Quantum interferometer capable of simultaneously amplifying signal and reducing noise

Abstract

The invention discloses a quantum interferometer capable of simultaneously amplifying signals and reducing noise. The quantum interferometer comprises a light source, a first non-degenerate optical parameter amplifier, a second non-degenerate optical parameter amplifier, a first degenerate optical parameter amplifier, a second degenerate optical parameter amplifier, a phase sensor and a measuring system. Two beams of polarized light which is vertical to each other are injected into the interferometer by the first non-degenerate optical parametric amplifier and have quantum correlation characteristics; the quantum characteristics of the two light fields are further improved through the first degenerate optical parameter amplifier and the second degenerate optical parameter amplifier respectively, one light field is interfered in the second non-degenerate optical parameter amplifier after being subjected to phase shift by a physical quantity to be measured, and an orthogonal component of the output light field contains a relative phase difference signal introduced by the physical quantity to be measured. The non-degenerate optical parametric amplifier and the degenerate optical parametric amplifier are cascaded, deterministic amplification of a measured signal in the interferometer and noise reduction of a detection light field are achieved at the same time, ultra-high-sensitivity phase measurement can be achieved, and important application value is achieved.

Description

Technical Field

[0001] The present invention relates to the field of quantum precision measurement technology, and particularly relates to a quantum interferometer that can simultaneously amplify signals and reduce noise. Background Art

[0002] Metrology is the foundation of quantitative science, helping humans to detect substances more accurately, obtain more comprehensive unknown information, and deepen the understanding of space and time. Optical interferometers can detect information comprehensively, with high precision, and can detect at a long distance. Moreover, their phase is very sensitive to many physical quantities (such as biological tissues, gravitational waves, displacement, etc.) that can affect the optical path, making them one of the important measurement tools. However, the ultimate sensitivity of the interferometer is limited by the shot noise limit determined by the vacuum fluctuations of the electromagnetic field. Being able to sensitively measure weak signals submerged in the shot noise limit is one of the current research hotspots and is extremely challenging.

[0003] Quantum interferometers can utilize quantum resources to improve the sensitivity of the interferometer for measuring phase, can overcome the influence of the shot noise limit, and can even achieve the measurement of weak phase changes beyond the standard quantum noise limit. Filling the idle ports of the interferometer with quantum states can enable the detection noise to break through the shot noise limit. Using quantum devices to expand the configuration of the interferometer and constructing an interferometer with a new structure can improve the phase measurement sensitivity of the interferometer and achieve higher-precision detection. A series of studies on new-structure quantum interferometers have been carried out. In 2020, the research group of Peng Kunchi at Shanxi University used an optical parametric amplifier to expand the configuration of a Mach-Zehnder interferometer and achieved phase measurement that breaks through the shot noise limit, and published a journal paper titled "Quantum Interferometer Combining Squeezing and Parametric Amplification" in Physical Review Letters 124, 173602.

[0004] The above research work has realized a quantum interferometer based on an optical parametric amplifier, solving the problem of breaking through the standard quantum limit of an optical interferometer. However, it has not achieved the amplification of the measured signal. When increasing the sensitivity by increasing the injection power, it will increase the reaction force noise caused by the radiation pressure on the transmission mirror, reducing the detection sensitivity. Summary of the Invention

[0005] In view of this, in order to solve the problem in the prior art that the noise cannot be made lower than the shot noise limit while amplifying the signal to be measured, the present invention proposes a quantum interferometer that can simultaneously amplify the signal and reduce the noise. By cascading non-degenerate and degenerate optical parametric amplifiers, the present invention simultaneously realizes the deterministic amplification of the signal to be measured in the interferometer and the reduction of the phase-sensitive optical field noise in detection, and can achieve ultra-high-sensitivity phase measurement; this quantum interferometer has good reliability, high sensitivity, and is easy to implement.

[0006] The present invention solves the above problems through the following technical means:

[0007] The present invention provides a quantum interferometer that can simultaneously amplify the signal and reduce the noise, including a light source, a first optical frequency doubler, a second optical frequency doubler, a first non-degenerate optical parametric amplifier, a second non-degenerate optical parametric amplifier, a first degenerate optical parametric amplifier, a second degenerate optical parametric amplifier, a phase sensor, and a measurement system;

[0008] The light source outputs three probe optical fields a S1 、a S2 、a S3 and a local oscillator optical field a L ; the probe optical fields a S1 、a S3 output by the light source are respectively connected to the input ends of the first optical frequency doubler and the second optical frequency doubler in one-to-one correspondence; the probe optical field a S2 output by the light source is connected to the input end of the first non-degenerate optical parametric amplifier;

[0009] The output end of the first non-degenerate optical parametric amplifier is respectively connected to the signal optical field input ends of the first degenerate optical parametric amplifier and the second degenerate optical parametric amplifier. The phase-sensitive optical field output by the second degenerate optical parametric amplifier is connected to the input end of the phase sensor. The phase sensor is used to perform a phase shift on the phase-sensitive optical field output by the second degenerate optical parametric amplifier according to the physical quantity to be measured. The phase-sensitive optical field output by the second degenerate optical parametric amplifier passes through the phase sensor and then is injected into the input end of the second non-degenerate optical parametric amplifier together with the output optical field of the first degenerate optical parametric amplifier, and interference occurs therein; the output optical field of the second non-degenerate optical parametric amplifier and the local oscillator optical field a L of the light source are injected into the input end of the measurement system together;

[0010] The pump optical fields a P1 and a P2 output by the first optical frequency doubler are respectively connected to the pump optical field input ends of the first non-degenerate optical parametric amplifier and the first degenerate optical parametric amplifier in one-to-one correspondence. The pump optical fields a P3 and a P4They are respectively and correspondingly connected to the pump light field input ends of the second degenerate optical parametric amplifier and the second non-degenerate optical parametric amplifier to provide pump light fields for them.

[0011] Preferably, the first non-degenerate optical parametric amplifier and the second non-degenerate optical parametric amplifier have the same structure; the first degenerate optical parametric amplifier and the second degenerate optical parametric amplifier have the same structure.

[0012] Preferably, the first non-degenerate optical parametric amplifier includes a first optical resonator, a wedge-shaped nonlinear crystal, and a temperature-controlled displacement system;

[0013] The first optical resonator includes a first plano-concave mirror, a second plano-concave mirror, and a first piezoelectric ceramic; wherein the first plano-concave mirror and the second plano-concave mirror form a two-mirror cavity structure; the first piezoelectric ceramic is fixed on the second plano-concave mirror;

[0014] The probe light field as of the light source 2 and the pump light field ap output by the first optical frequency doubler 1 both enter the first non-degenerate optical parametric amplifier from the first plano-concave mirror. The difference is that the probe light field exits from the second plano-concave mirror after passing through the wedge-shaped nonlinear crystal, and the pump light field exits from the first plano-concave mirror after being reflected by the second plano-concave mirror after passing through the wedge-shaped nonlinear crystal;

[0015] The first plano-concave mirror serves as an input mirror, with a high-reflection film deposited on it for the probe light field and a transmittance for the pump light field; the second plano-concave mirror has a transmittance for the probe light field and a high-reflection film deposited on it for the pump light field, enabling both the pump light field and the probe light field to resonate in the cavity;

[0016] The temperature-controlled displacement system is used to precisely control the temperature of the wedge-shaped nonlinear crystal by heating, and to translate the wedge-shaped nonlinear crystal along the direction perpendicular to the light propagation direction so that the pump light field and the probe light field can be precisely matched.

[0017] Preferably, the transmittance of the first plano-concave mirror for the pump light field is 10%; the transmittance of the second plano-concave mirror for the probe light field is 5%.

[0018] Preferably, the temperature-controlled displacement system includes a first copper furnace, a first temperature control instrument, and a two-dimensional micro translation stage. The first copper furnace is used to heat the wedge-shaped nonlinear crystal, the first temperature control instrument is used to precisely control the temperature, and the two-dimensional micro translation stage is used to translate the wedge-shaped nonlinear crystal along the direction perpendicular to the light propagation direction.

[0019] Preferably, the first degenerate optical parametric amplifier includes a second optical resonator, a nonlinear crystal, and a temperature control system;

[0020] The second optical resonator includes a third plano-concave mirror, a fourth plano-concave mirror, a first plane mirror, a second plane mirror, and a second piezoelectric ceramic. The third plano-concave mirror, the fourth plano-concave mirror, the first plane mirror, and the second plane mirror form a four-mirror eight-shaped ring cavity structure. The second piezoelectric ceramic is fixed on the fourth plano-concave mirror.

[0021] The output optical field of the first non-degenerate optical parametric amplifier is input into the first degenerate optical parametric amplifier from the first plane mirror, and sequentially passes through the second plane mirror, the third plano-concave mirror, the nonlinear crystal, and the fourth plano-concave mirror, and then exits from the first plane mirror. The pump optical field ap output by the first optical frequency doubler 2 passes through the third plano-concave mirror and the nonlinear crystal and exits from the fourth plano-concave mirror.

[0022] The first plane mirror serves as an input / output coupling mirror and has a transmittance for the probe optical field. The second plane mirror is coated with a high-reflection film for the probe optical field. Both the third plano-concave mirror and the fourth plano-concave mirror are coated with a high-reflection film for the probe optical field and an antireflection film for the pump optical field.

[0023] The temperature control system is used to heat the nonlinear crystal and precisely control the temperature.

[0024] Preferably, the transmittance of the first plane mirror for the probe optical field is 5%.

[0025] Preferably, the temperature control system includes a second copper furnace and a second temperature control instrument. The second copper furnace is used to heat the nonlinear crystal, and the second temperature control instrument is used to precisely control the temperature.

[0026] Preferably, the phase sensor includes a third piezoelectric ceramic, a high-reflection mirror, and a high-frequency signal source. The third piezoelectric ceramic is fixed on the back of the high-reflection mirror.

[0027] The output optical field of the second degenerate optical parametric amplifier is injected into the high-reflection mirror. After passing through the third piezoelectric ceramic, it is driven by the high-frequency signal source through an electrical path to generate a small displacement, so as to achieve the purpose of phase-shifting the phase-sensitive optical field output by the second degenerate optical parametric amplifier. The output optical field of the high-reflection mirror and the output optical field of the first degenerate optical parametric amplifier are injected into the second non-degenerate optical parametric amplifier together.

[0028] Preferably, the measurement system includes an optical beam splitter, a first photodetector, a second photodetector, a power subtractor, and a spectrum analyzer.

[0029] The local oscillator optical field a output by the light source LThe output optical signal of the second non-degenerate optical parametric amplifier interferes with that of the first non-degenerate optical parametric amplifier on an optical beam splitter. The interference signals are respectively injected into the input ends of a first photodetector and a second photodetector. The output ends of the first photodetector and the second photodetector are connected to the input end of a power subtractor. The output end of the power subtractor is connected to a spectrum analyzer, which is used to measure and analyze the signal power and noise power of the quadrature component of the output optical signal of the second non-degenerate optical parametric amplifier, so as to obtain a phase signal.

[0030] Compared with the prior art, the beneficial effects of the present invention at least include:

[0031] 1. A half-wave plate is placed in front of the first non-degenerate optical parametric amplifier (NOPA) of the present invention to inject two mutually perpendicular polarized light fields into an interferometer. After passing through the first non-degenerate optical parametric amplifier, a quantum entangled light field is generated. After these two beams of light are separated by the combination of the half-wave plate and the polarization beam splitter PBS and then respectively injected into the first and second degenerate optical parametric amplifiers (DOPAs), the quantum characteristics of the two light fields are further improved, and they are used as the phase-sensitive light fields acting on the signal to be measured inside the interferometer. The phase sensor converts the physical quantity to be measured into the relative phase difference between the two phase-sensitive light fields. Next, the two phase-sensitive light fields interfere in the second non-degenerate optical parametric amplifier, and the quadrature component of the output light field contains the relative phase difference signal introduced by the physical quantity to be measured. Finally, through detection by a balanced homodyne measurement system, the quadrature component of the output light field can be obtained. Since the cascade of degenerate and non-degenerate optical parametric amplifiers is used, not only the signal to be measured is amplified, but also the quantum noise of the phase-sensitive light field is reduced. Without increasing the intensity of the phase-sensitive light field, the phase measurement sensitivity of the interferometer can be improved, and at the same time, weak signals submerged in the shot noise limit can be detected. Therefore, the present invention significantly improves the sensitivity of the interferometer.

[0032] 2. The present invention cascades degenerate and non-degenerate optical parametric amplifiers to construct a new interferometer, realizing precise phase measurement that breaks through the standard quantum limit with high sensitivity. The phase measurement sensitivity is improved compared with the previous invention patent "A Quantum Interferometer Device Based on an Optical Parametric Amplifier" (ZL 202010067366.6) times and compared with the SNL by times.

[0033] 3. The present invention takes advantage of the different advantages of different types of optical parametric amplifiers in an interferometer, cascades degenerate and non-degenerate optical parametric amplifiers to construct a new type of interferometer, and realizes reducing quantum noise while deterministically amplifying the signal to be measured in the interferometer. Only using non-degenerate optical parametric amplifiers to expand the configuration of the interferometer, the obtained interferometer can keep the noise at the SNL level, only amplify the signal, and achieve an improvement in sensitivity, but it cannot detect weak signals submerged in the shot noise limit. Combining degenerate and non-degenerate optical parametric amplifiers not only greatly improves the sensitivity, but also can detect weak signals submerged in the shot noise limit, greatly enhancing the utilization rate of the interferometer under different measurement conditions.

[0034] 4. The present invention also has the advantages of the previous "Quantum Interferometer Device Based on Optical Parametric Amplifier" (ZL202010067366.6). In the presence of noise such as interferometer loss, it can also unconditionally achieve precise phase measurement that breaks through the standard quantum limit. By reducing the quantum noise of the phase-sensitive optical field in the interferometer, the sensitivity of the interferometer can be improved, and a main factor affecting the measurement sensitivity - the quantum noise of the phase-sensitive optical field inside the interferometer - can be solved. On the other hand, the intensity of the phase-sensitive optical field in the interferometer is one of the main factors affecting the measurement sensitivity; increasing the intensity of the phase-sensitive optical field in the interferometer can improve the sensitivity of the interferometer, but a high intensity of the phase-sensitive optical field will increase the radiation pressure on the mirror and cause reaction force noise. The present invention uses cascaded non-degenerate and degenerate optical parametric amplifiers to amplify the signal carried by the phase-sensitive optical field by several times, and it will not be limited by the intensity of the phase-sensitive optical field, so that the sensitivity of the interferometer can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0036] Figure 1 Schematic structural diagram of the quantum interferometer that simultaneously amplifies the signal and reduces noise provided in the embodiment of the present invention;

[0037] Figure 2 Schematic structural diagram of the non-degenerate optical parametric amplifier in the embodiment of the present invention;

[0038] Figure 3 Schematic structural diagram of the degenerate optical parametric amplifier in the embodiment of the present invention;

[0039] Figure 4 Schematic diagram of the phase sensor in the embodiment of the present invention;

[0040] Figure 5 Schematic diagram of the structure of the measurement system in the embodiment of the present invention;

[0041] Figure 6 Result diagram of the device of the present invention, wherein 6(a) is the result of the phase measurement sensitivity of the interferometer, 6(b) is the partial enlarged view of the phase measurement sensitivity of the interferometer, 6(c) is the result of reducing the phase-sensitive optical field intensity noise of the interferometer, and 6(d) is the result of amplifying the measured signal of the interferometer;

[0042] In the figure, 11--light source, 12--first optical frequency doubler, 13--second optical frequency doubling cavity; 21--first non-degenerate optical parametric amplifier, 22--second non-degenerate optical parametric amplifier, 2a--first plano-concave mirror, 2b--second plano-concave mirror, 2c--wedge-shaped nonlinear crystal, 2d--first piezoelectric ceramic; 31--first degenerate optical parametric amplifier, 32--second degenerate optical parametric amplifier, 3a--third plano-concave mirror, 3b--fourth plano-concave mirror, 3c--first plane mirror, 3d--second plane mirror, 3e--second piezoelectric ceramic, 3f--nonlinear crystal; 4--phase sensor; 4a--signal generator, 4b--third piezoelectric ceramic, 4c--high-reflection mirror; 5--measurement system, 5a--50:50 optical beam splitter, 5b--first photodetector, 5c--second photodetector, 5d--power subtractor, 5e--spectrum analyzer. Detailed implementation manners

[0043] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the technical solutions of the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0044] The terms "first", "second", and "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first", "second", and "third" may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a group" is two or more.

[0045] Such as Figure 1As shown in the figure, an embodiment of the present invention provides a quantum interferometer that simultaneously amplifies signals and reduces noise, including a light source 11, a first optical frequency doubler 12, a second optical frequency doubler 13, a first non-degenerate optical parametric amplifier 21, a second non-degenerate optical parametric amplifier 22, a first degenerate optical parametric amplifier 31, a second degenerate optical parametric amplifier 32, a phase sensor 4, and a measurement system 5.

[0046] The light source 11 is used to output three probe optical fields a S1 , a S2 , a S3 and a local oscillator optical field a L ; the probe optical fields a S1 , a S3 output by the light source 11 are respectively connected to the input ends of the first optical frequency doubler 12 and the second optical frequency doubler 13 in one-to-one correspondence; the output end of the first optical frequency doubler 12 outputs pump optical fields a P1 and a P2 , and the output end of the second optical frequency doubler 13 outputs pump optical fields a P3 and a P4 ; the probe optical field a S2 output by the light source 11 is connected to the input end of the first non-degenerate optical parametric amplifier 21. The output end of the first non-degenerate optical parametric amplifier 21 is respectively connected to the signal optical field input ends of the first degenerate optical parametric amplifier 31 and the second degenerate optical parametric amplifier 32. The phase-sensitive optical field output by the second degenerate optical parametric amplifier 32 is connected to the input end of the phase sensor 4. The phase sensor 4 is used to perform a phase shift on the phase-sensitive optical field output by the second degenerate optical parametric amplifier 32 according to the physical quantity to be measured. The phase-sensitive optical field output by the second degenerate optical parametric amplifier 32 is injected into the input end of the second non-degenerate optical parametric amplifier 22 together with the output optical field of the first degenerate optical parametric amplifier 31 after passing through the phase sensor 4, and interference occurs therein; the output optical field of the second non-degenerate optical parametric amplifier 22 and the local oscillator optical field a L of the light source 11 are injected into the input end of the measurement system 5 together.

[0047] The pump optical fields a P1 and the pump optical field a P2 output by the first optical frequency doubler 12 are respectively connected to the pump optical field input ends of the first non-degenerate optical parametric amplifier 21 and the first degenerate optical parametric amplifier 31 in one-to-one correspondence. The pump optical fields a P3 and the pump optical field a P4 output by the second optical frequency doubler 13 are respectively connected to the pump optical field input ends of the second degenerate optical parametric amplifier 32 and the second non-degenerate optical parametric amplifier 22 in one-to-one correspondence, providing pump optical fields for them.

[0048] Among them, the phase sensor 4 is a device that converts the physical quantity to be measured into the relative phase difference of two beams of phase-sensitive optical fields. For example, a piezoelectric ceramic can be used as a phase sensor to convert the displacement into a phase.

[0049] As Figure 2 shown, in this embodiment, the first non-degenerate optical parametric amplifier 21 includes a first optical resonator, a wedge-shaped nonlinear crystal 2c, and a temperature-controlled displacement system.

[0050] The first optical resonator includes two plano-concave mirrors - a first plano-concave mirror 2a, a second plano-concave mirror 2b, and a first piezoelectric ceramic 2d. Among them, the first plano-concave mirror 2a and the second plano-concave mirror 2b form a two-mirror cavity structure, and the first piezoelectric ceramic 2d is fixed on the second plano-concave mirror 2b.

[0051] The probe optical field as 2 of the light source 11 1 and the pump optical field ap output by the first optical frequency doubler 12

[0052] both enter the first non-degenerate optical parametric amplifier 21 from the first plano-concave mirror 2a. The difference is that the probe optical field exits from the second plano-concave mirror 2b after passing through the wedge-shaped nonlinear crystal 2c, and the pump optical field is reflected by the second plano-concave mirror 2b and exits from the first plano-concave mirror 2a after passing through the wedge-shaped nonlinear crystal 2c.

[0053] The temperature-controlled displacement system is used to precisely control the temperature of the wedge-shaped nonlinear crystal 2c by heating, and can translate the wedge-shaped nonlinear crystal 2c along the direction perpendicular to the light propagation direction so that the pump optical field and the probe optical field can be precisely matched.

[0054] Specifically, the temperature-controlled displacement system includes a first copper furnace, a first temperature control instrument, and a two-dimensional micro translation stage. The first copper furnace is used to heat the wedge-shaped nonlinear crystal 2c, the first temperature control instrument is used for precise temperature control, and the two-dimensional micro translation stage is used to translate the wedge-shaped nonlinear crystal 2c along the direction perpendicular to the light propagation direction.

[0055] In addition, in this embodiment, the structure of the second non-degenerate optical parametric amplifier 22 is the same as that of the first non-degenerate optical parametric amplifier 21.

[0056] As Figure 3 shown, the first degenerate optical parametric amplifier 31 includes a second optical resonator, a nonlinear crystal 3f, and a temperature control system.

[0057] The second optical resonator includes two plano-concave mirrors, i.e., the third plano-concave mirror 3a and the fourth plano-concave mirror 3b, two plane mirrors, i.e., the first plane mirror 3c and the second plane mirror 3d, and a second piezoelectric ceramic 3e. Among them, the third plano-concave mirror 3a, the fourth plano-concave mirror 3b, the first plane mirror 3c, and the second plane mirror 3d form a four-mirror eight-shaped ring cavity structure; the second piezoelectric ceramic 3e is fixed on the fourth plano-concave mirror 3b.

[0058] The output optical field of the first non-degenerate optical parametric amplifier 21 is input into the first degenerate optical parametric amplifier 31 from the first plane mirror 3c, and successively passes through the second plane mirror 3d, the third plano-concave mirror 3a, the nonlinear crystal 3f, and the fourth plano-concave mirror 3b and then exits from the first plane mirror 3c; the pump optical field ap output by the optical frequency doubler 12 2 passes through the third plano-concave mirror 3a and the nonlinear crystal 3f and exits from the fourth plano-concave mirror 3b.

[0059] The first plane mirror 3c serves as an input / output coupling mirror, and its transmittance for the probe optical field is 5%. The second plane mirror 3d is coated with a high-reflection film for the probe optical field. Both the third plano-concave mirror 3a and the fourth plano-concave mirror 3b are coated with high-reflection films for the probe optical field and anti-reflection films for the pump optical field.

[0060] The temperature control system is used to heat the nonlinear crystal 3f and precisely control the temperature.

[0061] Specifically, the temperature control system includes a second copper furnace and a second temperature control instrument. The second copper furnace is used to heat the nonlinear crystal 3f, and the second temperature control instrument is used to precisely control the temperature.

[0062] In addition, in this embodiment, the structure of the first degenerate optical parametric amplifier 32 is the same as that of the second degenerate optical parametric amplifier 31.

[0063] As Figure 4 shown, in this embodiment, the phase sensor 4 includes a third piezoelectric ceramic 4b, a high-reflection mirror 4c, and a high-frequency signal source 4a; and the third piezoelectric ceramic 4b is fixed on the back of the high-reflection mirror 4c;

[0064] The optical field at the output end of the second degenerate optical parametric amplifier 32 is injected into the high-reflection mirror 4c. After passing through the third piezoelectric ceramic 4b, it is driven by the high-frequency signal source 4a through an electrical path to generate a small displacement, so as to achieve the purpose of phase-shifting the phase-sensitive optical field output by the second degenerate optical parametric amplifier 32. The output optical field of the high-reflection mirror 4c and the output optical field of the first degenerate optical parametric amplifier 31 are injected into the second non-degenerate optical parametric amplifier 22 together.

[0065] As Figure 5As shown, in this embodiment, the measurement system 5 includes a 50:50 optical beam splitter 5a, a first photodetector 5b, a second photodetector 5c, a power subtractor 5d, and a spectrum analyzer 5e.

[0066] The local oscillator optical field a output by the light source 11 L and the output optical signal of the non-degenerate optical parametric amplifier 22 interfere on the 50:50 optical beam splitter 5a. The interference signals are respectively injected into the input ends of the first photodetector 5b and the second photodetector 5c. The output ends of the first photodetector 5b and the second photodetector 5c are connected to the input end of the power subtractor 5d. The output end of the power subtractor 5d is connected to the spectrum analyzer 5e. The spectrum analyzer 5e is used to measure and analyze the signal power and noise power of the quadrature component of the output optical signal of the non-degenerate optical parametric amplifier 22, and then obtain the phase signal.

[0067] The working principle of the present invention is as follows: A half-wave plate is placed in front of the first non-degenerate optical parametric amplifier to inject two mutually perpendicular polarized optical fields into the interferometer. After passing through the first non-degenerate optical parametric amplifier, a quantum entangled optical field is generated. These two beams of light are separated by the combination of a half-wave plate and a polarization beam splitter PBS and then injected into the first and second degenerate optical parametric amplifiers respectively to further enhance the quantum characteristics of the two optical fields, and they are used as the phase-sensitive optical fields acting on the measured signal inside the interferometer. The phase sensor converts the physical quantity to be measured into the relative phase difference between the two phase-sensitive optical fields. Next, the two phase-sensitive optical fields interfere in the second non-degenerate optical parametric amplifier, and the quadrature component of the output optical field contains the relative phase difference signal introduced by the physical quantity to be measured. Finally, through the balanced homodyne measurement system for detection, the quadrature component of the output optical field can be obtained. Due to the use of cascaded degenerate and non-degenerate optical parametric amplifiers, not only the measured signal is amplified, but also the quantum noise of the phase-sensitive optical field is reduced. Without increasing the intensity of the phase-sensitive optical field, the phase measurement sensitivity of the interferometer can be improved, and at the same time, weak signals submerged in the shot noise limit can be detected. Therefore, the present invention significantly improves the sensitivity of the interferometer.

[0068] As Figure 6As shown, in this embodiment, as shown by the solid lines in 6(a) and 6(b), at the same phase-sensitive optical field intensity, the phase measurement sensitivity of the interferometer exceeds that of "A Quantum Interferometer Device Based on an Optical Parametric Amplifier" (ZL202010067366.6) and can approach the quantum Cramér-Rao bound (QCRB), having good phase measurement capabilities; as shown by the solid line in 6(c), at the same phase-sensitive optical field intensity, by increasing the gain factor of the non-degenerate optical parametric amplifier so that it is much larger than the gain factor of the degenerate optical parametric amplifier, the noise level of the interferometer is lower than that of "A Quantum Interferometer Device Based on an Optical Parametric Amplifier" (ZL202010067366.6); as shown by the solid line in 6(d), at the same phase-sensitive optical field intensity, the signal level of the interferometer is higher than that of "A Quantum Interferometer Device Based on an Optical Parametric Amplifier" (ZL 202010067366.6), and this embodiment is successful and effective.

[0069] The present invention cascades degenerate and non-degenerate optical parametric amplifiers to construct a new interferometer, realizing precise phase measurement with high sensitivity that breaks through the standard quantum limit. The phase measurement sensitivity is increased compared to the previous invention patent "A Quantum Interferometer Device Based on an Optical Parametric Amplifier" (ZL202010067366.6) times, and increased compared to SNL times.

[0070] The present invention utilizes the different advantages of different types of optical parametric amplifiers in the interferometer, cascades degenerate and non-degenerate optical parametric amplifiers to construct a new interferometer, and realizes the reduction of quantum noise while deterministically amplifying the signal to be measured in the interferometer. Only using a non-degenerate optical parametric amplifier to expand the configuration of the interferometer, the resulting interferometer can keep the noise at the SNL level, only amplify the signal, and achieve an increase in sensitivity, but it cannot detect weak signals submerged in the shot noise limit. Combining both degenerate and non-degenerate optical parametric amplifiers not only results in a relatively high increase in sensitivity, but also can detect weak signals submerged in the shot noise limit, greatly enhancing the utilization rate of the interferometer under different measurement conditions.

[0071] The present invention also has the advantages of the previous "Quantum Interferometer Device Based on Optical Parametric Amplifier" (ZL202010067366.6). In the presence of noises such as interferometer losses, unconditional precision phase measurement beyond the standard quantum limit can also be achieved. The sensitivity of the interferometer can be improved by reducing the quantum noise of the phase-sensitive optical field of the interferometer, thereby solving one of the main factors affecting the measurement sensitivity - the quantum noise of the phase-sensitive optical field inside the interferometer. On the other hand, the intensity of the phase-sensitive optical field of the interferometer is one of the main factors affecting the measurement sensitivity; increasing the intensity of the phase-sensitive optical field of the interferometer can improve the interferometer sensitivity, but a high intensity of the phase-sensitive optical field will increase the radiation pressure on the mirror, causing reaction force noise. The present invention uses cascaded non-degenerate and degenerate optical parametric amplifiers to amplify the signal carried by the phase-sensitive optical field by a factor, which is not limited by the intensity of the phase-sensitive optical field, and the improvement of the interferometer sensitivity can be achieved.

[0072] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the present invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A quantum interferometer for simultaneously amplifying signals and reducing noise, characterized in that: It comprises a light source (11), a first optical frequency doubler (12), a second optical frequency doubler (13), a first non-degenerate optical parametric amplifier (21), a second non-degenerate optical parametric amplifier (22), a first degenerate optical parametric amplifier (31), a second degenerate optical parametric amplifier (32), a phase sensor (4) and a measurement system (5); The light source (11) outputs three probe light fields a respectively. S1 、a S2 、a S3 and the local oscillator light field a L ; The probe light field a output by the light source (11) S1 、a S3 The probe light field a output by the light source (11) is connected to the input end of the first optical frequency doubler (12) and the input end of the second optical frequency doubler (13) in a one-to-one correspondence. S2 connected to the input end of the first non-degenerate optical parametric amplifier (21); The output end of the first non-degenerate optical parametric amplifier (21) is respectively connected to the signal light field input ends of the first degenerate optical parametric amplifier (31) and the second degenerate optical parametric amplifier (32); the phase-sensitive light field output by the second degenerate optical parametric amplifier (32) is connected to the input end of the phase sensor (4); the phase sensor (4) is used to phase-shift the phase-sensitive light field output by the second degenerate optical parametric amplifier (32) according to the physical quantity to be measured; the phase-sensitive light field output by the second degenerate optical parametric amplifier (32) passes through the phase sensor (4) and is injected into the input end of the second non-degenerate optical parametric amplifier (22) together with the output light field of the first degenerate optical parametric amplifier (31) to interfere therewith; the output light field of the second non-degenerate optical parametric amplifier (22) and the local oscillator light field a of the light source (11) are mutually coupled; L Injected together into the input end of the measurement system (5); The pump light field a output by the first optical frequency doubler (12) P1 and the pump light field a P2 The pump light field a output by the second optical frequency multiplier (13) is connected to the pump light field input ends of the first non-degenerate optical parametric amplifier (21) and the first degenerate optical parametric amplifier (31) in a one-to-one correspondence. P3 and the pump light field a P4 They are respectively connected to the pump light field input ends of the second degenerate optical parametric amplifier (32) and the second non-degenerate optical parametric amplifier (22) in a one-to-one correspondence to provide them with a pump light field.

2. The quantum interferometer for simultaneously amplifying signals and reducing noise according to claim 1, characterized in that: The first non-degenerate optical parametric amplifier (21) and the second non-degenerate optical parametric amplifier (22) have the same structure; the first degenerate optical parametric amplifier (31) and the second degenerate optical parametric amplifier (32) have the same structure.

3. The quantum interferometer for simultaneously amplifying signals and reducing noise according to claim 1, characterized in that: The first non-degenerate optical parametric amplifier (21) comprises a first optical resonant cavity, a wedge-shaped nonlinear crystal (2c) and a temperature-controlled displacement system; The first optical resonant cavity comprises a first plano-concave mirror (2a), a second plano-concave mirror (2b) and a first piezoelectric ceramic (2d); wherein the first plano-concave mirror (2a) and the second plano-concave mirror (2b) form a two-mirror cavity structure; and the first piezoelectric ceramic (2d) is fixed on the second plano-concave mirror (2b); The probe light field as2 of the light source (11) and the pump light field ap1 output by the first optical frequency doubler (12) are both input into the first non-degenerate optical parametric amplifier (21) from the first plano-concave mirror (2a), the difference being that the probe light field is emitted from the second plano-concave mirror (2b) after passing through the wedge-shaped nonlinear crystal (2c), and the pump light field is emitted from the first plano-concave mirror (2a) after being reflected by the second plano-concave mirror (2b) after passing through the wedge-shaped nonlinear crystal (2c); The first plano-concave mirror (2a) serves as an input mirror, is coated with a high-reflection film for the probe light field, and has transmittance for the pump light field; the second plano-concave mirror (2b) has transmittance for the probe light field, and is coated with a high-reflection film for the pump light field, so that both the pump light field and the probe light field resonate in the cavity; The temperature control displacement system is used to heat the wedge-shaped nonlinear crystal (2c) to precisely control the temperature, and to translate the wedge-shaped nonlinear crystal (2c) perpendicular to the light propagation direction so that the pump light field and the probe light field are precisely matched.

4. The quantum interferometer for simultaneously amplifying signals and reducing noise according to claim 3, characterized in that: The transmittance of the first plano-concave mirror (2a) to the pump light field is 10%; the transmittance of the second plano-concave mirror (2b) to the probe light field is 5%.

5. The quantum interferometer for simultaneously amplifying signals and reducing noise according to claim 3, characterized in that: The temperature control displacement system comprises a first copper furnace, a first temperature control instrument and a two-dimensional micro translation stage, wherein the first copper furnace is used to heat the wedge-shaped nonlinear crystal (2c), the first temperature control instrument is used to accurately control the temperature, and the two-dimensional micro translation stage is used to translate the wedge-shaped nonlinear crystal (2c) in a direction perpendicular to the light propagation direction.

6. The quantum interferometer for simultaneously amplifying signals and reducing noise according to claim 1, characterized in that: The first degenerate optical parametric amplifier (31) comprises a second optical resonant cavity, a nonlinear crystal (3f) and a temperature control system; The second optical resonant cavity comprises a third plano-concave mirror (3a), a fourth plano-concave mirror (3b), a first plane mirror (3c), a second plane mirror (3d) and a second piezoelectric ceramic (3e), wherein the third plano-concave mirror (3a), the fourth plano-concave mirror (3b), the first plane mirror (3c) and the second plane mirror (3d) form a four-mirror figure-eight annular cavity structure; the second piezoelectric ceramic (3e) is fixed on the fourth plano-concave mirror (3b); The output light field of the first non-degenerate optical parametric amplifier (21) is input into the first degenerate optical parametric amplifier (31) from the first plane mirror (3c), and is sequentially transmitted through the second plane mirror (3d), the third plano-concave mirror (3a), the nonlinear crystal (3f), and the fourth plano-concave mirror (3b) before being emitted from the first plane mirror (3c); the pump light field ap2 output by the first optical frequency doubler (12) is transmitted through the third plano-concave mirror (3a) and the nonlinear crystal (3f) and is emitted from the fourth plano-concave mirror (3b); The first plane mirror (3c) serves as an input and output coupling mirror and has transmittance for the probe light field; the second plane mirror (3d) is coated with a high reflection film for the probe light field; the third plane concave mirror (3a) and the fourth plane concave mirror (3b) are both coated with a high reflection film for the probe light field and coated with an anti-reflection film for the pump light field; The temperature control system is used for heating the nonlinear crystal (3f) and controlling the temperature precisely.

7. The quantum interferometer for simultaneously amplifying signals and reducing noise according to claim 6, characterized in that: The transmittance of the first plane mirror (3c) to the probe light field is 5%.

8. The quantum interferometer for simultaneously amplifying signals and reducing noise according to claim 6, characterized in that: The temperature control system comprises a second copper furnace and a second temperature control instrument, wherein the second copper furnace is used for heating the nonlinear crystal (3f), and the second temperature control instrument is used for precise temperature control.

9. The quantum interferometer for simultaneously amplifying signals and reducing noise according to claim 1, characterized in that: The phase sensor (4) comprises a third piezoelectric ceramic (4b), a high-reflection mirror (4c) and a high-frequency signal source (4a); and the third piezoelectric ceramic (4b) is fixed on the back of the high-reflection mirror (4c); The light field at the output end of the second degenerate optical parametric amplifier (32) is injected into a high-reflection mirror (4c), and is driven by a high-frequency signal source (4a) through an electrical path through a third piezoelectric ceramic (4b) to produce a slight displacement, thereby achieving the purpose of performing a phase shift on the phase-sensitive light field output by the second degenerate optical parametric amplifier (32). The output light field of the high-reflection mirror (4c) is injected into a second non-degenerate optical parametric amplifier (22) together with the output light field of the first degenerate optical parametric amplifier (31).

10. The quantum interferometer for simultaneously amplifying signals and reducing noise according to claim 1, characterized in that: The measuring system (5) comprises an optical beam splitter (5a), a first photodetector (5b), a second photodetector (5c), a power subtractor (5d) and a spectrum analyzer (5e); The local oscillator light field a output by the light source (11) L The output optical signal of the first photodetector (5b) and the output optical signal of the second non-degenerate optical parametric amplifier (22) interfere with each other on the optical beam splitter (5a), and the interference signals are respectively injected into the input ends of the first photodetector (5b) and the second photodetector (5c). The output ends of the first photodetector (5b) and the second photodetector (5c) are connected to the input end of a power subtractor (5d), and the output end of the power subtractor (5d) is connected to a spectrum analyzer (5e). The spectrum analyzer (5e) is used to measure and analyze the signal power and noise power of the orthogonal component of the output optical signal of the second non-degenerate optical parametric amplifier (22), thereby obtaining a phase signal.

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