A system and method for generating frequency-coincident entangled photon pairs over a broad frequency range

Abstract

The application discloses a system for generating frequency-consistent entangled photon pairs in a wide frequency band, comprising a pump light source, an optical frequency space-time wave packet synthesis unit, a parametric conversion optical crystal, an optical path adjusting unit and a photon detection unit arranged in sequence; the pump light source is used for emitting pulsed laser; the optical frequency space-time wave packet synthesis unit is used for synthesizing a specific space-time wave packet light beam; the space-time wave packet light beam with adjustable group velocity is synthesized by the optical frequency space-time wave packet synthesis unit as the pump light of a spontaneous parametric down-conversion process, frequency-consistent entangled photon pairs at a specific frequency are generated, and by designing different spectral tilt angles, the conventional second-order nonlinear optical crystal can be used to generate frequency-consistent entangled photon pairs at any frequency in a wide frequency range, and the technical problem that the prior art cannot generate frequency-consistent entangled photon pairs at an arbitrarily selected frequency in a wide frequency band is solved.

Description

Technical Field

[0001] This invention belongs to the field of quantum light source technology and relates to frequency-consistent entangled photons, specifically a system and method for generating frequency-consistent entangled photon pairs over a wide frequency band. Background Technology

[0002] Frequency-coordinated entangled photons are an important resource in quantum precision measurement. Utilizing frequency-coordinated entangled photon states can improve the measurement precision of timing, positioning, and phase beyond the standard quantum limit, reaching the Heisenberg limit. Frequency-coordinated entangled photon pairs are typically generated using a spontaneous parametric down-conversion nonlinear optical process pumped by a broadband short-pulse laser. Specifically, the spontaneous parametric down-conversion process involves irradiating a second-order nonlinear optical crystal with a pump laser beam. Through a second-order nonlinear three-wave mixing process within the crystal, a small portion of the pump light photons split into two lower-frequency photons, called the signal photon and the idler photon. To ensure the efficiency of this process, the nonlinear optical crystal must be designed according to the "phase-matching condition," ensuring that the pump photon, signal photon, and idler photon maintain phase matching during propagation within the crystal. This phase-matching condition corresponds to the conservation of energy and momentum among these three photons during the conversion from a single pump photon into signal and idler photons. According to the conservation of energy and momentum, there is a frequency correlation and an emission direction correlation between signal photons and idler photons generated in and emitted from a crystal.

[0003] Due to the wide bandwidth of typical pulsed pump sources and the inverse frequency correlation of downconverted photon pairs, the spectra of signal photons and idler photons generated through spontaneous parametric downconversion are usually inconsistent. Therefore, to achieve the generation of frequency-consistent entangled photon pairs, precise manipulation and control of the joint spectral density of the two output states of the spontaneously parametric downconverted photons are required. A traditional method is to filter the signal and idler photons using narrowband optical filters, or to use very thin nonlinear crystals, but both of these measures significantly reduce the flux of the output photons. Another commonly used method is to utilize the characteristic that phase matching is a function of angle, and achieve this by controlling the spatial dispersion of the pump light. However, this method requires precise focusing and alignment of the optical path, making it difficult to design a robust light source system in practice. Another approach involves applying extended phase-matching conditions to a periodically polarized second-order nonlinear optical crystal. This requires satisfying not only the aforementioned phase-matching condition but also the group velocity matching conditions for the pump, signal, and idler photons. However, for a given nonlinear optical crystal, due to its inherent dispersion relation, the phase-matching and group velocity matching conditions for the pump and degenerate downconversion light can only be simultaneously satisfied within a very narrow frequency band. Furthermore, only a few nonlinear optical crystals are available. Therefore, the problem of how to flexibly generate frequency-consistent entangled photon pairs at any arbitrarily selected frequency within a wide frequency band remains unsolved. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a system and method for generating frequency-consistent entangled photon pairs in a wide frequency band, so as to solve the technical problem that the existing technology cannot generate frequency-consistent entangled photon pairs at any selected frequency in a wide frequency band.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A system for generating frequency-consistent entangled photon pairs over a wide frequency band includes a pump source, an optical frequency spatiotemporal wave packet synthesis unit, a parametric conversion optical crystal, an optical path adjustment unit, and a photon detection unit arranged sequentially.

[0007] The pump source is used to emit pulsed laser light;

[0008] The aforementioned optical frequency spatiotemporal wave packet synthesis unit is used to synthesize a beam of light with a specific spatiotemporal wave packet.

[0009] The parametric conversion optical crystal is used to convert some of the pump photons in a spacetime wave packet beam into frequency-consistent entangled photon pairs;

[0010] The frequency-consistent entangled photon pair consists of a signal photon and an idler photon;

[0011] The optical path adjustment unit is used to shield the pump light in the signal photons and idler photons, as well as the environmental stray noise light in the signal photons and idler photons;

[0012] The photon detection unit is used to detect and record the arrival time sequence of signal photons and idler photons, and to complete the coincidence measurement of entangled photon pairs with consistent frequencies.

[0013] This invention also includes the following technical features:

[0014] The optical frequency spatiotemporal wave packet synthesis unit includes a first diffraction grating, a first cylindrical lens, a phase modulation plate, a second cylindrical lens, and a second diffraction grating arranged sequentially.

[0015] The optical path adjustment unit includes a dichroic mirror and a bandpass filter arranged sequentially. The bandpass filter includes a first bandpass filter and a second bandpass filter. The first bandpass filter and the second bandpass filter are respectively disposed on the optical paths of the signal photon and the idler photon.

[0016] The photon detection unit includes a first single-photon detector, a second single-photon detector, and a multi-channel event timer. The first single-photon detector and the second single-photon detector are respectively disposed on the optical paths of the signal photon and the idler photon after passing through the optical path adjustment unit. The first single-photon detector and the second single-photon detector are electrically connected to the multi-channel event timer.

[0017] The pump source is a broadband pulsed laser.

[0018] The parametric conversion optical crystal is a second-order nonlinear crystal of β-phase barium borate.

[0019] A method for generating frequency-consistent entangled photon pairs over a wide frequency band, employing the aforementioned system for generating frequency-consistent entangled photon pairs over a wide frequency band, specifically includes the following steps:

[0020] Step 1: The pulsed laser emitted by the pump source is injected into the optical frequency spatiotemporal wave packet synthesis unit;

[0021] Step 2: Obtain a specific spatiotemporal wave packet beam by adjusting the spectral tilt angle of the pulsed laser;

[0022] The specific spatiotemporal wave packet beam mentioned above is a spatiotemporal wave packet beam that can propagate at any group velocity in free space or an optical medium;

[0023] Step 3: Inject the specific spatiotemporal wave packet beam obtained in Step 2 into the parametric conversion optical crystal to obtain specific frequency-consistent entangled photon pairs;

[0024] Step 4: The specific frequency entangled photon pair obtained in step 3 is injected into the optical path adjustment unit. The optical path adjustment unit shields the pump light and ambient stray noise light in the signal photon and idler photon, and emits the specific frequency entangled photon pair.

[0025] Step 5: The specific frequency-consistent entangled photon pairs obtained in Step 4 enter the photon detection unit. The photon detection unit detects and records the arrival time sequence of the signal photon and the idler photon, and completes the coincidence measurement of the frequency-consistent entangled photon pairs, thus obtaining the frequency-consistent entangled photon pairs.

[0026] In step 2, the range of the spectral tilt angle is -90° to 90°.

[0027] A method for generating frequency-consistent entangled photon pairs over a wide frequency band, employing the aforementioned system for generating frequency-consistent entangled photon pairs over a wide frequency band, specifically includes the following steps:

[0028] Step 1: The pulsed laser emitted by the pump source is injected into the optical frequency spatiotemporal wave packet synthesis unit;

[0029] Step 2: Obtain a specific spatiotemporal wave packet beam by adjusting the spectral tilt angle of the pulsed laser;

[0030] The specific spatiotemporal wave packet beam mentioned above is a spatiotemporal wave packet beam that can propagate at any group velocity in free space or an optical medium;

[0031] Specifically, different phase patterns are loaded onto a phase modulation plate to obtain different spectral tilt angles, thereby obtaining a specific spatiotemporal wave packet beam.

[0032] Step 3: Inject the specific spatiotemporal wave packet beam obtained in Step 2 into the parametric conversion optical crystal to obtain specific frequency-consistent entangled photon pairs;

[0033] Step 4: The specific frequency entangled photon pair obtained in step 3 is injected into the optical path adjustment unit. The optical path adjustment unit shields the pump light and ambient stray noise light in the signal photon and idler photon, and emits the specific frequency entangled photon pair.

[0034] Step 5: The specific frequency-consistent entangled photon pairs obtained in Step 4 enter the photon detection unit. The photon detection unit detects and records the arrival time sequence of the signal photon and the idler photon, and completes the coincidence measurement of the frequency-consistent entangled photon pairs, thus obtaining the frequency-consistent entangled photon pairs.

[0035] In step 2, the range of the spectral tilt angle is -90° to 90°.

[0036] Compared with the prior art, the beneficial technical effects of this invention are:

[0037] (I) In this invention, the spatiotemporal wave packet beam with adjustable synthesis group velocity of the optical frequency spatiotemporal wave packet synthesis unit is used as the pump light for the spontaneous parametric downconversion process to realize the generation of frequency-consistent entangled photon pairs at a specific frequency. By designing different spectral tilt angles, it is possible to generate frequency-consistent entangled photon pairs at any frequency in a wide frequency range using conventional ordinary second-order nonlinear optical crystals. This solves the technical problem that the prior art cannot generate frequency-consistent entangled photon pairs at any selected frequency in a wide frequency band.

[0038] (II) Since no external narrowband spectral filter is required in this invention, it is beneficial to improve the generation efficiency of entangled photon pairs. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the system structure of the present invention;

[0040] Figure 2 This is a schematic diagram of the optical path structure of the present invention;

[0041] Figure 3 The figure shows the implementation results of the numerical simulation for the example;

[0042] in, Figure 3 (a) is a graph of the phase matching function. Figure 3 (b) is a plot of the joint spectral function of entangled photon pairs;

[0043] Figure 4 The spatiotemporal spectrum of the spatiotemporal wave packet beam;

[0044] The meanings of the labels in the figure are as follows: 1-Pump source, 2-Optical frequency spatiotemporal wave packet synthesis unit, 3-Parallel conversion optical crystal, 4-Optical path adjustment unit, 5-Photon detection unit;

[0045] 201-First diffraction grating, 202-First cylindrical lens, 203-Phase modulation plate, 204-Second cylindrical lens, 205-Second diffraction grating;

[0046] 401 - Dichroic mirror, 402 - Bandpass filter, 40201 - First bandpass filter, 40202 - Second bandpass filter;

[0047] 501 - First single-photon detector, 502 - Second single-photon detector, 503 - Multi-channel event timer.

[0048] The specific content of the present invention will be further explained and described in detail below with reference to the embodiments. Detailed Implementation

[0049] It should be noted that, unless otherwise specified, all components in this invention are components known in the art.

[0050] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0051] This invention provides a system for generating frequency-consistent entangled photon pairs over a wide frequency band, such as... Figures 1 to 2 As shown, it includes a pump light source 1, an optical frequency spatiotemporal wave packet synthesis unit 2, a parametric conversion optical crystal 3, an optical path adjustment unit 4, and a photon detection unit 5 arranged sequentially.

[0052] Pump source 1 is used to emit pulsed laser light;

[0053] Optical frequency spatiotemporal wave packet synthesis unit 2 is used to synthesize beams of specific spatiotemporal wave packets;

[0054] Parametric conversion optical crystal 3 is used to convert some of the pump photons in the spatiotemporal wave packet beam into frequency-consistent entangled photon pairs;

[0055] Entangled photon pairs with the same frequency consist of a signal photon and an idler photon;

[0056] The optical path adjustment unit 4 is used to shield the pump light in the signal photons and idler photons, as well as the ambient stray noise light in the signal photons and idler photons;

[0057] The photon detection unit 5 is used to detect and record the arrival time series of signal photons and idler photons, and to complete the coincidence measurement of entangled photon pairs with consistent frequencies.

[0058] In the above technical solution, a specific spatiotemporal wave packet beam with an adjustable synthesis group velocity is used as the pump light for the spontaneous parametric downconversion process by utilizing the optical frequency spatiotemporal wave packet synthesis unit 2. This enables the generation of frequency-consistent entangled photon pairs at a specific frequency. By designing different spectral tilt angles, it is possible to generate frequency-consistent entangled photon pairs at any frequency within a wide frequency range using a conventional second-order nonlinear optical crystal. This solves the technical problem that existing technologies cannot generate frequency-consistent entangled photon pairs at any selected frequency within a wide frequency band.

[0059] Furthermore, since no external extremely narrowband spectral filter is required, it is beneficial to improve the generation efficiency of entangled photon pairs.

[0060] refer to Figure 4 The spatiotemporal wave packet is represented in the spectral domain as a conic section formed by the intersection of the light cone and the spectral hyperplane in the figure. The angle between the spectral hyperplane and the propagation direction wave vector is called the spectral tilt angle θ, which determines the group velocity of the wave packet.

[0061] Specifically, the optical frequency spatiotemporal wave packet synthesis unit 2 includes a first diffraction grating 201, a first cylindrical lens 202, a phase modulation plate 203, a second cylindrical lens 204, and a second diffraction grating 205 arranged sequentially.

[0062] Specifically, the optical path adjustment unit 4 includes a dichroic mirror 401 and a bandpass filter 402 arranged sequentially. The bandpass filter 402 includes a first bandpass filter 40201 and a second bandpass filter 40202. The first bandpass filter 40201 and the second bandpass filter 40202 are respectively disposed on the optical paths of the signal photon and the idler photon.

[0063] In the above technical solution, the dichroic mirror is used to block the pump light in the signal light and the idler light, and the long-pass filter is used to shield the environmental stray noise light in the signal photons and the idler photons.

[0064] Specifically, the photon detection unit 5 includes a first single-photon detector 501, a second single-photon detector 502, and a multi-channel event timer 503. The first single-photon detector 501 and the second single-photon detector 502 are respectively disposed on the optical paths of the signal photon and the idler photon after passing through the optical path adjustment unit 4. The first single-photon detector 501 and the second single-photon detector 502 are electrically connected to the multi-channel event timer 503.

[0065] In the above technical solution, the first single-photon detector is used to detect the signal photon, the second single-photon detector is used to detect the idler photon, and the multi-channel event timer is used to record the arrival time sequence of the signal photon and the idler photon to complete the coincidence measurement of the entangled photon pair with the same frequency.

[0066] Specifically, pump source 1 is a broadband pulsed laser.

[0067] Specifically, the parametric conversion optical crystal 3 adopts a second-order nonlinear crystal of β-phase barium borate.

[0068] In the above technical solution, some pump photons in the spatiotemporal wave packet beam are down-converted into signal photons and idler photons in a second-order nonlinear optical crystal.

[0069] This invention also provides a method for generating frequency-consistent entangled photon pairs over a wide frequency band, specifically including the following steps:

[0070] Step 1: The pulsed laser emitted by the pump source 1 is injected into the optical frequency spatiotemporal wave packet synthesis unit 2;

[0071] Step 2: Obtain a specific spatiotemporal wave packet beam by adjusting the spectral tilt angle of the pulsed laser;

[0072] A specific spatiotemporal wave packet beam is a spatiotemporal wave packet beam that can propagate at any group velocity in free space or an optical medium;

[0073] Step 3: The specific spatiotemporal wave packet beam obtained in Step 2 is incident onto the parametric conversion optical crystal 3 to obtain specific frequency-consistent entangled photon pairs;

[0074] Step 4: The specific frequency entangled photon pair obtained in step 3 is injected into the optical path adjustment unit 4. The optical path adjustment unit 4 shields the pump light and environmental stray noise light in the signal photon and idler photon, and emits the specific frequency entangled photon pair.

[0075] Step 5: The specific frequency-consistent entangled photon pairs obtained in step 4 enter the photon detection unit 5. The photon detection unit 5 detects and records the arrival time sequence of the signal photon and the idler photon, and completes the coincidence measurement of the frequency-consistent entangled photon pairs, thus obtaining the frequency-consistent entangled photon pairs.

[0076] Specifically, in step 2, the range of the spectral tilt angle is -90° to 90°.

[0077] A method for generating frequency-consistent entangled photon pairs over a wide frequency band, employing a system for generating frequency-consistent entangled photon pairs over a wide frequency band, specifically includes the following steps:

[0078] Step 1: The pulsed laser emitted by the pump source 1 is injected into the optical frequency spatiotemporal wave packet synthesis unit 2;

[0079] Step 2: Obtain a specific spatiotemporal wave packet beam by adjusting the spectral tilt angle of the pulsed laser;

[0080] A specific spatiotemporal wave packet beam is a spatiotemporal wave packet beam that can propagate at any group velocity in free space or an optical medium;

[0081] Specifically, different phase patterns are loaded onto the phase modulation plate 203 to obtain different spectral tilt angles, thereby obtaining a specific spatiotemporal wave packet beam.

[0082] Step 3: The specific spatiotemporal wave packet beam obtained in Step 2 is incident onto the parametric conversion optical crystal 3 to obtain specific frequency-consistent entangled photon pairs;

[0083] Step 4: The specific frequency entangled photon pair obtained in step 3 is injected into the optical path adjustment unit 4. The optical path adjustment unit 4 shields the pump light and environmental stray noise light in the signal photon and idler photon, and emits the specific frequency entangled photon pair.

[0084] Step 5: The specific frequency-consistent entangled photon pairs obtained in step 4 enter the photon detection unit 5. The photon detection unit 5 detects and records the arrival time sequence of the signal photon and the idler photon, and completes the coincidence measurement of the frequency-consistent entangled photon pairs, thus obtaining the frequency-consistent entangled photon pairs.

[0085] In step 2, the range of the spectral tilt angle is -90° to 90°.

[0086] Example:

[0087] This embodiment employs the system and method of the present invention, and the results can be obtained through numerical simulation. Figure 3 The implementation results shown illustrate the use of type II phase-matched SPDC on a 2mm thick β-phase barium borate (BBO) crystal. A pump source with a center wavelength of 390nm and a pulse duration of 25fs was employed. The pump light was converted into a specific spatiotemporal wave packet beam using an optical frequency spatiotemporal wave packet synthesizer with a spectral tilt angle of -0.71°. The combined spectral characteristics of the signal photons and idler photons generated by pumping the β-phase barium borate (BBO) crystal using this spatiotemporal wave packet beam are as follows: Figure 3 As shown, Figure 3 (a) is the phase matching function. Figure 3 (b) shows the joint spectral function of the entangled photon pairs. We can see that the phase-matching function exhibits a diagonal-symmetric distribution, and the joint spectral function also exhibits a diagonal-symmetric distribution, proving that the method described can generate frequency-coherent entangled photon pairs with a center wavelength of 780 nm in β-phase barium borate (BBO) crystals. However, using conventional Gaussian laser pulses (non-spatiotemporal wave packet beams), frequency-coherent entanglement in β-phase barium borate (BBO) crystals can only be generated at a pump source wavelength of 1514 nm. This demonstrates that the method of the present invention can flexibly generate frequency-coherent entangled photon pairs at any arbitrarily selected frequency within a wide frequency band.

Claims

1. A system for generating frequency-consistent entangled photon pairs over a wide frequency band, characterized in that, It includes a pump source (1), an optical frequency spatiotemporal wave packet synthesis unit (2), a parametric conversion optical crystal (3), an optical path adjustment unit (4), and a photon detection unit (5) arranged in sequence. The pump source (1) is used to emit pulsed laser light; The aforementioned optical frequency spatiotemporal wave packet synthesis unit (2) is used to synthesize a specific spatiotemporal wave packet beam; The optical frequency spatiotemporal wave packet synthesis unit (2) includes a first diffraction grating (201), a first cylindrical lens (202), a phase modulation plate (203), a second cylindrical lens (204), and a second diffraction grating (205) arranged sequentially. The parametric conversion optical crystal (3) is used to convert some of the pump photons in the spatiotemporal wave packet beam into frequency-consistent entangled photon pairs; The frequency-consistent entangled photon pair consists of a signal photon and an idler photon; The optical path adjustment unit (4) is used to shield the pump light in the signal photons and idler photons, as well as the environmental stray noise light in the signal photons and idler photons; The photon detection unit (5) is used to detect and record the arrival time sequence of signal photons and idler photons, and to complete the coincidence measurement of entangled photon pairs with consistent frequencies.

2. The system for generating frequency-consistent entangled photon pairs over a wide frequency band as described in claim 1, characterized in that, The optical path adjustment unit (4) includes a dichroic mirror (401) and a bandpass filter (402) arranged in sequence. The bandpass filter (402) includes a first bandpass filter (40201) and a second bandpass filter (40202). The first bandpass filter (40201) and the second bandpass filter (40202) are respectively disposed on the optical paths of the signal photon and the idler photon.

3. The system for generating frequency-consistent entangled photon pairs over a wide frequency band as described in claim 1, characterized in that, The photon detection unit (5) includes a first single-photon detector (501), a second single-photon detector (502), and a multi-channel event timer (503). The first single-photon detector (501) and the second single-photon detector (502) are respectively disposed on the optical paths of the signal photon and the idler photon after passing through the optical path adjustment unit (4). The first single-photon detector (501) and the second single-photon detector (502) are electrically connected to the multi-channel event timer (503).

4. The system for generating frequency-consistent entangled photon pairs over a wide frequency band as described in claim 1, characterized in that, The pump source (1) is a broadband pulsed laser.

5. The system for generating frequency-consistent entangled photon pairs over a wide frequency band as described in claim 1, characterized in that, The parametric conversion optical crystal (3) mentioned above is a second-order nonlinear crystal of barium borate in β phase.

6. A method for generating frequency-consistent entangled photon pairs over a wide frequency band, characterized in that, The system for generating frequency-consistent entangled photon pairs over a wide frequency band, as described in any one of claims 1 to 5, specifically includes the following steps: Step 1: The pulsed laser emitted by the pump source (1) is injected into the optical frequency spatiotemporal wave packet synthesis unit (2). Step 2: Obtain a specific spatiotemporal wave packet beam by adjusting the spectral tilt angle of the pulsed laser; The specific spatiotemporal wave packet beam is a spatiotemporal wave packet beam that can propagate at any group velocity in free space or an optical medium; Step 3: The specific spatiotemporal wave packet beam obtained in Step 2 is incident onto the parametric conversion optical crystal (3) to obtain specific frequency-consistent entangled photon pairs; Step 4: The specific frequency entangled photon pair obtained in step 3 is injected into the optical path adjustment unit (4). The optical path adjustment unit (4) shields the pump light and environmental stray noise light in the signal photon and idler photon, and emits the specific frequency entangled photon pair. Step 5: The specific frequency-consistent entangled photon pair obtained in step 4 enters the photon detection unit (5). The photon detection unit (5) detects and records the arrival time sequence of the signal photon and the idler photon, and completes the coincidence measurement of the frequency-consistent entangled photon pair, thus obtaining the frequency-consistent entangled photon pair.

7. The method for generating frequency-consistent entangled photon pairs over a wide frequency band as described in claim 6, characterized in that, In step 2, the range of the spectral tilt angle is -90° to 90°.

8. The method for generating frequency-consistent entangled photon pairs over a wide frequency band as described in claim 6, characterized in that, Step 2 specifically involves loading different phase patterns onto the phase modulation plate (203) to obtain different spectral tilt angles, thereby obtaining a specific spatiotemporal wave packet beam.

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