Isoidentical photon pair light source

Abstract

The utility model provides an identical photon pair light source, which comprises a pump laser, a nonlinear waveguide, a filter, a wavelength division multiplexer and a single photon frequency shifter, can output a plurality of identical photon pairs with different wavelengths through a single nonlinear waveguide, and is simple and compact in structure, high in integration level, wide in spectral range of the generated identical photon pairs, and high in efficiency. And multiple wavebands and multiple application scenes, such as a quantum communication waveband, a quantum measurement waveband and a quantum optical experiment waveband, are supported.

Description

Technical Field

[0001] This application belongs to the field of quantum information, specifically, it relates to a quantum light source with multiple outputs. Background Technology

[0002] Identical photons are photons that are identical in all degrees of freedom (such as frequency, polarization, and path). They play a crucial role in quantum communication and quantum computing. In quantum communication, the indistinguishability of identical photons helps improve the fidelity of quantum state transmission, thus ensuring communication security. Furthermore, in building quantum networks, identical photons can effectively distribute and exchange quantum entanglement, enabling the construction of multi-node quantum networks. In quantum computing, identical photons are used to realize the operation of qubits and the generation of quantum entanglement. For example, in linear optical quantum computing, the interference effect of identical photons is the foundation for realizing quantum logic gates. By precisely controlling the interaction of identical photons, complex quantum algorithms, such as boson sampling, can be executed, which helps demonstrate quantum supremacy.

[0003] Currently, methods for generating identical photons include quantum dot emission, parametric down-conversion (SPDC), and four-wave mixing (SFWM). Quantum dot emission requires complex micro / nano fabrication techniques and precise control of the quantum dot environment and excitation conditions, placing high demands on materials, processes, and practical operation, making it difficult to implement. SPDC and SFWM are currently the more commonly used methods for generating identical photons, and both are widely used in generating entangled photon pairs, with mature technologies. However, photon pairs generated using SPDC or SFWM generally suffer from low light source brightness, narrow spectral density, or difficulty in separating and using photon pairs. Utility Model Content

[0004] Based on the above problems and needs, this application proposes an identical photon pair light source capable of outputting multiple pairs of identical photons with different wavelengths through a single nonlinear waveguide. The specific scheme is as follows:

[0005] This application discloses an identical photon pair light source, comprising:

[0006] Laser light sources are used to generate continuous or pulsed laser light of a specific wavelength.

[0007] A nonlinear waveguide is connected to the output of a laser source. It is used to receive the laser light emitted by the laser source, perform nonlinear optical processes, and generate n pairs of entangled photons with different wavelengths. Each pair of entangled photons contains a signal photon and an idler photon. The polarization directions of the signal photon and the idler photon are the same.

[0008] A filter, connected to the output of a nonlinear waveguide, is used to filter out laser light output from a nonlinear waveguide that has not undergone nonlinear optical processes.

[0009] A wavelength division multiplexer, connected to the output of a filter, is used to separate the signal photon from the idler photon in the n pairs of entangled photons generated, and output them from n photon ports to n photon output paths respectively. The first to n / 2 photon ports output signal photons, and the (n / 2+1) to n photon ports output idler photons.

[0010] n / 2 single-photon frequency shifters are set on the photon output paths corresponding to the 1st to n / 2th photon ports, or on the photon output paths corresponding to the (n / 2+1)th to nth photon ports. They are used to perform frequency shifting operations on all signal photons so that their frequencies are consistent with their corresponding idler photons, or to perform frequency shifting operations on all idler photons so that their frequencies are consistent with their corresponding signal photons, thereby obtaining n pairs of identical photon pairs with the same polarization direction and photon frequency.

[0011] Optionally, a first polarization controller is also provided between the laser source and the nonlinear waveguide. The first polarization controller is used to precisely adjust the polarization state of the laser emitted by the laser source so that the intensity of its nonlinear optical process in the nonlinear waveguide is maximized.

[0012] Optionally, the nonlinear waveguide is a periodically polarized lithium niobate waveguide that generates entangled photon pairs through a type O or type I spontaneous parametric down-conversion process.

[0013] Optionally, the nonlinear waveguide is a silicon nanowire waveguide that generates entangled photon pairs through a spontaneous four-wave mixing process.

[0014] Furthermore, at least one photon output path is equipped with a second polarization controller to compensate for polarization changes that occur in the entangled photon pairs during transmission.

[0015] Furthermore, an optical delay device is set on at least one photon output path to compensate for the time difference caused by the difference in the transmission paths of the signal photon and the idler photon.

[0016] Optionally, the first polarization controller is an electro-optic polarization controller, the filter is an on-chip filter, and the wavelength division multiplexer is an on-chip wavelength division multiplexer. The first polarization controller, nonlinear waveguide, filter, and wavelength division multiplexer are integrated into the same chip.

[0017] Optionally, the single-photon frequency shifter includes an acousto-optic modulator, and the wavelength division multiplexer is connected to the acousto-optic modulator via optical fiber.

[0018] Optionally, the single-photon frequency shifter includes an electro-optic modulator, and the wavelength division multiplexer and the acousto-optic modulator are connected via optical fiber.

[0019] Furthermore, the single-photon frequency shifter includes a lithium niobate waveguide, and the first polarization controller, nonlinear waveguide, filter, wavelength division multiplexer, and single-photon frequency shifter are integrated into the same lithium niobate optical chip.

[0020] Overall, compared with the prior art, the above-conceptual technical solutions conceived in this application can achieve the following beneficial effects: This application provides an identical photon pair light source, including a pump laser, a nonlinear waveguide, a filter, a wavelength division multiplexer, and a single-photon frequency shifter, which can output multiple pairs of identical photon pairs with different wavelengths through a single nonlinear waveguide. It has a simple and compact structure, high integration, and produces a wide spectral range of identical photon pairs, supporting multiple bands and various application scenarios, such as quantum communication band, quantum measurement band, and quantum optics experimental band. Attached Figure Description

[0021] 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.

[0022] Figure 1 A schematic diagram of an identical photon pair light source provided in an embodiment of this application;

[0023] Figure 2 A schematic diagram of another identical photon pair light source provided in an embodiment of this application;

[0024] Figure 3 A schematic diagram of generating entangled photon pairs in a periodically polarized waveguide for lithium niobate;

[0025] Figure 4 A schematic diagram of entangled photon pairs generated in a silicon nanowire waveguide;

[0026] Figure 5 A schematic diagram of yet another identical photon pair light source provided in an embodiment of this application;

[0027] Figure 6 A schematic diagram of another identical photon pair light source provided in an embodiment of this application;

[0028] Figure 7 This is a schematic diagram of a single-photon frequency shifter based on a lithium niobate waveguide;

[0029] Figure 8 This is a schematic diagram of an identical photonic light source chip. Detailed Implementation

[0030] 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.

[0031] 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.

[0032] This application proposes an identical photon pair light source, including a laser source, a nonlinear waveguide, a filter, a wavelength division multiplexer, and a single-photon frequency shifter, such as... Figure 1 As shown. Specifically, the laser source can be a commonly used semiconductor laser, operating in either continuous or pulsed excitation mode, outputting continuous or pulsed laser light. A nonlinear waveguide is connected to the output of the laser source to receive the laser light emitted by the source, perform a nonlinear optical process, and generate n pairs of entangled photons with different wavelengths. Each pair of entangled photons contains one signal photon and one idler photon, with the signal and idler photons having the same polarization direction. The sum of the frequencies of the signal and idler photons in the n pairs of photons with different wavelengths is twice the frequency of the laser light emitted by the source (note that the frequency here refers to the frequency of the photon itself, i.e., the reciprocal of the wavelength). The wavelengths of the first pair of photons are λs⁻¹ (signal photon) and λi⁻¹ (idle photon), and so on, with the wavelengths of the nth pair being λs⁻ⁿ (signal photon) and λi⁻ⁿ (idle photon). The two photons in each pair have different frequencies but the same polarization and the same time interval, and can only be separated by their frequency (or wavelength).

[0033] A filter is connected after the nonlinear waveguide to allow only the generated signal photons and idler photons to continue propagating after the remaining laser light that has not undergone nonlinear optical processes. The filter can be a space fiber optic device or an on-chip device, i.e., a miniature device integrated inside a chip.

[0034] Wavelength division multiplexers (WDMs) can be either coarse-powder WDMs or dense WDMs. When n is relatively large (e.g., n≥10), dense WDMs are preferred as they can output more pairs of identical photons. The WDM, connected to the filter's output, separates the signal photons from the idler photons in the generated n pairs of entangled photons and outputs them to n photon output paths from n photon ports. The first to n / 2 photon ports output signal photons, and the (n / 2+1) to n photon ports output idler photons. Which photon ports output signal photons and which output idler photons depends on the output frequency of that photon port. Here, the photon ports outputting signal photons are simply designated or named sequentially (e.g., according to frequency or wavelength) as the first to n / 2 photon ports, and the photon ports outputting idler photons are designated or named sequentially (e.g., according to frequency or wavelength) as the (n / 2+1) to n photon ports.

[0035] n / 2 single-photon frequency shifters are configured on the photon output paths corresponding to the 1st to n / 2th photon ports, or on the photon output paths corresponding to the (n / 2+1)th to nth photon ports. These shifters are used to perform frequency shifting operations on all signal photons so that their frequencies match those of their corresponding idler photons, or to perform frequency shifting operations on all idler photons so that their frequencies match those of their corresponding signal photons, thereby obtaining n pairs of identical photon pairs with the same polarization direction and photon frequency. The identical photon pair light source provided in this application can output multiple pairs of identical photon pairs with different wavelengths through a single nonlinear waveguide. It has a simple and compact structure, high integration, and produces identical photon pairs with a wide spectral range, supporting multiple bands and various application scenarios, such as quantum communication bands, quantum measurement bands, and quantum optics experimental bands.

[0036] like Figure 1 As shown, assuming that the output of the first to n / 2 photon ports is the signal photon, and the output of the (n / 2+1) to n photon ports is the idler photon, a single-photon frequency shifter is set on the subsequent photon output path of the idler photon. After passing through the single-photon frequency shifter, the frequency of the idler photon is transformed into the frequency of the signal photon. Thus, the original signal photon and idler photon become a pair of identical photons, and are output from the original output path respectively. The two are indistinguishable in terms of time, polarization, and frequency.

[0037] In another embodiment of this application, such as Figure 2As shown, a first polarization controller is also installed between the laser source and the nonlinear waveguide. This controller precisely adjusts the polarization state of the laser emitted from the laser source, ensuring it is strictly aligned with the specific polarization direction required by the quasi-phase matching condition of the nonlinear waveguide. This maximizes the conversion efficiency of the nonlinear process, thereby maximizing the intensity of the nonlinear optical process within the nonlinear waveguide. Furthermore, the laser output from the laser source may itself exhibit some polarization uncertainty; the output polarization state may not be ideally linearly polarized, or the polarization direction may drift slightly with temperature, driving current, or time. The addition of the polarization controller allows for precise adjustment and control of its polarization state to meet the quasi-phase matching condition. The first polarization controller can be selected from waveplate-type polarization controllers, fiber-squeezed polarization controllers, electro-optic modulation polarization controllers, etc. Waveplate-type polarization controllers are suitable for systems where all optical devices are mounted and fixed on an optical platform with precise and fixed positions. The system cost is low, and the devices are mature and stable, but the size is relatively large. Fiber-squeezed polarization controllers are suitable for systems with fiber optic devices or fiber optic connections. Their advantages include flexible and variable device settings and strong adaptability to various scenarios. Electro-optic modulation polarization controllers are used in systems requiring high-precision control and are easy to adjust, but their cost is relatively high. In practical applications, the type of the first polarization controller can be selected according to specific conditions and requirements.

[0038] In another embodiment of this application, such as Figure 3 As shown, the nonlinear waveguide is a lithium niobate periodically polarized waveguide. A lithium niobate periodically polarized waveguide (PPLN waveguide) is a nonlinear optical crystal based on quasi-phase-matched (QPM) technology, formed by periodically reversing the internal domain structure of the lithium niobate waveguide. It possesses advantages such as a large nonlinear coefficient, wide transmission range, flexible phase matching, and high stability. PPLNs are key devices in the fields of quantum light sources and entangled light sources. When a pump laser is injected into a PPLN waveguide, a spontaneous parametric down-conversion (SPDC) process occurs due to its nonlinear optical effect. One pump photon annihilates, generating a pair of signal photons and idler photons, forming an entangled photon pair. Phase matching can be achieved by adjusting the polarization period, which can improve the generation efficiency. (Reference) Figure 3 The laser is input from the input port of the lithium niobate chip containing the PPLN waveguide and acts on the PPLN waveguide. By setting a specific polarization period of the PPLN waveguide (selecting a PPLN waveguide with a type 0 or type I polarization period), a type 0 or type I spontaneous parametric down-conversion process occurs in the PPLN waveguide, thereby generating entangled photon pairs with the same polarization. The remaining laser and entangled photon pairs that have not undergone spontaneous parametric down-conversion are output together from the output port of the lithium niobate chip.

[0039] In another embodiment of this application, such as Figure 4As shown, the nonlinear waveguide is a silicon nanowire waveguide, a type of nano-optical waveguide based on silicon material, possessing high refractive index contrast and strong light field confinement capabilities. It utilizes silicon's high third-order optical nonlinear coefficient and excellent optical properties to achieve efficient light-to-light interaction within a compact structure. Silicon nanowire waveguides are typically fabricated on silicon-on-insulator (SOI) substrates, offering advantages such as high integration density, compatibility with CMOS processes, and ease of integration with other optical and electronic components to form complex photonic integrated circuits. By implementing a four-wave mixing (FWM) process in the silicon nanowire waveguide, under specific phase-matching conditions, the pump photon can be converted into a pair of signal photons and idler photons, forming a time-energy entangled photon pair. (Reference) Figure 4 The laser is input from the input port of a silicon-based chip containing a silicon nanowire waveguide and acts on the silicon nanowire waveguide, resulting in a spontaneous four-wave mixing process, which generates entangled photon pairs with the same polarization. The remaining laser and entangled photon pairs that have not undergone spontaneous four-wave mixing are output together from the output port of the silicon-based chip.

[0040] PPLN waveguides with type 0 or type 1 polarization periods, as well as silicon nanowire waveguides, can generate multiple entangled photon pairs with a relatively wide spectral range (≥50nm) covering multiple communication bands. In contrast, ordinary PPLN crystals can only generate entangled photon pairs with a narrower spectral range. After passing through filters and wavelength division multiplexers, generally only one entangled photon pair remains, making them unsuitable for multi-user scenarios in optical quantum communication or optical quantum computing. This is why a nonlinear waveguide is used in this application. Furthermore, since it is a silicon-based waveguide, it is compatible with current mainstream CMOS processes, and using silicon nanowire waveguides as the source of entangled photon pairs can further reduce costs.

[0041] In another embodiment of this application, such as Figure 5 As shown, at least one photon output path is equipped with a second polarization controller to compensate for polarization changes occurring in entangled photon pairs during transmission. To ensure stable polarization states of photons in all channels, a second polarization controller can be installed on each photon output path. The compensated polarization changes are polarization errors caused by device errors or system optical path errors. The second polarization controller can be configured to adjust the polarization degree or compensate for the polarization based on the two-photon interference of the two photons in the photon pair, and this setting is fixed. As long as the light source is turned on, each photon output path uses the preset polarization compensation amount to ensure the indistinguishability of the output photons. In other words, as long as the indistinguishable photon pair light source is powered on and running, stable indistinguishable photon output can be achieved through stable laser pumping, filtering, wavelength division multiplexing, polarization compensation, and other processes.

[0042] In another embodiment of this application, such as Figure 6As shown, an optical delay unit is placed on at least one photon output path to compensate for the time difference caused by the difference in the transmission paths of signal photons and idler photons, thus maintaining the time indistinguishability of signal photons and idler photons. To eliminate the influence of device or system errors and ensure that the time of paired photons in all channels is consistent, an optical delay unit can be placed on each photon output path. The optical delay unit can be a fiber optic delay unit, which compensates for the time difference between signal photons and idler photons by setting different fiber lengths. The optical delay unit can also be an on-chip waveguide delay line. By setting curved waveguides and straight waveguides in series on the chip, different degrees of delay can be achieved within a chip area, and waveguide delay lines of different channels can be integrated on the same chip to reduce the system size and improve the system integration.

[0043] To further improve system integration and reduce size, the first polarization controller can be an electro-optic polarization controller, utilizing a waveguide capable of electro-optic modulation for polarization control. The filter is an on-chip filter, constructed using an MZ or MMI interferometer formed by the chip waveguide. The laser beam is output from one port of the interferometer and discarded, while the entangled photon pair is output from the other port and continues transmission to the wavelength division multiplexer (WDM). The WDM can be an on-chip WDM, such as a lithium niobate arrayed waveguide grating WDM. Thus, the first polarization controller, nonlinear waveguide, filter, and WDM can all be integrated into the same chip, preferably into the same optical chip.

[0044] In another embodiment of this application, the single-photon frequency shifter includes an acousto-optic modulator, and the wavelength division multiplexer is connected to the acousto-optic modulator via an optical fiber. The acousto-optic modulator (AOM) utilizes the periodic refractive index changes generated when sound waves propagate in an optical medium to modulate photonic properties. When a laser passes through a medium containing ultrasound, the frequency of the light changes. The frequency shift amount and accuracy of the acousto-optic modulator are mainly determined by the driving electrical power signal, and it can achieve high frequency shift accuracy and frequency stability. The acousto-optic modulator is generally a spatial optical device (distinguished from fiber-optic optical devices and on-chip optical devices; spatial optical devices are similar to lasers, being large, block-shaped devices requiring precise installation and alignment). The connection to the wavelength division multiplexer generally requires spatial alignment or an optical fiber connection.

[0045] In another embodiment of this application, the single-photon frequency shifter includes an electro-optic modulator, and the wavelength division multiplexer and the acousto-optic modulator are connected via optical fiber. In this case, the electro-optic modulator uses a bulk nonlinear crystal as the medium for single-photon frequency shifting. When a voltage is applied to these crystals, their refractive index changes, thereby altering the frequency, phase, or amplitude of the light. Compared to the acousto-optic modulator, the electro-optic modulator offers faster modulation speed, supports a larger bandwidth, and is easier to operate. Since it is a spatial optical device, the connection with the wavelength division multiplexer generally requires spatial alignment or optical fiber connection.

[0046] Furthermore, in another embodiment of this application, such as Figure 7 As shown, the single-photon frequency shifter includes a lithium niobate waveguide (non-periodic polarization). In this case, the single-photon frequency shifter can be regarded as an on-chip electro-optic modulator, mainly consisting of a lithium niobate waveguide and electrodes. The electric field generated by the electrodes changes the refractive index inside the lithium niobate waveguide, thereby achieving photon frequency shifting. In this case, except for lasers, all optical devices can be on-chip optical devices based on lithium niobate waveguides. All optical devices can be integrated into a single lithium niobate optical chip, referred to as an identical photon source chip, such as... Figure 8 As shown, a single laser and a lithium niobate photonic chip are all that is needed to achieve an identical photon pair light source with multiple photon pairs output.

[0047] Furthermore, single-photon frequency shifters can also be implemented using silicon-based waveguides in conjunction with an additional pump laser. In this case, all optical components except the laser can be fabricated using silicon-based waveguides, meaning that all optical components except the laser can be integrated into a single silicon chip. Compared to lithium niobate optical chips, silicon-based chip fabrication technology is more mature and less expensive, but it requires an additional laser as an auxiliary device. In this application, this scheme is presented as an optional combination, achieving the same effect as lithium niobate optical chips.

[0048] 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.

[0049] 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.

[0050] 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 light source with identical photon pairs, characterized in that, include: Laser light sources are used to generate continuous or pulsed laser light of a specific wavelength. A nonlinear waveguide is connected to the output of a laser source. It is used to receive the laser light emitted by the laser source, perform nonlinear optical processes, and generate n pairs of entangled photons with different wavelengths. Each pair of entangled photons contains a signal photon and an idler photon. The polarization directions of the signal photon and the idler photon are the same. A filter, connected to the output of a nonlinear waveguide, is used to filter out laser light output from a nonlinear waveguide that has not undergone nonlinear optical processes. A wavelength division multiplexer, connected to the output of a filter, is used to separate the signal photon from the idler photon in the n pairs of entangled photons generated, and output them from n photon ports to n photon output paths respectively. The first to n / 2 photon ports output signal photons, and the (n / 2+1) to n photon ports output idler photons. n / 2 single-photon frequency shifters are set on the photon output paths corresponding to the 1st to n / 2th photon ports, or on the photon output paths corresponding to the (n / 2+1)th to nth photon ports. They are used to perform frequency shifting operations on all signal photons so that their frequencies are consistent with their corresponding idler photons, or to perform frequency shifting operations on all idler photons so that their frequencies are consistent with their corresponding signal photons, thereby obtaining n pairs of identical photon pairs with the same polarization direction and photon frequency.

2. The identical photon pair light source according to claim 1, characterized in that, A first polarization controller is also provided between the laser source and the nonlinear waveguide. The first polarization controller is used to precisely adjust the polarization state of the laser emitted by the laser source so that the intensity of its nonlinear optical process in the nonlinear waveguide is maximized.

3. The identical photon pair light source according to claim 1, characterized in that, The nonlinear waveguide is a periodically polarized lithium niobate waveguide that generates entangled photon pairs through a type O or type I spontaneous parametric down-conversion process.

4. The identical photon pair light source according to claim 1, characterized in that, The nonlinear waveguide is a silicon nanowire waveguide that generates entangled photon pairs through a spontaneous four-wave mixing process.

5. The identical photon pair light source according to claim 1, characterized in that, At least one photon output path is equipped with a second polarization controller to compensate for polarization changes that occur in the transmission path of entangled photon pairs.

6. The identical photon pair light source according to claim 1, characterized in that, An optical delay device is set on at least one photon output path to compensate for the time difference caused by the difference in the transmission paths of signal photons and idler photons.

7. The identical photon pair light source according to claim 3, characterized in that, The first polarization controller is an electro-optic polarization controller, the filter is an on-chip filter, and the wavelength division multiplexer is an on-chip wavelength division multiplexer. The first polarization controller, nonlinear waveguide, filter, and wavelength division multiplexer are integrated into the same chip.

8. The identical photon pair light source according to claim 1, characterized in that, The single-photon frequency shifter includes an acousto-optic modulator, and the wavelength division multiplexer is connected to the acousto-optic modulator via optical fiber.

9. The identical photon pair light source according to claim 1, characterized in that, A single-photon frequency shifter includes an electro-optic modulator, a wavelength division multiplexer, and an acousto-optic modulator connected by optical fiber.

10. The identical photon pair light source according to claim 7, characterized in that, The single-photon frequency shifter includes a lithium niobate waveguide, and the first polarization controller, nonlinear waveguide, filter, wavelength division multiplexer, and single-photon frequency shifter are integrated into the same lithium niobate optical chip.

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