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

Abstract

This pulsed light output system for outputting pulsed light for controlling energy states of atoms includes: a first chirped light generation device that generates first chirped light on the basis of first pulsed light; a second chirped light generation device that generates second chirped light on the basis of second pulsed light; and a third pulsed light generation device that generates third pulsed light on the basis of the first chirped light and the second chirped light, and outputs the third pulsed light to atoms. The first pulsed light and the second pulsed light have different wavelengths, and one of the first chirped light and the second chirped light is down-chirped, and the other is up-chirped. The first chirped light and the second chirped light are set to have equal absolute values of frequency change rates with respect to time.

Description

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

[0001] The present invention relates to a pulsed light output system, a pulsed light output method, a neutral atom excitation method, and a quantum computer device. This application claims priority to Japanese Patent Application No. 2023-222087, filed on December 28, 2023, the contents of which are incorporated herein by reference.

[0002] Research into quantum computers is progressing. Utilizing the principles of quantum mechanics, such as quantum superposition, quantum computers achieve dramatically faster computing speeds, enabling them to solve problems that are difficult to solve with classical computers, and are expected to bring about disruptive innovation in society. Quantum computers can be divided into several types depending on how they are implemented, including superconducting, ion-trap, and cold-atom types.

[0003] In a cold-atom quantum computer, a gas of atoms is cooled using laser light and used as a quantum bit. The cooled atoms are trapped by optical tweezers and arranged in an appropriate position. Optical tweezers capture minute particles such as atoms by concentrating laser light. An array of many optical tweezers is called an optical tweezers array.

[0004] In principle, cold-atom quantum computers involve irradiating adjacent atoms trapped in optical tweezers with laser light of a different wavelength than the laser light used to cool the atoms, exciting each atom into an electronic state with a large orbital radius (the Rydberg state). Atoms excited into the Rydberg state have a long distance between the nucleus (+) and electron (-), resulting in a large electric dipole moment. As a result, the interaction between adjacent Rydberg atoms forms a quantum entanglement state, which is the basis of quantum computing. When continuous-wave lasers are used for Rydberg excitation, the period of this interaction becomes long, on the order of microseconds, resulting in the loss of quantum information due to decoherence. As a means of significantly reducing the effects of decoherence, a technique has been developed that uses pulsed laser light to excite atoms for periods of less than nanoseconds.

[0005] On the other hand, the energy levels of Rydberg states are close to each other. Therefore, to excite atoms to a specific Rydberg state, a laser beam with an extremely narrow (narrowband) frequency band that matches the state is required. However, pulsed laser beams have a wider (broadband) frequency band than continuous-wave lasers, which means that multiple Rydberg states can be excited simultaneously. Therefore, there is a need for narrowband pulsed laser beams that can excite atoms to a desired specific energy level while avoiding decoherence. As a method for generating narrowband pulsed light, for example, Non-Patent Document 1 discloses a technique for generating narrowband second harmonic waves using a chirp element and a non-optical element. Furthermore, Patent Document 1 discloses a technique for generating light with an even narrower bandwidth by generating chirp and sum-frequency light from single-wavelength light.

[0006] Special Publication 2017-530403

[0007] F. Raoult et al., "Efficient generation of narrow-bandwidth picosecond pulses by frequency doubling of femtosecond chirped pulses," Opt. Lett. 23, 1117-1119 (1998)

[0008] However, for applications such as cold-atom quantum computers, no wavelength conversion system using two input beams of different wavelengths, including design guidelines for the chirp element characteristics necessary to achieve narrowband excitation, is known, and there is no method for selectively exciting atoms to a desired energy level using a pulsed laser. An object of the present 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.

[0009] 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 comprising: a first chirped light generation device that generates first chirped light based on a first pulsed light; a second chirped light generation device that generates second chirped light based on a second pulsed light; and a third chirped light generation device that generates third pulsed light based on the first chirped light and the second chirped light and outputs the third pulsed light to atoms, wherein the first chirped light and the second chirped light have different wavelengths, one of the first chirped light and the second chirped light is down-chirped and the other is up-chirped, and the first chirped light and the second chirped light are set so that the absolute values ​​of the rates of change of frequency with respect to time are equal.

[0010] According to the present invention, it is possible to output narrow-band pulsed light suitable for Rydberg excitation.

[0011] Fig. 1 is a diagram illustrating the configuration of a pulsed light output system according to the present embodiment. Fig. 2 is a diagram illustrating the relationship between the time and frequency of first chirp light and second chirp light input to a third pulsed light generation device, and the generation of third pulsed light. Fig. 3 is a flowchart illustrating the operation of a pulsed light output system according to the present embodiment. Fig. 4 is an example of a configuration for generating second pulsed light P2 based on first pulsed light P1. Fig. 5 shows the probability of occurrence of a Rydberg state when the wavelength of third pulsed light P3 is changed.

[0012] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing the configuration of a pulsed light output system 1 according to this embodiment. The pulsed light output system 1 outputs pulsed light. When atoms are irradiated with the output pulsed light, the atoms are excited to a Rydberg state, which is expected to significantly reduce the effect of decoherence, which is a problem when excited by a continuous wave laser. The pulsed light output system 1 includes a first laser light source 11, a first chirped light generating device 12, a second laser light source 21, a second chirped light generating device 22, and a third pulsed light generating device 31.

[0013] The first laser light source 11 outputs a first pulsed light P1 to the first chirp light generating device 12 .

[0014] The first chirp light generation device 12 generates first chirp light C1 based on the first pulse light P1. The first chirp light generation device 12 outputs the first chirp light C1 to the third pulse light generation device 31. The first chirp light generation device 12 is, for example, a chirp Bragg grating (CBG). The chirp Bragg grating may be a reflective volume Bragg grating with a period that varies along the beam propagation direction. Alternatively, the chirp Bragg grating may be an optical fiber in which a grating is formed in the core, and the periods of the multiple gratings formed are different. The different grating periods cause the low-frequency and high-frequency components of the incident pulse light to be reflected at different positions, and each component is output at different times, generating chirp light. By increasing the grating period from the incident position, the high-frequency component is output from the chirp Bragg grating before the low-frequency component, resulting in down-chirped chirp light being output. By shortening the grating period from the incident position, the low frequency components are output from the chirped Bragg grating before the high frequency components, and chirped light that is up-chirped is output.

[0015] The rate of change (chirp rate) c (s / Hz) of the delay time with respect to the frequency of the first chirp light generating device 12 is set to the value shown in equation (1).

[0016] In equation (1), a is the frequency band (Hz) of the third pulsed light P3 described later, and b is the narrower frequency band (Hz) of the frequency band of the first pulsed light P1 and the frequency band of the second pulsed light P2 output from the second laser light source 21.

[0017] The second laser light source 21 outputs a second pulsed light P2 to the second chirp light generating device 22. The wavelength of the second pulsed light P2 is different from the wavelength of the first pulsed light P1.

[0018] The second chirp light generation device 22 generates second chirp light C2 based on the second pulse light P2. The second chirp light generation device 22 outputs the second chirp light C2 to the third pulse light generation device 31. Like the first chirp light generation device 12, the second chirp light generation device 22 is, for example, a chirp Bragg grating. Like the first chirp light generation device 12, the chirp rate of the second chirp light generation device 22 is calculated based on the frequency band of the third pulse light P3 and the frequency band of the second pulse light P2 using equation (1).

[0019] One of the first chirp light C1 and the second chirp light C2 is a down-chirp and the other is an up-chirp. That is, when the first chirp light C1 is a down-chirp whose frequency decreases over time, the second chirp light C2 is an up-chirp whose frequency increases over time, and when the first chirp light C1 is an up-chirp whose frequency increases over time, the second chirp light C2 is a down-chirp whose frequency decreases over time.

[0020] The first chirp light C1 and the second chirp light C2 are input to the third pulse light generation device 31. FIG. 2 shows the relationship between the time and frequency of the first chirp light C1 and the second chirp light C2 input to the third pulse light generation device 31. In FIG. 2, the first chirp light C1 is a down-chirp light, and the second chirp light C2 is an up-chirp light. CBGs are selected for the first chirp light C1 and the second chirp light C2 according to Equation (1) so that the absolute values ​​of the chirp rates of the first chirp light C1 and the second chirp light C2 are equal. In FIG. 2, CBGs are selected so that the slope of the graph showing the chirp rate of the first chirp light C1 is equal to the slope of the graph showing the chirp rate of the second chirp light C2, and are used as the first chirp light generation device 12 and the second chirp light generation device 22.

[0021] The pulsed light output system 1 includes optical elements such as optical filters, optical beam splitters, mirrors, and optical circulators at appropriate positions so that the first chirp light C1 and the second chirp light C2 are input to the third pulsed light generation device 31. In Fig. 1 , an optical beam splitter 13 is provided between the first laser light source 11 and the first chirp light generation device 12, an optical beam splitter 23 is provided between the second laser light source 21 and the second chirp light generation device 22, a dichroic mirror 25 is provided at the reflection destination of the optical beam splitter 13, and a mirror 24 is provided at the reflection destination of the optical beam splitter 23.

[0022] The optical beam splitter 13 reflects the first chirp light C1 reflected from the first chirp light generation device 12, and the first chirp light C1 is incident on the dichroic mirror 25. The first chirp light C1 is reflected by the dichroic mirror 25 and input to the third pulse light generation device 31. The optical beam splitter 23 reflects the second chirp light C2 reflected from the second chirp light generation device 22, and the second chirp light C2 is incident on the mirror 24. The second chirp light C2 is reflected by the mirror 24, passes through the dichroic mirror 25, and input to the third pulse light generation device 31.

[0023] The third pulsed light generation device 31 generates the third pulsed light P3 based on the first chirp light C1 and the second chirp light C2. The third pulsed light generation device 31 includes, for example, a nonlinear crystal (for example, a BBO crystal), and generates the third pulsed light P3 by sum frequency generation.

[0024] In the pulsed light output system 1, the delay time between the first chirp light C1 and the second chirp light C2 may be adjustable. For example, as shown in FIG. 1 , the pulsed light output system 1 includes a stage S1 and / or a stage S2. The first chirp light generation device 12 is installed on the stage S1. The second chirp light generation device 22 is installed on the stage S2. The stages S1 and S2 are movable. By moving the stage S1 or S2, the propagation distance of the first chirp light C1 or the second chirp light C2 is adjusted, and the delay time between the first chirp light C1 and the second chirp light C2 is adjusted. The first laser light source 11 or the second laser light source 21 may be installed on a movable stage, and the delay time between the first chirp light C1 and the second chirp light C2 may be adjusted by moving the stage. The movable stage installed below the stage S1, the first laser light source 11, or the second laser light source 21 is an example of a device for adjusting the delay time of the first pulsed light and / or the second pulsed light. This delay time adjustment allows fine adjustment of the wavelength of the third pulsed light P3 that is finally obtained, thereby making it possible to select from multiple Rydberg states of the atom to be excited and excite the atom to a specific Rydberg excited state.

[0025] 2 is a diagram illustrating the generation of the third pulsed light P3. The third pulsed light P3 is generated by sum frequency generation from the first chirp light C1 and the second chirp light C2, which are input at the same time. One of the first chirp light C1 and the second chirp light C2 is a down-chirp and the other is an up-chirp. Furthermore, the absolute values ​​of the chirp rates of the first chirp light C1 and the second chirp light C2 are set to be equal, so that the chirp rate of the generated third pulsed light P3 cancels out and becomes a value close to zero. This allows the third pulsed light generation device 31 to generate pulsed light with a narrow frequency band.

[0026] 3 is a flowchart showing the operation of the pulsed light output system 1 according to this embodiment. First, the first laser light source 11 generates a first pulsed light P1 and outputs it to the first chirp light generation device 12 (step S11). In parallel with step S11, the second laser light source 21 generates a second pulsed light P2 and outputs it to the second chirp light generation device 22 (step S12). Next, the first chirp light generation device 12 generates a first chirp light C1 based on the first pulsed light P1 and outputs it to the third pulsed light generation device 31 (step S13). In parallel, the second chirp light generation device 22 generates a second chirp light C2 based on the second pulsed light P2 and outputs it to the third pulsed light generation device 31 (step S14). The order of the operations from step S11 to step S14 is merely an example, and it is sufficient that the first chirp light C1 is generated after the first pulsed light P1, and the second chirp light C2 is generated after the second pulsed light P2.

[0027] The third pulsed light generating device 31 generates the third pulsed light P3 based on the first chirp light C1 and the second chirp light C2 (step S15).

[0028] The second pulsed light P2 may be generated by wavelength conversion of the first pulsed light P1. When the second pulsed light P2 is generated by wavelength conversion of the first pulsed light P1, the pulsed light output system 1 does not need to include the second laser light source 21. This allows the pulsed light output system 1 to be realized with fewer elements.

[0029] For example, the wavelength of the first pulsed light P1 is 780 nm, and the wavelength of the second pulsed light P2 is 1260 nm. In this case, the wavelength of the third pulsed light P3 can be 480 nm. The energy level of rubidium atoms used in cold-atom quantum computers is excited to an intermediate level by pulsed light with a wavelength of 780 nm, and excited to the Rydberg state by pulsed light with a wavelength of 480 nm. Therefore, by irradiating the rubidium atoms with the first pulsed light P1, which is pulsed light with a wavelength of 780 nm, and the third pulsed light P3, which is pulsed light with a wavelength of 480 nm, the energy of the rubidium atoms can be excited to the Rydberg state. Note that wavelength conversion from light with a wavelength of 780 nm to light with a wavelength of 1260 nm can be easily performed. Therefore, when the wavelength of the first pulsed light P1 is 780 nm and the wavelength of the second pulsed light P2 is 1260 nm, the second pulsed light P2 can be easily generated based on the first pulsed light P1.

[0030] 4 shows an example of a configuration for generating a second pulsed light P2 based on a first pulsed light P1. Laser light from a first laser light source 11 having a wavelength of 780 nm is split into two laser beams by a half mirror 33, and one laser beam is incident on an optical parametric amplifier (OPA) 41, whereby a laser beam having a wavelength of 1260 nm corresponding to the second pulsed light P2 can be generated by wavelength conversion. The wavelengths of the first pulsed light P1 and the second pulsed light P2 may be changed as appropriate depending on the atoms whose energy levels are excited.

[0031] The neutral atom can be excited to the Rydberg state by outputting the third pulsed light P3 having an appropriate wavelength for the neutral atom from the pulsed light output system 1 according to this embodiment. Furthermore, if the quantum computer has a neutral atom, the neutral atom can be excited to the Rydberg state by outputting the third pulsed light P3 having an appropriate wavelength for the neutral atom from the pulsed light output system 1 according to this embodiment.

[0032] (First Example) A pulsed light output system 1 having the configuration shown in FIG. 1 was constructed. The first pulsed light P1 output from the first laser light source 11 had a wavelength of 780 nm and a frequency band of 1 THz. The chirp rate was calculated with reference to Equation (1), and a chirp element with a chirp rate of 30 ps / THz was used for the first chirp light generation device 12. Meanwhile, the second laser light source 21 outputted second pulsed light P2 with a wavelength of 1260 nm and a frequency band of 2 THz. The second chirp light generation device 22 used a chirp element with a chirp rate of -30 ps / THz, which is the chirp rate opposite in sign to that of the first chirp light generation device. Furthermore, a BBO crystal element was provided as the third pulsed light generation device 31, and 480 nm light was generated, which is the sum frequency of 780 nm light and 1260 nm light. As a result, the characteristics of the generated 480 nm light were a pulse width of 10 ps and a frequency band of 50 GHz, and narrow-band pulsed light was generated.

[0033] Comparative Example The third pulsed light P3 (wavelength 480 nm) generated in a configuration similar to that of FIG. 1 but without using a chirp element had a pulse width of 10 ps and a frequency band of 2 THz.

[0034] Second Example Using the stage S2 shown in FIG. 1, it was confirmed that the wavelength of the third pulsed light P3 can be changed by finely adjusting the position of the stage S2.

[0035] Example 3 Rubidium atoms in an optical dipole trap were excited to a first excited state using a first pulsed light P1 (wavelength 780 nm), and then the rubidium atoms were excited to a Rydberg state using a third pulsed light P3 (wavelength 480 nm) generated in Example 1. The Rydberg atoms were ionized using an electrostatic field, and the Rydberg state assignment was determined from the detection time of the ions, confirming that irradiation with the third pulsed light P3 excited the rubidium atoms to a single Rydberg state.

[0036] (Fourth Example) After using the first pulsed light P1 to excite rubidium atoms in an optical dipole trap to a first excited state, it was confirmed that a desired Rydberg excited state could be selected from multiple Rydberg states of rubidium atoms using the third pulsed light P3 generated in the second example. Figure 5 shows the probability of Rydberg states occurring when the frequency of the third pulsed light P3 is changed. 33D to 41D show individual Rydberg states assigned by electrostatic field ionization. It was demonstrated that wavelength tuning can selectively excite multiple Rydberg states of rubidium atoms to a desired Rydberg state.

[0037] As described above, according to the present invention, it is possible to output narrow-band pulsed light suitable for Rydberg excitation.

[0038] Other Embodiments One embodiment of the present invention has been described in detail above with reference to the drawings, but the specific configuration is not limited to that described above, and various design changes and the like can be made within the scope that does not deviate from the gist of the present invention.

[0039] In this embodiment, the expression "the absolute values ​​of the chirp rates of the first chirp light C1 and the second chirp light C2 are equal" not only refers to the case where the absolute value of the chirp rate of the first chirp light C1 is equal to the absolute value of the chirp rate of the second chirp light C2, but also refers to the case where the difference between the absolute value of the chirp rate of the first chirp light C1 and the absolute value of the chirp rate of the second chirp light C2 is equal to or less than a predetermined value. For example, the difference between the absolute value of the chirp rate of the first chirp light C1 and the absolute value of the chirp rate of the second chirp light C2 is 1 / 2πb 2 The generated third pulsed light P3 can be a narrow-band pulsed light suitable for Rydberg excitation if: where b is the narrower frequency band (Hz) of the frequency band of the first pulsed light P1 defined in formula (1) or the frequency band of the second pulsed light P2 output from the second laser light source 21.

[0040] According to the present invention, it is possible to output narrow-band pulsed light suitable for Rydberg excitation.

[0041] REFERENCE SIGNS LIST 1 pulsed light output system, 11 first laser light source, 12 first chirp light generating device, 13 optical beam splitter, 21 second laser light source, 22 second chirp light generating device, 23 optical beam splitter, 24 mirror, 25 dichroic mirror, 26 mirror, 31 third pulsed light generating device, 33 half mirror, 41 optical parametric amplifier, P1 first pulsed light, P2 second pulsed light, P3 third pulsed light, C1 first chirp light, C2 second chirp light, S1 stage, S2 stage

Claims

1. A pulsed light output system that outputs pulsed light for controlling the energy state of an atom, comprising: a first chirped light generation device that generates first chirped light based on first pulsed light; a second chirped light generation device that generates second chirped light based on second pulsed light; and a third pulsed light generation device that generates third pulsed light based on the first chirped light and the second chirped light and outputs the third pulsed light to the atom, wherein the first pulsed light and the second pulsed light have different wavelengths, one of the first chirped light and the second chirped light is a down-chirp and the other is an up-chirp, and the absolute values of the rates of change of frequency with respect to time of the first chirped light and the second chirped light are equal.

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

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

4. The pulsed light output system according to claim 1 or 2, further comprising 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 pulsed light is generated by branching and wavelength-converting the first pulsed light.

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

7. A pulsed light output method for outputting pulsed light for controlling the energy state of an atom, comprising: a first chirped light generation step of generating first chirped light based on first pulsed light; a second chirped light generation step of generating second chirped light based on second pulsed light; and a third pulsed light generation step of generating third pulsed light based on the first chirped light and the second chirped light and outputting the third pulsed light to the atom, wherein the first pulsed light and the second pulsed light have different wavelengths, one of the first chirped light and the second chirped light is a down-chirp and the other is an up-chirp, and the absolute values of the rates of change of frequency with respect to time of the first chirped light and the second chirped light are equal. Pulsed light output method.

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

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

10. A method for exciting a neutral atom to a Rydberg state by outputting the pulsed light to the neutral atom by the pulsed light output system according to claim 1.

11. A quantum computer device using neutral atoms, wherein the neutral atoms are excited to a Rydberg state by outputting the pulsed light to the neutral atoms by the pulsed light output system according to claim 1. Quantum computer device.

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