Pulsed light output system, pulsed light output method, neutral atom excitation method, and quantum computer device

Abstract

A pulsed light output system outputs pulsed light for controlling the energy state of atoms. The pulsed light output system comprises: a first chirped light generating device for generating a first chirped light based on a first pulsed light; a second chirped light generating device for generating a second chirped light based on a second pulsed light; and a third pulsed light generating device for generating a third pulsed light based on the first and second chirped lights and outputting the third pulsed light to atoms. The first and second pulsed lights have different wavelengths, one of the first and second chirped lights is a lower chirp and the other is an upper chirp, and the first and second chirped lights are set to have equal absolute values ​​of their rates of change of frequency with respect to time.

Description

Technical Field

[0001] This invention relates to pulsed light output systems, pulsed light output methods, neutral atom excitation methods, and quantum computer devices.

[0002] This application claims priority to Japan Patent Application No. 2023-222087, filed on December 28, 2023, the contents of which are incorporated herein by reference. Background Technology

[0003] Research into quantum computers is underway. A type of computer, utilizing principles of quantum mechanics such as quantum superposition, has achieved a significant leap in computing speed, capable of solving problems that are difficult to solve with classical computers, and is expected to bring disruptive innovation to society. Quantum computers can be categorized into several types based on their implementation methods, including superconducting, ion trap, and cooled atom-based types.

[0004] In quantum computers with cooled atoms, lasers are used to cool an atomic gas, which is then used as qubits. The cooled atoms are captured by optical tweezers and arranged in appropriate positions. Optical tweezers are devices that capture tiny particles such as atoms by focusing a laser beam. An array of multiple optical tweezers is called an optical tweezers array.

[0005] In cooled atom-based quantum computers, neighboring atoms, captured by optical tweezers, are excited into electronic states (Rydberg states) with large orbital radii by irradiating them with a laser of a different wavelength than the laser used to cool the atoms. In these Rydberg states, the distance between the nucleus (+) and electron (-) is long, resulting in a large electric dipole moment. Consequently, through the interaction of neighboring Rydberg atoms, quantum entanglement, the foundation of quantum computing, is formed. If a continuous-wave oscillating laser is used for this Rydberg excitation, the interaction period becomes microseconds long, leading to quantum information loss due to decoherence. To significantly reduce the impact of this decoherence, methods have been developed to excite atoms using pulsed lasers in time intervals less than nanoseconds.

[0006] On the other hand, the energy levels of Rydberg states are close. Therefore, to excite atoms to a specific Rydberg state, a laser with an extremely narrow frequency bandwidth is required. However, pulsed lasers have a wider frequency bandwidth than continuous-wave lasers, thus presenting the problem of simultaneously exciting multiple Rydberg states. Therefore, a narrow-band pulsed laser capable of exciting atoms to the desired specific energy level while avoiding decoherence is desired.

[0007] As a method for generating narrowband pulsed light, for example, Non-Patent Document 1 discloses a method for generating narrowband second harmonics using chirped elements and non-optical elements. Furthermore, Patent Document 1 discloses a method for generating light with a narrower bandwidth by generating chirped and sum-frequency light from light of a single wavelength.

[0008] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2017-530403 Non-patent literature Non-patent literature 1: F.Raoult et al., "Efficient generation of narrow-bandwidth picosecondpulses by frequency doubling of femtosecond chirped pulses," Opt.Lett. 23,1117-1119 (1998) Summary of the Invention

[0009] However, in applications such as cooled atom-type quantum computers, the wavelength conversion system using two input lights with different wavelengths is unknown, including the design guidelines for the characteristics of chirped elements required to achieve narrowband, and there are technical problems with the lack of a method to selectively excite atoms at the desired energy level using pulsed lasers.

[0010] The purpose of this invention is to provide a pulsed light output system, a pulsed light output method, a neutral atom excitation method, and a quantum computer device that output narrowband pulsed light suitable for Rydberg excitation.

[0011] One aspect of the present invention is a pulsed light output system that outputs pulsed light for controlling the energy state of atoms. The pulsed light output system comprises: a first chirped light generating device for generating a first chirped light based on a first pulsed light; a second chirped light generating device for generating a second chirped light based on a second pulsed light; and a third pulsed light generating device for generating a third pulsed light based on the first and second chirped lights and outputting the third pulsed light to the atoms. The first and second pulsed lights have different wavelengths, one of the first and second chirped lights is a lower chirp and the other is an upper chirp, and the first and second chirped lights are configured such that the absolute values ​​of their rates of change of frequency with respect to time are equal.

[0012] According to the present invention, it is possible to output narrowband pulsed light suitable for Rydberg excitation. Attached Figure Description

[0013] Figure 1This is a diagram showing the structure of the pulsed light output system according to this embodiment.

[0014] Figure 2 It is a diagram illustrating the relationship between the time and frequency of the first and second chirped lights being input into the third pulse light generating device, and the generation of the third pulse light.

[0015] Figure 3 This is a flowchart illustrating the operation of the pulsed light output system according to this embodiment.

[0016] Figure 4 This is an example of a structure that generates a second pulse light P2 based on a first pulse light P1.

[0017] Figure 5 The probability of Rydberg states occurring is shown when the wavelength of the third pulse light P3 is changed.

[0018] Explanation of reference numerals in the attached figures: 1. Pulsed light output system; 11. First laser source; 12. First chirped light generating device; 13. Optical beam splitter; 21. Second laser source; 22. Second chirped light generating device; 23. Optical beam splitter; 24. Mirror; 25. Dichroic mirror; 26. Mirror; 31. Third pulsed light generating device; 33. Semi-transparent mirror; 41. Optical parametric amplifier; P1. First pulsed light; P2. Second pulsed light; P3. Third pulsed light; C1. First chirped light; C2. Second chirped light; S1. Stage; S2. Stage. Detailed Implementation

[0019] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0020] Figure 1 This diagram illustrates the structure of the pulsed light output system 1 according to this embodiment. The pulsed light output system 1 outputs pulsed light. By irradiating the atoms with the output pulsed light, the atoms are excited into Rydberg states, which is expected to significantly reduce the decoherence effect that is a problem in continuous-wave laser excitation.

[0021] The pulsed light output system 1 includes a first laser source 11, a first chirped light generating device 12, a second laser source 21, a second chirped light generating device 22, and a third pulsed light generating device 31.

[0022] The first laser source 11 outputs a first pulse light P1 to the first chirped light generating device 12.

[0023] The first chirped light generating device 12 generates a first chirped light C1 based on a first pulse light P1. The first chirped light generating device 12 outputs the first chirped light C1 to the third pulse light generating device 31.

[0024] The first chirped light generating device 12 is, for example, a chirped Bragg grating (CBG). The chirped Bragg grating can also be a reflective volume Bragg grating with a period varying along the beam propagation direction. Alternatively, the chirped Bragg grating can be formed in the fiber core, with multiple gratings having different periods. Because the grating periods are different, the low-frequency and high-frequency components of the incident pulsed light are reflected at different positions. Chirped light is generated by outputting each component at different timings. By increasing the grating period from the incident position, the high-frequency component is output from the chirped Bragg grating before the low-frequency component, resulting in lower-chirped light. By decreasing the grating period from the incident position, the low-frequency component is output from the chirped Bragg grating before the high-frequency component, resulting in upper-chirped light.

[0025] The rate of change of the delay time relative to the frequency (chirp rate) c (s / Hz) of the first chirped light generating device 12 is set to the value shown in equation (1).

[0026] In equation (1), a is the frequency bandwidth (Hz) of the third pulse light P3 described later, and b is the frequency bandwidth (Hz) of the narrower of the frequency bandwidth of the first pulse light P1 and the frequency bandwidth of the second pulse light P2 output from the second laser source 21.

[0027] The second laser source 21 outputs a second pulse light P2 to the second chirped light generating device 22. The wavelength of the second pulse light P2 is different from the wavelength of the first pulse light P1.

[0028] The second chirped light generating device 22 generates a second chirped light C2 based on the second pulse light P2. The second chirped light generating device 22 outputs the second chirped light C2 to the third pulse light generating device 31. The second chirped light generating device 22 is the same as the first chirped light generating device 12, for example, a chirped Bragg grating.

[0029] The chirp rate of the second chirped light generating device 22 is the same as that of the first chirped light generating device 12, and is calculated according to Equation (1) based on the frequency bandwidth of the third pulse light P3 and the frequency bandwidth of the second pulse light P2.

[0030] One of the first chirped light C1 and the second chirped light C2 is a down chirp, and the other is an up chirp. That is, when the first chirped light C1 is a down chirp with a frequency that decreases over time, the second chirped light C2 is an up chirp with a frequency that increases over time; when the first chirped light C1 is an up chirp with a frequency that increases over time, the second chirped light C2 is a down chirp with a frequency that decreases over time.

[0031] The first chirped light C1 and the second chirped light C2 are input into the third pulse light generating device 31. Figure 2 The diagram illustrates the relationship between the time and frequency of the input of the first chirped light C1 and the second chirped light C2 to the third pulse light generating device 31. Figure 2 In the first chirped beam C1, the chirped beam is the lower chirped beam, and the second chirped beam C2 is the upper chirped beam. The first chirped beam C1 and the second chirped beam C2 are selected according to equation (1) so that the absolute values ​​of the chirping rates of the first chirped beam C1 and the second chirped beam C2 are equal. Figure 2 In the process, CBG is selected so that the slope of the line representing the chirp rate of the first chirped light C1 is equal to the slope of the line representing the chirp rate of the second chirped light C2, and is used as the first chirped light generating device 12 and the second chirped light generating device 22.

[0032] The pulsed light output system 1 has optical components such as optical filters, optical beam splitters, mirrors, and optical circulators at appropriate locations to allow the first chirped light C1 and the second chirped light C2 to be input into the third pulsed light generating device 31. Figure 1 In this device, an optical beam splitter 13 is provided between the first laser source 11 and the first chirped light generating device 12, and an optical beam splitter 23 is provided between the second laser source 21 and the second chirped light generating device 22. A dichroic mirror 25 is provided at the reflection destination of the optical beam splitter 13, and a reflector 24 is provided at the reflection destination of the optical beam splitter 23.

[0033] The optical beam splitter 13 reflects the first chirped light C1 reflected from the first chirped light generating device 12, and the first chirped light C1 is incident on the dichroic mirror 25. The first chirped light C1 is reflected by the dichroic mirror 25 and input to the third pulse light generating device 31.

[0034] The optical beam splitter 23 reflects the second chirped light C2 reflected from the second chirped light generating device 22, and the second chirped light C2 is incident on the reflector 24. The second chirped light C2 is reflected by the reflector 24 and enters the third pulse light generating device 31 through the dichroic mirror 25.

[0035] The third pulse light generating device 31 generates a third pulse light P3 based on the first chirped light C1 and the second chirped light C2. The third pulse light generating device 31 includes, for example, a nonlinear crystal (e.g., a BBO crystal) and generates the third pulse light P3 by sum-frequency generation.

[0036] In the pulsed light output system 1, the delay time of the first chirped light C1 and the second chirped light C2 can also be adjusted. For example, as... Figure 1As shown, the pulsed light output system 1 includes a stage S1 and / or a stage S2. A first chirped light generating device 12 is disposed on the stage S1. A second chirped light generating device 22 is disposed on the stage S2. The stages S1 and S2 are movable. By moving the stage S1 or the stage S2, the propagation distance of the first chirped light C1 or the second chirped light C2 is adjusted, thereby adjusting the delay time of the first chirped light C1 and the second chirped light C2. Alternatively, a first laser source 11 or a second laser source 21 may be disposed on the movable stage, and the delay time of the first chirped light C1 and the second chirped light C2 may be adjusted by moving the stage.

[0037] The stage S1 and the movable stage disposed below the stage S1, the first laser light source 11 or the second laser light source 21 are an example of a device for adjusting the delay time of the first pulse light and / or the second pulse light.

[0038] By adjusting this delay time, the wavelength of the final third pulse light P3 can be fine-tuned, thus enabling the sorting of the multiple Rydberg states of the atom to be excited and exciting the atom to the specified Rydberg excited state.

[0039] Figure 2 This diagram illustrates the generation of the third pulse light P3. In the first chirped light C1 and the second chirped light C2, light input at the same time is used to generate the third pulse light P3 through sum-frequency generation. Since one of the first chirped light C1 and the second chirped light C2 is a down-chirped light and the other is an up-chirped light, and the absolute values ​​of the chirp rates of the first chirped light C1 and the second chirped light C2 are set to be equal, the chirp rate of the generated third pulse light P3 is canceled out and becomes close to zero. Therefore, the third pulse light generating device 31 can generate pulse light with a narrow frequency bandwidth.

[0040] Figure 3 This is a flowchart illustrating the operation of the pulsed light output system 1 according to this embodiment. First, the first laser source 11 generates a first pulsed light P1 and outputs it to the first chirped light generating device 12 (step S11). In parallel with step S11, the second laser source 21 generates a second pulsed light P2 and outputs it to the second chirped light generating device 22 (step S12). Next, the first chirped light generating device 12 generates a first chirped light C1 based on the first pulsed light P1 and outputs it to the third pulsed light generating device 31 (step S13). In parallel, the second chirped light generating device 22 generates a second chirped light C2 based on the second pulsed light P2 and outputs it to the third pulsed light generating device 31 (step S14). The order of operations from steps S11 to S14 is just an example; it is sufficient that the first chirped light C1 is generated after the first pulsed light P1 is generated, and the second chirped light C2 is generated after the second pulsed light P2 is generated.

[0041] The third pulse light generating device 31 generates a third pulse light P3 based on the first chirped light C1 and the second chirped light C2 (step S15).

[0042] The second pulsed light P2 can also be generated by changing the wavelength of the first pulsed light P1. When the second pulsed light P2 is generated by changing the wavelength of the first pulsed light P1, the pulsed light output system 1 may not need to have a second laser source 21. Thus, the pulsed light output system 1 can be implemented with fewer components.

[0043] For example, the wavelength of the first pulse P1 is 780 nm, and the wavelength of the second pulse P2 is 1260 nm. Then, the wavelength of the third pulse P3 can be 480 nm. In a cooled atom-type quantum computer, the energy levels of rubidium atoms are excited to intermediate energy levels by a 780 nm pulse of light and to Rydberg states by a 480 nm pulse of light. Therefore, by irradiating rubidium atoms with a 780 nm pulse of light (the first pulse P1) and a 480 nm pulse of light (the third pulse P3), the energy of the rubidium atoms can be excited to Rydberg states.

[0044] Furthermore, wavelength conversion from 780 nm to 1260 nm can be easily performed. Therefore, when the wavelength of the first pulse P1 is 780 nm and the wavelength of the second pulse P2 is 1260 nm, the second pulse P2 can be easily generated based on the first pulse P1.

[0045] Figure 4 This is an example of a structure that generates a second pulse P2 based on a first pulse P1. A 780nm wavelength laser from a first laser source 11 is split into two lasers by a semi-transparent mirror 33, and one of the lasers is incident on an optical parametric amplifier (OPA) 41. This allows a 1260nm wavelength laser, which is equivalent to the second pulse P2, to be generated through wavelength conversion.

[0046] The wavelengths of the first pulse P1 and the second pulse P2 can also be appropriately changed by the atoms that excite the energy levels.

[0047] For a neutral atom, by outputting a third pulse light P3 of an appropriate wavelength from the pulse light output system 1 according to this embodiment, the neutral atom can be excited into a Rydberg state. Furthermore, in the case where a quantum computer has a neutral atom, for that neutral atom, by outputting a third pulse light P3 of an appropriate wavelength from the pulse light output system 1 according to this embodiment, the neutral atom can be excited into a Rydberg state.

[0048] (First embodiment) Build Figure 1 The pulsed light output system 1 is shown. The first pulsed light P1 output from the first laser source 11 has a wavelength of 780 nm and a frequency bandwidth of 1 THz. The chirp rate is calculated with reference to Equation (1), and a chirped element with a chirp rate of 30 ps / THz is used in the first chirped light generating device 12. On the other hand, the second laser source 21 outputs a second pulsed light P2 with a wavelength of 1260 nm and a frequency bandwidth of 2 THz. In the second chirped light generating device 22, a chirped element with a chirp rate of -30 ps / THz is used as the chirp rate, which is the opposite of that of the first chirped light generating device. In addition, as the third pulsed light generating device 31, a BBO crystal element is provided to generate a wavelength of 480 nm light as the sum frequency for the wavelengths of 780 nm and 1260 nm. As a result, the generated wavelength of 480 nm light has a frequency bandwidth of 50 GHz with a pulse width of 10 ps, ​​and a narrowband pulsed light is successfully generated.

[0049] (Comparative example) and Figure 1 With the same structure, the characteristics of the third pulse light P3 (wavelength 480nm) generated without the use of chirped elements are a frequency bandwidth of 2THz at a pulse width of 10ps.

[0050] (Second Embodiment) Confirmed by using Figure 1 The stage S2 shown can be finely adjusted to change the wavelength of the third pulse light P3.

[0051] (Third embodiment) After the rubidium atoms in the optical dipole trap are excited to a first excited state using a first pulse light P1 (wavelength 780 nm), the rubidium atoms are excited to a Rydberg state using a third pulse light P3 (wavelength 480 nm) generated in the first embodiment. The Rydberg atoms are ionized by an electrostatic field, and the assignment of the Rydberg state is determined based on the detection time of the ions. This confirms that the rubidium atoms are excited to a single Rydberg state by irradiation with the third pulse light P3.

[0052] (Fourth embodiment) After the rubidium atoms in the optical dipole trap are excited to the first excited state using the first pulse light P1, the third pulse light P3 generated in the second embodiment is used to confirm that a specified Rydberg excited state can be selected from the multiple Rydberg states of the rubidium atoms and excited. Figure 5 The probability of Rydberg states occurring when the frequency of the third pulse P3 is changed is shown. 33D to 41D represent the individual Rydberg states assigned by electrostatic ionization. It is confirmed that, by wavelength tuning, it is possible to selectively excite desired Rydberg states from Rydberg states containing multiple rubidium atoms.

[0053] According to the present invention, it is possible to output narrowband pulsed light suitable for Rydberg excitation.

[0054] <Other Implementation Methods> The above description, with reference to the accompanying drawings, details one embodiment of the present invention. However, the specific structure is not limited to the above structure, and various design changes can be made without departing from the spirit of the present invention.

[0055] In this embodiment, "the absolute values ​​of the chirp rates of the first chirped light C1 and the second chirped light C2 are equal" means that it includes not only the case where the absolute values ​​of the chirp rates of the first chirped light C1 and the second chirped light C2 are equal, but also the case where the difference between the absolute values ​​of the chirp rates of the first chirped light C1 and the second chirped light C2 is less than a predetermined value.

[0056] For example, if the absolute value of the chirp rate of the first chirped light C1 is less than or equal to the absolute value of the chirp rate of the second chirped light C2, then the generated third pulse light P3 can be a narrow-band pulse light suitable for Rydberg excitation. Here, b is the narrower frequency bandwidth (Hz) of the first pulse light P1 and the second pulse light P2 output from the second laser source 21, as defined in equation (1).

[0057] Industrial applicability According to the present invention, it is possible to output narrowband pulsed light suitable for Rydberg excitation.

Claims

1. A pulsed light output system, outputting pulsed light for controlling the energy state of atoms, the pulsed light output system comprising: The first chirped light generating device generates first chirped light based on a first pulse light; The second chirped light generating device generates second chirped light based on the second pulse light; as well as The third pulse light generating device generates a third pulse light based on the first and second chirped light, and outputs the third pulse light to atoms. The first pulse light and the second pulse light have different wavelengths. One of the first chirped light and the second chirped light is a downward chirp, and the other is an upward chirp. The absolute values ​​of the rate of change of the frequencies of the first chirped light and the second chirped light with respect to time are equal.

2. The pulsed light output system according to claim 1, wherein, The second pulse light is generated by wavelength conversion of the first pulse light.

3. The pulsed light output system according to claim 1 or 2, wherein, The wavelength of the first pulse light is 780 nanometers.

4. The pulsed light output system according to claim 1 or 2, wherein, The pulsed light output system also includes a device for adjusting the delay time of the first pulsed light and / or the second pulsed light.

5. The pulsed light output system according to claim 2, wherein, The second pulse light is generated by branching the first pulse light and performing wavelength transformation.

6. The pulsed light output system according to claim 1 or 2, wherein, The first pulse of light irradiates the atom to excite its energy state to a first excited state. The third pulse of light is applied to the atom to excite the atom from the first excited state to the second excited state.

7. A pulsed light output method, outputting pulsed light for controlling the energy state of atoms, the pulsed light output method having: The first chirped light generation step involves generating the first chirped light based on the first pulse light; The second chirped light generation step generates a second chirped light based on the second pulse light; as well as The third pulse light generation step involves generating a third pulse light based on the first and second chirped light, and then outputting the third pulse light to the atoms. The first pulse light and the second pulse light have different wavelengths. One of the first chirped light and the second chirped light is a downward chirp, and the other is an upward chirp. The absolute values ​​of the rate of change of the frequencies of the first chirped light and the second chirped light with respect to time are equal.

8. The pulsed light output method according to claim 7, wherein, The second pulse light is generated by branching the first pulse light and performing wavelength transformation.

9. The pulsed light output method according to claim 7 or 8, wherein, The first pulse of light irradiates the atom to excite its energy state to a first excited state. The third pulse of light is applied to the atom to excite the atom from the first excited state to the second excited state.

10. A method for excitation of neutral atoms, The pulsed light output system of claim 1 excites the neutral atom into a Rydberg state by outputting the pulsed light to the neutral atom.

11. A quantum computer device using neutral atoms, The pulsed light output system of claim 1 excites the neutral atom into a Rydberg state by outputting the pulsed light to the neutral atom.

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