Integrated light source and control non-gate optical quantum computing chip and teaching system using the same
The optical quantum computing chip integrates a light source and control NOT gate on-chip, using silicon or lithium niobate waveguides, to reduce resource consumption and complexity, achieving stable, low-cost, and programmable quantum computing operations.
Patent Information
- Application Number
- CN202110581652.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2021-05-27
- Publication Date
- 2024-12-13
- Estimated Expiration
- 2041-05-27
AI Technical Summary
Optical quantum computing chips face challenges in reducing device resource consumption and achieving frequency degeneracy in four-wave mixing, which increases cost and technical difficulty, and suffer from issues like Bragg scattering and unilateral excitation, reducing photon homogeneity.
An optical quantum computing chip integrating a coherent excitation light source, single-bit gate, control NOT gate circuit, and detection module, utilizing silicon waveguide, silicon nitride microcavity, or periodically polarized lithium niobate waveguide structures, which avoids complex frequency degeneracy by on-chip integration and includes adjustable beam splitters and phase shifters for unitary transformations.
The solution achieves high integration, stable operation, low cost, and low optical loss, with programmable single-bit and CNOT gates, enabling efficient CNOT gate demonstration and entangled state preparation.
Smart Images
Figure CN115480614B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of quantum computing and quantum optics technology, and to the design of various optical quantum computing controlled NOT gate chips, and in particular to an optical quantum computing chip integrating a light source and a controlled NOT gate (CNOT) and a teaching system using the same, which is suitable for application fields such as optical quantum computing and teaching experiments. Background Art
[0002] Photons have the advantages of fast operation speed, simple and precise single-bit manipulation, strong anti-noise ability, etc., and can provide quantum interfaces between remote atoms and solid-state quantum systems. The realization of large-scale optical quantum computing and simulation will solve several computing problems that classical computers are unable to handle, and will have a profound impact on human society. In recent years, many large high-tech companies have strongly intervened in quantum computing, which has greatly promoted the development of this field. Therefore, talent training in this direction also needs to be trained as early as possible in college. However, due to the integration of many disciplines in this direction, expensive research equipment, and shortage of technical personnel, various universities currently lack professional equipment for quantum computing experiments. Therefore, it is very necessary and urgent to design several quantum computing teaching systems.
[0003] In the process of implementing the present invention, the inventors found that there are at least the following problems in the related art:
[0004] (1) Optical quantum logic gates have already been realized under various schemes. For example, non-deterministic control phase gates can be realized by relying on all-linear optical devices, single photon sources and photon detectors, and the success rate can be improved through quantum teleportation, but it consumes a lot of device resources and requires very high device precision.
[0005] (2) It is very complicated to achieve frequency degeneracy for a light source based on four-wave mixing. To achieve frequency degeneracy of four-wave mixing, two lasers with different wavelengths must be used to simultaneously excite the nonlinear material and meet the phase matching conditions. This will increase the cost and the technical difficulty, and there will be problems such as Bragg scattering and unilateral excitation, which will reduce the photon homogeneity.
[0006] Therefore, there is an urgent need for an optical quantum computing chip that can reduce device resource consumption and solve the problem of frequency degeneration of the light source of four-wave mixing. Summary of the invention
[0007] In view of this, the main purpose of the present invention is to provide an optical quantum computing chip integrating a light source and a control NOT gate and a teaching system using the same, in order to partially solve at least one of the above-mentioned technical problems.
[0008] In order to achieve the above-mentioned object, as one aspect of the present invention, a light quantum computing chip integrating a light source and a control NOT gate is provided, wherein the chip comprises a coherent excitation light source, a single-bit gate, a control NOT gate circuit and a detection module; wherein,
[0009] The coherent excitation light source emits two photons, and any single-bit state photons are prepared through the two single-bit gates, input into the control NOT gate circuit, and detected by the detection module after passing through the control NOT gate circuit.
[0010] The chip integrates the coherent excitation light source, the single-bit gate and the control NOT gate circuit part, or integrates the coherent excitation light source, the single-bit gate, the control NOT gate circuit and the detection module all on a semiconductor chip.
[0011] Wherein, the coherent excitation light source adopts a silicon waveguide structure, a silicon nitride microcavity structure or a periodically polarized lithium niobate waveguide structure.
[0012] Among them, the periodically polarized lithium niobate material absorbs two photons with a frequency of ω0, and emits signal light and idler light with frequencies of ω1 and ω2 respectively; two light sources are used to generate two pairs of photons, and one photon in each pair of photons will be directly sent to the detection module as a predicted single photon; and the two photons with the same frequency will be sent into the circuit to realize the operation of controlling the NOT gate.
[0013] Wherein, the single-bit gate and the control NOT gate circuit together form a photon quantum logic gate.
[0014] The control NOT gate circuit includes a beam splitter and a phase shifter, and the beam splitting ratio of the beam splitter and the phase of the phase shifter need to be arbitrarily adjustable to achieve unitary transformation.
[0015] The change of the displacement of the phase shifter is achieved by locally changing the temperature of the phase shifter in the waveguide to control the refractive index of the waveguide; and the beam splitting ratio of the beam splitter is changed by a Mach-Zehnder interferometer.
[0016] Wherein, the detection module includes an integrated superconducting nanowire single-photon detector or a photon number detector connected to an off-chip optical fiber via a grating coupler.
[0017] As another aspect of the present invention, a teaching system is provided, which includes the optical quantum computing chip as described above.
[0018] Wherein, the teaching system further comprises a teaching control system, and the teaching control system is used to control the phase shift of the phase shifter in the control NOT gate circuit.
[0019] Based on the above technical solutions, it can be seen that the optical quantum computing chip with integrated light source and control NOT gate and the teaching system using the same of the present invention have at least one of the following beneficial effects compared with the prior art:
[0020] (1) The present invention can avoid complex four-wave mixing frequency degeneracy by integrating the light source and the control NOT gate on the chip. At the same time, the on-chip integration approach has the advantages of high integration, stable working conditions, and low cost.
[0021] (2) By integrating light sources, low-loss integrated optical components, and optical coatings on-chip, this photonic quantum chip can achieve low optical loss.
[0022] (3) The optical path from the input mode collimator to the receiving light coupler is equal, that is, each receiving light coupler can have nearly the same coupling collection efficiency;
[0023] (4) The output of the CNOT gate is connected to a photon number detector, and the input end is connected to a light source and a single-bit gate, so that the CNOT gate demonstration operation experiment and the entangled state preparation and verification experiment can be realized;
[0024] (5) It has arbitrarily programmable single-bit gates and CNOT gates. Through the output end of the CNOT gate, a non-destructive detector of the number of photons can be connected to realize a programmable universal quantum computing chip according to specific needs;
[0025] (6) The CNOT gate operation can be canceled by adjusting the beam splitter reflection splitting ratio to 1, which increases the programmability of the chip after etching. BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Figure 1 A schematic diagram of the coupling of a coherent excitation light source, a control NOT gate circuit, a single photon detection module and a control system according to an embodiment of the present disclosure is illustrated;
[0027] Figure 2 The principle of the four-wave mixing process and the schematic diagram of the silicon-based predicted single photon source according to the embodiment of the present disclosure are illustrated;
[0028] Figure 3 A schematic diagram of a path-coded single-photon bit gate and a single-bit gate circuit implemented by a beam splitter and a phase shifter according to an embodiment of the present disclosure is illustrated;
[0029] Figure 4 A schematic diagram of a Mach-Zehnder interferometer circuit according to an embodiment of the present disclosure is illustrated;
[0030] Figure 5 A schematic diagram of a control NOT gate and a schematic diagram of a control NOT gate circuit according to an embodiment of the present disclosure are illustrated;
[0031] Figure 6 A schematic diagram of an integrated superconducting nanowire single-photon detector and an external single-photon detector according to an embodiment of the present disclosure is illustrated;
[0032] Figure 7The controlled NOT gate chip teaching system based on silicon waveguide predicted single photon source according to the embodiment of the present disclosure is illustrated;
[0033] Figure 8 The controlled NOT gate chip teaching system based on silicon nitride microcavity prediction single photon source according to the embodiment of the present disclosure is illustrated;
[0034] Fig. 9 The spontaneous parametric down-conversion process and the schematic diagram of the periodically poled lithium niobate waveguide are shown;
[0035] Fig.10 The invention illustrates a controlled NOT gate chip teaching system based on periodically poled lithium niobate waveguide predicting single photon source according to an embodiment of the present disclosure. DETAILED DESCRIPTION
[0036] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.
[0037] The overall structure diagram of the control NOT gate chip teaching system designed in this paper is as follows Figure 1 As shown, the coherent excitation light source emits two photons prepared to the path code |0>, and two single-bit gates can be used to prepare any single-bit state input of the control NOT gate input port. After passing through the control NOT gate, it is detected by the single-photon detection module, and the phase shift of the phase shifter in the control NOT gate circuit can be controlled by the control system. The light source part can be Figure 2 The four-wave mixing or parametric down-conversion process shown is implemented.
[0038] Universal quantum logic gates can be realized through arbitrary single-bit gates and controlled NOT gates (C-NOT). Figure 3 , the photon bits are encoded on two paths. To achieve any unitary transformation, the splitting ratio of the beam splitter and the phase of the phase shifter can be adjusted arbitrarily. The refractive index of the waveguide is controlled by locally changing the temperature of the phase shifter in the waveguide, thereby achieving the change of phase. The splitting ratio of the beam splitter is changed by a Mach Zehnder Interferometer (MZI). Figure 4 As shown in the figure, the interferometer includes two 50:50 beam splitters, one of which is equipped with an Au / Ti heating electrode. After the current passes through, the phase between the two paths of the interferometer will change, thereby changing the light intensity at the output port, achieving the purpose of adjustable splitting ratio. Ignoring the global phase, the phase shifter is equivalent to the Rz single-bit gate, and the Mach-Zehnder interferometer is equivalent to the Ry single-bit gate, so Figure 3 The structure of (ii) can realize arbitrary single-bit gate operations on a single photon bit.
[0039] Figure 5(i) To realize the integrated optical circuit connection of controlled NOT gate (CNOT), Figure 5 (ii) Schematic diagram of the optical path to realize the control NOT gate, where the reflection splitting ratio of three beam splitters is 1 / 3 and the reflection splitting ratio of two beam splitters is 1 / 2. In order to realize the programmable and accurate control of the optical path, the Mach-Zehnder interferometer is also used to realize the beam splitter with adjustable splitting ratio. The actual optical path is as follows Figure 5 (iii) as shown.
[0040] The input state of the CNOT line can be controlled by single-bit unitary transformation. The two outputs of the CNOT line c and t can be detected by the integrated superconducting nanowire single-photon detector, or connected to the photon number detector outside the chip through the optical fiber through the grating coupler. When the output of the CNOT line c and the output of the t each detect a photon, the CNOT operation is successful, with a success probability of 1 / 9. The detector is connected to an external electronic control device, which can display whether the CNOT operation is successful and perform subsequent output and counting.
[0041] The present invention provides a silicon-based, Si3N4 and laser-written lithium niobate integrated CNOT chip based on traditional CMOS technology. The chip integrates the light source and circuit part, or integrates the light source, circuit and detection part on a semiconductor chip. The light source part can be realized by a variety of materials. This patent provides a single photon through the process of four-wave mixing in a microcavity or waveguide of Si or Si3N4. Figure 2 As shown in (i), the material absorbs two photons with a frequency of ω0 and emits signal light and idler light with frequencies of ω1 and ω2 respectively. Since two light sources are used, the light source can generate two pairs of photons. During the experiment, one photon in each pair of photons will be directly sent to the detector as a forecast single photon; and the two photons with the same frequency will be sent into the circuit to realize the CNOT operation. The advantage of this design is that it does not need to generate frequency-degenerate photon pairs, which greatly reduces the requirements for the light source.
[0042] Figure 2 (ii) shows the waveguide-based light source part, where the input and output of the light source are coupled by a grating. This light source design is suitable for silicon-based waveguides. However, a better design is a four-wave mixing light source based on a silicon or silicon nitride micro-ring cavity. This design can naturally achieve phase matching conditions, and the photon coherence length can reach the millimeter or even centimeter level. The pump light input is coupled to the two-mode waveguide by a 50:50 beam splitter. The purity of the output photons can be improved by adding appropriate phase delays along the way in the low-order mode; the ring structure is to save space while increasing the purity and conversion efficiency of the output photons, and the output photons will be directly coupled into the waveguide. Coherently exciting multiple light sources with such structures can maintain a high degree of photon indistinguishability. The redundant excitation light is exported from the chip by a directional coupler and a waveguide to avoid affecting the stability of the entire chip.
[0043] Since the generated down-converted photons are directly coupled to the waveguide, their own efficiency is extremely high. In order to obtain high prediction efficiency, one method is to couple the generated photons to a single-mode fiber (or multimode fiber) through a waveguide, and the prediction efficiency can be as high as 80% or more. Another method is to grow a superconducting nanowire single-photon detector directly on the chip. The entire chip operates at a temperature of ~2K, and the prediction efficiency is expected to reach more than 95%.
[0044] Periodically poled lithium niobate materials can undergo a quasi-phase-matched second-order spontaneous parametric down-conversion nonlinear process. Since the second-order nonlinear coefficient is usually much higher than the third-order nonlinear coefficient, this process is more likely to occur than the third-order spontaneous four-wave mixing process. Under the same pump laser power, a compressed vacuum state with a compression coefficient far higher than that of silicon-based, silicon nitride and other materials can be obtained. Through the second-order spontaneous parametric down-conversion process, periodically poled lithium niobate waveguides can be made into single-photon sources with high prediction efficiency, high purity and high indistinguishability. Fig. 9 (i) Photons with a frequency of ω0 are converted into signal light and idler light of ω1 and ω2 through the spontaneous parametric down-conversion process. Lithium niobate is a ferroelectric crystal. The orientation of the electric dipole moment of each unit cell depends on the position of niobium and lithium ions in the unit. The crystal structure can be reversed by a strong electric field, so that periodically arranged polarized lithium niobate crystals can be made. Fig. 9 (ii) The periodic lithium niobate waveguide shown.
[0045] This design realizes a highly efficient predicted single photon source through spontaneous parametric down-conversion of periodically poled lithium niobate waveguides. Fig.10 shown.
[0046] Example 1
[0047] In Example 1 of the present invention, an integrated miniaturized photon-controlled NOT gate chip teaching system based on a silicon light source is provided. The integrated photon-controlled NOT gate chip integrates a predicted single photon source of coherent excitation, an integrated control NOT gate circuit, a single photon detector module and a teaching control system, and can be applied to photon-controlled NOT gate demonstration teaching, Bell state preparation and verification teaching demonstration.
[0048] In this embodiment, if Figure 1 As shown, it includes two coherently excited predicted single-photon sources, two single-bit gate circuits for preparing CNOT gate inputs, CNOT gate circuits and single-photon detection and control systems.
[0049] In this embodiment, if Figure 2As shown, the pump pulse laser is split by a beam splitter to coherently excite two silicon waveguide predictive single photon sources, and through the four-wave mixing process of the third-order nonlinearity in the silicon waveguide, signal light and idler photon pairs are generated as CNOT line input and predictive photons. Redundant background excitation light will be exported from the chip by the waveguide to avoid causing noise. Figure 2 (i) is the four-wave mixing process, Figure 2 (ii) Predicting single photon sources for silicon waveguides.
[0050] In this embodiment, the photon state output by the light source is the |0> state. To realize the input of any bit of CNOT gate port, a single-bit control gate needs to be connected between the light source and the CNOT input port, such as Figure 3 (i) It can be shown that the phase shifter can apply an Rz rotation operation to the single photon path encoding bit,
[0051]
[0052] Among them, U p represents the unitary transformation of the photon bit by the phase shifter, θ1 represents the phase shift of the upper path of the photon relative to the lower path, and R z (-θ1) is the quantum bit rotation operator, which rotates the quantum bit -θ1 degrees around the Z axis on the Bloch sphere.
[0053] Mach-Zehnder interferometer can apply an Ry rotation operation to encode bits on a single photon path.
[0054]
[0055] Among them, U m represents the unitary transformation of the photon bit by the Mach-Zehnder interferometer, θ2 represents the phase shift of the upper photon relative to the lower photon by the phase shifter in the Mach-Zehnder interferometer, and R y (θ2) is the quantum bit rotation operator, which rotates the quantum bit by θ2 degrees around the Y axis on the Bloch sphere.
[0056] through Figure 3 The circuit shown in (ii) can prepare the photon path encoding bit to any state. Figure 4 shown.
[0057] In this embodiment, if Figure 5 As shown, the controlled NOT gate (CNOT gate) is composed of three beam splitters with a splitting ratio of 1 / 3 and two beam splitters with a splitting ratio of 1 / 2. When the control bit output port c and the target bit output port simultaneously receive a photon signal, the controlled NOT gate operates successfully and the counting control system records the count. Otherwise, the controlled NOT gate operation fails and the count is discarded.
[0058] In this embodiment, the single-photon detector may be composed of a superconducting nanowire single-photon detector directly integrated on the chip, or coupled to an optical fiber through a grating coupler and connected to a single-photon detector outside the chip for detection. Figure 6 (i) is a schematic diagram of a superconducting nanowire single-photon detector. Figure 6 (ii) Schematic diagram of an external off-chip single-photon detector.
[0059] In this embodiment, if Figure 7 As shown, the coherent excitation light source, CNOT operation circuit, and single photon detector are connected as shown. The splitting ratio of each beam splitter in the control NOT gate circuit is adjusted, and the input state of the CNOT gate circuit is changed by changing the phase shift of each phase shifter in the single-bit gate circuit, and the count of the output port is observed to conduct a CNOT gate demonstration operation teaching experiment.
[0060] Example 2
[0061] In this embodiment, compared with the embodiment 1, the light source part adopts a silicon nitride microcavity structure, and a four-wave mixing process occurs in the microcavity to generate signal photons and idler photon pairs as CNOT gate input and forecast photons. Figure 8 As shown, the coherently excited silicon nitride microcavity light source, CNOT gate circuit and single photon detection module are connected as shown in the figure. The beam splitting ratio of each beam splitter in the control NOT gate circuit is adjusted, and the input state of the CNOT gate circuit is changed by changing the phase shift of each phase shifter of the single-bit gate circuit, and the photon count of the output port is observed to perform a demonstration teaching experiment of the CNOT gate circuit. In this implementation case, the detector can also be divided into two types: on-chip integrated type or external type.
[0062] Example 3
[0063] In this embodiment, compared with the embodiment 1, the light source part uses a periodically poled lithium niobate waveguide structure, and a quasi-phase-matched second-order nonlinear spontaneous parametric down-conversion process occurs in the periodically poled lithium niobate waveguide. Fig. 9 As shown in (i), the photon with a frequency of ω0 is converted into signal light and idler light of ω1 and ω2 through the spontaneous parametric down-conversion process, which serves as the input photon and prediction photon of the CNOT gate circuit. Lithium niobate is a ferroelectric crystal. The orientation of the electric dipole moment of each unit cell depends on the position of niobium and lithium ions in the unit. The crystal structure can be reversed by a strong electric field, so that periodically arranged polarized lithium niobate crystals can be made. Fig. 9 (ii) The periodic lithium niobate waveguide shown.
[0064] In this embodiment, according to Fig.10The coherently excited periodically polarized lithium niobate waveguide prediction light source, CNOT gate circuit and single photon detection module are connected in this way. The beam splitting ratio of each beam splitter in the NOT gate circuit is adjusted and controlled, and the input state of the CNOT gate circuit is changed by changing the phase shift of each phase shifter in the single-bit gate circuit, and the photon count at the output port is observed, and a demonstration teaching experiment of the CNOT gate circuit is carried out.
[0065] It should be noted that the embodiments and Figure 2 Only an equivalent single-bit quantum logic gate circuit is shown, and the number and connection method of Mach-Zehnder interferometers and phase shifters are not limited to this embodiment, that is, the single-bit gate circuit for preparing the input state of the CNOT gate circuit is not limited to this embodiment.
[0066] For the disclosed embodiments, the multi-mode optical quantum logic gate circuit of the present invention has the characteristic of full connectivity of all modes, that is, it can realize interference between all modes.
[0067] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.
Claims
1. An optical quantum computing chip integrating a light source and a control NOT gate, characterized in that: The chip includes a coherent excitation light source, a single-bit gate, a control NOT gate circuit and a detection module; wherein, The coherent excitation light source emits two photons, and any single-bit state photons are prepared through the two single-bit gates, input into the control NOT gate circuit, and detected by the detection module after passing through the control NOT gate circuit; The coherent excitation light source adopts a silicon waveguide structure, a silicon nitride microcavity structure or a periodically polarized lithium niobate waveguide structure; The periodically polarized lithium niobate material absorbs two photons with a frequency of ω0, and emits signal light and idler light with frequencies of ω1 and ω2 respectively; two light sources are used to generate two pairs of photons, one photon in each pair of photons is directly sent to the detection module as a forecast single photon; and two photons with the same frequency are sent to the circuit to realize the operation of controlling the NOT gate; and The detection module is used to be connected to an external electronic control device, and the electronic control device is used to display whether the control NOT gate circuit operation is successful and to perform subsequent output and counting.
2. The optical quantum computing chip according to claim 1, characterized in that: The chip integrates the coherent excitation light source, the single-bit gate and the control NOT gate circuit part, or integrates the coherent excitation light source, the single-bit gate, the control NOT gate circuit and the detection module all on a semiconductor chip.
3. The optical quantum computing chip according to claim 1, characterized in that: The single-bit gate and the control NOT gate circuit together form a photon quantum logic gate.
4. The optical quantum computing chip according to claim 1, characterized in that: The control NOT gate circuit includes a beam splitter and a phase shifter. The beam splitting ratio of the beam splitter and the phase of the phase shifter need to be arbitrarily adjustable to achieve unitary transformation.
5. The optical quantum computing chip according to claim 4, characterized in that: The change of the displacement of the phase shifter is achieved by locally changing the temperature of the phase shifter in the waveguide to control the refractive index of the waveguide; the beam splitting ratio of the beam splitter is changed by a Mach-Zehnder interferometer.
6. The optical quantum computing chip according to claim 1, characterized in that: The detection module includes an integrated superconducting nanowire single-photon detector or a photon number detector connected to an off-chip optical fiber via a grating coupler.
7. A teaching system, characterized in that: Comprising the optical quantum computing chip as described in any one of claims 1-6.
8. The teaching system according to claim 7, characterized in that: The teaching system further comprises a teaching control system, and the teaching control system is used for controlling the phase shift of the phase shifter in the control NOT gate circuit.