Device and method for enhancing intensity difference compression characteristic of output light field of non-phase sensitive amplifier

Abstract

The invention discloses a device and method for enhancing the intensity difference compression characteristic of an output light field of a non-phase-sensitive amplifier, and belongs to the technical field of quantum information. The device comprises a non-phase-sensitive amplifier, a feedback light path and a measurement and control circuit, the non-phase-sensitive amplifier is connected with the feedback light path and the measurement and control circuit, and the feedback light path is further connected with the measurement and control circuit; the non-phase-sensitive amplifier is used for outputting a probe light field and a conjugate light field, and the output probe light field and conjugate light field are fed back to a probe light field input end and a conjugate light field input end of the non-phase-sensitive amplifier through corresponding feedback light paths respectively; and the measurement and control circuit is used for measuring the intensity difference compression characteristics of the probe light field and the conjugate light field and realizing phase locking of the feedback light path. According to the invention, the output light field intensity difference compression characteristic of the non-phase-sensitive amplifier is enhanced, and the cost and power requirements are reduced.

Description

Technical Field

[0001] The present invention belongs to the field of quantum information technology, and in particular, relates to a device and method for enhancing the output light field intensity difference compression characteristic of a non-phase sensitive amplifier. Background Art

[0002] The intensity difference squeezed state light field is a special non-classical light field, which is not only of great significance for the basic scientific research of quantum physics, but also has important application potential in the field of quantum information technology. The non-phase-sensitive amplifier based on atomic vapor four-wave mixing is an ideal device for generating intensity difference squeezed state light fields. Using the intensity difference squeezed state light field prepared by the non-phase-sensitive amplifier, the application of this quantum light field in quantum communication and precision measurement has been demonstrated experimentally, including tunable delay of EPR entangled state, enhanced sensitivity of magnetometer and entanglement exchange. The fidelity of information transmission in quantum communication and the improvement of sensitivity in precision measurement both depend on the strength of the intensity difference squeezed characteristics of the quantum light field. Therefore, it is of great significance to improve the quantum properties of the output light field of the non-phase-sensitive amplifier.

[0003] Conventional methods to enhance the intensity difference compression characteristics of the output light field of a non-phase-sensitive amplifier require reducing the optical loss of the system and increasing the pump light power. To reduce the loss of the system, it is necessary to customize atomic vapor chambers and optical lenses with high optical quality and high-quality coatings, which is costly. By enhancing the pump power of the non-phase-sensitive amplifier, the intensity gain of the four-wave mixing increases, and theoretically the intensity difference compression characteristics will be enhanced. However, under high intensity gain, other nonlinear processes such as spontaneous radiation, Raman absorption, and optical self-focusing will be enhanced, which in turn will limit the improvement of the compressed state. Summary of the invention

[0004] The present invention aims to overcome the deficiencies of the prior art and proposes a device and method for enhancing the output light field intensity difference compression characteristics of a non-phase-sensitive amplifier, so as to achieve the purpose of enhancing the output light field intensity difference compression characteristics of the non-phase-sensitive amplifier while reducing costs and power requirements.

[0005] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a device for enhancing the intensity difference compression characteristics of the output light field of a non-phase-sensitive amplifier, the device comprising a non-phase-sensitive amplifier, a feedback optical path, and a measurement and control circuit, wherein the non-phase-sensitive amplifier is respectively connected to the feedback optical path and the measurement and control circuit, and the feedback optical path is also connected to the measurement and control circuit; the non-phase-sensitive amplifier is used to output a probe light field and a conjugate light field, and the output probe light field and conjugate light field are respectively fed back to the probe light field input terminal and the conjugate light field input terminal of the non-phase-sensitive amplifier through the corresponding feedback optical path, and the measurement and control circuit is used to measure the intensity difference compression characteristics of the probe light field and the conjugate light field and realize the phase locking of the feedback optical path.

[0006] Preferably, the non-phase-sensitive amplifier comprises a laser, a half-wave plate, a polarization beam splitter prism, a reflector, an acousto-optic modulator, a Glan laser prism, a rubidium atomic vapor cell, a Glan-Thompson prism, and a beam terminator; wherein the laser light output by the laser 1 passes through the half-wave plate 2 and the polarization beam splitter prism 3 in sequence and is divided into two beams of vertical polarization and horizontal polarization; the vertically polarized light passes through the reflector 4, the reflector 13, and the Glan laser prism 12 in sequence and then passes through the rubidium atomic vapor cell 14 as a pump light for four-wave mixing; the pump light passing through the rubidium atomic vapor cell 14 is then reflected by the Glan-Thompson prism 15 and then output to the beam terminator 26; the horizontally polarized light passes through the acousto-optic frequency shifter 5 and then passes through the reflector 7 and the reflector 8 in sequence; After being reflected by the projection mirror 6, the light passes through the Glan laser prism 12. The light exit end of the Glan laser prism 12 serves as the probe light field input end of the non-phase-sensitive amplifier. The input probe light field crosses with the pump light and passes through the rubidium atomic vapor pool 14. The rubidium atomic vapor pool 14 amplifies the probe light field under the nonlinear interaction of four-wave mixing and generates a conjugate light field on the other side relative to the pump light. Correspondingly, the probe light field input end serves as the conjugate light field input end of the non-phase-sensitive amplifier on the other side relative to the pump light. The probe light field that passes through the rubidium atomic vapor pool 14 and the newly generated conjugate light field serve as the probe light field output end and the conjugate light field output end of the non-phase-sensitive amplifier respectively after passing through the Glan-Thompson prism 15.

[0007] Preferably, the feedback optical path includes a beam splitter, a reflector, and a reflector with piezoelectric ceramics. For the probe light field and the conjugate light field output by the two paths of the non-phase-sensitive amplifier, the feedback optical path is correspondingly provided with two paths, one path is used to feed back the probe light field to the probe light field input end, that is, the probe light field output by the non-phase-sensitive amplifier passes through the beam splitter 16 and then passes through the reflector 17, the piezoelectric ceramic reflector 9, the beam splitter 8 in sequence and passes through the Glan laser prism 12 before being fed back to the probe light field input end by the original path; the other path is used to feed back the conjugate light field to the conjugate light field input end, that is, the conjugate light field output by the non-phase-sensitive amplifier passes through the beam splitter 18 and then passes through the reflector 19, the piezoelectric ceramic reflector 11, the reflector 10 in sequence and passes through the Glan laser prism 12 before being fed back to the conjugate light field input end by the original path.

[0008] Preferably, the measurement and control circuit includes a microcontroller and a light field intensity difference compression measurement system, wherein: the light field intensity difference compression measurement system includes the photodetector, the subtractor, and the spectrum analyzer, wherein the photodetector 20 is respectively connected to the conjugate light field output end of the non-phase-sensitive amplifier and the subtractor 24, the micro-photodetector 21 is respectively connected to the probe light field output end of the non-phase-sensitive amplifier and the subtractor 24, and the subtractor 24 is connected to the spectrum analyzer 25; the microcontroller 22 is respectively connected to the reflector 9 with piezoelectric ceramics and the photodetector 20; the microcontroller 23 is respectively connected to the reflector 11 with piezoelectric ceramics and the photodetector 21.

[0009] Preferably, the device also includes a power meter and a 50:50 beam splitter. The power meter is respectively connected to the probe light field output end and the conjugate light field output end of the non-phase-sensitive amplifier, and is used to measure the total power of the probe light field and the conjugate light field output by the non-phase-sensitive amplifier; the 50:50 beam splitter is connected to the laser, and is used to split the output laser of the laser.

[0010] At the same time, the present application also proposes a method for enhancing the compression characteristics of the output light field intensity difference of a non-phase-sensitive amplifier, the method is applied to the device for enhancing the compression characteristics of the output light field intensity difference of a non-phase-sensitive amplifier according to the above, and the method comprises the following steps:

[0011] S1, control the laser to output two strong and weak laser beams, the weak beam is frequency-shifted by the acousto-optic frequency shifter as the probe light field input, and the strong beam is used as the pump light. The two lights cross through the rubidium vapor cell to construct a non-phase-sensitive amplifier, which outputs the probe light field and the conjugate light field;

[0012] S2, sending the probe light field and the conjugate light field output by the non-phase-sensitive amplifier into a measurement and control circuit to measure the light field intensity difference compression degree;

[0013] S3, optimizing the physical parameters of the non-phase-sensitive amplifier to obtain the optimal intensity difference squeezed state light field output, and making the non-phase-sensitive amplifier work under the corresponding physical parameters;

[0014] S4, constructing a feedback optical path to feed back the probe light field and the conjugate light field output by the non-phase-sensitive amplifier to the input end of the non-phase-sensitive amplifier;

[0015] S5, using a microcontroller to lock the light field phase of the feedback light path;

[0016] S6. Optimize the reflectivity of the optical beam splitter used for feedback to obtain an intensity difference compressed state light field output with enhanced compression.

[0017] Preferably, in step S2, a power meter is used to measure the sum of the intensities of the probe light field and the conjugate light field output by the non-phase-sensitive amplifier; before four-wave mixing occurs, the laser 1 is controlled to separate a laser from the output laser and its power is adjusted to be equal to the sum of the intensities of the probe light field and the conjugate light field, and the laser is then split by the 50:50 beam splitter and sent to the photodetector 20 and the photodetector 21 respectively. The current signals output by the photodetector 20 and the photodetector 21 are processed by the subtractor 24 and then connected to the spectrum analyzer 25 to record the current noise power spectrum before four-wave mixing occurs; after four-wave mixing occurs, the probe light field and the conjugate light field output by the non-phase-sensitive amplifier are respectively sent to the photodetector 20 and the photodetector 21, and the current noise power spectrum is also recorded. The difference between the current noise before and after four-wave mixing occurs is the intensity difference compression degree.

[0018] Preferably, in step S3, the physical parameters of the non-phase-sensitive amplifier are changed, the parameters including single-photon detuning, two-photon detuning, temperature of atomic vapor, pump light power, angle between pump light field and probe light field, intensity gain of four-wave mixing, and the corresponding intensity difference compression degree is recorded to screen out the optimal intensity difference compression state light field output.

[0019] Preferably, in step S5, the reflector of the feedback light path is coarsely adjusted to make the feedback light field coincide with the initial probe light field and the initial space of the conjugate light field; the piezoelectric ceramics on the piezoelectric ceramic reflectors 9 and 11 of the feedback light path are scanned, and at the same time, the DC signals of the photodetectors 20 and 21 are sent to the oscilloscope to observe the interference signal; the reflector of the feedback light path is fine-tuned to maximize the visibility of the interference signal; the DC signals of the photodetectors 20 and 21 are then sent to the microcontrollers 22 and 23 respectively, and the microcontroller performs analog-to-digital conversion, data analysis and calculation on the input signal, and finally outputs the signal after the digital-to-analog conversion to the piezoelectric ceramic to control the piezoelectric ceramic to achieve phase locking of the feedback light path, and lock the phase at the maximum interference point.

[0020] Preferably, in step S6, the optimal reflectivity value of the optical beam splitter in the feedback optical path is calculated according to the physical parameters of the non-phase-sensitive amplifier under the optimal intensity difference compression state light field output, and the reflectivity of the optical beam splitters 16 and 18 is adjusted with the optimal reflectivity value as a reference, and the corresponding output end intensity difference compression degree is recorded, and finally the optimal result of the light field intensity difference compression degree after introducing feedback is obtained, and compared with the result without introducing feedback, so as to evaluate the enhancement of the feedback optical path on the output light field intensity difference compression characteristics of the non-phase-sensitive amplifier.

[0021] The technical effects of the present invention are:

[0022] (1) The present application only needs to add a simple feedback optical path to the non-phase-sensitive amplifier based on four-wave mixing to achieve the enhancement of the light field intensity difference compression characteristics. Compared with the conventional solution of the cascaded four-wave mixing system, the cost is lower.

[0023] (2) The present application is well compatible with the current intensity difference compression generating device, and there is no need to modify the device. After evaluating the physical parameters of the device, it is only necessary to adjust the reflectivity of the beam splitter in the feedback light path to achieve adaptation with the device and achieve the effect of enhancing the quantum characteristics of the output light field.

[0024] (3) The present application can obtain, at low pump power, an intensity difference compressed state light field equivalent to the output of a non-phase-sensitive amplifier at high pump power, which has important practical significance in constructing a multi-component intensity-correlated light field and can significantly reduce the power requirement of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A structural diagram of a device for enhancing the compression characteristics of the output light field intensity difference of a non-phase-sensitive amplifier in an embodiment of the present invention;

[0026] Figure 2 2 is a simulation result diagram of intensity difference compression degree changing with the reflectivity of the beam splitter when the intensity gain G=2 in an embodiment of the present invention;

[0027] Figure 3 : is a simulation result diagram of the intensity difference compression degree changing with the intensity gain G in an embodiment of the present invention, Figure 3 The inset in the figure is the simulation result diagram of the optimal beam splitter reflectivity k changing with the intensity gain G;

[0028] The reference numerals are as follows: 1 represents a laser, 2 represents a half-wave plate, 3 represents a polarization beam splitter prism, 4, 6, 7, 10, 13, 17 and 19 all represent reflectors, 5 represents an acousto-optic frequency shifter, 8, 16 and 18 all represent optical beam splitters, 9 and 11 represent reflectors with piezoelectric ceramics, 12 represents a Glan laser prism, 14 represents a rubidium atomic vapor cell, 15 represents a Glan-Thompson prism, 20 and 21 represent photodetectors, 22 and 23 represent microcontrollers, 24 represents a subtractor, 25 represents a spectrum analyzer, and 26 represents a beam terminator. DETAILED DESCRIPTION

[0029] The following is a further detailed description of the specific implementation of the present invention through the description of the embodiments with reference to the accompanying drawings, with the purpose of helping those skilled in the art to have a more complete, accurate and in-depth understanding of the inventive concept and technical solution of the present invention, and to facilitate its implementation. It should be noted that the connection described in this application includes both the connection between the components in the optical path using light as the transmission medium and the connection of the circuit. In order to make the technical solution of the present invention clearer, the present invention is explained through the following embodiments.

[0030] This embodiment proposes a device for enhancing the intensity difference compression characteristics of the output light field of a non-phase-sensitive amplifier, the device comprising a non-phase-sensitive amplifier, a feedback optical path, and a measurement and control circuit, wherein the non-phase-sensitive amplifier is connected to the feedback optical path and the measurement and control circuit respectively, and the feedback optical path is also connected to the measurement and control circuit; the non-phase-sensitive amplifier is used to output a probe light field and a conjugate light field, and the output probe light field and conjugate light field are respectively fed back to the probe light field input terminal and the conjugate light field input terminal of the non-phase-sensitive amplifier through corresponding feedback optical paths, and the measurement and control circuit is used to measure the intensity difference compression characteristics of the probe light field and the conjugate light field and realize the phase locking of the feedback optical path. The following is combined with Figure 1 The device shown is described in detail.

[0031] The non-phase-sensitive amplifier of this embodiment includes a laser, a half-wave plate, a polarization beam splitter prism, a reflector, an acousto-optic modulator, a Glan laser prism, a rubidium atomic vapor cell, a Glan-Thompson prism, and a beam terminator. The laser light output by the laser 1 is sequentially divided into two beams of vertical polarization and horizontal polarization after passing through the half-wave plate 2 and the polarization beam splitter prism 3, and the vertical polarization light is sequentially reflected by the reflector 4, the reflector 13, and the Glan laser prism 12, and then passes through the rubidium atomic vapor cell 14 as a pump light of four-wave mixing, and the pump light passing through the rubidium atomic vapor cell 14 is reflected by the Glan-Thompson prism 15 and then output to the beam terminator 26. The horizontally polarized light is first frequency-shifted by the acousto-optic frequency shifter 5, and then reflected by the reflector 7 and the reflector 6 in sequence before passing through the Glan laser prism 12. The light output end of the Glan laser prism 12 serves as the probe light field input end of the non-phase-sensitive amplifier. The probe light field inputted from the input end crosses with the pump light and passes through the rubidium atomic vapor pool 14. The rubidium atomic vapor pool 14 amplifies the probe light field under the nonlinear interaction of four-wave mixing and generates a conjugate light field on the other side relative to the pump light. Correspondingly, due to the reversibility of light, the probe light field input end serves as the conjugate light field input end of the non-phase-sensitive amplifier on the other side relative to the pump light. The probe light field passing through the rubidium atomic vapor pool 14 and the newly generated conjugate light field serve as the probe light field output end and the conjugate light field output end of the non-phase-sensitive amplifier respectively after passing through the Glan-Thompson prism 15.

[0032] The feedback optical path of this embodiment includes an optical beam splitter, a reflector, and a reflector with piezoelectric ceramics. In response to the probe light field and the conjugate light field output by the two-way non-phase-sensitive amplifier, the feedback optical path of this embodiment is correspondingly set with two paths, one of which is used to feed back the probe light field to the probe light field input end, that is, the probe light field output by the non-phase-sensitive amplifier passes through the optical beam splitter 16 and then passes through the reflector 17, the piezoelectric ceramic reflector 9, the optical beam splitter 8 and passes through the Glan laser prism 12, and then is fed back to the probe light field input end by the original path; the other path is used to feed back the conjugate light field to the conjugate light field input end, that is, the conjugate light field output by the non-phase-sensitive amplifier passes through the optical beam splitter 18 and then passes through the reflector 19, the piezoelectric ceramic reflector 11, the reflector 10 and passes through the Glan laser prism 12, and then is fed back to the conjugate light field input end by the original path. The present application can realize the enhancement of the light field intensity difference compression characteristics by simply adding a feedback optical path to the non-phase-sensitive amplifier based on four-wave mixing, and has a lower cost than the conventional solution of the cascaded four-wave mixing system.

[0033] The measurement and control circuit of this embodiment includes a microcontroller and a light field intensity difference compression degree measurement system, wherein: the light field intensity difference compression degree measurement system includes the photodetector, subtractor, and spectrum analyzer. Specifically, the photodetector 20 is respectively connected to the conjugate light field output end of the non-phase sensitive amplifier and the subtractor 24, the micro photodetector 21 is respectively connected to the probe light field output end of the non-phase sensitive amplifier and the subtractor 24, and the subtractor 24 is connected to the spectrum analyzer 25; the microcontroller 22 is respectively connected to the reflector 9 with piezoelectric ceramics and the photodetector 20; the microcontroller 23 is respectively connected to the reflector 11 with piezoelectric ceramics and the photodetector 21.

[0034] The device of this embodiment also includes a power meter and a 50:50 beam splitter. The power meter is respectively connected to the probe light field output end and the conjugate light field output end of the non-phase-sensitive amplifier, and is used to measure the total power of the probe light field and the conjugate light field output by the non-phase-sensitive amplifier; the 50:50 beam splitter is connected to the laser, and is used to split the output laser of the laser.

[0035] According to the above transposition, the present application further proposes a method for enhancing the output light field intensity difference compression characteristics of a non-phase-sensitive amplifier, the method comprising the following steps:

[0036] S1. Control the laser to output two strong and weak laser beams. The weak beam is frequency-shifted by the acousto-optic frequency shifter as the probe light field input, and the strong beam is used as the pump light. The two lights cross through the rubidium vapor cell to construct a non-phase-sensitive amplifier. The non-phase-sensitive amplifier outputs the probe light field and the conjugate light field.

[0037] Specifically, the laser operates at 85 Near the D1 transition line of Rb atoms, 85The blue detuning of the D1 line of the Rb atom is 1 GHz; the laser output is divided into two beams after passing through the half-wave plate 2 and the polarization beam splitter prism 3, the vertically polarized beam power is about 200 mW, which is reflected by the reflector 4, the reflector 13, and the Glan laser prism 12 in sequence and then passes through the rubidium atomic vapor pool 14, serving as the pump light for four-wave mixing; the other horizontally polarized beam is frequency-shifted by 3.04 GHz by the acousto-optic frequency shifter 5 as the probe light field, with a power of about 20 μW, which is reflected by the reflector 7 and the reflector 6 in sequence and then passes through the Glan laser prism 12, crosses the pump light at a small angle and passes through the rubidium atomic vapor pool 14; the rubidium atomic vapor pool 14 is heated to about 120 degrees, and the four-wave mixing effect occurs. Under the nonlinear interaction of the four-wave mixing, the probe light is amplified, and a conjugate light of the probe light blue-shifted relative to the pump light is generated on the other side of the pump light.

[0038] S2. Sending the probe light field and the conjugate light field output by the non-phase-sensitive amplifier to a measurement and control circuit to measure the light field intensity difference compression degree.

[0039] Specifically, a power meter is used to measure the sum of the intensities of the probe light field and the conjugate light field output by the non-phase-sensitive amplifier; before four-wave mixing occurs, the laser 1 is controlled to separate a laser from the output laser and its power is adjusted to be equal to the sum of the intensities of the probe light field and the conjugate light field, the laser is then split by the 50:50 beam splitter and sent to the photodetector 20 and the photodetector 21 respectively, the current signals output by the photodetector 20 and the photodetector 21 are processed by the subtractor 24 and then connected to the spectrum analyzer 25 to record the current noise power spectrum before four-wave mixing occurs; after four-wave mixing occurs, the probe light field and the conjugate light field output by the non-phase-sensitive amplifier are respectively sent to the photodetector 20 and the photodetector 21, and the current noise power spectrum is also recorded, and the difference between the current noise before and after four-wave mixing occurs is the intensity difference compression degree.

[0040] Assume that the probe light field input to the input of the non-phase-sensitive amplifier based on four-wave mixing is The conjugate input end is a vacuum light field, denoted as The outputs of the probe light field output terminal and the conjugate light field output terminal of the non-phase-sensitive amplifier are and They can be expressed as:

[0041]

[0042] in, The superscript numeral represents Hermitian conjugation. yes The Hermitian conjugate operator, G is the intensity gain of four-wave mixing, η1 represents the transmission efficiency of the probe light field and the conjugate light field in the atomic vapor cell, and Represents the vacuum field introduced by the loss. Due to the nonlinear effect of four-wave mixing, the output probe light field and conjugate light field have intensity difference compression characteristics, and their normalized intensity difference compression value DS PIA It can be expressed as:

[0043]

[0044] Among them, Var is the abbreviation of variance, is the photon number operator, that is and PIA is the abbreviation of non-phase sensitive amplifier, SQL is the abbreviation of standard quantum limit. PIA Between 0 and 1, the smaller the value, the stronger the compression. Another common way to describe the compression size is to use the DS PLd The value of is 10 times the common logarithm. If the value is negative, it is generally called compression degree. The larger the negative number, the greater the compression degree.

[0045] S3. Optimize the physical parameters of the non-phase-sensitive amplifier to obtain the optimal intensity difference squeezed state light field output, and make the non-phase-sensitive amplifier work under corresponding physical parameters.

[0046] Specifically, the physical parameters of the non-phase-sensitive amplifier are changed, including the single-photon detuning amount, the two-photon detuning amount, the temperature of the atomic vapor, the pump light power, the angle between the pump light field and the probe light field, the intensity gain of the four-wave mixing, etc., and the corresponding intensity difference compression degree is recorded to screen out the optimal intensity difference compression state light field output.

[0047] S4. Construct a feedback optical path to feed back the probe light field and the conjugate light field output by the non-phase-sensitive amplifier to the input end of the non-phase-sensitive amplifier. The present application realizes the enhancement of the intensity difference compression state light field through the feedback optical path, and can obtain the intensity difference compression state light field equivalent to the output of the non-phase-sensitive amplifier under high pump power under low pump power, which has important practical significance in constructing a multi-component intensity-correlated light field and can significantly reduce the power requirement of the device.

[0048] S5. Use a microcontroller to lock the phase of the light field of the feedback optical path. Specifically, roughly adjust the reflector of the feedback optical path to make the feedback light field coincide with the initial probe light field and the initial space of the conjugate light field; scan the piezoelectric ceramics on the piezoelectric ceramic reflectors 9 and 11 of the feedback optical path, and at the same time, send the DC signals of the photodetectors 20 and 21 to the oscilloscope to observe the interference signal; fine-tune the reflector of the feedback optical path to maximize the visibility of the interference signal; then send the DC signals of the photodetectors 20 and 21 to the microcontrollers 22 and 23 respectively, and the microcontroller performs analog-to-digital conversion, data analysis and calculation on the input signal, and finally outputs the signal after the digital-to-analog conversion to the piezoelectric ceramics to control the piezoelectric ceramics to achieve phase locking of the feedback optical path, and lock the phase at the maximum interference point.

[0049] The probe light field and the conjugate light field output by the non-phase-sensitive amplifier are split by the optical beam splitters 16 and 18, and fed back to the input end of the non-phase-sensitive amplifier through the feedback optical path. Assuming that the reflectivity of the two optical beam splitters is k, the following relationship exists on the optical beam splitters:

[0050]

[0051] in, and are the two input light fields of the optical beam splitter 16 in the probe optical path, and are the input light fields of the optical beam splitter 18 in the conjugate optical path, where: and is the coherent state light field, and are two output light fields of the optical beam splitter 16, and are two output light fields of the beam splitter 18, where the output light fields and When they are fed back to the input end of the non-phase-sensitive amplifier through their respective feedback optical paths, the following relationship can be obtained:

[0052]

[0053] Where η is the optical loss of the feedback optical path, and The vacuum field introduced to feedback the optical path loss, The phase delay introduced by the feedback optical path.

[0054] Combining equations (1)-(4), we can obtain the output of the non-phase-sensitive amplifier after the loss is introduced: and

[0055] in:

[0056]

[0057]

[0058]

[0059]

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066]

[0067]

[0068]

[0069] In summary, the compression degree of the output light field intensity difference of the non-phase-sensitive amplifier after the introduction of feedback is finally obtained:

[0070]

[0071] The superscript * indicates conjugation. is the photon number operator, TFPA is the abbreviation of two-end feedback non-phase-sensitive amplifier, and SQL is the abbreviation of standard quantum limit.

[0072] According to formula (6), the compression degree of the output light field intensity difference of the non-phase-sensitive amplifier after the feedback is introduced can be calculated. This embodiment sets the general conventional experimental parameters, namely, the steam pool transmission efficiency η l =0.9, feedback optical path loss η l =0.95, feedback optical path phase The intensity gain G=2. Based on the method of the present invention, the dependence of the light field intensity difference compression degree (Squeezing degree) before (PIA) and after (TFPA) the introduction of feedback on the change of the beam splitter reflectivity k (Reflectivity k of the beam splitter) can be obtained, such as Figure 2As shown; the dependence of the intensity difference compression degree of the non-phase sensitive amplifier (PIA) before introducing feedback (PIA) and after introducing feedback (TFPA) on the intensity gain G (Gain G) is further simulated, as shown in Figure 3 shown.

[0073] S6. Optimize the reflectivity of the beam splitter used for feedback to obtain an intensity difference compressed state light field output with enhanced compression. After evaluating the physical parameters of the non-phase-sensitive amplifier, it is only necessary to adjust the reflectivity of the beam splitter in the feedback optical path to achieve adaptation to the system and enhance the quantum characteristics of the output light field.

[0074] Specifically, according to the physical parameters of the non-phase-sensitive amplifier under the optimal intensity difference compression state light field output recorded in step S3, mainly the optimal intensity gain G, it is substituted into formula 7 to calculate the optimal reflectivity value of the optical beam splitter in the feedback optical path. With the optimal reflectivity value as a reference, the reflectivity of the optical beam splitters 16 and 18 is adjusted, and the corresponding output end intensity difference compression degree is recorded. Finally, the optimal result of the light field intensity difference compression degree after introducing feedback is obtained, and compared with the result without introducing feedback, the enhancement of the feedback optical path on the output light field intensity difference compression characteristics of the non-phase-sensitive amplifier is evaluated.

[0075] The present invention is described above by way of example in conjunction with the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-mentioned methods. As long as various non-substantial improvements are made using the method concept and technical solution of the present invention; or the above concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A device for enhancing the compression characteristics of the output light field intensity difference of a non-phase-sensitive amplifier, characterized in that: The device includes a non-phase-sensitive amplifier, a feedback optical path, and a measurement and control circuit, wherein the non-phase-sensitive amplifier is connected to the feedback optical path and the measurement and control circuit respectively, and the feedback optical path is also connected to the measurement and control circuit; the non-phase-sensitive amplifier is used to output a probe light field and a conjugate light field, and the output probe light field and conjugate light field are respectively fed back to the probe light field input terminal and the conjugate light field input terminal of the non-phase-sensitive amplifier through the corresponding feedback optical path, and the measurement and control circuit is used to measure the intensity difference compression characteristics of the probe light field and the conjugate light field and realize the phase locking of the feedback optical path.

2. The device for enhancing the compression characteristic of the output light field intensity difference of a non-phase-sensitive amplifier according to claim 1, characterized in that: The non-phase-sensitive amplifier comprises a laser, a half-wave plate, a polarization beam splitter prism, a reflector, an acousto-optic modulator, a Glan laser prism, a rubidium atomic vapor pool, a Glan-Thompson prism and a beam terminator; wherein the laser light outputted by the laser (1) passes through the half-wave plate (2) and the polarization beam splitter prism (3) in sequence and is divided into two beams of vertical polarization and horizontal polarization; the vertical polarization light passes through the reflector (4), the reflector (13) and the Glan laser prism (12) in sequence and is then reflected as pump light for four-wave mixing and passes through the rubidium atomic vapor pool (14); the pump light passing through the rubidium atomic vapor pool (14) is then reflected by the Glan-Thompson prism (15) and then output to the beam terminator (26); the horizontal polarization light passes through the acousto-optic frequency shifter (5) and is then shifted in frequency and passes through the reflector (7) in sequence ) and a reflector (6) and then pass through a Glan laser prism (12); the light exit end of the Glan laser prism (12) serves as the probe light field input end of the non-phase-sensitive amplifier; the input probe light field crosses with the pump light and passes through a rubidium atomic vapor pool (14); the rubidium atomic vapor pool (14) amplifies the probe light field under the nonlinear interaction of four-wave mixing and generates a conjugate light field on the other side relative to the pump light; correspondingly, the probe light field input end serves as the conjugate light field input end of the non-phase-sensitive amplifier on the other side relative to the pump light; the probe light field that passes through the rubidium atomic vapor pool (14) and the newly generated conjugate light field serve as the probe light field output end and the conjugate light field output end of the non-phase-sensitive amplifier respectively after passing through a Glan-Thompson prism (15).

3. The device for enhancing the compression characteristic of the output light field intensity difference of a non-phase-sensitive amplifier according to claim 2, characterized in that: The feedback optical path comprises an optical beam splitter, a reflector, and a reflector with piezoelectric ceramics. With respect to the probe light field and the conjugate light field outputted by the non-phase-sensitive amplifier in two paths, the feedback optical path is provided with two paths correspondingly. One path is used to feed back the probe light field to the probe light field input end, that is, the probe light field outputted by the non-phase-sensitive amplifier passes through the optical beam splitter (16), then sequentially passes through the reflector (17), the piezoelectric ceramic reflector (9), the optical beam splitter (8), and passes through the Glan laser prism (12), and then is fed back to the probe light field input end along the original path. The other path is used to feed back the conjugate light field to the conjugate light field input end, that is, the conjugate light field outputted by the non-phase-sensitive amplifier passes through the optical beam splitter (18), then sequentially passes through the reflector (19), the piezoelectric ceramic reflector (11), the reflector (10), and passes through the Glan laser prism (12), and then is fed back to the conjugate light field input end along the original path.

4. The device for enhancing the compression characteristic of the output light field intensity difference of a non-phase-sensitive amplifier according to claim 3, characterized in that: The measurement and control circuit comprises a microcontroller and a light field intensity difference compressibility measurement system, wherein: the light field intensity difference compressibility measurement system comprises the photoelectric detector, the subtractor, and the spectrum analyzer, wherein the photoelectric detector (20) is respectively connected to the conjugate light field output end of the non-phase sensitive amplifier and the subtractor (24), the micro photoelectric detector (21) is respectively connected to the probe light field output end of the non-phase sensitive amplifier and the subtractor (24), and the subtractor (24) is connected to the spectrum analyzer (25); the microcontroller (22) is respectively connected to the reflector (9) with piezoelectric ceramics and the photoelectric detector (20); the microcontroller (23) is respectively connected to the reflector (11) with piezoelectric ceramics and the photoelectric detector (21).

5. The device for enhancing the compression characteristic of the output light field intensity difference of a non-phase-sensitive amplifier according to claim 4, characterized in that: The device also includes a power meter and a 50:50 beam splitter. The power meter is respectively connected to the probe light field output end and the conjugate light field output end of the non-phase-sensitive amplifier and is used to measure the total power of the probe light field and the conjugate light field output by the non-phase-sensitive amplifier; the 50:50 beam splitter is connected to the laser and is used to split the output laser of the laser.

6. A method for enhancing the compression characteristics of the output light field intensity difference of a non-phase-sensitive amplifier, characterized in that: The method is applied to the device for enhancing the compression characteristic of the output light field intensity difference of a non-phase-sensitive amplifier according to any one of claims 1 to 5, and the method comprises the following steps: S1, control the laser to output two strong and weak laser beams, the weak beam is frequency-shifted by the acousto-optic frequency shifter as the probe light field input, and the strong beam is used as the pump light. The two lights cross through the rubidium vapor cell to construct a non-phase-sensitive amplifier, which outputs the probe light field and the conjugate light field; S2, sending the probe light field and the conjugate light field output by the non-phase-sensitive amplifier into a measurement and control circuit to measure the light field intensity difference compression degree; S3, optimizing the physical parameters of the non-phase-sensitive amplifier to obtain the optimal intensity difference squeezed state light field output, and making the non-phase-sensitive amplifier work under the corresponding physical parameters; S4, constructing a feedback optical path to feed back the probe light field and the conjugate light field output by the non-phase-sensitive amplifier to the input end of the non-phase-sensitive amplifier; S5, using a microcontroller to lock the light field phase of the feedback light path; S6. Optimize the reflectivity of the optical beam splitter used for feedback to obtain an intensity difference compressed state light field output with enhanced compression.

7. The method for enhancing the compression characteristic of the output light field intensity difference of a non-phase-sensitive amplifier according to claim 6, characterized in that: In step S2, a power meter is used to measure the total intensity of the probe light field and the conjugate light field output by the non-phase-sensitive amplifier; before four-wave mixing occurs, the laser (1) is controlled to separate a laser from the output laser and its power is adjusted to be equal to the total intensity of the probe light field and the conjugate light field; the laser is then split by the 50:50 beam splitter and sent to a photodetector (20) and a photodetector (21) respectively; the current signals output by the photodetector (20) and the photodetector (21) are processed by a subtractor (24) and connected to a spectrum analyzer (25) to record the current noise power spectrum before four-wave mixing occurs; after four-wave mixing occurs, the probe light field and the conjugate light field output by the non-phase-sensitive amplifier are sent to the photodetector (20) and the photodetector (21) respectively, and the current noise power spectrum is also recorded; the difference between the current noise before and after four-wave mixing occurs is the intensity difference compression degree.

8. The method for enhancing the compression characteristic of the output light field intensity difference of a non-phase-sensitive amplifier according to claim 6, characterized in that: In step S3, the physical parameters of the non-phase-sensitive amplifier are changed, including the single-photon detuning amount, the two-photon detuning amount, the temperature of the atomic vapor, the pump light power, the angle between the pump light field and the probe light field, and the intensity gain of the four-wave mixing, and the corresponding intensity difference compression degree is recorded to screen out the optimal intensity difference compression state light field output.

9. The method for enhancing the compression characteristic of the output light field intensity difference of a non-phase-sensitive amplifier according to claim 6, characterized in that: In step S5, the reflector of the feedback optical path is roughly adjusted to make the feedback light field coincide with the initial probe light field and the initial space of the conjugate light field; the piezoelectric ceramics on the piezoelectric ceramic reflectors (9) and (11) of the feedback optical path are scanned, and at the same time, the DC signals of the optical detectors (20) and (21) are sent to the oscilloscope to observe the interference signal; the reflector of the feedback optical path is finely adjusted to maximize the visibility of the interference signal; and the DC signals of the optical detectors (20) and (21) are respectively sent to the microcontrollers (22) and (23), and the microcontroller performs analog-to-digital conversion, data analysis and calculation on the input signal, and finally outputs the signal after the digital-to-analog conversion to the piezoelectric ceramic to control the piezoelectric ceramic to achieve phase locking of the feedback optical path, and lock the phase at the maximum interference point.

10. The method for enhancing the compression characteristic of the output light field intensity difference of a non-phase-sensitive amplifier according to claim 6, characterized in that: In step S6, the optimal reflectivity value of the optical beam splitter in the feedback optical path is calculated based on the physical parameters of the non-phase-sensitive amplifier under the optimal intensity difference compression state light field output, and the reflectivity of the optical beam splitters (16) and (18) is adjusted with the optimal reflectivity value as a reference, and the corresponding output end intensity difference compression degree is recorded, and finally the optimal result of the light field intensity difference compression degree after introducing feedback is obtained, and compared with the result without introducing feedback, so as to evaluate the enhancement of the feedback optical path on the output light field intensity difference compression characteristics of the non-phase-sensitive amplifier.

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