Gradient polarization BBO crystal quantum entanglement source device based on wavefront-power cooperative regulation and control method

Abstract

The invention relates to a gradient polarization BBO crystal quantum entanglement source device based on a wavefront-power cooperative regulation and control method. The gradient polarization BBO crystal quantum entanglement source device is mainly applied to the fields of quantum optics and nonlinear photonics. The device breaks through the limitation of a traditional entanglement source in the aspects of wavelength tuning range and long-term stability through the cooperative regulation and control of an integrated spatial light modulator (SLM) and an electro-optical modulator (EOM) and the design of a gradient polarization crystal, and can be widely applied to the fields of quantum precision measurement, super-resolution imaging, weak signal detection and the like. A traditional BBO crystal entangled source based on spontaneous parametric down-conversion (SPDC) has the problems of narrow wavelength tuning range, thermally induced phase mismatch, group velocity mismatch (GVM) and the like. According to the invention, through dynamic wavefront-power cooperative regulation and control and gradient polarization crystal design, the generation efficiency and quality of entangled photon pairs are significantly improved. The device comprises a pump light source, a light source adjusting assembly, a BBO crystal assembly and a test assembly. The light source adjusting assembly dynamically adjusts the phase distribution of a pump light field through the SLM loading hologram, and meanwhile, the EOM adjusts the laser power in real time to suppress phase mismatch caused by environmental disturbance. The BBO crystal adopts a gradient polarization design, the pumping wavelength is dynamically adapted, the group velocity mismatch is compensated, and the time entanglement fidelity is improved to 99.3%. And the test assembly is used for evaluating the quality of the entangled photon pair and ensuring high purity and high fidelity of the entangled photon pair.

Description

Technical Field

[0001] The present invention relates to quantum optics and nonlinear photonics, and specifically relates to a quantum entanglement source device and method based on dynamic laser regulation and wavefront optimization of a nonlinear crystal (β-barium borate, BBO). By integrating the collaborative regulation of a spatial light modulator (SLM) and an electro-optic modulator (EOM) and the design of a gradient polarization crystal, the limitations of traditional entanglement sources in terms of wavelength tuning range and long-term stability are broken through. The present invention can be widely applied to quantum precision measurement. By utilizing the sub-shot-noise limit correlation of entangled photon pairs, super-resolution imaging and weak signal detection can be realized. Background Art

[0002] The BBO crystal entanglement source based on spontaneous parametric down-conversion (SPDC) is a core device in quantum information technology, but there are still many limitations in traditional crystal design. First of all, the wavelength tuning range of the entanglement source is narrow and is easily affected by thermal phase mismatch and group velocity mismatch (GVM). Ordinary BBO crystals are limited by the quasi-phase matching condition and can only work near a fixed pump wavelength (such as 405 nm or 532 nm). Although the traditional method expands the wavelength range through periodic polarization (PPLN), the polarization period is fixed and cannot dynamically adapt to different pump wavelengths, which further leads to a narrow wavelength tuning range. In addition, the temperature gradient inside the crystal, especially the transverse gradient, will make the spatial distribution of the nonlinear coefficient uneven, thereby reducing the entanglement purity. At the same time, under the action of an ultrafast pulsed pump, the group velocity difference between the signal light and the idler light will destroy the temporal entanglement, further exacerbating the limitations of traditional crystal design in practical applications.

[0003] Existing regulation technologies also have many deficiencies at the same time. They cannot synergistically optimize the pump light power and wavefront characteristics, resulting in low SPDC efficiency and a single regulation dimension. Traditional regulation technology solutions only rely on a single parameter such as temperature or power to compensate for the phase mismatch Δk = k p -k s -k i -2π / Λ and cannot optimize the pump light field distribution at the same time.

[0004] In view of the above problems, the present invention proposes a gradient polarization BBO crystal quantum entanglement source device based on a wavefront-power collaborative regulation method, which greatly solves the problems of narrow wavelength tuning range, thermal phase mismatch, group velocity mismatch, etc. existing in the prior art. Summary of the Invention

[0005] In view of this, the embodiments of the present application provide a gradient polarization BBO crystal quantum entanglement source device based on a wavefront-power collaborative regulation method, aiming to solve many problems existing in the prior art, including narrow wavelength tuning range, thermal-induced phase mismatch, group velocity mismatch (GVM), etc., so as to provide an efficient, stable and high-fidelity entanglement source solution for quantum information processing.

[0006] The present application provides a quantum entanglement source device, including a pump light source, a light source adjustment component, and a BBO crystal component. The pump light source is used to generate linearly polarized light, the light source adjustment component adjusts the linearly polarized light into polarized light with a linearly polarized state of a predetermined angle, and the BBO crystal component generates entangled photon pairs based on this polarized light. Through this design, the device can achieve precise regulation of the pump light and efficiently generate entangled photon pairs.

[0007] In the light source adjustment component, the spatial light modulator (SLM) dynamically adjusts the phase distribution of the pump light field by loading a hologram, and through a Bessel wavefront (non-diffracting transmission), to precisely match the spatial modulation of the nonlinear susceptibility tensor distribution d of the BBO crystal. eff At the same time, the electro-optic modulator (EOM) adjusts the laser power in real time to suppress the phase mismatch Δk = k p -k s -k i -2π / Λ caused by environmental disturbances. The power adjustment range is 100 - 2500 mW, and the response time does not exceed 100 μs. This collaborative regulation mechanism of wavefront and power significantly improves the spontaneous parametric down-conversion (SPDC) efficiency to 5×10 4 pairs / s·mW, which is 3 times higher than the traditional scheme.

[0008] The BBO crystal component further optimizes the generation process of entangled photon pairs. The first fiber collimator focuses the adjusted polarized light onto the BBO crystal, and the crystal generates entangled photon pairs based on this polarized light, including a first optical signal (signal light) and a second optical signal (idler light) that form a first included angle with each other. The second fiber collimator and the third fiber collimator respectively transmit the first optical signal and the second optical signal to a predetermined optical signal processing device to ensure that the entangled photon pairs can be efficiently collected and processed.

[0009] The BBO crystal adopts a gradient polarization design, and the polarization period Λ of its periodic polarization structure is dynamically designed according to the pump wavelength λ p to meet the quasi-phase matching condition so as to adapt to the wide spectral tuning of 400 - 2000 nm. In addition, the wedge-shaped geometry of the crystal is used to compensate for the group velocity mismatch (GVM), and the crystal tilt angle θ is determined by the formula Confirmed. With this design, the GVM is reduced to 0.05 ps / m, and the time entanglement fidelity under pulsed pumping is increased to 99.3%.

[0010] To further improve the stability and performance of the device, the present application introduces a dual-temperature-zone dynamic equilibrium system. The dual-zone thermoelectric cooling (TEC) temperature control system sets a temperature difference ΔT = 0.1 - 2 °C between the input end (T 1 ) and the output end (T 2 ) of the crystal, and is independently temperature-controlled by the dual-zone TEC with an accuracy of ±0.01 °C. This system satisfies the heat diffusion equation where P abs is the power absorbed by the crystal, V is the volume, and the transverse temperature gradient is less than 0.01 °C / mm. This temperature control design suppresses the temperature gradient inside the crystal, and at the same time increases the wavelength sensitivity of the effective nonlinear coefficient d eff to 0.1 nm / °C, supporting the multiplexing of multi-wavelength entanglement sources.

[0011] The device of the present application includes a test component for evaluating the quality of entangled photon pairs. The test component includes a first single-photon detector and a second single-photon detector, which are respectively used for detecting and counting the first optical signal and the second optical signal; the coincidence counter is used for performing time coincidence measurement and counting on the two optical signals; and the quality analysis module evaluates the quality of the entangled photon pairs according to the single-channel count value and the coincidence count value. In addition, the device also includes a first fiber optic filter and a second fiber optic filter, which are respectively used for filtering out the photons that do not conform to the wavelength of the entangled photons in the first optical signal and the second optical signal, thereby improving the purity of the entangled photon pairs.

[0012] To ensure the stable transmission of the polarization state, one or more devices in the device are connected to the upstream and downstream devices through polarization-maintaining optical fibers, improving the overall performance of the device and enhancing its stability in complex environments.

[0013] The beneficial effects of the present application are significant, greatly improving the generation efficiency and quality of entangled photon pairs and the stability of the device. The device supports ultra-wide wavelength tuning, with the phase-matching wavelength coverage ranging from 405 nm to 1550 nm, compatible with silicon-based (1550 nm) and gallium nitride (405 nm) quantum devices, greatly expanding the application scenarios. Through dynamic wavefront-power co-regulation, the spontaneous parametric down-conversion (SPDC) efficiency of the device is significantly increased to 3 times that of the traditional scheme. In addition, the BBO crystal adopts a gradient polarization design, dynamically adapting to the pump wavelength, compensating for the group velocity mismatch (GVM), and increasing the time entanglement fidelity under pulsed pumping to 99.3%. The coincidence count rate fluctuation of the device does not exceed 1% during 48 hours of continuous operation, meeting the stability requirements of quantum network nodes. At the same time, by filtering out the photons that do not conform to the wavelength of the entangled photons through the fiber optic filter, the purity of the entangled photon pairs is significantly improved. Description of the Drawings

[0014] Figure 1 : Overall framework diagram

[0015] Figure 2 : Optical path diagram construction drawing

[0016] Figure 3 : Wavefront-power collaborative regulation diagram

[0017] Figure 4 : BBO crystal polarization design Specific implementation manners

[0018] Example 1: Ultrafast time-energy entanglement source (400nm pump)

[0019] This example provides an ultrafast time-energy entanglement source device and its optimized configuration, aiming to generate high-stability and high-precision time-energy entangled photon pairs through a high-precision laser system, a nonlinear coupling system, a time measurement module, and general optimization items.

[0020] The device includes a laser module and a nonlinear coupling system. The laser module is used to provide a high-precision pump light source, and the nonlinear coupling system is used to generate entangled photon pairs.

[0021] Optionally, the laser module includes a femtosecond laser (model: Spectra-Physics Mai Tai HP), whose output pulse width is 100 femtoseconds and the central wavelength is 400nm.

[0022] Further, in order to compress the pulse width to less than 20 femtoseconds, the laser module includes a chirped mirror group for compensating the dispersion effect of the pulse during propagation. By precisely adjusting the angle and position of the chirped mirror, the pulse width is successfully compressed to less than 20 femtoseconds, and the time jitter is controlled to be less than 50 attoseconds, ensuring the high-quality ultrashort pulses output by the laser and providing an ideal pump source for subsequent nonlinear processes.

[0023] Optionally, the nonlinear coupling system includes a BBO crystal with a thickness of 0.3mm for realizing the spontaneous parametric down-conversion (SPDC) process. In order to improve the focusing efficiency of the light beam, the nonlinear coupling system includes a hyperbolic lens (numerical aperture NA = 0.6), which is co-packaged with the BBO crystal in a vacuum chamber, and the chamber pressure is maintained at less than 1×10-3 Pascal to significantly reduce the interference of the air nonlinear effect.

[0024] Further, to optimize the spectral purity, the non-linear coupling system includes a first-order cascaded fiber grating with a bandwidth of 0.1 nanometers, which is used to suppress the spontaneous Raman scattering noise to below -35 dB, significantly improving the signal-to-noise ratio of the system and providing guarantee for the generation of high-quality entangled photon pairs.

[0025] Further, the device includes a time measurement module for verifying the time-energy correlation characteristics of the entangled photon pairs.

[0026] Optionally, the time measurement module builds a HOM interferometer based on a superconducting nanowire single photon detector (SNSPD, with an efficiency greater than 90%) and a time-to-digital converter (TDC, with a resolution of 1 picosecond).

[0027] Further, to achieve high-precision measurement of the photon arrival time, the time measurement module includes a piezoelectric displacement stage with a stepping accuracy of 10 nanometers for precisely adjusting the path difference. By precisely controlling the movement of the piezoelectric displacement stage, the time measurement module can achieve high-precision measurement of the photon arrival time, providing key technical support for subsequent time-energy correlation measurements.

[0028] Optionally, the device includes general optimization items to improve the overall performance of the system. The general optimization items include an optical fiber coupling system that uses an FC / APC connector with an end face angle of 8° to ensure that the return loss is greater than 65 dB. The fusion splice loss of all single-mode fibers (SMF-28) is strictly controlled to be less than 0.05 dB, and a V-groove precision alignment technology is used to control the alignment error to be less than 0.1 micrometer. This optimization ensures the efficient transmission and low loss of the optical fiber system.

[0029] Further, the general optimization items also include an automated control system that integrates a LabVIEW control platform for realizing closed-loop feedback control of the EOM drive voltage, the SLM phase diagram, and the temperature control parameters, with a sampling rate set to 1 kHz. The data acquisition system can synchronously trigger the laser pulse and the detector and correct the time jitter to be less than 5 picoseconds. This automated control system significantly improves the stability and repeatability of the experiment.

[0030] Further, the time-energy correlation measurement of the device verifies the high-quality generation of the entangled photon pairs.

[0031] Optionally, the time-energy correlation measurement uses the frequency-resolved optical gating method (FROG) to precisely measure the time-bandwidth product of the entangled photon pairs. The measurement results show that the time-bandwidth product is 0.41, close to the Fourier transform limit (0.44). The results indicate that the device has successfully achieved the generation of high time-energy entangled photon pairs and has excellent time-energy correlation characteristics.

[0032] Furthermore, the anti-disturbance verification of the device demonstrates its high stability in complex environments.

[0033] Optionally, the anti-disturbance verification is performed by applying simulated vibrations (amplitude ±5 μm, frequency range 10 - 100 Hz) in the system and introducing an adaptive optical system (response frequency 1 kHz) for real-time wavefront correction. The coincidence count fluctuation is successfully suppressed to less than 0.3%, demonstrating the high stability and reliability of the system in complex environments.

[0034] Furthermore, the reliability verification of the device demonstrates its long-term stability and environmental adaptability.

[0035] Optionally, the reliability verification includes an accelerated aging test (85°C / 85% relative humidity, lasting 1000 hours), and the performance degradation of key devices is less than 3%. In addition, the electromagnetic compatibility test complies with the IEC 61000-4-3 standard, and the radiation immunity is greater than 10 V / m. These test results further verify the long-term stability and environmental adaptability of the device.

[0036] Through the above detailed device configuration optimization and experimental verification process, the ultrafast time-energy entanglement source device of this embodiment performs excellently in terms of performance and stability. This device is applicable to fields such as high-precision quantum communication, quantum computing, and quantum precision measurement, providing a high-performance experimental platform for related research.

Claims

1. A gradient polarized BBO crystal quantum entanglement source device based on a wavefront-power coordinated control method, specifically comprising the following steps: S1 A quantum entanglement source device, characterized in that it uses a pump light source to generate linearly polarized light; S2: using a light source adjustment component to adjust the linearly polarized light into polarized light in a linear polarization state with a predetermined angle, wherein the light source adjustment component includes a spatial light modulator (SLM) and an electro-optical modulator (EOM); S3 uses a gradient polarization design BBO crystal. The polarization period Λ of its periodic polarization structure is dynamically designed according to the pump wavelength to meet the quasi-phase matching condition, and its wedge-shaped geometric structure is used to compensate for the group velocity mismatch (GVM); S4 uses the first optical fiber collimator to focus the adjusted polarized light onto the BBO crystal, and the second optical fiber collimator and the third optical fiber collimator respectively transmit the generated first optical signal (signal light) and second optical signal (idler light) to a predetermined optical signal processing device; S5 evaluates the quality of the entangled photon pair, and the test component includes: a first single-photon detector and a second single-photon detector, which are used to detect and count the first optical signal and the second optical signal respectively. A coincidence counter is used to measure and count the time coincidence of the two optical signals, and the quality of the entangled photon pair is evaluated according to the single-channel count value and the coincidence count value through a quality analysis module. A first optical fiber filter and a second optical fiber filter are used to filter out photons in the first optical signal and the second optical signal that do not conform to the wavelength of the entangled photons respectively; The S6 dual-zone dynamic balancing system includes a dual-zone thermoelectric cooling (TEC) temperature control system that sets the temperature difference between the crystal input (T1) and output (T2) and independently controls the temperature to a preset accuracy to suppress the temperature gradient inside the crystal.

2. The quantum entanglement source device according to claim 1, characterized in that: The device supports ultra-wide wavelength tuning, with a phase matching wavelength coverage range from 405nm to 1550nm, and is compatible with silicon-based (1550nm) and gallium nitride (405nm) quantum devices.

3. The quantum entanglement source device according to claim 1, characterized in that: The device filters out photons that do not conform to the wavelength of entangled photons through an optical fiber filter, thereby improving the purity of entangled photon pairs.

4. A method for generating a quantum entanglement source based on the device of claim 2, characterized in that: The following steps are involved: Generate linear polarized light, and adjust the linear polarized light to polarized light with a linear polarization state of a predetermined angle through a light source adjustment component, wherein a spatial light modulator (SLM) dynamically adjusts the phase distribution of the pump light field, and an electro-optic modulator (EOM) adjusts the laser power in real time. Focus the adjusted polarized light onto a BBO crystal, generate an entangled photon pair through the BBO crystal, transmit the generated first optical signal and the second optical signal to a predetermined optical signal processing device, and evaluate the quality of the entangled photon pair, including detection, counting, time coincidence measurement, and quality analysis of the optical signal. Filter out photons that do not conform to the wavelength of the entangled photons through an optical fiber filter, and use a dual-temperature zone dynamic equalization system to suppress the temperature gradient inside the crystal to ensure the stable operation of the device.

5. The quantum entanglement source device according to claim 3, characterized in that: The gradient polarization design of the BBO crystal can increase the temporal entanglement fidelity under pulse pumping to 99.3%.

6. The method for generating a quantum entanglement source according to claim 3, characterized in that: The gradient polarization design of the BBO crystal can dynamically adapt the pump wavelength, compensate for the group velocity mismatch (GVM), and increase the temporal entanglement fidelity under pulse pumping to 99.3%.

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