electrometer to overcome classical technology noise,thereby achieving quantum projection noise limit,which is far from meeting application requirements.At the same time,atomic electrometer cannot obtain the frequency and phase information of target microwave electric field,which greatly limits its application in important fields such as communication and remote sensing.In this thesis,a conceptually new quantum-based microwave measurement method is proposed to realizes frequency and phase resolvable,ultra-wideband,ultra-sensitive and SI-traceable measurement of microwave electric field.The innovations of this thesis are as follows:1.In this thesis,we proposes a conceptually new microwave measurement method based on quantum system,that is,microwave superheterodyne precision measurement method based on Rydberg atoms(atomic superhet method),which realizes frequency and phase resolvable,ultra-wideband,ultra-sensitive and SI-traceable measurement of microwave electric field.Compared with usual atomic electrometer,we innovatively introduce a controllable local microwave field.The local microwave field has two important functions:· The local microwave field provides frequency and phase references for heterodyne measurement of signal microwave field.When the local microwave field and signal microwave field simultaneous driving a same Rydberg transition of identical Rydberg atom,they interfere with each other,than the interference pattern is coherently transmitted from highly excited Rydberg transition to probe light through Rydberg EIT process,and can be optically readout to realize heterodyne measurement of signal microwave field;· The controllable local microwave field provides an additional adjustment dimension for quantum system.By adjusting the intensity of local microwave field,the effective coherence time of quantum system and the number of particles involved in measurement can be manipulated to make quantum system operate at a linear operating point with maximum intrinsic gain,thereby fully taking advantage of quantum measurement.2.In this thesis,a complete theoretical model of atomic superhet method is established.The theoretical model includes an accurate model based on numerical solve for simulating and fitting experimental measurement results;it also includes an analytical approximate model to clarify the working principle of atomic superhet method.The analytical approximate model also gives measurement equation of atomic superhet method.The measurement equation shows linear response of atomic superhet method to microwave electric field.Its linear response coefficient can be controlled by local microwave field and has the maximum intrinsic gain allowed by a quantum system at optimal point.The measurement equation also shows that the measurement results of atomic superhet method include the frequency and phase information of target microwave field.3.In this thesis,a Rydberg laser system for atomic superhet measurement system is developed.In order to achieve ultra-sensitive and accurate measurement of microwave electric field,this thesis proposes and implements a frequency noise servo loop with 3.5 MHz large feedback bandwidth to suppress the frequency noise of laser.Based on this frequency servo loop,we have achieved a low-noise ultra-stable laser system limited only by the thermal noise of cavity material,has a linewidth of the order of 10 Hz,and a center frequency drift of less than 100 k Hz per day.In order to realize ultra-wideband measurement of microwave electric field,we use the modulation sideband of fiber phase modulator as the locking target of frequency servo loop,and realize a 1.5 GHz mode-hop-free continuous scanning range of laser main frequency.This low-noise ultra-stable Rydberg laser system can also realize an excitation of arbitrary cesium Rydberg state with principle quantum number greater than30.4.In this thesis,an atomic superhet measurement system is built,and has completed experimental research on atomic superhet methods,which validates expected results given by theoretical model.Studies have shown that,benefit from the low noise characteristics of laser system,we have achieved a sensitivity of 5.5 V ? m-1? Hz-1/2,which is three orders of magnitude better than the best results of traceable atomic electrometer in the world[Nature Physics 8,819(2012)].Its smallest measurable electric field strength is better than traceable atomic electrometer more than four orders of magnitude.Its linear dynamic range can reach 90 d B,which is better than the atomic electrometer by about 60 d B.Compared with atomic electrometer,atomic superhet can realize the measurement of the frequency and phase of signal microwave field,with a frequency resolution of m Hz.Based on low noise ultra-stable laser system and the SI traceable property of atomic superhet method,we achieve a microwave electric field measurement uncertainty less than 5%.Benefit from the large mode-hop-free continuous scanning range and the property of achieving any Rydberg state excitation of the Rydberg laser system,the atomic superhet implemented in this paper has a microwave measurement bandwidth greater than 30 GHz,which is far beyond than traditional microwave measurement system. |
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