A three-optical cavity coupling system and a quantum control method based on the system

Abstract

The present invention discloses a three-optical cavity coupling system and a quantum control method based on the system. The three-optical cavity coupling system includes an incident cavity mirror M4, an exit cavity mirror M1, an intermediate cavity mirror M3 and an intermediate cavity mirror M2, wherein the intermediate cavity mirror M3 and the intermediate cavity mirror M2 are located between the incident cavity mirror M4 and the exit cavity mirror M1, forming a three-optical cavity coupling. The incident light field a in It enters the three-optical cavity coupling system through the incident cavity mirror M4 and undergoes multiple reflections in the cavity to form a reflected light field a ref Then it is reflected by the incident cavity mirror M4. Since we fix the reflection coefficients of the incident cavity mirror and the output cavity mirror, and ensure that the distance between each cavity mirror is unchanged, the coupling strength of the entire coupled cavity system can be changed by adjusting the reflection coefficients of the two intermediate cavity mirrors, thereby changing the reflection coefficient of the entire coupled cavity system, and finally realizing quantum control of the reflected light field, which can be applied to the field of quantum control.

Description

Technical Field

[0001] The present invention belongs to the field of quantum control of optical coupling cavities, and specifically relates to a three-optical cavity coupling system and a quantum control method based on the system. Background Art

[0002] Quantum computing and quantum communication are currently gaining much attention. Quantum computing uses the coherence, entanglement and non-cloning characteristics of quantum states to achieve computing tasks such as evolutionary coding of quantum states. Since quantum states have characteristics such as coherent superposition, the parallel scale of quantum computing is unlimited, which is also impossible for many classical calculations. Quantum communication mainly uses the characteristics of quantum mechanics to store and transmit information. Classical quantum communications include quantum teleportation, quantum key distribution and quantum dense coding.

[0003] When conducting research in the above fields, the manipulation of quantum systems is a crucial link. From quantum information science to quantum simulation to quantum sensing, precise manipulation of quantum systems is a fundamental goal in many fields of quantum science. Controlling the quantum state of a system is crucial because it is a preparatory step for subsequent calculations or simulations, or as a goal itself, such as adiabatic quantum computing.

[0004] The basic unit of quantum information processing is the quantum bit, which can exist in any dual quantum state system, such as photons, phonons, and atoms. Because photons have the characteristics of strong stability and fast speed, the optical system has become one of the ideal carriers for quantum information processing. In addition, in the traditional optoelectronic field, light has been used as a carrier for a relatively mature application. Therefore, people hope to use light to realize quantum optical devices that can be used for quantum information processing. In these quantum devices, the transmission or storage of light can be controlled, which makes the light signal after information encoding no longer sensitive to environmental disturbances. It is for this reason that people's research on quantum manipulation of optical systems has become one of the main directions of current quantum physics and quantum information research. Optical coupling cavities can be used to prepare light fields of appropriate intensity. The generation of light fields is the basis of quantum communication and quantum computing, and the characteristics of light fields are the necessary basis for realizing quantum communication. However, the existing quantum coding and quantum control methods based on optical devices all use the method of separating variables, which leads to low coding efficiency, which is also the main reason for the lack of practicality of quantum coding at the current stage. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a three-optical cavity coupling system and a quantum control method.

[0006] The technical solution adopted by the present invention is a three-optical cavity coupling system, including an incident cavity mirror M4, an exit cavity mirror M1, an intermediate cavity mirror M3 and an intermediate cavity mirror M2, wherein the intermediate cavity mirror M3 and the intermediate cavity mirror M2 are located between the incident cavity mirror M4 and the exit cavity mirror M1, and the distance between each cavity mirror is fixed, forming a three-optical cavity coupling, and the incident light field a in It enters the three-optical cavity coupling through the incident cavity mirror M4 and undergoes multiple reflections in the three-optical cavity coupling to form a reflected light field a ref Then it is reflected by the incident cavity mirror M4.

[0007] Furthermore, in the three optical cavities, the incident cavity mirror M4 and the intermediate cavity mirror M3 constitute the incident cavity C3, the intermediate cavity mirror M3 and the intermediate cavity mirror M2 constitute the intermediate cavity C2, and the intermediate cavity mirror M2 and the exit cavity mirror M1 constitute the exit cavity C1.

[0008] Furthermore, the coupling strength of the three optical cavities is determined by the reflection coefficients of the intermediate cavity mirror M3 and the intermediate cavity mirror M2.

[0009] Furthermore, the reflection coefficient r4 of the incident cavity mirror M4 is 2 =0.96, the reflection coefficient r1 of the output cavity mirror M1 2 =0.98.

[0010] Furthermore, the reflection coefficient of the intermediate cavity mirror M3 is greater than or equal to the reflection coefficient of the intermediate cavity mirror M2.

[0011] Furthermore, the incident cavity mirror M4 and the exit cavity mirror M1 are plane mirrors, and the intermediate cavity mirrors M3 and M2 are concave mirrors. Piezoelectric ceramics are arranged on the exit cavity mirror M1, the intermediate cavity mirror M3 and the intermediate cavity mirror M2 to adjust the relative positions of the cavity mirrors to remain unchanged.

[0012] The present invention also provides a quantum control method based on a three-optical cavity coupling system, comprising the following steps:

[0013] Step 1, constructing the above three-optical cavity coupling system;

[0014] Step 2, changing the reflection coefficients of the intermediate cavity mirror M3 and the intermediate cavity mirror M2 to change the coupling strength of the entire three-optical cavity coupling system; including:

[0015] When the incident light field a in When entering the three-optical cavity coupling system, ensure that the reflection coefficients of the intermediate cavity mirrors M3 and M2 are large enough to ensure that the coupling strength of the optical cavity is small at the beginning.

[0016] When the incident light field a inAfter entering the three-optical cavity coupling system, the reflection coefficients of the intermediate cavity mirror M3 and the intermediate cavity mirror M4 are gradually reduced, and the reflection coefficient of the intermediate cavity mirror M3 is ensured to be greater than or equal to the reflection coefficient of the intermediate cavity mirror M2.

[0017] When the reflection coefficients of the intermediate cavity mirrors M3 and M2 continue to decrease, the coupling strength of the three-optical cavity coupling system continues to increase, and its reflected light field a ref The quantum noise spectrum also shows different characteristics.

[0018] Step 3: Get the quantum noise curve of the coupled cavity reflected light field: The noise fluctuation of the orthogonal amplitude component of the optical cavity coupled reflected field injected by the vacuum compression field is:

[0019]

[0020]

[0021] The noise fluctuation of the quadrature phase component is:

[0022]

[0023] in is the annihilation operator of the output field, is the generator of the output field, is the output field quadrature amplitude operator, is the output field orthogonal phase operator, ρ is the amplitude function of the reflected field, θ is the phase function of the reflected field, is the quadrature amplitude operator of the input field, is the orthogonal phase operator of the input field, ω0 represents the center frequency of the quantum field, and Ω represents the measurement frequency. 2 represents the compression operator, and i is the imaginary unit.

[0024] The technical solution of the present invention has the following beneficial effects:

[0025] (1) For optical cavity mirrors, their reflectivity is flexible and controllable. By adjusting the reflection coefficient of the cavity mirror in the coupling cavity, the quantum noise characteristics of the reflected light field can be changed. Different quantum noise characteristics will be presented under different reflection coefficients, which enhances the operability of quantum control.

[0026] (2) The optical cavity coupling system is easy to manufacture, compact in structure, and highly controllable. Since the coupling strength of the entire system can be controlled by changing the reflectivity of the intermediate cavity mirror, this technology can be extended to other fields based on the quantum control of the coupled cavity. And since quantum communication is still under development, this technology may help further develop quantum communication. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the three-optical cavity coupling structure;

[0028] Figure 2 It is a technical flow chart of the method of the present invention;

[0029] Figure 3 Detailed description of the method of the present invention;

[0030] Figure 4 is a quantum noise curve of the reflected light field under the regulation in a specific implementation;

[0031] Where: 1- incident cavity mirror M4; 2- exit cavity mirror M1; 3- intermediate cavity mirror M3; 4- intermediate cavity mirror M2; 5- incident light field a in ; 6- reflected light field a ref . DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] like Figure 2 As shown, the present invention specifically comprises the following steps:

[0034] Step 1: Build a three-optical cavity coupling system, including the incident cavity mirror M4, the output cavity mirror M1, the intermediate cavity mirror M3, and the intermediate cavity mirror M2. in 5 enters the coupled optical cavity system through the incident cavity mirror, and after being reflected and refracted by the intermediate cavity mirrors M3 and M2, the reflected light field a ref 6 is then emitted from the incident cavity mirror M4, and the projected light field a t Then it is emitted through the exit cavity mirror M1, such as Figure 1 Finally, by analyzing the noise coefficient of the reflected light field, its quantum noise curve is obtained.

[0035] The incident cavity mirror M4 and the intermediate cavity mirror M3 constitute the incident cavity mirror C3, the intermediate cavity mirror M3 and the intermediate cavity mirror M2 constitute the intermediate cavity mirror C2, and the intermediate cavity mirror M2 and the exit cavity mirror M1 constitute the exit cavity mirror C1. In the experiment, a piezoelectric ceramic is attached to the back of each cavity mirror except the incident cavity mirror. The function of the piezoelectric ceramic is to adjust the relative position of each cavity mirror to remain unchanged.

[0036] When the incident light field passes through the incident cavity mirror and enters the three-optical cavity coupling, in order to prevent the formation of an over-coupled cavity, the reflection coefficient of the intermediate cavity mirror M3 should be greater than the reflection coefficient of the intermediate cavity mirror M2. And at the beginning, to prevent the coupling strength from being too large, the reflection coefficients of the intermediate cavity mirrors should be kept at a higher value. Then, by adjusting the reflection coefficient of the intermediate cavity mirror, the coupling strength of the coupled cavity system is slowly increased. By observing the reflected light field, its quantum noise curve can be obtained.

[0037] Step 2, injecting vacuum compression light into the three-optical cavity coupling system in step 1, and due to the incident light, the incident cavity mirror, the intermediate cavity mirror and the exit cavity mirror will be coupled with each other, thereby forming a three-coupled optical cavity system.

[0038] When the incident light field a in 5 When entering the three-optical cavity coupling system, ensure that the reflection coefficients of the intermediate cavity mirrors M3 and M2 are large enough to ensure that the coupling strength of the optical cavity is small at the beginning.

[0039] When the incident light field a in 5 After entering the three-optical cavity coupling system, the reflection coefficients of the intermediate cavity mirrors M3 and M4 are gradually reduced, and the reflection coefficient of the intermediate cavity mirror M3 is ensured to be greater than or equal to the reflection coefficient of the intermediate cavity mirror M2.

[0040] When the reflection coefficients of the intermediate cavity mirrors M3 and M2 continue to decrease, the coupling strength of the three-optical cavity coupling system continues to increase, and its reflected light field a ref The quantum noise spectrum also shows different characteristics.

[0041] Step 3, according to relevant theory, we can get the reflection coefficient R1 of cavity C1 as:

[0042]

[0043] φ1 represents the phase change of one cycle in the C1 cavity, r2 is the reflectivity of the M2 mirror, r1 is the reflectivity of the M1 mirror, α1 represents the loss of one round trip in the C1 cavity, and i is an imaginary unit.

[0044] Furthermore, according to the iterative formula, the reflection coefficient R2 of the coupling cavity composed of M1, M2 and M3 is obtained as follows:

[0045]

[0046] φ2 represents the phase change in one cycle in the C2 cavity, r3 is the reflectivity of the M3 mirror, and α2 represents the loss in one round trip in the C2 cavity.

[0047] Furthermore, considering the entire coupled cavity system, we only need to consider the latter cavities C1 and C2 as a whole cavity mirror, and the reflection coefficient R3 of the entire coupled optical cavity can be obtained as:

[0048]

[0049] in Indicates the phase change in one cycle in the cavity, L j is the cavity length, ω represents the frequency of the signal light in the cavity, n j represents the refractive index of light in the cavity, a j represents the loss of a round trip in the cavity, j=1, 2, 3 represent the corresponding optical cavity, and c represents the speed of light in vacuum.

[0050] Step 4. According to the formula in step 3, we know that the reflection coefficient of the entire coupled cavity system is affected by the reflection coefficient of each cavity mirror, so we keep the reflection coefficients of the incident cavity mirror and the output cavity mirror unchanged, and change the reflection coefficient of the coupled cavity system by changing the reflection coefficients of the two intermediate cavity mirrors.

[0051] Step 5, based on the amplitude and phase function of the reflected field of the coupled optical cavity:

[0052]

[0053] ρ represents the amplitude change, θ represents the phase change, and Abs represents the algorithm formula.

[0054] Furthermore, since the expressions of the annihilation operator and the production operator in the quantum field are as follows:

[0055]

[0056] is the annihilation operator, To generate the operator.

[0057] Furthermore, and They represent the orthogonal amplitude and orthogonal phase operators of the light field, respectively, and since they are a pair of conjugate quantities, they satisfy the commutation relation So their quantum fluctuations satisfy the Heisenberg uncertainty relation:

[0058]

[0059] δ 2 is the compression operator.

[0060] Furthermore, this determines that we cannot accurately measure the orthogonal amplitude and phase components of the light field at the same time, and there must be a certain degree of uncertainty. The limit of quantum fluctuations, or quantum noise, brought about by this uncertainty relationship is the shot noise limit (Shot Noise Limit, abbreviated as SNL) or the standard quantum limit (Standard Quantum Limit, abbreviated as SQL):

[0061]

[0062] Furthermore, we can get:

[0063]

[0064] Step 6. Since our study of noise is conducted in the frequency domain, we need to perform Fourier transform on the generation and annihilation operators of the quantum field to obtain:

[0065]

[0066]

[0067] Ω represents the measurement frequency.

[0068] Furthermore, the quantum amplitude and phase components in the frequency domain are obtained as follows:

[0069]

[0070]

[0071] represents the quadrature amplitude operator of the output field at the measurement frequency, represents the quadrature phase operator representing the output field at the measurement frequency, represents the quantum annihilation operator of the output field at the measurement frequency, Denote the quantum generation operator representing the output field at the measurement frequency.

[0072] Further, we can get:

[0073]

[0074]

[0075] in represents the vacuum loss term introduced by the cavity mirror after the optical coupling cavity, while ω0 represents the central frequency of the quantum field, Ω is the measurement frequency, ρ is the amplitude function of the reflected field, is the annihilation operator of the input field, is the generator of the input field, is the generation operator of the vacuum loss term.

[0076] Furthermore, we can obtain the noise fluctuation of the orthogonal amplitude component of the reflected field of the coupled optical cavity injected by the vacuum compression field as:

[0077]

[0078]

[0079] is the quadrature amplitude operator of the input field, is the orthogonal phase operator of the input field, is the quadrature amplitude operator of the input field loss term, is the quadrature phase operator of the input field loss terms.

[0080] Step 7: Based on the above principle of obtaining the noise fluctuation of the amplitude component, we can also obtain the noise fluctuation of the orthogonal phase component:

[0081]

[0082]

[0083] According to the above analysis, the specific experimental process of quantum control using the above three-optical cavity coupling system is as follows: Figure 3 As shown, the following steps are included:

[0084] Step 1, using a laser to output about 220mw of 532nm green light and about 60mw of 1064nm infrared light;

[0085] Step 2: Splitting the emitted 1064nm light and 532nm light, and injecting them into the mode cleaning system for mode cleaning;

[0086] Step 3: A small part of the transmitted light of the mode cleaner is used as the signal light of the locking cavity. After the locking cavity, the output light beam of the mode cleaner is divided into two beams, of which the stronger one is used as the intrinsic light during balanced zero-beat detection, and the other 1064nm light is injected into the DOPO system as the calibration light after mode adjustment and resonates in it. The 532nm green light is used as the pump light and combined with the 1064nm light and then injected into the DOPO cavity;

[0087] Step 4: The outgoing light of the DOPO system is adjusted by the lens group and then injected into the optical cavity coupling system. Its reflected field is extracted by the isolator and then sent to the detection system for detection and recording;

[0088] Step 5: First, we examine the EIT-like characteristics of the system under the weak coupling intensity. In the classical field, since coherent light is used as the incident light of the EIT-like system, we first block the 532nm green light and only allow the 1064nm light to enter the DOPO system. We adjust the optical path and the mode of the 1064nm light to make it resonate in the DOPO cavity, and then lock the mode of the DOPO cavity in the TEM. 00 On the die, its outgoing light is injected into the optical cavity coupling system to produce an EIT-like effect, and then a detector is used to detect the reflected field separated by the isolator;

[0089] Step 6: Next, we consider the EIT-like characteristics of the optical cavity coupling injected with compressed light field. At this time, we block the 1064nm infrared light, turn on the 532nm pump light, let it be injected into the incident cavity mirror of the DOPO cavity, and then pass through the PPKTP crystal for nonlinear conversion. The temperature controller is used to control the crystal temperature so that it works at the highest nonlinear efficiency. Then the optical path is adjusted to allow the vacuum compressed light generated by the DOPO cavity to be injected into the optical cavity coupling system. The quantum characteristics of the optical cavity coupling system composed of three optical cavities are examined. The reflection field is extracted with an isolator, and the mode of the reflection field is adjusted with a lens group so that the interference efficiency with the local oscillator light reaches more than 94%. Then the balanced zero-beat detection system is used to measure the noise spectrum.

[0090] In this embodiment, the reflection coefficient r4 of the incident cavity mirror is set 2 =0.96, the reflection coefficient of the output cavity mirror r1 2 =0.98, and keep it at this fixed value. And set the initial reflection coefficients of the two intermediate cavity mirrors to r2 2 =0.99999, r3 2 = 0.9999999. Then change r2 2 、r3 2 The value of r2 2 The range of variation is 0.99999~0.9, r3 2 The range of variation is 0.9999999~0.9, and the quantum noise curve of the reflected light field is as follows Figure 4 As shown in the figure (the left side is the noise curve of the orthogonal amplitude component, and the right side is the noise curve of the orthogonal phase component). For different coupling strengths, the quantum noise curve of the reflected light field also presents completely different characteristics. 2 =0.9, r3 2= 0.9, it can be seen that the quantum noise characteristic curves of the reflected light field (including the noise curve of the orthogonal amplitude component and the noise curve of the orthogonal phase component) are presented as three independent split Lorentz curves (noise curve of the orthogonal amplitude component) and three inverted split Lorentz curves (noise curve of the orthogonal phase component). This can achieve quantum control of the reflected light field coupled to the optical cavity.

[0091] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A three-optical cavity coupling system, characterized in that: The optical cavity comprises an incident cavity mirror M4(1), an exit cavity mirror M1(2), an intermediate cavity mirror M3(3) and an intermediate cavity mirror M2(4), wherein the intermediate cavity mirror M3(3) and the intermediate cavity mirror M2(4) are located between the incident cavity mirror M4(1) and the exit cavity mirror M1(2), and the distance between each cavity mirror is fixed, so as to form a three-optical cavity coupling. The incident light field a in (5) Enters the three-optical coupling cavity through the incident cavity mirror M4 (1), and undergoes multiple reflections in the three-optical coupling cavity to form a reflected light field a ref (6) and then reflected by the incident cavity mirror M4 (1); the reflection coefficients of the incident cavity mirror M4 (1) and the exit cavity mirror M1 (2) are fixed, and the reflection coefficients of the intermediate cavity mirror M3 (3) and the intermediate cavity mirror M2 (4) are variable; the coupling strength of the three optical cavities is determined by the reflection coefficients of the intermediate cavity mirror M3 (3) and the intermediate cavity mirror M2 (4).

2. A three-optical cavity coupling system according to claim 1, characterized in that: In the three optical cavities, the incident cavity mirror M4(1) and the intermediate cavity mirror M3(3) constitute the incident cavity C3, the intermediate cavity mirror M3(3) and the intermediate cavity mirror M2(4) constitute the intermediate cavity C2, and the intermediate cavity mirror M2(4) and the exit cavity mirror M1(2) constitute the exit cavity C1.

3. The quantum control method of a three-optical cavity coupling system according to claim 1, characterized in that: The reflection coefficient r4 of the incident cavity mirror M4(1) 2 =0.96, the reflection coefficient r1 of the output cavity mirror M1(2) 2 =0.

98.

4. The three-optical cavity coupling system according to claim 1, characterized in that: The reflection coefficient of the intermediate cavity mirror M3 (3) is greater than or equal to the reflection coefficient of the intermediate cavity mirror M2 (4).

5. A three-optical cavity coupling system according to any one of claims 1 to 4, characterized in that: The incident cavity mirror M4 (1) and the exit cavity mirror M1 (2) are plane mirrors, and the intermediate cavity mirror M3 (3) and the intermediate cavity mirror M2 (4) are concave mirrors.

6. The three-optical cavity coupling system according to claim 5, characterized in that: Piezoelectric ceramics are provided on the output cavity mirror M1 (2), the intermediate cavity mirror M3 (3) and the intermediate cavity mirror M2 (4) to adjust the relative positions of the cavity mirrors to remain unchanged.

7. A quantum control method based on a three-optical cavity coupling system, characterized in that: The following steps are involved: Step 1, constructing a three-optical cavity coupling system as described in any one of claims 1 to 6; Step 2, changing the reflection coefficients of the intermediate cavity mirror M3 (3) and the intermediate cavity mirror M2 (4) to change the coupling strength of the entire three-optical cavity coupling system; Step 3: Get the quantum noise curve of the coupled cavity reflected light field: The noise fluctuation of the orthogonal amplitude component of the optical cavity coupled reflected field injected by the vacuum compression field is: The noise fluctuation of the quadrature phase component is: in is the annihilation operator of the output field, is the output field generation operator, is the output field quadrature amplitude operator, is the output field quadrature phase operator, ρ is the amplitude function of the reflected field, θ is the phase function of the reflected field, is the quadrature amplitude operator of the input field, is the orthogonal phase operator of the input field, ω0 represents the center frequency of the quantum field, Ω represents the measurement frequency, δ 2 is a compression operator, i represents the imaginary unit, is the quadrature amplitude operator of the input field loss term, is the quadrature phase operator of the input field loss terms.

8. The quantum control method based on a three-optical cavity coupling system according to claim 7, characterized in that: The step 2 specifically includes: When the incident light field a in (5) When entering the three-optical cavity coupling system, ensure that the reflection coefficients of the intermediate cavity mirror M3 (3) and the intermediate cavity mirror M2 (4) are large enough to ensure that the coupling strength of the optical cavity is small at the beginning; When the incident light field a in (5) After entering the three-optical cavity coupling system, the reflection coefficients of the intermediate cavity mirror M3 (3) and the intermediate cavity mirror M4 (4) are gradually reduced, and the reflection coefficient of the intermediate cavity mirror M3 (3) is ensured to be greater than or equal to the reflection coefficient of the intermediate cavity mirror M2 (4); When the reflection coefficients of the intermediate cavity mirrors M3(3) and M2(4) continue to decrease, the coupling strength of the three-optical cavity coupling system continues to increase, and its reflected light field a ref The quantum noise spectrum of (6) also exhibits different characteristics.

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