Measurement device based on stimulated parametric down-conversion and quantum enhanced phase measurement method

Abstract

The present disclosure provides a measurement device based on stimulated parametric down-conversion and a quantum enhanced phase measurement method. The device includes: a laser light source for providing an initial pump light; a nonlinear crystal for performing a first stimulated parametric down-conversion and a second stimulated parametric down-conversion on the initial pump light from the laser light source; a concave reflector for reflecting a first parametric light and a first pump light from the nonlinear crystal to a plane mirror, and reflecting the first parametric light and the first pump light from the plane mirror back to the nonlinear crystal; a plane mirror for reflecting the first parametric light and the first pump light from the concave reflector back to the concave reflector; a wedge-shaped phase adjuster for adjusting the phase between the first pump light and the first parametric light from the concave reflector; and a single-photon detector for performing single-photon threshold detection on the second parametric light from the nonlinear crystal.

Description

Technical Field

[0001] The present disclosure relates to the field of quantum information processing technology, specifically to the field of quantum precision measurement and weak light detection, and in particular to a measurement device based on stimulated parametric down-conversion and a quantum enhanced phase measurement method. Background Art

[0002] The purpose of quantum precision measurement is to use quantum systems to improve the measurement accuracy of physical parameters. The measurement errors of physical parameters include technical errors and principle errors. The technical error of measuring physical parameters is the error introduced by the imperfect technical means in the measurement process, such as the noise caused by changes in ambient temperature. The principle error is caused by the limitations of basic physical principles. The most typical example is the use of Mach–Zehnder (MZ) interferometer to measure the phase between the two arms of the interferometer. When using classical laser input, due to the quantum uncertainty principle, the light intensity at the output port must have Poisson fluctuations, which leads to an upper limit on the phase measurement accuracy. Specifically, assuming that the average number of photons of the input laser is n, the phase error satisfies This is the minimum error that can be obtained through classical resources (laser) when the resources are certain, which is called the shot noise limit.

[0003] If quantum resources such as quantum entanglement are introduced, the shot noise limit can be broken. Theory shows that for quantum systems, the optimal phase estimation satisfies It's called the Heisenberg limit.

[0004] A typical approach to reaching the Heisenberg limit is based on the NOON state, an entangled state with a maximum number of photons. Although the NOON state can theoretically reach the Heisenberg limit, phase measurements based on the NOON state have significant limitations. First, NOON states with large photon counts are difficult to deterministically prepare; second, NOON states are sensitive to the photon loss exponent. To date, unconditional transcendence of the shot noise limit has only been achieved for the two-photon NOON state. Summary of the Invention

[0005] In view of the above problems, the present disclosure provides a measurement device based on stimulated parametric down-conversion and a quantum enhanced phase measurement method for achieving phase measurement reaching the Heisenberg limit.

[0006] According to a first aspect of the present disclosure, a measurement device based on stimulated parametric down-conversion is provided, comprising: a laser light source for providing an initial pump light; a nonlinear crystal for performing a first stimulated parametric down-conversion on the initial pump light from the laser light source to obtain a first parametric light and a first pump light, and performing a second stimulated parametric down-conversion on the first parametric light and the first pump light from a concave reflector to obtain a second parametric light and a second pump light; a concave reflector for reflecting the first parametric light and the first pump light from the nonlinear crystal to a plane mirror, and reflecting the first parametric light and the first pump light from the plane mirror back to the nonlinear crystal; a plane mirror for reflecting the first parametric light and the first pump light from the concave reflector back to the concave reflector; a wedge-shaped phase adjuster for adjusting the phase between the first pump light and the first parametric light from the concave reflector; and a single-photon detector for performing single-photon threshold detection on the second parametric light from the nonlinear crystal.

[0007] According to an embodiment of the present disclosure, it includes: a concave reflecting mirror and a plane mirror forming an optical 4f system, the distance between the concave reflecting mirror and the plane mirror is one times the focal length of the concave reflecting mirror; the distance between the concave reflecting mirror and the nonlinear crystal is one times the focal length of the concave reflecting mirror.

[0008] According to an embodiment of the present disclosure, the laser light source is configured such that a light source port of the laser light source faces the nonlinear crystal, so that initial pump light from the laser light source is vertically incident on the nonlinear crystal.

[0009] According to an embodiment of the present disclosure, it further includes: a dichroic mirror for separating the second pump light and the second parametric light generated by the second stimulated parametric down-conversion of the nonlinear crystal; and a beam splitter for separating the second parametric light of different polarization modes from the dichroic mirror.

[0010] According to an embodiment of the present disclosure, it also includes: a first focusing lens, which is arranged between the laser light source and the nonlinear crystal, and is used to focus the initial pump light from the laser light source; and a second focusing lens, which is arranged between the beam splitter and the dichroic mirror, and is used to collimate the second parametric light from the dichroic mirror.

[0011] According to an embodiment of the present disclosure, it further includes: a λ / 4 wave plate, which is arranged between the concave reflecting mirror and the plane mirror to ensure that the stimulated parametric down-conversion process does not affect the spectral decorrelation.

[0012] According to an embodiment of the present disclosure, the nonlinear crystal includes a periodically poled potassium titanyl phosphate crystal.

[0013] According to an embodiment of the present disclosure, the nonlinear crystal satisfies collinear type II phase matching at a selected pump light wavelength.

[0014] According to an embodiment of the present disclosure, a wedge-shaped phase adjuster is disposed between the concave reflector and the plane mirror. The cross section of the wedge-shaped phase adjuster is wedge-shaped, and the thickness variation is 200 microns.

[0015] A second aspect of the present disclosure provides a quantum enhanced phase measurement method based on stimulated parametric down-conversion, comprising: a laser light source provides initial pump light; a nonlinear crystal performs a first stimulated parametric down-conversion on the initial pump light from the laser light source to obtain a first parametric light and a first pump light, and performs a second stimulated parametric down-conversion on the first parametric light and the first pump light from a concave reflector to obtain a second parametric light and a second pump light; the concave reflector reflects the first parametric light and the first pump light from the nonlinear crystal to a plane mirror, and reflects the first parametric light and the first pump light from the plane mirror back to the nonlinear crystal; the plane mirror reflects the first parametric light and the first pump light from the concave reflector back to the concave reflector; a wedge-shaped phase adjuster adjusts the phase between the first pump light and the first parametric light from the concave reflector; and a single-photon detector performs single-photon threshold detection on the second parametric light from the nonlinear crystal.

[0016] The stimulated parametric down-conversion (SPD) measurement device provided by the present disclosure can, in principle, achieve Heisenberg-limited phase measurement while being highly tolerant to external losses, i.e., losses outside the measurement device, such as detector and line losses. Furthermore, the present invention has a simple structure, making it easy to integrate and expand. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematically shows a schematic diagram of a measurement device based on stimulated parametric down-conversion according to an embodiment of the present disclosure;

[0018] Figure 2 The figure schematically shows a schematic diagram of a measurement device based on stimulated parametric down-conversion according to another embodiment of the present disclosure. DETAILED DESCRIPTION

[0019] In order to make the objectives, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0020] According to a first aspect of the present disclosure, a measurement device based on stimulated parametric down-conversion is provided, comprising: a laser light source for providing an initial pump light; a nonlinear crystal for performing a first stimulated parametric down-conversion on the initial pump light from the laser light source to obtain a first parametric light and a first pump light, and performing a second stimulated parametric down-conversion on the first parametric light and the first pump light from a concave reflector to obtain a second parametric light and a second pump light; a concave reflector for reflecting the first parametric light and the first pump light from the nonlinear crystal to a plane mirror, and reflecting the first parametric light and the first pump light from the plane mirror back to the nonlinear crystal; a plane mirror for reflecting the first parametric light and the first pump light from the concave reflector back to the concave reflector; a wedge-shaped phase adjuster for adjusting the phase between the first pump light and the first parametric light from the concave reflector; and a single-photon detector for performing single-photon threshold detection on the second parametric light from the nonlinear crystal.

[0021] According to an embodiment of the present disclosure, it includes: a concave reflecting mirror and a plane mirror forming an optical 4f system, the distance between the concave reflecting mirror and the plane mirror is one times the focal length of the concave reflecting mirror; the distance between the concave reflecting mirror and the nonlinear crystal is one times the focal length of the concave reflecting mirror.

[0022] According to an embodiment of the present disclosure, the laser light source is configured such that a light source port of the laser light source faces the nonlinear crystal, so that initial pump light from the laser light source is vertically incident on the nonlinear crystal.

[0023] According to an embodiment of the present disclosure, it further includes: a dichroic mirror for separating the second pump light and the second parametric light generated by the second stimulated parametric down-conversion of the nonlinear crystal; and a beam splitter for separating the second parametric light of different polarization modes from the dichroic mirror.

[0024] According to an embodiment of the present disclosure, it also includes: a first focusing lens, which is arranged between the laser light source and the nonlinear crystal, and is used to focus the initial pump light from the laser light source; and a second focusing lens, which is arranged between the beam splitter and the dichroic mirror, and is used to collimate the second parametric light from the dichroic mirror.

[0025] According to an embodiment of the present disclosure, it further includes: a λ / 4 wave plate, which is arranged between the concave reflecting mirror and the plane mirror to ensure that the stimulated parametric down-conversion process does not affect the spectral decorrelation.

[0026] According to an embodiment of the present disclosure, the nonlinear crystal includes a periodically poled potassium titanyl phosphate crystal.

[0027] According to an embodiment of the present disclosure, the nonlinear crystal satisfies collinear type II phase matching at a selected pump light wavelength.

[0028] According to an embodiment of the present disclosure, a wedge-shaped phase adjuster is disposed between the concave reflector and the plane mirror. The cross section of the wedge-shaped phase adjuster is wedge-shaped, and the thickness variation is 200 microns.

[0029] A second aspect of the present disclosure provides a quantum enhanced phase measurement method based on stimulated parametric down-conversion, comprising: a laser light source provides initial pump light; a nonlinear crystal performs a first stimulated parametric down-conversion on the initial pump light from the laser light source to obtain a first parametric light and a first pump light, and performs a second stimulated parametric down-conversion on the first parametric light and the first pump light from a concave reflector to obtain a second parametric light and a second pump light; the concave reflector reflects the first parametric light and the first pump light from the nonlinear crystal to a plane mirror, and reflects the first parametric light and the first pump light from the plane mirror back to the nonlinear crystal; the plane mirror reflects the first parametric light and the first pump light from the concave reflector back to the concave reflector; a wedge-shaped phase adjuster adjusts the phase between the first pump light and the first parametric light from the concave reflector; and a single-photon detector performs single-photon threshold detection on the second parametric light from the nonlinear crystal.

[0030] Figure 1 The figure schematically shows a measurement device based on stimulated parametric down-conversion according to one embodiment of the present invention.

[0031] like Figure 1 As shown, the measuring device includes a laser light source 1 , a nonlinear crystal 4 , a concave reflector 5 , a wedge-shaped phase adjuster 6 , a plane mirror 8 and a single-photon detector 11 .

[0032] According to an embodiment of the present disclosure, laser light source 1 can employ a femtosecond pulse laser, with the femtosecond pulse laser light generated by laser light source 1 serving as the initial pump light. The initial pump light is horizontally polarized. The pulse laser light generated by laser light source 1 has a wavelength range of 760-790 nm and a linewidth of 2 nm-10 nm.

[0033] The nonlinear crystal 4 can perform a first stimulated parametric down-conversion on the initial pump light provided by the laser light source 1 to generate a first parametric light and a first pump light. The initial pump light undergoes the stimulated parametric down-conversion process of the nonlinear crystal 4 to obtain the first parametric light and the first pump light, wherein most of the initial pump light is converted into the first pump light, and the energy difference between the first pump light and the initial pump light is very small. The nonlinear crystal 4 can also perform a second stimulated parametric down-conversion on the first parametric light and the first pump light from the concave reflector 5, converting the first pump light and the first parametric light into a second parametric light and a second pump light. The second stimulated parametric down-conversion process of the nonlinear crystal 4 can enhance the first parametric light to obtain the second parametric light.

[0034] According to the disclosed embodiments, a temperature control device is installed externally on nonlinear crystal 4 to maintain a stable temperature and minimize wavelength shifts in the parametric light caused by temperature changes. Antireflection coatings for the pump and parametric light wavelengths are applied to both end faces of the nonlinear crystal, facing laser source 1 and concave reflector 5.

[0035] Concave reflector 5 is located behind nonlinear crystal 4 and can reflect the first pump light and first parametric light from nonlinear crystal 4 to plane mirror 8. After receiving the first parametric light and first pump light from concave reflector 5, plane mirror 8 reflects the first parametric light and first pump light back to concave reflector 5 along the original optical path. Subsequently, concave reflector 5 reflects the first parametric light and first pump light back to nonlinear crystal 4. The concave reflector and plane mirror can be used to precisely adjust the process of the first pump light and first parametric light from the nonlinear crystal, through the concave reflector and plane mirror, and then back to the nonlinear crystal 4, thereby ensuring the accuracy of the measurement device proposed in the present disclosure.

[0036] The wedge-shaped phase adjuster 6 adjusts the phase between the first pump light and the first parametric light from the concave reflector 5. By moving the wedge-shaped phase adjuster 6 up and down, the optical path lengths of the first pump light and the first parametric light passing through the wedge-shaped phase adjuster 6 gradually change. This relative phase is the measurement phase. The first pump light and the first parametric light are reflected from the plane mirror 8 back to the concave reflector 5, passing through the wedge-shaped phase adjuster 6 again.

[0037] According to an embodiment of the present disclosure, a wedge-shaped phase adjuster 6 is provided between the concave reflector 5 and the plane mirror 8. The wedge-shaped phase adjuster is formed by a K9 glass sheet with a wedge-shaped cross section, and the thickness of the wedge-shaped phase adjuster varies from top to bottom by 200 microns.

[0038] The single-photon detector 11 can perform single-photon threshold detection on the second parametric light from the nonlinear crystal 4 .

[0039] The stimulated parametric down-conversion (SPD) measurement device provided in this disclosure uses a wedge-shaped phase adjuster to adjust the measured phase and a single-photon detector for single-photon threshold detection. In principle, the phase measured by this device can reach the Heisenberg limit. Furthermore, the device is highly tolerant to losses external to the measurement device, such as detector and line losses. Furthermore, the SPD measurement device provided in this disclosure has a simple structure and is easy to integrate and expand.

[0040] According to the embodiments of the present disclosure, Figure 1As shown, the concave reflector 5 and the plane mirror 8 form an optical 4f system. The distance between the concave reflector 5 and the plane mirror 8 is equal to one focal length of the concave reflector 5, and the distance between the concave reflector 8 and the nonlinear crystal 4 is also equal to one focal length of the concave reflector 5. By adjusting the distances between the concave reflector, the plane mirror, and the nonlinear crystal, it is ensured that the first parametric light and the first pump light generated by the nonlinear crystal can be refocused at the same position in the nonlinear crystal after being reflected by the concave reflector and the plane mirror, thereby ensuring good spatial mode matching of the parametric light.

[0041] According to the embodiments of the present disclosure, Figure 1 As shown, the light source port of the laser light source 1 faces the nonlinear crystal, so that the initial pump light generated by the laser light source 1 is vertically incident on the nonlinear crystal.

[0042] According to an embodiment of the present disclosure, the nonlinear crystal includes a periodically poled potassium titanyl phosphate crystal (PPKTP).

[0043] According to embodiments of the present disclosure, the nonlinear crystal satisfies collinear type II phase matching at the selected pump light wavelength. By designing the nonlinear crystal for correlated spectral decorrelation and employing a PPKTP crystal, collinear type II phase matching is achieved, ensuring that the photon pairs generated by the stimulated parametric down-conversion process in the nonlinear crystal are highly pure, i.e., completely homogeneous.

[0044] According to the embodiments of the present disclosure, Figure 1 As shown, the measuring device also includes a dichroic mirror 3. The dichroic mirror 3 is arranged between the laser light source 1 and the nonlinear crystal 4, and has an angle of 45° with the horizontal direction, and is used to separate the second pump light and the second parametric light generated by the second stimulated parametric down-conversion from the nonlinear crystal 4. The dichroic mirror 3 is coated to fully transmit the second pump light incident at 45°, and fully reflect the second parametric light incident at 45°. Specifically, after the initial pump light from the laser light source 1 enters the dichroic mirror 3, the dichroic mirror 3 can transmit all the initial pump light to the nonlinear crystal 4; the second pump light and the second parametric light generated by the second stimulated parametric down-conversion from the nonlinear crystal 4 enter the dichroic mirror 3 at 45°, and the dichroic mirror 3 can fully reflect the second parametric light and fully transmit the second pump light.

[0045] The dichroic mirror 3 can completely reflect the second parametric light onto the beam splitter 10. The second parametric light includes parametric light in a horizontal polarization mode and parametric light in a vertical polarization mode. The beam splitter 10 can separate the parametric light in a horizontal polarization direction and the parametric light in a vertical polarization direction.

[0046] According to an embodiment of the present disclosure, the beam splitter includes a polarization beam splitter.

[0047] According to the embodiments of the present disclosure, Figure 1 As shown, the measurement device further includes a first focusing lens 2 and a second focusing lens 9. The first focusing lens 2 is disposed between the laser light source 1 and the nonlinear crystal 4, and can focus the initial pump light from the laser light source 1 onto the nonlinear crystal 4. The second focusing lens 9 is disposed between the dichroic mirror 3 and the beam splitter 10, and can collimate the second parametric light from the dichroic mirror 3 into approximately parallel light, which is then input into the beam splitter 10.

[0048] Figure 2 The following schematically shows a schematic diagram of a measurement device based on stimulated parametric down-conversion according to another embodiment of the present invention.

[0049] According to the embodiments of the present disclosure, Figure 2 As shown, a third focusing lens 12, a fourth focusing lens 13, and a single-mode optical fiber 14 are further included between the beam splitter 10 and the single-photon detector 11. The third focusing lens 12 and the fourth focusing lens 13 are disposed between the single-mode optical fiber 14 and the beam splitter 10, and can focus the second parametric light in the horizontal polarization direction and the second parametric light in the vertical polarization direction separated by the beam splitter 10 onto the single-mode optical fiber 14. The single-mode optical fiber 14 is connected to the single-photon detector 11, and transmits the second parametric light in the horizontal polarization direction and the second parametric light in the vertical polarization direction to the single-photon detector 11 for detection.

[0050] According to the embodiments of the present disclosure, Figure 1 As shown, the measurement device also includes a λ / 4 wave plate 7, which is designed for the wavelength of the parametric light. The λ / 4 wave plate 7 is arranged between the concave reflector 5 and the plane mirror 8 to ensure that the stimulated parametric down-conversion process does not affect the spectral decorrelation. The first pump light and the first parametric light pass through the λ / 4 wave plate 7 twice, namely, the concave reflector 5 reflects the first pump light and the first parametric light to the plane mirror 8 and passes through the λ / 4 wave plate 7; the plane mirror 8 reflects the first pump light and the first parametric light back to the concave reflector 5 and passes through the λ / 4 wave plate 7. The first pump light and the first parametric light pass through the λ / 4 wave plate 7 twice, and the parametric light in the horizontal polarization direction and the parametric light in the vertical polarization direction in the first parametric light are interchanged, and the polarization direction of the first pump light remains unchanged. The λ / 4 wave plate ensures that the stimulated parametric down-conversion process does not affect the spectral decorrelation.

[0051] According to the embodiments of the present disclosure, a measurement device based on stimulated parametric down conversion can be used to perform quantum enhanced phase measurement. Figure 1As shown, a laser light source 1 provides a pulsed initial pump light. The initial pump light passes through a nonlinear crystal 4 and undergoes a first stimulated parametric down-conversion process to produce a first pump light and a first parametric light. The first pump light and the first parametric light are reflected by a concave reflector 5 onto a plane mirror 8, then reflected back by the plane mirror 8 onto the concave reflector 5, passing through a wedge-shaped phase adjuster twice. The first pump light and the first parametric light are reflected by the concave reflector 5 onto the plane mirror 8, passing through the wedge-shaped phase adjuster once. The wedge-shaped phase adjuster can adjust the phase between the first pump light and the first parametric light, i.e., the phase to be measured. After being reflected back by the plane mirror 8 onto the concave reflector 5, the first pump light and the first parametric light are reflected back by the concave reflector 5 onto the nonlinear crystal 4. After undergoing a second stimulated parametric down-conversion process in the nonlinear crystal 4, the first pump light and the first parametric light are converted into a second pump light and a second parametric light. The second parametric light also undergoes quantum phase enhancement compared to the first parametric light. A single-photon detector 11 performs single-photon threshold detection on the second parametric light to obtain the phase to be measured.

[0052] This disclosure provides a measurement device based on stimulated parametric down-conversion. Under ideal conditions, the measured phase standard deviation can reach the Heisenberg limit. Furthermore, even with photon loss in the fiber collection process and single-photon detector, the measurement accuracy is reduced by only a constant factor, asymptotically still meeting the Heisenberg limit. Specific theoretical verification is as follows.

[0053] The parametric down-conversion process mathematically corresponds to a single-mode or dual-mode compression operation, taking the dual-mode compression operation as an example. After the first stimulated parametric down-conversion process, that is, the first dual-mode compression, a compressed light field in a dual-mode compressed vacuum state is first generated. The concave reflector reflects the compressed light field from the nonlinear crystal to the plane mirror. After the compressed light field passes through the wedge-shaped phase adjuster to produce a change in phase Φ, that is, the phase to be measured, the plane mirror returns the compressed light field to the concave reflector and the nonlinear crystal along the original path. After the compressed light field enters the nonlinear crystal, it undergoes a second stimulated parametric down-conversion process, that is, the second dual-mode compression, to generate a dual-mode light field after two compressions. The beam splitter separates the two polarization modes of the dual-mode light field after two compressions and sends them to the single-photon threshold detector to measure the single-path and two-body coincidence. The expression of the final output state satisfies formula (1):

[0054]

[0055] in is the bimodal compression operator, is the compression amount, is the phase shift operator. When threshold detection is performed on the output state, the Fisher information of a single measurement satisfies formula (2):

[0056]

[0057] The result i indicates that the detection result of the first detector is i, and the result j indicates that the detection result of the second detector is j. ij Represents the probability of the result ij occurring.

[0058] There are 4 possible results {00, 01, 10, 11}. A detection result of 0 indicates that the detector has no response, and a result of 1 indicates that the detector has responded. After direct calculation, it can be seen that the maximum value of Fisher information is F max =16sinh 2 (2r), and the average number of photons passing through the sample is Since the compressed light field passes through the nonlinear crystal twice, the optimal phase sensitivity satisfies:

[0059]

[0060] From the above formula, we can see that the optimal phase sensitivity reaches the Heisenberg limit.

[0061] When there is external photon loss in the measurement device, the optimal phase sensitivity satisfies formula (4):

[0062]

[0063] Here, η is the product of the stimulated parametric light collection efficiency and the single-photon detector efficiency.

[0064] From formula (4), we can see that when the external loss is constant, the photon loss will only reduce the measurement accuracy by a constant factor, and it still satisfies the Heisenberg limit in an asymptotic sense.

[0065] In summary, the present disclosure provides a measurement device based on stimulated parametric down-conversion. Under ideal conditions, the measured phase standard deviation can reach the Heisenberg limit. Furthermore, even when some photon loss occurs during the fiber collection process and the single-photon detector, the measurement accuracy is reduced by only a constant factor, asymptotically still meeting the Heisenberg limit.

[0066] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present disclosure. It should be understood that the above are only specific embodiments of the present disclosure and are not intended to limit the present disclosure. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present disclosure should be included in the scope of protection of the present disclosure.

Claims

1. A measurement device based on stimulated parametric down-conversion, comprising: A laser light source, used to provide initial pump light; a nonlinear crystal for performing a first stimulated parametric down-conversion on the initial pump light from the laser light source to obtain a first parametric light and a first pump light, and performing a second stimulated parametric down-conversion on the first parametric light and the first pump light from the concave reflector to obtain a second parametric light and a second pump light; An anti-reflection film for the initial pump light, the second parametric light and the second pump light band is provided on one end face of the nonlinear crystal facing the laser light source, and an anti-reflection film for the first parametric light and the first pump light band is provided on one end face of the nonlinear crystal facing the concave reflector; a concave reflecting mirror, configured to reflect the first parametric light and the first pumping light from the nonlinear crystal to the plane mirror, and reflect the first parametric light and the first pumping light from the plane mirror back to the nonlinear crystal; a plane mirror, configured to reflect the first parametric light and the first pump light from the concave reflecting mirror back to the concave reflecting mirror; a wedge-shaped phase adjuster, configured to adjust the phase between the first pump light and the first parametric light from the concave reflector; as well as a single-photon detector, configured to perform single-photon threshold detection on the second parametric light from the nonlinear crystal; The concave reflecting mirror and the plane mirror constitute an optical 4f system, and the distance between the concave reflecting mirror and the plane mirror is one times the focal length of the concave reflecting mirror; The distance between the concave reflecting mirror and the nonlinear crystal is one time the focal length of the concave reflecting mirror.

2. The measuring device according to claim 1, comprising: The laser light source is configured such that a light source port of the laser light source faces the nonlinear crystal, so that the initial pump light from the laser light source is vertically incident on the nonlinear crystal.

3. The measuring device according to claim 1, further comprising: a dichroic mirror for separating a second pump light and a second parametric light generated by the second stimulated parametric down conversion of the nonlinear crystal; A beam splitter is used to separate the second parametric light of different polarization modes from the dichroic mirror.

4. The measuring device according to claim 3, further comprising: a first focusing lens, disposed between the laser light source and the nonlinear crystal, and configured to focus the initial pump light from the laser light source; as well as The second focusing lens is arranged between the beam splitter and the dichroic mirror, and is used for collimating the second parametric light from the dichroic mirror.

5. The measuring device according to claim 1, further comprising: A λ / 4 wave plate is provided between the concave reflecting mirror and the plane mirror, and is used to ensure that the stimulated parametric down-conversion process does not affect spectral decorrelation. The measurement device according to claim 1 , wherein the nonlinear crystal comprises a periodically poled potassium titanyl phosphate crystal. 7 . The measurement device according to claim 1 , wherein the nonlinear crystal satisfies collinear type II phase matching at a selected pump light wavelength.

8. The measuring device according to claim 1, wherein the wedge-shaped phase adjuster is disposed between the concave reflecting mirror and the plane mirror, the cross section of the wedge-shaped phase adjuster is wedge-shaped, and the thickness variation is 200 microns.

9. A quantum enhanced phase measurement method based on stimulated parametric down-conversion, comprising: The laser light source provides the initial pump light; The nonlinear crystal performs a first stimulated parametric down-conversion on the initial pump light from the laser light source to obtain a first parametric light and a first pump light, and performs a second stimulated parametric down-conversion on the first parametric light and the first pump light from the concave reflector to obtain a second parametric light and a second pump light; An anti-reflection film for the initial pump light, the second parametric light and the second pump light band is provided on one end face of the nonlinear crystal facing the laser light source, and an anti-reflection film for the first parametric light and the first pump light band is provided on one end face of the nonlinear crystal facing the concave reflector; The concave reflecting mirror reflects the first parametric light and the first pumping light from the nonlinear crystal to the plane mirror, and reflects the first parametric light and the first pumping light from the plane mirror back to the nonlinear crystal; The plane mirror reflects the first parametric light and the first pump light from the concave reflecting mirror back to the concave reflecting mirror; A wedge-shaped phase adjuster adjusts the phase between the first pump light and the first parametric light from the concave reflector; as well as The single-photon detector performs single-photon threshold detection on the second parametric light from the nonlinear crystal; The concave reflecting mirror and the plane mirror constitute an optical 4f system, and the distance between the concave reflecting mirror and the plane mirror is one times the focal length of the concave reflecting mirror; The distance between the concave reflecting mirror and the nonlinear crystal is one time the focal length of the concave reflecting mirror.

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