An optical interferometer and phase detection method based on quantum entanglement

Abstract

The present invention discloses an optical interferometer and phase detection method based on quantum entanglement, comprising a dual-beam generation system, a hybrid interferometer, and a detection system, wherein the output end of the dual-beam generation system is respectively connected to the hybrid interferometer and the detection system, and the output end of the hybrid interferometer is connected to the detection system. The dual-beam generation system includes a first four-wave mixer amplifier, the input end of which is incident with coherent light and first vacuum light, and the output end of which generates a first conjugate beam and a first detection beam. The first conjugate beam enters the detection system, and the first detection beam and the second vacuum light are input into the second four-wave mixer amplifier of the hybrid interferometer to generate a second conjugate beam and a second detection beam. The above beams are combined to output a signal beam, which is connected to the detection system. The present invention has high detection efficiency, amplifies the total number of photons inside the interferometer, has low detection loss, and has a phase sensitivity that can break through the shot noise limit and approach the Heisenberg limit.

Description

Technical Field

[0001] The present invention relates to an optical interferometer and a phase detection method, and in particular to an optical interferometer and a phase detection method based on quantum entanglement. Background Art

[0002] In the process of ultra-sensitive quantum precision phase measurement using optical interferometers, the interferometer used in the optical transmission process is mostly a Mach-Zehnder interferometer. This is due to its advantages such as simple experimental principle, ease of implementation, easy internal configuration modification, wide internal working space, and high measurement accuracy. However, in these traditional interferometers, the phase measurement sensitivity is limited by the shot noise limit due to the injection of vacuum noise into the interferometer's unused input port. When one input of the Mach-Zehnder interferometer is a vacuum beam and the other is a quantum beam or classical beam, the phase sensitivity cannot exceed the shot noise limit. This view is only valid when there is no external source or dual phase estimation for comparison.

[0003] Experimentally, phase is not an actual observable physical quantity, and there is no corresponding Hermitian operator, so the true value of the phase cannot be measured directly. Quantum interference measurement schemes usually measure an observable physical quantity related to the phase, and indirectly estimate the true value of the phase to be measured based on the measurement results. In addition to the traditional direct intensity detection of the light field output by the interferometer, existing related detection schemes also include parity detection, balanced zero-beat detection, and correlation detection schemes. These measurement schemes can improve the measurement accuracy of the interferometer, but some of them have complex internal settings and low detection efficiency. Therefore, in this case, it is very meaningful to provide a method with simple internal settings that can increase the total number of photons inside the interferometer and reduce the external loss of the interferometer detection method. Summary of the Invention

[0004] Purpose of the invention: The purpose of the present invention is to propose an optical interferometer and phase detection method based on quantum entanglement. The interferometer is composed of simple optical devices and has low internal photon loss. The detection method has high detection efficiency and low external photon loss in interferometer phase estimation, and its detection phase sensitivity can be close to the Heisenberg limit.

[0005] Technical solution: The present invention includes a dual-beam generation system, a hybrid interferometer and a detection system, wherein the output end of the dual-beam generation system is respectively connected to the hybrid interferometer and the detection system, and the output end of the hybrid interferometer is connected to the detection system. The dual-beam generation system includes a first four-wave mixer amplifier, the input end of the first four-wave mixer amplifier is incident with coherent light and first vacuum light, and its output end generates a first conjugate beam and a first detection beam. The first conjugate beam enters the detection system, and the first detection beam and the second vacuum light are input into the second four-wave mixer amplifier of the hybrid interferometer to generate a second conjugate beam and a second detection beam. The above beams are combined to output a signal beam, and the signal beam is connected to the detection system.

[0006] The second conjugate beam and the second detection beam enter the two arms of the interferometer respectively, wherein a phase shifter is placed on the lower arm of the hybrid interferometer.

[0007] The second conjugate light beam and the second detection light beam are respectively reflected by a plane mirror and then enter a beam combiner for beam combination to output a signal light beam.

[0008] The signal light beam and the first conjugate light beam have quantum entanglement characteristics.

[0009] Pump light is incident on the input ends of the first four-wave mixer amplifier and the second four-wave mixer amplifier, and light blockers are provided at the output ends.

[0010] The first conjugate beam and the first detection beam are bright entangled twin beams.

[0011] The detection system includes a first photodetector and a second photodetector, which respectively detect the light intensity of the signal light beam and the first conjugate light beam.

[0012] A phase detection method based on quantum entanglement comprises the following steps:

[0013] Step 1: The first detection beam generated by the first four-wave mixer amplifier and the second vacuum beam enter the second four-wave mixer amplifier to generate a second conjugate beam and a second detection beam;

[0014] Step 2: a phase shifter placed on the lower arm of the hybrid interferometer creates a phase difference between the second conjugate beam and the second detection beam;

[0015] Step 3: The second conjugate beam and the second detection beam are respectively reflected by a plane mirror and enter a beam combiner for beam combination and output as a signal beam;

[0016] Step 4: The light intensity information of the signal light beam and the first conjugate light beam is detected by the first photodetector and the second photodetector respectively;

[0017] Step 5: Calculate the light intensities of the signal beam and the first conjugate beam through the photon annihilation generation operator, and calculate the phase sensitivity of the hybrid interferometer through the error propagation formula.

[0018] The step five specifically includes:

[0019] 5.1. The input and output relationship of the first four-wave mixer amplifier is:

[0020]

[0021] in, and are the annihilation production operators of the input coherent beam and the first vacuum beam, and are the annihilation generation operators of the first detection beam and the first conjugate beam amplified by the first four-wave mixing amplifier output, respectively; G1 is the gain parameter of the first four-wave mixing amplifier; θ1 is the phase of the first four-wave mixing amplifier;

[0022] 5.2. The intensity of the first conjugate beam is:

[0023]

[0024] Where N is the number of photons in the input coherent beam;

[0025] 5.3. The input and output relationship of the second four-wave mixer amplifier is:

[0026]

[0027] in, and are the annihilation generation operators of the second vacuum beam input to the hybrid interferometer, and are the annihilation generation operators of the second detection beam and the second conjugate beam outputted twice by the second four-wave mixer amplifier, respectively; G2 is the gain parameter of the second four-wave mixer amplifier; and θ2 is the phase of the second four-wave mixer amplifier;

[0028] 5.4. After passing through the phase shifter, the input and output relationship of the upper and lower arms is:

[0029]

[0030] in, and are the annihilation generation operators of the second probe beam and the second conjugate beam that are amplified twice by the phase shifter, respectively, and φ is the phase of the phase shifter;

[0031] 5.5. The input and output relationship of the hybrid interferometer combiner is:

[0032]

[0033] in, are the annihilation generation operators of the output signal beam of the interferometer beam combiner, T and R are the transmittance and reflectivity of the beam combiner, respectively;

[0034] 5.6. The intensity of the interferometer output signal beam is:

[0035]

[0036] 5.7. Calculation formula for interferometer phase sensitivity under intensity difference detection:

[0037]

[0038] Beneficial effects: The detection method of the present invention is simple and effective, with high detection efficiency, the total number of photons inside the interferometer is amplified, the detection loss is low, and the phase sensitivity can break through the shot noise limit and approach the Heisenberg limit; it provides a new solution for the precise measurement of external resource optical interferometers, and is of great help to gravitational wave detectors, quantum computing, optical imaging, magnetometry, gyroscopes and atomic clocks, as well as many other interferometers and plasma sensor enhancements; it converts optical phase measurement, which cannot be directly realized, into intensity difference measurement, which is a mature technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0040] Figure 2 : is a graph showing the relationship between the four-wave mixing parameter intensity and the number of photons and the optimal phase sensitivity of the interferometer in an embodiment of the present invention, wherein: Figure 2 (a) is the relationship between the number of photons and the optimal phase sensitivity. Figure 2 (b) is the relationship between parameter intensity and optimal phase sensitivity;

[0041] Figure 3 : is a diagram showing the relationship between the four-wave mixing parameter intensity and the phase shift in an embodiment of the present invention;

[0042] Figure 4 is a functional relationship diagram of phase shift, phase sensitivity and quantum compression in an embodiment of the present invention;

[0043] Figure 5 : is a diagram showing the relationship between optimal quantum compression, parameter intensity and photon number in an embodiment of the present invention, wherein: Figure 5 (a) is the relationship between the number of photons and the optimal quantum compression, Figure 5 (b) is a diagram showing the relationship between parameter intensity and optimal quantum compression. DETAILED DESCRIPTION

[0044] The present invention will be further described below with reference to the accompanying drawings.

[0045] like Figure 1 As shown, the present invention includes a dual-beam generation system, a hybrid interferometer, and a detection system. The output of the dual-beam generation system is connected to the hybrid interferometer and the detection system, respectively. The output of the hybrid interferometer is also connected to the detection system. The dual-beam generation system includes a first four-wave mixer amplifier 4. The input of the first four-wave mixer amplifier 4 is incident with coherent light 1, pump light 2, and first vacuum light 3. The pump light 2 is a high-intensity coherent light that provides energy for the four-wave mixing reaction. The output of the first four-wave mixer amplifier 4 is provided with a light blocker 6 to block the output pump light. The interaction of photons with rubidium atoms produces a four-wave mixing reaction, generating bright entangled twin beams. One beam is a first conjugate beam 5, and the other is a first detection beam 7. The first conjugate beam 5 and the first detection beam 7 have quantum entanglement properties. The first conjugate beam 5 is used directly for detection and does not enter the interferometer. It is called the external energy reference beam. The first detection beam 7 enters the hybrid interferometer.

[0046] The amplified first probe beam 7 and a second vacuum light beam 9 serve as the inputs of the hybrid interferometer. They are incident on a second four-wave mixer amplifier 10, generating a second conjugate beam 11 and a second-amplified second probe beam 12, which enter the two arms of the interferometer. A phase shifter 13 is placed on the lower arm of the hybrid interferometer to create a slight phase difference between the two arms. The second conjugate beam 11 and the second-amplified second probe beam 12 are each reflected by a plane mirror 14 and then combined by a beam combiner 17. Finally, a signal beam 18 carrying the phase information to be measured is output. Signal beam 18 exhibits quantum entanglement with the first conjugate beam 5. Similarly, the second four-wave mixer amplifier 10 receives pump light 2 at its input and a light blocker 6 at its output to block the output pump light. The first vacuum light beam 3 and the second vacuum light beam 9 are in a commutative relationship.

[0047] Compared with two coherent light inputs, bright entangled twin beams as hybrid interferometer input have better phase sensitivity. The working principle of the conjugate beam is similar to that of the intrinsic beam in balanced zero-beat detection. The intrinsic beam provides phase reference and power, and the conjugate beam provides energy reference. The conjugate beam in the interferometer system of the present invention is only used for measurement. When calculating the shot noise limit and the Heisenberg limit, the number of photons of the conjugate beam does not need to be considered. Based on the use of external resources, bright entangled twin beams or dual coherent beams are used as hybrid interferometer inputs to obtain optimal phase sensitivity at different phase points at the same time.

[0048] In addition to the beam splitting function, the four-wave mixer amplifier also has a photon amplification function. The bright entangled twin light beams generated by the first four-wave mixer amplifier 4 have very good quantum correlation in time. The quantum correlation is reflected in the intensity difference compression between the amplified first detection light beam 7 and the first conjugate light beam 5.

[0049] The detection system includes a first photodetector 19 and a second photodetector 20, which respectively detect the light intensity of the signal beam 18 and the first conjugate beam 5 output by the hybrid interferometer and perform subtraction operations, and calculate the phase information through the light intensity change at the output end. Calculate the specific phase sensitivity.

[0050] The phase detection method of the present invention mainly includes the following steps:

[0051] Step 1: The amplified first detection beam 7 and the second vacuum beam 9 generated by the first four-wave mixer amplifier 4 enter the second four-wave mixer amplifier 10 to generate the second conjugate beam 11 and the second amplified second detection beam 12;

[0052] Step 2: The phase shifter 13 placed on the lower arm of the hybrid interferometer causes a small phase difference between the second conjugate beam 11 and the second detection beam 12;

[0053] Step 3: The second conjugate beam 11 and the second detection beam 12 are respectively reflected by the plane mirror 14 and enter the beam combiner 17 to be combined and output as a signal beam 18;

[0054] Step 4: The light intensity information of the signal light beam 18 and the first conjugate light beam 5 is detected by the first photodetector 19 and the second photodetector 20 respectively;

[0055] Step 5: Calculate the light intensities of the signal beam 18 and the first conjugate beam 5 using the photon annihilation generation operator, and calculate the phase sensitivity of the hybrid interferometer using the error propagation formula, specifically including:

[0056] 5.1. The input and output relationship of the first four-wave mixer amplifier 4 is:

[0057]

[0058] in, and are the annihilation production operators of the input coherent beam and the first vacuum beam, and are the annihilation production operators of the first detection beam and the first conjugate beam amplified by the first four-wave mixing amplifier output, G1 is the gain parameter of the first four-wave mixing amplifier, and θ1 is the phase of the first four-wave mixing amplifier.

[0059] 5.2. The intensity of the first conjugate beam is:

[0060]

[0061] where N is the number of photons in the input coherent beam.

[0062] 5.3. The input and output relationship of the second four-wave mixer amplifier is:

[0063]

[0064] in, and are the annihilation generation operators of the second vacuum beam input to the hybrid interferometer, and are the annihilation production operators of the second detection beam and the second conjugate beam output by the second four-wave mixing amplifier, respectively. G2 is the gain parameter of the second four-wave mixing amplifier, and θ2 is the phase of the second four-wave mixing amplifier.

[0065] 5.4. After passing through the phase shifter, the input and output relationship of the upper and lower arms is:

[0066]

[0067] in, and are the annihilation production operators of the second detection beam and the second conjugate beam that are amplified twice by the phase shifter, and φ is the phase of the phase shifter.

[0068] 5.5. The input and output relationship of the hybrid interferometer combiner is:

[0069]

[0070] in, are the annihilation operators of the output signal beam of the interferometer beam combiner, T and R are the transmittance and reflectivity of the beam combiner, respectively.

[0071] 5.6. The intensity of the interferometer output signal beam is:

[0072]

[0073] 5.7. Calculation formula for interferometer phase sensitivity under intensity difference detection:

[0074]

[0075] The detection method of this invention surpasses the previous limitations of direct intensity detection of the interferometer output light field. The phase sensitivity of optical interferometers is limited by the shot noise limit. By using quantum entangled twin beams, the phase sensitivity in a hybrid interferometer can break through the shot noise limit and approach the Heisenberg limit. Optimal phase sensitivity can be achieved when the intensity loss of the photodetector and the intensity loss within the hybrid interferometer are less than 0.05.

[0076] like Figure 2 As shown in (a) and (b), as the FWM parametric intensity r increases and the photon number N amplifies, the optimal phase sensitivity of the hybrid interferometer improves for both bright entangled twin beams and two coherent beams. When the FWM parametric intensity approaches 0 and the photon number equals 100, the optimal phase sensitivity for bright entangled twin beams approaches the Heisenberg limit, while the optimal phase sensitivity for two coherent beams approaches the shot noise limit. When two coherent beams are used as input, only one enters the hybrid interferometer, while the other is a vacuum beam. In this case, the optimal phase sensitivity is below the shot noise limit. When the FWM parametric intensity is large (r = 1.5), the optimal phase sensitivity of the bright entangled twin beams does not reach the Heisenberg limit. When the FWM parametric intensity is 0, the detection scheme transforms into a conventional classical beam input scheme, with only the coherent beam entering the hybrid interferometer without any external resources, and the phase sensitivity is limited to the shot noise limit.

[0077] When the number of photons reaches zero, the bright entangled twin beams transform into a two-mode squeezed vacuum beam. At this point, even if the four-wave mixing parameter intensity changes, the phase sensitivity for both quantum and classical beams remains below the shot noise limit.

[0078] like Figure 3 As shown in the figure, by varying the parameter intensity, optimal phase sensitivity can be achieved at different phase points. When the parameter intensity approaches 0, optimal phase sensitivity is achieved at the point where the phase shift approaches 0. As the parameter intensity increases, the phase shift gradually approaches π. By varying the parameter intensity, optimal phase sensitivity can always be achieved. Therefore, the optimal phase point is independent of the photon number; to achieve optimal phase sensitivity, only the parameter intensity needs to be considered.

[0079] like Figure 4 、 Figure 5 As shown in (a) and (b), the hybrid interferometer has better phase sensitivity when the bright entangled twin beams have quantum compression. The degree of quantum compression can be described as 10log 10SD: Optimal quantum compression occurs when phase sensitivity is optimal. When losses are ignored or low, the maximum quantum compression can exceed 43dB, and the optimal sensitivity is less than 0.01. Quantum compression increases with increasing parametric intensity, reaching a maximum of 33dB. Hybrid interferometer sensitivity improves with increasing parametric intensity and photon number amplification, and optimal quantum compression also increases with increasing parametric intensity and photon number amplification.

[0080] The detection method of the present invention is simple and effective, with high detection efficiency, low internal and external photon losses, and a phase sensitivity approaching the Heisenberg limit. Under various loss rates, the measurement scheme based on bright entangled twin beams outperforms conventional measurement schemes based on coherent state input in terms of phase sensitivity, showing significant advantages under high-loss and high-photon count conditions. Even for single-mode input, the phase sensitivity of the measurement scheme can still exceed the shot noise limit. Compared with existing measurement schemes, the measurement scheme of bright entangled twin beams is simple and the experimental technology is more mature.

Claims

1. A phase detection method of an optical interferometer based on quantum entanglement, characterized in that: The invention comprises an optical interferometer based on quantum entanglement, which comprises a dual-beam generation system, a hybrid interferometer and a detection system, wherein the output end of the dual-beam generation system is respectively connected to the hybrid interferometer and the detection system, the output end of the hybrid interferometer is connected to the detection system, the dual-beam generation system comprises a first four-wave mixer amplifier, the input end of the first four-wave mixer amplifier is incident with coherent light and first vacuum light, and the output end thereof generates a first conjugate beam and a first detection beam, the first conjugate beam enters the detection system, the first detection beam and the second vacuum light are input into the second four-wave mixer amplifier of the hybrid interferometer, and a second conjugate beam and a second detection beam are generated, the above beams are combined to output a signal beam, and the signal beam is connected to the detection system; the above phase detection method specifically comprises the following steps: Step 1: The first detection beam generated by the first four-wave mixer amplifier and the second vacuum beam enter the second four-wave mixer amplifier to generate a second conjugate beam and a second detection beam; Step 2: a phase shifter placed on the lower arm of the hybrid interferometer creates a phase difference between the second conjugate beam and the second detection beam; Step 3: The second conjugate beam and the second detection beam are respectively reflected by a plane mirror and enter a beam combiner for beam combination and output as a signal beam; Step 4: The light intensity information of the signal light beam and the first conjugate light beam is detected by the first photodetector and the second photodetector respectively; Step 5: Calculate the light intensities of the signal beam and the first conjugate beam through the photon annihilation generation operator, and calculate the phase sensitivity of the hybrid interferometer through the error propagation formula.

2. The phase detection method of an optical interferometer based on quantum entanglement according to claim 1, characterized in that: The second conjugate beam and the second detection beam enter the two arms of the interferometer respectively, wherein a phase shifter is placed on the lower arm of the hybrid interferometer.

3. The phase detection method of an optical interferometer based on quantum entanglement according to claim 1 or 2, characterized in that: The second conjugate light beam and the second detection light beam are respectively reflected by a plane mirror and then enter a beam combiner for beam combination to output a signal light beam.

4. The phase detection method of an optical interferometer based on quantum entanglement according to claim 3, characterized in that: The signal light beam and the first conjugate light beam have quantum entanglement characteristics.

5. The phase detection method of an optical interferometer based on quantum entanglement according to claim 1, characterized in that: Pump light is incident on the input ends of the first four-wave mixer amplifier and the second four-wave mixer amplifier, and light blockers are provided at the output ends.

6. The phase detection method of an optical interferometer based on quantum entanglement according to claim 1, characterized in that: The first conjugate beam and the first detection beam are bright entangled twin beams.

7. The phase detection method of an optical interferometer based on quantum entanglement according to claim 1, characterized in that: The detection system includes a first photodetector and a second photodetector, which respectively detect the light intensity of the signal light beam and the first conjugate light beam.

8. The phase detection method based on quantum entanglement according to claim 1, characterized in that: The step five specifically includes: 5.

1. The input and output relationship of the first four-wave mixer amplifier is: (1) in, 、 、 and are the annihilation production operators of the input coherent beam and the first vacuum beam, 、 、 and are the annihilation generation operators of the first detection beam and the first conjugate beam amplified by the first four-wave mixing amplifier output, respectively; G1 is the gain parameter of the first four-wave mixing amplifier; is the phase of the first four-wave mixer amplifier; 5.

2. The intensity of the first conjugate beam is: (2) Where N is the number of photons in the input coherent beam; 5.

3. The input and output relationship of the second four-wave mixer amplifier is: (3) in, and are the annihilation generation operators of the second vacuum beam input to the hybrid interferometer, 、 、 and are the annihilation generation operators of the second detection beam and the second conjugate beam output by the second four-wave mixer amplifier, respectively. G2 is the gain parameter of the second four-wave mixer amplifier. is the phase of the second four-wave mixer amplifier; 5.

4. After passing through the phase shifter, the input and output relationship of the upper and lower arms is: (4) in, 、 、 and are the annihilation generation operators of the second detection beam and the second conjugate beam that are amplified twice by the phase shifter, is the phase of the phase shifter; 5.

5. The input and output relationship of the hybrid interferometer combiner is: (5) in, 、 are the annihilation generation operators of the output signal beam of the interferometer beam combiner, T and R are the transmittance and reflectivity of the beam combiner, respectively; 5.

6. The intensity of the interferometer output signal beam is: ； (6) 5.

7. Calculation formula for interferometer phase sensitivity under intensity difference detection: 。 (7)

Images