Tunable light-quantum memory entanglement generation device based on atomic transition interference

Abstract

The application relates to a tunable light-quantum memory entanglement generation device based on atomic transition interference and belongs to the technical field of quantum information science technology. In the application, a multi-energy-level atomic system is used as an atomic medium for preparing a quantum memory; atoms in an initial state in the atomic medium are transitioned to a coherent superposition state of multiple excited states under the action of excitation light; the atoms in the coherent superposition state of the multiple excited states are transitioned to a ground state, forming a coherent superposition state of multiple light-quantum memory entangled states, that is, atomic transition interference occurs; the frequency of the excitation light can be adjusted to change the coefficients of the coherent superposition of the light-quantum memory entangled states, so that the photons output from the atomic medium and the quantum memory of the spin state of the storage atom are in a tunable quantum entangled state. In the application, each component for preparing the tunable light-quantum memory entanglement can be obtained from a mature optoelectronic device.

Description

Technical Field

[0001] This invention belongs to the field of quantum information science and technology, specifically relating to a tunable optical-quantum memory entanglement generation device and method based on atomic transition interference. Background Technology

[0002] Quantum information technology is a technology that utilizes the principles of quantum mechanics to achieve information processing and transmission, possessing the potential and advantages to surpass classical information technology. Quantum entanglement is a core resource of quantum information technology; it is a physical phenomenon describing the non-classical correlation between two or more quantum systems. Maximum entanglement, as a crucial resource, can efficiently enable long-distance quantum state transmission, quantum key distribution, quantum computing, and other functions.

[0003] To achieve long-distance quantum information transmission, a reliable quantum network is needed, consisting of multiple nodes and channels. Each node can store and process quantum information, and each channel can transmit quantum information. However, due to the attenuation and noise during light transmission, directly using light as a channel to transmit quantum information is not feasible. Therefore, the concept of quantum repeaters is introduced, where one or more intermediate nodes are inserted between two remote nodes. Entanglement between light and the quantum memory is achieved at the intermediate nodes, and entanglement distribution between the remote nodes is achieved through entanglement exchange. A common method for preparing optical-quantum memory entanglement uses atoms as the medium. The atomic ground state is excited by weakly coherent light, and single photons associated with the atomic spin energy levels are scattered via Raman scattering, achieving a one-to-one correspondence between the photon polarization state and the atomic spin state. However, different polarizations often correspond to different atomic transition channels, and their relative amplitudes differ, resulting in different entangled states prepared by different nodes. To ensure that the quantum entanglement achieved after further entanglement exchange is the maximally entangled state, it is crucial to study the preparation of entangled states with tunable amplitudes for each component. Such entangled states can undergo component amplitude matching based on entangled states from different sources to ensure that entangled states with arbitrary component amplitudes are achieved after entanglement swapping. Currently, the main method for achieving entangled states with tunable component amplitudes is cavity enhancement. This involves designing cavities with different coupling strengths to different polarized light to adjust the probability of atoms within the cavity releasing photons with different polarization components, thereby achieving amplitude modulation of entanglement. This method requires the construction of external cavities, and the adjustment and operation are relatively difficult. Researching novel and simpler schemes to achieve tunable optical-storage entanglement remains an important goal in this field.

[0004] In summary, tunable optical-atomic entanglement is a crucial resource for quantum information technology and has broad application prospects. Currently, tunable optical-storage entanglement can only be achieved through cavity enhancement, which is relatively difficult to adjust and manipulate. Therefore, there is an urgent need to research a simpler and more easily controllable new method for generating tunable optical-atomic entanglement. Summary of the Invention

[0005] The technical problem to be solved by this invention is that, in the process of building a quantum entangled network, when multiple photon-quantum memory entangled states are further connected to realize a quantum memory-quantum memory entangled network, the maximum entangled state cannot be obtained due to the different amplitudes of the components in the entangled state. A photon-quantum memory entanglement generation device and method with tunable component amplitude is proposed.

[0006] To solve the above-mentioned technical problems, embodiments of the present invention provide a tunable optical-quantum memory entanglement generation device based on atomic transition interference, including a first pump light generation device, a second pump light generation device, an excitation light generation device, an atomic medium 11, a fourth fiber collimator 17, and a Fabry-Perot cavity 18.

[0007] The first pump light generating device and the second pump light generating device are used to generate the first tunable pump light and the second tunable pump light required for the preparation of the initial state of atoms in the atomic medium 11, respectively. The excitation light generating device is used to generate the excitation light required for the preparation of the entangled state of the optical-quantum memory.

[0008] The first and second tunable pump lights enter the atomic medium 11, causing the atoms in the atomic medium 11 to be in an initial state. Under the action of the excitation light, the atoms in the atomic medium 11 in the initial state transition to a coherent superposition of multiple excited states. The transition from the excited state to the ground state radiates photons. The radiated photons are coupled into the Fabry-Perot cavity 18 through the fourth fiber collimator 17 for noise photon filtering and output.

[0009] In the atomic medium 11, when an atom in an excited state transitions to the ground state and emits a photon, it also becomes a quantum memory that stores the spin state of the atom. There is a one-to-one correspondence between the polarization state of the emitted photon and the spin state of the atom. Therefore, there is quantum entanglement between the photon output from the Fabry-Perot cavity 18 and the quantum memory, that is, they are in an entangled state of light and quantum memory. The components of different polarization states of photons in the entangled state are determined by the transition coefficient of the atom that generates the polarization state of the photon.

[0010] When an atom in a coherent superposition of multiple excited states transitions to the ground state, it forms a coherent superposition of multiple entangled states of optical-quantum memory, i.e., atomic transition interference occurs. By adjusting the frequency of the excitation light, the coefficients of different optical-quantum memory entangled states in coherent superposition can be changed, thereby enabling the photons output from the Fabry-Perot cavity 18 and the quantum memory storing the spin states of atoms in the atomic medium 11 to be in a tunable quantum entangled state.

[0011] Based on the above technical solution, the present invention can be further improved as follows.

[0012] Furthermore, the first pump light generating device includes a first continuously tunable laser source 1, a first optical attenuator 2, a first acousto-optic modulator 3, a first polarization controller 4, and a first fiber collimator 5 connected in sequence.

[0013] The second pump light generating device includes a second continuously tunable laser source 6, a second optical attenuator 7, a second acousto-optic modulator 8, a second polarization controller 9, and a second fiber collimator 10 connected in sequence.

[0014] The excitation light generating device includes a third continuously tunable laser source 12, a third optical attenuator 13, a third acousto-optic modulator 14, a third polarization controller 15, and a third fiber collimator 16 connected in sequence.

[0015] The first fiber collimator 5, the second fiber collimator 10, and the third fiber collimator 16 are used to couple the light transmitted in the fiber to free space for transmission and to perform a beam waist transformation before inputting it into the atomic medium 11. There is a non-zero angle between the optical axis of the lens in the second fiber collimator 10 and the normal to the input end face of the atomic medium 11. There is a non-zero angle between the optical axis of the lens in the fourth fiber collimator 17 and the normal to the output end face of the atomic medium 11. The angle between the propagation direction of the light output by the third fiber collimator 16 and the propagation direction of the photons that can be collected by the fourth fiber collimator 17 should be less than 2 degrees.

[0016] Furthermore, the first continuously tunable laser source 1, the second continuously tunable laser source 6, and the third continuously tunable laser source 12 are solid-state lasers or semiconductor lasers.

[0017] Furthermore, the first optical attenuator 2, the second optical attenuator 7, and the third optical attenuator 13 are optical fiber attenuators.

[0018] Furthermore, the operating wavelength range of the first acousto-optic modulator 3, the second acousto-optic modulator 8, and the third acousto-optic modulator 14 covers the wavelength of atomic energy level transitions in the atomic medium 11, and the switching time is greater than or equal to 50 ns.

[0019] Furthermore, the first polarization controller 4, the second polarization controller 9, and the third polarization controller 15 are fiber optic polarization controllers.

[0020] Furthermore, the first fiber collimator 5, the second fiber collimator 10, the third fiber collimator 16, and the fourth fiber collimator 17 have built-in lenses and FC interfaces, which can adjust the beam waist of light coupled from the fiber to free space, and can also collect light transmitted in free space through the lens and couple it into the fiber optic device.

[0021] Furthermore, the atomic medium 11 is a rubidium atom ensemble, a cesium atom ensemble, a calcium ion ensemble, or a strontium ion ensemble that has a multi-level structure and can be used for quantum storage.

[0022] Furthermore, the Fabry-Perot cavity 18 is a plano-convex lens or an optical fiber filter cavity composed of fiber end face coating.

[0023] To solve the above-mentioned technical problems, this invention provides a method for generating entangled optical-quantum memory based on atomic transition interference, comprising the following steps: using a first pump light generating device and a second pump light generating device to generate a first tunable pump light and a second tunable pump light required for the preparation of the initial atomic state in the atomic medium 11, respectively; and using an excitation light generating device to generate excitation light required for the preparation of the entangled state of the optical-quantum memory.

[0024] By introducing the first and second tunable pump lights into the atomic medium 11, the atoms in the atomic medium 11 will be prepared to their initial state.

[0025] Atoms in the initial state in atomic medium 11 transition to a coherent superposition of multiple excited states under the action of excitation light. The transition from the excited state to the ground state emits photons. The emitted photons are coupled into the Fabry-Perot cavity 18 through the fourth fiber collimator 17 for noise photon filtering and output.

[0026] In the atomic medium 11, when an atom in an excited state transitions to the ground state and emits a photon, it also becomes a quantum memory that stores the spin state of the atom. There is a one-to-one correspondence between the polarization state of the emitted photon and the spin state of the atom. Therefore, there is quantum entanglement between the photon output from the Fabry-Perot cavity 18 and the quantum memory, that is, they are in an entangled state of light and quantum memory. The components of different polarization states of photons in the entangled state are determined by the transition coefficient of the atom that generates the polarization state of the photon.

[0027] When an atom in a coherent superposition of multiple excited states transitions to the ground state, it forms a coherent superposition of multiple entangled states of optical-quantum memory, i.e., atomic transition interference occurs. By adjusting the frequency of the excitation light, the coefficients of different optical-quantum memory entangled states in coherent superposition can be changed, thereby enabling the photons output from the Fabry-Perot cavity 18 and the quantum memory storing the spin states of atoms in the atomic medium 11 to be in a tunable quantum entangled state.

[0028] The beneficial effects of this invention are as follows: This invention provides a tunable optical-quantum memory entanglement generation device based on atomic transition interference. Atoms in an initial state in an atomic medium transition to a coherent superposition of multiple excited states under the action of excitation light. When these atoms in the coherent superposition of excited states transition to the ground state, atomic transition interference occurs, forming a coherent superposition of multiple optical-quantum memory entangled states. By adjusting the frequency of the excitation light, the coefficient of coherent superposition of these optical-quantum memory entangled states can be changed, thereby enabling photons output from the atomic medium to be in a tunable quantum entangled state with the quantum memory storing the atomic spin states. The tunable optical-quantum memory entanglement generation device provided by this invention adopts the DLCZ protocol, which utilizes a rich variety of atomic systems, thus offering advantages such as multiple selectable transition channels and strong operability. It avoids the difficulties of existing research requiring cavities to achieve the same function, making the device more complex and cumbersome to operate. Furthermore, the remaining components can all be derived from mature optoelectronic devices, which is beneficial for practical application and can promote the application of quantum storage and optical-quantum memory entanglement preparation technology in various fields. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a tunable optical-quantum memory entanglement generation device based on atomic transition interference, according to an embodiment of the present invention.

[0030] Figure 2 This is a schematic diagram illustrating the working principle of a tunable optical-quantum memory entanglement generation device based on atomic transition interference, according to an embodiment of the present invention.

[0031] The attached diagram lists the components represented by each number as follows:

[0032] 1. First continuously tunable laser source; 2. First optical attenuator; 3. First acousto-optic modulator; 4. First polarization controller; 5. First fiber collimator; 6. Second continuously tunable laser source; 7. Second optical attenuator; 8. Second acousto-optic modulator; 9. Second polarization controller; 10. Second fiber collimator; 11. Atomic medium; 12. Third continuously tunable laser source; 13. Third optical attenuator; 14. Third acousto-optic modulator; 15. Third polarization controller; 16. Third fiber collimator; 17. Fourth fiber collimator; 18. Fabry-Perot cavity. Detailed Implementation

[0033] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0034] like Figure 1 As shown, the first embodiment of the present invention provides a tunable optical-quantum memory entanglement generation device based on atomic transition interference, comprising: 1. a continuously tunable laser source; 2. an optical attenuator; 3. an acousto-optic modulator; 4. a polarization controller; 5. an optical fiber collimator; 6. a continuously tunable laser source; 7. an optical attenuator; 8. an acousto-optic modulator; 9. a polarization controller; 10. an optical fiber collimator; 11. an atomic medium; 12. a continuously tunable laser source; 13. an optical attenuator; 14. an acousto-optic modulator; 15. a polarization controller; 16. an optical fiber collimator; 17. an optical fiber collimator; and 18. a Fabry-Perot cavity.

[0035] In the above embodiments, the continuously tunable laser source 1 is a semiconductor continuous laser, used to provide tunable, narrow-linewidth continuous pump laser for the preparation of atomic initial states, located at energy level |F=1,m F Atoms on |F=1,1> are transferred to other energy levels under pumping action. The center wavelength of the narrow-linewidth continuous-pump laser is 795nm, the detuning between it and the transition |F=1>→|F′=1> in rubidium atoms is -75MHz, the linewidth is about 100kHz, and the power is set to 10mW.

[0036] The optical attenuator 2 is an optical fiber attenuator, connected to the continuously tunable laser source 1 via an optical fiber. The narrow-linewidth continuous-pump laser output from the continuously tunable laser source 1 is incident on the optical attenuator 2. The optical attenuator 2 adjusts the intensity of the incident pump laser to ensure that the peak power of the pump laser interacting with the atomic medium is approximately 1 mW.

[0037] The input end of the acousto-optic modulator 3 is connected to the output end of the optical attenuator 2 via an optical fiber. It is used to modulate the continuous pump laser output from the optical attenuator 2 into a pulsed pump laser and to perform frequency shifting. The operating wavelength of the acousto-optic modulator 3 is 650-1050 nm, the frequency shift is set to 80 MHz, and the switching time is set to 2 μs, so that the input continuous pump laser is modulated into a pulse with a pulse width of 2 μs.

[0038] The polarization controller 4 is an optical fiber polarization controller 4 with an operating wavelength of 795nm, and is connected to the acousto-optic modulator 3 via an optical fiber. The pulsed pump laser output from the acousto-optic modulator 3 is incident on the polarization controller 4, and the polarization controller 4 adjusts the polarization state of the pulsed pump laser to a horizontal polarization state |H>.

[0039] The fiber optic collimator 5 operates in the 650nm-1050nm wavelength range, uses an FC fiber optic interface, and contains an 18mm focal length adjustable lens. Its input end is connected to the output end of the polarization controller 4. The fiber optic collimator 5 couples the light output from the polarization controller 4 from the optical fiber into free space. The size of the beam output from the fiber optic collimator 5 is adjusted by the distance between the fiber end face and the lens. The pump light output from the fiber optic collimator 5 is input into the atomic medium 11.

[0040] The continuously tunable laser source 6 is a semiconductor continuous-wave laser used to provide a tunable, narrow-linewidth continuous-wave pump laser during the preparation of the initial atomic states, so that all atoms located at |F=2> are pumped to the |F=1> state. The laser has a center wavelength of 795nm, a detuning of -75MHz with the atomic state transition of rubidium atom |F=2>→|F′=2>, a linewidth of approximately 100kHz, and a power setting of 10mW.

[0041] The optical attenuator 7 is a fiber optic attenuator, and its input end is connected to the output end of the continuously tunable laser source 6 via an optical fiber. The optical attenuator 7 adjusts the power of the continuously pumped laser input to it.

[0042] The input of the acousto-optic modulator 8 is connected to the output of the optical attenuator 7 via an optical fiber. It is used to modulate the continuous pump laser output from the optical attenuator 7 into a pulsed pump laser and to perform frequency shifting. The acousto-optic modulator 8 operates at a wavelength of 650-1050 nm, with a frequency shift of 80 MHz and a switching time of 3 μs, thereby modulating the input continuous pump laser into a pulse with a pulse width of 3 μs.

[0043] The polarization controller 9 is a fiber optic polarization controller with an operating wavelength of 795 nm. The input terminal of the polarization controller 9 is connected to the output terminal of the acousto-optic modulator 8. The polarization controller 9 is used to adjust the polarization state of the input pulsed pump laser to horizontal polarization |H>.

[0044] The fiber optic collimator 10 operates in the 650nm-1050nm wavelength range, uses an FC fiber optic interface, and contains an 18mm focal length adjustable lens. Its input end is connected to the output end of the polarization controller 9. The fiber optic collimator 10 couples the light output from the polarization controller 9 from the optical fiber into free space. The size of the output beam is adjusted by the distance between the fiber end face and the lens in the fiber optic collimator 10. The pump light output from the fiber optic collimator 10 is input into the atomic medium 11.

[0045] The atomic medium 11 is a cold atom ensemble composed of rubidium 87 atoms trapped and confined in a magneto-optical trap, placed in a horizontal magnetic field environment with a magnetic field strength of 300 mG. Laser light input into the medium can interact with the atoms, causing them to be initialized or undergo Raman scattering.

[0046] The continuously tunable laser source 12 is a semiconductor continuous laser used to provide tunable continuous excitation light for the preparation of entangled states in the optical-quantum memory. Its center wavelength is 795nm, the detuning between it and the atomic state transition of rubidium atom |F=1>→|F′=2> is -407MHz, the linewidth is about 100kHz, and the power is set to 1mW.

[0047] The optical attenuator 13 is an optical fiber attenuator, and its input end is connected to the output end of the continuously tunable laser source 12 via an optical fiber. The optical attenuator 13 adjusts the power of the continuously excited light input into it.

[0048] The input of the acousto-optic modulator 14 is connected to the output of the optical attenuator 13 via an optical fiber. It is used to modulate the continuous excitation light output from the optical attenuator 13 into pulsed excitation light and to perform frequency shifting. The operating wavelength of the acousto-optic modulator 14 is 650-1050 nm, the frequency shift is set between -400 and 400 MHz, and the switching time is set to 50 ns, so that the continuous excitation light is modulated into pulsed excitation light with a pulse width of 50 ns.

[0049] The polarization controller 15 is an optical fiber polarization controller with an operating wavelength of 795nm. The input terminal of the polarization controller 15 is connected to the output terminal of the acousto-optic modulator 14, and is used to adjust the polarization state of the pulse excitation light output by the acousto-optic modulator 14 to right-hand circular polarization |R>.

[0050] The fiber optic collimator 16 operates in the 650nm-1050nm wavelength range, uses an FC fiber optic interface, and contains an adjustable lens with a focal length of 11mm. Its input end is connected to the output end of the polarization controller 15. The fiber optic collimator 16 couples the light output from the polarization controller 15 from the optical fiber into free space. The size of the output beam is adjusted by the distance between the fiber end face and the lens in the fiber optic collimator 16. The excitation light output from the fiber optic collimator 16 is input into the atomic medium 11.

[0051] The fiber optic collimator 17 operates in the 650nm-1050nm wavelength range, uses an FC fiber optic interface, and includes a position-tunable lens with a focal length of 11mm. The fiber optic collimator 17 can collect photons within a certain spatial range emitted from the atomic medium and guide them into the optical fiber. The size of the beam that can be received is adjusted by the distance between the fiber end face and the lens in the fiber optic collimator 17.

[0052] The Fabry-Perot cavity 18 is a fiber optic Fabry-Perot cavity composed of fiber end-face coatings, and its input end is connected to the output end of the fiber optic collimator 17. The Fabry-Perot cavity 18 uses an interference process to allow only photons of specific frequencies to pass through it. It can filter out noise photons generated in the atomic medium 11 via Rayleigh scattering (i.e., photons emitted when atoms transition back to their initial state after being scattered by excitation light), allowing only photons generated via Raman scattering to pass through.

[0053] A schematic diagram illustrating the principle of entanglement in tunable optical-quantum memory fabricated using rubidium atoms is shown below. Figure 2 As shown, the principle for preparing tunable entanglement is as follows:

[0054] like Figure 1 As shown, after the cold atom ensemble in atomic medium 11 is prepared, acousto-optic modulators 3 and 8 output pulsed pump lasers with pulse widths of 2 μs and 3 μs, respectively, so that the atoms in the cold atom ensemble are all prepared in the |a> state. Subsequently, acousto-optic modulator 14 outputs pulsed excitation light with a pulse width of 50 ns to excite the atoms in the cold atom ensemble to excited states |d> and |e>. The excited states radiate photons to the ground states |b> and |c>, and the atoms themselves also become quantum memories storing spin states. There is quantum entanglement between the radiated photons and the quantum memories. The radiated photons are collected by fiber collimator 17 and then filtered out by Rayleigh scattering noise photons through Fabry-Perot cavity 18. The polarization state of the photons output by Fabry-Perot cavity 18 satisfies the quantum entanglement condition with the spin states |b> and |c> stored in the quantum memories. By means of the interference between the atomic transitions from excited states |d> and |e> to ground states |b> and |c>, the amplitudes of each component in the entangled state of the optical-quantum memory can be tuned by adjusting the frequency shift of the acousto-optic modulator 14.

[0055] |a>, |b>, |c>, |d>, and |e> are the five atomic spin state energy levels used in this invention, composed of the energy levels after the Zeeman split of rubidium-87, respectively, with the initial state |a> = |5 2 S 1 / 2 F = 1, m F =0>;First ground state |b>=|5 2 S 1 / 2 F = 2, m F =0>;Second ground state |c>=|5 2 S 1 / 2 F = 2, m F =2>;First excited state |d>=|5 2 P 1 / 2 F′=2, m F =1>;Second excited state |e>=|52 P 1 / 2 F′=1, m F =1>. Photons coupled to transitions between different ground states and different excited states are in different polarization states: photons coupled to transitions |a>→|d>, |a>→|e>, |d>→|b>, and |e>→|b> are in right-handed polarization state |R>, and photons coupled to transitions |d>→|c> and |e>→|c> are in left-handed polarization state |L>. When a beam of right-handed polarized excitation light coupled to |a> and excited states is incident on an atomic medium, the atom will transition to either |b> or |c> via the excited state. When transitioning to |b>, it will emit photons in the right-handed polarization state |R>, and when transitioning to |c>, it will emit photons in the left-handed polarization state |L>. The polarization states |R> and |L> of the emitted photons correspond one-to-one with the spin states |b> and |c> of the atoms, that is, there is quantum entanglement between the emitted photons and the quantum memory storing the spin states. Because the Klebsch-Golden coefficients (CG coefficients) for transitions |d>→|b> and |e>→|b>, and |d>→|c> and |e>→|c> are different, the transition strengths differ, and therefore the amplitudes of the components |R>|b> and |L>|c> in the entangled state of the optical-quantum memory generated via the excited states |d> and |e> are also different. For example, the entangled state prepared via the |d> state is in the form of |ψ>. d =CG ad CG bd |R>|b>+CG ad CG ca The entangled state prepared via the |e> state is in the form of |ψ>. e =CG ae CG be |R>|b>+CG ae CG ce |L>|c>, where CG aa CG coefficients for the transition |a>→|d>; CG bd CG coefficients for the transition |d>→|b>; CG cd CG coefficients for the transition |d>→|c>; CG ae The CG coefficients for |a>→|e>; CG ce CG coefficients for the transition |c>→|e>; CG be The CG coefficients are for the transition |b>→|e>. The above spin-level transition coefficients are... Substitute | ψ> d and |ψ> e The expression can be obtained

[0056]

[0057] and

[0058]

[0059] When the excitation light output by laser 12 has a detuning amount Δ with the transitions |a>→|d> and |a>→|e> respectively. d and Δ e At that time, the transition intensities of |a>→|d> and |a>→|e> are respectively proportional to... and Where Γ d and Γ e The linewidths of the excited states |d> and |e> are approximately 6 MHz in the atomic medium. The two entangled photon-quantum memory states generated via the excited states |d> and |e> will coherently superimpose to form a quantum state. When the excitation frequency is set such that 2Δ d >>Γ d 2Δ e >>Γ e hour, At this point, the entangled state |ψ> can be approximated as |ψ>=-|ψ> d / Δ d +|ψ> e / Δ e Substituting expressions (1) and (2) into the expression for |ψ> and normalizing it, we obtain an entangled state of the form |ψ>=cosθ|R>|b>+sinθ|L>|c>. The expression for cosθ is...

[0060]

[0061] Its detuning Δ d and Δ e Related. Changing the frequency of the excitation light can change Δ. d and Δ e This alters the intensity of atomic transitions via different excited states, thereby enabling the relative amplitude adjustment of the |R>|b> and |L>|c> components in the entangled state |Ψ>, thus obtaining the entangled tunable optical-quantum memory described in this invention.

[0062] When the frequency shift of the acousto-optic modulator 14 is set to 400MHz, it can be approximated that the excitation light can only excite the transition |a>→|d>, therefore the prepared normalized entangled state is When the frequency shift of the acousto-optic modulator 14 is set to -400MHz, it can be approximated that the excitation light can only excite the transition |a>→|e>, and the prepared normalized entangled state is When the frequency shift of the acousto-optic modulator 14 is adjusted between -400 and 400 MHz, the relative amplitudes of the |R>|b> and |L>|c> components in the entangled state will be adjusted.

[0063] Optionally, the first continuously tunable laser source 1, the second continuously tunable laser source 6, and the third continuously tunable laser source 12 are solid-state lasers or semiconductor lasers.

[0064] Optionally, the first optical attenuator 2, the second optical attenuator 7, and the third optical attenuator 13 are fiber optic attenuators.

[0065] Optionally, the operating wavelength range of the first acousto-optic modulator 3, the second acousto-optic modulator 8, and the third acousto-optic modulator 14 covers the wavelength of atomic energy level transitions in the atomic medium 11, and the switching time is greater than or equal to 50 ns.

[0066] Optionally, the first polarization controller 4, the second polarization controller 9, and the third polarization controller 15 are fiber optic polarization controllers.

[0067] Optionally, the first fiber collimator 5, the second fiber collimator 10, the third fiber collimator 16, and the fourth fiber collimator 17 have built-in lenses and FC interfaces, which can adjust the beam waist of light coupled from the fiber to free space, and can also collect light transmitted in free space through the lens and couple it into the fiber optic device.

[0068] Optionally, the atomic medium 11 is a rubidium atom ensemble, a cesium atom ensemble, a calcium ion ensemble, or a strontium ion ensemble that has a multi-level structure and can be used for quantum storage.

[0069] Optionally, the Fabry-Perot cavity 18 is a plano-convex lens or an optical fiber filter cavity composed of fiber end face coating.

[0070] The second embodiment of the present invention provides a method for generating entangled optical-quantum memory based on atomic transition interference, comprising the following steps: using a first pump light generating device and a second pump light generating device to generate a first tunable pump light and a second tunable pump light required for the preparation of the initial state of atoms in the atomic medium (11), respectively; and using an excitation light generating device to generate excitation light required for the preparation of the entangled state of the optical-quantum memory.

[0071] By introducing the first and second tunable pump lights into the atomic medium 11, the atoms in the atomic medium 11 will be prepared to their initial state.

[0072] Atoms in the initial state in atomic medium 11 transition to a coherent superposition of multiple excited states under the action of excitation light. The transition from the excited state to the ground state emits photons. The emitted photons are coupled into the Fabry-Perot cavity 18 through the fourth fiber collimator 17 for noise photon filtering and output.

[0073] In the atomic medium 11, when an atom in an excited state transitions to the ground state and emits a photon, it also becomes a quantum memory that stores the spin state of the atom. There is a one-to-one correspondence between the polarization state of the emitted photon and the spin state of the atom. Therefore, there is quantum entanglement between the photon output from the Fabry-Perot cavity 18 and the quantum memory, that is, they are in an entangled state of light and quantum memory. The components of different polarization states of photons in the entangled state are determined by the transition coefficient of the atom that generates the polarization state of the photon.

[0074] When an atom in a coherent superposition of multiple excited states transitions to the ground state, it forms a coherent superposition of multiple entangled states of optical-quantum memory, i.e., atomic transition interference occurs. By adjusting the frequency of the excitation light, the coefficients of different optical-quantum memory entangled states in coherent superposition can be changed, thereby enabling the photons output from the Fabry-Perot cavity 18 and the quantum memory storing the spin states of atoms in the atomic medium 11 to be in a tunable quantum entangled state.

[0075] This invention employs a multi-level atomic system as the atomic medium for fabricating quantum memories. Atoms in the initial state within the atomic medium transition to a coherent superposition of multiple excited states under the influence of excitation light. When these atoms transition back to the ground state, atomic interference occurs, forming a coherent superposition of multiple entangled states between the optical and quantum memories. By adjusting the frequency of the excitation light, the coefficients of this coherent superposition can be changed, thereby enabling a tunable quantum entanglement between the photons emitted from the atomic medium and the quantum memory storing the atomic spin states. All components used in this invention for fabricating tunable optical-quantum memory entanglement can be derived from mature optoelectronic devices. This type of tunable optical-memory entanglement can be applied to prepare maximally entangled states between quantum nodes through entanglement swapping, and has significant implications for applications such as quantum repeaters, long-distance entanglement distribution, and quantum teleportation.

[0076] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0077] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0078] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0079] The above description is only a preferred 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 within the protection scope of the present invention.

Claims

1. A tunable optical-quantum memory entanglement generation device based on atomic transition interference, characterized in that, It includes a first pump light generating device, a second pump light generating device, an excitation light generating device, an atomic medium (11), a fourth fiber collimator (17), and a Fabry-Perot cavity (18); The first pump light generating device and the second pump light generating device are used to generate the first tunable pump light and the second tunable pump light required for the preparation of the initial state of atoms in the atomic medium (11), respectively. The excitation light generating device is used to generate the excitation light required for the preparation of the entangled state of the optical-quantum memory. The first tunable pump light and the second tunable pump light enter the atomic medium (11), causing the atoms in the atomic medium (11) to be in the initial state. The atoms in the atomic medium (11) in the initial state transition to a coherent superposition of multiple excited states under the action of the excitation light. The transition from the excited state to the ground state radiates photons. The radiated photons are coupled into the Fabry-Perot cavity (18) through the fourth fiber collimator (17) for noise photon filtering and output. In the atomic medium (11), the atoms in the excited state radiate photons as they transition to the ground state, and at the same time, they themselves become quantum memory that stores the spin state of the atoms. There is a one-to-one correspondence between the polarization state of the emitted photons and the spin state of the atoms. Therefore, there is quantum entanglement between the photons output from the Fabry-Perot cavity (18) and the quantum memory, that is, they are in the light-quantum memory entangled state. The components of different photon polarization states in the entangled state are determined by the transition coefficient of the atom that generates the polarization state of the photon. When an atom in a coherent superposition of multiple excited states transitions to the ground state, it forms a coherent superposition of multiple entangled states of optical-quantum memory, i.e., atomic transition interference occurs. By adjusting the frequency of the excitation light, the coefficients of different optical-quantum memory entangled states in coherent superposition can be changed, thereby making the photons output from the Fabry-Perot cavity (18) and the quantum memory storing the spin states of atoms in the atomic medium (11) in a tunable quantum entangled state.

2. The entanglement generation device for a tunable optical-quantum memory based on atomic transition interference according to claim 1, characterized in that, The first pump light generating device includes a first continuously tunable laser source (1), a first optical attenuator (2), a first acousto-optic modulator (3), a first polarization controller (4), and a first fiber collimator (5) connected in sequence. The second pump light generating device includes a second continuously tunable laser source (6), a second optical attenuator (7), a second acousto-optic modulator (8), a second polarization controller (9), and a second fiber collimator (10) connected in sequence. The excitation light generating device includes a third continuously tunable laser source (12), a third optical attenuator (13), a third acousto-optic modulator (14), a third polarization controller (15), and a third fiber collimator (16) connected in sequence. The first fiber collimator (5), the second fiber collimator (10), and the third fiber collimator (16) are used to couple the light transmitted in the fiber to free space for transmission and to perform a beam waist transformation before inputting it into the atomic medium (11). There is a non-zero angle between the optical axis of the lens in the second fiber collimator (10) and the normal of the input end face of the atomic medium (11). There is a non-zero angle between the optical axis of the lens in the fourth fiber collimator (17) and the normal of the output end face of the atomic medium (11). The angle between the propagation direction of the light output by the third fiber collimator (16) and the propagation direction of the photons that can be collected by the fourth fiber collimator (17) should be less than 2 degrees.

3. The entanglement generation device for a tunable optical-quantum memory based on atomic transition interference according to claim 2, characterized in that, The first continuously tunable laser source (1), the second continuously tunable laser source (6) and the third continuously tunable laser source (12) are solid-state lasers or semiconductor lasers.

4. The entanglement generation device for a tunable optical-quantum memory based on atomic transition interference according to claim 2, characterized in that, The first optical attenuator (2), the second optical attenuator (7) and the third optical attenuator (13) are optical fiber attenuators.

5. The entanglement generation device for a tunable optical-quantum memory based on atomic transition interference according to claim 2, characterized in that, The operating wavelength range of the first acousto-optic modulator (3), the second acousto-optic modulator (8), and the third acousto-optic modulator (14) covers the wavelength of atomic energy level transitions in the atomic medium (11), and the switching time is greater than or equal to 50 ns.

6. The entanglement generation device for a tunable optical-quantum memory based on atomic transition interference according to claim 2, characterized in that, The first polarization controller (4), the second polarization controller (9), and the third polarization controller (15) are fiber optic polarization controllers.

7. The entanglement generation device for a tunable optical-quantum memory based on atomic transition interference according to claim 2, characterized in that, The first fiber collimator (5), the second fiber collimator (10), the third fiber collimator (16) and the fourth fiber collimator (17) have built-in lenses and FC interfaces, which can adjust the beam waist of the light coupled from the fiber to free space, and can also collect the light transmitted in free space through the lens and couple it into the fiber optic device.

8. A tunable optical-quantum memory entanglement generation device based on atomic transition interference according to any one of claims 1-7, characterized in that, The atomic medium (11) is a rubidium atom ensemble, cesium atom ensemble, calcium ion ensemble or strontium ion ensemble that has a multi-level structure and can be used for quantum storage.

9. A tunable optical-quantum memory entanglement generation device based on atomic transition interference according to any one of claims 1-7, characterized in that, The Fabry-Perot cavity (18) is a plano-convex lens or an optical fiber filter cavity composed of fiber end face coating.

10. A method for generating entanglement in a tunable optical-quantum memory based on atomic transition interference, characterized in that, The process includes the following steps: using a first pump light generating device and a second pump light generating device to generate the first tunable pump light and the second tunable pump light required for the preparation of the initial atomic state in the atomic medium (11), respectively; and using an excitation light generating device to generate the excitation light required for the preparation of the entangled state of the optical-quantum memory. The first and second tunable pump lights are introduced into the atomic medium (11), and the atoms in the atomic medium (11) are prepared to their initial state. Atoms in the initial state in the atomic medium (11) transition to a coherent superposition of multiple excited states under the action of excitation light. The transition from the excited state to the ground state emits photons. The emitted photons are coupled into the Fabry-Perot cavity (18) through the fourth fiber collimator (17) for noise photon filtering and output. In the atomic medium (11), the atoms in the excited state radiate photons as they transition to the ground state, and at the same time, they themselves become quantum memory that stores the spin state of the atoms. There is a one-to-one correspondence between the polarization state of the emitted photons and the spin state of the atoms. Therefore, there is quantum entanglement between the photons output from the Fabry-Perot cavity (18) and the quantum memory, that is, they are in the entangled state of light and quantum memory. The components of different polarization states of photons in the entangled state are determined by the transition coefficient of the atom that generates the polarization state of the photon. When an atom in a coherent superposition of multiple excited states transitions to the ground state, it forms a coherent superposition of multiple entangled states of optical-quantum memory, i.e., atomic transition interference occurs. By adjusting the frequency of the excitation light, the coefficients of different optical-quantum memory entangled states in coherent superposition can be changed, thereby making the photons output from the Fabry-Perot cavity (18) and the quantum memory storing the spin states of atoms in the atomic medium (11) in a tunable quantum entangled state.

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