A pump light source for generating high-fidelity tensor network states

Abstract

The present invention discloses a pump light source for generating high-fidelity tensor network states, comprising: a pump laser system, an optical loop system, a polarization adjustment system, and a dispersion compensation system. The pump laser system generates pump laser pulses; the optical loop system periodically pumps a tensor network state generator with the pump laser pulses; the polarization adjustment system regulates the polarization of the pump laser pulses each time they pass through the tensor network state generator; and the dispersion compensation system compensates for the group velocity dispersion generated when the pump laser pulses circulate in the optical loop system. The pulse light source generated by this scheme exhibits stable relative phases between pulses. As a pump light source for an optical tensor network state generator, it can generate high-fidelity tensor network states.

Description

Technical Field

[0001] The present invention relates to the field of quantum information, and in particular to a pump light source for generating high-fidelity tensor network states. Background Art

[0002] In quantum many-body problems, the dimensionality of the Hilbert space grows exponentially with the number of particles involved. This fundamental difficulty makes the quantum many-body problem one of the most challenging problems in modern physics. Tensor networks represent a high-order tensor as a contraction of a series of lower-order tensors. The ground state and low-level excited states of quantum many-body systems can be described using tensor networks with relatively few parameters, providing an efficient numerical method for simulating quantum many-body systems.

[0003] The expressive power and required computational resources of a tensor network state are closely related to its tensor dimension D. The larger D is, the stronger the expressive power is, but the more computational resources are consumed. In the algorithms based on tensor networks, tensor network contraction and merging operations consume the main computational resources. For example, for a finite open-bounded two-dimensional tensor network with tensor dimension D, the approximate contraction and merging complexity of its tensor network is still as high as O(D 10 ). Therefore, it is still difficult to conduct large-scale numerical simulations based on the tensor network state method at this stage.

[0004] Directly generating tensor network states in physical systems and replacing tensor contraction operations in classical computers with measurements can effectively reduce the computational complexity of numerical methods based on tensor network states. Currently, schemes for generating tensor network states have been designed in physical systems such as cavity QED, Rydberg atom arrays, superconducting circuits, and optical loops. The scheme for generating tensor network states in optical loops is highly favored because it can operate at room temperature. In this scheme, periodic laser pulses are used as pump light to pump a nonlinear crystal to generate parametric down-conversion photon pairs. The resulting series of photon pairs undergo time-domain interference in the optical loop and then output tensor network states. However, in practice, the fidelity of the tensor network states generated experimentally using this scheme with the theoretical state is heavily dependent on the relative phase stability between the pump pulses. Without the use of complex phase-locking devices, it is difficult to obtain a pump light source that meets the experimental precision requirements. Summary of the Invention

[0005] The purpose of the present invention is to provide a pump light source for generating high-fidelity tensor network states. The relative phase between different pulses of the generated pump light source is stable. As the pump light source of an optical tensor network state generator, it can generate high-fidelity tensor network states.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A pump light source for generating high-fidelity tensor network states, comprising: a pump laser system, an optical loop system, a polarization adjustment system, and a dispersion compensation system; wherein:

[0008] The pump laser system is used to generate pump laser pulses;

[0009] The optical loop system is used to periodically pump the tensor network state generator with pump laser pulses;

[0010] The polarization adjustment system is used to adjust the polarization of the pump laser pulse each time it passes through the tensor network state generator;

[0011] The dispersion compensation system is used to compensate for the group velocity dispersion generated when the pump laser pulse circulates in the optical loop system.

[0012] The technical solutions provided by the present invention demonstrate that: 1) the cyclic multiplexing of single pulses to periodically pump the tensor network state generator makes it easier to lock different pump pulse phases compared to directly generating multiple pulses using a laser, thereby improving the quality of the tensor network generator's output states. 2) The addition of a dispersion compensation system to compensate for the dispersion of the pump laser pulses further increases the number of times the pump pulses can circulate within the optical ring, thereby increasing the scale of the tensor network generator's output states. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0014] Figure 1 A schematic diagram of a pump light source for generating high-fidelity tensor network states provided by an embodiment of the present invention;

[0015] Figure 2 A schematic diagram of the optical path structure of a pump light source for generating high-fidelity tensor network states provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0016] The following is a clear and complete description of the technical solutions in the embodiments of the present invention, in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0017] First, the following terms may be used in this article:

[0018] The terms "include," "comprises," "contains," "has," or other similar expressions should be interpreted as non-exclusive. For example, "including certain technical features (such as raw materials, components, ingredients, carriers, dosage forms, materials, dimensions, parts, components, mechanisms, devices, steps, procedures, methods, reaction conditions, processing conditions, parameters, algorithms, signals, data, products, or manufactured articles, etc.) should be interpreted as including not only the technical features explicitly listed, but also other technical features known in the art that are not explicitly listed.

[0019] The following describes in detail a pump light source for generating high-fidelity tensor network states, as provided by the present invention. Any information not described in detail in the present embodiments is prior art known to those skilled in the art. For any conditions not specified in the present embodiments, the process was performed according to conventional conditions in the art or the manufacturer's recommendations. Instruments used in the present embodiments, where the manufacturer is not specified, are commercially available conventional products.

[0020] like Figure 1 As shown, a pump light source for generating high-fidelity tensor network states mainly includes: a pump laser system, an optical loop system, a polarization adjustment system and a dispersion compensation system; wherein:

[0021] The pump laser system is used to generate pump laser pulses;

[0022] The optical loop system is used to periodically pump the tensor network state generator with pump laser pulses;

[0023] The polarization adjustment system is used to adjust the polarization of the pump laser pulse each time it passes through the tensor network state generator;

[0024] The dispersion compensation system is used to compensate for the group velocity dispersion generated when the pump laser pulse circulates in the optical loop system.

[0025] In this embodiment of the present invention, the polarization adjustment system and the dispersion compensation system are both incorporated into the optical loop system. A pump laser pulse enters the optical loop system and circulates within it. During one cycle, the pump laser pulse first undergoes polarization change through the polarization adjustment system, then pumps the tensor network state generator. The effective pump power of the polarized pump laser pulse is dependent solely on the power of its horizontally polarized component. Group velocity dispersion generated by the pump laser pulse after passing through the tensor network state generator is offset by the dispersion compensation system, and the pulse returns to the starting point of the optical loop system, completing a cycle.

[0026] For ease of understanding, the following Figure 2The optical path structure examples shown are used to introduce various parts of the present invention.

[0027] 1. Pump laser system.

[0028] like Figure 2 As shown, the pump laser system mainly includes: a pulse laser 1 and an acousto-optic modulator 2; wherein:

[0029] The pulse laser 1 is used to generate pump laser pulses;

[0030] The acousto-optic modulator 2 is used to change the propagation direction of the pump laser pulse and output the modulated pump laser pulse to the optical loop.

[0031] In the embodiment of the present invention, the pulse laser 1 uses a femtosecond pulse laser with a Gaussian wave packet approximation, with a central wavelength of 775 nm, which is consistent with the nonlinear crystal design pump wavelength used by the tensor network state generator to be pumped.

[0032] In the embodiment of the present invention, the pulse interval is fixed to T, and the phases between adjacent pulses generated by the initial pulse laser are not required to be stable.

[0033] 2. Optical loop system.

[0034] like Figure 2 As shown, the optical loop system is a loop structure, including: two dichroic mirrors (a first dichroic mirror 4 and a second dichroic mirror 5) and two reflecting mirrors (a first reflecting mirror 7 and a second reflecting mirror 6).

[0035] The two dichroic mirrors reflect the pump laser pulse wavelength and transmit the signal light wavelength, forming a side through which the pump laser pulse and signal light pass collinearly. This side houses the nonlinear crystal of the tensor network state generator; the signal light is the output signal of the tensor network state generator. In this embodiment of the present invention, the first dichroic mirror 4 and the second dichroic mirror 5 reflect light with a wavelength of 775 nm and transmit light with a wavelength of 1550 nm.

[0036] The two reflectors reflect the wavelength of the pump laser pulse and are used to form the remaining sides of the loop structure. In the embodiment of the present invention, the first reflector 7 and the second reflector 6 are ultrafast reflectors that reflect light with a wavelength of 775 nm and introduce a group dispersion close to zero, with a designed incident angle of 45°.

[0037] In the loop structure, the pump laser pulse circulates through the first dichroic mirror, the second dichroic mirror, the first reflector, the second reflector, and the first dichroic mirror. The time t required to complete one cycle satisfies T / t>N, where N is the number of tensor network state points to be prepared.

[0038] 3. Polarization adjustment system.

[0039] In an embodiment of the present invention, the polarization adjustment system includes: an electro-optical modulator, configured to adjust the polarization direction of the pump laser pulse output by the pump laser system to change the effective pump intensity.

[0040] like Figure 2 As shown, the electro-optic modulator 3 is provided in the optical loop system, and is located between the acousto-optic modulator 2 and the first dichroic mirror 4 .

[0041] 4. Dispersion compensation system.

[0042] In an embodiment of the present invention, the dispersion compensation system includes: a dispersion prism group, which is used to provide negative dispersion to compensate for the dispersion generated when the pump light passes through the nonlinear crystal and other components in the loop.

[0043] like Figure 2 As shown, a dispersive prism assembly 8 is disposed within the optical loop system, positioned between the first reflector 7 and the second reflector 6. The dispersive prism assembly 8 comprises four dispersive prisms, arranged in pairs, with the bases of each pair parallel to each other and their apex angles facing each other. The negative dispersion generated by the dispersive prism assembly 8 is equivalent to the sum of the dispersion generated by the pump light passing through the AOM 2, EO modulator 3, and the nonlinear crystal.

[0044] It should be noted that Figure 2 The number of dispersion prism groups and their internal structural relationships in the dispersion compensation system shown are examples and are not limiting. In actual operation, users can select other dispersion compensation system implementation methods based on actual conditions or experience to compensate for the dispersion generated when the pump light passes through the nonlinear crystal and other components in the loop.

[0045] See also Figure 2 In the optical path structure shown, the starting point and the end point of each cycle are both located at the polarization adjustment system (i.e., the electro-optical modulator 3). In one cycle, the pump laser pulse changes polarization through the electro-optical modulator 3 and pumps the nonlinear crystal in the tensor network state generator through the first dichroic mirror 4; then, it passes through the second dichroic mirror 5 and the first reflector 7 in sequence, and compensates for group velocity dispersion through the dispersion prism group 8, and then enters the electro-optical modulator 3 through the second reflector reflection 6 and the acousto-optic modulator 2, completing one cycle.

[0046] also, Figure 2 The bottom of the optical path structure shown, the nonlinear crystal between the two dichroic mirrors, and the reflectors on both sides of the two dichroic mirrors all belong to the structure of the tensor network state generator. The specific structure and working principle of the tensor network state generator can refer to conventional technology and will not be elaborated in the present invention.

[0047] It should be noted that the relevant parameters of each device provided in the above examples are only for illustration and do not constitute a limitation; in actual applications, the relevant parameters of each device can be adjusted by the user according to actual conditions or experience.

[0048] The above solution of the embodiment of the present invention has at least the following beneficial effects compared with the prior art:

[0049] 1) A single pulse cyclic multiplexing method is used to periodically pump the nonlinear crystal in the tensor network state generator. Compared with directly generating multiple pulses by the laser, different pump pulse phases are easier to lock, thereby making the output state quality of the tensor network generator higher.

[0050] 2) By adding a dispersion prism to the optical loop to compensate for the dispersion generated by the pump pulse during the circulation process, the number of times the pump pulse can circulate in the optical loop is further increased, making the output state of the tensor network generator larger in scale.

[0051] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A pump light source for generating high-fidelity tensor network states, characterized in that include: Pump laser system, optical loop system, polarization adjustment system and dispersion compensation system; including: The pump laser system is used to generate pump laser pulses; The optical loop system is used to periodically pump the tensor network state generator with pump laser pulses; The polarization adjustment system is used to adjust the polarization of the pump laser pulse each time it passes through the tensor network state generator; The dispersion compensation system is used to compensate for the group velocity dispersion generated when the pump laser pulse circulates in the optical loop system; The optical loop system is a loop structure, comprising: two dichroic mirrors and two reflecting mirrors; wherein: The two dichroic mirrors reflect the pump laser pulse wavelength and transmit the signal wavelength, and are used to form an edge through which the pump light and the signal light pass in a collinear manner, and the nonlinear crystal of the tensor network state generator is provided in the edge, and the signal light is the output signal of the tensor network state generator; The two mirrors reflect the wavelength of the pump laser pulse and are used to form the remaining sides of the loop structure; In the loop structure, the circulation path of the pump laser pulse is: the first dichroic mirror, the second dichroic mirror, the first reflecting mirror, the second reflecting mirror, and the first dichroic mirror.

2. A pump light source for generating high-fidelity tensor network states according to claim 1, characterized in that: The pump laser system includes: a pulse laser and an acousto-optic modulator; wherein: The pulse laser is used to generate pump laser pulses; The acousto-optic modulator is used to change the propagation direction of the pump laser pulse and output the modulated pump laser pulse.

3. A pump light source for generating high-fidelity tensor network states according to claim 1, characterized in that: The polarization adjustment system is arranged in the optical loop system, and comprises an electro-optical modulator for adjusting the polarization direction of the pump laser pulse output by the pump laser system.

4. A pump light source for generating high-fidelity tensor network states according to claim 1, characterized in that: The dispersion compensation system includes: a dispersion prism group, which is arranged in the optical loop system; The dispersion prism group includes four dispersion prisms, which are placed in pairs. The bottom sides of each pair of dispersion prisms are parallel to each other and the top angles are opposite.

5. The pump light source for generating high-fidelity tensor network states according to claim 1, characterized in that: The pump laser pulse is input into the optical loop system and circulates in the loop structure. In each cycle, the starting point and the end point are both located at the polarization adjustment system. In one cycle, the pump laser pulse changes polarization through the polarization adjustment system and pumps the nonlinear crystal in the tensor network state generator through the first dichroic mirror. Then, it passes through the second dichroic mirror and the first reflector in sequence, and compensates for the group velocity dispersion through the dispersion compensation system. Then, it enters the polarization adjustment system through the second reflector and the acousto-optic modulator in the pump laser system, completing one cycle.

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