A quantum light source based on optical frequency comb and a method for generating quantum states thereof

Abstract

The application discloses a quantum light source based on an optical frequency comb and a method for generating quantum states, and the quantum light source comprises a laser, a micro-ring resonant cavity, a wavelength division demultiplexer, an intensity modulation module, a beam combination module, a two-photon generation module and a first phase modulator, the micro-ring resonant cavity generates an optical frequency comb based on pump light output by the laser, the wavelength division demultiplexer separates light of different frequency components in the optical frequency comb and attenuates the light of different frequency components, and two frequency components which are symmetrical about a center frequency of the optical frequency comb after attenuation are transmitted to a spiral waveguide coil, and each spiral waveguide coil generates an entangled photon pair with the same wavelength with a certain probability; in the application, a plurality of spiral waveguide coils are arranged, all the light transmitted to the spiral waveguide coils comes from one optical frequency comb, and the optical frequency comb is generated based on pump light output by one laser, so that the effect of generating an array of quantum light sources by one laser is achieved, and the number of required lasers is reduced.

Description

Technical Field

[0001] This application belongs to the field of quantum information technology, and specifically relates to a quantum light source based on an optical frequency comb and a method for generating quantum states thereon. Background Technology

[0002] An optical frequency comb, also known as an optical frequency distribution, refers to a spectrum composed of a series of uniformly spaced frequency components with a stable coherent phase relationship. In the frequency domain, an optical frequency comb appears as a spectral sequence with equal frequency intervals, while in the time domain, it appears as an ultrashort pulse sequence. The frequency intervals in the frequency domain and the pulse widths in the time domain strictly follow a Fourier transform relationship. Currently, the main methods for generating optical frequency combs include: laser external modulation, modulator-based cyclic frequency shifting, Brillouin cyclic frequency shifting, fiber nonlinear effects, mode-locked lasers, or microcavity structures.

[0003] On-chip quantum light sources typically utilize a four-wave mixing process using a helical waveguide coil or micro-ring structure. When operations such as two-photon interference are required, the quantum light source needs to provide two entangled photon pairs with the same wavelength. This entangled photon pair can be generated using the four-wave mixing effect. However, according to the law of energy conservation, if two photons with the same wavelength are to be output, two photons with different wavelengths must be input. Therefore, two lasers of different wavelengths are needed to pump light of the corresponding wavelength, resulting in a complex structure, high cost, and system instability. Summary of the Invention

[0004] To address the aforementioned problems, this application provides a quantum light source based on an optical frequency comb and a method for generating quantum states. The optical frequency comb is generated using a micro-ring resonator based on pump light. A wave demultiplexer separates the light components of different frequencies within the optical frequency comb and attenuates these components. The two attenuated frequency components, symmetrical about the center frequency of the optical frequency comb, are then transmitted to the same helical waveguide coil. Each helical waveguide coil generates entangled photon pairs of the same wavelength with a certain probability. This application uses multiple helical waveguide coils, and all light transmitted to these coils originates from a single optical frequency comb, which is generated based on the pump light output from a laser, achieving the effect of generating a quantum light source array from a single laser. The specific scheme is as follows:

[0005] In a first aspect, this application discloses a quantum light source based on an optical frequency comb, including a laser, a micro-ring resonator, a wave demultiplexer, an intensity modulation module, a beam combining module, a two-photon generation module, and a first phase modulator;

[0006] The laser is used to output pump light and transmit the pump light to the micro-ring resonant cavity;

[0007] The microring resonant cavity generates an optical frequency comb based on the pump light. It consists of a bus straight waveguide and a microring. The bus straight waveguide is used to receive the pump light and input the pump light into the microring in an evanescent coupling manner. The microring generates multiple equally spaced discrete frequency components based on the four-wave mixing effect and forms an optical frequency comb. The optical frequency comb is symmetrical about its center frequency as the axis of symmetry.

[0008] The wave demultiplexer is connected to the microring resonator and is used to allocate the optical frequency comb path output by the microring resonator so as to separate the optical components of different frequencies.

[0009] The intensity modulation module includes N optical attenuators, each of which is used to receive light of a corresponding frequency component and modulate the intensity of the received light, where N is an even number ≥ 4;

[0010] The beam combining module includes N / 2 first 50:50 beam splitters. The two input terminals of each first 50:50 beam splitter are respectively connected to an optical attenuator for beam combining the light output from the two optical attenuators. The frequency components of the light received by the two optical attenuators connected to each first 50:50 beam splitter are symmetrical about the center frequency.

[0011] The two-photon generation module includes N / 2 helical waveguide coils, each of which is connected to a first 50:50 beam splitter to receive the combined light output from the first 50:50 beam splitter and generate entangled photon pairs with the same wavelength based on the combined light with a certain probability.

[0012] The number of the first phase modulators is (N / 2)-1, and they are connected one-to-one with the output terminals of the (N / 2)-1 spiral waveguide coils, respectively, for modulating the phase of the entangled photon pairs input to them.

[0013] Furthermore, the quantum light source also includes N waveguide beam splitters, N photodetectors, and a control chip. The input end of each waveguide beam splitter is connected to one of the optical attenuators, and the two output ends of each waveguide beam splitter are respectively connected to a photodetector and an input end of a corresponding first 50:50 beam splitter. The waveguide beam splitter receives the beam output from the corresponding optical attenuator and splits it, so that a portion of the beam is input to the photodetector and the other portion is input to an input end of the corresponding first 50:50 beam splitter. All N photodetectors and N optical attenuators are connected to the control chip. The photodetectors detect the intensity of the light transmitted to them and feed the intensity back to the control chip. The control chip adjusts the attenuation intensity of the corresponding optical attenuator based on the light intensity fed back by each photodetector.

[0014] Preferably, the wave demultiplexer is an arrayed waveguide grating.

[0015] Furthermore, the optical attenuator consists of two second 50:50 beam splitters, an upper interference arm, a lower interference arm, and a second phase modulator. The two ends of the upper interference arm are respectively connected to the upper output of the two second 50:50 beam splitters, and the two ends of the lower interference arm are respectively connected to the lower output of the two second 50:50 beam splitters. The second phase modulator is disposed on the upper or lower interference arm.

[0016] Preferably, the beam splitting ratio of the waveguide beam splitter is (90+M):(10-M), where M is a positive integer less than 10.

[0017] Preferably, the photodetector is a photodiode or a photomultiplier tube.

[0018] Furthermore, the arrayed waveguide grating includes an input waveguide, an input star coupler, an arrayed waveguide, an output star coupler, and several output waveguides. The input waveguide is used to input the optical frequency comb output from the micro-ring resonator to the input star coupler. The arrayed waveguide includes several transmission waveguides with equally spaced lengths. The two ends of each transmission waveguide are connected to the input star coupler and the output star coupler, respectively. The input star coupler is used to uniformly distribute the received light into the arrayed waveguide. The arrayed waveguide is used to generate a phase difference between the light received by different transmission waveguides and to focus light of different wavelengths at different positions on the output star coupler. The input port of the output waveguide is located at the focal point of the output star coupler and is used to output light of the corresponding wavelength.

[0019] Preferably, both the first phase modulator and the second phase modulator are thermally modulated phase modulators or electro-optic phase modulators.

[0020] Secondly, this application discloses a method for generating quantum states using a quantum light source based on an optical frequency comb. The method is applied to the aforementioned quantum light source based on an optical frequency comb. The quantum light source includes a laser, a micro-ring resonator, a wave demultiplexer, an intensity modulation module, a beam combining module, a two-photon generation module, and a first phase modulator. The micro-ring resonator is composed of a straight waveguide and a micro-ring. The intensity modulation module includes N optical attenuators. The beam combining module includes N / 2 first 50:50 beam splitters. The two-photon generation module includes N / 2 helical waveguide coils. The number of first phase modulators is (N / 2)-1, where N is an even number ≥ 4. The method includes:

[0021] The laser outputs pump light;

[0022] The bus straight waveguide of the microring resonator receives the pump light and inputs the pump light into the microring in an evanescent coupling manner. The microring generates multiple equally spaced discrete frequency components based on the four-wave mixing effect and forms an optical frequency comb.

[0023] The wave demultiplexer distributes the optical frequency comb path of the micro-ring resonator output, enabling the separation of optical components of different frequencies;

[0024] Each optical attenuator receives light of a specific frequency component and modulates the intensity of the received light.

[0025] Each first 50:50 beam splitter receives the light output from two optical attenuators and combines them into a single beam, with the frequency components of the light received by the two optical attenuators being symmetrical about the center frequency of the optical comb.

[0026] Each spiral waveguide coil receives the combined light output from the corresponding first 50:50 beam splitter and generates entangled photon pairs with the same wavelength based on the combined light with a certain probability.

[0027] The entangled photon pairs output from one spiral waveguide coil are directly output, while the entangled photon pairs output from another (N / 2)-1 spiral waveguide coils are respectively input to the first phase modulator for phase modulation, and then output after phase modulation.

[0028] Furthermore, when the quantum light source further includes N waveguide beam splitters, N photodetectors, and a control chip, the method further includes:

[0029] Each waveguide beam splitter receives the light output from the corresponding connected optical attenuator and splits it, so that part of the beam is input to the photodetector and the other part of the beam is input to one input terminal of the corresponding first 50:50 beam splitter.

[0030] Each photodetector detects the intensity of the light beam transmitted through it and feeds the detection results back to the control chip. The control chip adjusts the attenuation intensity of the corresponding optical attenuator based on the detection results fed back by each photodetector.

[0031] In summary, compared with the prior art, the above-described technical solutions conceived in this application can achieve the following beneficial effects:

[0032] This application provides a quantum light source based on an optical frequency comb and a method for generating quantum states. The quantum light source includes a laser, a micro-ring resonator, a wave demultiplexer, an intensity modulation module, a beam combining module, a two-photon generation module, and a first phase modulator. The micro-ring resonator generates an optical frequency comb based on the pump light output from the laser. The wave demultiplexer separates and attenuates the light of different frequency components in the optical frequency comb. The two frequency components symmetrical about the center frequency of the optical frequency comb after attenuation are transmitted to helical waveguide coils. Each helical waveguide coil generates entangled photon pairs with the same wavelength with a certain probability based on nonlinear interaction. This application uses multiple helical waveguide coils, and all light transmitted to the helical waveguide coils originates from one optical frequency comb, which is generated based on the pump light output from a single laser. Therefore, it achieves the effect of generating a quantum light source array from a single laser, reducing the number of lasers required, lowering costs, and enhancing system stability. Furthermore, since the frequency components in the optical frequency comb maintain coherence, this method can obtain high-dimensional quantum entangled states. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in this embodiment or the prior art, the drawings used in the description of the embodiment or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 A schematic diagram of a quantum light source based on an optical frequency comb is provided in an embodiment of this application;

[0035] Figure 2 This is a schematic diagram of the microring resonator structure in this application;

[0036] Figure 3 This is a schematic diagram of the pulse spectrum of an optical frequency comb formed in one embodiment of this application;

[0037] Figure 4 This is a schematic diagram of the arrayed waveguide grating in this application;

[0038] Figure 5 This is a schematic diagram of the optical attenuator in this application;

[0039] Figure 6 A schematic diagram of a quantum light source based on an optical frequency comb, provided for another embodiment of this application;

[0040] Figure 7 A flowchart illustrating a method for generating quantum states using a quantum light source based on an optical frequency comb, provided for this application;

[0041] Figure 8 This is a flowchart illustrating the modulation of the attenuation intensity of each optical attenuator in a method for generating quantum states using a quantum light source based on an optical frequency comb, as described in this application. Detailed Implementation

[0042] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the embodiments of this application will be further described in detail below with reference to the accompanying drawings and specific implementation methods. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0043] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0044] To facilitate understanding and explanation of the technical solutions provided in the embodiments of this application, the background technology of this application will be described first.

[0045] On-chip quantum light sources typically utilize a four-wave mixing process using a helical waveguide coil or micro-ring structure. When operations such as two-photon interference are required, the quantum light source needs to provide two entangled photon pairs with the same wavelength. This entangled photon pair can be generated using the four-wave mixing effect. However, according to the law of energy conservation, if two photons with the same wavelength are to be output, two photons with different wavelengths must be input. Therefore, two lasers of different wavelengths are needed to pump light of the corresponding wavelength, resulting in a complex structure, high cost, and system instability.

[0046] Based on this, this application provides a quantum light source based on an optical frequency comb, such as... Figure 1 As shown, it includes a laser, a micro-ring resonator, a wave demultiplexer, an intensity modulation module, a beam combining module, a two-photon generation module, and a first phase modulator.

[0047] The laser is used to output pump light and transmit the pump light to the microring resonator.

[0048] The microring resonator generates an optical frequency comb based on pump light. Specifically, the microring resonator consists of a main straight waveguide and a microring, such as... Figure 2 As shown, the bus straight waveguide is used to receive pump light and input it into the micro-ring via evanescent coupling. The micro-ring generates multiple equally spaced discrete frequency components based on a four-wave mixing effect, forming an optical frequency comb, such as... Figure 3 As shown, the optical frequency comb is symmetrical about its center frequency.

[0049] A typical characteristic of an optical frequency comb is that its frequency components are arranged at equal intervals like comb teeth, and the spacing between adjacent frequencies is determined by the free spectral range of the microring resonator.

[0050] A microring is typically a micro- or nano-sized ring resonator composed of a series of interconnected optical waveguides. Its basic working principle utilizes total internal reflection, employing a high-refractive-index material as the waveguide and air or a low-refractive-index material as the cladding. Light is confined within the microring for transmission. It possesses inherent filtering characteristics; only light frequencies meeting the resonance condition can be enhanced through interference, while other non-resonant frequencies will naturally cancel each other out.

[0051] refer to Figure 2 The pump light signal is input from the input end of the main straight waveguide and enters the microring through the coupling region between the main straight waveguide and the microring. After the light travels through the microring once, it interferes with the light wave itself in the main straight waveguide, resulting in a resonance enhancement effect in the microring. For light that meets the resonant frequency, a resonant electromagnetic field will be established in the microring, while light that does not meet the resonant frequency will be output at the output end of the main straight waveguide. Resonance occurs when the optical path length of the light traveling through the microring is exactly an integer multiple of the wavelength of the light wave, or when the phase difference between two adjacent beams is an integer multiple of 2π. Due to the frequency selectivity of the microring resonant cavity, the frequency components (optical frequency comb teeth) can only be generated at the resonant frequency and are distributed on both sides of the center frequency at intervals that are integer multiples of the free spectral range of the microring resonant cavity. The light coupled into the microring undergoes constructive interference with the light in the microring, and the optical power in the ring continuously increases until the loss in the ring and the coupling input reach a balance, obtaining the maximum optical intensity in the ring. In this process, multiple frequency components are generated, forming an optical frequency comb in the spectrum.

[0052] The wave demultiplexer is connected to the microring resonator and is used to allocate the optical frequency comb path of the microring resonator output, so as to separate the optical components of different frequencies.

[0053] Wavelength demultiplexers can separate optical signals of different wavelengths. In this application, the wavelength demultiplexer is an on-chip structure and can be an arrayed waveguide grating. Specifically, the arrayed waveguide grating includes an input waveguide, an input star coupler, an arrayed waveguide, an output star coupler, and several output waveguides, such as... Figure 4As shown. The input waveguide is used to input the optical frequency comb output from the micro-ring resonator to the input star coupler. The array waveguide includes several transmission waveguides with equally spaced lengths. The two ends of each transmission waveguide are connected to the input star coupler and the output star coupler, respectively. The input star coupler is used to uniformly distribute the received light into the array waveguide. The array waveguide is used to generate a phase difference between the light received by different transmission waveguides and to focus light of different wavelengths at different positions of the output star coupler. The input port of the output waveguide is set at the focal point of the output star coupler to output light of the corresponding wavelength.

[0054] An arrayed waveguide is a group of waveguides with equal length differences, equivalent to a concave grating. The principle of an arrayed waveguide grating is as follows: an optical frequency comb signal containing multiple wavelengths is input to the input star coupler via the input waveguide. After free propagation, it is distributed into the arrayed waveguide. This distribution process is wavelength-independent; all wavelengths are distributed indiscriminately into the arrayed waveguide. Light incident on the arrayed waveguide arrives at the arrayed waveguide end face with the same phase. After propagation through the arrayed waveguide, because adjacent arrayed waveguides maintain the same length difference, different wavelengths of light propagate to the output star coupler with different phase differences. The phases of different wavelength beams form an arithmetic progression, with a one-to-one correspondence between wavelength and phase. Beams of different wavelengths are dispersed and focused at different positions in the output star coupler. The input ports of multiple output waveguides are respectively located at the focal points of the output star coupler. The output waveguides and wavelengths have a one-to-one correspondence; light of different wavelengths is output through the corresponding output waveguides, completing the wavelength distribution and demultiplexing function.

[0055] The intensity modulation module includes N optical attenuators, each of which is used to receive light of a corresponding frequency component and modulate the intensity of the received light, where N is an even number ≥ 4.

[0056] In this application, the optical attenuator is an on-chip waveguide type optical attenuator. It attenuates the intensity of the light beam to ensure that the intensity of the light incident on each helical waveguide coil meets preset requirements. Specifically, the optical attenuator consists of two second 50:50 beam splitters, an upper interference arm, a lower interference arm, and a second phase modulator, as shown below. Figure 5 As shown, the two ends of the upper arm of the interference are respectively connected to the upper output of two second 50:50 beam splitters, and the two ends of the lower arm of the interference are respectively connected to the lower output of two second 50:50 beam splitters. The second phase modulator is set on the upper arm or the lower arm of the interference.

[0057] The intensity of the output light is controlled by modulating the phase of a second phase modulator located on the upper or lower arm of the interferometer. Assuming the second phase modulator is located on the lower arm, its modulation principle is as follows: the second phase modulator modulates the phase of the light input to the lower arm, creating a phase difference with the light transmitted on the upper arm. The phase-modulated light on the lower arm and the light on the upper arm then interfere destructively at one of the second 50:50 beam splitters, thus attenuating the intensity of the beam.

[0058] The beam combining module includes N / 2 first 50:50 beam splitters. The two input terminals of each first 50:50 beam splitter are respectively connected to an optical attenuator for beam combining the light output from the two optical attenuators. The frequency components of the light received by the two optical attenuators connected to each first 50:50 beam splitter are symmetrical about the center frequency.

[0059] The beam combining module is used to combine the light from each group of optical attenuators. Here, each group of optical attenuators refers to two attenuators whose frequency components of the received light are symmetrical about the center frequency. In one embodiment of this application, assuming N = 6, such as... Figure 1 As shown, the micro-ring resonator in the quantum light source generates an optical frequency comb with six frequency components. The intensity modulation module includes six optical attenuators, and the beam combining module includes three first 50:50 beam splitters. For ease of understanding, in this embodiment, it is assumed that the six optical attenuators in the intensity modulation module, from top to bottom, are the first optical attenuator, the second optical attenuator, ..., the sixth optical attenuator. The first optical attenuator is used to attenuate the light intensity of the f1 frequency component, the second optical attenuator is used to attenuate the light intensity of the f6 frequency component, the third optical attenuator is used to attenuate the light intensity of the f2 frequency component, the fourth optical attenuator is used to attenuate the light intensity of the f5 frequency component, the fifth optical attenuator is used to attenuate the light intensity of the f3 frequency component, and the sixth optical attenuator is used to attenuate the light intensity of the f4 frequency component. (Reference) Figure 3 It can be seen that the frequency components f1 and f6 are symmetrical about the center frequency f0 of the optical frequency comb, the frequency components f2 and f5 are symmetrical about the center frequency f0 of the optical frequency comb, and the frequency components f3 and f4 are symmetrical about the center frequency f0 of the optical frequency comb. The first and second optical attenuators form one group of optical attenuators, the third and fourth optical attenuators form another group, and the fifth and sixth optical attenuators form yet another group. The two input terminals of each first 50:50 beam splitter are respectively connected to two optical attenuators in a group, thus combining the corresponding groups of optical attenuators.

[0060] The two-photon generation module includes N / 2 helical waveguide coils, each of which is connected to a first 50:50 beam splitter. The beam splitter receives the combined light output from the first 50:50 beam splitter and generates entangled photon pairs with the same wavelength based on the combined light with a certain probability.

[0061] refer to Figure 1 The two-photon generation module includes three helical waveguide coils, each corresponding one-to-one with a first 50:50 beam splitter. Each helical waveguide coil generates entangled photon pairs of the same wavelength through a four-wave mixing process based on the combined light output from a set of optical attenuators, with a certain probability. In this application, only when one helical waveguide coil generates an entangled photon pair is it considered a valid output. When at least two helical waveguide coils generate entangled photon pairs, they can be discarded through a post-selection process.

[0062] In this application, the number of first phase modulators is (N / 2)-1, which are connected one-to-one with the output terminals of (N / 2)-1 spiral waveguide coils, and are used to modulate the phase of entangled photon pairs input to them.

[0063] It should be noted that only one of the spiral waveguide coils' output terminals is not equipped with the first phase modulator; this output is for reference only. This application does not specifically limit which spiral waveguide coil's output terminal is not equipped with the first phase modulator.

[0064] The following will combine Figure 1 and Figure 2 The process and principle of generating quantum states in this application are explained.

[0065] The micro-ring resonator generates an optical frequency comb based on the pump light output from the laser. A wave demultiplexer separates the different frequency components of the optical frequency comb, and each component is input to a corresponding optical attenuator. After attenuation, two frequency components symmetrical about the center frequency of the optical frequency comb are transmitted to the first 50:50 beam splitter. The quantum state of the optical frequency comb output from the three first 50:50 beam splitters is:

[0066]

[0067] In the formula, The terms θ1, θ2, and θ3 represent the phase changes caused by the devices themselves along the corresponding paths. In this embodiment, these are the phase changes caused by the optical path difference between the optical attenuator and the corresponding spiral waveguide coil on the three paths. θi is the imaginary unit. Since photons of different wavelengths output from the micro-ring resonator reach the corresponding spiral waveguide coils via different optical attenuators and transmission waveguides, the device and waveguide fabrication precision is generally on the order of hundreds of nanometers during micro / nano fabrication. Compared to C-band photons, a path difference of hundreds of nanometers introduces a subwavelength-level optical phase difference. Here, θ1, θ2, and θ3 are used to represent the corresponding phase changes for the three paths in this embodiment. α1 represents the probability amplitude of |f1>|f6>, determined by the product of the light intensity of the corresponding frequency components f1 and f6 in the optical frequency comb and the attenuation values ​​of the first and second optical attenuators; α2 represents the probability amplitude of |f2>|f5>, determined by the product of the light intensity of the corresponding frequency components f2 and f5 in the optical frequency comb and the attenuation values ​​of the third and fourth optical attenuators; α3 represents the probability amplitude of |f3>|f4>, determined by the product of the light intensity of the corresponding frequency components f3 and f4 in the optical frequency comb and the attenuation values ​​of the fifth and sixth optical attenuators; α1, α2, and α3 satisfy the normalization condition.

[0068] The generation of entangled photon pairs through a four-wave mixing process on a helical waveguide coil requires the energy conservation condition to be satisfied: f s +f t =2f r Here f s f t These are the frequencies of the input light, f and f, respectively. r Let f1 be the frequency of the output light. In this application, since the two frequency components input to the spiral waveguide coil are symmetrical about the center frequency of the optical frequency comb, the spiral waveguide coil can generate entangled photon pairs of the same wavelength for output. For example, for the spiral waveguide coil input to frequency components f1 and f6, f1 + f6 = f0 - Vf + f0 + Vf = 2f0. Since f1 and f6 are symmetrical about the center frequency f0 of the optical frequency comb, the interval between f1 and f0 is the same as the interval between f6 and f0. After simplification, f1 + f6 = 2f0. Therefore, it can be seen that two quantum lights of the same wavelength are output.

[0069] Three helical waveguide coils generate entangled photon pairs through a four-wave mixing process with a certain probability. (Reference) Figure 1 The output paths of the three helical waveguide coils are named path 1, path 2, and path 3, respectively. Assuming a first phase modulator is placed on paths 1 and 2, but not on path 3 (as a reference term), the output quantum state can be represented as:

[0070]

[0071] In the formula, This indicates the modulation phase of the first phase modulator on path 1. This represents the modulation phase of the first phase modulator on path 2. Quantum state |1> corresponds to two entangled photons on path 1, and quantum state |2> corresponds to two entangled photons on path 2. As can be seen from the formula, the quantum light source based on this application can prepare high-dimensional quantum states for arbitrary targets.

[0072] To adjust the attenuation intensity of the optical attenuators in real time, in another embodiment of this application, the quantum light source further includes N waveguide beamsplitters, N photodetectors, and a control chip. Each waveguide beamsplitter's input is connected to an optical attenuator, and each waveguide beamsplitter's two outputs are connected to a photodetector and an input of a corresponding first 50:50 beamsplitter, respectively. The waveguide beamsplitters receive the beam output from the corresponding optical attenuators and split the beam, so that a portion of the beam is input to the photodetector and the other portion is input to an input of the corresponding first 50:50 beamsplitter. The N photodetectors and N optical attenuators are all connected to the control chip. The photodetectors detect the intensity of the light transmitted to them and feed the intensity back to the control chip. The control chip adjusts the attenuation intensity of the corresponding optical attenuator based on the light intensity fed back by each photodetector. The photodetectors in this application can be photodiodes or photomultiplier tubes.

[0073] To ensure that more light output from the optical attenuator is transmitted to the helical waveguide coil, the waveguide beam splitter uses a splitting ratio of (90+M):(10-M), where M is a positive integer less than 10. This means the waveguide beam splitter can split the input light into two beams at a ratio of (90+M):(10-M). One beam is input to a photodetector, and the other beam is input to one input terminal of a correspondingly connected first 50:50 beam splitter. Specifically, the splitting ratio of the waveguide beam splitter can be 99:1 or 95:5, etc.

[0074] Specifically, when N=6, the quantum light source also includes 6 waveguide beam splitters, 6 photodetectors, and a control chip, such as... Figure 6As shown in the diagram. For ease of description, the six waveguide beamsplitters are named from top to bottom as the first waveguide beamsplitter, second waveguide beamsplitter, ..., sixth waveguide beamsplitter. The six photodetectors are named as the first photodetector, second photodetector, ..., sixth photodetector. The six optical attenuators in the intensity modulation module and the three first 50:50 beamsplitters in the beam combining module are also named as described above. The input of the first waveguide beamsplitter is connected to the output of the first optical attenuator, and its two outputs are respectively connected to the upper inputs of the first photodetector and the first 50:50 beamsplitter. The input of the second waveguide beamsplitter is connected to the output of the second optical attenuator, and its two outputs are respectively connected to the lower inputs of the second photodetector and the first 50:50 beamsplitter. The input of the third waveguide beamsplitter is connected to the output of the third optical attenuator, and its two outputs are respectively connected to the upper inputs of the third photodetector and the second 50:50 beamsplitter. The input of the fourth waveguide beamsplitter is connected to the output of the fourth optical attenuator. The two outputs of the fourth waveguide beamsplitter are respectively connected to the lower inputs of the fourth photodetector and the second 50:50 beamsplitter. The input of the fifth waveguide beamsplitter is connected to the output of the fifth optical attenuator. The two outputs of the fifth waveguide beamsplitter are respectively connected to the upper inputs of the fifth photodetector and the third 50:50 beamsplitter. The input of the sixth waveguide beamsplitter is connected to the output of the sixth optical attenuator. The two outputs of the sixth waveguide beamsplitter are respectively connected to the lower inputs of the fifth photodetector and the third 50:50 beamsplitter. The control chip is connected to all six photodetectors and six optical attenuators. The six photodetectors are used to detect the intensity of the light output from the corresponding optical attenuator and feed the intensity back to the control chip. The control chip adjusts the attenuation level of the corresponding optical attenuator based on the detection results to ensure that the intensity of the light incident on each spiral waveguide coil meets the preset requirements.

[0075] In this application, the first phase modulator on path 1 and the second phase modulator on path 2 can both be connected to the control chip, and the phase of the two phase modulators can be modulated by the control chip. Of course, these two first phase modulators can also be connected to other control chips or host computers to achieve real-time phase modulation.

[0076] Furthermore, both the first and second phase modulators in this application are thermally modulated phase modulators or electro-optic phase modulators. When the first and second phase modulators are thermally modulated phase modulators, the optical waveguide is directly heated by modulating the applied current or voltage to change the temperature and thus change the effective refractive index of the optical waveguide, thereby changing the phase of the photons or light pulses input to it. When the first and second phase modulators are electro-optic phase modulators, the voltage applied to the electro-optic crystal is modulated to change the refractive index of the electro-optic crystal, causing a change in the optical wave characteristics passing through the electro-optic crystal, thereby achieving phase modulation of the photons or light pulses input to it.

[0077] Based on the above, it can be seen that the micro-ring resonator generates an optical frequency comb based on the pump light output from the laser. A wave demultiplexer separates and attenuates the light of different frequency components in the optical frequency comb. The two frequency components, symmetrical about the center frequency of the optical frequency comb, are then transmitted to helical waveguide coils. Each helical waveguide coil generates entangled photon pairs with the same wavelength with a certain probability based on nonlinear interaction. In this application, multiple helical waveguide coils are used, and all light transmitted to the helical waveguide coils originates from a single optical frequency comb, which is generated based on the pump light output from a single laser. Therefore, the effect of generating a quantum light source array from a single laser is achieved, reducing the number of lasers required, lowering costs, and enhancing system stability. Furthermore, since the frequency components in the optical frequency comb maintain coherence, high-dimensional quantum entangled states can be obtained based on this method.

[0078] In relation to the quantum light source based on an optical frequency comb provided in this application, this application also provides a corresponding method for generating quantum states using a quantum light source based on an optical frequency comb, such as... Figure 7 As shown, the method includes:

[0079] S11: Pump light output from the laser.

[0080] S12: The bus straight waveguide of the micro-ring resonator receives the pump light and inputs the pump light into the micro-ring in an evanescent coupling manner. The micro-ring generates multiple equally spaced discrete frequency components based on the four-wave mixing effect and forms an optical frequency comb.

[0081] S13: The wave demultiplexer distributes the optical frequency comb path of the micro-ring resonator output, enabling the separation of optical components of different frequencies.

[0082] S14: Each optical attenuator receives light of a frequency component and modulates the intensity of the received light.

[0083] S15: Each first 50:50 beam splitter receives the light output from two optical attenuators and combines them, and the frequency components of the light received by the two optical attenuators are symmetrical about the center frequency of the optical comb.

[0084] S16: Each spiral waveguide coil receives the combined light output from the corresponding first 50:50 beam splitter and generates entangled photon pairs with the same wavelength based on the combined light with a certain probability.

[0085] S17: Entangled photon pairs output from one spiral waveguide coil are directly output, and entangled photon pairs output from another (N / 2)-1 spiral waveguide coils are respectively input to the first phase modulator for phase modulation, and then output after phase modulation.

[0086] In S17, the number of first phase modulators is N, which is one less than the number of spiral waveguide coils. That is, a first phase modulator is not set at the output end of one of the spiral waveguide coils as a reference.

[0087] Since the frequency components in the optical frequency comb maintain coherence, this method can be used to obtain arbitrary high-dimensional quantum entangled states.

[0088] When the quantum light source also includes N waveguide beam splitters, N photodetectors, and a control chip, such as Figure 8 As shown, the method further includes:

[0089] S21: Each waveguide beam splitter receives the light output from the corresponding connected optical attenuator and splits it, so that part of the beam is input to the photodetector and the other part of the beam is input to one input terminal of the corresponding first 50:50 beam splitter.

[0090] S22: Each photodetector detects the intensity of the light beam transmitted to it and feeds back the detection result to the control chip. The control chip adjusts the attenuation intensity of the corresponding optical attenuator based on the detection result fed back by each photodetector.

[0091] The above process enables real-time adjustment of the attenuation intensity of the optical attenuator to ensure that the intensity of the light incident on each spiral waveguide coil meets the preset requirements.

[0092] The various embodiments in this specification are described in a progressive, parallel, or combined manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the embodiments can be referred to each other.

[0093] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or apparatus comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or apparatus that includes the aforementioned element.

[0094] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A quantum light source based on an optical frequency comb, characterized in that, It includes a laser, a micro-ring resonator, a wave demultiplexer, an intensity modulation module, a beam combining module, a two-photon generation module, and a first phase modulator; The laser is used to output pump light and transmit the pump light to the micro-ring resonant cavity; The microring resonant cavity generates an optical frequency comb based on the pump light. It consists of a bus straight waveguide and a microring. The bus straight waveguide is used to receive the pump light and input the pump light into the microring in an evanescent coupling manner. The microring generates multiple equally spaced discrete frequency components based on the four-wave mixing effect and forms an optical frequency comb. The optical frequency comb is symmetrical about its center frequency as the axis of symmetry. The wave demultiplexer is connected to the microring resonator and is used to allocate the optical frequency comb path output by the microring resonator so as to separate the optical components of different frequencies. The intensity modulation module includes N optical attenuators, each of which is used to receive light of a corresponding frequency component and modulate the intensity of the received light, where N is an even number ≥ 4; The beam combining module includes N / 2 first 50:50 beam splitters. The two input terminals of each first 50:50 beam splitter are respectively connected to an optical attenuator for beam combining the light output from the two optical attenuators. The frequency components of the light received by the two optical attenuators connected to each first 50:50 beam splitter are symmetrical about the center frequency. The two-photon generation module includes N / 2 helical waveguide coils, each of which is connected to a first 50:50 beam splitter to receive the combined light output from the first 50:50 beam splitter and generate entangled photon pairs with the same wavelength based on the combined light with a certain probability. The number of the first phase modulators is (N / 2)-1, and they are connected one-to-one with the output terminals of the (N / 2)-1 spiral waveguide coils, respectively, for modulating the phase of the entangled photon pairs input to them.

2. A quantum light source based on an optical frequency comb according to claim 1, characterized in that, The quantum light source further includes N waveguide beam splitters, N photodetectors, and a control chip. Each waveguide beam splitter's input is connected to one of the optical attenuators, and each waveguide beam splitter's two outputs are connected to a photodetector and an input of a corresponding first 50:50 beam splitter, respectively. The waveguide beam splitter receives the beam output from the corresponding optical attenuator and splits it, so that a portion of the beam is input to the photodetector and the other portion is input to an input of the corresponding first 50:50 beam splitter. All N photodetectors and N optical attenuators are connected to the control chip. The photodetectors detect the intensity of the light transmitted to them and feed the intensity back to the control chip. The control chip adjusts the attenuation intensity of the corresponding optical attenuator based on the light intensity fed back by each photodetector.

3. A quantum light source based on an optical frequency comb according to claim 1 or 2, characterized in that, The wave demultiplexer is an arrayed waveguide grating.

4. A quantum light source based on an optical frequency comb according to claim 1 or 2, characterized in that, The optical attenuator consists of two second 50:50 beam splitters, an upper interference arm, a lower interference arm, and a second phase modulator. The two ends of the upper interference arm are respectively connected to the upper output of the two second 50:50 beam splitters, and the two ends of the lower interference arm are respectively connected to the lower output of the two second 50:50 beam splitters. The second phase modulator is disposed on the upper or lower interference arm.

5. A quantum light source based on an optical frequency comb according to claim 2, characterized in that, The beam splitting ratio of the waveguide beam splitters is (90+M):(10-M), where M is a positive integer less than 10.

6. A quantum light source based on an optical frequency comb according to claim 2, characterized in that, The photodetector is a photodiode or a photomultiplier tube.

7. A quantum light source based on an optical frequency comb according to claim 3, characterized in that, The arrayed waveguide grating includes an input waveguide, an input star coupler, an arrayed waveguide, an output star coupler, and several output waveguides. The input waveguide is used to input the optical frequency comb output from the micro-ring resonator to the input star coupler. The arrayed waveguide includes several transmission waveguides with equally spaced lengths. The two ends of each transmission waveguide are connected to the input star coupler and the output star coupler, respectively. The input star coupler is used to uniformly distribute the received light into the arrayed waveguide. The arrayed waveguide is used to generate a phase difference between the light received by different transmission waveguides and to focus light of different wavelengths at different positions on the output star coupler. The input port of the output waveguide is located at the focal point of the output star coupler and is used to output light of the corresponding wavelength.

8. A quantum light source based on an optical frequency comb according to claim 4, characterized in that, Both the first phase modulator and the second phase modulator are thermally modulated phase modulators or electro-optic phase modulators.

9. A method for generating quantum states using a quantum light source based on an optical frequency comb, characterized in that, The method is applied to the quantum light source based on an optical frequency comb as described in any one of claims 1-8. The quantum light source includes a laser, a micro-ring resonator, a wave demultiplexer, an intensity modulation module, a beam combining module, a two-photon generation module, and a first phase modulator. The micro-ring resonator is composed of a bus straight waveguide and a micro-ring. The intensity modulation module includes N optical attenuators. The beam combining module includes N / 2 first 50:50 beam splitters. The two-photon generation module includes N / 2 helical waveguide coils. The number of first phase modulators is (N / 2)-1, where N is an even number ≥ 4. The method includes: The laser outputs pump light; The bus straight waveguide of the microring resonator receives the pump light and inputs the pump light into the microring in an evanescent coupling manner. The microring generates multiple equally spaced discrete frequency components based on the four-wave mixing effect and forms an optical frequency comb. The wave demultiplexer distributes the optical frequency comb path of the micro-ring resonator output, enabling the separation of optical components of different frequencies; Each optical attenuator receives light of a specific frequency component and modulates the intensity of the received light. Each first 50:50 beam splitter receives the light output from two optical attenuators and combines them into a single beam, with the frequency components of the light received by the two optical attenuators being symmetrical about the center frequency of the optical comb. Each spiral waveguide coil receives the combined light output from the corresponding first 50:50 beam splitter and generates entangled photon pairs with the same wavelength based on the combined light with a certain probability. The entangled photon pairs output from one spiral waveguide coil are directly output, while the entangled photon pairs output from another (N / 2)-1 spiral waveguide coils are respectively input to the first phase modulator for phase modulation, and then output after phase modulation.

10. A method for generating quantum states using a quantum light source based on an optical frequency comb, as described in claim 9, characterized in that, When the quantum light source further includes N waveguide beam splitters, N photodetectors, and a control chip, the method further includes: Each waveguide beam splitter receives the light output from the corresponding connected optical attenuator and splits it, so that part of the beam is input to the photodetector and the other part of the beam is input to one input terminal of the corresponding first 50:50 beam splitter. Each photodetector detects the intensity of the light beam transmitted through it and feeds the detection results back to the control chip. The control chip adjusts the attenuation intensity of the corresponding optical attenuator based on the detection results fed back by each photodetector.

Images