CN114166359A - Measuring device based on conversion under stimulated parameters and quantum enhanced phase measuring method - Google Patents
Measuring device based on conversion under stimulated parameters and quantum enhanced phase measuring method Download PDFInfo
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Abstract
The disclosure provides a measuring device based on stimulated parameter down-conversion and a quantum enhanced phase measuring method. The device includes: a laser light source for providing initial pump light; the nonlinear crystal is used for performing first stimulated parametric down-conversion and second stimulated parametric down-conversion on initial pump light from the laser light source; the concave reflector is used for reflecting the first parametric light and the first pump light from the nonlinear crystal to the 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 mirror back to the concave mirror; a wedge-shaped phase adjuster for adjusting a phase between the first pump light from the concave reflecting mirror and the first parametric light; and the single-photon detector is used for carrying out single-photon threshold detection on the second parameter light from the nonlinear crystal.
Description
Technical Field
The disclosure relates to the technical field of quantum information processing, in particular to the field of quantum precision measurement and weak light detection, and particularly relates to a measuring device based on stimulated parameter down-conversion and a quantum enhanced phase measuring method.
Background
The purpose of quantum precision measurement is to improve the measurement precision of the measured physical parameters by using a quantum system. And measuring errors of the measured physical parameters comprise technical errors and principle errors. Technical errors in measuring physical parameters are errors introduced by technical imperfections in the measurement process, such as noise due to changes in ambient temperature. The principle error is generated due to the limitation of the basic physical principle. The most typical example is the Mach-Zehnder (MZ) interferometer used for measuring the phase between two arms of the interferometer, and when the classical laser input is adopted, the light intensity of an output port inevitably has Poisson fluctuation due to the quantum uncertainty principle, and the fluctuation causes an upper limit to the phase measurement precision. Specifically, assuming that the average photon number of the input laser light is n, the phase error satisfies
This is the smallest error that can be obtained with classical resources (lasers) in the case of resource determination, called shot noise limit.
If quantum entanglement and quantum resources are introduced, the shot noise limit can be broken through. Theory shows that for quantum systems, the best phase estimation satisfies
Known as the heisenberg limit.
A typical way to reach the heisenberg limit is based on the NOON state, a maximum number of photons entangled state. Although the NOON regime can theoretically reach the heisenberg limit, phase measurements based on the NOON regime have significant limitations. On one hand, the NOON state with large photon number is difficult to be prepared deterministically; on the other hand, the NOON state is sensitive to the photon loss exponent, and unconditional exceeding of the shot noise limit has been achieved only in the 2-photon NOON state so far.
Disclosure of Invention
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, which are used for realizing phase measurement reaching the heisenberg limit.
According to a first aspect of the present disclosure, there is provided a measurement device based on stimulated parametric down-conversion, comprising: a laser light source for providing initial pump light; the nonlinear crystal is used for performing first stimulated parametric down-conversion on initial pump light from the laser light source to obtain first parametric light and first pump light, and performing second stimulated parametric down-conversion on the first parametric light and the first pump light from the concave reflector to obtain second parametric light and second pump light; the concave reflector is used for reflecting the first parametric light and the first pump light from the nonlinear crystal to the 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 mirror back to the concave mirror; a wedge-shaped phase adjuster for adjusting a phase between the first pump light from the concave reflecting mirror and the first parametric light; and the single-photon detector is used for carrying out single-photon threshold detection on the second parameter light from the nonlinear crystal.
According to an embodiment of the present disclosure, includes: the concave reflector and the plane mirror form an optical 4f system, and the distance between the concave reflector and the plane mirror is one time of the focal length of the concave reflector; the distance between the concave mirror and the nonlinear crystal is one focal length of the concave mirror.
According to an embodiment of the present disclosure, includes: the laser light source is configured such that a light source port of the laser light source is directed toward the nonlinear crystal such that initial pump light from the laser light source is incident perpendicularly to the nonlinear crystal.
According to an embodiment of the present disclosure, further comprising: the dichroic mirror is used for separating second pump light and second parameter light generated by conversion under second excited parameters of the nonlinear crystal; and the beam splitter is used for separating the second parametric light with different polarization modes from the dichroic mirror.
According to an embodiment of the present disclosure, further comprising: the first focusing lens is arranged between the laser light source and the nonlinear crystal and used for focusing initial pump light from the laser light source; and the second focusing lens is arranged between the beam splitter and the dichroic mirror and used for collimating the second parameter light from the dichroic mirror.
According to an embodiment of the present disclosure, further comprising: and the lambda/4 wave plate is arranged between the concave reflecting mirror and the plane mirror and is used for ensuring that the spectrum decorrelation is not influenced in the conversion process under the excited parameters.
According to an embodiment of the present disclosure, the nonlinear crystal includes a periodically poled potassium titanium oxygen phosphate crystal.
According to embodiments of the present disclosure, a nonlinear crystal satisfies collinear type II phase matching at a selected pump light wavelength.
According to the embodiment of the disclosure, the wedge-shaped phase adjuster is arranged 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 micrometers.
A second aspect of the present disclosure provides a quantum-enhanced phase measurement method based on stimulated parametric down-conversion, including: the laser light source provides initial pump light; the nonlinear crystal performs first stimulated parametric down-conversion on initial pump light from a laser light source to obtain first parametric light and first pump light, and performs second stimulated parametric down-conversion on the first parametric light and the first pump light from the concave reflector to obtain second parametric light and second pump light; the concave reflector reflects the first parametric light and the first pump light from the nonlinear crystal to the 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 reflecting mirror back to the concave reflecting mirror; the wedge-shaped phase adjuster adjusts the phase between the first pump light and the first parametric light from the concave reflector; and the single-photon detector performs single-photon threshold detection on the second parameter light from the nonlinear crystal.
The measuring device based on the conversion under the stimulated parameter can achieve the phase measurement of the Heisebarg limit in principle, and has high tolerance to external loss, namely loss outside the measuring device, such as detector and line loss. In addition, the invention has simple structure, thus being easy to integrate and expand.
Drawings
FIG. 1 schematically illustrates a schematic view of a measurement device based on stimulated parametric down-conversion according to one embodiment of the present disclosure;
fig. 2 schematically shows a schematic view of a measurement device based on stimulated parametric down-conversion according to another embodiment of the present disclosure.
Detailed Description
For the purpose of promoting a better understanding of the objects, aspects and advantages of the present disclosure, reference is made to the following detailed description taken in conjunction with the accompanying drawings.
According to a first aspect of the present disclosure, there is provided a measurement device based on stimulated parametric down-conversion, comprising: a laser light source for providing initial pump light; the nonlinear crystal is used for performing first stimulated parametric down-conversion on initial pump light from the laser light source to obtain first parametric light and first pump light, and performing second stimulated parametric down-conversion on the first parametric light and the first pump light from the concave reflector to obtain second parametric light and second pump light; the concave reflector is used for reflecting the first parametric light and the first pump light from the nonlinear crystal to the 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 mirror back to the concave mirror; a wedge-shaped phase adjuster for adjusting a phase between the first pump light from the concave reflecting mirror and the first parametric light; and the single-photon detector is used for carrying out single-photon threshold detection on the second parameter light from the nonlinear crystal.
According to an embodiment of the present disclosure, includes: the concave reflector and the plane mirror form an optical 4f system, and the distance between the concave reflector and the plane mirror is one time of the focal length of the concave reflector; the distance between the concave mirror and the nonlinear crystal is one focal length of the concave mirror.
According to an embodiment of the present disclosure, includes: the laser light source is configured such that a light source port of the laser light source is directed toward the nonlinear crystal such that initial pump light from the laser light source is incident perpendicularly to the nonlinear crystal.
According to an embodiment of the present disclosure, further comprising: the dichroic mirror is used for separating second pump light and second parameter light generated by conversion under second excited parameters of the nonlinear crystal; and the beam splitter is used for separating the second parametric light with different polarization modes from the dichroic mirror.
According to an embodiment of the present disclosure, further comprising: the first focusing lens is arranged between the laser light source and the nonlinear crystal and used for focusing initial pump light from the laser light source; and the second focusing lens is arranged between the beam splitter and the dichroic mirror and used for collimating the second parameter light from the dichroic mirror.
According to an embodiment of the present disclosure, further comprising: and the lambda/4 wave plate is arranged between the concave reflecting mirror and the plane mirror and is used for ensuring that the spectrum decorrelation is not influenced in the conversion process under the excited parameters.
According to an embodiment of the present disclosure, the nonlinear crystal includes a periodically poled potassium titanium oxygen phosphate crystal.
According to embodiments of the present disclosure, a nonlinear crystal satisfies collinear type II phase matching at a selected pump light wavelength.
According to the embodiment of the disclosure, the wedge-shaped phase adjuster is arranged 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 micrometers.
A second aspect of the present disclosure provides a quantum-enhanced phase measurement method based on stimulated parametric down-conversion, including: the laser light source provides initial pump light; the nonlinear crystal performs first stimulated parametric down-conversion on initial pump light from a laser light source to obtain first parametric light and first pump light, and performs second stimulated parametric down-conversion on the first parametric light and the first pump light from the concave reflector to obtain second parametric light and second pump light; the concave reflector reflects the first parametric light and the first pump light from the nonlinear crystal to the 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 reflecting mirror back to the concave reflecting mirror; the wedge-shaped phase adjuster adjusts the phase between the first pump light and the first parametric light from the concave reflector; and the single-photon detector performs single-photon threshold detection on the second parameter light from the nonlinear crystal.
Fig. 1 schematically shows a schematic view of a measuring device based on stimulated parametric down-conversion according to an embodiment of the invention.
As shown in fig. 1, the measuring device includes a laser light source 1, a nonlinear crystal 4, a concave mirror 5, a wedge-shaped phase adjuster 6, a plane mirror 8 and a single photon detector 11.
According to the embodiment of the present disclosure, the laser light source 1 may adopt a femtosecond pulse laser, and the femtosecond pulse laser generated by the laser light source 1 is used as the initial pump light, and the polarization direction of the initial pump light is horizontally polarized. The wavelength range of the pulse laser generated by the laser source 1 is 760-790nm, and the line width is 2-10 nm.
The nonlinear crystal 4 can perform first stimulated parametric down-conversion on the initial pump light provided by the laser light source 1 to generate first parametric light and first pump light. The initial pump light is converted under the excited parameter of the nonlinear crystal 4 to obtain first parametric light and 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 small. The nonlinear crystal 4 may also perform a second stimulated parametric down-conversion on the first parametric light and the first pump light from the concave mirror 5, and convert the first pump light and the first parametric light into second parametric light and second pump light. The first parametric light can be enhanced by the conversion process of the second stimulated parameter of the nonlinear crystal 4, and second parametric light can be obtained.
According to the embodiment of the present disclosure, a temperature control device is disposed outside the nonlinear crystal 4 to keep the temperature of the nonlinear crystal 4 stable and reduce the parametric optical wavelength shift caused by temperature change. Two end faces of the nonlinear crystal facing the laser light source 1 and the concave reflector 5 are provided with antireflection films aiming at pump light and parameter light wave bands.
The concave mirror 5 is located behind the nonlinear crystal 4, and can reflect the first pump light and the first parametric light from the nonlinear crystal 4 to the plane mirror 8. After receiving the first parametric light and the first pump light from the concave mirror 5, the plane mirror 8 reflects the first parametric light and the first pump light to the concave mirror 5 along the original optical path, and then the concave mirror 5 reflects the first parametric light and the first pump light to the nonlinear crystal 4. The process that the first pump light and the first parameter light return to the nonlinear crystal 4 from the nonlinear crystal through the concave reflector and the plane mirror can be accurately adjusted through the concave reflector and the plane mirror, and the accuracy of the measuring device provided by the disclosure is guaranteed.
The wedge-shaped phase adjuster 6 can adjust the phase between the first pump light from the concave reflecting mirror 5 and the first parametric light. By moving the wedge-shaped phase adjuster 6 up and down, the optical paths of the first pump light and the first parametric light through the wedge-shaped phase adjuster 6 gradually change, and the relative phase is the measured phase. The first pump light and the first parametric light are reflected from the plane mirror 8 back to the concave reflecting mirror 5 and also pass through the wedge-shaped phase adjuster 6.
According to an embodiment of the present disclosure, the wedge-shaped phase adjuster 6 is disposed between the concave mirror 5 and the plane mirror 8. The wedge phase adjuster consists of a K9 glass plate with a wedge-shaped cross section, the thickness of which varies from top to bottom to 200 μm.
The single photon detector 11 can perform single photon threshold detection on the second parametric light from the nonlinear crystal 4.
The measuring device based on the conversion under the stimulated parameter adjusts the phase to be measured through the wedge-shaped phase adjuster, single-photon threshold detection is carried out through the single-photon detector, and the phase measured through the measuring device can reach the Heisebarg limit in principle. Meanwhile, the measuring device has high tolerance to loss outside the measuring device, such as detector and line loss. In addition, the measuring device based on the conversion under the stimulated parameter provided by the disclosure has a simple structure and is easy to integrate and expand.
According to the embodiment of the present disclosure, as shown in fig. 1, the concave mirror 5 and the plane mirror 8 constitute an optical 4f system, the distance between the concave mirror 5 and the plane mirror 8 is equal to one focal length of the concave mirror 5, and the distance between the concave mirror 8 and the nonlinear crystal 4 is also equal to one focal length of the concave mirror 5. By relating to the distances between the concave reflector, the plane mirror and the nonlinear crystal, the first parametric light and the first pumping light generated by the nonlinear crystal can be focused on the same position of the nonlinear crystal again after being reflected by the concave reflector and the plane mirror, and the spatial mode matching of the parametric light is ensured to be good.
According to the embodiment of the present disclosure, as shown in fig. 1, the light source port of the laser light source 1 is directed toward the nonlinear crystal, so that the initial pump light generated by the laser light source 1 is perpendicularly incident into the nonlinear crystal.
According to an embodiment of the present disclosure, the nonlinear crystal includes a periodically poled potassium titanyl phosphate crystal (PPKTP).
According to embodiments of the present disclosure, a nonlinear crystal satisfies collinear type II phase matching at a selected pump light wavelength. The nonlinear crystal is designed to be associated spectrum decorrelation, and the PPKTP crystal is adopted, so that collinear II-type phase matching is met, and the photon pair generated in the conversion process under the excited parameter of the nonlinear crystal is guaranteed to have high purity, namely isotropy.
According to an embodiment of the present disclosure, as shown in fig. 1, the measurement device further comprises a dichroic mirror 3. The dichroic mirror 3 is arranged between the laser light source 1 and the nonlinear crystal 4, and has an included angle of 45 degrees with the horizontal direction, and is used for separating second pump light and second parameter light generated by conversion under second excited parameters from the nonlinear crystal 4. The dichroic mirror 3 is coated to completely transmit the second pump light incident at 45 degrees and completely reflect the second parameter light incident at 45 degrees. Specifically, after 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 parameter light generated by the second time of the down-conversion of the excited parameter from the nonlinear crystal 4 are incident to the dichroic mirror 3 at 45 degrees, and the dichroic mirror 3 can completely reflect the second parameter light and completely transmit the second pump light.
The dichroic mirror 3 may reflect the second parametric light completely onto the beam splitter 10. The second parametric light includes parametric light of a horizontal polarization mode and parametric light of a vertical polarization mode. The beam splitter 10 can separate the parametric light of the horizontal polarization direction and the parametric light of the vertical polarization direction.
According to an embodiment of the present disclosure, the beam splitter comprises a polarizing beam splitter.
According to an embodiment of the present disclosure, as shown in fig. 1, the measurement apparatus 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 to 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 input to the beam splitter 10.
Fig. 2 schematically shows a schematic view of a measuring device based on stimulated parametric down-conversion according to another embodiment of the invention.
According to the embodiment of the present disclosure, as shown in fig. 2, a third focusing lens 12, a fourth focusing lens 13 and a single mode 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 fiber 14 and the beam splitter 10, and can focus the second parametric light with the horizontal polarization direction and the second parametric light with the vertical polarization direction, which are separated by the beam splitter 10, onto the single-mode fiber 14. The single-mode fiber 14 is connected to the single-photon detector 11, and sends 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.
According to an embodiment of the present disclosure, as shown in fig. 1, the measurement device further comprises a λ/4 plate 7, the λ/4 plate 7 being designed for parametric light wavelengths. The lambda/4 wave plate 7 is arranged between the concave reflecting mirror 5 and the plane mirror 8 and used for ensuring that the spectrum disassociation is not influenced in the conversion process under the excited parameters. The first pump light and the first parametric light pass through the lambda/4 wave plate 7 twice, the concave reflector 5 reflects the first pump light and the first parametric light to the plane mirror 8, and the first pump light and the first parametric light pass through the lambda/4 wave plate 7; the plane mirror 8 reflects the first pump light and the first parametric light back to the concave mirror 5, passing through the λ/4 plate 7. The first pump light and the first parametric light pass through the lambda/4 wave plate 7 twice, the parametric light in the horizontal polarization direction and the parametric light in the vertical polarization direction in the first parametric light are exchanged, and the polarization direction of the first pump light is unchanged. The lambda/4 wave plate ensures that the conversion process under the excited parameter does not influence the spectrum decorrelation.
According to the embodiment of the disclosure, quantum-enhanced phase measurement can be performed by using a measurement device based on stimulated parametric down-conversion. As shown in fig. 1, a laser light source 1 provides pulsed initial pump light, and the initial pump light passes through a nonlinear crystal 4 and is converted into first pump light and first parametric light through a first stimulated parametric down-conversion process. The first pump light and the first parametric light are reflected to the plane mirror 8 by the concave mirror 5, and then reflected to the concave mirror 5 by the plane mirror 8, and pass through the wedge-shaped phase adjuster twice. The first pump light and the first parametric light are reflected to the plane mirror 8 by the concave reflecting mirror 5 and pass through the wedge-shaped phase adjuster for the first time, and the wedge-shaped phase adjuster can adjust the phase between the first pump light and the first parametric light, namely the phase to be measured. The first pump light and the first parameter light are reflected to the concave reflecting mirror 5 by the plane mirror 8 and then reflected to the nonlinear crystal 4 by the concave reflecting mirror 5; through the second stimulated parametric down-conversion process of the nonlinear crystal 4, the first pump light and the first parametric light are converted into second pump light and second parametric light, and the second parametric light is further subjected to quantum phase enhancement compared with the first parametric light. And the single-photon detector 11 performs single-photon threshold detection on the second parameter light to obtain a phase to be detected.
The present disclosure provides a measuring device based on the conversion under the stimulated parameter, under the condition that each element is ideal, the measurement standard deviation of the phase to be measured can reach the heisenberg limit. Meanwhile, even if certain photon loss exists in the optical fiber collection process and the single photon detector process, only one constant factor reduction is brought to the measurement precision in principle, and the Heisenberg limit is still met in a gradual sense. The specific theory is verified as follows.
The parametric down-conversion process mathematically corresponds to a single mode or dual mode compression operation, taking dual mode compression operation as an example. Through a first stimulated parameter down-conversion process, namely first double-mode compression, a compressed light field in a double-mode compressed vacuum state is generated firstly. The concave reflector reflects the compressed light field from the nonlinear crystal to the plane mirror, the compressed light field generates the change of phase phi through the wedge-shaped phase adjuster, namely the phase to be measured, and the plane mirror returns the original path of the compressed light field to the concave reflector and the nonlinear crystal. After the compressed light field enters the nonlinear crystal, the compressed light field is subjected to a second stimulated parameter down-conversion process, namely, a second double-mode compression, so that a double-mode light field after two times of compression is generated. The beam splitter separates two polarization modes of the double-mode light field after the two times of compression, and the two polarization modes are sent to the single-photon threshold detector to measure the coincidence of a single path and two modes. The expression of the final output state satisfies formula (1):
wherein
For a bi-modal compression operator, for the amount of compression,
is a phase shift operator. When the threshold detection is carried out on the output state, the Fisher information quantity (Fisher information quantity) of single measurement meets the formula (2):
wherein the result i represents that the detection result of the 1 st detector is i, and the result j represents that the detection result of the 2 nd detector is j, pijIndicating the probability of occurrence of the result ij.
There are 4 possible results {00, 01, 10, 11}, with a detection result of 0 indicating no response of the detector and a result of 1 indicating a response of the detector. Through direct calculation, the maximum value of Fisher information quantity is Fmax＝16sinh2(2r) and the average number of photons passing through the sample is
Since the compressed optical field passes through the nonlinear crystal twice, the optimal phase sensitivity satisfies:
from the above formula, the optimal phase sensitivity reaches the heisenberg limit.
When there is an external photon loss in the measurement device, the optimal phase sensitivity at this time satisfies equation (4):
wherein eta is the product of the stimulated parametric light collection efficiency and the single photon detector efficiency.
As can be seen from the formula (4), when the external loss is fixed, the photon loss only brings a reduction of a constant factor to the measurement precision, and the Heisenberg limit is still met in a gradual sense.
In summary, the present disclosure provides a measurement apparatus based on stimulated parameter down-conversion, and under the ideal condition of each element, the measurement standard deviation of the phase to be measured can reach the heisenberg limit. Meanwhile, even if certain photon loss exists in the optical fiber collection process and the single photon detector process, only one constant factor reduction is brought to the measurement precision in principle, and the Heisenberg limit is still met in a gradual sense.
The above-mentioned embodiments are intended to illustrate the objects, aspects and advantages of the present disclosure in further detail, and it should be understood that the above-mentioned embodiments are only illustrative of the present disclosure and are not intended to limit the present disclosure, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present disclosure should be included in the scope of the present disclosure.
Claims (10)
1. A measurement device based on stimulated parametric down-conversion, comprising:
a laser light source for providing initial pump light;
the nonlinear crystal is used for performing first stimulated parametric down-conversion on the initial pump light from the laser light source to obtain first parametric light and first pump light, and performing second stimulated parametric down-conversion on the first parametric light and the first pump light from the concave reflector to obtain second parametric light and second pump light;
the concave reflector is used for reflecting the first parametric light and the first pump light from the nonlinear crystal to the 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 mirror back to the concave mirror;
a wedge-shaped phase adjuster for adjusting a phase between the first pump light from the concave reflecting mirror and the first parametric light; and
and the single-photon detector is used for carrying out single-photon threshold detection on the second parameter light from the nonlinear crystal.
2. The measurement device of claim 1, comprising:
the concave reflecting mirror and the plane mirror form an optical 4f system, and the distance between the concave reflecting mirror and the plane mirror is one time of the focal length of the concave reflecting mirror;
the distance between the concave reflector and the nonlinear crystal is one time of the focal length of the concave reflector.
3. The measurement device of claim 1, comprising:
the laser light source is configured such that a light source port of the laser light source faces the nonlinear crystal such that initial pump light from the laser light source is incident perpendicularly to the nonlinear crystal.
4. The measurement device of claim 1, further comprising:
the dichroic mirror is used for separating second pump light and second parameter light generated by the second time of excited parameter down-conversion of the nonlinear crystal;
and the beam splitter is used for separating second parametric light with different polarization modes from the dichroic mirror.
5. The measurement device of claim 4, further comprising:
a first focusing lens disposed between the laser light source and the nonlinear crystal for focusing an initial pump light from the laser light source; and
and the second focusing lens is arranged between the beam splitter and the dichroic mirror and is used for collimating the second parameter light from the dichroic mirror.
6. The measurement device of claim 1, further comprising:
and the lambda/4 wave plate is arranged between the concave reflecting mirror and the plane mirror and is used for ensuring that the spectrum decorrelation is not influenced in the conversion process under the excited parameter.
7. The measurement device of claim 1, the nonlinear crystal comprising a periodically poled potassium titanium oxygen phosphate crystal.
8. The measurement device of claim 1, said nonlinear crystal satisfying collinear type ii phase matching at a selected pump light wavelength.
9. The measurement apparatus as set forth in claim 1, wherein the wedge-shaped phase adjuster is disposed between the concave reflecting mirror and the plane mirror, and the wedge-shaped phase adjuster has a wedge-shaped cross section and a thickness variation of 200 μm.
10. A quantum enhanced phase measurement method based on stimulated parametric down-conversion comprises the following steps:
the laser light source provides initial pump light;
the nonlinear crystal performs first stimulated parametric down-conversion on the initial pump light from the laser light source to obtain first parametric light and first pump light, and performs second stimulated parametric down-conversion on the first parametric light and the first pump light from the concave reflector to obtain second parametric light and second pump light;
the concave reflector reflects the first parametric light and the first pump light from the nonlinear crystal to the 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 reflecting mirror back to the concave reflecting mirror;
a wedge-shaped phase adjuster adjusts a phase between the first pump light and the first parametric light from the concave reflecting mirror; and
and the single-photon detector performs single-photon threshold detection on the second parameter light from the nonlinear crystal.
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