JP2023168069A - Quantum arithmetic unit and quantum computing unit - Google Patents

Abstract

To realize a quantum arithmetic unit having both functions of quantum operation, and an imparting function of entanglement with a quantum system to a photon having a wavelength different from that of a photon used for the quantum operation.SOLUTION: A quantum arithmetic unit includes: a nano optical fiber (20); and a quantum system (22) disposed on the nano optical fiber. The quantum system includes a ground level, a first excitation level, a second excitation level, and a third excitation level having energy differing from that of the second excitation level, and a first resonance wavelength (λ1) equivalent to a level difference between the ground level and the first excitation level and a second resonance level (λ2) equivalent to a level difference between the second excitation level and the third excitation level differ mutually. The quantum system also mutually operates with a first photon having a first resonance wavelength, and further generates a second photon that has an entanglement with the quantum system and has a second resonance wavelength in the nano optical fiber.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a quantum operation unit and a quantum operation unit including the quantum operation unit.

In recent years, quantum computing devices have been devised that include quantum computing units that include atoms, ions, diamond NV centers, semiconductor quantum dots, etc. as quantum systems. For example, by connecting multiple quantum computing units of the quantum computing device through a quantum channel, the quantum computing unit can be used as a quantum repeater for long-distance quantum communication, or as a quantum computing unit of a distributed quantum computing device. It can be used as

Here, the quantum operation using the quantum operation unit is executed by using, for example, retention of quantum information in the quantum system and quantum state manipulation for the quantum system. Here, in order to perform the above-mentioned quantum operation, it is necessary to use a level having a relatively long coherence time among the levels of the quantum system. Therefore, quantum operations using a quantum operation unit usually utilize the transition between the ground level and the excited level of a quantum system, and the wavelength of light that resonates with the transition is often less than 1.0 μm. be.

On the other hand, optical fibers are often used for quantum channels that connect quantum processing units. In this case, in order to sufficiently reduce the loss of quantum information in the optical fiber, the wavelength of the photon propagating in the optical fiber falls within the wavelength band of 1.3 μm to 1.6 μm, which is also generally called the communication wavelength band. You are required to be able to

Therefore, in order to achieve both quantum computation using quantum computation units and low-loss quantum communication between quantum computation units, it is necessary to convert the wavelength of photons output from the quantum computation units into a communication wavelength band. Quantum wavelength conversion was required. Non-Patent Documents 1 to 3 disclose quantum wavelength converters that convert the wavelength of photons.

R. Ikuta et al., "Wide-band quantum interface for visible-to-telecommunication wavelength conversion", Nature Communications 2, 537 (2011) S. Zaske et al., “Visible-to-Telecom Quantum Frequency Conversion of Light from a Single Quantum Emitter”, Phys. Rev. Lett. 109, 147404 (2012) K. De Greve et al., “Quantum-dot spin-photon entanglement via frequency downconversion to telecom wavelength”, Nature 491, 421 (2012)

When the quantum wavelength converters described in Non-Patent Documents 1 to 3 are introduced into a quantum computing unit, the structure of the quantum computing unit becomes complicated. Further, when performing quantum wavelength conversion using the quantum wavelength converters described in Non-Patent Documents 1 to 3, noise may be mixed in, photon loss, etc. may occur.

In order to solve the above problems, a quantum operation unit according to one aspect of the present disclosure includes a nano-optical fiber that connects to an optical fiber that propagates photons via a tapered part, and a quantum computing unit that is arranged on the nano-optical fiber. The quantum system has a ground level, a first excited level, a second excited level, and a third excited level having a different energy from the second excited level, a first resonance wavelength corresponding to a level difference between the ground level and the first excited level; and a second resonance wavelength corresponding to the level difference between the second excited level and the third excited level. are different from each other, the quantum system interacts with a first photon having the first resonant wavelength, is entangled with the quantum system, and transmits a second photon having the second resonant wavelength to the nano-optical fiber. to be generated.

A quantum calculation unit that has both the functions of quantum calculation and the function of imparting entanglement with the quantum system to a second photon having a wavelength different from the first photon used for the quantum calculation is created using a quantum wavelength converter. It can be achieved without With this quantum operation unit, it is possible to realize a quantum operation unit that can impart entanglement between photons having different wavelengths while eliminating the need for a quantum wavelength converter.

FIG. 2 is an enlarged schematic diagram of the vicinity of a resonator QED system of a quantum operation unit according to an embodiment of the present disclosure, and an energy diagram showing each level of the quantum system. FIG. 1 is a schematic diagram of a quantum computing unit according to an embodiment of the present disclosure. 1 is an enlarged schematic diagram of a single photon source according to an embodiment of the present disclosure; FIG. FIG. 1 is a schematic diagram showing a first operational mode of a quantum computing unit according to an embodiment of the present disclosure. It is an energy diagram showing a transition process in a quantum system of a quantum operation unit in a first operation mode of a quantum operation unit according to an embodiment of the present disclosure. FIG. 2 is a schematic diagram illustrating a second operational form of a quantum computing unit according to an embodiment of the present disclosure. It is an energy diagram showing the transition process in the quantum system of the quantum operation unit in the second operation mode of the quantum operation unit according to the embodiment of the present disclosure. It is an energy diagram showing another example of the transition process in the quantum system of the quantum operation unit in the second operation mode of the quantum operation unit according to the embodiment of the present disclosure. It is an energy diagram showing another example of the transition process in the quantum system of the quantum operation unit in the second operation mode of the quantum operation unit according to the embodiment of the present disclosure.

[Embodiment]
<Quantum computing unit>
The quantum computing unit 2 according to this embodiment will be explained with reference to FIG. 2. FIG. 2 is a schematic diagram showing the quantum computing unit 2 according to this embodiment. As shown in FIG. 2, the quantum computing unit 2 includes a plurality of quantum computing units 4, a single photon source 6, a polarizing beam splitter 8, a first single photon detector 10, at least one half beam splitter 12, and a second single photon detector 14. Further, the quantum computing unit 2 includes a single mode optical fiber F that propagates a single photon between each of the above-mentioned members.

The quantum operation unit 4 according to this embodiment includes a resonator QED (quantum electrodynamics) system 16 and a laser light source 18. The resonator QED system 16 is a unit that includes a quantum system and implements quantum operations using the quantum system. The laser light source 18 is a light source for irradiating the quantum system of the resonator QED system 16 with laser light for quantum computation using the resonator QED system 16. Details of the laser light source 18 will be described later.

<Resonator QED system>
The resonator QED system 16 will be explained in more detail with reference to FIG. FIG. 1 is a schematic diagram showing an enlarged view of the vicinity of the resonator QED system 16, and an energy diagram D1 showing each level of the quantum system included in the resonator QED system 16.

As shown in FIG. 1, resonator QED system 16 includes a nano-optical fiber 20 and at least one quantum system 22. As shown in FIG. The nano-optical fiber 20 is connected to a single-mode optical fiber F via tapered portions 24 located at both ends. Therefore, photons propagating through the single mode optical fiber F propagate through the nano-optical fiber 20 via the tapered portion 24.

Note that, as shown in FIG. 1, the optical fiber F may include a core portion FA and a cladding portion FB around the core portion FA, and photons may be propagated in the core portion FA. Further, the nano-optical fiber 20 is formed in the heated portion by heating a portion of the optical fiber F using a ceramic heater or various heating methods including oxygen-water flame, etc., and pulling the heated portion from both ends. Good too. In this case, the nano-optical fiber 20 may also include a core portion for propagating photons and a cladding portion around the core portion.

Quantum system 22 is placed on nano-optical fiber 20 . The quantum system 22 has, for example, a plurality of levels. For example, as shown in the energy diagram D1 of FIG. 1, the quantum system 22 has a first ground level g and a second ground level u as ground levels, and a first excited level e ₁ as an excited level. , a second excited level e ₂ , and a third excited level e ₃ . The first excited level e ₁ , the second excited level e ₂ , and the third excited level e ₃ have higher energy than the first ground level g and the second ground level u.

Here, at least the second excited level e ₂ and the third excited level e ₃ have different energies. In particular, as shown in the energy diagram D1 of FIG. 1, the second excited level _e2 may have a higher energy than the first excited level _e1 and the third excited level _e3 . However, the first excited level _e1 may be degenerate with either the second excited level _e2 or the third excited level _e3 , or the second excited level _e2 and the third excited level e3 may be degenerate with each other. It may be at the same level as any of the levels e and ₃ . Further, each level included in the quantum system 22 may have a magnetic sublevel.

In this specification, the states of the quantum system 22 corresponding to the first ground level g and the second ground level u are defined as a state |g> and a state |u>, respectively. Further, the states of the quantum system 22 corresponding to the first excited level e ₁ , the second excited level e ₂ , and the third excited level e ₃ are respectively expressed as state |e ₁ > and state |e ₂ >, and the state |e ₃ >.

Here, in general, the state |g> and the state |u> are stable and have a long coherence time compared to the state |e ₁ >, the state |e ₂ >, and the state |e ₃ >. Therefore, the first ground level g and the second ground level u can function as a quantum memory that retains a quantum state for a relatively long time.

As shown in the energy diagram D1 of FIG. 1, the wavelength that resonates with the transition from state |g> to state |e ₁ > is the first resonance wavelength λ ₁ , and the transition between state |e ₂ > and state |e ₃ > Let the wavelength that resonates with the transition be the second resonant wavelength λ ₂ . Note that in this specification, the wavelength that resonates with the transition between certain levels refers to the wavelength of a photon that has energy corresponding to the energy difference between the levels, in other words, the wavelength that resonates with the transition between the levels. This is the wavelength corresponding to the difference. In other words, the wavelength corresponding to the energy difference between the first ground level g and the first excited level _e1 is the first resonance wavelength _λ1 , and the second excited level _e2 and the third excited level _e3 Let the wavelength corresponding to the energy difference between the two resonant wavelengths λ 2 be the second resonant wavelength λ ₂ .

Here, the energy difference between the first ground level g and the first excited level e ₁ and the energy difference between the second excited level e ₂ and the third excited level e ₃ are different from each other. Therefore, the first resonant wavelength λ ₁ and the second resonant wavelength λ ₂ are different from each other. In particular, the energy difference between the first ground level g and the first excited level _e1 may be larger than the energy difference between the second excited level _e2 and the third excited level _e3 . In this case, the second resonant wavelength λ ₂ is longer than the first resonant wavelength λ ₁ . For example, the first resonant wavelength λ ₁ is less than 1.0 μm, and the second resonant wavelength λ ₂ is 1.3 μm or more and 1.6 μm or less.

In this embodiment, the wavelength that resonates with the transition from the state |e ₁ > to the state |e ₂ > is defined as the third resonance wavelength λ ₃ , and the wavelength that resonates with the transition from the state |g> to the state |e ₃ > Let the wavelength be the fourth resonance wavelength λ ₄ . Furthermore, the wavelength that resonates with the transition from the state |g> to the state |e ₂ > is defined as a fifth resonant wavelength λ ₅ .

In this embodiment, the quantum system 22 may be, for example, a cesium atom. In this case, in this embodiment, the state |g> can be filled with 6 ² S _1/2 , F=4 states, and the state |u> can be filled with 6 ² S _1/2 , F=3 states. Further, in this embodiment, the state |e ₁ > has 6 ² P _3/2 , F=3 states, and the state |e ₂ > has 7 ² S _1/2 , F=4 states, the state |e ₃ > can be filled with 6 ² P _1/2 , F=3 states.

When each level of the quantum system 22 takes the state shown in the energy diagram D1 of FIG. 1, the first resonance wavelength λ ₁ corresponding to the energy difference between the first ground level g and the first excited level e ₁ is , 852 nm. Further, the second resonance wavelength λ ₂ corresponding to the energy difference between the second excitation level e 2 and the third excitation level e ₃ is 1470 nm, and the second resonance wavelength λ ₂ corresponding to the energy difference between the first base level g and the third excitation level e _{3 is} 1470 nm. The fourth resonant wavelength λ ₄ corresponding to the energy difference between the two is 894 nm.

The quantum system 22 interacts with a first photon having a first resonant wavelength λ ₁ that propagates through the nano-optical fiber 20 . More specifically, state transition occurs in the quantum system 22 due to interaction with the first photon propagating through the nano-optical fiber 20. The interaction between the quantum system 22 and the first photon propagating through the nano-optical fiber 20 is such that when the first photon propagates through the nano-optical fiber 20, an evanescent wave seeping out from the nano-optical fiber 20 interacts with the quantum system 22. It may also occur due to

Here, in this specification, "the quantum system 22 is arranged on the nano-optical fiber 20" does not mean only that the quantum system 22 is in contact with the nano-optical fiber 20. For example, in this embodiment, the quantum system 22 may be spaced apart from the nano-optical fiber 20 to the extent that interaction between the quantum system 22 and the first photon propagating through the nano-optical fiber 20 is possible. .

The quantum system 22 also generates a second photon having a second resonant wavelength λ ₂ in the nano-optical fiber 20 . In particular, the second photon generated from the quantum system 22 has a correlation with the state of the quantum system 22, in other words, it has entanglement with the quantum system 22. A detailed method of generating the second photon from the quantum system 22 will be described later.

In this embodiment, an example will be described in which the quantum system 22 is a cesium atom having the above-mentioned levels, but the present invention is not limited to this. For example, as long as the quantum system 22 has a ground level, a first excited level, a second excited level, and a third excited level that has a different energy from the second excited level, it can be used for various types of quantum operations. May include quantum systems. For example, the quantum system 22 may include ions, diamond particles having nitrogen defects, quantum dots, etc. in addition to atoms.

<Resonator>
Returning to the resonator QED system 16 of FIG. 1, the resonator QED system 16 further includes a first resonator 26 and a second resonator 28 located inside the nano-optical fiber 20 or inside the optical fiber F. including. The first resonator 26 and the second resonator 28 are configured such that at least a portion of each resonant optical path includes the nano-optical fiber 20. The first resonator 26 has a first resonant wavelength λ ₁ as a resonant wavelength, and the second resonator 28 has a second resonant wavelength λ ₂ as a resonant wavelength. Quantum system 22 thus interacts with a first photon propagating in first resonator 26 and quantum system 22 also generates a second photon in second resonator 28 .

Each of the first resonator 26 and the second resonator 28 includes, for example, a pair of first fiber Bragg gratings 30 and a second fiber Bragg grating formed on each of two optical fibers F connected to the nano-optical fiber 20. It includes a grid 32. The first fiber Bragg grating 30 and the second fiber Bragg grating 32 each include a first resonant wavelength λ ₁ and a second resonant wavelength λ ₂ in their reflection bands. The pair of first fiber Bragg gratings 30 and second fiber Bragg gratings 32 are arranged such that the optical path length of the propagating first photon and second photon in one round trip is an integral multiple of the wavelength of each photon. .

Note that at least one of the first fiber Bragg grating 30 and the second fiber Bragg grating 32 may be formed in the nano-optical fiber 20 instead of the optical fiber F. The first fiber Bragg grating 30 or the second fiber Bragg grating 32 formed in the nano optical fiber 20 is a photonic crystal formed by a method such as forming periodic defects in a part of the nano optical fiber 20. may have.

<Quantum bit>
In this embodiment, in order to have the first resonant wavelength λ ₁ that resonates with the transition from the state |g> to the state |e ₁ > as the resonant wavelength, the first resonator 26 is configured to move from the state |g> to the state |e ₁ Combines with the transition to >. On the other hand, the first resonator 26 is not coupled to the transition from state |u> to state |e ₁ >. Furthermore, in this embodiment, since the second resonant wavelength λ ₂ that resonates with the transition from the state |e ₂ > to the state |e ₃ > is the resonant wavelength, the second resonator 28 has the second resonant wavelength λ 2 that resonates with the transition from the state |e 2 > to the state |e ₃ >. is coupled with the transition from to state |e ₃ >.

However, for example, by irradiating the quantum system 22 with control light that resonates with each transition from state |g> and state |u> to state |e ₁ >, a two-photon stimulated Raman process is generated in the quantum system 22. can be done. Alternatively, the quantum system 22 may be irradiated with electromagnetic waves that resonate with the transition from the state |g> to the state |u>. In this way, by irradiating the quantum system 22 with control light from the laser light source 18 having a certain amplitude, the transition from the state |u> to the state |e ₁ > can also be controlled. Here, the control light irradiated from the laser light source 18 to the quantum system 22 includes a laser beam having a wavelength corresponding to the transition from the state |g> to the state |e ₁ > and a laser light having a wavelength corresponding to the transition from the state |u> to the state |e ₁ > may also include a laser beam having a wavelength corresponding to the transition to >.

Therefore, by controlling the interaction between the quantum system 22 and the first photon and the irradiation of the control light from the laser light source 18 to the quantum system 22, the state of the entire quantum system 22 can be controlled. . Therefore, the quantum system 22 takes, for example, an arbitrary superposition state ρ g |g>+ρ _u |u> based on the relatively stable state | _g > and state |u>. Note that ρ _g and ρ _u are complex coefficients satisfying |ρ _g ² |+|ρ _u ² |=1.

As a result, in the resonator QED system 16, the quantum system 22 constitutes a quantum bit |Ψ>=ρ _g |g>+ρ _u |u>. In this case, the one-qubit gate using the quantum system 22 may be configured such that, for example, the quantum system 22 is irradiated with control light that resonates with each transition from the state |g> and the state |u> to the state |e ₁ >. This is realized by

<Single photon source>
Next, the single photon source 6 will be explained in more detail with reference to FIG. FIG. 3 is an enlarged schematic diagram showing the vicinity of the single photon source 6. As shown in FIG. Each of the single photon sources 6 according to this embodiment is a single photon source that generates a single first photon having a first resonant wavelength λ ₁ and inputs it to each quantum operation unit 4 . For example, as shown in FIG. 3, the single photon source 6 is different from the resonator QED system 16 except that it has a single quantum system 22 and does not have the second resonator 28. They may have the same configuration. In other words, the single photon source 6 resonates with the nano-optical fiber 20 whose both ends are connected to the optical fiber F via the tapered portion 24, the quantum system 22 disposed on the nano-optical fiber 20, and the first photon. A first resonator 26 is included.

In the single photon source 6, for example, the spontaneous emission of a single first photon accompanying the transition from the state |g> to the state |e ₁ > is emphasized due to the coupling between the quantum system 22 and the first resonator 26. A single first photon may be generated in the first resonator 26 based on the Purcell effect. In other words, the single photon source 6 uses the fact that a single photon is generated when the state of the quantum system 22 is excited by control light from a laser light source (not shown) and returns to the ground state. One photon may be generated.

Alternatively, the single photon source 6 may generate a single first photon in the first resonator 26 by causing the quantum system 22 to irradiate control light whose amplitude gradually increases from 0. In this case, the waveform of the first photon can be controlled by controlling the temporal change in the amplitude of the control light. In addition, the single photon source 6 may be a conventionally known single photon source that generates a single first photon; for example, it may be a single photon source equipped with a messenger.

In this embodiment, an example in which the single photon source 6 has a single quantum system 22 has been described, but the present invention is not limited to this. For example, the single photon source 6 may have a plurality of quantum systems 22, similar to the quantum systems 22 included in the resonator QED system 16. In this case, for example, none of the plurality of quantum systems 22 included in the single photon source 6 are coupled to the first resonator 26, and by irradiating any one quantum system 22 with a light shifted beam or the like, , the quantum system 22 and the first resonator 26 may be coupled to each other. With the above configuration, the single photon source 6 can generate the first photon only by the quantum system 22 coupled to the first resonator 26.

<Single photon detector>
Referring back to FIG. 2, the polarizing beam splitter 8 is a beam splitter that changes whether to reflect or transmit an incident photon depending on the polarization of the incident photon. In this embodiment, the polarizing beam splitter 8 reflects photons with V polarization and transmits photons with H polarization. For example, photons generated in each resonator QED system 16 by a method described later are propagated from each resonator QED system 16 to each polarizing beam splitter 8 . Note that, as shown in FIG. 2, the quantum computing unit 2 may include a half-wave plate 34, and the photons incident on each polarizing beam splitter 8 may be transmitted through the half-wave plate 34.

The first single photon detector 10 includes a first photon detection element 36 that detects photons with V polarization reflected by the polarizing beam splitter 8 and detects photons with H polarization that have passed through the polarizing beam splitter 8. and a second photon detection element 38. Therefore, the first single photon detector 10 detects a single photon by reflecting or transmitting it through the polarizing beam splitter 8.

The half beam splitter 12 reflects incident photons with a probability of approximately 50% and transmits them with a probability of approximately 50%. Single photons output from two resonator QED systems 16 are respectively incident on the half beam splitter 12 by a method described later. Here, the half beam splitter 12 is arranged so that when two single photons incident at the same time have the same wavelength, the two single photons interfere.

The second single photon detector 14 includes a third photon detection element 40 and a fourth photon detection element 42. The third photon detection element 40 detects a single photon generated in one resonator QED system 16 and transmitted through the half beam splitter 12, and a single photon generated in the other resonator QED system 16 and reflected from the half beam splitter 12. and detect. On the other hand, the fourth photon detection element 42 detects a single photon generated in one resonator QED system 16 and reflected by the half beam splitter 12, and a single photon generated in the other resonator QED system 16 and transmitted through the half beam splitter 12. Detect one photon. Therefore, the half beam splitter 12 separates the mode (wave packet) of the second photon generated in one resonator QED system 16, the mode (wave packet) of the second photon generated in the other resonator QED system 16, to interfere.

The optical fiber F propagates photons between the above-mentioned parts of the quantum computing unit 2. Here, the quantum computing unit 2 further includes an optical circulator 44. The optical circulator 44 propagates photons incident from each single photon source 6 to each resonator QED system 16, and propagates photons incident from each resonator QED system 16 to an optical fiber F on each polarizing beam splitter 8 side. . The optical circulator 44 may include, for example, a half-wave plate 46 in the optical path from each single photon source 6 to each resonator QED system 16, and may include a half-wave plate 46 in the optical path from each single photon source 6 to each resonator QED system 16. Photons incident on nano-optical fiber 20 may be transmitted through half-wave plate 46 . Further, the quantum computing unit 2 further includes an optical switch 48. The optical switch 48 switches to which of the polarization beam splitter 8 and the half beam splitter 12 the photons generated from each resonator QED system 16 are propagated.

Note that, instead of the optical switch 48, the quantum computing unit 2 has an element that distributes the incident photon to either the polarization beam splitter 8 or the half beam splitter 12, depending on the wavelength of the incident photon. You can leave it there. For example, the quantum computing unit 2 may include a WDM filter or a dichroic mirror instead of the optical switch 48.

Note that the quantum computing unit 2 includes, in addition to those shown in FIG. A second single photon detector 14 may also be provided. In this case, the quantum computing unit 2 may include an optical switch 50 that switches to which half beam splitter 12 the photons generated from each resonator QED system 16 are propagated. Further, the quantum computing unit 2 may include a plurality of quantum computing units 4 for each single photon source 6.

The quantum computing unit 2 may include a control section (not shown) for operating each section provided therein. The control unit may control each unit of the quantum computing unit 2 based on a program recorded in a memory (not shown) or the like.

<First operational form>
A first mode of operation of the quantum computing unit 2 according to this embodiment will be described with reference to FIGS. 4 and 5. FIG. 4 is a schematic diagram of the quantum computing unit 2 for explaining the operation of each part of the quantum computing unit 2 in the first operation mode of the quantum computing unit 2 according to the present embodiment. FIG. 5 is a diagram showing an energy diagram D2 representing the state transition of the quantum system 22 in the first operation mode of the quantum computing unit 2 according to the present embodiment.

In the first operation mode of the quantum computing unit 2 according to the present embodiment, first, quantum gate operations between the quantum systems 22 within a single quantum computing unit 4 will be described. In the first operation mode of the quantum computing unit 2 according to the present embodiment, the quantum computing unit 2 first generates a single photon having the first resonant wavelength λ ₁ from each single photon source 6 by the above-mentioned method or the like. A first photon SF1 is generated. Here, the first photon SF1 has a specific state such as horizontal polarization |h>, for example.

Next, the quantum computing unit 2 causes the first photon SF1 to pass through the optical circulator 44 and enter the resonator QED system 16 of the quantum computing unit 4. Thereby, the first photon SF1 incident on the optical circulator 44 from the single photon source 6 propagates to the resonator QED system 16. In addition, in the quantum gate operation between the quantum systems 22 in a single quantum operation unit 4, the polarization of the first photon SF1 is changed by making the angle of the optical axis of the half-wave plate 46 parallel to the horizontal polarization |h>. may not change. The first photon SF1 incident on the resonator QED system 16 resonates in the first resonator 26 having the first resonant wavelength λ ₁ as the resonant wavelength. Here, the quantum operation unit 4 controls the irradiation of the control light L1 from the laser light source 18 to the specific quantum system 22.

When the control light L1 is not irradiated from the laser light source 18 to a specific quantum system 22, the transition of the quantum system 22 from the state |g> to the state |e ₁ > is caused by coupling with the first resonator 26. There is. On the other hand, in the above case, the transition of the quantum system 22 from the state |u> to the state |e ₁ > is not coupled to the first resonator 26 . Therefore, when the quantum system 22 is in the state |g> and in the state |u>, when the first photon SF1 is reflected in the resonator QED system 16, the resonator QED system 16 The phase shift given to is different.

The quantum operation unit 4 changes the wavelength that resonates with the transition of the quantum system 22 from the state |g> to the state |e ₁ > by irradiating the control light L1 from the laser light source 18 to the specific quantum system 22. let Thereby, the quantum operation unit 4 can effectively release the coupling between the transition and the first resonator 26. In this case, the phase shift that the resonator QED system 16 gives to the first photon SF1 is approximately the same when the quantum system 22 is in the state |g> and when it is in the state |u>. As described above, through irradiation of the control light L1 to the specific quantum system 22, the quantum operation unit 4 can determine the resonator QED system 16 when the quantum system 22 is in the state |g> and the state |u>. It is possible to control whether there is a difference in the phase shift given to the first photon SF1.

In this embodiment, by irradiating the quantum system 22 with the control light L1, the transition of the quantum system 22 from the state |g> to the state |e ₁ > and the coupling with the first resonator 26 are effectively released. Although the example described above is not limited to this example. For example, in the present embodiment, when the quantum system 22 is not irradiated with the control light L1, the transition from the state |g> to the state |e ₁ > of the quantum system 22 is coupled to the first resonator 26. It doesn't have to be. In this case, the transition of the quantum system 22 from the state |g> to the state |e ₁ > may be coupled to the first resonator 26 by irradiating the quantum system 22 with the control light L1.

After the first photon SF1 is incident on the resonator QED system 16, a first photon SF1', which is the first photon SF1 reflected in the resonator QED system 16, is emitted from the resonator QED system 16. Here, as described above, depending on the state of the specific quantum system 22, there is a difference in the phase shift that the resonator QED system 16 gives to the first photon SF1 when the first photon SF1 is reflected in the resonator QED system 16. Whether or not it is present changes depending on whether or not the control light L1 is irradiated. For this reason, the quantum operation unit 4 irradiates the specific quantum system 22 with the control light L1 to detect the first photon SF1 and the first photon SF1 when the quantum system 22 is in the state |g> and the state |u>, respectively. The presence or absence of a difference in phase shift from the one-photon SF1' can be controlled.

Note that, by controlling the irradiation of the control light L1 to the specific quantum system 22, the quantum operation unit 4 controls, for example, a state transition from the state |e ₁ > to the state |g> in the specific quantum system 22. A certain transition T ₁ ' may occur. Due to the state transition, a first photon SF1′ that is entangled with the superposition state ρ _g |g>+ρ _u |u> of the quantum system 22 may be generated in the first resonator 26 . Note that since _the transition from the state |e ₁ > to the state |g Ru.

Returning to FIG. 4, in the first operation mode of the quantum computing unit 2 according to the present embodiment, following the emission of the first photon SF1' from the resonator QED system 16, the quantum computing unit 2 The photon SF1' is propagated to the polarization beam splitter 8. For example, the quantum computing unit 2 controls the optical switch 48 so that the first photon SF1' transmitted through the optical circulator 44 and the optical switch 48 propagates to the polarization beam splitter 8. Here, in the quantum gate operation between the quantum systems 22 in the single quantum operation unit 4, the polarization of the first photon SF1' may not change in the half-wave plate 34 either.

Thereby, the quantum computing unit 2 causes the first photon SF1' from the quantum computing unit 4 to enter the polarizing beam splitter 8. However, the polarization of the first photon SF1' remains unchanged from the horizontal polarization |h>. Therefore, by summing the detection results of the two photon detection elements of the first single photon detector 10, it can be effectively considered that the first photon SF1' has been measured with a single photon detector. .

Here, for example, if the states of the two quantum systems 22 included in the resonator QED system 16 are both |u>, the optical response in the quantum systems 22 is equal to the case where the quantum systems 22 do not exist, so the first Photon SF1 is reflected with almost no loss, and its phase is shifted by π. On the other hand, if either of the states of the two quantum systems 22 included in the resonator QED system 16 is not |u>, the optical response in the quantum system 22 is a transition between |g> and |e>. Therefore, the incident first photon SF1 is reflected without a phase shift.

Therefore, the state of the two quantum systems 22 that interacted with the first photon SF1 corresponds to the state obtained by applying the CPF gate to the state before interacting with the first photon SF1. Furthermore, if the number of quantum systems that interact with the first photon SF1 is N, which is an integer of 3 or more, the states of the N quantum systems 22 that interacted with the first photon SF1 are mutually exclusive with the first photon SF1. This corresponds to applying an N-bit controlled phase gate to the state before acting. As described above, in the first operating method, a gate between a plurality of quantum systems 22 is realized.

As described above, the quantum operation unit 4 can perform a quantum gate operation using the interaction between the first photon SF1 and an arbitrary quantum system 22. Therefore, in the first operation mode of the quantum computing device 2, the quantum computing device 2 can perform quantum computing using the interaction between the first photon SF1 and any quantum system 22 in each quantum computing unit 4.

In addition, as mentioned above, when quantum gate operation between the quantum systems 22 in the single quantum operation unit 4 is performed by the quantum operation unit 2, the quantum operation unit 2 is not limited to the above-mentioned configuration. For example, when performing the quantum gate operation described above, the quantum operator 2 does not need to include the polarizing beam splitter 8, the half-wave plate 34, and the half-wave plate 46, and the first single photon detector 10 , may have only a single photon detection element.

Next, the quantum gate operation between the quantum systems 22 between the plurality of quantum operation units 4 in the first operation mode of the quantum operation unit 2 according to the present embodiment will be explained. In this case, the quantum computing unit 2 includes a plurality of quantum computing units 4 for each single photon source 6.

In the quantum gate operation between the quantum systems 22 between the plurality of quantum operation units 4, first, from each single photon source 6, transversely polarized light having the first resonant wavelength λ ₁ is generated using the same method as described above. A first photon SF1 having a specific state such as |h> is generated. Next, the quantum computing unit 2 causes the first photon SF1 to enter the resonator QED system 16 of any quantum computing unit 4.

Here, instead of the optical circulator 44, the quantum computing unit 2 installs an optical switch for each quantum computing unit 4 to determine which quantum computing unit 4's resonator QED system 16 the first photon SF1 is made to enter. You may be prepared. Further, the quantum computing unit 2 may change the polarization state of the first photon SF1 from each single photon source 6 using the half-wave plate 46.

Thereby, the first photon SF1 incident on the optical circulator 44 from the single photon source 6 propagates to the resonator QED system 16. As a result, the first photon SF1 described above is reflected by the resonator QED system 16, and the first photon SF1' is emitted from the resonator QED system 16. Here, the quantum computing unit 2 propagates the first photon SF1' emitted from the resonator QED system 16 so that the first photon SF1' is incident on another different resonator QED system 16. Thereby, the quantum computing unit 2 causes the first photon SF1 to enter the plurality of resonator QED systems 16, and also causes the first photon SF1' to be reflected in each resonator QED system 16. Note that the phase shift of the first photon SF1' in each resonator QED system 16 is controlled through control of the state of the quantum system 22 in each resonator QED system 16, as described above.

Next, the quantum operator 2 propagates the first photon SF1' to the polarization beam splitter 8. The quantum computing unit 2 may change the polarization state of the first photon SF1' from each resonator QED system 16 using a half-wave plate 34.

The polarizing beam splitter 8 reflects or transmits the first photon SF1' depending on the polarization state of the incident first photon SF1'. Thereafter, the first single photon detector 10 detects the first photon SF1' emitted from the polarizing beam splitter 8, and thereby the quantum operator 2 measures the polarization state of the first photon SF1'.

Here, the first photon SF1' is entangled with each quantum system 22 of the plurality of reflected resonator QED systems 16. Therefore, the state of each quantum system 22 of the plurality of resonator QED systems 16 and the polarization state of the first photon SF1' have a correlation.

Next, the quantum operation unit 4 performs an operation on the quantum system 22 of the other quantum operation unit 4 according to the polarization state of the measured first photon SF1'. When the quantum computing unit 2 has the two resonator QED system 16, for example, the polarization state of the first photon SF1' is the horizontally polarized light |h that is the state of the first photon SF1 when the first photon SF1 is generated. >, Z gate operation is performed on the quantum system 22 of another quantum operation unit 4. The Z gate operation for a specific quantum system 22 is realized, for example, by the quantum operation unit 4 controlling the irradiation of the control light L1 to the quantum system 22. On the other hand, when the polarization state of the first photon SF1' is not horizontal polarization |V> or horizontal polarization |h>, no operation is performed on the particular quantum system 22. In other words, the specific quantum system is 22, perform the rotation operation.

Through the above operation, the quantum operator 2 can separate the first photon SF1' from the entanglement between the first photon SF1' and the quantum system 22 of each resonator QED system 16. In other words, the quantum computing unit 2 can leave only the entanglement between the quantum systems 22 of the plurality of resonator QED systems 16 by the above operation. As described above, the quantum computing unit 2 can project the state of the quantum system 22 of the plurality of resonator QED systems 16 onto a specific entangled state. Here, the case where the quantum operator 2 has two resonator QED systems 16 has been explained as an example, but even when the quantum operator 2 has three or more resonator QED systems 16, the first photon SF1' It is possible to separate the

As described above, the quantum computing unit 2 can perform a quantum gate operation using the interaction between the first photon SF1 and an arbitrary quantum system 22 in each of the plurality of quantum computing units 4. Therefore, in the first operation mode of the quantum computing unit 2, the quantum computing unit 2 performs quantum computing using the interaction between the first photon SF1 and an arbitrary quantum system 22 between the plurality of quantum computing units 4. Can be executed.

Note that the quantum gate operation in the quantum operation unit 4 described above is an example, and in this embodiment, the quantum operation unit 2 uses various conventionally known gate operations using the quantum system 22 in the quantum operation unit 4. Quantum operations may also be performed. For example, in the first operation mode of the quantum computing unit 2, each quantum computing unit 4 may irradiate the plurality of quantum systems 22 with the control light L1 to perform quantum computation using the plurality of quantum systems 22. . Further, the quantum computing unit 2 causes the first photon SF1 to enter a plurality of resonator QED systems 16, detects the reflected first photon SF1', and then transmits the first photon SF1' only to a specific resonator QED system 16. may be incident, and the reflected first photon SF1' may be detected.

<Second operation form>
A second mode of operation of the quantum computing unit 2 according to this embodiment will be described with reference to FIGS. 6 and 7. FIG. 6 is a schematic diagram of the quantum computing unit 2 for explaining the operation of each part of the quantum computing unit 2 in the second operation mode of the quantum computing unit 2 according to the present embodiment. FIG. 7 is a diagram showing an energy diagram D3 representing the state transition of the quantum system 22 in the second operation mode of the quantum computing unit 2 according to the present embodiment.

In the second operation mode of the quantum computing unit 2 according to the present embodiment, first, in each quantum computing unit 4, an arbitrary quantum system 22 is irradiated with pump light L2 from the laser light source 18. Here, the pump light L2 includes, for example, a first laser beam having a first resonant wavelength λ ₁ , a third laser beam having a third resonant wavelength λ ₃ , and a fourth laser beam having a fourth resonant wavelength λ ₄ . including.

Here, the respective frequencies of the first laser beam, the third laser beam, and the fourth laser beam are defined as a first resonant frequency ω ₁ , a third resonant frequency ω ₃ , and a fourth resonant frequency ω ₄ . Further, the frequency of a photon having a second resonant wavelength λ ₂ is defined as a second resonant frequency ω ₂ . Here, the first laser beam having the first resonance wavelength λ ₁ causes a transition T ₁ from the state |g> to the state |e ₁ >, as shown in the energy diagram D3 of FIG. Further, the third laser beam having the third resonance wavelength λ ₃ causes a transition T ₂ from the state |e ₁ > to the state |e ₂ >, and furthermore, the fourth laser beam having the fourth resonance wavelength λ ₄ causes a transition T 2 from the state |e 1 > to the state |e 2 >. , a transition T ₃ from state |e ₃ > to state |g > occurs.

Thereby, by irradiating the quantum system 22 with the pump light L2, a non-degenerate four-wave mixing process occurs in the quantum system 22. For example, in the present embodiment, a single element having a second resonant wavelength λ 2 that resonates with the transition from state | _{e 2 >} to state |e ₃ > via transition T ₁ , transition T 2 , and transition _{T 3} is used. One second photon SF2 is generated from the quantum system 22. Note that the quantum system 22 generates a second photon SF2 in the second resonator 28. Since the transition from the state |e ₂ > to the state |e ₃ > is coupled to the second resonator 28, the generation of the second photon SF2 by the non-degenerate four-wave mixing process is promoted by the second resonator 28. be done.

In this embodiment, when a non-degenerate four-wave mixing process in the quantum system 22 is used to generate the second photon SF2, in other words, the first excitation level e ₁ and the third excitation level e ₃ are Although the case where the energies are different has been described, the case is not limited to this. For example, the energy of the first excited level e ₁ and the third excited level e ₃ may be the same.

Here, it is assumed that at the time when the second photon SF2 is first generated from the quantum system 22, the quantum system 22 is in an arbitrary superposition state ρ _g |g>+ρ _u |u> which is an initial state. In this case, in the second operation mode of the quantum computing unit 2 according to the present embodiment, the quantum computing unit 4 generates the second photon SF2, and then performs the following operations using a method such as the two-photon stimulated Raman process described above. An inversion operation is performed on the quantum system 22. As a result, the state of the quantum system 22 is reversed from ρ _g |g>+ρ _u |u> to ρ _u |g>+ρ _g |u>. Following the inversion operation on the quantum system 22, the quantum operation unit 4 again causes the non-degenerate four-wave mixing process in the quantum system 22 by controlling the irradiation of the pump light L2 to the quantum system 22.

The second photon SF2 generated from the quantum system 22 by the non-degenerate four-wave mixing process has entanglement with the quantum system 22. Therefore, the second photon SF2 generated before and after the above-mentioned inversion operation assumes an arbitrary superposition state ρ _g |u>|pE>+ρ _u |g>|pL>. Here, the state |pE> and the state |pL> are the states of the second photon SF2 generated before and after the reversal operation, respectively. Therefore, the second photon SF2 is entangled with the quantum system 22 and constitutes a time bin qubit based on the state |pE> and the state |pL>.

Returning to FIG. 6, in the second operation mode of the quantum computing unit 2 according to the present embodiment, after generating the second photon SF2 to the second resonator 28, the quantum computing unit 2 generates the second photon SF2. SF2 is propagated to the half beam splitter 12. For example, the quantum computing unit 2 causes the second photon SF2 in the second cavity 28 to be emitted from the cavity QED system 16 of the quantum computing unit 4 to the outside of the cavity QED system 16. Here, the quantum computing unit 2 controls the optical switch 48 so that the second photon SF2 transmitted through the optical circulator 44 and the optical switch 48 propagates to the half beam splitter 12.

Thereby, the quantum computing unit 2 causes the second photon SF2 from the quantum computing unit 4 to enter the half beam splitter 12. Here, the quantum computing unit 2 causes the second photons SF2 from each of the two quantum computing units 4 to enter the same half beam splitter 12. In particular, the quantum computing unit 2 causes the two quantum computing units 4 to emit the second photons SF2 so that the plurality of second photons SF2 enter the same half beam splitter 12 substantially simultaneously.

Therefore, in this embodiment, in response to the two second photons SF2 that are incident on the same half beam splitter 12 at approximately the same time, the half beam splitter 12 causes interference between the modes (wave packets) of the two second photons SF2. occurs.

Therefore, through the above operation, the quantum computing unit 2 imparts entanglement to the specific quantum system 22 of each of the resonator QED systems 16 of two mutually different quantum computing units 4. In other words, by the above operation, the quantum computing unit 2 can transfer the state of the quantum system 22 included in a specific quantum computing unit 4 to the state of the quantum system 22 included in another quantum computing unit 4. Therefore, by combining the first operation mode and the second operation mode, the quantum operation unit 2 uses the results of quantum operations in a specific quantum operation unit 4 for quantum operations in other quantum operation units 4. be able to. Note that the quantum computing unit 2 is not limited to the above, and the quantum computing unit 4 can be operated without transferring the state of the quantum system 22 included in a specific quantum computing unit 4 to the state of the quantum system 22 included in another quantum computing unit 4. The entanglement generated in step may be used as is for subsequent quantum calculations.

<Summary>
The quantum operation unit 4 according to the present embodiment executes a quantum operation using the quantum system 22 through the interaction between the first photon SF1 incident on the resonator QED system 16 and the quantum system 22 included in the resonator QED system 16. do. Further, the quantum operation unit 4 according to the present embodiment generates a second photon SF2 that is entangled with the quantum system 22 through irradiation of the pump light L2 to the quantum system 22.

Here, the first photon SF1 has a first resonant wavelength λ ₁ and the second photon SF2 has a second resonant wavelength λ ₂ different from the first resonant wavelength λ ₁ . For this reason, the quantum operation unit 4 has a function of performing a quantum operation using the quantum system 22 and imparting entanglement with the quantum system 22 to a second photon SF2 having a wavelength different from the first photon SF1 used for the quantum operation. Both functions are achieved without using a quantum wavelength converter.

Here, in general, quantum operations using a quantum system require that quantum information be retained in the quantum system for a certain amount of time. The transition between is used. For example, as mentioned above, quantum operations using cesium atoms involve the ground state 6 ² S _1/2 , F=3 state and the excited state directly above it 6 ² P _3/2 , F=3 state. The state transition between is used. In this case, generally, the wavelength corresponding to the energy difference between the ground level of the quantum system and the excited level immediately above it is often less than 1.0 μm. Therefore, by setting the wavelength of photons to less than 1.0 μm, quantum operations using interaction between a quantum system and photons can be efficiently performed.

Additionally, in general, the loss of photons propagating through a single mode optical fiber increases as the propagation distance increases. Here, the loss of the photon is large when the wavelength of the photon is less than 1.0 μm; If it is below, it will be relatively small. More preferably, when the wavelength band of the photon is 1.3 μm or more and 1.6 μm or less, the loss of the photon propagating through the optical fiber becomes smaller. In other words, when the wavelength of a photon is 1.0 μm or more and 1.8 μm or less, more preferably 1.3 μm or more and 1.6 μm or less, it is possible to propagate the photon over a long distance while reducing the loss of the photon. It is.

In this embodiment, the first resonant wavelength λ ₁ , which is the wavelength of the first photon SF1, is shorter than the second resonant wavelength λ ₂ , which is the wavelength of the second photon SF2. In particular, the first resonant wavelength λ ₁ is less than 1.0 μm, and the second resonant wavelength λ ₂ is 1.3 μm or more and 1.6 μm or less. Therefore, the quantum operation unit 4 according to this embodiment can efficiently perform quantum operations using the interaction between the first photon SF1 and the quantum system 22. Further, the quantum operation unit 4 can generate a second photon SF2 that is entangled with the quantum system 22 and has a small loss even if it propagates over a relatively long distance.

The length of the optical fiber F between each single photon source 6 and each quantum operation unit 4 and between each quantum operation unit 4 and each polarization beam splitter 8 is such that the loss of the first photon SF1 is sufficiently reduced. It may be as short as possible. Thereby, the quantum computing unit 2 can efficiently perform the quantum computing using the first photon SF1 in each quantum computing unit 4 while reducing the loss of the first photon SF1.

Also, the length of the optical fiber F between each quantum processing unit 4 and each half beam splitter 12 is compared with the length of the optical fiber F between each quantum processing unit 4 and each polarizing beam splitter 8. It doesn't have to be long. As a result, the quantum computing unit 2 can propagate the calculation results of the specific quantum computing unit 4 over a relatively long distance using the second photon SF2, which has a relatively small loss even when propagated over a long distance through the optical fiber F. can. Therefore, the quantum computing device 2 can make the distance between the two quantum computing units 4 longer.

Therefore, the quantum computing unit 2 efficiently performs the quantum computing using the first photon SF1 in each quantum computing unit 4, and transmits the results of the quantum computing in a specific quantum computing unit 4 to other quantum computing units located far away. 4 can be efficiently propagated.

<Specific operating method of quantum computing unit>
As a more specific operating method of the quantum computing unit 2, for example, the quantum computing unit 2 uses the first photon SF1 and the quantum system 22 in the first quantum computing unit 4 according to the above-mentioned first operating mode. Perform calculations. Next, the quantum computing unit 2 uses the second photon SF2 entangled with the quantum system 22 to generate a second quantum computing unit 4 different from the first quantum computing unit 4 according to the second operation mode described above. The result of the quantum operation is propagated to the quantum system 22 of.

Here, in the propagation of the result of the quantum operation using the second photon SF2 according to the second operation mode of the quantum operator 2, although the loss of the second photon SF2 in the optical fiber F is reduced, The second photon SF2 may be lost.

In this case, the quantum computing unit 2 can perform quantum computing using the second quantum computing unit 4 having the quantum system 22 to which the results of the quantum computing are propagated, according to the first operation mode described above. Thereby, the quantum computing unit 2 may use the second quantum computing unit 4 to correct a quantum error that occurs due to the loss of the second photon SF2. Further, the quantum computing unit 2 may propagate the corrected quantum information to the quantum system 22 of yet another quantum computing unit 4 using the second photon SF2 according to the second operation mode described above.

Note that even if entanglement is first generated between distant quantum operation units 4 and quantum operations are then executed, by repeatedly trying to generate and propagate the second photon SF2 until entanglement generation is successful. good. Thereby, even if the second photon SF2 is lost in the first trial, entanglement between the quantum operation units 4 can be generated more reliably by performing a plurality of trials.

Thereby, the quantum computing unit 2 can efficiently propagate the result obtained by the quantum computing in a certain quantum computing unit 4 to the distant quantum computing unit 4 while restoring the quantum information. Therefore, the quantum computing device 2 achieves a quantum communication device that propagates the results obtained by the quantum computing in the specific quantum computing unit 4 over long distances with lower loss. In this case, each quantum operation unit 4 functions as a quantum repeater of the quantum communication device.

As another specific operating method, for example, the quantum computing unit 2 transfers the result of the quantum computing in the first quantum computing unit 4 to the first quantum computing unit 4 by the above-mentioned first and second operating modes. It is propagated to the quantum system 22 of the second quantum operation unit 4 different from . Next, the quantum computing unit 2 uses the second quantum computing unit 4 having the quantum system 22 to which the result of the quantum computing has been propagated, and performs the quantum computing using the quantum system 22 according to the first operation mode described above. Execute.

In this case, the quantum computing unit 2 can perform quantum computing in yet another quantum computing unit 4 using the result obtained by the quantum computing in a specific quantum computing unit 4. Therefore, the quantum computing unit 2 is a distributed type that can increase the number of quantum systems 22 that can be used for quantum computing as a whole by performing quantum computing in each of a plurality of mutually separated quantum computing units 4. Achieve a quantum computing device. In this case, each quantum operation unit 4 functions as a quantum operation unit of a distributed quantum operation unit.

In the operation method, the quantum operations in the plurality of quantum operation units 4 according to the first operation mode may be executed in parallel. In addition, in the operation method, the propagation of the quantum state or the sharing of entanglement between the plurality of quantum operation units 4 according to the second operation mode is performed multiple times during the quantum operation according to the first operation mode described above. Good too.

<Addendum>
In this embodiment, each resonator QED system 16 includes a first resonator 26 having a first resonant wavelength λ ₁ as a resonant wavelength, and a second resonator 28 having a second resonant wavelength λ ₂ as a resonant wavelength. . In each quantum operation unit 4, the first photon SF1 in the first resonator 26 interacts with the quantum system 22, and the second photon SF2 entangled with the quantum system 22 in the second resonator 28. is generated.

The quantum operation unit 4 causes the first photon SF1 in the first resonator 26 coupled with the transition of the quantum system 22 used for the quantum operation to interact with the quantum system 22. Therefore, in the quantum operation unit 4, the interaction between the quantum system 22 and the first photon occurs more efficiently, and the quantum operation using the quantum system 22 is executed more efficiently.

In addition, the quantum operation unit 4 is connected to a second resonator 28 coupled to a transition corresponding to a second resonant wavelength λ ₂ which is the wavelength of a second photon SF2 generated using a non-degenerate four-wave mixing process in the quantum system 22. During the photon generation, the second photon SF2 is generated. Therefore, in the quantum operation unit 4, the second photon SF2 is generated more efficiently using the non-degenerate four-wave mixing process in the quantum system 22.

The first resonator 26 and the second resonator 28 include a first fiber Bragg grating 30 and a second fiber Bragg grating 32 formed in the optical fiber F or nano-optical fiber 20, respectively. For this reason, the first resonator 26 and the second resonator 28 are formed by relatively simple methods such as forming the first fiber Bragg grating 30 and the second fiber Bragg grating 32 by irradiating the optical fiber F or the nano-optical fiber 20 with laser light. It can be formed using various methods. Furthermore, the quantum operation unit 4 can configure the first resonator 26 and the second resonator 28 with a simpler structure than in the case where a ring resonator or the like is included.

In addition, in this embodiment, in both the quantum calculation using the quantum system 22 and the generation of the second photon SF2 that is entangled with the quantum system 22, there is a transition from the state |g> to the state |e ₁ >. Although _T1 was used, the present invention is not limited to this. For example, the quantum system 22 may further have a fourth excited level e4 having a different energy from the second excited level _e2 , and a state |e corresponding to the _{fourth excited level e4 . 4} > may be specified. The fourth excited level _e4 may be, for example, a magnetic sublevel of the first excited level _e1 .

In this case, the above transition T ₁ is used for quantum computation using the quantum system 22, and the transition T ₁ from the state |g> to the state |e ₄ > is used to generate the second photon SF2 instead of the transition T 1. ₄ may be used. In this case, the above-described transition T ₂ can be read as a transition from state |e ₄ > to state |e ₂ >. In other words, the quantum operation unit 4 performs the transition T ₄ from the state |g> to the state |e ₄ >, the transition T ₂ from the state |e ₄ > to the state |e ₂ >, and the state The second photon SF2 may be generated by a four-wave mixing process using the transition T ₃ from |e ₃ > to the state |g>.

In the four-wave mixing process, the pump light L2 from the laser light source 18 that irradiates the quantum system 22 is used instead of the first laser light between the first base level g and the fourth excitation level _e4 . A second laser beam that resonates with the transition may be included. Further, the third laser beam included in the pump light L2 may be a laser beam that resonates with the transition between the fourth excitation level _e4 and the second excitation level _e2 .

[Modification 1]
<Other example 1 of second photon generation method>
Another example of the method for generating the second photon SF2 that is entangled with the quantum system 22 in the second operation mode according to the present embodiment will be described as a first modification with reference to FIG. 8 . FIG. 8 is a diagram showing an energy diagram D4 representing another example of the state transition of the quantum system 22 in the second operation mode of the quantum computing unit 2 according to the present modification.

The quantum computing unit 2 according to this modification is the same as the quantum computing unit 2 according to the present embodiment, and pump light L2 irradiated to the quantum system 22 when generating the second photon SF2 in the second operation mode. , and only the state transition in the quantum system 22 irradiated with the pump light L2 is different. In the second operation mode according to this modification, for example, the pump light L2 irradiated to the quantum system 22 when generating the second photon SF2 is a combination of the above-mentioned fourth laser light and the second harmonic that is based on the first reference standard. and a fifth laser beam that resonates with the transition between the excited level g and the second excited level _e2 .

For example, the fifth laser beam is a laser beam having a frequency ω', where the frequency ω' satisfies ω'=(ω ₁ +ω ₃ )/2. Therefore, the fifth laser beam has an energy that is approximately half the energy difference between the first ground level g and the second excited level _e2 . Therefore, the second harmonic of the fifth laser beam resonates with the transition from the state |g> to the state |e ₂ >.

When the quantum system 22 is irradiated with the fourth laser beam and the fifth laser beam described above, as shown in the energy diagram D4 of FIG. 8, there is a transition T ₃ from the state |e ₃ > to the state |g>, and a transition A transition occurs from state |g> to state |e ₂ > via T ₄ and transition T ₅ . Here, transition T ₄ and transition T ₅ are successively generated by the fifth laser beam. Specifically, the fifth laser beam causes a transition _T4 from the state |g> to a state excited to a substantially intermediate energy between the first ground level g and the second excited level _e2 . Furthermore, the transition T 5 from _the state excited by the fifth laser beam to approximately the intermediate energy between the first ground level g and the second excited level e ₂ to the state |e ₂ > is the transition T ₄ . Occurs continuously. As a result, in this modification, a three-level four-wave mixing process occurs in the quantum system 22 irradiated with the pump light L2, and the second photon SF2 described above is generated.

Also in this modification, the second photon SF2 has the second resonance wavelength λ ₂ and is entangled with the quantum system 22. Therefore, also in this modification, the quantum operation unit 4 has the functions of performing quantum operation using the interaction between the first photon and the quantum system 22, and providing entanglement with the quantum system 22 to the second photon SF2. , without using a quantum wavelength converter.

[Modification 2]
<Other example 2 of second photon generation method>
Another example of the method for generating the second photon SF2 that is entangled with the quantum system 22 in the second operation mode according to the present embodiment will be described as a second modification with reference to FIG. FIG. 9 is a diagram showing an energy diagram D5 representing another example of the state transition of the quantum system 22 in the second operation mode of the quantum computing unit 2 according to the present modification.

The quantum computing unit 2 according to this modification is the same as the quantum computing unit 2 according to the present embodiment, and pump light L2 irradiated to the quantum system 22 when generating the second photon SF2 in the second operation mode. , and only the state transition in the quantum system 22 irradiated with the pump light L2 is different. In the second operation mode according to this modification, for example, the pump light L2 that irradiates the quantum system 22 when generating the second photon SF2 includes the above-mentioned fourth laser light, the first base level g, and the second photon SF2. 2 excitation level e and a sixth laser beam that resonates with the transition between e and ₂ .

For example, the sixth laser beam is a laser beam having a frequency ω ₅ , where the frequency ω ₅ satisfies ω ₅ =ω ₁ +ω ₃ . Therefore, the sixth laser beam has energy corresponding to the energy difference between the first ground level g and the second excited level _e2 . Therefore, the sixth laser beam resonates with the transition from the state |g> to the state |e ₂ >.

When the quantum system 22 is irradiated with the fourth laser beam and the sixth laser beam described above, as shown in the energy diagram D5 of FIG. 9, there is a transition T ₃ from the state |e ₃ > to the state |g>, and a transition A transition occurs from state |g> to state |e ₂ > via T ₆ . Here, transition _T6 is generated by the sixth laser beam. Specifically, the sixth laser beam causes a transition T ₆ from the state |g> to the state |e ₂ > without passing through another excited level.
As a result, in this modification, a three-level parametric downward conversion occurs in the quantum system 22 irradiated with the pump light L2, and the above-mentioned second photon SF2 is generated. Also in this modification, the second photon SF2 has the second resonance wavelength λ ₂ and is entangled with the quantum system 22. Therefore, also in this modification, the quantum operation unit 4 has the functions of performing quantum operation using the interaction between the first photon and the quantum system 22, and providing entanglement with the quantum system 22 to the second photon SF2. , without using a quantum wavelength converter.

The present disclosure is not limited to the embodiments described above, and various changes can be made within the scope of the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. are also included within the technical scope of the present disclosure.

2 Quantum operator 4 Quantum operation unit 6 Single photon source 8 Polarizing beam splitter 10 First single photon detector 12 Half beam splitter 14 Second single photon detector 16 Cavity QED system 18 Laser light source 20 Nano optical fiber 22 Quantum system 24 Tapered part 26 First resonator 28 Second resonator 30 First fiber Bragg grating 32 Second fiber Bragg grating SF1 First photon SF2 Second photon

Claims (10)

A nano-optical fiber that connects an optical fiber that propagates photons through a tapered part,
a quantum system disposed on the nano-optical fiber,
The quantum system has a ground level, a first excited level, a second excited level, and a third excited level having a different energy from the second excited level,
a first resonance wavelength corresponding to a level difference between the ground level and the first excited level; and a second resonance wavelength corresponding to the level difference between the second excited level and the third excited level. are different from each other,
The quantum system interacts with the first photon having the first resonant wavelength, is entangled with the quantum system, and generates a second photon having the second resonant wavelength in the nano-optical fiber. calculation unit. The quantum operation unit according to claim 1, wherein the second resonance wavelength is longer than the first resonance wavelength. The quantum operation unit according to claim 2, wherein the first resonance wavelength is less than 1.0 μm, and the second resonance wavelength is 1.0 μm or more and 1.8 μm or less. The quantum operation unit according to claim 3, wherein the second resonance wavelength is 1.3 μm or more and 1.6 μm or less. A first resonator having a resonant wavelength equal to the first resonant wavelength and a second resonator having a resonant wavelength having the second resonant wavelength formed in at least one of the inside of the nano-optical fiber or the inside of the optical fiber. More prepared,
5. The quantum computing unit according to claim 1, wherein the quantum system interacts with the first photon in the first resonator and generates the second photon in the second resonator. The first resonator includes a pair of first fiber Bragg gratings whose reflection band includes the first resonant wavelength, and the second resonator includes a pair of second fiber Bragg gratings whose reflection band includes the second resonant wavelength. The quantum operation unit according to claim 5, comprising: The quantum operation unit according to any one of claims 1 to 4, further comprising a laser light source that irradiates the quantum system with a first laser light having the first resonance wavelength. The quantum system further includes a fourth excited level having a different energy from the second excited level,
The laser light source further includes a second laser beam that resonates with the transition between the ground level and the fourth excited level, and a second laser beam that resonates with the transition between the fourth excited level and the second excited level. 8. The quantum operation unit according to claim 7, wherein the quantum system is irradiated with a third laser beam that resonates with the transition between the third excited level and the ground level, and a fourth laser beam that resonates with the transition between the third excited level and the ground level. . The laser light source further includes a fourth laser beam that resonates with the transition between the third excited level and the ground level, and a second harmonic that resonates between the ground level and the second excited level. 8. The quantum operation unit according to claim 7, wherein the quantum system is irradiated with a fifth laser beam that resonates with the transition of . A plurality of quantum operation units according to any one of claims 1 to 4,
a plurality of single photon sources that generate single photons having the first resonant wavelength and input them to each of the quantum processing units;
a plurality of polarization beam splitters into which single photons having the first resonance wavelength output from each of the quantum operation units are incident;
a plurality of first single photon detectors that detect single photons emitted from each of the polarizing beam splitters;
at least one half beam splitter that causes single photons having the second resonant wavelength output from each of the two quantum operation units to interfere with each other;
at least one second single photon detector for detecting single photons emitted from the half beam splitter;
A quantum computing unit equipped with

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