CN105092541A - Device for measuring inhomogeneous broadening at highest energy level during cascade radiation - Google Patents

Abstract

The invention discloses a device for measuring the non-uniform broadening of the uppermost energy level in the cascade radiation process. The device comprises: a Franson type interferometer system and a feedback control system; photon pairs emitted by the cascade radiation process pass through the Franson type interferometer , to detect their two-photon correlation signals, so as to obtain the interference fringes of the Franson interferometer system, by changing the arm length difference of the Franson type interferometer system, read the size of the fanson interference visibility in various cases, so as to obtain the highest energy level non-uniformity In the case of widening; the feedback control system is used to calculate the change of the phase difference of the Franson type interferometer system, so as to maintain the relative stability of the Franson type interferometer system. By adopting the device disclosed by the invention, the non-uniform broadening of the uppermost energy level of cascade radiation can be directly measured, thereby expanding the scope of energy level research.

Description

A device for measuring the non-uniform broadening of the uppermost energy level in the cascade radiation process

technical field

The invention relates to the field of atomic molecule and condensed matter science, in particular to a device for measuring the non-uniform broadening of the uppermost energy level in the cascade radiation process.

Background technique

In many scientific research fields, the non-uniform broadening of the energy level reflects the influence of the material substance by the physical environment in which it is located, and is one of the important physical properties of the material. For the luminous energy level of a single particle, this non-uniform broadening is manifested as some changes in the energy of the emitted photons at different times. Especially in quantum dots, the non-uniform broadening of the energy levels of excitons and biexcitons will affect the entanglement properties of the entangled photon pairs emitted by it.

In the prior art, there are roughly the following methods that can directly measure the non-uniform broadening of energy levels:

1) The method of directly comparing the spectra. This method generally uses a continuous laser as the excitation light source. When the sample is continuously excited, the luminescence spectrum of the energy level is directly measured at different times, and a series of spectra obtained are compared together, and the position of the emission spectrum line is obtained. As a result of the time change, the non-uniform broadening of the energy level can be obtained. The measurement method of the spectrum is basically to use a grating spectrometer to split the light and detect the intensity of the fluorescence emitted by the substance at each wavelength. However, due to the color resolution capability of the grating and the size limitation of the detection device, it is difficult to obtain sufficient resolution when measuring the energy level of a single particle with a linear spectrum. If a FP cavity with high precision is used to scan, the obtained spectrum is not emitted at the same time, and a single particle energy level emits a single photon, and it takes a certain amount of time to count when it is detected as a wavelength, so that it cannot be accurately obtained The intrinsic linewidth of the spectral line cannot accurately explain the size of the non-uniform broadening.

2) Spectral segmentation correlation. Specifically, this method uses a spectroscopic system, such as an FP cavity, to filter out different parts from the fluorescence spectrum for time-correlated analysis. Since the time-correlated analyzer can achieve a time resolution of tens of ps, this method The non-uniform broadening of the energy level spectrum caused by environmental disturbances in sub-nanosecond time can be observed.

The above two methods are limited in the study of the uppermost energy level broadening of cascade radiation because they involve direct detection of the actual spectrum of energy level luminescence. Because the spectral broadening of the first photon emitted by the cascade radiation process is the sum of the broadening of the uppermost energy level and the middle energy level, the influence of the middle energy level broadening cannot be removed only from the spectrum, so the non-uniform broadening of the uppermost energy level cannot be directly obtained .

Contents of the invention

The object of the invention is to provide a device for measuring the non-uniform broadening of the uppermost energy level in the cascade radiation process, which expands the scope of energy level research.

The purpose of the present invention is achieved through the following technical solutions:

A device for measuring the non-uniform broadening of the uppermost energy level in the cascade radiation process, the device includes: a Franson type interferometer system and a feedback control system;

The photon pairs emitted by the cascade radiation process pass through the Franson-type interferometer system, and the two-photon correlation signal of the photon pair is detected by the Franson-type interferometer system, thereby obtaining the interference fringes of the Franson interferometer system, by changing the Franson-type interferometer The arm length difference of the system can read the fanson interference visibility in various situations, so as to obtain the situation of non-uniform broadening of the upper energy level;

The feedback control system is used to calculate the change of the phase difference of the Franson type interferometer system, so as to maintain the relative stability of the Franson type interferometer system.

Further, the Franson-type interferometer system includes: polarizers, first and second half-wave plates, first and second polarizing beam splitters, first and second quarter-wave plates, first and second Two total reflection mirrors, first and second phase plates, first and second single photon detectors, and a time-correlated analyzer; wherein:

The cascaded radiation photon pairs injected into the Franson-type interferometer are separated in parallel in space, and after passing through the polarizer and the first half-wave plate, they are divided into two beams by the first polarizing beam splitter; the reflected light passes through The first quarter-wave plate enters the first total reflection mirror, is reflected by the first total reflection mirror, returns to the first polarization beam splitter in the same way, and is transmitted to the second half-wave through the first polarization beam splitter The transmitted light passes through the second quarter-wave plate, then passes through the first phase plate and the second phase plate respectively and enters the second total reflection mirror, and is reflected by the second total reflection mirror and then returns by the original path To the first polarizing beam splitter, reflected to the second half-wave plate through the first polarizing beam splitter;

The two beams of light transmitted through the first polarizing beam splitter and reflected to the second half-wave plate are combined together, and then received by the first and second single photon detectors after passing through the second polarizing beam splitter;

After receiving and detecting by the first and second single-photon detectors, corresponding single-photon pulse signals are generated and input to a time-correlation analyzer, and after being analyzed by the time-correlation analyzer, interference fringes of the Franson interferometer system are obtained.

Further, the Franson type interferometer system also includes: a translation stage;

The second total reflection mirror is fixed on the translation platform, and the arm length difference of the Franson interferometer system can be changed by adjusting the translation platform.

Further, the feedback control system includes: a semiconductor continuous laser, a third and a fourth single photon detector, a feedback circuit and a precision translation stage; wherein:

The semiconductor continuous laser emits a continuous laser whose coherence length is much greater than the arm length difference of the Franson type interferometer system. After attenuation, it is spatially separated from the photon pairs in the cascade radiation process and is incident on the second polarization beam splitter;

A part of the light is reflected by the second polarization beam splitter to the third detector, received and detected by the third detector, and the generated photoelectric signal is input to the feedback loop as a reference laser;

The other part of the light is transmitted to the second half-wave plate by the second polarizing beam splitter and then enters the first polarizing beam splitter, and is divided into two beams by the first polarizing beam splitter; the reflected light passes through the second quarter wave plate After one wave plate, it passes through the first phase plate and the second phase plate respectively and enters the second total reflection mirror, and is reflected by the second total reflection mirror and returns to the first polarization beam splitter according to the original path, and passes through the first polarization beam splitter. The beam splitter is transmitted to the first half-wave plate; the transmitted light enters the first total reflection mirror through the first quarter-wave plate, and is reflected by the first total reflection mirror and returns to the first polarization splitter according to the original path. The beam device is reflected to the first half-wave plate through the first polarizing beam splitter;

The two beams of light transmitted by the first polarizing beam splitter and reflected to the first half-wave plate are combined together, and then detected by the fourth detector after passing through the polarizing plate to form a photoelectric signal and input to the feedback loop;

The feedback loop analyzes and processes the photoelectric signals input by the third detector and the fourth detector, obtains the change of interference intensity, and feeds back the result to the precision translation stage;

The precision translation stage is adjusted according to the received results to drive the translation of the first total reflection mirror placed on it, so as to maintain the relative stability of the Franson interferometer system and keep the interference intensity stable.

It can be seen from the above-mentioned technical solution provided by the present invention that when measuring the non-uniform broadening of the uppermost energy level of the cascade radiation process, the spectrum of the emitted photon is not involved, and only the uppermost energy level broadening determines the visibility of the two-photon Franson interference, so it can be The inhomogeneous broadening of the uppermost energy level of the cascade radiation is directly measured, thereby expanding the scope of energy level research.

Description of drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the accompanying drawings that need to be used in the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For Those of ordinary skill in the art can also obtain other drawings based on these drawings on the premise of not paying creative work.

Figure 1 is a schematic structural diagram of a device for measuring the non-uniform broadening of the uppermost energy level in the cascade radiation process provided by Embodiment 1 of the present invention;

FIG. 2 is a schematic diagram of a fluorescent spectrum of a cascaded radiated photon pair provided in Embodiment 2 of the present invention;

3 is a schematic diagram of a measurement of a cascaded radiation photon pair cross-correlation function provided by Embodiment 3 of the present invention;

4 is a schematic diagram of the interference phenomenon of cascaded radiation photons on the Franson interferometer system provided by Embodiment 3 of the present invention;

5 is a schematic diagram of the relationship between the interference intensity of the cascaded radiation photons to the Franson interferometer system and the phase of the optical path provided by Embodiment 3 of the present invention;

FIG. 6 is a schematic diagram of the relationship between the interference visibility of the cascaded radiation photons to the Franson interferometer system and the difference in the arm length of the interferometer provided by Embodiment 3 of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Embodiment one

An embodiment of the present invention provides a device for measuring the non-uniform broadening of the uppermost energy level in the cascade radiation process, which mainly includes: a Franson type interferometer system and a feedback control system;

The photon pairs emitted by the cascade radiation process pass through the Franson-type interferometer system, and the two-photon correlation signal of the photon pair is detected by the Franson-type interferometer system, thereby obtaining the interference fringes of the Franson interferometer system, by changing the Franson-type interferometer The arm length difference of the system can read the fanson interference visibility in various situations, so as to obtain the situation of non-uniform broadening of the upper energy level;

The feedback control system is used to calculate the change of the phase difference of the Franson type interferometer system, so as to maintain the relative stability of the Franson type interferometer system.

As shown in FIG. 1 , it is a schematic structural diagram of the above-mentioned device. in:

1. The Franson type interferometer system includes: polarizer 1101, first and second half-wave plates (1102, 1109), first and second polarizing beam splitters (1103, 1110), first and second quarter-wave plates A wave plate (1104, 1111), first and second total reflection mirrors (1105, 1112), first and second phase plates (1106, 1113), first and second single photon detectors (1107, 1114) , and time correlation analyzer 1115; wherein:

The cascaded radiation photon pairs injected into the Franson-type interferometer are spatially separated in parallel, and then enter the polarizer 1101 to become linearly polarized light; the linearly polarized light passes through the first half-wave plate 1102 to change the polarization direction is 45 degrees, and then enters the first polarization beam splitter 1103, and is divided into two beams according to horizontal polarization and vertical polarization through the first polarization beam splitter 1103;

The reflected light (vertically polarized light) passes through the first quarter-wave plate 1104, transforms the polarization into circularly polarized light, and is reflected back along the original path by the first total reflection mirror 1105 placed on the precision translation stage 125 , passes through the first quarter-wave plate 1104 again, becomes horizontally polarized light, and transmits to the second half-wave plate through the first polarizing beam splitter 1103; wherein the transmitted light (horizontally polarized light) passes through the second quarter-wave plate A wave plate 1111 converts the polarization into circularly polarized light, and then passes through the first phase plate 1106 and the second phase plate 1113 to generate additional phases, and is placed on the translation stage 1108 along the original path by the second total reflection mirror 1112 Reflected back, pass through the second quarter-wave plate 1111 again, become vertically polarized light, and reflect to the second half-wave plate through the first polarizing beam splitter 1103;

The two beams transmitted through the first polarizing beam splitter 1103 and reflected to the second half-wave plate are combined together, pass through the second half-wave plate 1109, become polarized at plus or minus 45 degrees, and then pass through the second polarizing beam splitter respectively Received by the first and second single photon detectors

After receiving and detecting by the first and second single-photon detectors, corresponding single-photon pulse signals are generated and input to the time-correlation analyzer 1115, and after being analyzed by the time-correlation analyzer 1115, the interference fringes of the Franson interferometer system are obtained.

Specifically, after analysis by the time-correlation analyzer 1115, the correlation signal obtained by the first photon of the cascade radiation passing through the long arm of the interferometer and the second photon passing through the short arm of the interferometer, and the first photon of the cascade radiation passing through the interferometer The long arm and the associated signal obtained by the second photon passing through the short arm of the interferometer, and the associated signal with the interference effect obtained by the two photons of the cascaded radiation passing through the long arm of the interferometer or both passing through the short arm; and the The associated signal strength with interference effects varies as the first and second phase plates are adjusted.

Wherein, in the light beams combined into one path through the first polarization beam splitter 1103, the photons can be in two positions, one in front and one in the back, wherein the front position is the result of photons passing through the short arm of the interferometer, and the back position The position is the result of the photon passing through the long arm of the interferometer. As shown in Figure 1, the second total reflection mirror 1112 is placed on the translation platform 1108, so the short arm and the long arm of the interferometer are not fixed, and can be changed by adjusting the translation platform 1108; The distance difference is much larger than the range that the translation stage 1108 can move.

In the above-mentioned Franson interferometer system, the difference in arm length of the Franson interferometer system can be changed by adjusting the translation stage 1108 .

2. The feedback control system mainly includes: semiconductor continuous laser 121, third and fourth single photon detectors (122, 123), feedback circuit 124 and precision translation stage 125; wherein:

The semiconductor continuous laser 121 emits a continuous laser whose coherence length is much greater than the arm length difference of the Franson type interferometer system. After attenuation, it is spatially separated from the photon pairs in the cascade radiation process and is incident on the second polarization beam splitter. 1110;

Part of the light is reflected by the second polarization beam splitter to the third detector 122, received and detected by the third detector 122, and the generated photoelectric signal is input to the feedback loop 124 as a reference laser;

The other part of the light is transmitted to the second half-wave plate 1109 by the second polarization beam splitter 1110, and is rotated to 45-degree polarization by the second half-wave plate; then enters the first polarization beam splitter 1103, passes through the first polarization beam splitter 1103 is divided into two beams according to horizontal polarization and vertical polarization;

Wherein the reflected light (vertically polarized light) passes through the second quarter-wave plate 1111 and becomes circularly polarized light, then passes through the first phase plate 1106 and the second phase plate 1113 respectively to generate an additional phase, and enters the second phase plate 1111 Two total reflection mirrors 1112, and are reflected back along the original path by the second total reflection mirror 1112, become horizontally polarized through the second quarter-wave plate 1111 again, and are transmitted to the first half-wave through the first polarization beam splitter 1103 plate 1102; the transmitted light (horizontally polarized light) in it becomes circularly polarized light through the first quarter-wave plate 1104, and enters the first total reflection mirror 1105, and is reflected by the first total reflection mirror 1105 along the original path Come back, pass through the first quarter-wave plate 1104 again to become vertically polarized, and reflect to the first half-wave plate 1102 through the first polarization beam splitter 1103;

The two beams of light transmitted through the first polarizing beam splitter 1103 and reflected to the first half-wave plate 1102 are combined together, pass through the first half-wave plate 1102, become polarized at plus or minus 45 degrees, and then form interference through the polarizing plate 1101 to be The fourth detector 123 accepts detection, forms a photoelectric signal, and inputs it to the feedback loop 124;

The feedback loop 124 analyzes and processes the photoelectric signals input by the third detector 122 and the fourth detector 123, obtains the change of the interference intensity, and feeds back the result to the precision translation stage 125;

The precision translation stage 125 performs translation adjustment according to the received results to drive the translation of the first total reflection mirror 1105 placed on it, so as to maintain the relative stability of the Franson interferometer system and keep the interference intensity stable.

In the embodiment of the present invention, the feedback loop 124 is based on the tiny difference between the interference intensity of the reference laser (that is, the output signal of the third detector 122 ) relative to the intermediate value of the interference maximum and minimum (that is, the output signal of the fourth detector 123 ). Change, calculate the change of the phase difference of the interferometer, and convert it into the change of the optical path difference, and feed it back to the precision translation stage 125 to change its position by a corresponding distance, keeping the interference intensity still in the middle of the maximum value and the minimum value.

In order to obtain the Franson-type interference visibility of the cascaded radiation photon pair, under the condition of maintaining a certain arm length difference, the phase plate 1106 and 1113 can be rotated to obtain the change of the Franson-type interference intensity, and the maximum and minimum values can be searched to obtain the interference visibility . Further, under the condition of ensuring that the arm length difference of the interferometer is much greater than the radiation lifetime of the intermediate energy level, changing the arm length difference of the interferometer can obtain the visibility of Franson type interference at different positions, and the change of visibility with the arm length difference is fitted by the e exponential function, The fitting parameter is the broadening of the uppermost energy level of the cascade radiation.

In the above scheme of the embodiment of the present invention, a stable unequal arm interferometer is used to perform Franson interference on the photon pairs emitted by the cascade radiation process, and the interference visibility can be obtained under the condition of different arm length differences, and then the highest level of the cascade radiation can be obtained. Broadening of energy levels. This above-mentioned procedure allows the direct detection of cascade radiative uppermost energy level broadening without the influence of intermediate energy levels.

Embodiment two

In order to further introduce the present invention, the embodiment of the present invention cites specific numerical values to introduce the component parameters in the device; it should be noted that the numerical values of the exemplified component parameters are only for the convenience of understanding the present invention, and do not constitute limitations; In the application, users can use components with different parameters according to their needs or experience.

In the example of the present invention, the spectrum of the cascaded radiation photon pair is shown in FIG. 2 . The reference laser wavelength is 920nm, the line width is 1MHz, and the coherence length is 300m.

In the embodiment of the present invention, after the cascaded radiation photon pairs are collected, the diameter of the outgoing spot is 2 mm, and the spatial parallel separation distance is 5 mm. The first and second polarizing beam splitters are coated with 700-1100 nanometer anti-reflection coatings, and are in the shape of a cube with a side length of 20 mm.

In the embodiment of the present invention, after the cascaded radiation photon pairs are collected, the diameter of the outgoing spot is 2 mm, and the spatial parallel separation distance is 5 mm. The first and second polarizing beam splitters are coated with 700-1100 nanometer anti-reflection coatings, and are in the shape of a cube with a side length of 20 mm.

In the embodiment of the present invention, the first and second total reflection mirrors are silver-coated total reflection mirrors, and the size is a circular substrate of 25.4 mm.

In the embodiment of the present invention, the precision translation stage 125 is a PI nanoscale piezoelectric ceramic translation stage with a stroke of 100 microns and an accuracy of 0.1 nanometers.

In the embodiment of the present invention, the first and second phase plates 1106 and 1113 are 0.2mm thick glass plates with a size of 5mm*3mm, coated with a 920nm anti-reflection film.

In the embodiment of the present invention, the feedback system is based on the data acquisition card of NI, and LabVIEW software control, and the feedback speed is 50 milliseconds.

In the embodiment of the present invention, the single photon detector is an avalanche photodiode APD, and the dark count is 100 per second. The average intensity of the photon signal is 2000 per second.

In the embodiment of the present invention, the model of the time correlation analyzer is ID800, and the time resolution is 81 ps.

Embodiment three

The embodiment of the present invention measures and compares the uniform broadening and total broadening of the uppermost energy level of the cascaded radiation.

For the uniform broadening of the energy level, it is only related to the radiation lifetime of the emitted photon, so the photon cross-correlation function of the cascaded radiation can be used for analysis, and the single-photon signal generated by the photon pair of the cascaded radiation can be directly input into the time analyzer to obtain the result As shown in Figure 3, its curve is described by the following differential equations:

$\frac{{\mathrm{<span\; class="notranslate">\; dn</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}}}{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}}}{{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}{{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}$

$\frac{{\mathrm{<span\; class="notranslate">\; dn</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}}}{{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; x</span>}}}{{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; x</span>}}}<span\; class="notranslate">\; ;</span>$

$\frac{{\mathrm{<span\; class="notranslate">\; dn</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; x</span>}}}{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}}}{{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; x</span>}}}{{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; x</span>}}}$

Among them, n _G , n _X , n _XX are the population numbers of the three energy levels of the cascade radiation, τ _X , τ _XX are the radiation lifetimes of the uppermost energy level and the middle energy level, τ _e is the parameter of the excitation intensity, and the fitting The result of the curve is that the radiation lifetime of the uppermost energy level is 1.1 ns, and the radiation lifetime of the middle energy level is 1.3 ns. From this, it can be obtained that the uniform broadening of the uppermost energy level is 1/1.1 ns-1/1.3 ns=0.14 GHz.

The total broadening of the uppermost energy level of the cascade radiation is obtained from the Franson interferometric visibility. Fixing an arm length difference and detecting the coincidence of photon pairs at the output end of the interferometer, three peaks will appear in time, as shown in Figure 4. The first peak corresponds to the signal obtained when the first photon passes through the long arm and the second photon passes through the short arm; the third peak corresponds to the signal obtained when the first photon passes through the short arm and the second photon passes through the long arm Signal; the peak in the middle is the result of Franson interference when both photons pass through the short arm or both pass through the long arm. By changing the phase difference between the long and short arms of the interferometer through the phase plate, you can see the change in the size of the interference signal. The interference intensity obtained at different phase differences is fitted with a sine function, as shown in Figure 5, and the delay at the arm length is 7ns. Under the condition of , the interference visibility is 0.35.

Further, the arm length difference between the long and short arms of the interferometer is gradually changed, and the Franson-type interference detection of two-photon pairs is repeated to obtain the visibility corresponding to different arm length differences. The change of visibility with the arm length difference can be expressed as follows:

$\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}}}<span\; class="notranslate">\; \&Proportional;</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; \&Lambda;b</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}<span\; class="notranslate">\; ;</span>$

Among them, R _max and R _min are the maximum and minimum values of interference intensity, ΔT is the time difference required for photons to pass through the long path and short circuit, that is, the difference in arm length divided by the speed of light, Λb' is the broadening of the uppermost energy level of the cascade radiation, fitting The experimental results are shown in Figure 6, the dotted line is the fitting curve, and the actual broadening of the uppermost energy level can be obtained to be 0.154GHz.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person familiar with the technical field can easily conceive of changes or changes within the technical scope disclosed in the present invention. Replacement should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (4)

1. A device for measuring the non-uniform broadening of the uppermost energy level in the cascade radiation process, characterized in that the device comprises: a Franson type interferometer system and a feedback control system; The photon pairs emitted by the cascade radiation process pass through the Franson-type interferometer system, and the two-photon correlation signal of the photon pair is detected by the Franson-type interferometer system, thereby obtaining the interference fringes of the Franson interferometer system, by changing the Franson-type interferometer The arm length difference of the system can read the fanson interference visibility in various situations, so as to obtain the situation of non-uniform broadening of the upper energy level; The feedback control system is used to calculate the change of the phase difference of the Franson type interferometer system, so as to maintain the relative stability of the Franson type interferometer system. 2. The device according to claim 1, wherein the Franson-type interferometer system comprises: polarizers, first and second half-wave plates, first and second polarization beam splitters, first and second Two quarter-wave plates, first and second total reflection mirrors, first and second phase plates, first and second single-photon detectors, and a time-correlated analyzer; wherein: The cascaded radiation photon pairs injected into the Franson-type interferometer are separated in parallel in space, and after passing through the polarizer and the first half-wave plate, they are divided into two beams by the first polarizing beam splitter; the reflected light passes through The first quarter-wave plate enters the first total reflection mirror, is reflected by the first total reflection mirror, returns to the first polarization beam splitter in the same way, and is transmitted to the second half-wave through the first polarization beam splitter The transmitted light passes through the second quarter-wave plate, then passes through the first phase plate and the second phase plate respectively and enters the second total reflection mirror, and is reflected by the second total reflection mirror and then returns by the original path To the first polarizing beam splitter, reflected to the second half-wave plate through the first polarizing beam splitter; The two beams of light transmitted through the first polarizing beam splitter and reflected to the second half-wave plate are combined together, and then received by the first and second single photon detectors after passing through the second polarizing beam splitter; After receiving and detecting by the first and second single-photon detectors, corresponding single-photon pulse signals are generated and input to a time-correlation analyzer, and after being analyzed by the time-correlation analyzer, interference fringes of the Franson interferometer system are obtained. 3. The device according to claim 2, wherein the Franson type interferometer system further comprises: a translation stage; The second total reflection mirror is fixed on the translation platform, and the arm length difference of the Franson interferometer system can be changed by adjusting the translation platform. 4. The device according to claim 2, wherein the feedback control system comprises: a semiconductor continuous laser, a third and a fourth single photon detector, a feedback circuit and a precision translation stage; wherein: The semiconductor continuous laser emits a continuous laser whose coherence length is much greater than the arm length difference of the Franson type interferometer system. After attenuation, it is spatially separated from the photon pairs in the cascade radiation process and is incident on the second polarization beam splitter; A part of the light is reflected by the second polarization beam splitter to the third detector, received and detected by the third detector, and the generated photoelectric signal is input to the feedback loop as a reference laser; The other part of the light is transmitted to the second half-wave plate by the second polarizing beam splitter and then enters the first polarizing beam splitter, and is divided into two beams by the first polarizing beam splitter; the reflected light passes through the second quarter wave plate After one wave plate, it passes through the first phase plate and the second phase plate respectively and enters the second total reflection mirror, and is reflected by the second total reflection mirror and returns to the first polarization beam splitter according to the original path, and passes through the first polarization beam splitter. The beam splitter is transmitted to the first half-wave plate; the transmitted light enters the first total reflection mirror through the first quarter-wave plate, and is reflected by the first total reflection mirror and returns to the first polarization splitter according to the original path. The beam device is reflected to the first half-wave plate through the first polarizing beam splitter; The two beams of light transmitted by the first polarizing beam splitter and reflected to the first half-wave plate are combined together, and then detected by the fourth detector after passing through the polarizing plate to form a photoelectric signal and input to the feedback loop; The feedback loop analyzes and processes the photoelectric signals input by the third detector and the fourth detector, obtains the change of interference intensity, and feeds back the result to the precision translation stage; The precision translation stage is adjusted according to the received results to drive the translation of the first total reflection mirror placed on it, so as to maintain the relative stability of the Franson interferometer system and keep the interference intensity stable.